Changes in the content of humus in gray forest soils under long-term fertilization

The effect of different fertilizing systems on the content of humus in gray forest soils of the Opolie region has been studied during three cycles of eightand seven-course crop rotations. At the application of phosphorus–potassium fertilizers and without fertilization, the content of humus in the plow layer has decreased by 0.02% annually in the first rotation cycle and by 0.011% in the second and third cycles. In the first cycle, the addition of 1 t of litter manure and 1 kg of nitrogen increased the humus content by 55 and 9.8 kg, respectively; in the second and third cycles, the humus increment due to the organic and mineral fertilizers decreased by 2–3 times.