Monitoring Wheat (Triticum aestivum L.) Leaf Nitrogen using Diagnostic Tools for Fertilizer Nitrogen Management

Abstract

A field experiment was conducted to evaluate the leaf colour chart (LCC) and chlorophyll meter (SPAD and fieldscout (FS) chlorophyll meter (FSCM)) for developing site specific nitrogen (N) management strategy in wheat (Triticum aestivum L.). Four levels of fertilizer N (0, 70, 140 and 210 kg ha-1) were used to determine the growth stage specific optimum LCC, SPAD and FSCM chlorophyll meter values for achieving economic optimum grain yield. A positive and significant (R2 = 0.93-0.97, p<0.01) quadratic response between N application levels and wheat grain yield was observed. Economic optimum grain yield of 4.68 t ha-1 (first year) and 4.57 t ha-1 (second year) corresponding to economic optimum dose of 141 and 144 kg N ha-1, respectively were observed using quadratic response function. Nitrogen concentration in fully expanded youngest leaf correlated significantly (p<0.01) and positively with LCC score (r = 0.89), SPAD value (r = 0.94), FSCM value (r = 0.68) and total chlorophyll concentration (r = 0.91). Two chlorophyll meters used in the study were calibrated with a significant (p<0.01) linear response as ‘FSCM value = 11.3×SPAD value – 221.5’ (R2 = 0.60). The LCC score, SPAD and FSCM values observed at maximum tillering, booting and flowering stages were highly and significantly correlated with wheat grain yield. The optimum LCC score, SPAD values, FSCM values, leaf chlorophyll and N concentration at maximum tillering (most important crop growth stage for N management) to fetch economic optimum grain yield were found to be 4.5, 45, 295, 2.47 mg g-1 and 2.74%, respectively. Growth stage specific optimum and critical values of the above mentioned leaf N indicators for achieving economic optimum and critical grain yield of wheat crop were developed in the present investigation.