Challenges in Integrating Soil-Based and Plant-Based Predictions of Optimum N Rates for Crops.

Applying the optimum rate of nitrogen to crops is critically important to maximizing the profitability of crop production while minimizing N losses through leaching or denitrification.  Identifying the optimum rate is challenging, however, since both the N supply from the soil and the N demand from the crop vary both spatially and temporally.  Numerous indicators have been proposed to improve predictions of optimum N rates, focusing on either the N supply from the soil or the N status of the growing crops.  These two groups of indicators have normally been considered in isolation, ignoring the potential for synergies between soil- and plant-based indicators.  Following a brief discussion of the various indicators, the challenges of integrating the information from soil- and plant-based indicators will be described, and a possible solution to these challenges described.