Spatial Variability Of Nutrients In Irrigation-siltedSoilinYinchuan, Ningxia

Scientific management of the soil nutrients and rational application of fertilizers are important issues related to agricultural sustainable development in China. The spatial variability of nutrients were studied to improve efficiency of fertilizer and output and quality of crops, as well as to decrease pollution potential from unreasonable fertilizat -ion. In this paper, Lingwu and Huinong County Spot-site, located in south and north of Yichuan Plain respectively, were selected to explore the spatial variability of nutrients in topsoils.The hundreds of soil samples were collected with lOOmxlOOm grid and the content of pH, Organic Matters(OM), ammonium N and available Ca, Mg, K, P, S, B, Cu, Fe, Mn, Zn were tested with the systematic approach for soil nutrients evaluation. By statistical and geo-statistical analysis, contend variability, spatial autocorrelation and correlation of nutrients were studied, and the maps of nutrients were kriged. The main conclusions are as follows: (1): In Huinong Spot-siteThe OM content is low and the average was 0. 23%. In all 110 samples, the amount whose ammonium N, available K, P, Cu, Fe, Mn, Zn were less than correspondent critical values was 110, 13, 25, 11, 32, 6, 109 respectively. The contents of Ca, Mg, S, B were high. Coefficient of variation of Ca, B, S, P, Mg were 131%, 87%, 75%, 77%, 56% respectively and the coefficient of variation of others were between 30% and 40%. The correlation analysis showed the relationships among OM-pH-Mg-S-B, Mg-K, Mg-N, K-pH-Mn, K-P, K-S-B, N-Cu-Fe-Zn, OM-Fe-Mn-Zn, Ca-Cu-P, Ca-Mg-S-B-Fe, Ca-Mn-Zn-Fe-P, Cu-Fe -Mn-Zn, S-B-Cu, S-B-Zn were remarkable. The factor analysis showed that low salt contents was benefit for the OM accumulation, and the more OM would make more Cu, Fe, Zn release in the soil. To balance soil nutrients, the more combined K, N, P fertilizers should be applicated, as well as Cu , Fe, Zn fertilizers. The variogram analysis showed that the ammonium Ndid not show the spatial autocorrelation as well as Mg> Zn in 135°direction. The others showed the spatial autocorrelation and variograms can be simulated by spherical models. The Fe, (ak Mn showed higher spatial autocorrelation in 45° direction with the reasons of irrigation, fertilization, cultivation and other anthropic factors. Ordinary kriging interpolation was chosed to map nutrients distribution in the topsoil and the precision fertilization should be implemented. The more K> P, Fe, Cu> Mn fertilizers should be applied than fertilizers contained Ca, Mg, S and B. (2) In Lingwu Spot-siteThe contents of Ca> Mg> S> Cu, Fe, Mn in all samples were higher than respective critical values.The number of the samples whose the contents of N> K> P> Bx Zn was lower than respective critical values were 128, 78, 68, 35, 80. The coefficient of variation of B and P were 94% and 66% and the others were lower, varying from 19% to 35%. The correlation analysis showed that there were not any relationship between N and OM as well as other elements. However relationships among pH-OM-Ca-Mg, pH-Fe-Mn-Ca, pH-S-B-P, pH-K-OM, K-Mg-P, P-B-Mn, Ca-P-S, OM-Mg-Mn, OM-S-Mg, Ca-Cu-Fe, K-Cu-Zn, Zn-Mg, P-Fe were remarkable. The factor analysis showed that the N, S, K and Zn fertilizers application should be increased. In addition, in order to increase the OM accumulation, the crop straw should be kept back in the fields. The variogram analysis showed that the ammonium N and available S did not show the spatial autocorrelation as well as K in 45° and B in both 45° and 135°. The variograms of Ca in 0° and 90° and Fe in 45° direction could be simulated by linear non-sill model. The variograms of others could be simulated by spherical models in all directions. The ordinary kriging method was used to map subsoil nutrients. Analysis of kriging interpolation showed the spatial variability of soil nutrients in Lingwu were obvious and the precision fertilization were necessary. Due to the deficiency in OM and ammonium N, the more N fertilizers, aswell as K> P> Zn should be applied. (3) comparing of the characterization of the two spot-sitesThe contents of ammonium N were less than critical value in the two spot-sites .The contents of available Cax Mg> S> K^ P> B were higher in Huinong , and available Cu> Fe, Mn> Zn were higher in Lingwu. Variogram analysis showed that the ammonium N did not represent the spatial auto-correlation in the both of two sites, so did the available S in the Lingwu. The range of O1VL available P, IK Cu were longer in the Huinong than the range of them in the Lingwu. The nugget effect of available B was 38. 1% and of other nutrients were less than 25%.