Scale Effects Of Soil Nutrient Spatial Variation In Farmland And The Responses Of Winter Wheat Growth

Variability of soil nutrients at different scales,crop growth stages and their effects on crop growth and development under traditional tillage mode were the basis of realizing precision agriculture on field scale and well crop management.With the development of urbanization and industrialization,the pressure of cultivated land in China is increasing day by day.Correspondingly,the traditional farmland management and tillage mode continues to be used,resulting in polarization of soil nutrients in farmland: Fertile land has become overnourished and fertilizer utilization has been reduced,polluting these high-quality tillage fields;nutrients in poor soils are still in short supply and cannot be improved to meet crop growth needs.In order to effectively deal with the huge amount of soil information,the traditional management methods cannot meet the needs.It is necessary to use modern technology to dynamically and comprehensively understand the spatial and temporal variation characteristics of soil nutrients during crop growth period.In this paper,Huantai County was taken as the research area,and three spatial scales of county,field and plot were designed.Winter wheat was taken as the research object,and four growth stages were tracked,including before sowing,reviving stage,jointing stage and filling stage.The spatial variability and scale effect of available nitrogen(AN),available phosphorus(AP)and available potassium(AK)under different scales and their spatio-temporal dynamic variability in different growth stages were studied by combining classical statistics,geostatistics and GIS techniques.Meanwhile,Pearson correlation analysis was used to study the response of wheat growth and development to soil nutrient variation.The main conclusions are as follows.1)Study on scale effect of spatial variability of soil nutrients.(1)AN,AP and AK all exhibited moderate variation intensity at the three scales;the spatial variability of AN was affected most by a change of sampling scale;AK showed the second-largest effect in terms of spatial variability,while AP showed the least.As the sampling scale decreased,the coefficient of variation for AN increased,while AP and AK decreased gradually.(2)AN,AP,and AK all exhibited a strong spatial correlation at the three scales.The spatial variability was primarily affected by structural factors.As the sampling scale decreased,the spatial autocorrelation of nutrients first became stronger and then decreased,while the ranges became obviously smaller.(3)As the sampling scale decreased,the spatial structure of the nutrients changed.First,the nutrient information that was not contained at a large scale appeared at the small scale.Second,the proportion of different nutrient levels changed and formed the proportions that correspond to different scales.Third,the number of nutrient map patches increased gradually,while the patch density became larger.2)Spatial and temporal variability of soil nutrients during winter wheat growth period and its growth response.(1)The contents of three nutrients all showed the characteristics of decreased-increaseddecreased and moderate variability.The AN content reached a turning point at the reviving stage,while the AP and AK contents reached turning points at the jointing stage.AN had the largest CV,followed by AP and AK.(2)The semi-variance function models of three nutrients were the same before sowing as the exponential model;AP and AK were the same at the reviving stage as the spherical models;these three nutrients were different at jointing stage as spherical,exponential and gauss models in turn;and then AN and AP were the same at the filling stage as the gauss models.The three nutrients all showed medium to strong spatial correlation.The three nutrients showed the weakest spatial correlation at the reviving stage;the strongest spatial correlation of AN occurred before sowing,while the strongest spatial correlations of AP and AK were at the jointing stage.The correlation of soil nutrients decreased from before sowing to the reviving stage,from the jointing stage to the filling stage,and increased from the reviving stage to the jointing stage.(3)The high AN contents gradually decreased,and the spatial distribution continuously increased;the high AP contents decreased slightly,the change in the spatial distribution continuity was not obvious;the high AK contents significantly decreased,and the spatial distribution continuity continuously decreased.The nutrient content of each nutrient has roughly experienced the process of increasing first and then decreasing gradually,and the nutrient grade number,especially the high content grade number,decreases gradually.(4)AN exhibited the highest correlation with wheat growth status,followed by AK and AP.At the reviving stage,the effect of nutrients before sowing on the growth of wheat was slightly higher than that at the reviving stage.At the jointing stage,the effect of the nutrients in the jointing stage on the growth of wheat was much higher than that in the reviving stage.At the filling stage,the status of wheat growth was affected by the nutrients in both the jointing stage and filling stage.Fertilization of winter wheat should pay attention to the application of sufficient base fertilizer,attach importance to jointing stage fertilizer,supplementary fertilizer stage can be properly moved back.(5)The superposition analysis of soil nutrient maps and crop growth maps showed that the degree of influence on the growth and development of winter wheat was AN > AK > AP in turn.Compared with LAI values of wheat plants,SPAD values of wheat leaves were more responsive to spatial and temporal variability of soil nutrients.The effect of soil nutrients on nutrient accumulation of winter wheat was higher than that on plant development.In this study,the scale characteristics and effects of spatial variability of available nutrients in soils of farmland were well understood.The dynamics of soil nutrients and their growth responses during the growing period of Winter Wheat under the traditional field model could provide theoretical basis for precise management of field nutrients in northern winter wheat region,and provide theoretical basis for grasping the status of regional farmland nutrients and directing fertilization.