Elucidating the Role of Microarthropods in Nitrogen Cycling

Progress report for GNE19-204

Project Type: Graduate Student
Funds awarded in 2019: $14,715.00
Projected End Date: 06/30/2022
Grant Recipient: Cornell University
Region: Northeast
State: New York
Graduate Student:
Faculty Advisor:
Kyle Wickings
Cornell University
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Project Information

Project Objectives:

The long-term goal of my work is to improve fertility management on organic and sustainable farms by providing farmers with information and recommendations to enable them to better utilize soil biological processes. To achieve this goal, for this project I will focus on the following objectives:

Objective 1. Quantify the effects of the cover crop and tillage practices on soil microarthropod communities, soil microbial activity, soil and plant tissue nitrogen and carbon pools, and crop yield.

Objective 2. Quantify the impact of soil microarthropods on microbial nutrient cycling and crop productivity under different organic crop production practices.

Introduction:

The purpose of my research is to elucidate the functional roles of soil microarthropods in agroecosystems, specifically regarding nutrient cycling and plant pathogen suppression and transmission. This research project will expand our understanding of how soil microarthropods impact nutrient cycling, and how specific crop management practices can indirect impact nutrient cycling through direct impacts on the soil microarthropod community. These results will not only be applicable to organic farmers, but will also be beneficial to any farmer that is seeking to making their cropping systems more environmentally sustainable and resource efficient.

An increased understanding of the important functional roles microarthropods have in agroecosystems will enable farmers to harness these ecosystem services and make informed crop management decisions that will lead to more sustainable agroecosystems that use fertilizers more efficiently. This project will advance our understanding of how to manage soil biotic properties, specifically regarding the soil microarthropod communities that mediate multiple soil processes. Increasing the management possibilities surround soil microarthropods will allow farmers strengthen the linkage between soil and plant health, a well-known factor in the long-term sustainability of agroecosystems.

Research

Materials and methods:

The Integrated Cover Cropping Experiment (ICCE) was designed to test the effect of rolled cereal rye on white mold and weed suppression. The soybeans or dry beans are the main plot treatments, and the sub plot treatments are: 1) no cover crop (control treatment), 2) cereal rye with tillage, and 3) cereal rye mulch. The no cover crop treatment does not have cereal rye planted in the fall and uses shallow tillage to control weeds as needed. The cereal rye with tillage and cereal rye mulch treatments have cereal rye planted in the fall at a rate of 200 kg seed ha-1. The cereal rye with tillage treatment and the no cover crop treatment are both plowed prior to stem elongation in the cereal rye in the spring. The cereal rye mulch treatment is instead mechanically terminated and flattened using a roller-crimper (no soil tillage). Prior to planting the soybeans and dry beans in the spring, poultry manure and potassium sulfate are applied based on needs as determined by soil testing. The current ongoing measurements within this experiment include cereal rye biomass, soybean and dry bean establishment, carpogenic germination of Sclerotinia sclerotiorum, Sclerotinia sclerotiorum ascorporic inoculum density, microclimate conditions, white mold disease incidence, weed suppression, and cash crop performance.

For this research project, I have been building upon this established field experiment to address my objectives. I completed soil sampling events in June 2019 (pre-SARE grant) and October 2019 to measure soil biological metrics (microarthropod community abundance, microbial biomass, microbial enzymes), physical metrics (soil aggregate stability), and chemical metrics (carbon, nitrogen, soil protein). In 2020 I sampled soil for all of these metrics again in June, July, and September.

To measure the microarthropod community we collected three composite soil samples in each plot, each composed of three soil cores collected from randomized locations in the plots. Each composite soil sample was placed on a Berlese funnel and the microarthropods were extracted into 70% ethanol over a 3‐day period. After extraction, the microarthropods will be identified and quantified under a dissecting microscope. Work on microarthropod identification and quantification began in 2020 and will continue during 2021. 

We collected additional soil to send to the Cornell Soil Health Lab for analysis of the soil protein and soil aggregate stability. A hand trowel was used to collect three composite samples in each plot, each composed of a trowel full of soil collected from 3 randomized locations in the plots. Soil was sent to the lab for analysis.

To measure the other soil metrics (microbial biomass, microbial enzymes, soil carbon and nitrogen) one composite soil sample composed of 10 soil cores was collected in each plot. Cores were taken with a soil fertility probe (1.75 cm diameter) to a depth of 15 cm. Microbial biomass was measured using a chloroform (CHCl3) fumigation incubation and extraction. Samples have been extracted from the soil and are currently in storage and will be processed through the total organic carbon/nitrogen analyzer in 2021. Fresh soil was frozen from each soil sampling date to analyzer for microbial enzyme activity, which will be processed in 2021. Microbial enzyme activity will be analyzed using the appropriate microplate assays for each of the following enzymes: B-1, 4-N-acetyl-glucosaminidase, Leucine amino peptidase, and Phenol oxidase.

