Effect of Compost and Brassica Cover Crops on Soil Microbial Biomass and Asparagus Performance

Most of the asparagus (Asparagus officinalis) in Michigan is grown on sandy soils with low organic matter. Due to the perennial nature of asparagus, crop rotation during production is not possible. Increasing soil organic matter and enhancing biodiversity with cover crops may help improve soil quality and crop performance. Therefore, studies were conducted from 2007 to 2010 to test effects of compost application and Brassica cover crops on soil microbial activity and asparagus growth and yield. Treatments included dairy compost, Brassica cover crops (a mixture of oilseed radish (Raphanus sativus) and Oriental mustard (Brassica juncea)), and control with no soil amendment. Fertilizer rates were adjusted to take into consideration the nutrient contribution of compost. A randomized complete block design with four replications was used. Treatment rows were separated with a guard row to avoid contamination. Plots were managed following commercial production practices. Evaluations consisted of total shoot biomass immediately after the first killing frost (in November), spear yield (in April-June) and soil microbial biomass. Compost application improved asparagus fern growth in all years. This resulted in a significant yield increase and spear counts. Yield in the compost treatment was higher compared to the control. Cover crops on the other hand reduced fern growth in comparison to the control in 2009. However, yield from the cover crop treatment was similar to that from the control treatment indicating no negative effects from the cover crops. The application of compost seemed to be a promising practice for long-term soil management in asparagus production.