Dryland Soil Carbon and Nitrogen after Thirty Years of Tillage and Cropping Sequence Combination

Abstract

Little is known about the long‐term management impact on soil C and N contents in the northern Great Plains. We evaluated the 30‐yr effect of tillage and cropping sequence combination on dryland crop biomass yield and soil bulk density, soil organic carbon (SOC), soil inorganic carbon (SIC), soil total nitrogen (STN), NH4–N, and NO3–N contents at the 0‐ to 120‐cm depth in a Dooley sandy loam (fine loamy, mixed, frigid Typic Argiboroll) in eastern Montana. Treatments were no‐till continuous spring wheat (Triticum aestivum L.) (NTCW), spring till continuous spring wheat (STCW), fall and spring till continuous spring wheat (FSTCW), fall and spring till spring wheat–barley (Hordeum vulgare L., 1984–1999) followed by spring wheat–pea (Pisum sativum L., 2000‐2013) (FSTW–B/P), and spring till spring wheat–fallow (STW–F, traditional system). Mean annualized crop biomass returned to the soil was 23 to 30 % greater in NTCW, STCW, FSTCW, and FSTW–B/P than STW–F. At 0 to 7.5 cm, bulk density was 13 to 21% greater in STW–F, but SOC, SIC, and STN were 12 to 98% greater in STCW than other treatments. Ammonium‐N and NO3–N contents were 25 to 74 % greater in FSTCW than other treatments. At other depths, SOC, SIC, STN, NH4–N and NO3–N contents varied among treatments. Reduced tillage with increased crop residue returned to the soil increased soil C and N storage in NTCW and STCW, but increased tillage intensity increased mineral N content in FSTCW compared with STW–F. Improved management practices, such as NTCW and STCW, may be adopted to improve dryland soil C and N stocks.