Agrochemical and Biological State of Sod-Podzolic Soil after Continuous Joint and Separate Application of Straw and Mineral Fertilizers

In a long-term field experiment, the influence of long-term (from 1997–1998) joint and separate application of straw and mineral fertilizers (MF) on the indicators characterizing the biological and agrochemical state of sod-podzolic soil was studied. The study was carried out at the end of the 5th rotation of the 5-field grain crop rotation (winter wheat–annual lupine for grain–potatoes–barley–annual grasses (lupine + oats)) after harvesting annual grasses. To compare the arable soil of crop rotation with natural soil analogues, biological parameters in the soil of fallow and deposits were studied. It was found that the 25-year return of straw from grain and leguminous crops in combination with average doses of MF contributed most to the optimization of the biological state of the arable layer of the studied soil. The highest indicators of microbial carbon content (Cmicr), its share in total organic carbon (Cmicr : Corg), and the transformation coefficient (Kt) are noted, indicating the predominance of the accumulative orientation of the transformation processes of mobil organic matter (MOM), as well as the number of ecological and trophic groups of microorganisms (TGMO) involved in the carbon cycle and nitrogen, basal respiration (BR). On the contrary, such indicators, which can be used to assess the intensity of destructive processes, as the coefficients of oligotrophy (Kolig), oligonithophilicity (Kolign), and specific respiration (qCO2), were minimal. With the annual application of MF, the phosphorus and potassium content in the soil increased significantly compared to the initial one – by 108 and 29 mg/kg, respectively. With straw embedded in the arable layer in the amount of 45 t/ha, 515 kg/ha of potassium was returned to the soil over 5 rotations of crop rotation, which led to an increase in its content by another 24–25 mg/kg relative to the background.