Spatial Variability of Irrigated Desert Soil Fertility in Gansu Province

The spatial variability of irrigated desert soil nutrients has been analyzed for Hexi region in Gansu province by using mathematical statistics and geo-statistics methods. The results from mathematical statistics showed that the spatial variability of the tested soil nutrients was sharp; the variance coefficient of available NH~+_4-N was the highest(62\^656%), that of pH was the lowest(1\^284%), that of Phosphorous(P) was the second(47\^369%), and that of organic matter(OM) and available potassium(K) were 13\^208% and 38\^075% respectively. The results from geo-statistics analysis revealed that the nugget-sill ratios of all indices of soil nutrients varied from 0.041 3% to 13.780 1% and they showed that there were strong spatial dependences for soil NH~+_4-N, available P, available K, OM and pH. Among the tested soil nutrients the spatial dependences of NH~+_4-N and pH were the strongest and their nugget-sill ratios were (0\^041 3%) and (0\^097 8%), and the spatial dependence of the available P is weakest and the nugget-sill ratio was (13\^780 1%). The effective range of soil fertilities varied from 176 to 294 meters. The results of Kriging showed that to some extend soil nutrients had spatial dependence and geo-statistics method could be used to analyze the spatial variability of soil nutrients.