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Spatial variability of pH, organic carbon and available nutrients at Sripurdanga village of Murshidabad district in the alluvial zone of West Bengal
 The current study evaluates the spatial variations of soil properties at Sripurdanga village of Murshidabad district in the alluvial zone of West Bengal. The soil type of the study area is Typic Ustifluvent with fine loamy texture. Average rainfall is 1340 mm and average temperature varies between 8șC to 40șC. Rice is the major crop in this area, grown twice a year during February-May and July-October. A variety of other crops namely, vegetables, pulses, oilseeds, jute and flowers make up the cropping sequences. Average farm size is 1 ha or less and fertilizer applications are limited to farmer’s perception or at best on general recommendations provided for the whole state. A total of 32 soil samples were collected from 0-15cm depth at a 100 m x 100 m grid during April, 2006. GPS (Global Positioning System) coordinates of the sampling points were recorded using a GARMIN GPS Map 60 instrument. Soil physico-chemical properties and available nutrient status were measured by standard procedures. Spatial variability maps of available nutrients for the study area were developed by ArcView Geographical Information System (GIS). Detailed soil analysis of the study area indicated deficiencies of K, S, Zn and Fe in this village but P deficiency is practically absent. Descriptive statistics of the measured soil properties showed that pH varied over a very short range while organic carbon content is low (Table 1). Phosphorus content is medium to mostly high in all the soil samples and suggests P build-up. Potassium status is low to medium and the variability is also low probably owing to the generally low application rates. Except for pH, all the other parameters had CV more than 24%, the highest being 90% in case of Fe.
Table 1. Descriptive statistics of the measured soil properties at the experimental site
Property | Minimum | Maximum | Mean | Standard Deviation | CV (%) |
pH | 6.78 | 7.88 | 7.42 | 0.27 | 3.63 |
EC (ds m-1) | 0.09 | 0.66 | 0.38 | 0.22 | 57.9 |
Organic C (%) | 0.20 | 1.08 | 0.67 | 0.17 | 25.4 |
Total N (%) | 0.017 | 0.093 | 0.058 | 0.014 | 24.1 |
P2O5 (kg/ha) | 50.35 | 366.40 | 194.02 | 98.67 | 50.9 |
K2O (kg/ha) | 87.0 | 448.0 | 254.22 | 92.99 | 36.7 |
S (ppm) | 7.75 | 82.5 | 19.47 | 12.75 | 65.5 |
Zn (ppm) | 0.24 | 3.82 | 0.90 | 0.66 | 73.3 |
B (ppm) | 0.38 | 4.96 | 2.02 | 1.16 | 57.4 |
Fe (ppm) | 1.76 | 40.4 | 7.77 | 6.98 | 89.8 |
Cu (ppm) | 1.10 | 3.52 | 1.96 | 0.48 | 24.5 |
Mn (ppm) | 2.58 | 35.82 | 12.05 | 8.93 | 74.1 |
Spatial variability maps (Figure 1) showed that available P content is high in the study area with variable distribution around the study area. This is probably due to high input of P2O5, mostly through Di-ammonium Phosphate, to all crops in this area. Except for some isolated patches of high K2O content, most of the soils have low to medium fertility. In general, the study area was found to be deficient in available sulphur. Farmers' survey in the study area showed that sulphur deficiency was particularly widespread in fields where one or two oilseed crops are included in the cropping sequence. High variability of S in the soils could be explained by the application of Single Super Phosphate by some of the farmers. High variability of micronutrients are quite surprising as micronutrient application are rare among farmers. High spatial variability of micronutrients can be partially explained with in-situ knowledge of the study area's production systems. Relatively high concentration of Cu can be related to the frequent use of pesticides containing Cu. The maps of Zn and Fe show deficient areas in the southeast and northwest. Both of these areas have extended rice/vegetable sequences and the resulting nutrient removal would be high. Rice demand for Zn and Fe is high and removal would be further accelerated under the higher nutrient input situation of growing vegetables. The northwestern part of the study area also represents a significant area of boron deficiency. The northwest represents a transition zone between the uplands and lowlands and continuously higher moisture contents would contribute to higher leaching of B from this area.
Figure 1. Distribution of available P, K, S, B, Cu, Fe, Mn, Zn, soil pH and organic carbon at the experimental site
The current study revealed major variability in soil nutrient status within a small area of an intensively cultivated village. The cropping pattern and fertilization history of individual plots seemed to be the cause of such variability. The fertilization history of an individual farmer should take into account this variability to optimize nutrient application rates for better yield and economics of crop production. Field experiments are going on in this village to validate use of such maps to tailor optimum fertilizer use for individual farmer.
Collaborator: Department of Agriculture, Govt. of West Bengal, India
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