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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: 10/1/2007
                                    Publication  Date: 10/1/2007
                                    Citation: Sainju, U.M., Caesar, T., Lenssen, A.W., Evans, R.G., Kolberg, R.L. 2007. Long-term tillage frequency and cropping intensity effects on dryland residue and soil carbon fractions. Soil Science Society of America Journal. 71(6):1730-1739.Interpretive Summary: Maintaining soil organic matter levels in drylands of the northern Great Plains is needed not only to increase C sequestration for C trading and mitigate greenhouse gases, such as CO2, but also to improve soil quality for increasing crop production. An increase in soil organic C content of 0.58 Mg ha-1 in the surface 3 cm of soil can increase wheat grain yield by 15.6 kg ha-1 due to enhanced soil structure and improved soil water-nutrient-crop productivity relationships. The enhanced soil aggregation and crop residue C can also reduce soil erosion, especially in semi-arid regions where soil erosion due to action of wind is greater than in humid regions. 
The 21-yr effects of combinations of three tillage frequencies and three cropping systems were evaluated on dryland crop biomass returned to the soil, residue C, and soil C fractions at the 0 to 20 cm depth in eastern Montana. Tillage frequencies were no-till (NT), spring till (ST), and fall and spring till (FST) and cropping systems were continuous spring wheat (CW), spring wheat-barley (1984-1999) followed by spring wheat-pea (2000-2004) (W-B/P), and spring wheat-fallow (W-F). Carbon fractions were soil organic C (SOC), soil inorganic C (SIC), particulate organic C (POC), microbial biomass C (MBC), and potential C mineralization (PCM). 
Mean annualized crop biomass was greater in NTCW, STCW, FSTCW, and FSTW-B/P than in STW-F. Soil surface residue amount and C content in 2004 were  greater in NTCW and FSTCW than in STW-F. As a result, soil C fractions at 0 to 20 cm were also greater in all other treatments than in STW-F due to increased C input. At 0 to 5 cm, SOC, SIC, POC, and PCM were greater in NTCW than in FSTW-B/P. At 5 to 20 cm, POC was greater in NTCW than in FSTW-B/P and PCM was greater in STCW than in FSTCW. 
Reduced tillage with continuous cropping increased dryland crop biomass, residue C, and soil C fractions compared with the conventional system, such as STW-F, after 21 yr, thereby increasing soil C sequestration and biological soil quality in the northern Great Plains. The NTCW and STCW sequestered C at 214 kg C ha-1 yr-1 while STW-F lost C at 186 kg C ha-1 yr-1. Increase in tillage frequency, followed by replacement of CW by W-B/P in the continuous cropping system, however, reduced soil C fractions.
                                Technical Abstract: Long-term soil and crop management practices are needed to increase dryland C sequestration for C trading and C fractions to improve soil quality. We evaluated the 21-yr effects of combinations of three tillage frequencies and three cropping systems on dryland crop biomass returned to the soil, residue C, and soil C fractions at the 0 to 20 cm depth. Tillage frequencies were no-till (NT), spring till (ST), and fall and spring till (FST) and cropping systems were continuous spring wheat (Triticum aestivum L.) (CW), spring wheat-barley (Hordeum vulgare L) (1984-1999) followed by spring wheat-pea (Pisum sativum L.) (2000-2004) (W-B/P), and spring wheat-fallow (W-F). Carbon fractions were soil organic C (SOC), soil inorganic C (SIC), particulate organic C (POC), microbial biomass C (MBC), and potential C mineralization (PCM). A field experiment was conducted from 1984 to 2004 in Dooley sandy loam (fine-loamy, mixed, frigid, Typic Argiboroll) in eastern Montana. Mean annualized crop biomass was 53 to 66% greater in NTCW, STCW, FSTCW, and FSTW-B/P than in STW-F. Soil surface residue amount and C content in 2004 were 46 to 60% greater in NTCW and FSTCW than in STW-F. As a result, soil C fractions at 0 to 20 cm were 23 to 141% greater in all other treatments than in STW-F due to increased C input. At 0 to 5 cm, SOC, SIC, POC, and PCM were greater in NTCW than in FSTW-B/P. At 5 to 20 cm, POC was greater in NTCW than in FSTW-B/P and PCM was greater in STCW than in FSTCW. Reduced tillage with continuous cropping increased dryland crop biomass, residue C, and soil C fractions compared with the conventional system, such as STW-F, after 21 yr, thereby increasing soil C sequestration and biological soil quality. Increase in tillage frequency, followed by replacement of CW by W-B/P in the continuous cropping system, however, reduced soil C fractions.


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