Cover crop/dairy manure management systems: Water quality and soil system impacts

A field study was conducted to determine impacts of corn silage production systems that included a rye cover crop and application of liquid dairy manure in the spring and fall on water quality and soil characteristics. Four management systems were each replicated four times: traditional, double-crop, roll-down, and undercut. Manure was applied below the soil surface during the undercutting process; otherwise, manure was surface applied. In the roll-down system, the rye crop was fattened with a heavy roller after manure application. Rainfall was simulated within 48 h of manure application to produce runoff events. Grab samples of runoff were collected and composited for analysis. Soil samples were collected prior to treatments in the fall and spring. The roll-down system had no significant effect on water quality (sediment, nutrients, bacteria) as compared to the traditional system. While the roll-down system may require an occasional tillage operation to prevent surface compaction, it is recommended in situations where reduction of residual herbicide applications is a primary concern. The undercut system displayed evidence of a compaction layer developing below the disturbed soil layer. The undercut system reduced loadings of all nutrients, but increased losses of total suspended solids, as compared with all other systems. Mean volume of runoff from the undercut system was less than half that from any other system. Overall, the undercut system is recommended over the other systems analyzed for preventing transport of manure constituents to surface water, but should be evaluated in a complete dairy system before it is implemented by producers.