[Influence of land-use type on moisture-effect of nitrification in subtropical red soils]

Air-drying is always accompanied by soil moisture loss. The different influences of air-drying on soil nitrification might due to the different nitrification responses to moisture changing of acid subtropical soils. So, after applying 0 and 150 mg x kg(-1) of ammonium bicarbonate, a 35-day incubation study was conducted to determine the nitrification potential of four acid subtropical soils under 5 soil moisture levels, namely 30% water-holding capacity (WHC), 45% WHC, 60% WHC, 75% WHC and 90% WHC. Four soils, designated QR, QU, SR and SU, derived from Quaternary red earth and Tertiary red sandstone, were collected from rice and upland field. The results indicated that the soil nitrification was significantly influenced by the moisture content (p < 0.01), and the nitrification sensitivities to soil moisture content varied with land-use types. For the treatments without ammonium input, the ranges of nitrification ratio were 11% and 8% in upland soils, QU and SU respectively, which were obviously lower than those in paddy soils (35% for QR, and 20% for SR). The ammonium input would increase the ranges of nitrification ratio which were 56%, 26%, 31%, and 26% for soil QR, QU, SR, and SU, respectively. And the ammonium input would accelerate soil acidification under high moisture levels. In a word, the land-use type presents a significant influence on the nitrification response to moisture content, which might lead to the difference of air-drying effect.