Effects of Adding Clinoptilolite Zeolite on Dairy Manure Composting Mix on the Compost Stability and Maturity

The purpose of this project was to demonstrate the effects of adding natural clinoptilolite zeolites to a dairy manure compost mix at the moment of initiating the composting process on characteristics of the final compost and nitrogen (N) retention. On-farm composting of manure is one Best Management Practice (BMP) available to dairy producers. Composting reduces the volume of composted wastes by 20 to 60% and weight by 30 to 60%, which allows the final product to be significantly more affordable to transport than raw wastes. When done properly, composting can convert a considerable fraction of the N present in the raw manure into a more stable form, which is released slowly over a period of years and thereby not partially lost to the environment (Rynk et al., 1992; Magdoff and Van Es, 2009). During the manure handling and composting process, between 50 and 70% of the N can be lost as ammonia (NH3) if additional techniques are not used to increase nitrogen retention. Most of the time, manures from dairies and other livestock operations don’t have the proper carbon to nitrogen ratio (C:N) to be composted efficiently without added carbon. A balanced mix for composting should be between C:N of 30:1 to 40:1 (Rynk et al., 1992; Fabian et al., 1993). Since manures are richer in nitrogen (C:N ratios below 15:1), and bedding doesn’t add enough carbon during most of the year, a great proportion of the available N is lost as NH3 due to the lack of carbon to balance the composting process, resulting in a lower grade compost that can generate local and regional pollution due to NH3 emissions. In many arid zones there are not enough sources of carbon to balance the nitrogen present in the manure. Due to this lack of adequate carbonaceous material, additional methods to reduce the loss of N as NH3 during the composting process are needed. Several amendments have been evaluated in the past to achieve this reduction in N loss (Ndegwa et al., 2008). Zeolites are minerals defined as crystalline, hydrated aluminosilicates of alkali and alkaline earth cations having an infinite, open, three-dimensional structure. Clinoptilolite zeolite is mined in several western states including Idaho, where mining is near the dairy production areas.

This paper showcases an on-farm project that explored the effects of adding clinoptilolite to dairy manure at the time of composting as a tool to reduce NH3 emissions, retain N in the final composted product, and evaluate its effect on the final product.

What did we do?

This on-farm research was conducted at an open-lot dairy in Southern Idaho with 100 milking Jersey cows. Manure stockpiled during the winter and piled after the corral’s cleaning was mixed with fresh pushed-up manure from daily operations and straw from bedding and old straw bales, in similar proportions for each windrow. The compost mixture was calculated using a compost spreadsheet calculator (WSU-Puyallup Compost Mixture Calculator, version 1.1. Puyallup, WA). Moisture was adjusted by adding well water to reach approximately 50% to 60% moisture on the initial mix. Windrows were mixed and mechanically turned using a tractor bucket. Three replications were made for control and treatment. The control (CTR) consisted of the manure and straw mix as described. The treatment (TRT) consisted of the same mix as the control, plus the addition of 8% w/w (15%DM) of clinoptilolite zeolite during the initial mix. Windrows were actively composted for 149 days on average. Ammonia emissions were measured using passive samplers (Ogawa & Co. Kobe, Japan) and results were described in a previous Waste to Worth proceeding paper (de Haro Martí, et al. 2017). Complete initial manure (compost feedstock mix) and final screened compost nutrient lab analyses were performed for each windrow. Compost maturity tests were performed using the SOLVITA® test (Woods End Laboratories, Mt Vernon, ME). Statistical analyses were conducted using SAS 9.4 (SAS Institute, Cary, NC). Analyses included ANOVA (PROC MIXED) and paired t-test when applicable.

What have we learned?

The initial mix lab analysis revealed no significant differences in all parameters between control and treatment, except for ammonium (NH4+) where a tendency was observed. Many of the most stable parameters were very close to one another numerically, indicating a good management of the on-farm feedstock formulation and mixing. Ammonium at 553.4±100 mg/kg for CTR and 256.77±100 mg/kg for TRT showed a tendency (0.05<p≤0.1, Figure 1).

Figure 1. Ammonium ppm before and after composting   
Figure 1. Ammonium ppm before and after composting

This difference from the beginning of the process indicates that clinoptilolite has an immediate impact on NH4+ when added to the compost mix, changing the NH4+ and NH3 behavior and volatilization even during the construction of the windrow.

Nitrate (NO3) concentration in the TRT compost, 702±127 mg/kg was three times higher than the CTR, 223±127 (p= 0.05, Figure 2).

Figure 2. Nitrate ppm before and after composting
Figure 2. Nitrate ppm before and after composting

The presence of such high amount of NO3 compared to the control indicates a strong prevalence of nitrification processes (Sikora and Szmidt, 2001; Weil and Brady, 2017). Elevated NO3 concentrations are desirable in high quality compost used in plant nurseries, green houses, and horticulture, and are usually obtained from feedstock with much higher carbon content than the one used in this research. The NO3 to NH4+ ratio (NO3:NH4) in the treated windrows is also indicative of a much more stable compost than what is to be expected in a dairy compost with such low initial C:N (Sikora and Szmidt, 2001). High NO3 concentrations in compost could, however, generate a concern for NO3 leaching if the compost is not managed properly during storage and at the time of application (Miner et al., 2000; Weil and Brady, 2017). Total nitrogen (TN) on the compost was 14,933±1,379 mg/Kg (1.5%) for CTR and 11,300±1,379 mg/Kg (1.1%) for TRT (p=0.13), showing no significant difference.

