MOLECULAR ASSESSMENT OF SOIL NITROGEN CYCLE UNDER ORGANIC AMENDMENTS IN COTTON BROAD-ACREAGE PRODUCTION

<p><span>Background: The cotton production belt in Australia covers vast areas from subtropical to temperate and grassland. Soil types are mostly different variations of clay, with mainly black, grey, and red clay soil containing variable proportions of sand. Growers often grow cotton in rotation with other crops, such as wheat, beans, and corn, and soil fertilization varies with a number of growers using organic amendments such as manure or compost before planting as a supplementary source of nutrients. Aim: The objective of this study is to understand the influence of various crop production management strategies on soil microbial communities and soil microbial function. Thus, it assists in improving the soil quality and sustaining crop production with high yields at a lower cost. Methods: To achieve the aim of this study, had been used qPCR to estimate the abundance of functional genes involving nitrogen-cycle (nifH, ureC, nirS, nirK, nosZ as well as bacterial and archaeal amoA) genes in the soil. Results: It showed increased soil organic carbon compared to solely commercially fertilized soil. However, there were differences in the effects of compost and manure on soil organic carbon and nitrogen-cycling microbial communities. Compost-increased organic carbon pre-planting correlated with an increase in the nifH gene, whereas manure-amended soils sustained nifH abundance in the soil post-planting during seedling growth when nifH abundance decreased elsewhere. In contrast, the greatest abundance of ureolytic microbes carrying the ureC gene was found in inorganic urea-fertilized soil. Denitrification genes nirS, nirK, and nosZ were also more abundant in cotton soils receiving organic amendments. Bacterial and archaeal nitrifiers responded differently to compost and manure, with bacterial amoA abundance greater with manure supplementation and archaeal amoA greater with compost supplementation. Discussion: Organic amendment using mulch or manure as a supplement to commercial fertilization enhanced cotton soil prospects for microbial functions necessary for N input and output into the biosphere, particularly N fixation and denitrification. Conclusions: We concluded that greater soil organic carbon supported an increased potential for microbial functions essential for the input and output of nitrogen into the biosphere, namely nitrogen fixation and denitrification.</span></p>