2024 Scholarship Winner - Taqdeer Gill - Unlocking the Benefits of Summer Cover Crops

Written By Taqdeer Gill

Cover crops are plants grown to improve both the soil health and ecosystem sustainability. They are usually planted between the growing seasons of the main crops when the soil would otherwise be left bare. According to the Sustainable Agriculture Research and Education (SARE), cover crops (Clark, 2015) are defined as “an indispensable tool. They are planted to slow erosion, improve soil health, enhance water availability, smother weeds, help control pests and diseases, increase biodiversity, and bring a host of other benefits to your farm.” Cover crops are planted on 4.7% cropland in United States with crop acreage increasing 17% from 2017 to 2022 (2022 Census of Agriculture, 2022).

Importance of Cover Crops:

Cover crops play a vital role in contributing to sustainable agriculture (Figure 1).

1. Soil erosion prevention: Cover crops provide continuous ground cover during winters and protect the soil surface from the wind and water erosion. They help in maintaining the agricultural productivity (Chen et al., 2022).

2. Soil fertility improvement and nutrient cycling: Leguminous cover crops such as clover and alfalfa could fix atmospheric nitrogen into the soil. They reduce the need for nitrogen fertilizers during the growing season which are cost-intensive and leads to groundwater contamination (Peterson and Russelle, 1991).

3. Weeds suppression: The dense growth of cover crops could reduce the weed proliferation and could reduce the use of chemical herbicides (Brust et al., 2014).

4. Soil structure improvement: The roots of cover crops reduce the soil compaction and increase the water holding capacity and soil porosity of the soil (Blanco‐Canqui and Ruis, 2020).

5. Moisture retention: Cover crops reduce the evapotranspiration and improve soil organic matter content in drought-prone areas.

6. Biodiversity: Cover crops enhance the biodiversity in agricultural landscapes by providing habitat and food sources for beneficial insects, pollinators, and microorganisms (Wilson et al., 2018).

7. Carbon sequestration: Cover crops reduce the greenhouse gas emissions thus mitigating climate chance since they capture the atmospheric carbon dioxide and store it in the soil as organic matter (Poeplau and Don, 2015).

8. Pest and disease management: Certain cover crops from Brassica spp. could reduce the soil-borne pests through natural bio fumigation and reduce the need for pesticides (Nagila et al, 2022).

9. Crop yield: Past research shows that there was increase in the yield of crops following cover crops since cover crop provides nutrients (Blanco‐Canqui et al., 2012).

10. Long-term benefits: There are long-term economic benefits associated with the cover crops such as improved soil health, reduced need of fertilizers and pesticides and enhanced crop yield, leading to longer-term economic benefits for the farmers.

Types of Cover Crops:

Cover crops could be classified based on their functions and benefits:

1. Legumes: Plants having the ability to fix atmospheric nitrogen into the soil and reduce the need for synthetic nitrogen fertilizers. Legumes improve the soil fertility, reduce the input-cost for fertilizers and minimize the risk of groundwater contamination. These include clover, peas, cowpeas, alfalfa.

2. Grasses: Cover crop grasses could improve the soil structure and prevent soil erosion. These include oats, barley, rye.

3. Brassica spp: Plants from the Brassica spp have deep tap root system and break up the compacted soil and improve the soil structure. Additionally, they reduce the pest outbreak though bio fumigation.

4. Cover crop mixes or cocktails: There have been recommendations for cover crop mixtures including both legumes and grasses since different species mix could address various nutrient needs and outcome weeds more effectively than a single species. Furthermore, a diversity of root systems leads to higher amount of soil organic matter and improved microbial activity.

Considerations For Selecting Cover Crop Mixtures:

1. Selection of cover crop: Species could be selected based on the specific goals such as nitrogen fixation, soil erosion control. Moreover, the local climatic conditions such as temperature, precipitation, humidity and soil type should also be considered for selecting the suitable plant species.

2. Seeding rate: The seeding rate for each crop could be selected based on the seed size since over-seeding of one species could reduce the emergence of other species.

3. Planting time: Planting date should be selected based on the climatic conditions of a specific region.

4. USDA cold-hardiness zones: It is crucial to select seeds for cover crop mixes based on USDA cold hardiness zones because USDA hardiness zone map divides the regions based on their winter temperature. Since various cover crops have varying levels of tolerance to temperature, selection based on the USDA growing zone ensures the effective plant establishment and growth.

Cover Crop Mixes:

My Experimental Study:

While cover crops are traditionally grown during the fall, there are several reasons to consider for planting them during the summer season.

1. Allowing the soil to rest by cultivating the summer cover crops could help in enhancing the soil fertility since legumes such as cowpeas and kidney beans could fix atmospheric nitrogen.

2. Inter-cropping cover crops with corn or soybean during the summer season might lead to the weed suppression, reduced pest incidence and attract pollinators. Furthermore, legume cover crops incorporation might provide soil nutrients to the main crop and lower the input cost.

