Increasing the quantity of carbon (C) inputs is a pathway to build soil C stores. One way to achieve this is using cover crop mixtures which can increase the amount and types of root exudates, supporting greater microbial activity and biomass. However, few studies use stoichiometry i.e., C:Nitrogen (N) ratios (the amount of C in relation to the amount of N present) to select cover crop mixes. Our major objective is to understand plant-soil feedback in the context of the legacy effects of cover crop stoichiometry on soil health, C-sequestration, and crop yields. We hypothesized that cover crops with a lower C:N ratio will increase nitrogen availability for the next crop cycle and increase C-sequestration.
What Did We Do?
We are conducting a multi-year, random-block field experiment comparing cover crop mixtures with low, medium-low, medium-high, and high C:N ratios (Table 1), and a fallow control (n=5). We are also interested in the effect of cover crop termination (herbicide vs. roller-crimper) on subsequent barley cash crop. The experiment was established in Southern Idaho, at the Kimberly Research and Extension Center. Soil samples were taken at the start of the experiment in fall 2023, spring, and fall 2024 to compare cover crop effects on soil health.
Table 1. Treatments implemented in this study
“Soil health is the continued capacity of soil to function as a vital living ecosystem that sustains plants, animals and humans, and connects agricultural and soil science to policy, stakeholder needs and sustainable supply-chain management” (Lehmann, et al. 2020). Moreover, natural or anthropogenic actions can change soil properties rapidly. It makes these properties be considered as good soil health indicators, that can be physical, chemical and biological. The first two have a slow response compared to the microbiological and biochemical properties.
The soil health properties evaluated in this research are:
*Physical properties: water holding capacity (the amount of water that a soil can retain).
*Chemical properties: pH, soil organic matter (decayed material that originated from a living organism), nutrient analysis (NH4-N, NO3-N, PO4, major ways that nutrients can be taken by plants).
*Biological properties: enzyme activities involved in the main biogeochemical cycles mineralizing organic matter (α- and β- glucosidase, cellobiosidase, acid and alkaline phosphatase, leucine aminopeptidase, N-acetyl-glycosaminidase), substrate induce respiration (response of microbial respiration to the addition of a nutrient as glucose), carbon mineralization (process for capturing, storing, and utilizing CO2 to synthesize other products). Also, we included agronomic parameters such as yield, crop biomass, full and empty grain.
Statistical analysis was conducted using R software version 4.4.0. Evaluating these attributes allow to verify the soil status and apply better management to get a desire outcome, e.g. increase organic matter in soil.
What Have We Learned?
Overall, the results in the first year of the study showed that medium-high C:N ratio treatment has the potential to improve soil health (Fig. 1), while herbicide termination performed better in comparison to roller crimper termination treatment.
The preliminary results show among all treatments an increase in moisture and pH with a decrease in water holding capacity during the spring compared with the fall seasons compared to fallow treatment. Active microbial biomass (i.e., substrate-induced respiration) did not differ between treatments for fall 2023 and spring 2024; however, carbon and nitrogen mineralization was higher before the treatments were established. Additionally, phosphorous did not vary across time.
Fig. 1. Potential nitrification rates in soil samples under cultivation with different C:N stoichiometry of cover crops. Lowercase letters above columns indicate differences at P < 0.05
Agronomic parameters showed that herbicide termination method gave more barley height, dry aboveground biomass, seed counts, grain weight, total full grain, and barley yield (Fig. 2). On the other hand, the roller crimper termination method increased the amount of empty grain and the presence of weeds in the field.
Fig. 2. Barley yield in 2024 following different cover crops based on their C:N stoichiometry. Lowercase letters above columns indicate differences at P < 0.05
Future Plans
To understand if the environmental condition has a positive or negative influence in soil health parameters, we replicate it at the Plant Materials Center (NRCS, USDA, Pullman, WA) where the environmental conditions are distinct from those in Southern Idaho. Also, we plan to conduct two more years of the experiment. We expect that the information obtained at the end of the study can provide fundamental information to the research community and guide farmers in the selection of cover crops and the termination methods for them in different environmental conditions.
Authors
Presenting authors
Vanessa Otero Jiménez, Postdoctoral Fellow, University of Idaho
Linda Schott, Assistant Professor and Extension Specialist, University of Idaho
Michael Strickland, Research Associated Professor, University of Idaho
Corresponding author
Vanessa Otero Jiménez, Postdoctoral Fellow, Soil and Water System Department, University of Idaho, Vanessao@uidaho.edu
Additional author
Steven Lee, Plant Materials Center, Natural Resources Conservation Service, United States Department of Agriculture
Acknowledgements
This work is supported by grant no. 2021-09118-1027664 from the USDA National Institute of Food and Agriculture. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.
The authors are solely responsible for the content of these proceedings. The technical information does not necessarily reflect the official position of the sponsoring agencies or institutions represented by planning committee members, and inclusion and distribution herein does not constitute an endorsement of views expressed by the same. Printed materials included herein are not refereed publications. Citations should appear as follows. EXAMPLE: Authors. 2025. Title of presentation. Waste to Worth. Boise, ID. April 7–11, 2025. URL of this page. Accessed on: today’s date.
New technologies have been developed to extract and recover concentrated nitrogen (N) and phosphorus (P) from animal manure which can be upcycled as substitutes for conventional nitrogen (Urea) and triple super phosphate (TSP) fertilizers. In this study, the effectiveness of recovered nitrogen (RN) and phosphorus (RP) from liquid swine manure were compared with conventional N (CN) and conventional P (CP). Further, the availibility of RP to crop was enhanced using acidification of the material.
What Did We Do?
The RN was captured from liquid swine manure using a gas permeable membrane technology (Vanotti and Szogi, 2015). The RP was also captured from liquid swine manure using nitrification followed by chemical precipitation with calcium hydroxide (Vanotti et al., 2005). We evaluated annual ryegrass growth response to conventional and recovered nutrients using four nutrient combinations: CN+CP, RN+CP, CN+RP, and RN+RP at five N rates and three P rates (Figures 1 & 2). In a subsequent experiment, the solubility of RP was modified by acidifying the material before its application.
Figure1. Annual ryegrass N uptake in response to N and P under the different nutrient combinations. CN, conventional nitrogen, CP, conventional phosphorus, RN, recovered nitrogen, RP, recovered phosphorus. (Paye et al., 2024a)Figure 2. Annual ryegrass P uptake in response to N and P applications under the different nutrient combinations. CN, conventional nitrogen, CP, conventional phosphorus, RN, recovered nitrogen, RP, recovered phosphorus. (Paye et al., 2024a)
What Have We Learned?
The experimental soil was deficient in N and P, thus, the ryegrass responded to application of both nutrients. The ryegrass N uptake under RN was similar to N uptake under CN when using CP (Figure 1). When RN was blended with RP, the N uptake was significantly greater than the N uptake of conventional (CN+CP) nutrients blend. The P uptake of CP was greater than RP when using CN. However, the P uptake of RP blended with RN was substantially greater than CN+CP (Figure 2). The Acidification of RP improved its solubility and agronomic effectiveness (Paye et al., 2024b). Ryegrass supplied with acidified RP produced 8 – 38% greater dry matter yield and had 48 – 72% greater P uptake than ryegrass supplied with CP or non-acidified RP. The greater overall biomass yield and nutrient uptake of the recovered N and P combination demonstrate this as a novel nutrient combination that could be critical for improving crop yield and nutrient use efficiency in a circular agricultural system.
Future Plans
Crop response to these recovered nutrient blends will be evaluated using other crops under both greenhouse and field conditions.
