Nitrogen Credits and Fertilizer Dollars Saved: Identifying benefits for seeding diverse legume-based cover mixes into or after winter small grains

View the project final report

Commodities

• Agronomic: clovers, corn, rye, wheat

Practices

• Crop Production: cover crops, cropping systems, crop rotation, nutrient cycling, nutrient management
• Education and Training: demonstration, on-farm/ranch research

Among grain growers in the Midwest, interest is growing in cultivating winter small grains followed by a legume cover crop to take advantage of the growing window after small grain harvest in July. While frost seeding red clover into small grains was historically utilized and nitrogen (N) credits have been published in the past, the system has been understudied using modern approaches. Moreover, research on the soil health benefits and nitrogen credits from newer practices like planting diverse mixes after small grains are harvested in summer, lags behind grower adoption of diverse cover crop adoption. Our project recruited 7 growers in southeast Wisconsin who employ a small grain-cover crop phase in rotation with corn, and we measured soil health indicators, fall and spring cover crop biomass accrual, and preplant and presidedress soil nitrate tests to compare summer cover cropping after small grains with a small grain-summer fallow control. We also deployed a nitrogen rate response study to quantify the N credit to corn by measuring corn yields on each farm. On one farm with a history of frost seeding red clover into rye, we observed a N credit of 212 lb N/acre in corn; on this farm; corn yields following rye-red clover without additional N fertilizer were more than 20 bu/ac greater than the highest N fertilizer rate (160 lb N/ac) applied to the no-cover control. On the second farm frost seeding red clover into wheat, we did not observe a significant N credit; however, corn leaf N content was greater following cover crops vs. the control. On farms employing diverse cover crop mixes, we did not observe significant N credits. Our results suggest that cover crop mixes will likely need to contain a high percentage of legumes to result in significant N effects, and N credits, in corn the following year. However, we did observe benefits of diverse cover crop mixes on corn uptake of phosphorus and sulfur, suggesting that diverse cover crops may enhance non-N nutrient cycling processes in soils. We are continuing research with a larger grower cohort to build a larger dataset to gain more insight into the benefits of diverse cover crop mixes, and to identify which species constituents exert an effect on corn nutrient uptake and yield benefits.

1. Quantify spring and fall biomass production of several legume-based cover mixes by collecting data on 6 collaborating farms.
2. Identify nitrogen credits of legume-based mixes to the following corn crops by measuring corn yield in nitrogen fertilizer response field trials on each collaborating farm.
3. Investigate diverse cover crop mix effects on nutrient cycling in the following corn crop for nutrients other than nitrogen, including phosphorus, potassium, and sulfur, significant fertility factors for corn.
4. Present results and disseminate published products alongside collaborating growers at 2 on-farm field days and at 3 annual grower conferences.