Development of Soil Fertility Map as a Decision Support Tool for Fertilizer Recommendations in Citrus

Development of a Soil Fertility Map as a Decision Support Tool for Fertilizer Recommendations for Citrus in India, 2012

Citrus is a highly nutrient responsive crop. But it's productivity in India is low due to multiple nutrient deficiencies, caused by generalized fertilizer application. Application of GIS technology in mapping the fertility status of soil and fruit yields has been useful to provide the desired accuracy and effectiveness in fertilizer recommendations. Geo-referenced soil samples were collected from the upper 0 to 20 cm of a Khasi Mandarin orchard at Umsaitining Ribhoi district of Meghalaya at four grid sizes (10 m x10 m, 20 m x 20 m, 40 m x 40 m, and 60 m x 60 m).

The predicted fruit yield in the orchard varied from 21.2 to 142.3 kg/tree, 16.4 to 151.4 kg/tree, 15.2 to 148.2 kg/tree, and 18.2 to 112.4 kg/tree under grid sizes of 10 m x 10 m, 20 m x 20 m, 40 m x 40 m, and 60 m x 60 m, respectively. Collected soil samples were analyzed for different parameters, and predicted values from GIS-based fertility maps varied [soil pH (3.2 to 6.8), organic C (1.11 to 3.12 g/kg), KMNO₄-N (132 to 172 mg/kg), Olsen-P (5.2 to 10.1 mg/kg), NH₄OAc-K (138 to 572 mg/kg)] for different sampling grid sizes. Similar variations were observed in the predictability of soil micronutrients (DTPA-Fe, DTPA-Mn, DTPA-Cu, and DTPA-Zn) with fertility maps using different grid sizes. Spatial variograms of these parameters suggested 40 m x 40 m as the optimum grid size for soil sampling and for predicting fruit yield in orchards in northeast India. A Nagpur mandarin orchard at Ladgaon (Katol) area of Nagpur district in Maharashtra was also identified for soil fertility assessment. Surface samples were collected in grid sizes of 20 m x 20 m, 40 m x 40 m and 60 m x 60 m, and analyzed for available nutrients. Available N (96 to 131 mg/kg), available P (8 to 17 mg/kg), available K (104 to 201 mg/kg), available Fe (6 to 16 mg/kg), available Mn (4 to 11 mg/kg), available Cu (0.4 to 0.9 mg/kg), and available Zn (0.4 to 1 mg/kg) in the orchard varied in relation to fruit yield of 10 to 79 kg/tree. The studies highlighted within and between location variability of nutrients, and the need for site-specific nutrient management to optimize yields in mandarin orchards in India. India-003