Sunday, November 12, 2006

Management of Manure, Crop Residues and other Organic Nitrogen Inputs.

Paul Hepperly, The Rodale Institute, 611 Siegfriedale Road, Kutztown, PA 19530, United States of America


Nitrogen from organic sources (e.g. legumes, manure, and compost) is less soluble and concentrated than synthetic nitrogen. Crops can quickly respond to synthetic nitrogen. On the other hand, synthetic nitrogen can accelerate soil organic matter degradation and loss, increase environmental pollution from N-leaching and volatilization, and accelerate soil acidification and aging. Skyrocketing costs of synthetic nitrogen challenges its  traditional hold as the “cheap” nitrogen source. Organic nitrogen sources suffer less from external energy cost escalations. Compost nutrients are slowly released giving more long term  feeding  of crops while also building soil nitrogen reserves more effectively. With time, this lowers N-input requirements. Organic N-sources also have added benefits in improving soil, plant and food health.



The Rodale Institute® Farming Systems and Compost Utilization Trials show cover crops and organic inputs supply nitrogen for optimum crop production. Compost, manure, and synthetic fertilizers all produced optimum cropping under favorable environments. Under drought, however, plots receiving compost consistently produce superior yield. Composts increase soil carbon and this in turn increases water percolation, retention, and plant use.  Besides increasing soil carbon,  composts increased soil nitrogen, while reducing nitrate leaching. From 1993 to 2002, nitrogen nitrate losses were 100, 75 and 30 pounds/acre for raw manure, synthetic fertilizer, and compost treatments, respectively. Over the life of the experiment, soil carbon changed from 2.0% to 2.1, 1.9, and 2.5% for raw manure, synthetic fertilizer and compost, respectively. Soil carbon levels were directly associated with soil nitrogen levels. For every 1% increase in soil carbon, soil nitrogen increased by 0.5%.  


Organic management featuring extended rotation and cover crops, increased microbial activity and biomass over three times that of a conventional corn/soybean production system.  Soil Nitrogen buildup from compost amendment translated into higher nitrogen and protein content in corn and wheat  grain compared to that from synthetic fertilizer.