Adapting the Oregon State University Cover Crop Calculator for Southern Idaho Conditions.

Idaho growers are interested in accounting for the plant available nitrogen that is released from the incorporation of annual cover crops. While there are cover crop calculators that predict plant available N based on cover crop tissue analysis, these calculators are only appropriate to use in the regions that they were developed in. The objective of this study was to develop an Idaho cover crop calculator, using N mineralization data collected from Idaho. To achieve this objective, a 70 day lab incubation study was conducted using Idaho soils and Idaho cover crop plant tissue, following similar protocols as were used for the incubation studies conducted to support the Oregon State University cover crop calculator. To achieve a wide variety of tissue N concentrations, we included lower N cover crops (wheat and triticale), higher N cover crops (Austrian winter peas, hairy vetch, mustard, and clover), and various mixtures of both low and high N cover crops. For tissue N concentrations ranging from 1.5 to 4.5, Plant available N (%) = (7.34*tissue N (%)) + 1.7, with an r²=0.80. While the Oregon State University and the University of Idaho calculators predicted similar PAN rates (12 % PAN) at lower tissue N concentration (~1.5 % N), OSU calculators predicting much higher PAN rates (30-60 % PAN) than the Idaho calculator (20-35 % PAN) at higher tissue N concentrations (2.5 to 4.5 % N). Based on our findings, Idaho growers would likely over-estimate PAN at tissue N % greater than 2.0 % N if they were to use the Oregon State University cover crop calculator.