Spatiotemporal Variability Of Soil Nutrients At Field Scale Based On Grid Sampling

As a very important index to measure crop yield and quality,soil nutrient abundance index is very important for agricultural research.Xinjiang,as the main cotton producing area in China,has a high proportion of cotton planting and a long continuous cropping period,which may lead to the deficiency of some nutrients in the soil and the imbalance of the proportion of soil nutrients.Therefore,understanding the distribution and spatial-temporal variation of soil nutrients can make more scientific and reasonable land use.This experiment was conducted in a cotton field with long-term drip irrigation in Baotou Lake Farm,Korla,Xinjiang,to explore the changing trend and rules of various nutrient indexes in soil surface and profile under different planting years and the influence of different soil texture on various nutrients in soil.The main results are as follows:In the surface soil,the contents of total carbon,organic carbon and inorganic carbon firstly decreased and then increased with the increase of planting years,and the contents of total carbon and inorganic carbon in the plots planted for 10 years were significantly higher than those planted for 14 and 16 years(P<0.05).With the increase of planting years,soil total nitrogen content increased significantly;the alkali-hydrolyzed nitrogen firstly decreased and then increased;the content of available phosphorus increased,ranging from 71.23% to 127.39%;the content of available potassium decreased gradually,and the content of 10 years was significantly higher than that of the other two years.The contents of total carbon,organic carbon and inorganic carbon in soil were significantly correlated;there was a significant positive correlation between organic carbon and total nitrogen.The contents of total carbon,inorganic carbon,total nitrogen,available phosphorus and available potassium in soil were significantly affected by the change of planting years(P<0.01).With the increase of planting years,the changes of total carbon and inorganic carbon were similar,and the depth of 0-80 cm soil layer showed a trend of decreasing first and then increasing;the content of total nitrogen increased significantly in all soil layers,and the content of total nitrogen in 16 years was significantly higher than that in 10 years;In the 0-20 cm soil layer,The available phosphorus showed an obvious increasing trend.In other soil layers,the content of available P in 14 and16 year plots was similar,and was higher than that in 10 year plots;the content of available potassium decreased gradually.In 0-40 cm soil layer,the content of available potassium in 10 years was significantly higher than that in14 and 16 years.Different soil depths had significant effects on soil organic carbon,inorganic carbon,total nitrogen and available nitrogen,available phosphorus and available potassium(P<0.01).The content of organic carbon decreased with the deepening of soil layer,while the content of inorganic carbon increased gradually.The contents of total nitrogen,alkali-hydrolyzable nitrogen and available phosphorus decreased with the increase of soil depth.The content of available potassium increased with the deepening of soil layer.In the 100 cm soil layer of the study area,sand and silt are the main parts of mechanical composition,and the content of clay is low.The soil texture is divided into silt loam,sandy loam and loam.There was a significant positive correlation between soil clay and total carbon,inorganic carbon and available potassium contents.There was a significant positive correlation between total nitrogen and particle size.The sand content in soil was negatively correlated with total nitrogen and alkali-hydrolyzable nitrogen.In the plots planted for 14 years,the content of inorganic carbon in silty loam was significantly higher than that in loam;the content of available potassium in silty loam was significantly higher than that in sandy loam.The contents of alkali-hydrolyzable nitrogen and available phosphorus in sandy loam were significantly higher than those in silty loam after planting for 16 years.