Reduction of the Content of Total Nitrogen in the Soil in the Permanent Sowing of Cotton

Abstract

This article presents analytical scientific data on the change in the content of total nitrogen over 96 years in some variants of the experiment with cotton monoculture, conducted since 1926 for 96 years at the Research Institute of Breeding, Seed Production and Agricultural Technology of Cotton Cultivation, located in the Kibrai district of the Tashkent region. In the 20th year of the study, the nitrogen content in the 1st variant was 0.129%, which, in terms of hectare, it decreased by 0.15 t/ha, in the 2nd variant with the application of mineral fertilizers NPK-250:175:125 kg/ha its content was 0.092% or 0.75 t/ha per hectare; in the 3rd control variant, these figures were 0.087% and 0.96 t/ha, respectively. This process was also observed during subsequent years, after 40 years these indicators in variants 1, 2 and 3 respectively decreased by 0.18, 1.09 and 1.71 t/ha, after 60 years, respectively, by 0.93, 1.39 and 2.12 t/ha, after 80 years by 1.56, 1.99 and 2.46 t/ha and after 96 years by 1.82, 1.35 and 2.40 t/ha. In the 1st option, with an annual application of 30 t/ha of manure + 25 kg/ha Р2О5 in the 40th year of the study, the nitrogen content in the soil decreased much more slowly, but in subsequent years a sharp decrease was observed and over 96 years it decreased by 1.82 t/ha compared to the initial value. In the 2nd variant, with the annual application of mineral fertilizers at the rate of NPK-250:175:125 kg/ha, the nitrogen content in the soil over 96 years decreased by 32.7% or 1.35 t/ha compared to the initial content, and on the control in the variant without fertilization, the decrease in nitrogen over 96 years was 56.6% or 1.82 t/ha.