Predicting Nitrogen Losses in Potato Crop with Soil Nitrogen and Plant Tests

There is a lack of information on how to determine N-use efficiency and monitoring and diagnosing N losses in irrigated potato (Solanum tuberosum L.) production. This study was conducted to determine and validate a simple model to estimate inorganic N leaching losses (N-losses) from gravitational water and to determine N-losses thresholds using the soil N and canopy sensor tests. We conducted field experiments (n = 6) from 2008 to 2012 to evaluate the effects of N rates and/or managements and gravitational water on tuber yield, crop N uptake (N-uptake) and N-losses on the cultivar Innovator in the Argentinean Pampas. The N nutrition index (NNI), normalized chlorophyll meter reading (NNI-CM), relative chlorophyll meter reading (CMr), and relative normalized difference vegetative index (NDVIr) were determined 70 d after planting. Tuber yield, residual N, and Nlosses varied from 40.8 to 70.3 t ha(-1), 23.2 to 78.7 kg N ha(-1) and 6.4 to 219.4 kg N ha(-1), respectively. The Nlosses were directly associated with the amount of gravitational water in the soil profile (r(2) = 0.79). Threshold values of 255 kg N ha(-1) for N available, 1.0 for NNI, 1.03 for NNI-CM, 0.94 for CMr and 0.98 for NDVIr were defined. We determined linear increases in N-losses above these thresholds (r(2) = 0.75, 0.35, 0.53, 0.40, and 0.46, respectively). High N rates and gravitational water increased the N losses in potato crops under irrigation. This information could be useful to adjust N fertilizer recommendation and monitoring the Nlosses in potato crops under irrigation.