Abstract
The increase of concentrated animal feeding operations (CAFOs) across the United States has led to increased efficiency in animal production, such as in the dairy industry, but the intensification of animal production has also led to a growth of waste streams. To handle the large volumes of both liquid and solid waste, dairies apply nutrient rich waste to meet crop macronutrients demand but without proper management, can lead to overapplication and can cause leaching and runoff of nutrients into both surface water and ground water resources. In the Magic Valley of Southcentral Idaho, the dairy industry has seen growth entirely due to CAFOs over the last two decades and has experienced an imbalance of nutrients produced by dairies applied to nutrients used by crops.Cover cropping can provide various environmental benefits including increased nutrient uptake. This thesis investigates using cover crops in a dual or double cropped system in corn silage systems common for dairies in the Magic Valley. The management practices of double cropping and dual cropping cover crops will be evaluated on dairy compost amended fields to determine the practices that decrease soil nutrient concentrations and increase nutrient uptake in harvested biomass while not impacting the yield and forage quality of corn silage. Research was carried out from 2021 to 2024 on research plots located in Kimberly Idaho where planting timing, height, and termination on of cover crops in a dual cropping system were evaluated for their environmental benefits. For the double cropping system, their spring management was evaluated for environmental benefits.
In dual cropped systems, interseeded cover crops proved management intensive as pressure from cover crops and weeds due to mismanagement led to decreased yield and caused soil nitrate nitrogen (NO3-N) concentrations to increase at the lowest sampled depths of the study from 5.6 ppm NO3-N to 11.9 ppm NO3-N by the end of the study. Cover crop establishment in the double crop system was difficult due to delayed plantings but in the spring of 2024, successful cover crop establishment reduced soil NO3-N content in the surface to levels lower than the beginning of the study. For both studies, phosphorus concentrations in the soil were not managed by cover crop uptake and increased with each year of the study even under successful cover crop establishment due to the higher phosphorus to nitrogen ratio of applied compost than the phosphorus to nitrogen ratio of crop uptake. This was observed as crop uptake of nitrogen exceeded 100% of what was available for plant uptake due to mineralization of N from dairy compost while phosphorus uptake of crops only removed less than 10% of what was applied. Under properly managed years, corn silage yield and quality was unaffected by cover crop management in either the dual cropping or double cropping system but was affected by the long-term applications of compost and synthetic fertilizer.
This research provided emphasis on the management required to successfully implement cover crops in a dual cropping or double cropping system. Some environmental benefits were observed without affecting corn silage yield and quality but the application of nutrients from compost was a greater factor in increasing or decreasing nutrient concentrations in the soil. Future research should investigate dual cropping in the Magic Valley region of Idaho due to the lack of published research for those systems but emphasize the need for nutrient management when using dairy waste to meet crop nutrient needs.