Enhancing soil carbon and nitrogen storage with sheep grazing in dryland cropping sequences

Dr Upendra Sainju1

1USDA-ARS, Sidney, MT, Sidney, United States

Sheep grazing to manage weeds and crop residue in dryland cropping systems can enhance soil C and N storage by returning feces and urine to the soil. This study evaluated the effect of sheep grazing to manage weeds compared to tillage on soil total C (STC) and N (STN) at the 0-120 cm depth in dryland cropping sequences from 2012 to 2015 in western Montana, USA. Weed management practices were sheep grazing with no chemical input (GO), minimum tillage with chemical input (MT), and conventional tillage with no chemical input (TO). Cropping sequences were clover cover crop following safflower/clover intercrop (C-SC), lentil following winter wheat (L-W), winter wheat following clover cover crop (W-C), and winter wheat following lentil (W-L) employed in a 5-yr crop rotation of safflower/clover cover crop – clover cover crop – winter wheat – lentil – winter wheat. At 60-90 and 90-120 cm, STC increased with GO compared to TO, but STN increased with TO compared to GO and MT. The STC was greater with C-SC than other crop rotations at 15-30 cm, but was greater with W-C than C-SC and L-W at 60-90 cm. The STN was greater with C-SC than W-C at 30-60 cm. From 2012 to 2015, STC at 15-50 cm increased at 300 kg C ha-1 yr-1 with GO and STN at 60-90 and 90-120 cm increased at 20-50 kg N ha-1 yr-1 with TO. Sheep grazing enhanced soil C storage compared to tillage at the upper soil layer, but the trend reversed with soil N storage at the bottom layers. Clover cover crop following safflower/clover intercrop increased soil C and N storage compared to other crop rotations in the middle soil layers.


Dr. Upendra M. Sainju has been working as a Senior Research Soil Scientist in dryland and irrigated cropping systems for the past 14 years in USDA, Agricultural Research Service, Sidney, Montana, USA. Prior to this, he worked as postdoctoral associate and visiting scientist in Rutgers University, Washington State University, Fort Valley State University, and Tribhuvan University, Nepal from 1983 to 2004 and as a soil scientist and horticulturist in the Department of Agriculture, Government of Nepal from 1973 to 1982. He received Ph.D. from University of Kentucky, M.S. from University of Florida, and B.S. from University of Udaipur, India.  He is nationally and internationally renowned in developing soil and crop management practices that increase crop yields and quality, sequester carbon (C) and nitrogen (N) in the soil, increase organic matter, improve soil quality and productivity, reduce N fertilization rate and N leaching, and mitigate greenhouse gas emissions. Over the past 44 years, he has conducted extensive research on the effects of tillage, cropping systems, crop rotation, cover crops, N fertilization rates, poultry litter application, sheep grazing, and irrigation on C and N cycling in agroecosystems, greenhouse gas emissions, and crop yields. His research accomplishments have been documented in 130 peer-reviewed journals, 15 book chapters, 20 proceedings, 40 popular press, 4 technical reports, and 150 abstracts. He has actively participated in American Society of Agronomy (ASA) and Soil Science Society of America (SSSA) by serving in ASA community leader (Soil Carbon and Greenhouse Gas Emissions), committees (ASA and SSSA Fellows Committees, Best Paper Review Committee, Applied Soil Science Award Committee, Environmental Quality Award Committee), meetings (session chair, moderator, and paper presentation), reviewer of more than 30 journals, and Associate and Academic Editors in Agronomy Journal (2009-2012), Journal of Environmental Quality (2015-present), and PLOS ONE (2014-present). He received Soil Science Society of America Fellow in 2014 and American Society of Agronomy Fellow in 2015. He received Outstanding Contribution in Reviewing Journals (Applied Soil Ecology, November 2017; Agriculture, Ecosystem, and Environment, July 2017; and Field Crops Research, October 2018),He also received outstanding certificate of merit award in USDA (2011-present), outstanding research awards (Fort Valley State University, Georgia, 2004 and Northwest University, Xian, China, 2015), and phenomenal and worthy keynote presentation in 5th International Conference in Agriculture and Horticulture, June 27-19, 2016, Cape Town, South Africa. He has received more than $5 million research grants from USDA and other organizations in collaboration with national and international universities to conduct research in soil, environmental, and crop sciences.


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