Authors
Presenting & Corresponding Author
Wooiklee S. Paye, Research Soil Scientist, USDA-ARS Coastal Plains Soil, Water and Plant Research Center, Florence, SC, wooiklee.paye@usda.gov
Additional authors
Raul Moral, Professor, Miguel Hernandez University, Orihuela, 03312 Alicante, Spain.
Matias B. Vanotti and Ariel A. Szogi, Research Soil Scientists, USDA-ARS Coastal Plains Soil, Water and Plant Research Center, Florence, SC 29501 USA.
Quentin D. Read, Statistician, USDA-ARS Southeast Area, 840 Oval Drive, Raleigh, NC 27606 USA.
Additional Information
Paye, W. S., Herrero, R. M. Vanotti, M. B., Szogi, A. A., & Read, Q.D. (2024a). Agronomic Effectiveness of Nitrogen and Phosphorus Recovered from Swine Manure. Agrosystems, Geosciences and Environment. (In Press).
Paye, W. S., Vanotti, M. B., Szogi, A. A., & Herrero, R. M. (2024b). Enhancing the Agronomic Efficiency of Calcium Phosphate Recovered from Swine Manure. In ASA, CSSA, SSSA International Annual Meeting. ASA-CSSA-SSSA.
Vanotti, M.B., & Szogi, A.A. (2015). Systems and methods for reducing ammonia emissions from liquid effluents and for recovering the ammonia. U.S. Patent No. 9,005,333 B1, U.S. Patent and Trademark Office.
Vanotti, M.B., Szogi, A.A., & Hunt, P.G. (2005). Wastewater treatment system. U.S. Patent No. 6,893,567, U.S. Patent and Trademark Office.
Acknowledgements
This research was part of USDA-ARS National Programs 212 Soil and Air, ARS Project 6082-12630-001-00D. Raul Moral’s scientific visit to USDA-ARS Florence, SC, was funded by the Government of Spain, Ministry of Science & Innovation, through Fellowship Award PRX21/002116. The authors are thankful to Paul Shumaker and William Brigman for greenhouse and laboratory assistance. Mention of trade names or commercial products in this article is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the U.S. Department of Agriculture.
The authors are solely responsible for the content of these proceedings. The technical information does not necessarily reflect the official position of the sponsoring agencies or institutions represented by planning committee members, and inclusion and distribution herein does not constitute an endorsement of views expressed by the same. Printed materials included herein are not refereed publications. Citations should appear as follows. EXAMPLE: Authors. 2025. Title of presentation. Waste to Worth. Boise, ID. April 7–11, 2025. URL of this page. Accessed on: today’s date.
Due to a technical glitch, the beginning of the recorded presentation was not recorded. Please accept our apologies.
Purpose
A common media used for woody ornamental production is a mixture of 8 parts pine bark and 1 part sand on a volume basis combined with various amounts of peat moss, sphagnum moss, or vermiculite to improve the aeration porosity (AP) and water holding capacity (WHC). Lime is also added to raise the pH to the level needed for the plant to be grown, and slow-release pellet fertilizer (14-14-14) is mixed in the range of 3 to 8 lb per cubic yard of media to provide a base level of fertility.
While materials such as peat moss and vermiculite hare valuable ingredients to improve the physical characteristics of potting media, there are some significant concerns. Peat moss is obtained from wetlands (peat bogs) and is a non-renewable resource that has increased in price. Vermiculite is a product of heat-treating ore mined from the earth to make the product used in horticulture. The rising energy costs associated with mining and heat processing have caused the costs of vermiculite to increase.
The purpose of this study was to determine if blending 20%, 40%, and 60% (volume basis) of composted poultry litter (CPL) with a bark-sand base mix could replace or reduce the need to mix in non-renewable ingredients to improve the physical properties (AP, WHC, bulk density, pH), and reduce the amount of pellet fertilizer (14-14-14) needed to provide typical levels of fertility for potting media used in ornamental plant production. The anticipated benefits would be reduced production costs for the horticulturalist and development of a consistent market for producers of compost products made from poultry litter mixed with locally sourced plant waste.
What Did We Do?
The first step in the study was to obtain large amounts of composted poultry litter (broiler or breeder litter mixed with wood and other plant waste) and screened pine bark from two separate manufacturers in South Carolina. The other material that was included in the media blends was builder’s sand. Three well-mixed pine bark and compost samples were sent to the Clemson University Agricultural Services Laboratory to determine the concentrations of major and minor plant nutrients, organic matter, carbon, pH, electrical conductivity (EC5), moisture content, and the dry matter bulk density. The only measurements obtained for the sand were the moisture content (3.7%) and density (1.143 g DM/cm3). The pH was assumed to be 7.0 based on published information. The average chemical and physical characteristics of the pine bark and compost are provided in Table 1. The complete details are given by Chastain et al. (2023).
The next step was to make the four different potting mixes using the three ingredients. The base mix was made by blending 8 parts pine bark with 1 part sand. The other three mixes were blends of the base mix and the compost product (CPL) on a volume basis. The 20% CPL mix was 1 part CPL blended with 4 parts of the base mix. The 40% CPL mix was 2 parts CPL blended with 4 parts of the base mix, and the 60% CPL mix was 3 parts CPL blended with 2 parts of the base mix.
The third step was to measure the dry matter bulk density, aeration porosity (AP), water holding capacity (WHC), and pot water capacity. The density of the four mixes was determined as the dry mass of material in a container with a calibrated volume. The AP and WHC were measured in the laboratory using a test chamber and procedure designed for this purpose (Chastain et al., 2023). The pot water capacity (g water/pot) was measured by filling 6, 6-inch pots with the same volume of each of the 4 mixes (24 pots total). The pots were brought to saturation and the water contained in the pots was measured. The pots were allowed to dry in the laboratory for 4 days and the mass of water in each pot was measured again. The complete details are provided by Chastain et al. (2023).
Table 1. Chemical and physical characteristics of the bark and composted poultry litter used to make the four potting mixes (mean of 3 reps). The moisture content of the sand used was 3.7%, the pH was 7.0, and the bulk density was 1.143 g DM/cm3.
Screened Pine Bark
(% d.b.)
Composted Poultry Litter
(% d.b.)
TAN (NH4-N + NH3-N)
0.00
0.00
Organic-N
0.33
0.96
Nitrate-N
0.00
0.12
Total-N
0.33
1.08
P2O5
0.12
2.45
K2O
0.22
0.82
Calcium
0.33
4.35
Magnesium
0.11
0.36
Sulfur
0.05
0.20
Zinc
0.004
0.02
Copper
0.001
0.02
Manganese
0.014
0.02
Sodium
0.023
0.15
Organic Matter
92.6
13.7
Carbon
52.4
9.94
C:N
161:1
9.2:1
EC5 (mmhos/cm)
2.56
0.71
pH
5.10
7.33
Moisture (%)
59.4
25.6
Density (g DM/cm3)
0.164
0.607
The final step involved calculating the concentrations of plant nutrients and other characteristics from the data shown in Table 1 as a weighted mean based on mass. These nutrient concentrations were converted to a volume basis (lb/yd3) using the mix bulk densities. The volumetric nutrient concentrations of the three CPL and base mix blends were compared with the range of nutrient concentrations that would result from mixing a 14-14-14 pellet fertilizer with the base mix at the rate of 3 to 8 lb per cubic yard.
What Have We Learned?
