Comparative Losses of Nutrients and Sediment in Surface Runoff From Watersheds in Conservation Tillage and Reduced-Input Management Practices.

Conservation tillage can reduce soil losses resulting from corn and soybean production compared to conventional tillage. There is a concern, however, that this can result in increased nutrient losses, particularly with no-till, due to lack of incorporation of surface-applied mineral fertilizers. Therefore, we investigated whether reducing the amount of mineral fertilizer and replacing it with manure and red clover in a disked tillage treatment can reduce nutrient losses without increasing soil loss to unacceptable levels. We monitored surface runoff from two no-till and two chisel-plowed, small (0.5-0.8 ha), watersheds in a 2-yr corn/soybean-rye cover crop rotation 16 crop years (1990-2005). In addition, three reduced-input watersheds in a 3-yr corn/soybean/wheat-red clover rotation were also monitored. Manure was added to these watersheds prior to corn planting and they were shallowly disked prior to corn and soybean planting and cultivated for weed control.  One watershed in each tillage treatment was in each crop each year. Average soil loss was lowest from the no-till (807 kg/ha/yr), intermediate from the chisel (1073 kg/ha/yr) and highest from the reduced-input watersheds (1177 kg/ha/yr). This figure increases to 1667 kg/ha/yr when the non-row crop, wheat years are excluded.  For all tillage treatments nitrate-N losses were greatest during the corn phase of the rotations with average losses ranging from 5.8 (no-till) to 9.0 kg/ha/yr (chisel). Similarly, dissolved P losses were highest during the corn phase of the rotations and ranged from 0.13 kg/ha/yr for the chisel to a high of 0.74 kg/ha/yr for the disked, reduced-input, watersheds. Likewise, total P losses were greatest during the corn years and ranged from a low of 0.86 kg/ha/yr for the no-till to 2.33 kg/ha/yr for the reduced-input watersheds. Thus, the reduced-input treatment slightly increased phosphorus losses compared to the chisel-plowed and no-till treatments while also increasing soil loss.