Mapping of Variability in Major and Micro Nutrients for Site-Specific Nutrient Management

Background: Spatial variation of soil physical and chemical properties influences soil and crop management efficiency causes uneven crop growth and decreases the effectiveness of uniformly applied fertilizers.
Purpose: Therefore, a comprehensive survey was made to determine the spatial variability of soil properties and their mapping in Charsadda district of Khyber Pakhtunkhwa Province (KP) of Pakistan to delineated area into low, medium and high level of plant nutrients for site-specific nutrient management using variable rate fertilizer technology.
Method: Soil sampling was done on a grid system using Global Position System (GPS) from two depths (0-15, and 15-45 cm) during 2004; and the samples were analyzed for soil physical (soil texture and saturation percentage), soil chemical (pH, ECe, SAR, lime, and organic matter) and soil fertility status (mineral N, AB-DTPA extractable P, K, Zn, Cu, Fe, Mn and HCl extractable B). Geostatistical techniques of semivariogram analysis and kriging were used to model the spatial variability and interpolation of data values at unsampled locations and mapping of the district. Semivariogram analyses of data showed some spatial patterns for soil properties. Silt (r2=0.48), clay (r2=0.71) contents and saturation percentage (r2=0.71) were described by linear model in both the depths (0-15, and 15-45 cm). Electrical conductivity was described by a linear model in both the depths with strong spatial structure in surface soil (r2=0.81). Calcium carbonate (CaCO3) in the surface soil had strong spatial structure (r2=0.59), organic matter content in the surface soil was described by a spherical model with a range of influence 6.65 km, while in the subsoil (15-45 cm) it was described by a linear model with moderate spatial structure (r2=0.41). Mineral N and P were described by linear models with strong spatial structure for P in both the depths (r2=0.77, 0.73) and moderate spatial structure (r2=0.36) for surface soil N. Potash content was described by a linear model in surface soil with moderate structure (r2=0.24), while in subsoil it was explained by a spherical model with strong spatial structure (r2=0.64) and a range of about 9 km. Zinc and Cu in the surface soil were randomly distributed, while they have strong spatial structure (r2=0.63 and 0.54, respectively) with a linear model in subsoil. Boron content in both the depths was described by a linear model with strong spatial structure in surface (r2=0.61) and moderate structure (r2=0.31) in subsoil.
Results: The maps of various measured soil properties showed that soil mineral N and boron (B) increases from north-east toward west-south, available P form south-east towards north-west and lime form northern towards southern parts of the district. Soil organic matter, sand and silt contents showed little spatial variation within sampled areas.
Conclusion: Texture of Charsadda district ranged from silt to sandy loam. Sand content in the east and silt in the whole area was higher, while clay was found low throughout the soil surveyed. All the soils were alkaline in reaction and calcareous in nature to different degrees as indicated in maps of surface soil pH and CaCO3. Organic matter content of both the depths was low. surface soils was deficient in N in all soils of district Charsadda while deficiencies of P, Zn and B were observed to a greater extent, while K, Cu and Mn are also appearing deficient in soil.