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Title:   Author  item
                                            Acosta-Martinez, Veronicaitem
                                            KLOSE, S - UNIV OF CA - DAVIS, CAitem
                                            Zobeck, Teddy
  Submitted to: Journal of Soil Biology and Biochemistry
                                    Publication Type: Peer Reviewed Journal
                                    Publication Acceptance Date: 9/11/2003
                                    Publication  Date: 12/1/2003
                                    Citation: Acosta Martinez, V., Klose, S., Zobeck, T.M. 2003. Enzyme activities in semiarid soils under conservation reserve program, native rangeland, and cropland. Journal of Soil Biology and Biochemistry. 166(6): 699-707.Interpretive Summary: It is important to continuously monitor the status of semiarid soils under different land uses such as native rangeland, conservation reserve program, and cropland in order to select practices that will maintain the quality of our soils.  The conservation reserve program, for example, is established to take land out of crop production in order to decrease soil erosion.  However, little information is available about the changes that occur to the soil properties when land is placed in the conservation reserve program.  We also need to investigate the best management for the soils when the land is brought back under cultivation.  Soil properties such as the levels of enzyme (produced by microbes) activities can provide an indication of the changes in soil due to land use and management.  We found that the enzyme activities were generally higher in native rangeland and the conservation reserve program, in comparison to cropland under continuous cotton and conventional tillage.  However, cropland under wheat-cotton rotation and no-tillage showed similar enzyme activities to either native rangeland or conservation reserve program, depending on the enzyme studied.  Wheat-cotton rotation and no-tillage also had generally higher enzyme activities than continuous cotton under conventional tillage.  These trends indicate that microbes and the production of enzymes can be increased, and thus organic matter may increase, under more conservative land uses (i.e., conservation reserve program) and management practices (i.e., crop rotations with reduced or no-tillage).
                                Technical Abstract: Knowledge of biochemical processes in low carbon content soils of the semiarid regions in West Texas, USA, in response to different land management is limited.  The activities of seven soil enzymes involved in C, N, P, or S cycling were compared in the Olton loam (Fine, mixed, thermic, superactive, Aridic Paleustolls) under the conservation reserve program (CRP), native rangeland (NR), sunflowers (Eriophyllum ambiguum (Gray)), continuous cotton (Gossypium hirsutum L.), or wheat (Triticum aestivum L.)-cotton rotation.  Soil samples (0-5, 5-10 and 10-15, and 15-30 cm) were taken in January 2001 and analyzed for organic C, total N, pH, and the activities of ¿-glucosidase, ¿-glucosaminidase, arylamidase, acid phosphatase, alkaline phosphatase, phosphodiesterase, and arylsulfatase.  The soil pH (7.1-8.4), organic C (6.60-13.10 g kg-1 soil) and total N (0.55-1.03 g kg-1 soil) varied among the management systems.  Linear regression analyses indicated the enzyme activities were positively correlated with organic C (r values up to 0.96, P<0.01).  There was a trend of positive correlation between the enzyme activities with total N, but soil pH showed the opposite trend.  ¿-glucosidase and arylamidase activities showed a more pronounced decrease with increasing depth than the other enzyme activities.  Enzyme activities were significantly intercorrelated with r values up to 0.98 (P<0.001).  Generally, the soil enzyme activities were significantly (P<0.05) lower under continuous cotton in comparison to the other systems.  Alkaline phosphatase showed the higher enzyme activity in the systems and it was highest in NR and CRP with values of 251 and 238 mg p-nitrophenol (PN) kg-1 soil h-1, respectively.  The enzyme activities were lower than corresponding values reported for soils from other regions.  The values of the specific activities (mg product g-1 organic C) were also significantly (P<0.05) lower in continuous cotton in comparison to the uncultivated soils (i.e., NR and CRP).  This study found there was an increase in the soil biochemical reactions studied under CRP or wheat-cotton rotations compared to the common agricultural practice in these regions, i.e., continuous cotton under conventional tillage.


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