Progress report for GW22-240
Project Information
Maintaining soil health in agricultural systems is vital for long term sustainable food production, increasing environmental protection, and achieving food security. Organic inputs through post-harvest crop residue can be a critical component of building soil health by supplying organic matter and nutrients for the next growing season. This project addresses the question of how residue and biomass inputs from different crop rotations impact soil health traits in dryland agricultural systems. To assess the impacts of crop residue, aboveground and root biomass will be quantified after harvest in diverse cereal, legume, and oil seed crop rotations. The following spring, we will sample soils to measure capacity for nutrient cycling, enzyme activity, and soil organic matter dynamics. We will present research results to over 1,500 producers and ag professionals across Montana through Field Days at Montana State University’s Agricultural Research Centers and Extension Presentations about soil health. Development of outreach materials such as a Montguide, Soil Scoop, research article, and interviews on the Northern Ag Network radio station will extend the outreach of this project to 4,000 producers and ag professionals throughout the Northern Great Plains. The results of this study will help inform farmer’s decision making regarding crop residue management and selection of crop rotations based on their soil health goals.
Project Objectives:
- To assess the impacts of different crop’s post-harvest residue and root biomass on soil activity during the following growing season;
- To measure soil health traits that contribute to soil’s capacity to capture and retain water and promote nutrient cycling across crop rotations;
- To identify target crop rotations and their residue metrics that contribute to soil health;
- To present soil health impacts from crop residue to at least 1,000 producers and agricultural professionals by December 2023;
- To develop a Montguide, write a research article, give interviews, and prepare other communication materials on crop residue effects on biological soil health parameters to extend outreach to 4,000 individuals indirectly.
Cooperators
- (Researcher)
- - Producer
- - Producer
- (Researcher)
Research
The research portion of this proposal addresses three objectives:
- To assess the impacts of different crop’s post-harvest residue and root biomass on soil activity during the following growing season;
- To measure soil health traits that contribute to soil’s capacity to capture and retain water and promote nutrient cycling across crop rotations;
- To identify target crop rotations and their residue metrics that contribute to soil health
Site Description
This research was conducted on two farms in Montana that incorporate a variety of cropping systems, management practices, and harvest techniques, allowing for a comparison of soil health traits in response to crop rotations and post-harvest organic matter inputs. Both farms produce grains, legumes, and oilseed crops. However, the two sites differ in their management practices, from crops included in rotations to inclusion of occasional grazing, and often in harvest practices, impacting the crop residue left on the fields after harvest. Further, these sites were selected because of the producer’s commitment to incorporating soil health principles in their land management practices.
Cavin Steiger’s farm is near Forsyth, Montana, along the Yellowstone River. This area of east central Montana receives an average of 12.6” of precipitation annually, with an average temperature of 46.8 °F, and a cold semi-arid climate type. The soil is a frigid, Aridic Ustifluvent loam. Steiger incorporates 17 crops into rotation, including winter wheat, spring wheat, malt barley, sunflowers, canola, lentil, alfalfa hay, yellow pea, many cover crop mixes, and occasionally rotates with fallow for moisture accumulation. He utilizes a stripper header to harvest grains and has been no-till since 2007, maximizing the crop residue left on the fields after harvest for erosion protection and moisture retention. This diverse crop rotation and harvest technique allows for a comparison of various legumes, oil seed crops, and cereals in rotation with their residual impacts on surface residues and soil health characteristics.
Casey Bailey’s farm is located in Fort Benton, in the "Golden Triangle" region of north central Montana, near the upland slopes of the Missouri River. This area receives an average of 13.2” of precipitation each year, with an average annual temperature of 45.6 °F, and a cold semi-arid climate. The soil type is a frigid, Typic Argiustoll clay loam. Bailey includes wheat, barley, Kernza®, alfalfa hay, lentil, and oilseed crops. Additionally, he incorporates no-till strategies, buffer strips between fields, and some grazing. Bailey's array of crop rotations and management techniques provide a different gradient of residue cover and crop rotations to assess a relationship to soil health traits.
Objective 1: To assess the impacts of different crop’s post-harvest residue on soil activity during the following growing season.
