Short-Term Increase of Nitrogen Leaching in a Tea Field after Heavy Application of Organic Fertilizer

Since 1999, the annual amount of fertilizer applied to tea fields has been restricted to 50 kgN/10a as much as possible to avoid nitrate pollution of groundwater; however, the nitrogen application tends to be similar to the previous high fertilizer levels to sustain high yields and superior tea quality in recent years. We investigated how this restoration of the previous heavy application affects nitrogen leaching and the forms of nitrogen in the soil.

According to our measurements, the increase in the application of organic fertilizer from 50 to 87-100 kgN/10a increased the concentration of nitrate leaching into underdrainage after ten months of heavy application. After another month, the nitrate concentration in the underdrainage reached the levels obtained previously under heavy application of organic fertilizer. This period (11 months) was six months shorter than the period required for the reduction of nitrate concentration to a prescribed plateau following the restriction of nitrogen application. Protein-like organic nitrogen in the soil increased one year after the heavy application of organic fertilizer with little increase in total nitrogen content. These results show that restoration of reduced nitrogen application to areas with previous heavy application rapidly increases nitrate leaching from the tea field with little increase in nitrogen accumulation in the soil.

Our results suggest that restoration of the previous heavy application of organic fertilizer has the effect of rapidly increasing nitrogen loading to groundwater in tea cultivation areas.