SPATIAL VARIABILITY OF SOME SOIL PROPERTIES IN AN AGRICULTURAL FIELD OF HALABJA CITY OF SULAIMANIA GOVERNORATE, IRAQ

摘要

The soils of Sulaimania Governorate have been used to meet food demand of people in northern Iraq. Longstanding wars and strict trade restrictions have caused farmers of the region facing difficulties in sustaining the agricultural production. Although soils have been subjected to agricultural production practices and are susceptible to degradation, reliable information on soils of the region is not available. This study has been carried out to characterize some physical and chemical soil properties and to determine the spatial structure of soil properties in a 100- ha agricultural field of Halabja at Sulaimania governorate, Iraq. The study area was divided into 100 x 100 m grid squares, and 100 soil samples were collected from the corners of each grid representative of the surface (0-20 cm) horizons. In addition, a total of 16 soil samples was taken along four transects with sampling intervals of 5, 10, 40 and 50 m. The measured properties were: clay, sand, silt, calcium carbonate and organic matter contents, exchangeable cations (Na, K, Ca, and Mg), micronutrients (Fe, Zn, Cu and Mn) and plant available phosphorus (P) concentrations, pH and electrical conductivity. The data were analyzed using classic statistics and geostatistics by constructing semivariograms and mapping by ordinary kriging. Semivariograms were calculated for soil characteristics and their spatial distributions were mapped. Soils were poor in available P and Zn contents. Soil organic matter showed significant positive correlations with EC, P concentration, clay content, extractable Ca and Na concentrations whereas the correlation was negative with sand content and Zn concentration. Nugget/sill ratio for modelled variables indicated high and moderate spatial dependences. The range of spatial dependence varied from 102 m (calcium carbonate) to 1248 m (pH). The distribution maps of soil attributes could be utilized as a guide for site-specific crop management in similar soils.