The specific fields and rotation of crops selected were informed by planting decisions made by the participating farmers in spring of 2022, which were impacted by spring precipitation patterns, particularly because of the record drought during 2021 and the relatively dry winter.
At the Steiger farm, six plots were delineated within five fields at a different stage of their crop rotation, representing four crop types: cereal (wheat), legume (lentil or pea), oilseed crop (canola or flax), and sugar beets. At the Bailey farm, fields strip-planted in perennial wheat, annual wheat, and perennial alfalfa were selected for sampling to assess impacts of annual vs. perennial crop types. In each of the plot within the five fields, quantity of residue inputs was measured by the following methods:
- Crop residue biomass: In spring 2022 and spring 2023, aboveground residue biomass was sampled by hand in the 6 plots within each of the crop rotation categories to assess residue that had overwintered. The residue biomass associated with each root core was collected, including the loose residue, plant litter, and standing stalks cut at the soil surface. This residue was dried for 72 hours at 60 °C and weighed immediately out of the oven.
- Root biomass: During spring 2022 sampling, we extracted root cores (root auger, 3” diameter, 20” depth) at a randomized location within each of the six plots. Roots were cleaned and analyzed for root biomass to assess the belowground biomass inputs to the soil for each crop rotation.
Objective 2: To measure soil health traits that contribute to soil’s capacity to capture and retain water and promote nutrient cycling across crop rotations.
In spring 2023, composited soil samples (1” diameter, 6” depth) were collected from the six plots in each of the crop rotation treatment groups. Soil cores were taken from the same subplots where biomass residue was collected (Objective 1). The soil biological indicators that were measured in this study were selected based on their responsiveness to management practices and crop rotation sequences, correlation with ecosystem processes, and integration of a soil’s chemical, physical, and biological properties. Residue management, tillage, and other farming practices can change soil characteristics and microbial community structure because of their impacts to food supply, changes in the populations of decomposers, altered physical properties, and changes to SOM distribution (Busari et al., 2015). As such, the following biological parameters included on the NRCS list of indicators were sampled for soil health assessment: potentially mineralizable nitrogen (PMN), five soil enzymes, soil organic matter (SOM) proxies such as permanganate oxidizable carbon (POXC), and total carbon and nitrogen (NRCS, 2015).
Mineralizable nitrogen (N) is a measure of the microbial activity that makes N available from SOM, and has been shown to be correlated with crop growth (Wang et al. 2018). Potentially mineralizable nitrogen (PMN) provides an estimate of the N available for plant-uptake throughout the growing season. PMN was analyzed using a 14-day anaerobic lab incubation at 30 °C on 5-gram field-moist soil samples, following methods from Keeney and Nelson (1982). Soils were analyzed for ammonium, NH4+, at day zero and at day 14, using a 1M potassium chloride (KCl) extraction and Lachat autoanalyzer (Lachat Instruments, Loveland, CO) in MSU’s Environmental Analytical Laboratory. Plant available nitrogen is calculated from the difference in pre- and post-incubation NH4+ concentrations.
Soil enzymes are a catalyst for nutrient cycling and are an indication of microbial activity, as they are released into soils primarily by soil bacteria and fungi. We have used them as an indicator of impacts of cover crops on soils in dryland production (Housman et al. 2021). Enzymes respond quickly to disturbances, providing an early indication of the trajectory of soil quality with changes in land management practices and crop rotation. Soil extracellular enzyme activity was analyzed in 1-gram of field-moist soil and incubated with the p-nitrophenol enzyme-specific substrate at 37 °C for 1-hour, and assayed for a colorimetric response spectrophotometrically. Controls and duplicates for each sample were analyzed following the procedure outlined by Dick et al. (1996) and Parham and Deng (2000). Five enzymes were analyzed, including β-1,4,-N-acetyl glucosaminidase (nitrogen cycle), β-1,4-glucosidase (carbon cycle), arylsulfatase (sulfur cycle), and alkaline and acid phosphatases (phosphorus cycle), in the Zabinski Laboratory. The geometric means were used to compare enzyme activity between the different crop rotations and residual organic matter inputs at each site.