The results of mixing 20%, 40% and 60% CPL with the base mix on important properties of potting media are given in Table 2 along with target values from the literature. As the amount of composted litter (CPL) was increased the aeration porosity decreased from an unacceptable value of 30% for the base mix to 18% for the 20% CPL mix and 12% for the 60% CPL mix. The target range for water holding capacity is 45% to 65%. The highest WHC of 50% was for the 40% CPL mix followed by a WHC of 48% for the 20% CPL mix. The most limiting media characteristic appeared to be pH. The desirable range for media pH ranges from 5.5 to 6.4 depending on the plant to be grown. Based on the upper limit of this range, the highest amount of this compost product that would be recommended based on this study was 40%. Therefore, these results indicate that the amount of CPL that should be considered for most potting media would be in the range of 20% to 40% of the mix. The actual percentage of CPL that should be used will depend on the pH requirements of the plants to be grown. The pot water capacity results also showed that increasing the percentage of CPL in the mix increased the amount of water that would be held in a container at saturation and after 4 days of evaporation. If a media pH of 6.1 is suitable for the plant to be grown then these results suggest that the 40% CPL mix would be the best since it would provide an AP of 15%, a WHC of 50%, and an increase in pot water capacity of 20% at saturation and 29% following 4 days of evaporation with no irrigation. Using 40% CPL in a potting mix would also provide a 35% increase in dry bulk density which should reduce pot tipping in a production or retail nursery.
Table 2. Impact of adding composted poultry litter (CPL) to a bark-sand base mix on key potting media characteristics. The amount of CPL in the mix was 0%, (100% Base Mix), 20% (20% CPL), 40% (40% CPL), and 60% (60% CPL). AP is the aeration porosity, and WHC is the water holding capacity.
Media Property
100% Base Mix
20% CPL
40% CPL
60% CPL
AP (%) – Target: 10% to 20%
30
18
15
12
WHC (%) – Target: 45% to 65%
46
48
50
46
pH – Target: 5.5 to 6.4
5.3
5.7
6.1
6.5
Density (g DM/cm3)
0.31
0.37
0.42
0.47
Pot Water Capacity – at saturation (g/pot) A
390
420 (+8%)
468 (+20%)
523 (+34%)
Pot Water Capacity – after 4 days (g/pot) B
316
355 (+12%)
407 (+29%)
413 (+31%)
A The average mass of water contained in a 6-inch pot after adding enough water to bring the contents to saturation.
B The average mass of water contained in a 6-inch pot after allowing water to evaporate from the pots for 4 days.
The volumetric nutrient contents of the base mix, the fertilized base mix, and the 20% and 40% CPL mixes are compared in Table 3. The results for the 60% CPL mix were not included since the pH of 6.5 (Table 2) exceeded the upper value of the target range (pH = 6.4). Addition of the pellet fertilizer to the base mix and the 20% and 40% CPL mixes were able to reduce the C:N of the mix and change the plant available-N estimate from – 0.36 lb /yd3 to a positive value. That is, one of the goals of fertilizing a potting mix is to overcome the impact of nitrogen immobilization from the large amount of carbon in the pine bark. The actual target for plant available-N will vary with the plant to be grown. A similar result can be seen for the plant available P2O5. The base mix was not estimated to contain any useful P2O5. The addition of pellet fertilizer or using a CPL blend provided similar amounts of P-fertility. The two CPL mixes provided more K2O than the typical range of pellet fertilized mixes included in this study. The use of CPL instead of pellet fertilizer also added calcium, magnesium, sulfur, and other minor plant nutrients. The only elevated element that was undesirable was sodium. These results point out that potential minor nutrient toxicities (e.g. Mn, Zn) should also be considered when selecting the precise percentage of compost product to use in a potting mix.
Table 3. Comparison of the plant nutrients contained in the bark-sand base mix, fertilized base mix (3 to 8 lb slow-release fertilizer / cubic yard), and the 20% and 40% CPL mixes. The units are pounds of nutrient per cubic yard (lb/yd3)
Plant Nutrients
Base Mix
Fertilized
Base Mix
20% CPL
40% CPL
TAN (NH4-N + NH3-N)
0
0.28 to 0.69
0
0
Organic-N
0.81
0.80 to 0.81
2.61
4.41
Nitrate-N
0
0.20 to 0.49
0.24
0.48
Total-N
0.81
1.28 to 1.98
2.85
4.89
C:N
159:1
65:1 to 101:1
43:1
24:1
Plant Available-N A
– 0.36
0.29 to 1.09
0.19
0.70
P2O5
0.29
0.77 to 1.47
5.25
10.20
Plant Available P2O5B
0
0.47 to 1.17
0.42
1.63
Potash (K2O)
0.54
1.01 to 1.71
2.11
3.68
Calcium
0.82
0.82
9.56
18.3
Magnesium
0.27
0.27
0.95
1.62
Sulfur
0.11
0.11
0.50
0.89
Zinc
0.008
0.008
0.054
0.099
Copper
0.003
0.003
0.039
0.074
Manganese
0.034
0.034
0.072
0.111
Sodium
0.057
0.057
0.359
0.661
A Plant Available-N = m f CS [Org-N] + TAN + NO3-N, where m f CS = 0.139 – 0.0036 C:N, R2 = 0.84 (regression by Franklin et al., 2015, method given by Chastain et al., 2023).
P Plant Available P2O5 = PRf [P2O5] Potting MIX + [P2O5] Fertilizer, PRf = 0 for the base mix and blends with fertilizer and 0.40 for CPL. (data from Franklin et al., 2015, method given by Chastain et al., 2023).
The results of this study indicated that composted poultry litter can replace a significant portion or all the expensive, non-renewable ingredients that are currently used to improve the AP, and WHC of a potting mix. The additional water capacity per pot may also reduce irrigation frequency, but additional work is needed. Also, use of CPL in the range of 20% to 40% of the mix can eliminate or reduce the need for lime for pH adjustment and pellet fertilizer to provide common levels of potting mix fertilization. These results only apply directly to the compost product used in this study. A similar study using composted cow manure (Owino et al., 2024) showed similar positive results. However, that product could not be used to adjust AP and WHC and media fertility in the same way as the product used in this study. These studies (Chastain et al., 2023; Owino et al., 2024) are intended to be used as a guide to determine the best compost and base mix proportions based on analysis of the initial ingredients. The final choice concerning the amount of compost to use should be made after growing trial pots of the plant to be produced in a the most beneficial mix.
Future Plans
This information has been used to develop extension programs for poultry and livestock producers that manufacture compost or who are considering composting litter as a treatment option. The other target audience for this information is producers of container ornamentals. Additionally, plant specific trials would be helpful to communicate information concerning the use of compost products in container production. An easy-to-use program or spreadsheet that would allow comparison of potting mix characteristics based on laboratory analysis would allow producers to design one or two mixes that may meet the specific needs of their plants. This would greatly reduce the amount of time needed to test the most beneficial blends.
Authors
Presenting & corresponding author
John P. Chastain, Professor and Extension Agricultural Engineer, Clemson University, jchstn@clemson.edu
Additional authors
Hunter F. Massey, Principle Lecturer, Department of Agricultural Sciences; Tom O. Owino, Associate Professor, Department of Environmental Engineering and Earth Sciences, Clemson University
Additional Information
Chastain, J.P., Massey, H.F., Owino, T.O. 2023. Benefits of Adding Composted Poultry Litter to Soilless Potting Media for the Production of Woody Ornamentals. In: Barbosa, J.C., Silva, L.L., Rico, J.C., Coelho, D., Sousa, A., Silva, J.R.M., Baptista, F., Cruz, V.F., (Eds.) Proceedings of the XL CIOSTA and CIGR Section V International Conference: Sustainable Socio-Technical Transition of Farming Systems. Évora, Universidade de Évora, pp. 10-21, https://rdpc.uevora.pt/rdpc/handle/10174/35910.
