The effect of cover crop biomass on row-crop yields in a rotational system is mediated through topographical features

The use of cover crops provides important benefits to soil quality and row-crop production in rotational agricultural systems. However, cover crop growth is not even in space or time, and little is known about the drivers that affect its performance. The spatial variability in cover crop growth and corn yields could be explained by topographical features; however, there is a lack of knowledge about the contribution of topography to the spatial variability in cover crop production. Since spatially variable cover crop growth produces variable biomass inputs for the following row-crop, the magnitude in cover crop effects on the row-crop might vary as a function of topography as well. The objectives of this study are to describe the effect of topography on cover crop production; and to describe the combined effect of topography and cover crop biomass input on corn yield.

This study was conducted in the Scale up experiment of Kellogg Biological Station LTER, Michigan. The samples were collected from ten different fields with diverse topographies during three years. Due to the rotational agricultural system, different fields were used each year. Red clover biomass measurements were collected at random locations within each field. Corn yield was measured from1 m distance in each of two contiguous rows. Continuous corn yield was also available via yield monitors. Topographical classification was performed and three positions, summit, steep slope and depression, were identified.

A hierarchical structural equation model was used to describe the relationship of topography with red clover biomass; and the relationships of topography and red clover with corn yield. Results indicate that topographical features partially described the variability in clover biomass and corn yield; however these results highly varied in different fields and years. Slope, flow accumulation and curvature index were significant predictors of red clover biomass. Slope and flow accumulation were significant predictors of corn yield in 2008 and 2009; whereas elevation, flow accumulation, flow length, curvature index and solar radiation index were predictors of corn yield in the year 2011. The partial effect of red clover biomass on corn yield was positive for years 2008 and 2009; however the same effect was not observed in year 2011, the year with unusually wet spring. A hierarchical ANCOVA model was used to explore the relationship between red clover and corn yield across topographical positions. Results indicate that the positive effect of red clover biomass on corn yield occurs in summits and steep slopes and is absent in depressions.