Soil organic matter (SOM) is the portion of soil composed of plant residue and decomposing organisms, humus, and the active decomposing organic matter. Post-harvest crop residue provides a source of SOM and ample nutrient supply, water holding capacity and increased infiltration rate, soil aggregation, and erosion prevention. Because of the difficulty in directly measuring SOM, permanganate oxidizable carbon (POXC) was measured as a proxy for SOM. Soil POXC was analyzed in duplicates with 2.5-gram of air-dried and pulverized soil, ground for 12-hours to a fine consistency of <0.1-mm. The soils were combined with 18-mL of deionized water and 2-mL of 0.2 M potassium permanganate (KMnO4) in 1 M calcium chloride (CaCl2). A diluted aliquot of the sample was assessed for a colorimetric response that was measured spectrophotometrically, following methods developed by Weil et al. (2003). This method is more sensitive to land management impacts than TOC, and has been closely linked to soil respiration, microbial biomass, and soil aggregation (Bongiorno et al. 2019).
Timeframe of Sampling for Objectives 1 & 2
|
Time |
Sampling Event |
|
Spring 2022** |
Initial soil sampling, crop residue and root biomass sample collection** |
|
Spring 2023 |
Soil sampling, crop residue and root biomass sample collection |
**This sampling event and its related analyses are not included in this proposal and are already a part of the applicant’s masters thesis work. However, these results will be utilized in the statistical analysis of this project for comparison to spring 2023 soil analyses.
Objective 3: To identify target crop rotations and their residue metrics that contribute to different components of soil health.
This research will inform the understanding of the effects of specific crop rotations on organic matter inputs and soil health. Specifically, the results of this project are expected to assist in guiding management decisions for crop rotations in respect to farmer’s specific rotation and soil health goals. The residue biomass and soil analyses will be compared within the treatments at each site to identify trends that will inform target rotation and residue metrics for reaching soil health goals.
At each of the sites in Forsyth and Fort Benton, MT, the four treatment groups of differing crop rotation (i.e. cereals, legumes, oilseeds, and fallow) were compared for differences in crop residue and root biomass. Analysis of variance (ANOVA) was utilized to test for differences in residue quantity between the rotation groups at each site. Further, an assessment for correlations between residue quantity and soil health parameters within each crop rotation was performed. This will guide the process for identifying target crop rotations and their respective residue metrics for specific soil health goals. It is possible that biomass quantity has more of an effect on soil quality than the crop type itself. Research in semi-arid systems with cover crops has suggested that in biomass-limited systems, the quantity of the biomass produced as residue may be more important than the identity of the species for soil health traits (Housman et al., 2021).
We expect that legumes will have the biggest impact on soil biological activity, specifically on PMN and enzymatic activity, because of their capacity to add nitrogen to the system when used as a legume green manure (Miller et al., 2006). Soil organic matter will likely decrease following crop types with lower residue contributions because there are limited residue contributions to the SOM pool (Acosta-Martinez et al., 2007). Further, it is anticipated that within cereals and oilseed fields, areas associated with higher quantities of crop residue biomass will result in an increase in labile carbons due to organic matter inputs (Vázquez et al., 2016).
To address our primary objectives, we conducted on-farm research in Forsyth, Montana, to compare the effects of different crop types and their associated residues that persisted overwinter on soil biological response, following cereals (winter wheat, spring wheat, and millet), legumes (soybean, yellow pea, and faba bean), oilseeds (sunflower), and root crops (sugar beets) in both dryland and irrigated fields over two years. We also conducted on-farm research in Fort Benton, Montana, to compare the effects of an annual pea-spring wheat crop rotation and a perennial intermediate wheatgrass on soil health response. Specifically, we measured biological indicators of nutrient cycling capacity because of their sensitivity to changes in land management practices, namely potentially mineralizable nitrogen (PMN), soil enzyme activity, and permanganate oxidizable carbon (POxC).
Based on the research design, we had three primary driving hypotheses:
- Crop types will affect soil biological activity differently. Specifically, we expected that crop types with high quality residues (i.e., low C:N ratio) would increase PMN, a measure of nitrogen availability.
-
Crop types with high residue quantity (i.e., high biomass inputs) will build SOM. We expected that high quantities of crop residue would increase POxC, PMN, and SOM. Further, we expected that high SOM would increase soil enzyme activity.
