Effect of forecrop on yield of spring durum wheat and soil potassium in chernozems of southern steppe zone in Southern Urals during long-term research

The goal of the study was to determine the infl nce of forecrops on spring durum wheat productivity and content of soil potassium in monoculture, double-cropping and six-year crop rotation at two types of nutrient statuses. The information obtained as a result of long-term experiments is of great interest, since systematic determination of nutrient elements in soil gives a correct assessment of the effect of the longterm use of fertilizers on soil fertility. Content of available forms of potassium in soil under spring durum wheat depending on different forecrops and nutrient statuses was studied. The best forecrops for durum wheat in 31-year experiments were black, soil-protecting and green fallows. The yield of durum wheat after black fallow was 1.20 t/ha under fertilization and 1.27 t/ha without using fertilizers. Vegetative mass of cropped fallow ploughed into soil and use of mineral fertilizers led to an increase in content of soil potassium. The use of mineral fertilizers has a positive effect on yield of durum wheat; the yield increase was 0.10 t/ha after soil protecting fallow, 0.11 t/ha after common wheat and 0.13 t/ha after winter rye. Content of soil potassium was higher in six-year crop rotation and it increased durum wheat productivity compared to double-cropping and monoculture.