Location: Agricultural Systems ResearchTitle: Sheep grazing to control weeds enhances soil carbon, not nitrogen
|HATFIELD, PATRICK - Montana State University|
|RAGEN, DEVON - Montana State University|
Submitted to: Soil Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/7/2020
Publication Date: 7/6/2020
Citation: Sainju, U.M., Hatfield, P., Ragen, D. 2020. Sheep grazing to control weeds enhances soil carbon, not nitrogen. Soil Research. https://doi.org/10.1071/SR19353.
Interpretive Summary: In the northern Great Plains, sheep grazing during fallow periods is a common practice to control weeds and reduce feed cost by grazing on crop residue. To what extent sheep grazing can affect soil carbon and nitrogen is not known. Scientists at ARS, Sidney, MT in collaboration with Montana State University reported that sheep grazing on weeds and crop residue during fallow periods on a five-year crop rotation enhanced soil carbon storage to a depth of 4 ft, but not nitrogen storage and soil residual nitrogen compared to tillage and herbicide application of weed control. Producers can use sheep grazing to improve soil health by enhancing soil organic matter compared to tillage and herbicide application.
Technical Abstract: Sheep (Ovis aries L.) grazing on weeds and crop residue during the fallow period may enhance soil C and N through urine and feces returned to the soil. We compared sheep grazing compared to tillage and herbicide application as weed management practices on soil total C (STC), total N (STN), NH4-N, and NO3-N contents in a dryland 5-y crop rotation from 2012 to 2015 in the northern Great Plains, USA. 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-y 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 with GO than MT and TO, but STN was 2.1-2.2 Mg N ha-1 greater with TO than GO and MT. The NH4-N and NO3-N contents were 5-21 kg N ha-1 greater with MT than GO and TO. While STC and STN tended to increase with year for all treatments, NH4-N and NO3-N 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.