Franklin, D., D. Bender-Ӧzenҫ, N. Ӧzenҫ, and M. Cabrera. 2015. Nitrogen mineralization and phosphorus release from composts and soil conditioners found in the southeastern United States. Soil Science Society of America Journal 79:1386-1395. doi:10.2136/sssaj2015.02.0077.
Owino. T.O., Chastain, J.P., Massey, H.F. 2024. Using Composted Cow Manure to Improve Nutrient Content, Aeration Porosity, and Water Retention of Pine Bark-Based Potting Media. In: Cavallo, E., Cheein, F.A., Marinello, F., Saҫilil, K., Muthukumarappan, K., Abhilash, P.C., (Eds.) 15th International Congress on Agricultural Mechanization and Energy in Agriculture ANKAgEng’2023, Lecture Notes in Civil Engineering, Springer Nature Switzerland, 458, pp. 240–261, https://doi.org/10.1007/978-3-031-51579-8_23.
Acknowledgements
This work was supported by the Confined Animal Manure Managers (CAMM) Program of Clemson University Extension. Composted poultry litter was supplied by Mr. Tim McCormick, and the pine bark was supplied by a manufacturer of soil amendments located in, Anderson, SC. Dr. R.F. Polomski, Associate Extension Specialist–Horticulture/Arboriculture at Clemson University, provided valuable assistance in selecting the ingredients for the base mix and provided valuable insight concerning woody ornamental production. Dr. K. Moore, retired director of the Agricultural Service Laboratory, directed the chemical analyses.
The authors are solely responsible for the content of these proceedings. The technical information does not necessarily reflect the official position of the sponsoring agencies or institutions represented by planning committee members, and inclusion and distribution herein does not constitute an endorsement of views expressed by the same. Printed materials included herein are not refereed publications. Citations should appear as follows. EXAMPLE: Authors. 2025. Title of presentation. Waste to Worth. Boise, ID. April 7-11, 2025. URL of this page. Accessed on: today’s date.
The forms of nitrogen contained in poultry litter are organic-N, ammonium-N, ammonia-N, and nitrate-N. One of the challenges in using poultry litter as a fertilizer substitute is making a good estimate of the plant available nitrogen (PAN). The value of PAN will depend on estimates of the amount of N that is lost to the air as ammonia following land application and the amount of organic-N that will be mineralized in the soil. The objectives of this workshop are to: (1) summarize organic-N mineralization data, (2) summarize the available data concerning ammonia loss following surface application of poultry litter, (3) review data concerning how fast ammonia is lost from a field to determine how quickly incorporation should be scheduled post-application, (4) provide means values from data to provide a practical guide for PAN calculations, and (5) compare the PAN estimates from the new method with current recommendation used by Clemson University Cooperative Extension.
What Did We Do?
Not all the nitrogen in poultry litter is available for plant use during the first growing season. The amount of N that can be used as a fertilizer substitute is the fraction of the organic-N (Org-N) that will be mineralized to ammonium-N following land application, the fraction of the ammonium-N (NH4-N) that is not lost as ammonia (NH3-N) and any nitrate-N (NO3-N) that is present in the litter. The recommended equation to estimate the plant available-N (PAN) is:
(1) PAN = mf Org-N + Af TAN + NO3-N (Evanylo, 2000; Chastain et al., 2001).
The amount of organic-N that will be mineralized depends on the organic-N content of the litter (lb Org-N/ton) and the mineralization factor, mf. The total ammoniacal-N (TAN) is usually reported on a litter analysis sheet as ammonium-N, but it is the sum of the ammonium-N and ammonia-N contained in the litter (TAN = NH4-N + NH3-N). It is the ammonia part of TAN that can be lost to the air following broadcast application of litter. Loss of PAN as volatilized ammonia is of concern because it represents a loss of N that may be used for plant production, and it contributes to air pollution. The amount of TAN that remains contributes to the estimate of PAN and is described by an availability factor, Af. The value of Af is the percentage of TAN lost as ammonia (AL) following application of litter is calculated as Af = 1 – (AL/100) where the value of AL is obtained from field measurements. Poultry litter generally only contains very small amounts of nitrate-N (1 to 5 lb NO3-N/ton) and all of it counts toward PAN.
Several publications have reported measurements of the mineralization factor, mf, for a variety of manure types. A summary of the literature was provided by Evanylo (2000) and the practical range of values for poultry litter are compared with other types of manure in Table 1. In South Carolina, an mf of 0.60 has shown to work well in practice. However, in cooler climates the best value may be 0.50 since low soil temperatures generally slow the mineralization rate. Other factors such as soil pH, and moisture content can result in variation in the amount of organic-N that will actually be mineralized in a particular field. The values shown in the table are good recommendations for practical use unless a better value is available for a particular state or region. Some organizations (e.g. Clemson University Extension) use a single value of mf for manure from all types of animals. However, the available data indicates that the value of mf to be used in equation 1 should vary with animal type.
Table 1. Mineralization factors (mf) for common types of animal manure (Evanylo, 2000; Chastain et al., 2001).
Recommended mineralization factors
Poultry
0.60 (0.50 to 0.70)
Swine
0.45 (0.40 to 0.50)
Dairy
0.35 (0.25 to 0.35)
Beef
0.40 (0.30 to 0.45)
Several studies and literature reviews provided data concerning the maximum amount of ammonia that was lost after applying poultry litter to hay or ryegrass fields (Lockyer et al., 1989; Marshall et al., 1998; Meisinger and Jokela, 2000; Nathan and Malzer, 1994; Montes, 2002). The theory and data contained in these publications indicated that the amount of ammonia that was lost from surface applied broiler and turkey litter was influenced by the pH of the litter, the pH of the soil or residue that was on the field at time of application, and the temperature. In general, it was shown that if the litter was applied to residue with a high pH (8+) the amount of ammonia lost following broadcast application was increased and if the pH of the residue was low (about 5, Montes, 2002) the amount of ammonia lost decreased. The air temperature on the day of application also influenced the amount of ammonia that was lost with an increase in temperature from 68 degrees to 85 degrees causing an increase in ammonia loss by a factor of about 2. The average maximum ammonia loss (AL) following broadcast of bedded poultry litter to a mowed grass field was determined to be 37% (n = 6, coefficient of variation = ± 19.7%) with a 95% confidence interval that ranged from 29% to 44%. Much less data was available concerning the amount of ammonia lost after application of bedding-free poultry litter. This type of litter is removed from high-rise layer buildings, manure below the roost areas in broiler breeder barns, and un-bedded litter removed from some broiler barns. The data indicated that less ammonia was lost as compared to bedded litter due to the lower pH of the material. The recommended estimate of AL for un-bedded litter is 28%. Therefore, the recommended values for Af to be used in equation 1 for broadcast application of litter during the cooler weather of spring and fall is 0.63 for bedded poultry litter (most broiler and turkey barns) and 0.72 for un-bedded litter. If litter is applied during summer, which is not common, the AL values were doubled based on theory and practical measurements and gave a summertime Af value of 0.26 for bedded litter and a summertime Af value of 0.44 for un-bedded litter.
