Effects Of The Wheat-cotton Double Cropping Systems On Cotton Growth And The Spatial And Temporal Distribution Of Soil Nutrients

Cotton is an important economic crop in China and an important guarantee for Chinese textile industry.Cotton production is directly or indirectly related to the development of Chinese cotton circulation and cotton textile industry.As an important cotton producer,consumer and importer in the world,cotton production plays an important role in China.The Yangtze River and Yellow River Basin are not only the main producing areas of grain,but also an important production area of cotton in China.In recent years,due to the contradiction between grain and cotton competition,the planting area of cotton in China has been declining year after year.The double-cropped planting of wheat and cotton is an effective way to solve the contradiction between grain and cotton.Through using the spatial statistics to study the spatial and temporal distribution characteristics of soil nutrients in cotton field under the double-crop planting systems,we can more accurately understand the spatial heterogeneity and spatial-temporal variation of soil nutrients in the double-cropped and single-cropped cotton fields.The change of time and space and the accumulation of nutrients in the aboveground cotton can pay more attention to the fate of the underground nutrient,so as to formulate more detailed cultivation and cultivation measures for different planting patterns and guide the field production.This study firstly used grid sampling method for sampling in the long-term experimental field of wheat and cotton double-cropped field and cotton monoculture.The geo-statistics was used as the analysis principle.The semi-variance function was used as the basic analysis tool to analyze the soil nutrients in the two-crop and single-crop cotton fields.Spatial heterogeneity has examined the effects of planting patterns on spatial heterogeneity of soil nutrients at field sampling scales.Secondly,in order to continue to explore the spatial and temporal distribution of soil nutrients and the accumulation of cotton nutrients under different planting patterns,Using cotton monoculture as the control,we conducted a two years field experiment: wheat-cotton 3:1(3 rows wheat,1 row cotton)and wheat-cotton 6:2(6 rows wheat,2 rows cotton)cropping systems.The double-crop planting patterns of wheat and cotton used the spatial grid sampling method to extract the soil during the whole growth period of the cotton,and explored the temporal and spatial variation characteristics of its nutrients.The main findings are as follows:1.It clear that the double-crop planting patterns of wheat and cotton in the field sampling scales has changed the spatial heterogeneity pattern of available phosphorus(P)and available potassium(K)in cotton field.Under the sampling scale of 10×10 m2 in the double-cropped planting pattern,the soil P and K have obvious spatial correlation in the 0-20 cm soil layer,and the semi-variance fitting function is obtained at the sampling scale of 30×50 m2.For the linear model,there is no spatial correlation;soil Mg has a spatial correlation at 30×50 m2 and a linear model at 10×10 m2.In the monoculture,except for Mg at the sampling scale of 30×50 m2,the semi-variogram function in the 20-40 cm soil layer is fitted as a spherical model,the P,K and Mg are in different sampling scales and two different planting patterns are all liner models in the two soil layers and there is no spatial correlation.2.The soil AP is significantly influenced by the planting patterns,and changing with the date according to the ANOVA.In the vertical direction,the AP contents is decreased with the soil depth increasing,regardless of the cropping systems,and it mainly in the 0-60 cm soil depth,the change is occurred mainly in 0-40 cm soil depth;in vertical direction,the AP contents are changed with the crops growth and the roots distribution;about the temporal distribution of AP,the difference of AP distribution is not only occurred in the co-growth stage,but also occurred in the cotton growth stage,the residual effect is also important.3.Compared with single-crop cotton,the double-cropped planting of wheat and cotton significantly affected the accumulation and growth of nutrients in the early stage of cotton.The accumulated biomass of cotton monoculture was higher than cotton in 6-2,but at the final,the biomass per plant was lower than 6-2.And the 6-2 type of cotton showed a more obvious phenomenon of greedy and late maturity;under the 3-1 type planting system,the rapid accumulation the biomass and P in cotton were significantly shortened.There was a significant positive correlation between biomass per plant,P accumulation,biomass per plant,reproductive biomass,P accumulation per plant,and reproductive P accumulation under the three planting patterns.