Soil spatial variation is observed under similar management situation in cotton growing soils of Northern Karnataka. In view of this an experiment was conducted to study the spatial variability in soil with respect soil reaction (pH), Electrical conductivity (Ec), Organic carbon (OC%), all major (N,P,K), secondary (Ca, Mg and S) and micronutrients (Fe, Zn, Cu and Mn) by assessing soil nutrients in deep black cotton soils of the experimental station for precision nutrient management. Totally, 73 soil samples were drawn from 15 cm soil depth from 4 hectare area at 20 m grid. The location of the sample was recorded using GPS. The experimental site distributed from latitude: 15o 27.58’’ to 15o 27.55 N and longitude 75o 2.82 to 75o 2.95 East. The altitude also varied from 2263 to 2217 foot above MSL. Results show that, soil spatial variability observed with respect to all chemical properties within the 4 hectare of cotton growing soil. The soil pH varied from 7.36 to 8.82, , EC varied from of 0.06 - 0.28 dS/m, organic carbon from 0.19 and 1.44 %. Similarly, major nutrients also varied widely ranging from 100.8 to 756 kg N/ha, 0.81 to 52.2 kg P/ha and 102 to 1245 kg K/ha with an average value of 153.8, 7.63 and 218 kg N, P and K /ha, respectively. Further, soil fertility status shows that, 98 per cent of the soil samples were low and 2 per cent samples were high in available N status. With respect to P, 79 per cent samples were low and 19 per cent samples were medium in available status. However, in majority of the grids, available K status was medium (81%) to high (19%). Similar to N, 95 percent of the grids shown low soil available S status as compared to medium (4%) and high level (1%). Micronutrient status was not different from major nutrients. Most of the soil samples were below the critical level in available Fe (100%), Mn (97%), and Zn (95%) status. However, only Cu status was above the critical limit. Available Fe, Zn, Mn, Cu ranged from 0.36 to 1.63, 0.13 to 1.07, 0.69 to 5.40, and 0.69 to 1.80 ppm , respectively. The soil fertility status shows that the soil is hunger with respect to all major, secondary and micronutrients. Therefore, Based on this soil fertility status, a field experiment on precision nutrient management was carried out on an area of 4 ha by fixing 4 target seed cotton yields of 25, 30, 35 and 40 q/ha by delineating 5 management zones based on major soil nutrient status (LLM, LMM, LMH, LLH and STCR (Soil test crop response). The soil fertility maps for different management zones are generated using Arc GIS. The required soil nutrient maps were generated based on site specific nutrient management (SSNM) concept by considering soil available nutrient status, crop uptake/ ton of seed cotton yield, and the target yield. Pest and disease scoring was carried out grid wise. The observations on crop spatial variability recorded at 90 and 120 days after planting of cotton revealed that, all the growth (plant height, Monopodium and Sympodium branches) and yield parameters (Number of squares and green bolls/plant) were higher with 40 quintal target yield grids in LMH management zone (Low in N, Medium in P and High in K) wherein it received maximum inputs. Further, grid wise spatial variation with respect to dry matter production and accumulation, nutrient uptake, chlorophyll estimation, IRGA and SPAD readings are being recorded.