A common recommendation to reduce ammonia loss after spreading poultry litter, or granular N fertilizer, is to incorporate the litter into the soil with a disk harrow on the same day or provide irrigation of more than 0.25 inches of water. Light disking has been shown to reduce ammonia loss significantly (Chastain et al., 2001; Pote and Meisinger, 2014). The resulting value of Af that has been recommended for use is 0.80 if litter is incorporated on the same day that it was spread. The key question is how much time can lapse between spreading litter and incorporation to get an Af of 0.80? The measurements provided by Montes (Montes, 2002; Montes and Chastain, 2005) indicated that 98% of the total ammonia loss occurred 24 hours after application and 70% of the total had already been lost to the air after 8 hours. The results provided by Montes along with the average maximum ammonia loss values from the literature were combined to provide the recommended Af values given in Table 2. These results indicate that if the goal of incorporation is to yield an Af of 0.80 the litter must be incorporated within 2 to 8 depending on the season of the year and whether the litter contained bedding.
Table 2. Recommended TAN availability factors, Af, for application of poultry litter with and without incorporation.
Bedded Litter
Un-Bedded Litter
Spring and Fall
Summer
Spring and Fall
Summer
Af
Af
Af
Af
Broadcast – no incorporation
0.63
0.26
0.72
0.44
Time lapse before incorporation
1 hour
0.95
0.90
0.96
0.92
2 hours
0.90
0.81
0.93
0.85
3 hours
0.87
0.73
0.90
0.80
4 hours
0.83
0.67
0.87
0.75
6 hours
0.78
0.56
0.83
0.67
8 hours
0.74
0.48
0.80
0.61
What Have We Learned?
The impact of the method to estimate PAN using the Af values developed from the literature (Table 2) is best demonstrated by a practical example using nitrogen concentrations obtained from a broiler barn with bedded litter. The nitrogen contents and the estimates of PAN based on the current Clemson Extension recommendation and the PAN estimates using the new information are compared in Table 3. For this litter analysis, the PAN estimate using the new recommendation was 6% larger indicating a small increase in useful N. It was assumed that the litter application rate would be based on an agronomic rate of 100 lb N/ac. The calculated application rates were rounded to the nearest ton/ac and gave 3 tons of litter per ac in both cases. The estimate of ammonia emissions per 100 acres was decreased from 1650 lb NO3-N/ac using the old values to 1221 lb NO3-N/ac based on the mean Af from the available data. These results indicate that the current Clemson Extension recommendations are under predicting the amount of PAN that could be used as an N-fertilizer substitute. The more significant impact is that the current recommendations over predict ammonia-N emissions by 26%.
Table 3. Comparison of the PAN estimates and the ammonia-N emissions per 100 acres using the current Clemson Extension recommendations and the new values of Af based on a review of the literature. The calculations are for bedded broiler litter that contains 42 lb Org-N/ton, 11 lb TAN/ton, 1.4 lb NO3-N/ton and spread to provide 100 lb of N/acre. Both litter application rates rounded to 3.0 tons/acre.
Clemson Extension Recommendation
New Recommendation Based on Tables 1 & 2
mf
0.60
0.60
Af
0.50
0.63
PAN estimate (equation 1) – lb PAN/ton
32
34
Percent difference
+6%
Litter Application Rate – tons/acre
3.0
3.0
Ammonia loss – lb NH3-N/100 ac
1650
1221
Percent difference
(-26%)
Future Plans
The immediate plans are to use these results to provide a more realistic estimate of PAN and ammonia emissions for poultry litter in South Carolina. These results can also be used by Extension Educators in other states and regions to revise estimates of PAN for their conditions. The method presented in this paper can also be used in the future as better estimates of mf and Af are empirically determined.
Authors
Presenting & corresponding author
John P. Chastain, Professor and Extension Agricultural Engineer, Clemson University, jchstn@clemson.edu
Additional Information
Chastain, J.P., J.J. Camberato, and P. Skewes. 2001. Poultry Manure Production and Nutrient Content. Chapter 3B in Confined Animal Manure Managers Certification Program Manual: Poultry Version, Clemson University Extension, Clemson SC, pp 3b-1 to 3b-17. https://www.clemson.edu/extension/camm/manuals/poultry/pch3b_00.pdf.
Lockyer, D., B. F. Pain, J. V. Klarenbeek. 1989. Ammonia Emissions from Cattle, Pig and Poultry Wastes Applied to Pasture. Environmental Pollution 56:19-30.
Marshall, S.B., C. W. Wood, L. C. Braun, M. L. Cabrera, M. D. Mullen, E. A. Guertal. 1998. Ammonia Volatilization from Tall Fescue Pastures Fertilized with Broiler Litter. Journal of Environmental Quality 27(5): 1125-1129.
Meisinger, J.J., W.E. Jokela. 2000. Ammonia Volatilization from Dairy and Poultry Manure. In: Managing Nutrients and Pathogens from Animal Agriculture (NRAES-130). 334-354. Ithaca, NY: NREAS, Cooperative Extension, Cornell University.
Nathan, M.V., G. L. Malzer. 1994. Dynamics of Ammonia Volatilization from Turkey Manure and Urea Applied to Soil. Journal of Environmental Quality 58(3): 985-990.
Montes, F. 2002. Ammonia Volatilization Resulting from Application of Liquid Swine Manure and Turkey Litter in Commercial Pine Plantations. MS Thesis, Clemson University, Clemson, SC.
Montes, F., J.P. Chastain, 2005. Ammonia Volatilization from Turkey Litter Application in a Pine Plantation in South Carolina. ASAE Paper No. 054077, St. Joesph, Mich.: ASABE.
Pote, D., J.J. Meisinger. 2014. Effect of Poultry Litter Application Method on Ammonia Volatilization from a Conservation Tillage System. Journal of Soil and Water Conservation 69(1):17-25.
Acknowledgements
This work was supported by the Confined Animal Manure Managers (CAMM) Program of Clemson University Extension.
The authors are solely responsible for the content of these proceedings. The technical information does not necessarily reflect the official position of the sponsoring agencies or institutions represented by planning committee members, and inclusion and distribution herein does not constitute an endorsement of views expressed by the same. Printed materials included herein are not refereed publications. Citations should appear as follows. EXAMPLE: Authors. 2025. Title of presentation. Waste to Worth. Boise, ID. April 7-11, 2025. URL of this page. Accessed on: today’s date.
According to the latest estimation of Food and Agriculture Organization of the United Nations, the global dairy cattle stocks reached over 265 million in 2019. The massive stocks of dairy cows excrete an enormous amount of manure, which is a huge burden to the environment if unproperly disposed of, thus necessitating proper manure treatment. As such, anaerobic digestion (AD) has been widely adopted as a practice to manage dairy cattle manure. Within the United States, digesters at dairy farms started to be widely constructed after 2000, and the number of these on-farm digesters in operation or under construction has increased to over 400 in 2024. During the AD treatment of dairy manure, the sulfate-reducing microorganisms are active under anaerobic conditions, therefore high levels of hydrogen sulfide (H₂S) are common in biogas because of the degradation and conversion of sulfur-bearing organics in feeding materials and sulfate-bearing minerals in bedding materials within the manure stream. As an extremely toxic gas with an acute rotten egg odor, H₂S is one of the leading causes of workplace gas inhalation deaths in the US according to the Bureau of Labor Statistics. In addition to the health risks, high H₂S levels can be also very corrosive to the equipment and infrastructure: long-term exposure to concentration of H₂S greater than 1 ppm reduces the lifespan of structural materials, equipment, and electronic devices inside the facilities. Therefore, it is an urgent task to mitigate the H₂S emissions in manure management.
