Chlorophyll meter-based leaf nitrogen status to manage nitrogen in tropical potato production

Potato (Solanum tuberosum L.) is a N intensive crop, and meeting its requirements with N fertilization is the primary practice to improve N recovery and achieve suitable tuber yield. A 3-site-year (SY) study was conducted to assess soil plant analysis development (SPAD)-502 chlorophyll meter efficacy for providing potato leaf real-time N status to adjust N timing and rate using nitrogen sufficiency index (NSI) thresholds of 90 or 95%. We evaluated effects of in-season SPAD-based N managements, as well as a reference with non-limiting N application, a fixed-timing (planting and hilling) conventional N fertilization, and a zero-N control on crop N uptake, tuber yield, and N-use efficiency of potato cultivar Agata grown in tropical clay soils. Tuber yields were similar in both SPAD-based managements. Under no intensive rainfall events after N applications, SPAD-based managements reduced N applications by 38-63% and resulted in comparable tuber set, bulking, and yield relative to conventional N fertilization. Additionally, SPAD-based management at a NSI threshold of 90% resulted in greater potato N-uptake efficiency and tuber yield per unit of N applied. SPAD-502 sensor was efficient for detecting plant N status when environmental conditions were more conducive for potato production and optimized N management by reducing application rates. However, with less favorable temperature and solar radiation for potato cultivation, and with intensive rainfall events following N application, SPAD readings did not guide to a proper N fertilization and resulted in reduced tuber yield. Therefore, under such conditions, a more accurate method for detecting plant N status should be used. (AU)