Winter Cover Crops Influence Bacterial Community Structure.

Crop management practices that incorporate winter cover crop treatments reportedly increase nitrogen use efficiency, decrease water contamination by nitrate leaching, and minimize soil erosion. Cover crops assimilate residual nutrients after cash crop harvest, especially N, reducing losses. The decomposition of cover crops, and microbial driven N assimilation/ mineralization, following spring termination, returns accessible nutrients to the soil, for subsequent crops. Information detailing bacterial community responses to cover crop and nitrogen fertilization management is lacking at a molecular level. This study investigated the bacterial community structure of surface soils (0-5 cm depth) under corn-soybean rotation in Illinois. Five treatments were evaluated: control, zero control, daikon radish cover crop, cereal rye cover crop, and a daikon radish/cereal rye mix cover crop. All treatments received a fall application of 200 N kg ha^-1, in the form of anhydrous ammonia, except for zero control. Next-generation sequencing (Miseq Illumina) of the 16S rRNA gene amplicon was used to detail the bacterial community structure of the soil samples. In ranking order, the predominant 4 phyla were Proteobacteria, Bacteroidetes, Acidobacteria, and Actinobacteria. The % relative abundance of Proteobacteria varied among treatments: cereal rye (39.5%), cereal rye/radish mix (37.7%), and each non-cereal rye amended treatment revealed a % relative abundance of < 35.5 %. Zero control soils contained 11.4% Bacteroidetes and 8.9% Acidobacteria. The averages of other fertilized and cover cropped soils disclosed slightly higher Bacteroidetes (17.4 %) and lower Acidobacteria (6.6 %). This study found significant differences in microbial community structure due to the influence of nitrogen fertilization and different cover crop species in this corn- soybean rotation system, which can have implications in soil fertility, nutritional value, and yield of each crop.