Using leaf chlorophyll meter for N-fertilizer management in precision farming of potato

A leaf chlorophyll meter, SPAD 502, providing rapid non-destructive field measurement of relative chlorophyll content was tested for suitability and accuracy as a tool for N-fertilization in potato. SPAD values were positively correlated (r = 0.88) with N-fertilization from 25 to 60 days after planting (DAP). It also correlated positively with laboratory determined leaf chlorophyll and leaf N contents during this period with varying degrees among cultivars and at different growth periods. The deficiency/sufficiency (critical) limits of these plant indices of N-nutrition decreased linearly with advancing growth period. The critical limit of SPAD values was 48.03, 44.80 and 36.89 at 25, 40 and 60 DAP, respectively. The corresponding critical limits of total chlorophyll content were 1.55, 1.74 and 1.30 mg/g fresh leaf, while that of leaf tissue N were 6.50, 6.03 and 4.52% dry matter. The best period to detect N deficiency in potato for corrective N-fertilization was found to be 33–47 DAP. Linear models to accurately compute the critical limit of SPAD values and leaf N content at any given time during 25 to 60 DAP were derived to aid N-fertilization in potato. Nitrogen fertilization linearly increased the tuber yield of potato cultivars Kufri Ashoka (330 q/ha) and Kufri Badshah (282 q/ha) upto 150 kg N/ha, and in Kufri Sindhuri (292 q/ha) upto 200 kg N/ha.