Integrating liquid manure and cover crops to measure their impact on soil health, nutrient cycling, and agronomic performance in the upper Midwest

Abstract

On their own, cover crops and manure have been shown to have a positive impact on various soil biological, chemical, and physical parameters related to soil health. However, there is limited information about the integration of both practices on soil health, nutrient cycling, and agronomic performance of the major crops. This is especially the case for the agronomically important region of the upper Midwest. A two-year study was set up to measure the effects integrating cover crops and liquid-injected manure have on various soil health parameters, nutrient cycling, and corn (Zea mays L.) yield. The study was conducted at the University of Minnesota Southern and West Central Research and Outreach Centers located near Waseca and Morris, MN, respectively. Three agronomic production systems were used: sweet corn-grain corn (System 1); silage corn-silage corn (System 2); and soybean (Glycine max [L.] Merr.)-grain corn (System 3). Plots were laid out in a randomized complete block design with split plots. Nutrient source/timing served as the main plot and cover crop type and planting time/method served as the split plots. Cover crops were drilled after sweet corn harvest in System 1 and were interseeded into standing cash crops or drilled after harvest in Systems 2 and 3. Cover crops were given approximately one month to grow before applying manure. Liquid manure was sweep-injected in the fall when soils were above or below 10°C for Systems 1 and 2 and applied only when soils were at or below 10°C in System 3. Plots without manure were fertilized with urea in the spring (SpringN) with equivalent nitrogen rates to manured plots. To represent typical practices in the region, plots with no cover crop and SpringN application served as the control. Cover crops were sampled for above-ground biomass yield and corn was sampled to measure corn grain or silage yield and their tissue was analyzed for nutrient uptake of macro- and micro-nutrients. Soils were sampled throughout the cover crop and corn growing season to measure soil mineral nitrogen across various soil depths in addition to various soil health indicators. Applying manure when soils were above 10°C in the fall reduced corn grain yield by 0.9 Mg ha-1 compared to SpringN but applying manure when soils were at or below 10°C was as good or better than SpringN in System 1. In System 2, manure, regardless of application time, was more effective than SpringN regarding corn silage yield. Corn grain yield did not differ between manure and SpringN in System 3. However, there is increased risk of losing nitrogen from manure through leaching or other pathways when manure is applied too early as soil mineral nitrogen concentration was similar to plots not yet receiving a nitrogen application in the 0–15-cm soil depth. Therefore, producers are encouraged to follow the University of Minnesota guidelines to apply manure when soils are at or below 10°C in order to minimize nitrogen losses. Furthermore, cover crops had a hard time establishing and producing adequate biomass throughout the study in all systems. Therefore, the integration of cover crops and liquid injected manure did not have an impact (statistically and biologically) on the various soil health indicators measured in the short-term.