Genotypic variation of leaf SPAD value, nitrogen and nitrate content in maize

As the index of nitrogen(N)status diagnosis in crops, leaf SPAD value, N and nitrate content are affected by soil types, cultivars and maize growth stages. In order to optimize the index of N status diagnosis, leaf SPAD value, N and nitrate content of four cultivars of maize was investigated in two sites(Xinlicheng and Dehui)with three N rates. The results indicated that leaf SPAD value was significantly correlated with grain yield, N accumulation and biomass. The correlation coefficient was mainly influenced by nitrogen levels and soil fertility. The average variation during maize growth coefficient(CV)between two locations was 17.7%. In contrast, SPAD value was slightly affected by cultivars, and the CV among cultivars was only 4.3%, suggesting that the index of SPAD value need not to be adjusted with cultivars. In Xinlicheng where the soil fertility was low, the critical values of leaf SPAD were 46.1 and 57.8 at 12th leaf stage(V12) and tasselling(VT), respectively. In Dehui where the soil fertility was high, the critical SPAD values were 59.9 and 60.3 at V12 and VT, respectively. Leaf nitrate-N varied highly with soil fertility and cultivars, with the CV of 43.1% and 29.3%, respectively. Furthermore, the correlation coefficients between leaf nitrate-N content and grain yield, N accumulation and biomass were not significant. Therefore, the leaf nitrate-N was not appropriate as a sole index for evaluating plant N status diagnosis at large scale.