耕翻和秸秆还田深度对东北黑土物理性质的影响

为了明确耕翻和秸秆还田深度对土壤物理性质的影响,在东北黑土区中部进行了6 a的耕翻和秸秆还田定位试验,设置了免耕(D0)、浅耕翻(0～20 cm)(D20)、浅耕翻+秸秆(D20S)、深耕翻(0～35 cm)(D35)、深耕翻+秸秆(D35S)、超深耕翻(0～50 cm)(D50)和超深耕翻+秸秆(D50S)7个处理开展研究,秸秆还田处理将10 000 kg/hm2秸秆均匀地还入相应的耕翻土层。结果表明,耕翻和秸秆还田深度是影响土壤物理性质的重要农艺措施。与初始土壤相比,免耕显著增加了0～20cm土层土壤容重,减少了孔隙度、持水量、饱和导水率和0.25mm水稳性团聚体的含量(WAS0.25)(P0.05),而对20～50 cm土层没有显著影响(P0.05)。在0～20 cm土层,除了D50处理显著降低了WAS0.25含量以外,D20,D35和D50处理对各项土壤物理指标均没有显著影响;而D20S和D35S处理则显著改善了该层各项土壤物理指标。在20～35 cm土层,D35、D35S、D50和D50S处理显著改善了该土层各项土壤物理指标(除了2014年的容重)。在35～50cm土层,D50和D50S处理对各项土壤物理指标改善效果显著,特别是相应土层通气孔隙度和饱和导水率显著增加。研究结果表明耕翻配合秸秆对土壤物理指标的改善效果优于仅耕翻处理。综合评分结果也表明D35S和D50S处理分别对20～35 cm和35～50 cm土层土壤物理性质的改善效果最好,说明在质地黏重的黑土上深翻耕或者超深翻耕配合秸秆还田通过土层翻转秸秆全层混合施用能够显著改善全耕作层土壤的物理性质,增加耕层厚度,扩充土壤的水分库容,提高黑土的水分调节能力。

Effects of incorporation depth of tillage and straw returning on soil physical properties of black soil in Northeast China

Black soil in northeast China is well known as high natural fertility for grain production, but the growth and yield of crop can be limited due to the high clay content of black soil can deteriorate physical properties. In this case, both tillage and straw return can be expected to serve as the important agronomic practices, in order to efficiently improve soil physical properties. However, the optimal depth of tillage and straw return into soil for favorable soil physical properties still remained unknown, particularly in black soil region. In this study, a field experiment, referred to the depth of tillage and straw return into soil, was conducted for six years in the black soil region in northeast China, in order to investigate the effects of incorporation depth of tillage and straw return into soil on soil physical properties of black soil. Seven treatments consisted of four replicates and random block design, including no tillage (D0), shallow tillage (0-20 cm) without or with straw return (D20 or D20S), deep tillage (0-35 cm) without or with straw return (D35 or D35S), super deep tillage (0-50 cm) without or with (D50 or D50S) straw return. In the treatments with straw return, a straw rate of 10 000 kg/hm2 was set to return into the corresponding tilled soil layer. Bulk density and water holding capacity were measured using cutting ring method, while the hydraulic conductivity was determined using constant head method, and the aggregate was measured using wet sieving method. The results showed that: 1) Compared with initial soil values, D0 treatment significantly increased soil bulk density, while decreased soil porosity, water holding capacity, hydraulic conductivity and >0.25 mm water stability aggregate (WAS>0.25) within 0-20 cm soil layer (P<0.05). However, there was no significantly impact on those indicators in soil layer within 20-50 cm (P>0.05). 2) In D20, D35 and D50 treatments, there was no obvious impact on the soil physical properties within 0-20 cm soil layer with exception for WAS>0.25 in D50 treatment, but D20S and D35S treatments remarkably all indicators of soil physical properties within 0-20 cm soil layer. 3) D35, D35S, D50 and D50S treatments significantly improved soil physical properties within 20-35 cm soil layer with exception of bulk density in 2014, while D50 and D50S treatments dramatically enhanced soil physical properties within in 35-50 cm soil layer (P<0.05). Specially, aeration porosity and hydraulic conductivity increased significantly, within the corresponding soil layers, while the higher effect was found in the treatment with straw return, compared with only tilled treatments. The comprehensive evaluation also showed that D35S and D50S treatments reached the best effect for improving soil physical properties. Therefore, the findings demonstrated that deep tillage or super deep tillage with straw return can efficiently improve soil physical properties within the whole tilled soil layers, concurrently to increase the depth of tilled soil layer, and thereby to enhance the water infiltration rate and soil water storage in black soil with heavy clay. In view of the positive effect of deep tillage and super tillage with straw return on soil physical properties and the limit of no tillage, the combined tillage practices of deep tillage (or with straw return) and no tillage were proposed for the black soil with high clay in northeast China and other regions.