Dangerous Times: Critical Periods for N Losses in Organic Vegetable Systems.

Effective agronomic management of soil mineral nitrogen is critical for crop performance and mitigating environmental impact. In organic cropping systems, which rely on mineralization processes for in-season availability of amendment and soil inorganic N, understanding the environmental and management factors which influence the rate and periodicity of these processes is especially important. A field experiment has been conducted since 2011 on the University of California Santa Cruz farm in Santa Cruz, California to monitor soil inorganic N in sixteen crop rotation and fertility management regimes representative of the typical organic vegetable/strawberry production systems in California’s central coast region. Despite long-term organic management, limited fertilization, and high levels of soil organic carbon, large peaks of loss-vulnerable mineral-N consistently appear following incorporation of crop residues. Using findings from the past 5 years of data, strategies to limit these peaks and prevent N losses from organic vegetable systems are presented.