Soil properties after one year of interseeded cover cropping in topographically diverse agricultural landscape

Planting cover crops within or following a cash crop may improve soil-based ecosystem services due to increased plant diversity and a longer duration of live vegetation coverage. We examined the effect of three different cover cropping systems on soil properties after one year of a three-year organic transition rotation at four agricultural field sites with contrasting topographical positions, namely depressions, slopes, and summits. The four studied systems were (1) cereal rye (Secale cereal L.) planted after corn (Zea mays L.) harvest (Rye); (2) a mixture of cold susceptible cover crop species, namely, oat (Avena sativa), winter pea (Pisum sativum), and radish (Raphanus sativus), interseeded into corn (WK); (3) a mixture of cold tolerant cover crop species, namely, annual ryegrass (Lolium multiflorum), Dwarf Essex rapeseed (Brassica napus), and crimson clover (Trifolium incarnatum), interseeded into corn (WH); and (4) a no-cover control (NC). While soil moisture was affected by topography, interseeding cover crops into corn did not influence soil moisture levels at the 0–10 cm depth for the studied year. Soil NO3- content was markedly higher in the WK system compared to cereal rye and WH cover crop treatments. The difference was especially pronounced in depressions and summits. Soil N mineralization rates followed the pattern WH>WK>Rye>NC and the effects were most pronounced in slopes. Soil microbial biomass C was the highest in depressions followed by summits and slopes, and in depressions the WH had higher microbial biomass than the other systems. There were no effects of cover crops and topography on soil C mineralization one year after the organic transition was initiated. The WH system increased the fraction of 0.053–2 mm aggregates and decreased > 2 mm aggregates in depressions. The results suggest that the effect of cover cropping can become evident already one year after the organic transition begins. The WH mixture interseeded into the cash crop was an optimal cover crop choice for improving soil characteristics as well as decreasing soil N leaching risks during organic transition in undulating agricultural terrain. However, the magnitude of the benefit provided by WH was mediated by topography.