Submitted to: Biology and Fertility of Soils
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/15/2003
Publication Date: 7/16/2003
Citation: Acosta Martinez, V., Zobeck, T.M., Gill, T.E., Kennedy, A.C. 2003. Enzyme activities and microbial community structure in semiarid agricultural soils. Biology and Fertility of Soils. 38:216-227. Interpretive Summary: Microbes (i.e., fungi and bacteria) are needed to maintain the quality of semiarid soils and crop production. Enzyme (produced by microbes) activities were increased in the soil when cotton was rotated with sorghum or wheat under reduced or no-tillage in comparison to continuous cotton under tillage. Soil bacteria and fungi did not change, according to one analysis conducted, due to crop rotation under reduced or no-tillage in comparison to continuous cotton under tillage. The increases in enzyme activities, however, are indicating that microbes and their enzymes will be increased, and thus nutrients will be more available to plants, more organic matter will be formed, and other soil properties will also positively change if crop rotations with reduced or no-tillage are applied to semiarid soils in comparison to the typical current practice of continuous cotton with tillage.
Technical Abstract: The effect of management on the enzyme activities and microbial community structure of semiarid soils from West Texas was investigated. Surface samples (0-5 cm) were taken from a fine sandy loam, sandy clay loam, and loam that were under continuous cotton (Gossypium hirsutum L.) or in cotton rotated with peanut (Arachis hypogaea L.), sorghum (Sorghum bicolor L.), or wheat (Triticum aestivum L.), and had different water management (irrigated or dryland) and tillage (conservation: reduced or no-tillage, or conventional). The activities of the following enzymes were investigated: beta-glucosidase, beta-glucosaminidase, alkaline phosphatase, and arylsulfatase. In the sandy clay loam, except for beta-glucosidase, the enzyme activities were significantly (P<0.05) increased under crop rotations in comparison to continuous cotton. In the loam, the enzyme activities were significantly (P<0.05) increased under crop rotations in comparison to continuous cotton when conservation tillage was used. In the fine sandy loam, the enzyme activities were not always significantly (P<0.05) different under crop rotation in comparison to continuous cotton. No significant differences were detected in fatty acid methyl esters (FAME) profiles due to management within the same soil. High variability in the FAME profiles of the fine sandy loam compared to the loam was explained by PC1 (20% of the variance), while the variability between the sandy clay loam and loam was explained by PC2 (13% of the variability). The levels of a15:0 (bacteria indicator) ranged from 1.61±0.25% in cotton-peanut/irrigated/no-till (fine sandy loam) to 3.86±0.48% in cotton-sorghum/dryland/con-servation tillage (sandy clay loam) and 18:3w6c (fungi indicator) ranged from non-detectable in most samples of the sandy clay loam to 4.03±0.21% in sorghum-cotton/irrigated/conventional tillage (loam). Results from enzyme activities are early indications of the changes that will be observed in the microbial populations and activities and organic matter by using crop rotations and conservation tillage for semiarid soils instead of the typical practice of continuous cotton with conventional tillage.