Site-specific fertilizer nitrogen management for timely sown irrigated wheat (Triticum aestivum L. and Triticum turgidum L. ssp. durum) genotypes

Site-specific fertilizer nitrogen management (SSNM) could be the best management option to avoid excessive and untimely nitrogen (N) applications in wheat. Field experiments were conducted in soils of varying inherent fertility in diverse agro-climatic zones to provide SSNM strategy for wide range of wheat genotypes. The intensity of leaf colour greenness of the first fully exposed top leaf was measured using leaf colour chart (LCC) and chlorophyll meter (SPAD) at different growth stages. The spectral properties of leaves at different growth stages differed among the different wheat genotypes except at Feekes 6 stage, thus the leaf greenness measured only at this stage can be used to make SSNM decisions. After applying 25 kg N ha−1 at planting and 45 kg N ha−1 at Feekes 2 stage, the leaf greenness of the first fully exposed top leaf measured with LCC at Feekes 6 stage was used to decide the amount of site-specific fertilizer N to be applied as topdressing. The LCC guided fertilizer N dose sustained grain yield to the level as obtained with soil test based N applications with the less use of 20–50 kg N ha−1. The practice of applying additional N or just increasing number of split doses in soils with low Walkley–Black organic carbon content may not improve grain yield unless plants really need it. The SSNM strategy improved agronomic efficiency of applied fertilizer N in different wheat genotypes grown under diverse range of agro-climatic conditions and in soils with variable indigenous N supply.