Evaluating the Effects of Cover Crop Type, Planting Date and Removal On Nitrogen Dynamics in a Cucumber Cover Crop Cucumber Rotation.

Cover crops are used for improving agro-ecosystem processes including; soil quality, erosion control, foraging and nutrient management. Our objectives were to determine the effects of planting date, cover crop type and biomass removal for livestock feed on N cycling in a cucumber-cover crop-cucumber rotation from 2008-2010. Cover crop treatments were no cover, no cover + N (84 kg N ha^-1 applied before cucumber planting in 2009), rye (Secale cereale L.), oats (Avena sativa L.), oilseed radish (OSR) (Raphanus raphanistrum [L.] var. oleiferus Metzg [Stokes]), peas (Pisum sativum L.) and hairy vetch (Vicia villosa L.). In a split-plot design, cover crops were planted in early August and early September.  By November 2008/2009, early-planted vetch, peas and oats produced significantly higher biomass (2212-5314 kg ha^-1) and had higher N content (65-153 kg N ha^-1) compared to the late-planted (562-1293 kg ha^-1 and 18-46 kg N ha^-1). Early-planted OSR produced significantly higher biomass (4597 and 5307 kg N ha^-1) compared to the late-planted (1469 and 2330 kg N ha^-1), which did not translate into higher N content between early (67 and 98 kg N ha^-1) and late-planted (44 and 74 kg N ha^-1). Cover crop planting time had no effect on cucumber yield income. Cover crop treatments provided cucumber yield income that was higher or not different (1871-2988$ ha^-1) than the no cover (2235$ ha^-1). The no cover + N had the highest cucumber yield income (3405$ ha^-1) which was not different from OSR and oats (2933 and 2988$ ha^-1). The low yield income of rye (1871$ ha^-1) may be due to late biomass incorporation in the spring which lowered cucumber stand count compared to all other treatments. These results suggest that optimum planting date for cover crop biomass accumulation, N uptake and subsequent cucumber yield income is dependent on cover crop type and grower management practices. Moreover, nitrogen dynamics will be characterized by soil, crop and lysimeter sampling over the rotation.