Assessment and mapping of spatial variation of soil physical health in a farm

Productivity rating systems are important tools to quantitatively assess soil health. In precision farming such information is required for planning appropriate soil and crop management strategies. In order to demonstrate a proper procedure for assessing the soil physical health of a farm, an experiment was conducted in a rice-wheat field. Spatial variability analysis of soil physical properties measured on a rectangular grid (30 m x 45 m) was carried out by using geostatistical analyst extension of Arc GIS software. Indicators for soil physical health assessment included bulk density (BD), field saturated hydraulic conductivity (K-fs), available water retention capacity (AWRC), organic carbon content (OC) and non capillary porosity (NCP). Rating values of soil physical parameters were different for wheat and rice as the optimum physical environment for both systems were different. Physical rating index (PI) at each sampling point was determined by multiplying the rating values for all five parameters. Results revealed that for BD, K-fs, OC and soil physical health index (PI), major and minor ranges of semivariogram varied between 300-380 m and 5590 m, respectively. Whereas for NCP and AWRC, they were relatively short (major range between 114-140 m and minor around 60 m). Results also revealed that BD and PI for both surface and subsurface layers showed strong spatial dependence whereas the rest of the parameters showed moderate spatial dependence. Rating maps of mentioned parameters for wheat and rice cultivations were prepared as series of coloured contours by using kriging or other appropriate interpolation techniques and suitable semivariogram models. Overall soil physical health of the farm was medium to good for paddy cultivation but was not suitable for succeeding wheat crop mainly because of increased BD and reduced K-fs, NCP and AWRC of the farm during wheat growth. Correlations between PI and grain yield of both wheat and rice were fairly good (r(2) = 0.67). The results thus supported earlier findings that good soil physical health is essential for optimum sustained crop production. (C) 2010 Elsevier B.V. All rights reserved.