轮耕对渭北旱塬麦田土壤有机质和全氮含量的影响

【目的】研究由秸秆覆盖免耕、秸秆覆盖深松和秸秆还田翻耕组成的不同保护性轮耕模式对渭北旱塬连作麦田土壤肥力的影响。【方法】2007—2014年在陕西合阳实施夏闲期免耕/深松轮耕(NT/ST)、深松/翻耕轮耕(ST/CT)、翻耕/免耕轮耕(CT/NT)、连续免耕(NT/NT)和连续翻耕(CT/CT)5种不同耕作模式定位试验,测定并分析2011—2014年小麦收获后不同耕作处理下土壤有机质和全氮变化规律及产量差异。【结果】与连续翻耕相比,连续免耕有利于表层土壤有机质和全氮积累,而免耕、深松和翻耕组成的3种轮耕处理更有利于提高20—40和40—60 cm土层土壤有机质和全氮含量,其中随着耕作年限延长,连续免耕处理下土壤养分逐渐表现出"上层富集,下层贫化"的现象;而免耕/深松轮耕更有利于耕层及耕层以下土壤养分均匀分布。随着轮耕年限增加,各耕作处理0—60 cm土层土壤有机质含量和总量均呈现出整体增加趋势,其中以免耕/深松处理增加趋势比较明显。与2007年相比,免耕/深松、深松/翻耕和翻耕/免耕3种轮耕处理的0—60 cm土层年平均有机质含量增加速率分别为4.53%、3.02%和2.26%,2014年土壤有机质总量分别增加了4.07、2.68和1.65 kg·m-3。轮耕7年后,免耕/深松、深松/翻耕和翻耕/免耕轮耕处理较连续翻耕处理0—60 cm土层土壤有机质含量分别显著增加25.3%、15.2%和10.2%,有机质总量分别增加31.57%、21.45%和13.94%,其中免耕/深松处理较连续免耕有机质含量增加9.20%,总量增加3.84%。在2011—2014年期间,与连续翻耕相比,连续免耕和3种轮耕处理0—60 cm土层土壤全氮含量及总量均有不同程度增加。其中2014年免耕/深松、深松/翻耕和翻耕/免耕轮耕处理较连续翻耕处理0—60 cm土层土壤全氮含量分别增加17.3%、8.0%和6.4%,氮总量分别显著增加了0.21、0.13和0.09 kg·m-3,其中,免耕/深松处理较连续免耕全氮含量增加了3.02%,总量减少了2.26%。2011—2014年冬小麦平均产量表现为深松/翻耕免耕/深松连续翻耕翻耕/免耕连续免耕,其中深松/翻耕和免耕/深松处理冬小麦平均产量接近,分别较连续翻耕处理显著增产10.36%和9.80%,较连续免耕处理显著增产17.84%和17.24%;翻耕/免耕较连续翻耕处理减产1.59%,较连续免耕处理增产5.08%,但差异不显著。不同保护性轮耕措施下,各土层土壤有机质含量与全氮含量间呈显著正相关;0—20 cm土层有机质含量与轮耕年限呈显著线性相关。【结论】3种轮耕模式较连续翻耕有利于提高0—60 cm土壤有机质和全氮总量,且较连续免耕有利于土壤养分含量在耕层及耕层以下土层均匀分布,其中以免耕/深松轮耕处理效果最优,且增产效应较佳,为渭北旱塬连作麦田较适宜的休闲轮耕模式。

Effects of Rotational Tillage on Soil Organic Matter and Soil Total Nitrogen Contents of Continuous Cropping Wheat Field in Weibei Highland

【Objective】 Effects of different rotational tillage patterns, which were pairwise combined with no-tillage (NT), subsoiling (ST) and conventional tillage (CT) with straw mulching, on soil fertility were studied in continuous cropping wheat field in Weibei Highland. 【Method】 The experiments of NT/ST (no-tillage in first year, subsoiling in second year, again no-tillage followed by alternating the next year), ST/CT (subsoiling in first year, conventional tillage in second year, again subsoiling followed by alternating the next year), CT/NT (conventional tillage in first year, no-tillage in second year, again conventional tillage followed by alternating the next year) rotational tillage, NT/NT (continuous no-tillage) and CT/CT (continuous conventional tillage) were conducted in summer fallow period during 2007-2014 in Heyang, Shaanxi, and soil organic matter, soil total nitrogen contents and yield were measured and analyzed in wheat harvesting periods from 2011 to 2014. 【Result】Compared with CT/CT, the NT/NT treatment increased soil organic matter and soil total nitrogen contents of surface soil, and the three rotational tillage treatments increased soil organic matter and soil total nitrogen contents in 20-40 and 40-60 cm soil layers. With increasing cultivation, the NT/NT treatment increased soil nutrients of surface and depleted that of lower layer, and the NT/ST treatment increased soil nutrients of surface and subsurface soil. The soil organic matter and storage in 0-60 cm soil layer under the five tillage treatments showed a trend of overall increase with increasing cultivation, and the increase trend under NT/ST treatment was obvious. Compared to pretreatment, the soil organic matter increase rate under NT/ST, ST/CT, and CT/NT treatments were 4.53%, 3.02%, and 2.26%, and the soil organic storage in 2014 increased by 4.07, 2.68 and 1.65 kg·m^-3, respectively. After 7 years of rotational tillage, the soil organic matter in 0-60 cm layer under NT/ST, ST/CT, and CT/NT treatments were 25.3%, 15.2%, and 10.2% higher than CT/CT treatment, and the total soil organic matter significantly increased by 31.57%, 21.45%, and 13.94%, respectively. Compared to NT/NT, the soil organic matter under NT/ST was increased by 9.20%, and the soil organic storage was increased by 3.84%. Compared with CT/CT, the soil total nitrogen contents and storage of 0-60 cm soil depth under three rotational tillage and NT/NT treatment were increased differently. The soil total nitrogen contents under NT/ST, ST/CT, and CT/NT treatments were 17.3%, 8.0% and 6.4% higher than CT/CT treatment in 2014, and the soil total nitrogen storage were significantly increased by 0.21, 0.13 and 0.09 kg·m^-3, respectively. Compared to NT/NT, the soil total nitrogen contents under NT/ST was increased by 3.02%, and the total nitrogen storage was decreased by 2.26%. The average wheat yield under ST/CT treatment in 2011-2014 was close to NT/ST, and the wheat yields of ST/CT and NT/ST treatments were 10.36% and 9.80% higher than CT/CT, and 17.84% and 17.24% higher than NT/NT, respectively. The wheat yield of CT/NT was 1.59% lower than CT/CT and 5.08% higher than NT/NT treatment. The correlation analysis demonstrated that soil organic matter was significantly correlated with soil total nitrogen contents in different soil layers, and the soil organic matter in 0-20 cm soil layer was significantly correlated with soil tillage years.【Conclusion】Compared with CT/CT, the rotational tillage patterns of NT/ST, ST/CT, and CT/NT increased the storage of soil organic matter and soil total nitrogen, and also increased soil nutrient contents of surface and subsurface soil. The NT/ST was the best one among the three rotational tillage patterns, under which also had a higher production of winter wheat. So the NT/ST is a more appropriate rotational tillage pattern for the continuous cropping wheat field in Weibei Highland.