Conventional H₂S removal technologies typically include two categories, namely ex-situ and in-situ. The ex-situ biogas cleaning technologies (e.g., biofilters, aqueous solutions, iron sponge, etc.) require a separate unit to house the facilities and are chemical- and energy-intensive. In-situ H₂S mitigation methods usually require less energy and chemical input as well as an easier operation. In our previous study which employed bio-electrochemical (BEC) treatment concurrently with AD of dairy manure, a H₂S removal efficiency of over 95% was successfully achieved, thus offering a very promising in-situ H₂S remediation method. Nonetheless, it was operated in a continuous mode with electrodes inserted into the digester, which would require significant modification of existing AD systems when scaled up. Therefore, developing new strategies that can advance the application of BEC H₂S remediation within the conventional AD system is critical.
What Did We Do?
Most large sized farms collect liquid manure and slurry in a reception pit (or transition pit) before manure is pumped to the anaerobic digesters. This pit is usually open to the air, thereby offering a great opportunity to integrate the BEC treatment in dairy manure management. In the present lab-scale study, a BEC unit was applied to pretreat the dairy manure collected from the transition pit. On the basis of our previous study, a combination of low carbon steel (LCS) anode and stainless-steel cathode was selected as the electrode pair. At the applied voltages of 1.0-2.5 V, the dairy manure was pretreated for 24 hours prior to AD tests. After the BEC pretreatment, the peak H₂S concentration in the biogas was reduced from approximately 6,000 ppm (in the control without BEC pretreatment) to below 420 ppm in the groups at the applied voltages over 1.5 V. The total H₂S removal efficiencies reached 48.9%, 89.1%, 98.5%, and 100% at 1.0 V, 1.5 V, 2.0 V, and 2.5 V, respectively, equivalent to the sulfide removal of 18.6, 33.4, 36.9, and 37.4 mg S²⁻/g wet dairy manure. Nonetheless, higher voltages did not trigger higher biogas production. Besides, due to the anodic oxidation that released some CO₂ and the precipitation of carbonate (e.g., CaCO₃) in BEC pretreatment, the CH₄ contents in the yielded biogas from BEC groups (64.5-65.6%) were all slightly higher than that from the control (63.4%). Moreover, it was noteworthy that the technical digestion time (T80) (i.e., the time needed to produce 80% of the maximal digester gas production) was shortened to 28.0-29.3 d in the BEC groups at 1.5-2.5 V as compared to 32.8 d in the control. This suggests that the BEC pretreatment can remarkably accelerate biogas production in addition to the H₂S remediation. Groups using non-sacrificial electrodes (e.g., graphite sheets and rods) were also established for the 24-h BEC pretreatment of dairy manure. However, in subsequent AD tests, a large quantity of gaseous H₂S was still emitted. The comparison between the groups with and without sacrificial LCS anodes indicates that the formation of insoluble ferrous sulfide (FeS) was the main route of sulfide removal, whereas the contribution of anodic sulfide oxidation to sulfate and elemental sulfur was relatively limited.
With all the selections and optimizations above, a pilot-scale electrochemical unit was accordingly designed and then installed and operated in the dairy manure pit in a local dairy farm in Minnesota for over two months (as shown in Fig. 1), and its effects in in-situ H₂S remediation in a real application scenario were documented. This pilot-scale BEC system reduced the headspace H₂S level from 1,808 ppb to 390 ppb with a removal efficiency of 78.4%.
Fig. 1 Pilot-scale BEC system installation and operation in dairy manure transition pit
What Have We Learned?
This lab-scale success as well as the pilot-scale implementation supports BEC as a promising method for integration into existing on-farm AD systems treating dairy manure. With its incorporation of a BEC unit into the open-air manure transition pit, the operation could be simplified to a large extent without the considerable modification of existing AD systems, whilst the H₂S remediation and the improvement in biogas production (in both CH₄ content and technical digestion time) could be simultaneously achieved at an optimum applied voltage. In summary, this proposed BEC system can successfully reduce the H₂S and improve the safety of a dairy farm during manure storage and treatment.
Future Plans
In our future research, we will further assess the sulfur distribution and microbial community changes after both lab-scale and pilot-scale BEC treatment and also optimize the BEC strategy to reduce anode consumption. Besides, a techno-economic analysis and a life cycle assessment are now under evaluation, based on the data obtained through both the lab-scale tests and the pilot-scale demonstration, to further explore the feasibility and applicability of a full-scale BEC system in a real dairy farm scenario.
Authors
Presenting author
Lingkan Ding, Researcher Pro 5, University of Minnesota
Corresponding author
Bo Hu, Professor, University of Minnesota, bhu@umn.edu
Acknowledgements
The authors greatly appreciate funding support from USDA NRCS Conservation Innovation Grant (NR213A750013G029) and the assistance of Dennis Haubenschild for on-site work on the farm.
The authors are solely responsible for the content of these proceedings. The technical information does not necessarily reflect the official position of the sponsoring agencies or institutions represented by planning committee members, and inclusion and distribution herein does not constitute an endorsement of views expressed by the same. Printed materials included herein are not refereed publications. Citations should appear as follows. EXAMPLE: Authors. 2025. Title of presentation. Waste to Worth. Boise, ID. April 7-11, 2025. URL of this page. Accessed on: today’s date.
Dairy manure was once considered a waste, but it can be transformed into a valuable resource. As demand for sustainable waste management grows, innovative ways for converting dairy manure are being actively researched to enhance both dairy productivity and environmental sustainability. One such method, hydrothermal carbonization (HTC), has recently garnered significant attention due to its ability to convert wet biomass into value-added products. HTC involves treating wet biomass, such as dairy manure with high water content, at moderate temperatures (180℃-250℃) and pressure. The outcome of HTC is hydrochar, a solid product with high carbon and nutrient content.
Hydrochar has strong potential as a means of soil amendment, carbon sequestration and/or biofuel. Our lab scale experiments showed that hydrochar retains more than 90% phosphorus (P) from dairy manure. For hydrochar production to become a viable technology for dairy farms, a continuous system is essential. Such a system would offer numerous benefits, including increased production, enhanced efficiency, and greater potential for commercialization. The purpose of this study is to design a pre-commercial conceptual process for the continuous production of hydrochar from dairy manure.
What Did We Do?
Manure management consists of collecting manure from the floor to utilize it in the best possible way. Most dairy farms treat manure through anaerobic digestion to produce energy, separate the solids for use as a bedding material, and/or apply directly to field applications. To explore alternative ways of handling the large quantities of manure in a quick chemical method and recycling nutrients back to the cropland, dairy manure is processed into P-rich hydrochar via an HTC process. Based on the results of our laboratory experiments, a conceptual process was developed, which is capable of treating dairy manure from a mid-size farm with 1,000 lactating cows and equates to 38,000 tons of manure per year with 8-10% solids. The process design includes engineering designing details of manure preparation and handling, feeding and discharge mechanisms, main equipment (such as HTC reactor and heat exchangers), heating and temperature controls, and schemes for post-HTC process wastewater (post-water) handling. Figure 1 is the schematic of the conceptual process with major process equipment, where the thick, black lines indicate the flow of dairy manure slurry containing solids, while the thin, blue lines represent the flow of post-processed water.
