摘要:为了探明陇中黄土高原旱作农田土壤水稳性团聚体崩解机制，以连续进行15年的不同耕作措施长期定位试验为研究对象，利用LB湿筛法（快速湿润法、慢速湿润法和预湿润后扰动法）和传统湿筛法探索了传统耕作（T）、传统耕作+秸秆还田（TS）、免耕（NT）、免耕+秸秆覆盖（NTS）4种耕作措施对陇中黄土高原旱作农田土壤水稳性团聚体稳定性的影响及其破坏机制。结果表明：不同耕作措施下，4种湿筛法处理后， < 0.25 mm非水稳性团聚体含量排序为：传统湿筛法>快速湿润法>预湿润后扰动法>慢速湿润法；4种湿筛法处理后，团聚体平均重量直径排序为：慢速湿润法>预湿润后扰动法>快速湿润法>传统湿筛法；不同耕作措施下，土壤团聚体相对崩解指数高于相对机械破坏指数。不同湿筛法处理后，在0~5 cm和5~10 cm土层均以NTS的水稳性团聚体含量和平均重量直径最高，且NTS处理的平均重量直径显著（P≤5%）高于NT和T处理；而10~30 cm土层，TS处理的水稳性团聚体含量和平均重量直径最高，且显著高于T处理的平均重量直径，但与NTS处理的平均重量直径无显著差异。不同耕作措施下的团聚体崩解指数和机械破坏指数均以T处理最高，NT次之，NTS处理最低。秸秆对0~5 cm、5~10 cm、10~30 cm土层的团聚体崩解指数和机械破坏指数的降低均具有显著效应，而免耕仅在0~5 cm土层具有显著效应。因此，该区水稳性团聚体分散主要是由于水分入渗而引起的，且快速湿润时的破坏最大；同时，NTS处理可有效提升土壤水稳性团聚体稳定性，更有利于该区农田水土保持。
关键词:旱作农田/
秸秆还田/
免耕/
Le Bissonnais法/
土壤水稳性团聚体/
相对崩解指数/
相对机械破坏指数
Abstract:The semiarid western Loess Plateau is characterized by hilly landscape that is severely prone to soil erosion. Stability and distribution of soil water-stable aggregates could be affected by soil tillage methods in dry land areas. An improved understanding of the effect on soil and water erosion associated with the production of land is required for enhancement of agricultural sustainability in semiarid areas. A 15-year local field experiment was carried out to study the effects of different tillage methods and straw applications on soil water-stable aggregates and aggregate destruction mechanisms under spring-wheat/pea rotation using three Le Bissonnais (LB) and routine wet sieving (RW) methods. Three LB wet sieving methods used in the experiment were slow wetting sieving (SW) method simulating light rains (micro-cracking), fast-wetting sieving (FW) method simulating heavy rains (slaking), and wet stirring sieving (WS) method simulating disturbance (mechanical breakdown). Four aggregate size ranges were obtained by the sieving methods:2-5 mm (larger aggregate, LA); 0.25-2 mm (small aggregate, SA); 0.053-0.25 mm (micro-aggregate, MA); and < 0.053 mm (slit plus clay, SC). The results of the three LB methods and RW method were then compared and the mean weight diameter (MWD), relative slaking index (RSI) and relative mechanical breakdown index (RMI) of soil aggregates were calculated. The field experiment was located in the Rainfed Agricultural Experimental Station (35°28'N, 104°44'E) which belongs to Gansu Agricultural University in Dingxi, Gansu Province, China. The experimental work included the following tillage and straw mulching treatments:conventional tillage (T), no tillage (NT), no tillage with straw mulching (NTS), and conventional tillage with straw incorporation (TS). The treatments were arranged in a complete randomized block design with three replications. The soil samples were taken at three soil depths (0-5 cm, 5-10 cm and 10-30 cm). The results showed that after wetting treatments except the slow wetting method, the dominant fraction of fragments in each soil layer was < 0.25 mm under all four tillage treatments. The order of sieving method as for < 0.25 mm non water-stable aggregates content was RW > FW > WS > SW. MWD of soil aggregates for four sieving methods was in the order of SW > WS > FW > RW under all the four tillage treatments. This trend indicated that aggregate breakdown mechanism was in the order of:slaking > mechanical breakdown > micro-cracking. While NTS treated soils exhibited the highest MWD and water-stable aggregates content for all wet sieving methods in the 0-5 cm and 5-10 cm soil layers. MWD for NTS treatment was significantly greater (P ≤ 5%) than T and NT treatments. Also TS treatment showed the highest MWD and water-stage aggregates content in the 10-30 cm soil layer, but with no significant difference in MWD from NTS. Compared with T treatment, TS treated soils significantly improved MWD. RSI and RMI of soil aggregates were suppressed by NTS, TS and NT treatments, and NTS treatment had the highest effect. Straw addition significantly suppressed RSI and RMI of soil aggregates in all three observed soil layers. No tillage significantly suppressed RSI of soil aggregate in the 0-5 cm soil layer. The results suggested that heavy rain was the main factor destroying soil aggregates in rainfed farmlands in the Loess Plateau region in Central Gansu Province. NTS treatment performed best for sustainable agricultural development and soil and water conservation in the Loess Plateau region in Central Gansu Province.
Key words:Dry farmland/
Straw retention/
No tillage/
Le Bissonnais method/
Soil water-stable aggregates/
Relative slaking index/
Relative mechanical breakdown index
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