California Agriculture

The need for fertilizer nitrogen (N) highly depends on site-specific factors. In addition to fertilizers, residual soil nitrate, nitrate in the irrigation water and N mineralized from soil, organic matter can provide significant amounts of crop-available N. The need for fertilizer N can be more accurately determined by having estimations of N contribution from these sources. In this paper we discuss the factors affecting the amount of N available to summer annual crops from these sources. We introduce an online tool that calculates the amount of fertilizer N required to meet average yields expected at the field scale based on user supplied site-specific input.