深耕结合秸秆还田提高作物产量并改善耕层薄化土壤理化性质

  【目的】  小麦–玉米轮作区土壤耕层变薄，直接深耕往往导致土壤肥力降低。在存在该类问题的土壤上，研究不同耕作方式和秸秆还田对作物产量和土壤理化性质的影响，以期实现在增加耕层厚度的同时维持作物产量，并提升土壤肥力。  【方法】  试验于2012—2016年在华北平原南部濉溪县进行，供试土壤为砂姜黑土。在人工剥离5 cm土层的耕层薄化土壤上开展试验，设旋耕 (RT)、深耕 (DT)、旋耕 + 秸秆还田 (RTS)、深耕 + 秸秆还田 (DTS) 4个处理。在每年玉米和小麦成熟期进行田间测产；在第4季小麦收获后采集0—10和10—20 cm土层土样，分析土壤有机碳各组分和土壤养分含量、土壤团聚体分布。  【结果】  与旋耕 (RT) 相比，单纯深耕 (DT) 不能明显提高玉米和小麦产量，显著降低土壤总有机碳含量、0—10 cm土层有机碳各组分含量和土壤速效钾含量，并显著降低10—20 cm土层胡敏酸与富里酸比值及各土层粒径 > 0.25 mm水稳性团聚体的比例。深耕配合秸秆还田 (DTS) 处理玉米和小麦4季平均分别增产7.72%和8.06%，旋耕配合秸秆还田 (RTS) 处理分别增产7.55%和7.05%。在0—10 cm土层，DTS和RTS处理均明显提升土壤胡敏酸与富里酸比值，提高总有机碳及多数组分碳含量、提高土壤养分含量，RTS处理效果好于DTS处理；而在10—20 cm土层，DTS处理显著提高土壤胡敏酸、全氮和有效磷含量，效果好于RTS处理。DTS和RTS处理均可以显著提高粒径 > 0.25 mm水稳性团聚体的比例，在0—10 cm土层，以DTS处理效果最高，比RT处理增加23.09%，而在10—20 cm土层，以RTS处理效果最好，相比RT处理增加6.32%。  【结论】  在耕层薄化处理的土壤上，单纯深耕提升作物产量的效果不显著，也不利于土壤有机碳及各组分含量、土壤养分含量的提升，还破坏了土壤团粒结构。秸秆还田配合深耕或者旋耕均能显著提高作物产量，秸秆还田配合旋耕能有效培肥0—10 cm土层土壤，但对10—20 cm土层土壤肥力改善效果有限；秸秆还田配合深耕在增加耕层厚度的同时，还改善了土壤养分状况，明显减弱了单纯深耕对10—20 cm土层土壤结构稳定性的不利影响。

Deep tillage with straw returning increase crop yield and improve soil physicochemical properties under topsoil thinning treatment

  【Objectives】  The tillage layer become thin in the farmland of wheat-maize rotation system area, simply increase of tillage depth tends to deteriorate soil fertility. We studied the effects of deep tillage coupled with straw returning in the farmland through four years of continuous experiments.  【Methods】  The experiment was carried out in Suixi County in the southern part of the North China Plain in 2012–2016. The tested soil was lime concretion black soil. Before the start of the experiment, 5 cm of soil on the surface soil in the test area was artificially peeled off to simulate the soil with topsoil thinning. The experiment consisted of 4 treatments: rotary tillage (RT), deep tillage (DT), rotary tillage with straw returning (RTS), deep tillage with straw returning (DTS). At maturity, wheat and maize yields were investigated in field. After the fourth harvest, soil samples at 0–10 cm and 10–20 cm deep were collected, the soil organic carbon components, soil nutrient content and the weight of size > 0.25 mm soil aggregates were determined.  【Results】  Compared with the RT treatment, the DT did not increase maize and wheat yield significantly, but significantly reduced the contents of total soil organic C, organic C fractions and available K, the ratio of humic acid to fulvic acid in 10–20 cm soil layer, and the proportion of water-stable aggregates size > 0.25 mm in each soil layer. Straw returning coupled with deep tillage or rotary tillage had a good effect on increasing crop yield. The average yield increase of DTS in maize and wheat in the 4 seasons were 7.72% and 8.06%, and those of RTS were 7.55% and 7.05%, respectively. Both of DTS and RTS significantly increased the ratio of humic acid to fulvic acid in the soil. In the 0–10 cm soil layer, the contents of total and each organic C fraction, and the soil available K were higher in RTS, while in 10–20 cm soil layer, the soil humic acid, total N and available P content were higher in DTS. The proportion of size > 0.25 mm water-stable aggregates was highest in DTS in the 0–10 cm soil layer, which was increased by 23.09%, and that was highest in RTS in the 10–20 cm soil layer, which was increased by 6.32%, compared with those in RT.  【Conclusions】  In soil with thinning tillage layer, simply deep plough cannot increase crop yield, but against the increase of soil organic C and nutrient content, meanwhile destroy the soil aggregate structure. The straw returning coupled with tillage can significantly increase crop yield, and with rotary tillage can only effectively fertilize 0–10 cm soil, while with deep tillage can increases the topsoil thickness and improves the nutrient status of the 10–20 cm soil layer, and offset the adverse effect of simply deep tillage in soil structure stability in the 10–20 cm soil layer.