- Perennial crops would will increase soil health measures compared to annual crops within the same field.
Results
For our first hypothesis on the impacts of crop residue quality, we discovered that PMN, a proxy of nitrogen availability, was higher in soils following a root crop than oilseeds or cereals (p < 0.05), but not significantly different than those intercropped in legume-cereal or legumes alone (p > 0.1). Specifically, PMN ranged from less than 5 mg N·kg soil-1 in soils following oilseed to over 20 mg N·kg soil-1 following root crops across both study years. PMN was higher in root crop soils than oilseed soils in Year 1 (Figure 1; F3,20 = 5.5, p < 0.01) and higher than cereals in Year 2 (Figure 1; F3,20 = 3.26, p < 0.05), but similar to PMN following cereals in Year 1 and similar to legumes in both study years.
Figure 1. Potentially mineralizable nitrogen (mg N·kg soil-1) by field and crop type for both study years. Stripes indicate intercropped crop types of legumes and cereals. Different letters indicate significant differences between fields within that year (a = 0.05).
For our second hypothesis about residue quantities, we found that overwintered crop residue was not a robust indicator of soil biological response, as there were no consistent correlations between quantity of crop residue and soil biological activity that persisted over both study years. However, high quantities of crop residue have been demonstrated to build SOM. Therefore, we assessed relationships between SOM and soil health responses. First, SOM did differ between fields, where SOM was higher in Field 2 R-L (i) than all other fields, with 2.8% SOM (F3,20 = 24.12, p < 0.001). The SOM ranged from 1.2 – 1.9% in dryland soils, and the other irrigated field had 2.1% SOM. This contributed to differences in soil health response, where the geometric mean of extracellular enzyme activity, a measure of nutrient cycling capacity, was positively correlated with soil organic matter over both study years (Figure 2; r = 0.61, p < 0.001).
Figure 2. Correlation of soil organic matter vs. geometric mean of enzyme activity across both study years, represented by both crop type and field.
And lastly for our third hypothesis regarding perennial vs annual crop types, we found that SOM was higher in soils with perennial crop types at 3.2% on average, compared to soils with annual crop types at 2.6% on average. The geometric mean of enzyme activity was 16 mg PNP·kg soil-1·h-1 higher in perennial cropped soils compared to annual cropped soils. Potentially mineralizable nitrogen was also 22 mg N·kg soil-1 higher in perennially cropped soils compared to annual cropped soils. However, annually cropped soils had nearly double the POxC, a measure of labile C, compared to perennially cropped soils.
Discussion
PMN was the only soil health indicator that had a notable link with specific crop type across both study years, namely PMN was greater after sugar beet. One possible reason for higher available N in soils following sugar beet is the high N content of sugar beet leaves, which are severed from the root and redistributed on the soil surface, then during root harvest, buried under a layer of soil. Sugar beet residues can contribute between 100-150 kg N·ha-1 to the soil. The sugar beet leaves, which are composed of 4-6% N, with a C:N around 11, can rapidly decompose, ultimately increasing mineralization rates and mineral N. This was evident by increased PMN following sugar beet in two separate fields over the two-year study period.
Extracellular enzyme activity in these soils did not follow a clear pattern based on the previous crop, but it did follow a pattern based on field. For both study years, the geometric mean of enzyme activity was highest in Field 2 R-L (i), which was cropped in a root crop, sugar beet, for the first study year and a legume, soybean, in the second year. Two notable characteristics about the soil of Field 2 R-L (i) are its high SOM content and high clay content compared to other fields in this study. This field had an average of 2.8% SOM, nearly a full percentage point greater than the other fields. It was also classified as a clay loam, with 27% clay, compared to the sandy loam and loam soils found in the other fields. Both SOM and clay provide increased surface area to bind extracellular enzymes, stabilizing the enzymes within the soil matrix. These immobilized enzymes often have reduced activity levels when compared to their free-living counterparts, but their stability results in persistent activity for prolonged time periods. Therefore, it is likely that SOM, and potentially soil texture, are driving the increased geometric mean of enzyme activity observed in Field 2 R-L (i), demonstrated by a strong positive correlation between enzyme activity and SOM.
