Sheep (Ovis aries L.) grazing on weeds and crop residue during the fallow period may enhance soil carbon (C) and nitrogen (N) through urine and faeces returned to the soil. We compared sheep grazing, tillage, and herbicide application as weed management practices on soil total C (STC), total N (STN), ammonium (NH4+)-N, and nitrate (NO3–)-N contents in a dryland 5-year crop rotation from 2012 to 2015 in the northern Great Plains, USA. The treatments were sheep grazing with no chemical input in organic crop production (GO), minimum tillage with chemical inputs (MT), and conventional tillage with no chemical input in organic crop production (TO). The 5-year crop rotation was safflower (Carthamus tinctorius L.)/sweet clover (Melilotus officinalis L.) cover crop–sweet clover cover crop–winter wheat (Triticum aestivum L.)–lentil (Lens culinaris L.)–winter wheat. At the 0–1.20 m depth, STC was 14–20 Mg C ha–1 greater in GO than MT and TO, but STN was 2.1–2.2 Mg N ha–1 greater in TO than GO and MT. The NH4+-N and NO3–-N contents were 5–21 kg N ha–1 greater in MT than GO and TO. While STC and STN tended to increase with year for all treatments, NH4+-N and NO3–-N contents varied with treatments and years. Sheep grazing enhanced soil C storage, but had a variable effect on N storage and residual N compared to tillage and herbicide application for weed control.

中文翻译：

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放牧以控制杂草增加土壤碳，而不是氮

绵羊（Ovis aries L.）在休耕期间吃杂草和作物残留物可能会通过尿液和粪便返回土壤来增加土壤碳（C）和氮（N）。我们比较了绵羊放牧、耕作和除草剂作为杂草管理实践对旱地 5 年土壤总碳 (STC)、总氮 (STN)、铵 (NH4+)-N 和硝酸盐 (NO3-)-N 含量的影响美国大平原北部 2012 年至 2015 年的轮作。处理是有机作物生产中无化学投入的绵羊放牧（GO）、化学投入少的耕作（MT）和有机作物生产中无化学投入的常规耕作（TO）。5年轮作是红花（Carthamus tinctorius L.）/甜三叶草（Melilotus officinalis L.）覆盖作物-甜三叶草覆盖作物-冬小麦（Triticum aestivum L.）-扁豆（Lens culinaris L.）)——冬小麦。在 0-1.20 m 深度，GO 中的 STC 比 MT 和 TO 大 14-20 Mg C ha-1，但 TO 中的 STN 比 GO 和 MT 大 2.1-2.2 Mg N ha-1。MT 中的 NH4+-N 和 NO3--N 含量比 GO 和 TO 高 5-21 kg N ha-1。所有处理的STC和STN均呈随年份增加的趋势，NH4+-N和NO3--N含量随处理和年份而变化。放牧提高了土壤碳储量，但与耕作和使用除草剂控制杂草相比，对氮储量和残留氮有不同的影响。NH4+-N和NO3--N含量随处理和年份而变化。放牧提高了土壤碳储量，但与耕作和使用除草剂控制杂草相比，对氮储量和残留氮有不同的影响。NH4+-N和NO3--N含量随处理和年份而变化。放牧提高了土壤碳储量，但与耕作和使用除草剂控制杂草相比，对氮储量和残留氮有不同的影响。