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

This 3-year project has a special focus on optimization of fertilizer K rates for crops with high response to K, such as sugar beet, grain maize, rape, and soybean. The objectives of this project are to determine optimal potash fertilizer rates for major crops in crop rotation that have a high K demand, evaluate the validity of currently used soil test K interpretation classes for proper assessment of plant K requirements, and develop proposals for the Russian Ministry of Agriculture on possible fine-tuning of the current practice of fertilizer K 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) and established on Chernozem soils with medium and “increased” (higher than medium) content of routinely extracted K. Total number of field trials is 48, including 24 studying the residual effect of K application.

Potassium fertilization increased the yield of sugar beet roots and grain maize substantially, regardless of the initial content of plant-available K in the Chernozem soil. In Voronezhskaya oblast, the maximum yield of sugar beet roots was 80 t/ha with a fertilizer K rate of 140 kg/ha. This demonstrated a 21% increase in yield due to K fertilization. In Lipetzkaya oblast, the maximum yield of sugar beet roots was 70 t/ha with a fertilizer K rate of 280 kg/ha, demonstrating a 22% increase in yield due to K fertilization. The maximum yield of sugar beet roots achieved in the trials in Central Russia was almost 2 to 3 times higher than the average regional yield (32 t/ha) in Central Russia (between 2006 to 2010). In Rostovskaya oblast, the maximum yield of sugar beet roots was 59 t/ha with an application rate of 70 kg K/ha, a 4% increase in yield over NP treatment. In all trails with sugar beet, the sugar content in roots was also increased due to potash fertilization, which resulted in substantial increases in sugar yield (25, 28 and 3% in Voronezhskaya, Lipetzskaya and Rostovskaya oblast, respectively) compared with the NP treatment). For maize, the maximum grain yield was 11.2 t/ha, achieved with a fertilizer K rate of 140 kg/ha in Voronezhskaya oblast and 9.4 t/ha with a fertilizer K rate of 280 kg/ha in Belgorodskaya oblast. This represented respective yield increases of 15 and 24% due to potash application as compared with the NP treatments. The high grain yield achieved for maize in this experiment was substantially higher than the average regional yields (4.2 and 6.1 t/ha in Voronezhskaya and Belgorodskaya oblast, respectively (between 2006 and 2010). Similarly, K application increased rapeseed yield up to 2.6 t/ha, which was 14% more than the yield obtained with NP treatment. Thus, for all crops from Central Russia, adequate K fertilization resulted in greater profitability from crop production.