3. Summer cover crops also might conserve the soil moisture and act as beneficial crops during dry spell in summer.

4. If the market conditions are unfavorable for a particular main crop, farmers might consider planting the summer cover crop.

Selecting Plants Based on the Cold Hardiness Zone

According to the new USDA hardiness zone map, Madison, WI is classified as USDA hardiness zone 5b. This zone has a short growing season with long cold winters. It is recommended to plant cover crops in late summer or early fall for better establishment.

I conducted a small experiment testing the cover crop mixture specifically suitable for Madison, WI in a small plot.

Experiment Objectives:

• 1. Evaluation of seeding rate for summer cover crop mixtures.
• 2. Determination of the plant emergence and canopy cover of various cover crop species.

Materials and Methods:

The cover crop mix was planted on June 1st, 2024 in a 1.524 meters x 1.828 meters at Eagle Heights community gardens (Figure 2). The soil type is silty loam and only organic farming management practices for managing pests and for applying fertilizers. The garden plot was heavily infested with various species of weeds and manual weeding was performed to eradicate the weeds. Five different species of cover crops namely kidney beans (Phaseolus vulgaris), buckwheat (Fagopyrum esculentum), cowpeas (Vigna unguiculata), sunflower (Helianthus annuus) and black peas were planted. Kidney beans and cowpeas are legume crops and have the potential to fix atmospheric nitrogen and improve the soil fertility. Sunflower is an oilseed crop and attracts pollinators. Buckwheat adds organic matter into the soil and has pollinator attraction potential. The seeds were mixed and broadcasted into the soil (Table 1). Various in-season measurements were undertaken. Plant emergence, canopy cover using Canopeo app and growth stage were measured.

Results:

Crop Emergence: The results suggest that kidney beans and cowpeas had better emergence and plant stand as compared to other crops.

Crop Cover: Preliminary results indicated that there was better emergence of kidney beans and cowpea as compared to the other plant species. Five different images were collected randomly from the plot at the same height to measure the canopy cover. The average canopy cover was 42.084% (Table 2, Figure 3).

Growth stage evaluation of kidney beans: Kidney beans have vegetative (V1-Vn) and reproductive (R1-Rn) growth stages. Growth stage of the kidney beans ranged between V1-V2 (Figure 5).

Challenges: The poor emergence of sunflower and buckwheat could be due to various reasons.

Termination Methods: Cover crop could be terminated using mowing, tillage (incorporation of cover crop into soil) and through grazing by goats and sheep.

Strategies For Enhancing Germination Rate and Seedling Establishment:

• Measuring the soil pH and nutrient content: Soil test could be performed to measure the pH and various nutrients.
• Seed rates could be adjusted to increase the seed rate of sunflower and buckwheat.
• The planting date could be adjusted since the optimal planting date for sunflower is between March and May. The planting for the cover crop mixture could be done in May for better establishment.

Future Prospects: Further studies are needed to test the cover crop mixes across different environmental conditions, soil type. Additionally, different combinations and seed rates of cover crops could be evaluated in a randomized complete block design. Moreover, different planting and termination dates for the cover crops could be tested out.

References:

Blanco‐Canqui, H., & Ruis, S. J. (2020). Cover crop impacts on soil physical properties: A review. Soil Science Society of America Journal, 84(5), 1527-1576.

Blanco‐Canqui, H., Claassen, M. M., & Presley, D. R. (2012). Summer cover crops fix nitrogen, increase crop yield, and improve soil–crop relationships. Agronomy journal, 104(1), 137-147.

Brust, J., Weber, J., & Gerhards, R. (2014). Do cover crop mixtures have the same ability to suppress weeds as competitive monoculture cover crops?.

Chen, L., Rejesus, R. M., Aglasan, S., Hagen, S. C., & Salas, W. (2022). The impact of cover crops on soil erosion in the US Midwest. Journal of Environmental Management, 324, 116168.

Clark, A. (2015). Cover crops for sustainable crop rotations. SARE Outreach.

Nagila, A., Sanogo, S., Idowu, O. J., & Schutte, B. J. (2022). Biomass production of an overwinter cover crop with biofumigation properties in New Mexico. HortTechnology, 32(6), 559-566.

Peterson, T. A., & Russelle, M. P. (1991). Alfalfa and the nitrogen cycle in the Corn Belt. Journal of Soil and Water Conservation, 46(3), 229-235.

Poeplau, C., & Don, A. (2015). Carbon sequestration in agricultural soils via cultivation of cover crops–A meta-analysis. Agriculture, Ecosystems & Environment, 200, 33-41.

Wilson, H., Wong, J. S., Thorp, R. W., Miles, A. F., Daane, K. M., & Altieri, M. A. (2018). Summer flowering cover crops support wild bees in vineyards. Environmental Entomology, 47(1), 63-69.