Ultimately, the quantity of crop residue that remained on the soil surface until the beginning of the next growing season was not a robust predictor for soil biological indicators, as we initially hypothesized. We found no clear relationship between residue quantity and any of the biological soil health indicators assessed that persisted across both study years. Some soil enzymes, POxC, TC, TN, and SOM were negatively correlated with overwintered crop residue in the first year, suggesting that decomposed residue, resulting in lower quantities of residue that remained on the surface by spring of the next year, had contributed to increased biological activity. However, none of these biological responses maintained a consistent relationship with crop residue across study years. This could be due to differences in abiotic conditions between years, like wind and moisture.
Research Outcomes
Overwintered crop residue does not stand alone as a predictor of the soil biological response associated with PMN, soil enzyme activities, or POxC at the beginning of the next growing season. However, the relationship between crop residues and soil biological activity may be better explained by measuring crop residues at harvest and those remaining the following spring, to get an understanding of the potential quantity of residue that may have decomposed, contributing to nutrient release and SOM building. Early in the decomposition process, some C is lost to the atmosphere, with legumes exhibiting the highest CO2 emissions per gram of C added, followed by oilseeds then cereal crops. Further, the quality, or C:N, of residues plus their biochemical composition controls decomposition rates, meaning that different crop types will have varying rates of decomposition, impacting the timeframe where crop residues impact soil microbial activity. Understanding the proportion of residues that decompose from harvest to the following spring may help to predict biological responses to crop residue, and the timeframe when those responses can be expected, which may differ based on residue quality and composition.
This research was a two-year observational study that took place on two farms in Montana with the aim of identifying how crop sequences with various crop types and their residues impact biological soil health indicators. Future research that aims to understand the dynamic relationship between crop types, residue, and soil health will need to incorporate more residue sampling at various times throughout the year, increase the number of research sites across the region, and include full rotations to understand the longer lasting impacts of crop sequence. Further, it may be beneficial to include more comparisons of the impacts of various crop types in both dryland and irrigated systems to understand how water regimes affect both crop residue biomass and subsequent decomposition rates.
Education and Outreach
Participation Summary:
The primary outreach goal for this project is to provide information that will help an agricultural producer select crop rotations that improve soil health through their returned residue. By comparing the effects of different rotations, namely cereals, legumes, oil seed crops, perennials, and sugar beets on post-harvest residual crop organic inputs and the subsequent effects on various soil health traits at the start of the following growing season, producers will have more information to make decisions about specific crops’ contributions toward soil health goals. The biological parameters measured in this project are responsive to management techniques, therefore this will be indicative of how rotations and management decisions regarding residue cover may impact measures of soil health.
The education plan of this proposal aimed to address two primary objectives:
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To present soil health impacts from crop residue to at least 1,000 producers and agricultural professionals by December 2023;
-
To develop a Montguide, write a research article, give interviews, and prepare other communication materials on crop residue effects on biological soil health parameters to extend outreach to 4,000 individuals indirectly.
Objective 1: To present soil health impacts from crop residue to at least 1,000 producers and agricultural professionals by December 2023;
The outreach program for this research and education project started in the summer of 2023 with presentations at the MSU Agricultural Research Center Field Days. Field Days typically begin late June and continue through late July. The table below provides the estimated number of attendees at each Agricultural Research Center’s Field Days provided by Darrin Boss, Superintendent and Department Head of Research Centers. Ashford presented research findings at the Field Day at the Post Farm (near Bozeman) and at Central ARC near Moccasin. There is potential to reach nearly 300 producers and ag professionals through the Field Days.
|
MSU ARC |
Nearest Producer from Advisory Committee |
Expected Attendees at 2023 Field Days |
|
Post Farm |
Located in Bozeman, MT |
150 |
|
Central ARC |
Located in Moccasin, MT |
100 |
Further, Zabinski and Jones will include the results of this information in their future soil health presentations to agricultural producers and professionals across the state. Previously, Zabinski organized a day-long workshop for the Montana NRCS Soil Health Committee, which was an overview of soil ecology. Zabinski will reach out to the same committee to present the results of this work, and encourage a discussion of how to efficiently manage crop residues for soil health benefits. Jones presents to producers across the state regularly as part of his MSU extension work and will further distribute the results of this research in his teachings and talks about soil health. Dr. Jones, as MSU’s Extension Soil Fertility Specialist, typically delivers 25 talks per year to over 1,000 individuals. A minimum of 5 of these talks are on soil health, and that number grows each year. Many of the remaining talks have the opportunity to discuss soil health (e.g. to increase fertilizer use efficiency, decrease water quality impacts, etc.), so Dr. Jones will present results from this study when appropriate.
