Submitted to: Applied Soil Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/26/2007
Publication Date: 8/23/2007
Citation: Acosta Martinez, V., Mikha, M.M., Vigil, M.F. 2007. Microbial communities and enzyme activities in soils under alternative crop rotations compared to wheat-fallow for the Central Great Plains. Applied Soil Ecology. 37:41-52. Interpretive Summary: How soil is managed in Central Great Plains Region (Tillage practices and cropping intensity) can have long-term effects on soil properties related to soil and environmental quality such as soil microbial populations and activities, soil nutrient dynamics, organic matter content. The objective of this study was to examine the effect of different cropping intensities and tillage in long-term cropping system on soil microbial populations and the activities of several soil enzymes. Result of this study indicated that the combination of no-tillage and continuous cropping intensity (100% cropping intensity) and reduced fallow frequency (67% cropping intensity) increases soil microbial biomass, bacteria and fungal populations, and enzyme activities compared with the typical system of the region, wheat-fallow under conventional tillage (50% cropping intensity).
Technical Abstract: Winter wheat-fallow (W-F) rotation is the predominant cropping system in the Central Great Plains. However, other cropping systems are being suggested because reduced tillage and fallow can provide more residues that can increase soil organic carbon (SOC) content and other parameters related to soil quality. This study compared properties related to soil quality and functioning such as microbial biomass and community composition and enzyme activities in research plots under different crop intensities (CI) established for 15 years in Akron, CO. The soil (Weld loam; fine, smectitic, mesic Aridic Paleustolls) was under alternative CI rotations (100 and 67%) of winter wheat (Triticum aestivum L.) (W), corn (Zea mays L.) (C), proso millet (Panicum miliaceum L.) (M), and fallow (F) under no-tillage (nt) compared to the typical 50% CI rotation (W-F) under either conventional tillage (ct) and nt. Relative to W-Fct, the 100 and 67% CI rotations increased soil microbial biomass C and N. Enzyme activities (0-5 and 5-15 cm) of C (beta-glucosaminidase, beta-glucosidase, and alpha-galactosidase) and P cycling (alkaline phosphatase, acid phosphatase and phosphodiesterase) as a group separated the 100 and 67% rotations (W-C-M, W-C-F) from W-Fct. Separation in these enzyme activities was observed for rotations sampled under a crop (W-C-F) compared to when sampled under fallow (F-W-C). Similarly, principal component analyses (PCA) of fatty acids methyl esters (FAME) suggested a shift in the microbial community structure with greater fungal populations in the 100 and 67% CI rotations compared to W-F. Significant correlations (r > 0.60; P<0.05) were found between the sum of fungal indicators (18:2'6c, 18:3'6c, 18:1'9c, 16:1'5c) and some of the enzyme activities (beta-glucosaminidase, beta-glucosidase, acid phosphatase and alpha-galactosidase). Our results show that the combination of no-tillage and continuous cropping with reduced fallow frequency have a positive effect on soil quality parameters such as the soil microbial populations and processes investigated.