INFLUENCE OF LONG-TERM USE OF FERTILIZERS ON THE DYNAMICS OF HUMUS IN THE ARABLE LAYER OF SODDY-PODZOLIC SOIL OF THE KOSTROMA REGION
The article represents the results of evaluating of fertilizer systems on the content and fractional composition of humus in the soddy-podzolic soil of the Kostroma region. Field research was conducted in 1992-2012 in the conditions of long-term, stationary field experience of the Kostroma State Agricultural Academy. Variants were studied in the field crop rotation: vetch-oat mixture for green mass - flax - barley + perennial grasses - perennial grasses 1st year - spring wheat - oat. Organic fertilizers were applied for vetch-oat mixture and spring wheat, and mineral fertilizers for all crops. Ammonium nitrate, double superphosphate, and potassium chloride were used as mineral fertilizers. The saturation of organic fertilizers was 12.8 and 6.4 t/ha per year for organic and organic-mineral fertilizer systems, respectively. Over a twenty-year period, the mineral fertilizer system caused a decrease in humus reserves by 0.46-0.69%, which means that soil lose 0.02-0.03% over the year. The use of organic fertilizers, especially in the last three rotations, tended to increase the humus. Over a twenty-year period, the use of litter manure on the first level led to an increase in the humus content by 1.32%. The humus content reached 2.83-2.85% by 2012, which significantly exceeded the control on plots of the second level with the use of manure. In humification processes, the use of organic matter was dominated by the formation of humic acids associated with calcium, in contrast to the control and mineral fertilizer system, where free fulvic acids were formed.