Reduced-nutrient leachates in cash cover crop-soybean systems
Over-wintering crops are known to reduce nutrients in soil leachate in spring, but little economic incentive is available to grow these crops in the Upper Midwest. New oilseed-bearing cash cover crops, such as winter camelina and pennycress, may provide the needed incentives. However, the abilities of these crops to sequester labile soil nutrients are unknown. We used lysimeters buried at 30, 60, and 100 cm to examine nitrate and soil reactive phosphorus (SRP) in six soybean cropping system treatments: clean till, no-till, and autumn-seeded radish, winter rye, pennycress, and winter camelina. Radish winter-killed naturally, winter rye was killed with a glyphosate, and pennycress and winter camelina were allowed to mature naturally after relay sowing of soybean. Leachate chemistry was studied for the autumn, spring, and summer periods over two growing season. In autumn, leachates under radish and winter rye tended to have the lowest nitrate levels. In spring, differences among nitrate levels across treatments were greater than at any other time period, with values much lower under pennycress and winter camelina treatments than other treatments. In summer, nitrate levels were more uniform, with the lowest values occurring where soybean grew best. In general, cash cover crops like pennycress and winter camelina provide both environmental and economic resources to growers in that they represent cash-generating grain crops that sequester labile soil nutrients, especially in spring, and protect and promote soil health from autumn through early summer.