Firstly, dairy manure collected from the dairy barns (approx. 10% solids) is stored in a storage tank (T-101) before being pumped into the feeding tank (T-102), where it is heated to 167°F (75°C) by the recycled post-water from preheater I (E-201) through internal heating coils. The feeding tank is equipped with a marine-style impeller for agitation to maintain solid suspension. Two preheaters (E-201 and E-202) are used to further heat the slurry to the required HTC temperature before entering the reactor (R-301). Preheater I is a shell-and-tube heat exchanger to heat the slurry up to 320°F (160°C) by heat recovery using the hot post-water from post-water tank (T-304). Preheater II is a tubular electric heater and is to finish the last stage of heating to 437°F (225°C). A continuously stirred tank reactor (CSTR) with agitation is the main equipment to thermochemically process dairy manure into hydrochar. After a 30-minute retention time in the reactor, the resulting product mixture is collected in the receiving tank/separator (T-302). Then the hot post processed-water is separated from the solid (the wet hydrochar cake) and collected in a storage tank (T-304) before being used as a heating medium for heat recovery. The wet hydrochar cake coming out of decanter centrifuge (T-303) is dewatered through an air-drying unit (C-305) to a water content of 12% or less, which can be used directly for land applications or packaged and transported to other markets.
Figure 1 Schematic of the conceptual process with major process equipment.
What Have We Learned?
Continuous hydrochar production holds great potential for recycling phosphorus from dairy manure back into the cropland as a soil amendment and for sequestrating carbon back to the soil. The conceptual process represents a significant step towards practically promoting this alternative manure treatment technology and creating a value-added product for nutrient cycling. This process is capable of producing approximately 5 million pounds (2,300 metric tons) of air-dried hydrochar per year, a yield of about 60% of the solid matter from dairy manure, and with a phosphorus concentration of approx. 1.4 lb/100 lb. Hydrochar is hydrophobic and can be sufficiently dried by ambient air. The air dried hydrochar contains a moisture content of 12% or less (as low as 5% per laboratory results due to hydrochar’s hydrophobic characteristics) and is suitable for long term storage and/or distance transportation. Because the raw, wet dairy manure can be processed directly from the farm without any pretreatment, the HTC process offers a good possibility for a cost-effective waste management alternative while producing valuable hydrochar for phosphorus recycling.
Future Plans
Upon completing this continuous flow process design, we will conduct a techno-economic assessment (TEA) to provide insights into the system’s economic feasibility, cost structure, and profitability. The TEA study will also offer a better perspective on the economic viability, technical challenges, and potential profitability of adopting and investing in the continuous hydrochar production system from dairy manure for waste management and nutrient cycling.
Authors
Presenting author
Imran Hussain Mahdy, Graduate Student (Ph.D.), University of Idaho
Corresponding author
Brian He, Professor, University of Idaho, bhe@uidaho.edu
Acknowledgements
USDA AFRI, UADA NIFA and Idaho Agricultural Experiment Station are acknowledged for their financial support through Sustainable Agricultural Systems (SAS) program (Grant 2020-69012-31871), and hatch project of IDA0-1716 (Accession number1012741).
The authors are solely responsible for the content of these proceedings. The technical information does not necessarily reflect the official position of the sponsoring agencies or institutions represented by planning committee members, and inclusion and distribution herein does not constitute an endorsement of views expressed by the same. Printed materials included herein are not refereed publications. Citations should appear as follows. EXAMPLE: Authors. 2025. Title of presentation. Waste to Worth. Boise, ID. April 7–11, 2025. URL of this page. Accessed on: today’s date.
In Nebraska, approximately 117 out of nearly 550 groundwater-based community public water systems are required to conduct quarterly sampling due to elevated nitrate-N levels, with ten systems having already implemented costly treatment measures such as reverse osmosis to mitigate this issue. The intensive production of row crops under irrigation in the state are a primary reason for elevated nitrate concentrations in groundwater. However, the environmental impact of nitrate leaching from agricultural fields is not confined to Nebraska; it is a widespread issue across the US Midwest, where intensive crop production is prevalent.
Despite advances in N management stemming from studies comparing nitrogen fate and transport under synthetic versus manure fertilizers, cover crops versus no cover crops, and other practices, research indicates that when manure is applied following research-based best management practices (BMPs), the risk of nitrate leaching is significantly lower compared to when synthetic fertilizers are applied following BMPs. While individual practices such as cover cropping or manure application have been shown to reduce nitrate leaching, their combined effects on both nitrate leaching potential and crop productivity, particularly in corn (Zea mays L.) systems, have not been thoroughly studied. There remains a critical need to comprehensively evaluate implementation of BMPs that can reduce nitrogen losses to groundwater in Nebraska and utilize evidence-based research to motivate the implementation of BMPs.
This study was conducted to evaluate the effects of the integrated use of beef manure, woodchips, and cover crops on corn (Zea mays L.) productivity and nitrate leaching.
What Did We Do?
A two-year study was conducted on drip-irrigated land with a loamy sand soil having 0 to 2% slopes at UNL’s Haskell Agricultural Laboratory research site near Concord, Nebraska from 2022 to 2023. A total of 24 plots were established, each measuring 6.1 m x 30.48 m, and six treatments were randomly assigned to plots in a factorial combination of two fertilizer sources (manure and inorganic fertilizer), two cover crops (rye cover crop and no cover crop), and two carbon amendment treatments (woodchips of mixed species and no woodchips). Each year, all the plots received the same total N rate, equating to 30% of the total N application broadcasted at planting in the form of Agrotain coated urea, which was calculated using University of Nebraska’s N rate algorithm. The manure plots received the remaining N (70% of the total) in the form of beef manure at planting using a manure spreader. The inorganic plots received the remaining N in the form of UAN side-dressed at the V6 corn growth stage. Each year, inorganic fertilizer plots received additional P, S, and Zn at the time of planting to balance the amount of these nutrients supplied by the manure.
Data collected included:
Soil. Deep core soil samples up to 120 cm were collected before planting in the spring and after harvest each fall, divided into four depths of 30 cm increment, composited by depth within each plot, and stored in a cooler before being transported to the lab for analysis.
Crop. Plant growth parameters assessed at V10 (±1) stage included plant height, leaf chlorophyll, and canopy fullness. Grain yield, harvest index, nitrogen harvest index and partial factor productivity were determined at harvest.
Water. Concentration of NO3-N and NH4-N in the pore water below the root zone was measured one to two times each week throughout the growing season with the help of suction cup lysimeters, two of which were installed 6 m apart between the center two rows of each plot at a depth of 1.2 m.
Cover crop failed to establish in 2023 spring due to dry conditions, therefore, cover crop data and its effects are not reported in this paper.
What Have We Learned?
Key results of this study include:
Manure significantly reduced nitrate leaching by providing a slower, more synchronized N release compared to inorganic fertilizers.
Woodchip mulch initially delayed N availability and biomass N uptake but ultimately helped reduce nitrate leaching by improving soil moisture retention and temperature moderation.
Aboveground biomass N uptake was significantly affected by fertilizer source with manure improving biomass N uptake by 11% compared to inorganic fertilizer.
Inorganic fertilizers boosted corn yields by 9% compared to manure treatments, but increased the risk of nitrate leaching, highlighting a trade-off between productivity and environmental impact.
Integrated management of manure and mulch was deemed crucial for optimizing N use efficiency and minimizing environmental risks in irrigated corn systems.
Future Plans
Identifying nutrient and land management practices that support sustainable agricultural practices by safeguarding groundwater quality while maintaining farm productivity are critical to the future of agriculture. Future research is expected to focus on refining the practices used in this study to maximize their benefits, including other practices such as in-season nitrogen management, and assessing outcomes under varying environmental conditions and soil types. Nitrogen availability from manure is heavily influenced by environmental and soil conditions, so multi-year data from this site and others should help determine when in-season nitrogen supplementation with inorganic fertilizer is needed to offset nitrogen deficits caused by slow conversion of organic nitrogen.
