Spatial variation in phosphorus accumulation and the driving factors in cultivated lands in Fujian Province

Phosphorus is one of the largest nutrient elements needed for plant growth. Under the intensive production conditions, most farmland soils in China have had phosphorus enrichment problem, mainly due to excessive application of phosphate fertilizers, strong fixation and inefficient use of phosphorus. The enrichment of phosphorus in cropland soils is one of the important causes of non-point pollution, which has also restricted sustainable agricultural development in China. In this study, the 1:250 000 spatial database on farmland soil types and the available phosphorus data on tillage layer soil samples of cultivated land (1 676 samples in 1982 and 200 322 samples in 2008) in Fujian Province were used to determine the spatial variation in the degree of phosphorus enrichment and the related driving factors in cultivated lands for the past 26 years. To do so, an integrated GIS with grey correlation analysis model was used. The aim of the study was to clarify the enrichment characteristics of soil available phosphorus, and its spatial variability and driving factors. The results showed that soil available phosphorus had been abundant in Fujian Province in the past 26 years. In addition, soil available phosphorus enrichment area reached 1 216 777 hm², accounting for 92.81% of the total area of cultivated land in the province. The yearly average enrichment amount and rate of available phosphorus were 24.38 mg·kg^-1 and 10.01%, respectively, which showed obvious spatial variations. While cropland soils in Xiamen (which is in southern subtropics) had the largest degree of available phosphorus enrichment, those in Nanping (which is in mid-subtropics) showed the lowest degree of available phosphorus enrichment in Fujian Province. The soil types with high available phosphorus enrichment included purplish soils, fluvo-aquic soils, paddy soils and latosolic red soils. Then the soils with less available phosphorus enrichment included coastal solonchaks and calcareous soils. Soil subtypes with larger degrees of available phosphorus enrichment included submerged paddy soils and bleached paddy soils, while those with lower levels of available phosphorus enrichment included brown calcareous soils and coastal solonchaks. In general, enrichment of available phosphorus in tillage layer of cultivated land soil had happened in large area with wide distribution range and significant spatial variation in Fujian Province. Grey correlation analysis showed that soil available phosphorus enrichment and its spatial variation were mainly affected by annual application rate of phosphate fertilizer, soil pH, mean temperature and soil clay content, which were with grey correlation coefficients higher than 0.722. However, the effect of soil sand content, precipitation and soil organic matter content on phosphorus enrichment in cultivated soils in study areas was relatively weaker. Their gray correlation coefficients were less than 0.720. Based on the degree of phosphorus enrichment and spatial variation, inorganic phosphate fertilizer application should be controlled strictly to deal with the phosphorus enrichment in cultivated soils in Fujian Province. At the same time, there was the need to optimize fertilization management by increasing organic fertilizer and reducing chemical fertilizer use.