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Title:   Author  item
                                            Sainju, Upendraitem
                                            Lenssen, Andrew
  Submitted to: Soil and Tillage Research
                                    Publication Type: Peer Reviewed Journal
                                    Publication Acceptance Date: 2/14/2011
                                    Publication  Date: 3/24/2011
                                    Citation: Sainju, U.M., Lenssen, A.W. 2011. Dryland Soil Carbon Dynamics under Alfalfa and Durum-Forage Cropping Sequences. Soil and Tillage Research. 113:30-37.Interpretive Summary: In dryland cropping systems, crop-fallow has been the conventional cropping systems for the last several decades. The alternate-year fallow system conserves soil water which is the main factor for crop production in dryland cropping systems because of limited precipitation. The system has not only decreased crop yields and became uneconomical by the absence of crops during fallow  but also reduced soil quality and productivity due to loss of soil organic matter from increased soil erosion. One of the options to reduce the fallow period and increase water-use efficiency, crop yields, and net return is continuous cropping, such as cereal-annual forage sequences. Inclusion of annual forages in rotation with cereals maintains both cereal and forage yields because forages are harvested earlier for hay than cereals, which results in sustained soil water content and succeeding crop yields. Little is known about the effect of cereal-forage sequences on soil C dynamics under dryland cropping systems.

We evaluated the effect of alfalfa and durum-annual forage cropping sequences on above- (stems + leaves) and belowground (roots) biomass C inputs and dryland soil organic C (SOC), inorganic C (SIC), particulate organic C (POC), microbial biomass C (MBC), and potential C mineralization (PCM) at the 0- to 120-cm depth. Cropping sequences were continuous alfalfa (CA), durum-barley hay (D-B), durum-foxtail millet hay (D-M), durum-Austrian winter pea/barley mixture hay (D-P/B), and durum-fallow (D-F) from 2002 to 2005 in eastern Montana.
  
Except in 2003, aboveground biomass yield and C content were lower in CA than in other treatments from 2002 to 2005. Similarly, belowground biomass yield and C content were lower in D-F than in other treatments from 2003 to 2005. In 2005, soil surface residue amount and C content were greater in D-F than in other treatments. The SOC at 0- to 15-cm was greater in CA than in D-B and D-M but at 30- to 60-cm was greater in D-B than in CA. The SIC at 0- to 90-cm was greater in D-F or D-M than in other treatments. The POC at 0- to 15-cm was greater in CA than in other treatments but varied with treatments at other depths. The PCM at 0- to 120-cm was greater in CA than in D-F. The MBC at 30- to 120-cm was greater in CA or D-P/B than in D-B.
 
Although aboveground biomass C input was lower, greater belowground biomass C probably increased soil C storage and microbial biomass and activities under perennial forages, such as alfalfa, than under annual durum-forage sequences. Greater aboveground biomass C input, however, increased C storage in surface residue and soil in D-F than in D-P/B.
                                Technical Abstract: Forages grown in rotation with or without cereals to sustain dryland soil water content and crop production may influence C dynamics. We evaluated the effect of alfalfa (Medicago sativa L.) and durum (Triticum turgidum L.)-annual forage cropping sequences on above- (stems + leaves) and belowground (roots) biomass C inputs and dryland soil organic C (SOC), inorganic C (SIC), particulate organic C (POC), microbial biomass C (MBC), and potential C mineralization (PCM) at the 0- to 120-cm depth. Cropping sequences were continuous alfalfa (CA), durum-barley (Hordeum vulgare L.) hay (D-B), durum-foxtail millet (Setaria italica L.) hay (D-M), durum-Austrian winter pea (Pisum sativum L.)/barley mixture hay (D-P/B), and durum-fallow (D-F). The experiment was conducted in a Williams loam (fine-loamy, mixed, superactive, Typic Argiustoll) from 2002 to 2005 in eastern Montana. Except in 2003, aboveground biomass yield and C content were lower in CA than in other treatments from 2002 to 2005. Similarly, belowground biomass yield and C content were lower in D-F than in other treatments from 2003 to 2005. In 2005, soil surface residue amount and C content were greater in D-F than in other treatments. The SOC at 0- to 15-cm was greater in CA than in D-B and D-M but at 30- to 60-cm was greater in D-B than in CA. The SIC at 0- to 90-cm was greater in D-F or D-M than in other treatments. The POC at 0- to 15-cm was greater in CA than in other treatments but varied with treatments at other depths. The PCM at 0- to 120-cm was greater in CA than in D-F. The MBC at 30- to 120-cm was greater in CA or D-P/B than in D-B. Although aboveground biomass C input was lower, greater belowground biomass C probably increased soil C storage and microbial biomass and activities under perennial forages, such as alfalfa, than under annual durum-forage sequences. Greater aboveground biomass C input, however, increased C storage in surface residue and soil in D-F than in D-P/B.


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