2017 ASHS Annual Conference

Anthropogenic nitrogen, reactive forms of nitrogen (N) converted from atmospheric N₂ gas for human activities, is threatening the environment at a global and regional scale. The main source of anthropogenic nitrogen that enters the biosphere comes from high inputs of N fertilizers in crop production systems. Using an N mass balance approach, synchronization of N fertilizer applications with plant nitrogen uptake can be optimized with knowledge of crop N demand and soil nitrogen status; hence, reducing environmental impacts and increasing farmer profits. In developing a framework to guide N fertilizer management in Hawaii, two critical parameters of the N mass balance equation were addressed through cooperation with Hawaii farmers. Through six crop cycles of selected brassica crops, models of crop N demand were developed. The use of a soil nitrate quick test (SNQT) was also assessed as a diagnostic tool to measure soil nitrogen status in tropical soils. To validate the SNQT as a viable tool, accuracy assessment of the SNQT procedure was conducted in a range of soil types critical to Hawaii agriculture. Results showed that the SNQT highly correlates with the standard laboratory analysis (r²= 0.97). In addressing two parameters of the N mass balance equation, substantial progress has been made in the development of an N management framework specific for intensive vegetable systems of Hawaii.