耕作方式对土壤不同粒径团聚体氮素矿化的影响

研究了常规耕作和垄作免耕两种耕作方式下紫色水稻土不同粒径团聚体中氮的矿化过程。结果表明,不同粒径团聚体氮素矿化强度具有显著差异:潜在矿化势(Np)的最高值均出现在2.0～0.25 mm大团聚体中,最低值在>2.0 mm的宏团聚体中;2.0～0.25 mm团聚体的潜在矿化速率(Vp)和实际矿化速率(Va)比其他团聚体高1.2～1.6倍。常规耕作和垄作免耕两种耕作方式下不同团聚体的净矿化率随时间的变化趋势相同;垄作免耕显著增加了氮素的净矿化量,以原土为例:垄作免耕处理Np比常规耕作处理高33.9%,Vp和Va分别比常规耕作处理高85.2%和52.0%。虽然垄作免耕可以显著促进土壤中氮素的矿化作用,但是耕作方式对不同粒径团聚体内的氮矿化动力学过程并无显著影响,表明耕作方式对不同大小团聚体中可矿化氮和微生物的分布影响较小。

Effects of Tillage on Nitrogen Mineralization in Aggregate-size Fractions of Subtropical Rice Soil

Large proportion of available nitrogen in soil is produced by mineralization, which can be changed by tillage management. However, tillage effects on soil N supply in cropping systems remain unclear. This study addressed dynamics of nitrogen mineralization within soil aggregates of a subtropical purple soil under two different tillage: conventional tillage (CT) and combination of ridge with no-tillage (RNT). Soil samples were separated into large aggregates (> 2.0 mm), macro-aggregates (2.0 - 0.25 mm), micro-aggregates (0.25 - 0.053 mm) and silt + clay fractions (< 0.053 mm) by wet-sieving method. Regression analysis showed that the time-dependent kinetics of net nitrification were best fitted with a first-order model for soil aggregates and whole soil, but net nitrification rate within different aggregate sizes were found significantly different. Similar patterns of net nitrification rate changes with the time were found in aggregates under CT and RNT. The highest mineralization potential (Np) was observed for 2.0 - 0.25 mm fraction and the lowest for >2.0 mm fraction, regardless of tillage regime. Potential mineralization rate (Vp) and actual average net mineralization rate (Va) associated with macro-aggregates (2.0-0.25 mm) were significantly higher than other sizes of aggregates and whole soil. For whole soil, CT regime, in comparison to RNT, increased Np by 33.9%, but the kinetics model of nitrification was not affected by tillage. This inferred that although nitrogen mineralization could be stimulated in no-tillage, mineralization associated with aggregates was not altered by tillage.