Rolled cereal rye tissue was collected in June 2019 and again in October 2019 when the beans were harvested. Bean plant tissue was also collected in October 2019 at time of harvest. The plant tissue was dried in oven to remove moisture so the tissue can be ground up and analyzed from carbon and nitrogen content using a combustion elemental analyzer. Yield data was collected for the bean crops at time of harvest. This process was completed again during the 2020 field season.

To tackle the second objective of this project, during the 2020 fields season I added a stable nitrogen isotope tracer (15N) to microplots in the experiment which allows us to track nitrogen as it cycles through the system. Tracking the 15N isotope will allow us to quantify the amount of nitrogen partitioned into the different nitrogen pools measured (bulk soil in microplots, soil microarthropods, microbial biomass, cereal rye tissue, and bean plant tissue). Shortly after the beans were planted in the field, I set up two microplots in each plot. Within each plot, one microplot was covered with cereal rye tissue that was labelled with additional 15N, and the other microplot was covered with non-labeled cereal rye. Over the growing season the cereal rye was decomposed by the soil biota and presumably the nitrogen that was released moved through the soil food web into the bean crop. Near the time of the bean harvest, I collected soil for microarthropod extraction, microbial biomass, and bulk soil nitrogen pools. I also collected any remaining cereal rye tissue in the microplots, and two bean plants from each microplot. Currently, the samples collected from the microplots are being processed and prepared to be set to the Cornell Stable Isotope Lab which has the equipment necessary to determine the 15N content of the samples submitted. 

Setting up a microplot in the no rye-plowed plot.
Microplot set up in a rye-no till plot.

Research results and discussion:

I am currently in the sample processing phase of this project, therefore the only results to report as of now are the soil protein and soil aggregate stability results from both the 2019 and 2020 field seasons. Soil protein had no significant differences between any treatments in 2019. However, in 2020 the cover crop treatment affected soil protein. We observed that the rye-no till treatment plots had greater soil protein than the rye-plow plots. This contrast between the results for each year may be due to differences in weather and precipitation that would have effected the microbial communities’ processing of organic matter and nitrogen in the soil.

In 2019, soil aggregate stability was affected by an interaction between the cover crop treatment and bean type. Within the dry bean treatments, the no rye-plowed plots had significantly lower aggregate stability that the other cover crop treatments. Within the soybean treatments, the no-till rye plots had significantly higher aggregate stability than the other cover crop treatments. As anticipated, for both the dry beans and soybeans we found that reducing tillage and adding a cover crop increased soil aggregate stability.

In 2020, soil aggregate stability was impacted by the cover crop treatment. Both the no rye-plow and rye-no till plots had significantly greater aggregate stability that the no rye-plow plots.

It is interesting is how quickly soil aggregate stability changed in this experiment. Prior to this experiment each of the fields for each growing season had been treated the same for many years, so it is presumed that the soil aggregate stability would have been similar across the entire field. Since the soil aggregate stability changed in the experiment plots significantly in one year in two separate fields, this suggests that even incorporating just one season of reduced tillage and cover cropping into a farmer’s rotation can help to improve soil aggregate stability.

Participation Summary

Education & Outreach Activities and Participation Summary

3 Consultations
1 Curricula, factsheets or educational tools

Participation Summary

3 Farmers
Education/outreach description:

Education and outreach efforts have been facilitated through an Extension and Outreach Activity (EOA) coordinated by Cornell’s entomology department. During the fall of 2020 I worked with three farmers in the Finger Lakes region that farm varying cropping systems. Each farmer selected multiple fields of interest, then I collected microarthropod samples from each field which will allow us to compare how different crop management practices influence microarthropod communities. Samples from these farms are currently being processed and the data will be used to create future outreach materials. I have also began working on a factsheet that discusses what microarthropods are and why they are important for crop production. 

Project Outcomes

1 New working collaboration
Project outcomes:

This project has the potential to contribute to future sustainability by informing farmers how to best steward their soil to promote a well-functioning agroecosystem that is less reliant on external inputs. Improved soil functioning has the potential to reduce external inputs that can have environmental consequences (fertilizers, pesticides) and can cause economic strain to farm operations.

Knowledge Gained:

Currently, since we are still in the sample processing phase, my adviser and I have not reflected upon the results of this project at this point.

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 or SARE.