Interaction of Soil Nutrients and Arsenic (As) in Paddy Soil in a Long-Term Fertility Experiment

In this study, we examined the interaction between arsenic (As) and nutrients in paddy soil which received pig manure and chemical fertilizers for 36 years (since 1984). The treatments consisted of: CK (without fertilization); NPK (chemical nitrogen, phosphorus and potassium fertilization); NPK30%M (70% NPK plus 30% manure); NPK50%M (50% NPK plus 50% manure); and NPK70%M (30% NPK plus 70% manure). The combined application of pig manure and chemical fertilizer improved grain yield, soil pH and nutrient levels compared to chemical fertilizer application treatment. In comparison to CK, grain yield increased by 55.9%, 75.0%, 74.9% and 71.9%, respectively under the NPK, NPK30%M, NPK50%M and NPK70%M treatments. Soil As concentration increased by increasing the amount of manure input, and the highest concentration of As was 0.64 mg kg(-1) found in the NPK70%M treatment. Increasing the rate of manure application decreased the As bioaccumulation coefficient (BAC) for rice grain. SOC, total N and P showed a positive correlation with the soil-available As concentration and negative correlation with BAC. Furthermore, the partial least square model (PLS) showed that the soil pH and SOC were the most influencing factors on BAC among the different properties of soil, which explained the 75.4% and 17.6% of total variations, respectively. This study concluded that the addition of pig manure together with chemical fertilizers can increase crop production by supplying essential nutrients, but the concentration of As in manure should be monitored to reduce soil and food contamination.