Assessing the effectiveness of spatial and temporal separation of a cereal rye cover crop from corn on nutrient reduction and corn yield.

Issue

Adding a cereal rye cover crop (CR) to corn-soybean rotations is a proven strategy to consistently reduce nutrient loads entering surface waters via subsurface drainage. Despite these co-benefits, farmers are hesitant to adopt CR cover crops in their productions systems because of higher management costs and higher risk of corn yield declines. The goal of this research is to identify management practices for CR that maintain nutrient reduction goals, maximize co-benefits and eliminate barriers to adoption.

Corn seedling disease is an important factor in yield reduction because CR acts a “green bridge” for soil borne pathogens that infect corn seedlings in spring. The research team has demonstrated the duration between CR termination and corn planting reduced seedling disease and mitigated yield decline. In some years, however, cold temperatures and frequent precipitation events during spring prevent farmers from terminating CR early enough to avoid seedling disease. It has also been demonstrated that separating CR from the corn rows in space by varying CR row orientations mitigated the negative effects of CR on corn growth, seedling disease and yield. However, separating the CR from corn both temporally (i.e., early termination) and spatially (i.e., planting orientation) has the potential to limit co-benefits provided by CR by reducing biomass production and soil surface coverage.

In this study, researchers aim to combine two CR management practices, i.e. planting CR in the corn interrow and terminating it the time of corn planting, to answer: (i) could spatially separating the CR from the corn crop alleviate the need to terminate the CR prior to planting the corn, and could combining the two practices allow for more CR growth and provide improved ecosystem services? Assessing these management scenarios could provide farmers with more flexibility when implementing CR as part of their rotations.

Objective

The results from this study will improve understanding of how spatial and temporal management of CR affect corn growth, development and yield, seedling disease, nutrient recycling, soil erosion and water infiltration. The following objectives will guide comparison of the effect of cereal rye (CR) planting proximity to corn rows and CR termination dates on:

1. CR biomass growth and N accumulation;
2. Nitrate and dissolved organic carbon losses via leaching;
3. Corn seedling disease, growth, development and yield; and
4. Soil surface cover, infiltration rates, runoff rates, erosion and soil carbon and nitrogen dynamics.

Approach

Researchers will conduct a field trial at the Iowa State University (ISU) Boyd Farm in 2022-2023 and 2023-2024. The field study will utilize a randomized complete block design with five treatments with four replications of each:

(i) Corn planted 15” from CR, terminated 7 to 10 days before planting (DBP);

(ii) Corn planted 15” from CR, terminated 0 to 3 days after planting (DAP);

(iii) Corn planted 7.5” from CR, terminated 7 to 10 DBP,

(iv) Corn planted 7.5” from CR, terminated 0 to 3 DAP;

(v) No CR (control)

Once emerged, the corn row will be located either 7.5 inches (treatments i and ii) or 15 inches (treatments iii and iv) on either side from the terminated winter rye. CR will be drilled immediately after soybean harvest in early to mid-September to ensure good cover crop establishment. Most data collection will occur in summer 2023 and 2024.