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 optimizing K fertilizer application rates for crops with high response to K, such as sugar beet, grain maize, rapeseed, and soybean. The project goals are to: 1) determine optimal fertilizer rates for major crops in crop rotation, 2) evaluate the validity of current soil test K interpretation classes for assessment of plant K requirements, and 3) develop proposals to the Russian Ministry of Agriculture on possible fine-tuning of current practice to develop K fertilizers recommendations. The project includes short-term field experiments executed on large industrial farms located in Central Russia (Lipetskaya, Voronezhskaya, Belgorodskaya oblast) and South of Russia (Rostovskaya oblast) established on Chernozem soils with medium and “increased” (higher than medium) content of routinely extracted K.

In the season of 2013-14, K fertilization increased the yield of sugar beet tubers by 15 to 21% in Voronezhskaya and by 7 to 14% in Lepetskaya regardless of the high initial content of plant-available K. Sugar yield increased from 6.7 to 8.0 t/ha in Voronezhskaya and from 6.5 to 8.2 t/ha in Lepetskaya. In maize, K fertilization increased yield by 5 to 15% in Voronezhskaya. The optimal rate of K application was 120 kg K₂O/ha, which resulted in 0.5 t/ha of additional grain yield, or 4.0 kg grain/kg K₂O applied. For rapeseed, K fertilization increased yield by 6 to 28% in trials in Lepetskaya. The optimal rate of K was 60 kg K₂O/ha, which resulted in 0.15 t/ha of additional seed yield or 2.5 kg seed/kg K₂O applied. For soybean, K fertilization increased yield in Belgorodskaya by 6 to 7%. The best rate of K was 90 kg K₂O/ha, which resulted in 0.12 t/ha of additional soybean or 1.3 kg soybean/kg K₂O applied.

Significant residual effect of K application conducted in the previous season resulted in substantial yield increase of cereals – the next crop in crop rotation. In Central Russia, the yield increase from residual K application was 9 to 20%, 5 to 18%, and 8 to 33% for spring wheat, barley, and winter wheat, respectively. Potassium fertilization has substantially improved the profitability of crop production in Central Russia.