Objective 2: To develop a Montguide, write a research article, give interviews, and prepare other communication materials on crop residue effects on biological soil health parameters to extend outreach to 4,000 individuals indirectly.
In effort to reach a broader audience than those able to participate in select Field Days and other presentations, Ashford will produce a Montguide in collaboration with Dr. Jones to disseminate information regarding crop residue management and effects on soil biological health. These free and publicly available resources are a primary outreach effort of MSU Extension and allow for self-learning through concise and accessible communication to a broad audience. Development of the Montguide will be completed by December 2023.
Ashford and Jones will develop a Soil Scoop that will be published on Jones’ Soil Fertility Extension website. The Soil Scoop consists of one to two page fact sheets on a variety of soil fertility topics. These are intended for quick reference and to pass along to others, maximizing the reach of this research to a greater audience. This Soil Scoop will be directly distributed to extension agents and certified crop advisers (CCAs), with encouragement to send to their distribution lists in the Fall of 2023. Dr. Jones is Chair of the Rocky Mountain CCA program and often shares MSU Extension documents and research findings with WY and MT CCAs.
In addition, one of the stakeholders engaged in this project, the Montana Association of Conservation Districts (MACD), has agreed to assist in outreach related to this project. As described in the letter from MACD Executive Director Rebecca Boslough, the MACD will help extend the reach of this project by distributing outreach materials on their website to conservation districts across the state. Additionally, a short article will be written about the project in The Montana Conservationist, a monthly publication that is distributed to statewide conservation districts, partners, producers, and other stakeholders.
To expand the reach of this research, at least one scholarly research article will be published, summarizing the results of the research at the two farms by August December 2023. Contribution to the academic journals reaches a different audience that includes researchers and agricultural professionals who are working on meeting the same challenge in other parts of the country. Additionally, Ashford’s M.S. thesis will be published through Montana State University’s Scholarworks and will be searchable and freely accessible globally .
Finally, the project team will be interviewed on Northern Ag Network in fall 2023, a radio station listened to by ~60% of large acreage farmers in Montana. This format will provide another mode of communication in effort to reach all interested farmers and professionals across the state. With a broad approach including printed and digital communication, in-person verbal presentations, and radio presentations, we hope to far exceed our goal of reaching 1,000 producers and ag professionals directly and 4,000 indirectly. The education portion of our proposed project builds on work that has been supported and carried out by ag professionals around the state and the country. The NRCS has invested heavily in educating producers and supporting soil health initiatives. The contribution and significance of this education component is to add to the interest in crop residue management for soil health.
We selected Montana State University Agriculture Research Center Field Days as ideal outreach opportunities, because of the ability to connect with producers, researchers, and agricultural professionals such as certified crop advisors. Ashford, the graduate student on the research team, presented preliminary results from soil enzyme analyses and introduced the importance of soil biology for soil health at the Post Farm Field Day in July 2023 to over 100 attendees. The Central ARC Field Day in Moccasin, MT was cancelled and therefore we were not able to present at this Field Day.
Ashford presented preliminary results to 40 people at the Land Resources and Environmental Sciences Research Colloquium in April of 2023.
Zabinski discussed the results of this study with 31 participants at the PNW Farmer's Network Soil Health Coffee Hour in November 2023.
Ashford presented the results of this study at the Montana Grain Growers Association Annual Convention to 425 attendees, 250 of which were producers.
Zabinski presented results of this study at the Montana Organics Association meeting to 50 people.
Ashford presented the final results of this study at her thesis defense to 30 people.
The results of this study have been published in Ashford's thesis titled "Soil Health Response to Cropping Systems in Semi-Arid Montana", which is publicly available via ScholarWorks. We are currently working on completing outreach efforts by preparing manuscripts to submit to journals, as well as other educational materials.