Effects of cropping systems on soil physicochemical properties and abundances and spatial distributions of nitrogen-cycling bacteria

Authors: NETTHISINGHE, ANNESLY - Western Kentucky University; GALLOWAY, HUNTER - Western Kentucky University; Agga, Getahun; GUNTER, PHILLIP - Western Kentucky University; Sistani, Karamat

Submitted to: Agronomy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/23/2023
Publication Date: 5/25/2023
Citation: Netthisinghe, A., Galloway, H., Agga, G.E., Gunter, P., Sistani, K.R. 2023. Effects of cropping systems on soil physicochemical properties and abundances and spatial distributions of nitrogen-cycling bacteria. Agronomy. 13(6). Article 1461. https://doi.org/10.3390/agronomy13061461.
DOI: https://doi.org/10.3390/agronomy13061461

Interpretive Summary: Soil nitrogen is essential for plant growth. Nitrogen cycling is a natural process that is mediated through soil bacteria. Over a two year period, field studies were conducted to examine the impact of three cropping systems, namely wheat and soybean with and without grazing for two to three weeks, and tall fescue pasture grazed similarly, on soil properties and bacteria responsible for nitrogen cycling. The tall fescue pasture resulted in higher concentrations of bacteria involved in the nitrogen cycle than the wheat and soybean cropping systems, with no effect of grazing. The organic content and the pH of the soil were the two major factors identified that greatly influenced the abundances of nitrogen cycling bacteria. Soil pH and nitrogen cycling bacteria showed a unique gradient across the experimental field which can be further explored to identify local management practices to increase soil fertility. Although more studies are required, the results indicated that bacterial nitrogen transformation processes are very important in natural agricultural systems which can be modified by local management practices.

Technical Abstract: Soil Nitrogen (N) is a common limiting factor where soil N cycling is a key component of agro-ecosystems. Soil N transformation processes are largely mediated by microbes and understanding bacteria involvement in soil N cycling in agricultural systems has both agronomic and environmental importance. This 2-yr field scale study examined abundance and spatial distribution of total bacteria community (16s RNA), bacteria functional genes involved in nitrification (amoA), and de-nitrification (narG, nirK, and nosZ) and soil physicochemical properties of wheat-soybean double cropping with 2-3 weeks of spring grazing (WGS) and without grazing (WS) and of tall fescue pasture (TF) managed to near natural conditions with similar grazing. The TF harbored significantly higher densities of 16S rRNA, amoA, narG, nirK, and nosZ genes than the WS and WGS, but were similar between them. Soil organic matter (OM) and soil pH posed major control on the N cycling bacteria gene densities. All bacteria genes and soil pH exhibited non-random distribution patterns with 141-186 m range autocorrelation. Although the generality of the results should be tested in similar other environments, these results indicated that biological N transformation processes are more important in natural agricultural systems and can be manipulated by field scale management strategies.