[Response of soil nitrification characteristics in subtropical area to air-drying]

Populations and activities of nitrifier can be significantly influenced by air-drying. A 35-day incubation study was conducted to determine the effects of air-drying on nitrification potential of four acid subtropical soils after applying 0 and 150 mg x kg(-1) of ammonium bicarbonate. 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, without ammonium input, the responses of nitrification in upland soils to air-drying were insignificant (p > 0.05). The nitrification ratio in fresh and air-dried samples of soil QU were 48% and 54% respectively, and 76% and 78% for SU; however, air-drying did have a significant effect on the nitrification in paddy soils (p < 0.01). Nitrification ratios were 40% and 89% for fresh and air-dried samples of QR, 76% and 94% for SR, and there was a lag-phase of the nitrification in air-dried paddy soils. Ammonium input would accelerate nitrification and make the nitrification ratios of fresh samples significantly higher than those of air-dried ones. In generally, land-use type presents a significant impact on the response of nitrification to air-drying effect, and there was a significant interaction of land-use type and fertilization.