Fate of Nitrate in Organic Crop-Livestock Systems With Direct and Conventionally Seeded Catch Crops.

Benefits of green manure can be further supplemented by livestock grazing. However, readily available NO₃^- from livestock manure can potentially be lost from the system by leaching from the root zone. The objective of this study was to determine how two management factors; type of catch crop and tillage; affected NO₃^- leaching and N uptake in a subsequent crop. A three year experiment was established in Manitoba, Canada in 2010 and repeated in 2011. In the first year, upon grazing (termination) of mixture of pea/oat/soybean green manure, catch crops (barley and oil seed radish) were seeded directly (reduced-till) or after cultivation (tilled). Control plots had no catch crops. Second and third year tests crops were wheat and fall rye. Measurements included aboveground biomass and N content of catch crops and wheat, as well as wheat grain. Soil samples were taken to 120 cm, before grazing, after grazing, upon termination of catch crops, before seeding wheat and after wheat harvest. In 2010 the oil seed radish catch crop biomass contained significantly more N than barley; 85 kg ha^-1 and 73 kg ha^-1 respectively. Higher soil profile N in control (117 kg ha^-1) vs catch crop treatments (average 59 kg ha^-1) suggests reduced N leaching with catch crops. Significantly lower wheat yield in the catch crop vs control plot suggests that catch crops restricted N availability to the following crop. No significant tillage effects were observed. Catch crops reduced leaching of NO₃^- regardless of tillage system, but also reduced wheat yield.