Stretching Soil Sampling to Watershed: Evaluation of Soil-Test Parameters in a Semi-arid Tropical Watershed

Soil sampling is an integral component of fertility evaluation and nutrient recommendation for efficient use of nutrients in crop production. Little attention has been devoted to evaluating methodology for sampling watersheds under dryland agriculture. A stratified random sampling methodology for sampling the Appayapally watershed in Mahabubnagar district of Andhra Pradesh state in the semi-arid tropical region of India was adopted and evaluated. The watershed has an area of about 500 ha, with gentle sloping lands (,1% slope), and 217 farmers own land in the watershed. The soils are Alfisols. A total of 114 soil samples were collected from the top 15-cm layer to represent the entire watershed. Each sample was a composite of 7–8 cores, randomly collected from the area represented by a crop and group of farmers. The soil samples were air dried, ground, and analyzed for pH, electrical conductivity (EC), organic carbon (C), total nitrogen (N), and extractable phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), sodium (Na), sulfur (S), zinc (Zn), manganese (Mn), iron (Fe), copper (Cu), and boron (B). Statistical analysis of the results on soil fertility parameters showed that the meanor median-based results of soil tests performed in the study did not differ significantly when the sample set size varied from 5 to 114 (100% of the population). Our results indicate that farmers’ fields in the Appayapally watershed are uniform in the chemical fertility parameters studied, and even a small sample set size can represent the whole population. However, such a sampling strategy may be applicable only to watersheds that are very Received 30 April 2007, Accepted 8 September 2007 Address correspondence to K. L. Sahrawat, International Crops Research Institute for the Semi-arid Tropics (ICRISAT), Patancheru, Andhra Pradesh, India. E-mail: [email protected] Communications in Soil Science and Plant Analysis, 39: 2950–2960, 2008 Copyright # Taylor & Francis Group, LLC ISSN 0010-3624 print/1532-2416 online DOI: 10.1080/00103620802432857 2950 D o w n l o a d e d B y : [ S a h r a w a t , K a n w a r L . ] A t : 0 3 : 3 5 1 9 N o v e m b e r 2 0 0 8 gently sloping and where fertilizer use is very low, resulting in an overall low fertility in the whole watershed.