Quantifying changes in soil biochemical properties is important in understanding the response to soil management practices. Our objectives were to evaluate the single and combined effects of three different crop rotations (maize (Zea mays)‐soybean (Glycine max) (2 years), maize‐soybean‐oat (Avena sativa) (3 years), maize‐soybean‐oat‐winter wheat (Triticum aestivum) (4 years)), and two winter cover‐type (cover crop and no cover crop) managements under long‐term conventional‐till (CT) and no‐till (NT) systems on water‐extractable carbon and nitrogen fractions, microbial biomass carbon (MBC) and enzymatic activities. The experimental site under silty clay loam in southeastern South Dakota was sampled before planting in early spring, after planting in early summer, and during the maize grain‐filling stage in early autumn of 2017, from the surface 0–7.5‐cm depth in 2017. In general, the cover crops had 9, 17 and 19% higher geometric mean of enzyme activities than the no‐cover‐crop plots at pre‐planting, after planting and the grain‐filling stage of maize, respectively. Although there were not many differences between “NT vs. CT” and “2‐year vs. 3‐year vs. 4‐year rotation” treatments, additive effects between “tillage and cover crops” and “rotation and cover crops” were observed. The MBC and β‐glucosidase activity were 31 and 54% higher, respectively, with cover crop vs. no cover crop under 4‐year rotation after planting of maize. Similarly, significant interactions between “cover crop and tillage” for hot water‐extractable nitrogen and urease activity at pre‐planting, and β‐D‐glucosidase after planting of maize, were observed. At the grain‐filling stage, the hot water‐extractable contents were significantly greater under cover crop as compared to the no‐cover‐crop plots. Furthermore, this study also concluded that seasonal fluctuations are important for understanding the management impacts on soil carbon fractions and biochemical properties.

中文翻译：

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长期轮作和耕作制度下冬季覆盖作物的土壤碳组分和酶活性的季节性变化

量化土壤生化特性的变化对于理解对土壤管理实践的响应非常重要。我们的目标是评估三种轮作（玉米（Zea mays）-大豆（Glycine max）（2年），玉米-大豆-燕麦（Avena sativa）（3年），玉米-大豆-玉米燕麦冬季小麦（普通小麦））（4年）），并在长期常规耕作（CT）和免耕（NT）系统下，对水可提取的碳和氮组分，微生物进行两次冬季覆盖类型（覆盖作物和无覆盖作物）管理生物质碳（MBC）和酶促活性。在南达科他州东南部粉质粘土壤土下的实验地点在早春播种前，夏初播种后以及2017年秋初玉米籽粒充实阶段取样，取样时间为2017年表面0-7.5-cm深度通常，在种植前，种植后和玉米灌浆期，覆盖作物的酶活性几何平均数分别比无覆盖地块高9、17和19％。尽管“ NT vs. CT”治疗与“ 2年vs.3年vs.4年轮换”治疗之间的差异不大，观察到“耕作和覆盖作物”与“轮作和覆盖作物”之间的累加效应。玉米种植4年后，覆盖作物与不覆盖作物的MBC和β-葡萄糖苷酶活性分别提高了31％和54％。同样，观察到“覆盖作物与耕作”之间在种植前对热水可提取的氮和脲酶活性以及玉米种植后的β-D-葡萄糖苷酶之间存在显着的相互作用。在灌浆阶段，与无盖作物地块相比，地下作物的热水可提取物含量要高得多。此外，这项研究还得出结论，季节性波动对于了解管理对土壤碳含量和生化特性的影响非常重要。玉米种植4年后，覆盖作物与不覆盖作物的MBC和β-葡萄糖苷酶活性分别提高了31％和54％。同样，观察到“覆盖作物与耕作”之间在种植前对热水可提取的氮和脲酶活性以及玉米种植后的β-D-葡萄糖苷酶之间存在显着的相互作用。在灌浆阶段，与无盖作物地块相比，地下作物的热水可提取物含量要高得多。此外，这项研究还得出结论，季节性波动对于了解管理对土壤碳含量和生化特性的影响非常重要。玉米种植4年后，覆盖作物与不覆盖作物的MBC和β-葡萄糖苷酶活性分别提高了31％和54％。同样，观察到“覆盖作物与耕作”之间在种植前对热水可提取的氮和脲酶活性以及玉米种植后的β-D-葡萄糖苷酶之间存在显着的相互作用。在灌浆阶段，与无盖作物地块相比，地下作物的热水可提取物含量要高得多。此外，这项研究还得出结论，季节性波动对于了解管理对土壤碳含量和生化特性的影响非常重要。观察到“覆盖作物与耕作”之间在种植前对热水可提取的氮和脲酶活性以及玉米种植后的β-D-葡萄糖苷酶之间存在显着的相互作用。在灌浆阶段，与无盖作物地块相比，地下作物的热水可提取物含量要高得多。此外，这项研究还得出结论，季节性波动对于了解管理对土壤碳含量和生化特性的影响非常重要。观察到“覆盖作物与耕作”之间在种植前对热水可提取的氮和脲酶活性以及玉米种植后的β-D-葡萄糖苷酶之间存在显着的相互作用。在灌浆阶段，与无盖作物地块相比，地下作物的热水可提取物含量要高得多。此外，这项研究还得出结论，季节性波动对于了解管理对土壤碳含量和生化特性的影响非常重要。