s:805:"%T Direct Drivers of California’s Nitrogen Cycle 
%A Tomich, T.P. 
%A Leverenz, H. 
%A Liptzin, D. 
%A Meyer, D. 
%A Munk, D. 
%A Phelan, P.L. 
%A Six, J. 
%A Rosenstock, T.S. 
%X Since World War II and continuing to the present day University of California (UC) research has established crop-specific “N rate guidelines” (Proebsting 1948; Hartz and Bottoms 2009). An N rate guideline is a range of N application rates expressed as a unit of weight area-1 (e.g. kg ha-1) that are generally able to achieve maximum yield. Most often N application rate guidelines are printed in University of California Department of Agriculture and Natural Resources (UC DANR) publications and are extended to producers through information channels including: bulletins production manuals and field days. 
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