Improvement of Recommendations for Potash Fertilizer Use and Adjustment of Currently Used Soil Potassium Test Interpretation Classes in Intensive Cropping Systems

This three-year project has a special focus on optimization of K fertilizer application rates for crops with high response to K, such as sugar beet, maize, rapeseed, and soybean. The project goals are to : 1) determine optimal potash fertilizer rates for these major crops in rotation, 2) evaluate the validity of currently used soil test K interpretation classes for proper assessment of plant K requirements, 3) develop proposals to the Russian Ministry of Agriculture on possible fine-tuning of current K fertilizer recommendations. The project includes short-term field experiments conducted on farms located in central Russia (Lipetskaya, Voronezhskaya, Belgorodskaya oblast) and southern Russia (Rostovskaya oblast). The trials were established on Chernozem soils with medium and “increased” (higher than medium) content of routinely extracted soil K.

In 2014-15, all trials located in central Russia showed significant yield response to K. Due to K fertilization, yield of sugar beet tubers increased by 10 to 14% in Voronezhskaya, 9 to 12% in Lepetskaya, and 6% in Belgorodskaya oblasts, regardless of the initially high concentrations of plant-available soil K. Sugar yield increased from 8.1 to 9.2 t/ha in Voronezhskaya, 8.3 to 10 t/ha in Lepetskaya, and 6.8 to 7.7 t/ha in Belgorodskaya oblasts. In Voronezhskaya oblast, maize yield increase due to K fertilization was 41 to 49%. The optimal rate of K (180 kg K₂O/ha) resulted in 2.5 t/ha of additional maize grain or 14 kg grain/kg of K₂O applied. In Lepetskaya oblast, rapeseed yield increase due to K fertilization was 14 to 24%. The best rate of K (90 kg K₂O/ha) resulted in 0.16 t/ha of additional seed yield or 2.5 kg/kg of K₂O applied. In Belgorodskaya oblast, soybean yield increase due to K fertilization was 8%. The best rate of K (60 kg K₂O/ha) resulted in 0.18 t/ha of additional yield or 3 kg/kg of K₂O applied.

A significant residual effect of K applications during previous seasons resulted in a substantial yield increase in crops that followed in rotation. In central Russia, the yield increase was 15 to 23% for maize, 8 to 27% for spring wheat, and 9 to 11% for soybean. Potassium fertilization also improved crop quality and profitability.