Varinderpal SinghJagdeep Singh2019-11-112019-11-112019http://krishikosh.egranth.ac.in/handle/1/5810134993Synchronizing fertilizer nitrogen (N) supply and plant N demand remains a major constraint due to spatial variability in soil N supply especially when fixed time fertilizer N applications are made as per soil test-based recommendations. Precision N management strategies to define in-season optimum N dose and appropriate topdressing timings are desired to achieve high N use efficiencies while sustaining potential grain yield. Field experiments were conducted at PAU, Ludhiana and KVK, Gurdaspur with spring maize cultivars DKC- 9108 and PMH-10 for two years to study spectral properties of spring maize to help guide need-based fertilizer N applications using leaf color chart (LCC), chlorophyll meter (SPAD meter) and GreenSeeker (GS) optical sensor. The spectral properties measured using the gadgets were strongly correlated with leaf N, plant biomass, biomass N content and grain yield at different crop growth stages. A close linear relationship (R2 = 0.75) between SPAD meter readings and LCC score indicated that LCC can be used as an inexpensive and reliable substitute of SPAD for real-time need-based N applications in spring maize. The statistical analysis of spectral reflectance recorded at different growth stages revealed that NDVI readings at V9 growth stage could precisely predict the in-season N requirements for spring maize production. Algorithm to predict grain yield and to draw in-season need-based fertilizer N topdressing decisions using GreenSeeker optical sensor was established. Fertilizer N topdressings based on threshold leaf greenness of LCC 5, SPAD 50 and sufficiency index value of SPAD 0.95 and NDVI 0.90 produced significantly higher grain yield with improved recovery and agronomic efficiencies of applied fertilizer N in comparison to soil-test based N recommendations. The improved congruence of fertilizer N supply and crop N demand in LCC, SPAD and NDVI-based N management treatments reduced N2O emission and global warming potential, produced more number of grains per cob and plant height than soil testbased N management. Insignificant differences in N indices of different soil layers between no N control and fertilizer N treatments expressed that higher fertilizer N applications were not helpful in increasing total soil N and N supplying capacity of the soil.enThesis