Net and gross nitrification in tea soils of varying productivity and their adjacent forest and vegetable soils

Abstract

Tea (Camellia sinensis (L.) O. Kuntze) is a globally important crop and is unusual because it both requires and acidifies the soil in which it grows. In spite of the low pH, high nitrate ( ) accumulates in tea soils, resulting in a great potential for diffuse pollution. Nitrification in tea soils remains poorly understood. The purpose of this study was to investigate net and gross nitrification in three tea soils with varying productivity, their adjacent forest and vegetable soils. The results showed that neither net nor gross nitrification rates were significantly related to soil pH. The net nitrification rate increased with increasing tea production, and when soils were incubated with ammonium sulfate. The ammonium ( ) added to the vegetable soil was immediately and completely nitrified, but that in the tea and forest soils was nitrified more slowly. About 60–80% of the in the tea and forest soils was nitrified during 35 d of incubation, indicating nitrifiers do exist in these soils. Significantly higher gross nitrification rates were observed in vegetable and tea soils with high and medium production than in forest and tea soils with low production. Microbial consumption (immobilization and nitrate respiration) accounted for 30 to 70% of the mineralized nitrate nitrogen ( −N) with the lowest in the forest soil, and no significant difference between the tea and vegetable soils. Nitrogen fertilizer stimulated soil nitrification. In conclusion, the types of land use and their management are more important than soil pH for soil nitrification. High nitrogen application rate is the main cause of accumulation in tea soils and should be reduced to minimize pollution of water resources.