Influence of perennial grasses usage duration on fertility of irtysk oma meadow-black earth soil

Abstract

Studies were carried out in order to establish the in uence of legume- cereal grass mixtures on the fertility indicators of irrigated meadow- chernozem soil, depending on the duration of their cultivation in grain- grass crop rotation. Two factors were studied in the experiment: A - grass mixture: 1) awnless brome + alfalfa 6 years old, 2) awnless brome + eastern goat’s rue + eastern goat’s rue 12 years old, 3) awnless brome + eastern goat’s rue 21 years old; B - mineral fertilizers: 1) without fertilizers. Nitrogen fertilizers were applied for each of the two mowings, and phosphorus fertilizers were applied as reserves. The dependence of the amount of agronomically valuable aggregates and their resistance to water erosion action on the age of legume-bluegrass grass mixtures was revealed. With an increase in the age of herbs, the number of these aggregates in the soil layer 0…20 cm increased from 48 % under the grass mixture of 6 years of life to 69 % under the grass mixture of 12 years, reaching 79 % under the grass mixture of 21 years of life. When introducing nitrogen-phosphorus fertilizers, a decrease in fractions of agronomically valuable aggregates under the grass stand of 12 and 21 years of life was established by 7…9 % in relation to options without fertilizers. With the increase in the age of grass stand, the content of humus and humic acids in its composition, exchange cations and the reaction of the medium did not change significantly, to a greater extent the changes are associated with the influence of mineral fertilizers. The amount of humus under the herbs in the soil layer 0…20 cm was high and reached 6.7…7.1 % in fertilized versions and 7.5…7.8 % in versions without fertilizers. In the composition of humus, the share of humic acid carbon accounted for from 1.9…2.4 to 2.6…2.7 %, respectively, options. The reaction of the medium in the test variants varied from 5.8 to 6.8 units of pH the aqueous suspension. In the composition of exchangeable cations, calcium accounted for 70 to 87 %. In the experimental variants without fertilizers, the content of mobile phosphorus (according to Chirikov) in the soil was 55…90 mg/ kg; when applying fertilizers, its amount increased by 68…95 mg/kg in a layer of 0…20 cm and by 40 …70 mg/kg in a layer of 20…40 cm. Indicators of the chemical and physicochemical properties of the soil reached optimal parameters after 6 years of cultivating the legume-poa grass mixture, so further use (12 and 21 years) of the soil under grass is not practical.