Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 10, 2008
Publication Date: February 7, 2009
Repository URL: http://hdl.handle.net/10113/28311
Citation: Sainju, U.M., Lenssen, A.W., Caesar, T., Evans, R.G. 2009. Dryland crop yields and soil organic matter as influenced by long-term tillage and cropping sequence. Agronomy Journal. 101(2):243-251. Interpretive Summary: The conventional spring-tilled spring wheat-fallow system has not only decreased crop yields and became uneconomical by the absence of crops during the fallow period but also reduced soil quality and productivity due to loss of soil organic matter from increased mineralization and soil erosion in the northern Great Plains. In the last 50 to 100 yr, this system has resulted in a decline of soil organic matter by 30 to 50% of their original levels. Therefore, improved soil and crop management practices are needed to sustain dryland crop yields, increase soil organic matter, and improve soil quality and productivity to reduce the dependence of producers on federal aids transfer programs. We evaluated the long-term (21-yr) effects of combinations of tillage and cropping sequences on grain and biomass (stems + leaves) yields of spring wheat, barley, and pea and soil carbon, nitrogen, and pH at the 0- to 20-cm depth in eastern Montana. Treatments were no-till continuous spring wheat (NTCW), spring-tilled continuous spring wheat (STCW), fall- and spring-tilled continuous spring wheat (FSTCW), fall- and spring-tilled spring wheat-barley (1984-1999) followed by spring wheat-pea (2000-2004) (FSTW-B/P), and spring-tilled spring wheat-fallow (STW-F). Spring wheat grain and crop biomass yields varied with treatments and years and mean yields were greater in NTCW, STCW, FSTCW, and FSTW-B/P. Soil organic carbon and total nitrogen contents in 2004 were greater in NTCW and STCW than in STW-F but ammonium- and nitrate-nitrogen were greater in FSTW-B/P than in NTCW and FSTCW. Soil pH was not influenced by treatments. Both soil organic carbon and total nitrogen were linearly related with spring wheat grain and crop biomass yields. Long-term reduced tillage with continuous cropping increased dryland spring wheat grain and crop biomass yields and soil organic matter compared with the conventional system, such as STW-F. Inclusion of pea in the rotation with wheat increased soil inorganic nitrogen, thereby increasing the potential for nitrogen fertilization reduction.
Technical Abstract: Novel management practices are needed to improve the declining dryland crop yields and soil organic matter using conventional farming practices in the northern Great Plains. We evaluated the 21-yr effect of tillage and cropping sequence on dryland grain and biomass (stems + leaves) yields of spring wheat (Triticum aestivum L.), barley (Hordeum vulgare L.), and pea (Pisum sativum L.) and soil organic matter at 0- to 20-cm depth in eastern Montana, USA. Treatments were no-tilled continuous spring wheat (NTCW), spring-tilled continuous spring wheat (STCW), fall- and spring-tilled continuous spring wheat (FSTCW), fall- and spring-tilled spring wheat-barley (1984-1999) followed by spring wheat-pea (2000-2004) (FSTW-B/P), and the conventional spring-tilled spring wheat-fallow (STW-F). Spring wheat grain and biomass yields increased with increased crop growing season precipitation (GSP) and were greater in STW-F than in FSTCW and FSTW-B/P when GSP was <250 mm. Although mean grain and biomass yields were greater, annualized yields were lower in STW-F than in other treatments. In FSTW-B/P, barley and pea grain and biomass yields also increased with increased GSP. Soil organic C and total N were lower in STW-F than in other treatments and linearly related (R2 = 0.64 to 0.78) with total annualized biomass residue returned to the soil from 1984 to 2004. Alternate-year summer fallowing increased spring wheat grain and biomass yields compared with annual cropping but reduced annualized yields and soil organic matter. For sustaining dryland crop yields and soil organic matter, no-tillage with annual cropping system can be adopted in the northern Great Plains.