Table 1. Solvita® test results on finished compost
Sample TRT or CTR



Maturity Index Compost Condition O2 depletion Phytotoxicity Noxious hazard pH NH4+ Estimate (ppm) N-Loss potential
W 1 CTR 6.5 3.5 5.5 Curing 1.60% Medium/ Slight Moderate /Slight 9.1 500 Moderate/Low
W 2 CTR 6.5 2 4.5 Active 2.50% High Severe 9.3 1500 M/ High
W 5 CTR 6.5 2 4.5 Active 2.50% High Severe 9.8 1500 M/ High
W 3 TRT 7 5 7 Finished 0.70% None None 9.5 <200 V Low-None
W 4 TRT 7 5 7 Finished 0.70% None None 8.9 <200 V Low-None
W 6 TRT 6 5 6 Curing 1.20% None None 9.3 <200 V Low-None

The Solvita® test results from the screened composts (Table 1) show a significant difference (p=0.007) in the NH3 test results between CTR, index 2.5±0.35 and TRT, index 5.0±0.35. Carbon Dioxide (CO2) test results showed no significant differences between CTR and TRT. All other calculated parameters showed a significant difference between control and treatment. Maturity index was 4.8±0.33 for CTR and 6.7±0.33 for TRT (p<0.02). Oxygen depletion was 0.022±0.002 for CTR and 0.009±0.002 for TRT (p<0.02). NH4+ estimate was 1167 for CTR and <200 for TRT (p=0.05). Other estimated test parameters indicate a significant difference between CTR and TRT results. Control windrows showed more unstable conditions, reaching the active or curing status, medium to high phytotoxicity, moderate to severe noxious hazard, and moderate to low N-loss potential. In contrast, treatment windrows showed more stable conditions, including reaching finished and curing status, no phytotoxicity or noxious hazard, and very low to no N-loss potential.

These results, coupled with the NO3:NH4 ratio and much higher NO3 values in the zeolite amended compost, indicate that the addition of clinoptilolite zeolite to a dairy manure compost mix in this study induced nitrification processes, produced NH4+ retention, NH3 emissions reduction, and lower oxygen depletion without significantly modifying the CO2 production. It also led to compost maturity characteristics that are regularly achieved only in compost mixes with much higher carbon content  and C:N ratios, usually associated with high quality composts. No negative effects were observed in the composting process or final product.

Future Plans

A greenhouse trial on silage corn comparing treatment and control compost effects followed. Results need to be analyzed and published.


Mario E. de Haro-Martí. Extension Educator. University of Idaho Extension, Gooding County, Gooding, Idaho. mdeharo@uidaho.edu  

Mireille Chahine. Extension Dairy Specialist. University of Idaho Extension, Twin Falls R&E Center, Twin Falls, Idaho.

Additional information



de Haro-Martí, M.E., H. Neibling, M. Chahine, and L. Chen. 2017. Composting of dairy manure with the addition of zeolites to reduce ammonia emissions. Waste to Worth, Advancing Sustainability in Animal Agriculture conference. Raleigh, North Carolina.

Fabian, E. E., T. L. Richard, D. Kay, D. Allee, and J. Regenstein. 1993. Agricultural composting: a feasibility study for New York farms. Available at:  http://compost.css.cornell.edu/feas.study.html . Accessed 04/28/2011.

Lorimor, J., W. Powers, A. Sutton. 2000. Manure Characteristics. Manure Management System Series. Midwest Plan Service. MPWS-18 Section 1. Iowa State University.

Magdoff, F., & Van Es, H. (2009). Building soils for better crops – Sustainable soil management (3rd ed.). Brentwood, MD, USA: Sustainable Agriculture Research and Education program.

Miner, J. R., Humenik, F. J., & Overcash, M. R. 2000. Managin livestock wastes to preserve environmental quality (First ed.). Ames, Iowa, USA: Iowa State University Press.

Mumpton, F.A. 1999. La roca magica: Uses of Natural Zeolites in Agriculture and Industry. Proceedings of the National Academy of Sciences of the United States of America, Vol.     96, No. 7 (Mar. 30, 1999), pp. 3463-3470

Ndegwa, P. M., Hristov, A. N., Arogo, J., & Sheffield, R. E. 2008. A review of ammonia emission mitigation techniques for concentrated animal feeding operations. Biosystems Eng. (100), 453-469.

Rink, R., M. van de Kamp, G.B. Willson, M.E. Singley, T.L. Richard, J.J. Kolega, F.R. Gouin, L.L. Laliberty Jr., D.K. Dennis. W.M. Harry, A.J. Hoitink, W.F.Brinton. 1992. On-Farm Composting Handbook. NRAES-54. Natural Resource, Agriculture, and Engineering Service. Cooperative Extension. Ithaca, New York.

Sikora, L. J., & Szmidt, R. A. 2001. Nitrogen sources, mineralization rates, and nitrogen nutrition benefits to plants from composts. In P. J. Stofella, & B. A. Kahn (Eds.), Compost utilization in horticultural cropping systems (pp. 287-306). Boca Raton, Florida, USA: CRC Press LLC.

Weil, R. R., & Brady, N. C. 2017. The nature and properties of soils (Fifteenth. Global Edition ed.). Harlow, Essex, England: Pearson Education Limited.


This project was made possible through a USDA- ID NRCS Conservation Innovation Grants (CIG) # 68-0211-11-047. The authors also want to thank the involved dairy farmer and colleagues that helped during this Extension and research project. Thanks to USDA-ARS Kimberly, ID for the loan and sample analysis of the Ogawa passive samplers.

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. 2019. Title of presentation. Waste to Worth. Minneapolis, MN. April 22-26, 2019. URL of this page. Accessed on: today’s date.