Influence of mineral fertilizers on fertility of sod-podzolic soils in fodder crop rotations

In the period 2001...2012 in the experimental field of Mari Agricultural Research Institute the productivity of three fodder crop rotations, galega-bromopsis herbage was evaluated and their effect on soil fertility was determined. The main difference between rotations was in a different saturation with perennial legumes and grasses (I rotation -16,6%, II - 33,0, III - 50,0%) at the application of recommended for the central zone of the Republic of Mari El (N6oP6oK60) and increased (N90P90K90) doses of mineral fertilizers. The results showed that the fertilizer application in crop rotation for 12 years contributed to the increase in the percentage of humus content in soil by 0.4-0.6 %. Оп noncrop rotation area it is observed the largest increase in content of humus in soil; this area was constantly cultivated with herbage of galega-bromopsis grass mixture in the background of recommended and high doses of PK fertilizers. The same increase was in rotations I and III on the background of high doses of NPK. The relationship between the saturation of crop rotations with perennial grasses and a mass fraction of humus in soil were not detected. The acidity of the topsoil in two of the rotation fof odder crop rotation tended to increase by 0.1...0.3 units of pH, significant differences between variants were not detected. The content of phosphorus mobile forms in soil increased by 40-170 mg/kg (5.9 20.2 %) in two rotations and sowing of galega with bromopsis over the study years. A slight downward trend is marked in the potassium content in the soil up to 15 mg/kg (8 %). Increasing the proportion of legumes-cereal grasses to monoculture in the structure of the rotation from 16.6 to 50 % of feed units per unit area on average within 12 years increased to 3.6 %. Input of higher doses of mineral fertilizers over the recommended one leads to increase in productivity by 200.445 fodder units per ha (4.7.11.2%); less addition was obtained at existence of two or three fields of perennial grasses in crop rotation. Use of highest doses of PK-fertilizers in perennial sowing of galega-bromopsis grass mixture allowed highest addition of productivity - 613 fodder units per ha (14.1%).