As producers of livestock and agricultural crops continue to focus significant efforts on improving the environmental, economic, and social sustainability of their systems, increasing the utilization of livestock manure in cropping systems to offset inorganic fertilizer use benefits both sectors of agriculture. However, promoting manure based purely upon nutrient availability may not be sufficient to encourage use of organic versus inorganic fertilizer. The value of livestock manure could increase significantly with evidence of improved soil fertility and quality following manure application. Therefore, understanding the impact of manure addition and application method on both soil quality and biological health is an important step towards improving the value and desirability of manure for agricultural cropping systems.
For edaphic ecosystems, collection, analysis, and categorization of soil microarthropods has proven to be an inexpensive and easily quantified method of gathering information about the biological response to anthropogenic changes to the environment (Pankhurst et al., 1995; Parisi et al., 2005). Arthropods include insects, crustaceans, arachnids, and myriapods; nearly all soils are inhabited by a vast number of arthropod species. Agricultural soils may contain between 1,000 and 100,000 arthropods per square meter (Wallwork, 1976; Crossley et al., 1992; Ingham, 1999). Soil microarthropods show a strong degree of sensitivity to land management practices (Sapkota et al., 2012) and specific taxa are positively correlated with soil health (Parisi et al., 2005). These characteristics make soil microarthropods exceptional biological indicators of soil health.
This study focused on assessing the chemical and biological components of soil health, described in terms of soil arthropod population abundance and diversity, as impacted by swine slurry application method and time following slurry application.
What did we do?
A field study was conducted near Lincoln, Nebraska from June 2014 through June 2015 on a site that has been operated under a no-till management system with no manure application since 1966. Experimental treatments included two manure application methods (broadcast and injected) and a control (no manure applied).
Soil samples were collected twelve days prior to treatment applications, one and three weeks post-application of manure, and every four weeks, thereafter, throughout the study period. Samples were not collected during winter months when soil was frozen.
Two types of soil samples were collected. Samples obtained with a 3.8-cm diameter soil probe were divided into 0-10 and 10-20 cm sections for each of the plots for nutrient analysis at a commercial laboratory. Samples measuring 20 cm in diameter and 20 cm in depth, yielding a soil volume of 6,280 cm3, were stored in plastic buckets with air holes in the lids, placed in coolers with ice packs, and transported to the University of Nebraska-Lincoln West Central Research & Extension Center in North Platte, Nebraska within 12 h of collection. These samples were then transferred to Berlese-Tullgren funnels for extraction of arthropods, a commonly used technique to assess microarthropods in the soil (Ducarme et al., 2002). A 70% ethanol solution was used to preserve the organisms for later analysis.
The QBS method of classification was employed to assign an eco-morphological index (EMI) score on the basis of soil adaptability level of each arthropod order or family (Parisi et al., 2005). Preserved arthropods from each soil sample were identified and quantified using a Leica EZ4 stereo microscope (Leica Biosystems, Inc., Buffalo Grove, IL) and a dichotomous key (Triplehorn and Johnson, 2004). Arthropods were classified to order or family based on the level of taxonomic resolution necessary to assign an EMI value as described by Parisi et al. (2005). For some groups, such as Coleoptera, characteristics of edaphic adaptation were used to assign individual EMI scores.
The impacts of swine slurry application method and time following manure application on soil arthropod populations and soil chemical characteristics was determined by performing tests of hypotheses for mixed model analysis of variance using the general linear model (GLM) procedure (SAS, 2015). The samples were tested for significant differences resulting from time and treatment, as well as for variations within the treatment samples. Following identification of any significant differences, the least significant differences (LSD) test was employed to identify specific differences among treatments. P <0.05 was considered statistically significant.
What have we learned?
A total of 13,311 arthropods representing 19 orders were identified, with Acari (38.7% of total arthropods), Collembola: Isotomidae (26.8%), Collembola: Hypogastruridae (10.4%), Coleoptera larvae (1.6%), Diplura (1.2%), Diptera larvae (0.9%), and Pseudoscorpiones (0.6%) being the most abundant soil-dwelling taxa. These taxa had the greatest relative abundance in samples throughout the study and were, therefore, chosen for statistical analysis of their response to manure application method and time since application.
The most significant responses to application method were found for collembolan populations, specifically for Hypogastruridae and Isotomidae. However, Pseudoscorpiones were also significantly affected by application method. Time following slurry application had a significant impact on most of the analyzed populations including Hypogastruridae, Isotomidae, mites, coleopteran larvae, diplurans, and dipteran larvae. The positive response of Hypogastruridae and Isotomidae collembolans to broadcast swine slurry application was likely due to the addition of nutrients (in the form of OM and nitrates) to the soil provided by this form of agricultural fertilizer.
Research focused on the role of livestock manure in cropping systems for improved soil quality and fertility is underway with additional soil characteristics being monitored under multiple land treatment practices with and without manure.
Corresponding author, title, and affiliation
Dr. Amy Millmier Schmidt, Assistant Professor, University of Nebraska – Lincoln
Corresponding author email
Nicole R. Schuster, Julie A. Peterson, John E. Gilley and Linda R. Schott
Dr. Amy Millmier Schmidt can also be reached at (402) 472-0877.
Dr. Julie Peterson, Assistant Professor of Entomology, University of Nebraska – Lincoln can be reached at (308) 696-6704 or Julie.Peterson@unl.edu.
Eric Davis, Ethan Doyle, Mitchell Goedeken, Stuart Hoff, Kevan Reardon, and Lucas Snethen are gratefully acknowledged for their assistance with field data collection. Kayla Mollet, Ethan Doyle, and Ashley Schmit are acknowledged for their assistance with data processing. This research was funded, in part, by faculty research funds provided by the Agricultural Research Division within the University of Nebraska-Lincoln Institute of Agriculture and Natural Resources.
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