The phosphorus (P) content in agricultural soils in catchments of lakes or rivers is an important issue, because P is both an essential nutrient for high plant yields and a major contributor to eutrophication of water bodies.    

The research team led by Prof. LIU Yi from Wuhan Botanical Garden investigated the spatial distribution of soil P, clarified effects of environmental factors, and assessed associated pollution risks in farmland in the Danjiangkou reservoir area, China. 

Farmland soils across the Danjiangkou reservoir area had low TP (total phosphorus ) levels  (lower than the threshold of <1 g kg^-1 TP for low nutrient status). However, the Olsen-P (a measure of available P) levels were higher in 40% of the area than levels generally required for optimal crop growth (at most 25 mg kg^-1).   

TP had strong spatial dependence, mainly influenced by soil properties (soil pH and organic matter), precipitation and topographic aspect. While Olsen-P had moderate autocorrelations, mainly driven by land use and topographic aspect.  

The P index models identified parts of the study area with the greatest potential risk of P losses, and others that act as P sources. Mapping of the P loss risk indicators showed that high P loss risk sites were mainly distributed in the northeastern and northwestern parts, including along the Zhangwan and Shendinghe tributaries of the reservoir.    

The main contributors to P pollution were transport factors, so the priority is to reduce nutrient diffusion, such as planting contour hedgerows, slope-toladder engineering and/or conservation tillage.   

Results entitled “Phosphorus spatial distribution and pollution risk assessment in agricultural soil around the Danjiangkou reservoir, China” have been published in Science of the Total Environment. It was supported by the National Key Research and Development Program of China, National Natural Science Foundation of China, and Knowledge Innovative Program of the Chinese Academy of Sciences. 

 P indices (a), and component transport (b) and source factor indices (c), of farmland in the area around the Danjiangkou reservoir. Red coloration indicates greater risk than green coloration (Image by WBG)