Objectives The paper studied the spatial variability of paddy soil fertility in typical county of northeast China, aiming to provide a scientific basis for rational fertilization management of paddy soil in this region.
Methods The study was conducted in Fangzheng County of Heilongjiang Province, where total of 114 representative paddy soil samples were taken in 2017. Soil bulk density, pH, total N content, available P content, available K content, organic matter content and CEC were selected as factors of soil fertility evaluation. The correlation coefficient method was used to determine the weight of each factor. According to the characteristics of the paddy soil in northeast China, appropriate membership function curves and turning points were selected to determine membership values. According to the multiplication principle of fuzzy mathematics, the soil integrated fertility index was calculated by weight values and membership values. The spatial variability and distribution pattern of fertility factors and integrated fertility index were determined by the combination of GIS and geostatistics. Principal component analysis was used to explore the contribution factors of soil fertility difference.
Results The integrated fertility index of paddy fields in Fangzheng County was between 0.18 and 0.99, with an average of 0.60. The coefficient of variation (CV) of soil bulk density and pH were 9.15% and 5.69%, respectively, which belonged to weak variation intensity. The CV of other fertility factors ranged from 20.01% to 36.18%, belonging to moderate variation intensity. The nugget coefficients of soil bulk density, total N content, organic matter content and CEC were between 39% and 50%, which belonged to moderate spatial autocorrelation. The nugget coefficients of soil pH, available P content, available K content and integrated fertility index were below 25%, belonging to strong spatial autocorrelation. There was 16% of paddy fields with soil integrated fertility index value above 0.70, and 45% ranging from 0.60 to 0.70. The soil integrated fertility index was high in the south and low in the north, accordant to the distribution of available P and K content in soil. Soil pH and CEC decreased gradually in the paddy fields from middle to the north-south direction, and soil bulk density decreased gradually from northwest to southeast. The proportion of paddy fields with organic matter content above 30 g/kg was 97%, and that of paddy fields with soil total N content above 1.5 g/kg was 84%. The contents of total N, available P, available K and organic matter in the soil along the northern Ant River were relatively low. The general scores of fertility factors obtained by principal component analysis were as follows: soil available P content, available K content, organic matter content, CEC, total N content, pH and bulk density.
Conclusions The soil fertility of 61% of paddy fields in Fangzheng County is at medium or above level, and the paddy field fertility generally high in the south and low in the north. Soil available P and K content are the main factors causing differences in soil fertility.
DownLoad: