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Ontario Grain Farmer Magazine

Efficacy of using cover crops in 2 of the 3 growing seasons on nitrogen supply in an organic soybean-winter wheat-corn rotation

Principal Investigator: Xueming Yang

Research Institution: Agriculture and Agri-Food Canada

Timeline: April 1, 2018 – March 31, 2023  

Objectives:

  • Examine how winter-hardy leguminous cover crops (red clover, crimson clover, white clover, and hairy vetch) planted after winter wheat harvest perform.
  • Determine if these legumes (when under-seeded into the standing corn at the V-5-6 stage of corn) will survive under corn shade and regrow in the following spring.
  • Determine cover crop biomass N in the spring before termination for corn planting vs. the cover crop biomass N in the previous late fall (at freeze-up).
  • Understand the impact of cover crop type and crop residue incorporation methods on soil mineral nitrogen status during the corn growing season.  
  • Determine the grain yield and protein content in corn, as well as in wheat and soybean. 
  • Determine the impacts of cover crops on soil quality/fertility by measuring:
    • soil nutrients, mainly N, P, K, Ca, Mg and S.
    • soil organic matter content.
    • labile organic matter pools (particulate organic matter / water soluble carbon).

Impacts:

  • Best management practices (BMPs) will be developed for an effective leguminous cover crop strategy and tillage practice in a soybean – winter wheat – corn rotation that provides leguminous fixed-N to both corn and winter wheat while maintaining/improving soil fertility and soil health.

Scientific Summary:

The overall goal of this study was to develop a new rotation system for organically managed cropping systems in southern Ontario.  This rotation may include two seasons of winter-hardy legume cover crops in an organically managed soybean-wheat-corn rotation (two legume crops and three main crops in three years), which can supply corn and wheat with sufficient amounts of nitrogen (fixed by legumes) and at the same time maintain/improve soil fertility/health. The proposed rotation would have living crops in the summer growing period as well as in the late fall and spring (i.e., winter wheat would be the winter cover in one of the years and the winter-hardy legume cover crops would be the winter cover in the other two years). Farmland under this rotation would have year-round cropping.

For 2022 cropping year, legume above-ground biomass samples were collected at two time points, one in November 2021 and another one in spring 2022 before cover crop termination. Cover crop biomass nitrogen and carbon contents determination were complete. Main crops (corn, soybean, winter wheat) were planted as planned. Soil samples were taken for NPK analyses, and the nitrogen nutrient status of corn plants were also evaluated by taking chlorophyll meter (SPAD) readings on corn ear leaves in the R1 growing stage. Corn, soybean, and winter wheat yields were recorded and evaluated.

Results

The 2022 data showed: 1) by plowing down cover crop for corn planting in spring, the amounts of N in-above-ground biomass were 222 kg N/ha for organic control (O-CK, frost-seeded red clover) 194 kg N/ha for crimson clover and red clover and 176 kg N/ha for hairy vetch 2) great corn yield was associated with moldboard plow termination of cover crop (12.3 tonnes/ha) than with chisel plow (9.6 t/ha); 3) for the corn under moldboard plow termination the grain yields were similar for all cover crop treatments, varying from 12.0 to 12.7 t/ha; 4) soybean yields ranged from 3.5 to 4.0 t/ha, which were 5-10% greater in  no cover crop control (CK) than in other treatments (p=0.10); and 5) wheat yield stayed lower under the organically managed treatments (5.1-5.6 t/ha) than under the conventional CK (6.9 t/ha) and the winter wheat yield was 8-9% lower in frost-seeded red clover (5.1 t/ha) relative to in the summer-seeded cover crops (5.5 – 5.6 t/ha).

Although this project does not include an economic analysis of production, we still did an input-output analysis (production Margin = Net Sales – Total Variable Expenses) of the benefits of production. Based on the market price premium for the organic produce during the study period (2018-2022), the organic production has achieved more than double returns, $1,940 – 2,130 / ha / year, relative to $864 / ha / year for conventional production for the moldboard plow down treatments. Note: notable economic loss occurred during the transition period due to no price premium for the produce; and the big loss for the O-CK was more due to no frost-seeded RC for the O-CK in the period 2014-2017.

Summer-seeding legumes as a primary nitrogen source in corn, soybean and winter wheat rotation is strongly recommended in southern Ontario or where the soil and climate are a fit for the rotation. This practice can assist organic farmers to maintain soil health, produce organic grains and significantly increase income. Simplified practice procedures are:

1) After the winter wheat harvest, plow-down the wheat stubble and plant legumes (hairy vetch, crimson clover, or red clover) immediately; let legumes grow until the following spring.

2) Incorporating (mowing and then plow-down) the legume biomass into the soil in late May and then planting corn as soon as possible after incorporation of legumes.

3) Plow-down crop stubble before planting the following crop for good germination / emergence and weed suppression.

4) For corn and soybean, timely weeding (mechanical).

5) Conducting soil testing and managing P, K and other soil nutrients following the soil testing results.

Overall, this legume cover crop rotation also has a range of impacts, including the following:

1) In terms of production and economics: it has the potential for conventionalizing organic corn, soybean and winter wheat production and increasing growers’ incomes and organic food security.

2) In terms of soil health: it eliminates the need for chemical nitrogen fertilizers, reduces nitrogen leaching, adds organic matter to the soil, reduces soil erosion, prevents nutrient runoff, preserves soil moisture, and protects water quality.

3) In terms of environmental health: it increases biodiversity, provides habitat and food for beneficial insects, birds, and other wildlife, which can help increase biodiversity on farms and the surrounding landscape. This can have positive ecological and social impacts including pollination services and pest control. It could also help to mitigate global warming.

External Funding Partners:

Organic Science Cluster-3 via Agriculture and Agri-Food Canada.

Funding for this project has been provided by Agriculture and Agri-Food Canada.

Project Related Publications

Slater, S. 2023. AAFC explores options for cover crops in organic rotation. Farmtario.

Yang, X., Reynolds, D., Drury, C., Reeb, M. 2023. Impacts of summer-seeded legume cover crops and termination-tillage method on nitrogen availability to corn in rotation. Frontiers in Soil Science. 2.