ABSTRACT
718In an long term experiment, the orange fruit yield difference of 30.2 and 48.9 kg/tree initially observed on shallow soil (Typic Ustorthent) and deep soil (Typic Haplustert) in an orchard size of 11 ha, reduced to respective fruit yield of 62.7 and 68.5 kg/tree with corresponding fertilizer does (g/tree) of 1200 N – 600 P – 600 K – 75 Fe – 75 Mn -75 Zn – 30 B, and 600 N – 400 P – 300 K – 75 Fe – 75 Mn –75 Zn – 30 B, suggesting the necessity of fertilizer application on variable rate application for rationality in fertilizer using SSNM as rationale of fertilizer use. Optimum grid size soil mapping using specific nutrient-based spatial variograms as a interpretation tool popularly known as DRIS developed for Khasi mandarin of northeast India and Nagpur mandarin of central India aided in measuring the magnitude of changes in pool of soil available nutrients before and after fertilization. Grid sampling is integrated into Global Positioning System (GPS) based soil sampling and nutrient-mapping that in turn uses a Geographic Information Systems (GIS) to employ variable rate technology (VRT) for fertilizer. Hence, it is necessary to realize the full impact of SSNM, unless the usefulness of grid soil/ leaf sampling, production zone vis-à-vis management zone strategies, aerial imagery vis-a-vis canopy reflectance is exploited in tandem with ultimate aim of rationalizing fertilizer use with productivity maximization.
