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Title:   Author  item
                                            Sainju, Upendraitem
                                            Caesar, Thecanitem
                                            Lenssen, Andrewitem
                                            Evans, Robertitem
                                            Kolberg, Robert
  Submitted to: Soil Science Society of America Journal
                                    Publication Type: Peer Reviewed Journal
                                    Publication Acceptance Date: 5/30/2007
                                    Publication  Date: 11/1/2007
                                    Citation: Sainju, U.M., Caesar, T., Lenssen, A.W., Evans, R.G., Kolberg, R.L. 2007. Long-term tillage and cropping sequence effects on dryland residue and soil carbon fractions. Soil Science Society of America Journal. 71(6):1730-1739.Interpretive Summary: Long-term traditional farming system, such as conventional tillage with wheat-fallow, has resulted in the decline of soil organic matter and total nitrogen content by 30 to 50% of their original levels in the last 50 to 100 yr in the northern Great Plains. As a result, the traditional farming system has become inefficient, uneconomical, and unsustainable due to reduced soil productivity, increased soil erosion, and increased dependence of producers on federal aids. Improved soil and crop management practices are needed to increase soil nitrogen conservation and mineralization so that the cost and rate of N fertilization to crops can be reduced and environmental quality [reduced potentials for N leaching and nitrous oxide (a greenhouse gas) emission] can be improved.	
A long-term (21-yr) experiment was conducted to examine the effects of combinations of tillage and cropping sequences on dryland crop biomass returned to the soil, residue N, and soil N fractions in eastern Montana. Treatments were no-till continuous spring wheat (NTCW), spring till continuous spring wheat (STCW), fall and spring till continuous spring wheat (FSTCW), fall and spring till spring wheat-barley  (1984-1999) followed by spring wheat-pea (2000-2004) (FSTW-B/P), and spring till spring wheat-fallow (STW-F). Nitrogen fractions were soil total N (STN), particulate organic N (PON), microbial biomass N (MBN), and potential N mineralization (PNM), NH4-N, and NO3-N. 
Mean crop biomass was 53 to 66% greater in NTCW, STCW, FSTCW, and FSTW-B/P than in STW-F. As a result, soil surface residue amount and N content in 2004 were 30 to 127% greater in other treatments than in STW-F. The STN, PON, and PNM at the 0- to 20-cm depth were 24 to 107% greater in other treatments than in STW-F. At 0 to 5 cm, STN, PON, and MBN were greater in STCW than in FSTW-B/P and STW-F. At 5 to 20 cm, STN and PON were greater in NTCW and STCW than in STW-F, PNM and MBN were greater in STCW than in NTCW and STW-F, and NO3-N was greater in FSTW-B/P than in NTCW and FSTCW. 
Long-term reduced tillage with continuous cropping increased dryland crop biomass, residue N, and soil N conservation and mineralization compared with the conventional system, such as STW-F. Increased tillage frequency with spring wheat-pea rotation, however, increased N availability compared with other treatments at the subsurface soil.
                                Technical Abstract: Dryland soil N conservation and mineralization as influenced by long-term management practices is needed to reduce N fertilization rate, N leaching, and N2O (a greenhouse gas) emission. We evaluated the 21-yr effects of combinations of tillage and cropping sequences on dryland crop biomass (stems + leaves) returned to the soil, residue N, and soil N fractions at the 0- to 20-cm depth in 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.) (2000-2004) (FSTW-B/P), and spring till spring wheat-fallow (STW-F). Nitrogen fractions were soil total N (STN), particulate organic N (PON), microbial biomass N (MBN), and potential N mineralization (PNM), NH4-N, and NO3-N. Mean crop biomass was 53 to 66% greater in NTCW, STCW, FSTCW, and FSTW-B/P than in STW-F. As a result, soil surface residue amount and N content in 2004 were 30 to 127% greater in other treatments than in STW-F. The STN, PON, and PNM at 0 to 20 cm were 24 to 107% greater in other treatments than in STW-F. At 0 to 5 cm, STN, PON, and MBN were greater in STCW than in FSTW-B/P and STW-F. At 5 to 20 cm, STN and PON were greater in NTCW and STCW than in STW-F, PNM and MBN were greater in STCW than in NTCW and STW-F, and NO3-N was greater in FSTW-B/P than in NTCW and FSTCW. Long-term reduced tillage with continuous cropping increased dryland crop biomass, residue N, and soil N conservation and mineralization compared with the conventional system, such as STW-F. Increased tillage frequency with spring wheat-pea rotation, however, increased N availability at the subsoil.


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