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Title:   Author  item
                                            Sainju, Upendraitem
                                            Jabro, Jalal

                                                         - *Jay*item
                                            Caesar, Thecan
  Submitted to: Journal of Environmental Quality
                                    Publication Type: Peer Reviewed Journal
                                    Publication Acceptance Date: 1/20/2010
                                    Publication  Date: 4/16/2010
                                    Citation: Sainju, U.M., Jabro, J.D., Caesar, T. 2010. Tillage, Cropping Sequence, and Nitrogen Fertilization Effects on Dryland Soil Carbon Dioxide Emission and Carbon Content. Journal of Environmental Quality. 39(3):935-945.Interpretive Summary: 	Carbon dioxide (CO2) emission from agricultural practices has been considered as a significant anthropogenic source (25%) of greenhouse gas responsible for global warming. The emission occurs primarily from oxidation of soil organic matter and root respiration due to cropping, return of nonharvestable crop residue in the soil, tillage, and other management practices. In contrast, soil is also an important sink of atmospheric CO2, where CO2 absorbed by plant biomass through photosynthesis is converted into soil organic matter after the residue is returned to the soil.
Traditional farming systems, such as conventional tillage with crop-fallow, have resulted in a decline of dryland soil organic carbon (C) by 30 to 50% of their original levels in the last 50 to 100 yr in the northern Great Plains. Intensive tillage increases the mineralization of organic C and fallowing increases its loss by reducing the amount of plant residue returned to the soil and by increasing soil water and temperature. Therefore, novel management practices are needed to increase C sequestration and reduce CO2 emission in dryland soils.
	The effects of tillage and cropping sequence combination and nitrogen (N) fertilization on dryland soil surface CO2 flux, temperature and water content at the 0- to 15-cm depth, and total (organic + inorganic) C content at 0- to 120-cm was evaluated from May to October, 2006 to 2008, in eastern Montana. Treatments were no-tilled continuous malt barley (NTCB), no-tilled malt barley-pea (NTB-P), no-tilled malt barley-fallow (NTB-F), and conventional-tilled malt barley-fallow (CTB-F), each with 0 and 80 kg N ha-1. 
Crop residue (stems + leaves) returned to the soil varied among years and was greater in NTCB and NTB-P than in NTB-F and CTB-F or greater with 80 than with 0 kg N ha-1. While soil temperature was generally similar among treatments, water content was higher in NTB-F and CTB-F than in other treatments during dry periods. Soil CO2 flux increased from 7 kg CO2-C ha-1 d-1 in early May to 210 kg CO2-C ha-1 d-1 in mid-June as temperature increased and then declined to 3 kg CO2-C ha-1 d-1 in September-October, with sharp increases immediately following substantial precipitation, especially in NTCB and NTB-P. Mean CO2 flux was greater in NTCB and NTB-P than in NTB-F. Tillage increased CO2 flux compared with no-tillage initially in 2006 while N fertilization affected variably in 2008. Soil total C was not influenced by treatments but varied with measurement dates. 
While no-tilled crop-fallow reduced dryland soil CO2 flux, annual cropping increased the flux probably by increasing crop residue returned to the soil and root respiration. Inclusion of pea in rotation with no-tilled malt barley, however, resulted in CO2 flux similar to that in CTB-F, which could also reduce N fertilization rate and sustain barley production.
                                Technical Abstract: Management practices are needed to reduce dryland soil CO2 emission and increase C sequestration that can influence global warming. We evaluated the effects of tillage and cropping sequence combination and N fertilization on dryland soil surface CO2 flux, temperature and water content at the 0- to 15-cm depth, and total (organic + inorganic) C content at 0- to 120-cm in Williams loam (fine-loamy, mixed, Typic Argiborolls) from May to October, 2006 to 2008, in eastern Montana. Treatments were no-tilled continuous malt barley (Hordeum vulgaris L.) (NTCB), no-tilled malt barley-pea (Pisum sativum L.) (NTB-P), no-tilled malt barley-fallow (NTB-F), and conventional-tilled malt barley-fallow (CTB-F), each with 0 and 80 kg N ha-1. Crop residue (stems + leaves) returned to the soil varied among years and was greater in NTCB and NTB-P than in NTB-F and CTB-F or greater with 80 than with 0 kg N ha-1. While soil temperature was generally similar among treatments, water content was higher in NTB-F and CTB-F than in other treatments during dry periods. Soil CO2 flux increased from 7 kg CO2-C ha-1 d-1 in early May to 210 kg CO2-C ha-1 d-1 in mid-June as temperature increased and then declined to 3 kg CO2-C ha-1 d-1 in September-October, with sharp increases immediately following substantial precipitation, especially in NTCB and NTB-P. Mean CO2 flux was greater in NTCB and NTB-P than in NTB-F. Tillage increased CO2 flux compared with no-tillage initially in 2006 while N fertilization affected variably in 2008. Soil total C was not influenced by treatments but varied with measurement dates. While no-tilled crop-fallow reduced dryland soil CO2 flux, annual cropping increased the flux probably by increasing crop residue returned to the soil and root respiration. Inclusion of pea in rotation with no-tilled malt barley, however, resulted in CO2 flux similar to that in CTB-F, which could also reduce N fertilization rate and sustain barley production.


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