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, 2011

Citrus is one of the most important fruit crops in India. Average yield levels of citrus has remained stagnant over the past two decades. This project aims to break this yield stagnation through estimation of spatial nutrient variability in citrus orchards and use such information to develop site-specific nutrient management (SSNM) strategies. Two Khasi Mandarin orchards, one each at village Nong Khrah (20 year old) and Umsaitning (11 year old) of Ribhoi district in Meghalaya were studied. Geo-referenced rhizosphere soil samples (0 to 20 cm) were collected using three grid sizes (10 m x 10 m, 20 m x 20 m and 40 m x 40 m) at Nong Khrah and four grid sizes (10 m x 10 m, 20 m x 20 m, 40 m x 40 m and 60 m x 60 m) at Umsaitning. Fruit yield data were recorded from the orchards to delineate different production zones within the orchards. Soil samples were analyzed for pH, organic carbon, available macro and micronutrients and spatial variograms of these parameters were generated using a Geographical Information System (GIS).

Fruit yield variograms of different sampling scale showed that predicted yield levels within the orchard remained similar for 10 and 20 m grid sizes, but varied significantly at the 40 m grid size at Nong Khrah. In Umsaitning, fruit yields remained unchanged up to the 40 m grid, but changed abruptly at 60 m. This suggest that 20 m grid size is appropriate sampling scale in locations with greater topographical variations in terms of frequent piedmont (slope) and pediment (valley) variations, while the 40 m grid sampling density is sufficient where such variations are low. This was well highlighted in the fruit yield variograms where larger grid sizes often predicted erroneous fruit yield zones as compared to the ground truth data. Similar observations were found while interpreting variograms for pH, organic carbon as well as available macro and micronutrients. Variograms of soil test values at a 20 m grid sampling density were superimposed along with fruit yield variograms and distinct classes of soil properties were found for different yield zones within the orchards studied. This information will be used for developing SSNM recommendations for the different yield zones within the orchard. Similar studies will be done in Maharashtra and Madhya Pradesh. India-003