Submitted to: Soil Science Society of America Journal
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/3/2010
Publication Date: 7/1/2010
Citation: Acosta Martinez, V., Burow, G.B., Zobeck, T.M., Allen, V. 2010. Soil microbial diversity, structure and functioning under alternative systems compared to continuous cotton. Soil Science Society of America Journal. 74(4):1181-1192. Interpretive Summary: Conventionally tilled monoculture cotton (Gossypium hirsutum) is the predominant cropping system in the Southern High Plains region, but this system can reduce soil organic matter content and microbial populations and can increase soil erosion potential. Scientists at ARS and Texas Tech University evaluated the properties of a representative soil under continuous cotton (Ct-Ct) compared to alternative systems: Conservation Reserve Program (CRP), pasture (Bothriochloa bladhii) (P) and a cotton-winter wheat-corn (Zea mays L.) (Ct-W-Cr) rotation. Soil microbial populations were improved under CRP, P and Ct-W-Cr compared to continuous cotton. Similar trends were found for soil total C and enzyme activities important in carbon and phosphorus nutrient cycling. Shifts in soil microbial community composition to higher fungal and bacterial populations under CRP and Ct-W-Cr compared to Ct-Ct were found. Differences in the bacterial diversity were also found among these systems. Most bacterial species identified in CRP and P soils were decomposers under the phylum Proteobacteria. This study demonstrated the benefits in microbial communities and metabolic potential of soil and thus, potential benefits in soil quality and functioning, by other cropping systems and land uses with reduced tillage, higher residue crops, and/or elimination of fallow periods compared to continuous cotton.
Technical Abstract: Continuous monoculture cotton (Gossypium hirsutum) under conventional tillage is the predominant cropping system in the Southern Plains region of USA. However, other cropping systems and land uses with reduced tillage, higher residue crops, and/or elimination of fallow periods are being evaluated in their potential to improve soil parameters related to soil quality and functioning. This study evaluated the microbial community structure, bacterial diversity and metabolic potential of soil (Pullman soil; Fine, mixed, thermic Torrertic Paleustolls; 38% clay and 34% sand) under continuous cotton (Ct-Ct) compared to alternative systems: Conservation Reserve Program (CRP), pasture (Bothriochloa bladhii) (P) and a cotton-winter wheat (Triticum aestivum L.)-corn (Zea mays L.) [Ct-W-Cr] rotation. Soil microbial biomass C (MBC) was significantly higher under alternative systems compared to Ct-Ct at 0-5 (CRP>P=Ct-W-Cr>Ct-Ct), 5-10 cm (CRP=Ct-W-Cr>P>Ct-Ct) and 10-20 cm (CRP=P=Ct-W-Cr>Ct-Ct). Significant correlations were found between DNA concentration and microbial biomass C (r=0.52, P<0.05) or microbial biomass N (r=0.53, P<0.05, n=24), which indicated that the DNA concentration is suitable to determine differences in microbial biomass between different management systems. Comparison of 16S rRNA gene banding pattern and sequences revealed higher number of bacteria species under tilled systems Ct-Ct and Ct-W-Cr compared to CRP and P soils. Similar number of fatty acids methyl esters (FAMEs) were detected among the systems, but indicators for fungi and bacteria populations were more abundant under CRP and Ct-W-Cr compared to Ct-Ct at 0-5, 5-10 and 10-20 cm soil depths. The mycorrhiza FAME indicator 16:1'5c was significantly higher in the alternative systems (CRP, P and Ct-W-Cr) compared to Ct-Ct at all soil depths. Several enzyme activities were similarly affected by the higher microbial biomass and modified microbial community structure of soils under CRP, P and Ct-W-Cr systems compared to Ct-Ct. This study demonstrated the potential increases in soil microbial populations and enzyme activities by rotating cotton with a high residue crop (i.e., corn) relative to continuous monoculture of cotton. In addition, results indicated that there was higher bacteria species diversity in soils under Ct-Ct and Ct-W-Cr, but in less abundance compared to the non-disturbed systems CRP and P.