Production and soil effects of sorghum biofuel cropping systems in semiarid marginal regions

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Title: Production and soil effects of sorghum biofuel cropping systems in semiarid marginal regions
Author: Cotton, Jon
Abstract: In order to meet the growing demands for food , fiber , and biofuels , land management decisions will require identification of lands most suitable for each crop . Biofuel production that occurs on lands otherwise constrained for other intensive agricultural production by soil or water limitations (i .e . , marginal lands ) may not only meet some of these demands but , if managed properly , may also help improve soil function . For large -scale application to be sustainable , identification of crop type most efficient for feedstock production as well as impacts on soil and water resources are necessary . In this study , forage sorghum (Sorghum bicolor L . Moench ) cropping systems were initiated in the semiarid Southern High Plains (SHP ) of the U .S . to evaluate potential biofuel production and potential benefits on soils that are depleted of organic matter ( < 0 .7 % ) due to previous cropping history . Systems consisted of two sorghum cultivars (Sorghum Partners 1990 = SP 1990 and PaceSetter bmr = PS bmr ) differing in lignin content due to brown midrib trait (bmr -12 ) that were tested under two different water levels (non -irrigated or deficit irrigation of 2 .88 mm day -1 ) , and biomass removal rate treatments of 50 % and 100 % . Forage sorghum SP1990 (non bmr ) produced significantly higher weight and volumes of biomass than PS bmr under both deficit irrigation and no irrigation in the two years of study . However , PS bmr biomass was converted into ethanol (EtOH ) 54 % more efficiently during both years . When below average precipitation occurred during the first year of the study , both cultivars produced similar amounts of EtOH at each irrigation level (1 ,600 to 3 ,380 L ha -1 ) . When higher than average precipitation occurred during the second year , higher biomass production of SP 1990 resulted in more EtOH production than PS bmr (3 ,380 vs . 2 ,640 L ha -1 ) . Irrigation resulted in 26 -49 % more biomass and 28 -72 % more EtOH production during both growing seasons , indicating that non -irrigated production resulted in deficit water conditions regardless of precipitation . Overall EtOH production ranged from 1 ,600 to 3 ,380 L ha -1 during both years of the study . Changes in soil microbial properties (0 -10 cm ) , known to be sensitive econsensors , were measured during the two year transition from previous long -term cotton cropping systems to the sorghum biofuel cropping systems . Increases in microbial biomass C (MBC ) and N (MBN ) (16 -17 % ) and differences in fatty acid methyl ester (FAME ) profiles were observed after one growing season . Additionally , soil enzyme activities (EAs ) targeting C , N , P , and S increased 15 -75 % after two growing seasons . Increases in EAs 16 -19 % ) and differences in FAME profiles were seen due to the irrigation treatment , which may be due to the increase in belowground biomass production even under deficit irrigation . When biomass was not fully removed (50 % removal treatment ) , increases in MBC and MBN (11 -15 % ) , b -glucosidase (C cycling ) and alkaline phosphatase (P cycling ) (12 -22 % ) occurred , which is likely attributed to the protection of the soil surface from aeolian erosion provided by the surface residue . The cultivars tested , which produced biomass with different chemical composition , had little effect on the soil microbial properties measured during the time frame of this study . This study indicates that chemical modifications and biomass yield potential are critical factors when selecting sorghum characteristics for use as biofuel feedstocks under marginal water -deficit conditions . These cropping systems also have the potential to improve sandy , low organic matter soils in this semiarid region , as was shown by increases in microbial biomass and soil functionality indicated by EAs after only two growing seasons . Early results from this study suggest sorghum biofuel cropping systems can be a sustainable practice for marginal lands in the SHP ; however , tracking of long -term changes are necessary to fully evaluate effects . It is hypothesized that soil properties will continue to improve , especially in the lower biomass removal level as more above -ground biomass will be incorporated and decomposed . It is unclear how the chemical composition of biomass from different sorghum cultivars will impact soil properties but differences in organic matter accumulation and enhanced biochemical cycling are possible . Finally , additional research on incorporating biofuel production into traditional cotton production , along with the evaluation of novel sorghum cultivars specifically bred for use as feedstock , are important focuses for the application of biofuel production in the semiarid SHP .
URI: http : / /hdl .handle .net /2346 /45219
Date: 2012-05

Citation

Production and soil effects of sorghum biofuel cropping systems in semiarid marginal regions. Master's thesis, Texas Tech University. Available electronically from http : / /hdl .handle .net /2346 /45219 .

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