A soil management strategy for ameliorating soil acidification and reducing nitrification in tea plantations

The cultivation of tea requires acidic soils which further acidify in plantations due to increased levels of nitrogen fixation. Ameliorating soil acidification by increasing pH is commonly implemented but as consequence, soil microbial nitrification causes losses of nitrate and limits the availability of NH4+ for tea, the latter being the preferred nitrogen source. Thus, the aim of this study was to analyze a strategy which can ameliorate soil acidification and simultaneously minimize the stimulation of nitrification in a typical tea soil. Net N transformation rates in different amounts of quicklime (CaO) and rice straw biochar addition treatments were determined through an incubation experiment, to test the effects of quicklime and biochar on acidification and nitrification in a typical tea soil. Our results showed that the addition of quicklime resulted in a significant increase in soil nitrification rate when soil pH increased from 3.77 to 4.10, but it decreased when soil pH increased to >5.10. Soil nitrification rate with biochar application continued to rise with increasing soil pH (3.77-3.85-4.01-4.38). When nitrification rates from all treatments were plotted against soil pH, we found that nitrification rate increased linearly with increasing soil pH from 3.63 to 4.38, then sharply declined to the values lower than that in the original soil pH when soil pH was increased from 4.38 to 5.10, and finally remained stable. Our results suggest that nitrification may be optimized in tea soil at ca. pH 4.40. Therefore, when we employed pH-raising practices to alleviate soil acidification, the soil pH should be enhanced to more than the optimum pH range for nitrification (approximately 5.10 in this study) to avoid stimulating soil nitrification.