Because of the failure of cover crops to thrive in this study, future research to assess multiple practices in combination should include a cover crop versus no cover crop treatment.
Combining crop productivity and nitrogen fate and transport data with measures of soil biological conditions may also help identify trends in biological characteristics that contribute significantly to factors like nitrogen conversion and plant nitrogen uptake.
Authors
Presenting & corresponding author
Amy Millmier Schmidt, Professor and Livestock Bioenvironmental Engineering Specialist, University of Nebraska-Lincoln, aschmidt@unl.edu
Additional authors
Swetabh Patel, Assistant Professor, University of Minnesota; Michael Kurtzhals, Graduate Research Assistant, University of Nebraska-Lincoln; Arshdeep Singh, Graduate Research Assistant, University of Nebraska-Lincoln; Leslie Johnson, Extension Educator, University of Nebraska-Lincoln; Javed Iqbal, Assistant Professor, University of Nebraska-Lincoln
This research was funded by USDA-NIFA Award No. 2022-68008-36509.
The authors extend their sincere gratitude to Logan Dana, Operations Manager at the UNL Haskell Ag Lab, for his role in supporting this project.
The authors are solely responsible for the content of these proceedings. The technical information does not necessarily reflect the official position of the sponsoring agencies or institutions represented by planning committee members, and inclusion and distribution herein does not constitute an endorsement of views expressed by the same. Printed materials included herein are not refereed publications. Citations should appear as follows. EXAMPLE: Authors. 2025. Title of presentation. Waste to Worth. Boise, ID. April 7–11, 2025. URL of this page. Accessed on: today’s date.
Microbes are abundant in manure and food waste. Harnessing and/or controlling microbial action in a treatment process is challenging – but some technologies are making headway. This webinar will present pilot-scale research for manure and food waste treatment. This presentation was originally broadcast on March 21, 2025.Continue reading “Mobilizing Microbes in Treatment Processes”
*note: due to a technical glitch, the audio at the beginning of this recorded presentation was not captured. Please accept our apologies.
Purpose
Sustainable intensification of agriculture aims to boost food production while minimizing environmental damage. Current farming practices often lead to inefficient nutrient cycling, contributing significantly to water and air pollution. Agricultural runoff, especially from livestock systems, introduces pollutants like nitrogen and phosphorus into waterways, causing issues like eutrophication and anoxic conditions, which harm aquatic ecosystems. Agricultural emissions also account for a large portion of global methane and nitrous oxide emissions. To meet increasing food demands, farms have intensified production, further worsening environmental impacts due to increased use of nutrients and feed. Addressing these issues requires innovative solutions that can balance productivity and sustainability.
One promising approach is pyrolysis, which thermochemically converts biomass into syngas, bio-oils, and biochar. While syngas and bio-oils are used for energy, biochar can improve soil health, reduce nutrient leaching, and sequester carbon. Research shows biochar can effectively retain nitrogen and phosphorus, making it a potential candidate for use in wastewater treatment and as a manure storage cover to reduce emissions. Additionally, converting manure into biochar could improve transport logistics by densifying nutrients, making it more economically feasible for farms to manage nutrient surpluses. However, more research is needed to expand biochar’s use beyond fields and into broader agricultural applications to fully realize its environmental and economic benefits.
What Did We Do?
A pilot pyrolysis system, the Pilot Activator from ARTi (Figure 1), was installed at UW-Platteville to process biomass under controlled conditions, allowing for plot-scale studies on biochar applications in agriculture. Biochar was made from separated manure solids at 400 and 600 degrees C at the pilot system at UW-Platteville. Additional biochar was produced from wood chips from a full-scale system integrated at a site in Wisconsin. Biochar was applied to plot trials (Figure 2) to assess the impacts to yield, soil nutrient cycling, crop nutrient uptake, and greenhouse gas and ammonia emissions with varying manure and biochar applications. The trials have been divided into two concurrent field trials to assess various aspects of biochar incorporation practices into livestock-cropping systems.
Figure 1. Pilot scale pyrolysis unit
Trial 1 – Separated manure solids biochar as a phosphorus fertilizer
The main objective in this study is to examine the impacts of applying separated manure solids versus biochar made from separated manure solids to assess the impact of pyrolysis on the phosphorus availability. Separated manure solids (10.9 tons/acre) and biochar produced from separated manure solids at 400 and 600 degrees C was applied based on phosphorus demands for corn silage and supplemented with urea after biochar application, incorporated into soil, to meet recommended nitrogen application. Crop yield and soil impact were assessed at the end of the trial.
Trial 2 – Biochar amended slurry manure
The main objective in this second trial is to examine the impacts of integrating biochar with slurry manure applications to assess the impacts to corn silage production systems, ammonia and greenhouse gas emissions. Slurry manure was applied at a rate of 10,000 gal/acre and biochar was applied and incorporated. Treatments included manure control, biochar made from separated solids at 400 and 600 degrees C at 1 ton/acre, wood biochar made at 600 degrees C applied at 1, 2,5, 5 and 10 tons per acre, and a control that received no manure or biochar. Plots were assessed for the impact to soil nutrient concentration, corn silage yield, nutrient use efficiency, and emissions (measured using a Gasmet Technologies Inc. model DX4015 Portable Fourier-transform infrared spectroscopy (FTIR) Multi-component Gas Analyzer).
For each trial, soil sampling and analysis was conducted prior to amendment application, post application, and post-harvest. Corn silage was grown in all trials and harvested and weighed at the end of each trial. Biochar was always applied to the soil following manure application and then incorporated within 24 hours. At the end of the season, plant tissue samples were collected, dried, and analyzed for nutrient uptake to be used to calculate nutrient use efficiency.
Figure 2: Land application of biochar to field trial plots before and after incorporation
What Have We Learned?
Data is currently being analyzed from year one of the field trial to assess the impacts with biochar application. Thus far, we have determined little difference in yields in the treatments for both trials. This indicates for trial 1 that phosphorus availability from biochar produced from separated manure solids is similar to that of the separated solids. Additional data analysis will allow for comparison of emissions and impacts to soil nutrients.
Future Plans
Additional data analysis will be completed this spring to determine statistical differences in treatments for the parameters measured. In addition, as biochar is thought to have greater impacts in future cropping years, the fields will have manure applied in year 2 and the plots analyzed again for the same impacts as year one to determine further impacts as biochar ages in the soil.
Authors
Presenting and Corresponding author
Rebecca A. Larson, Professor, Nelson Institute for Environmental Studies, University of Wisconsin-Madison, rebecca.larson@wisc.edu
Additional author(s)
Tyler Liskow, Engineer, Nelson Institute for Environmental Studies, University of Wisconsin-Madison; Brian Langolf, Researcher, Nelson Institute for Environmental Studies, University of Wisconsin-Madison; and Joseph Sanford, Assistant Professor, University of Wisconsin-Platteville
This material is based on work that is supported by the National Institute of Food and Agriculture, U.S. Department of Agriculture, NLGCA under award number 2022-70001-37309.
Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.
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Scheduling conflicts, equipment breakdowns, and wet field conditions can wreak havoc on spring manure application and planting schedules. This webinar will provide valuable insights into maximizing the efficiency and timing of manure application for growing crops, especially corn. By exploring innovative techniques for liquid manure application and the potential for in-season poultry litter application, participants will learn possible ways to navigate challenges in crop management while ensuring nutrient efficiency and maintaining crop yield and quality. This presentation was originally broadcast on January 17, 2025. Continue reading “Application of Manure on Growing Crops”
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