Microbiological and ecophysiological parameters of Sod-podzolic soil upon long-term application of straw and mineral fertilizers, the correlation with the yield

Abstract

In modern agriculture, top priority is given to requirements for environmentally friendly application of fertilizers, providing for the intensification of use of biological sources of soil fertility recovery, primarily bioresources of farming ecosystems. One of significant, easily renewable biological resources is field residues of agricultural crops, which, according to many researchers, are the key to sustainable crop production and biosphere preservation. In this regard, one of main requirements for biologically based resource-saving methods and agrotechnologies is the returning of afterharvesting residues back into the soil without alienating the ones from the field, which ensures the enhancement of organic carbon input, improvement of biological status of soils, and their fertility and productivity, in general. A number of domestic and foreign papers prove the plant residues (PR), the structure of which consists of over 80 % of straw of cereals and leguminous crops, to be important for the preservation of favorable microbiological state of the soil. However, there is uncertainty in the qualitative and quantitative evaluations of the effect of the straw on the soil microbial community since the PR burial that may have both positive and negative consequences, which is often noted when introducing straw with a wide C to N ratio. Experimental data available in the scientific literature were obtained mainly when conducting research in laboratory and short-term field experiments with single use of straw as a fertilizer. The data of long field experiments with the repeated introduction of straw in crop rotation are useful for a more complete understanding of the straw effect on the microbial community and the use of this knowledge for the development of effective methods for managing the plant residues. The purpose of this study was to assess the effect of long-term use of straw of cereals and leguminous crops and mineral fertilizers (MF), separately and in combination, on the biological status of sod-podzolic sandy-loam soil. The indicators characterizing the composition, structure and metabolic activity of the microbial community of sod-podzolic soil were determined at the end of the 4th rotation of the 5-course row-crop rotation in a long field experiment: microbial biomass (Cmic.), microbial number and ratio of ecotrophic groups of microorganisms (ETGM), basal respiration (BR), and ecophysiological coefficients. It has been established that the return of afterharvesting residues in combination with medium doses of MF provides a balanced supply of nutrients and organic carbon to the microbial community and contributes to the reduction of mineralization processes and to the accumulation of Cmic. The microbial biomass closely correlated with the content of total (r = 0.94, p < 0.05) and easily decomposable carbon (r = 0.89, p < 0.05) and nitrogen (r = 0.95, p < 0.05) in the soil, and the yield of annual grasses closely correlated with the most part of indicators being determined in the experiment.