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

The project has the following goals: a) determine optimal potash fertilizer rates for major crops in crop rotation that have a high demand for potassium, b) evaluate the validity of currently used soil test potassium interpretation classes for proper assessment of plant potassium requirements, c) develop proposals to the Ministry of Agriculture on possible fine-tuning of current practice to develop K fertilizers recommendations and adjustment of currently used soil test potassium interpretation classes. Locations of field experiments - Lipetsk, Voronezh, Belgorod, and Rostov Oblasts (Russia). Soil types - Chernozem soils with medium and “increased” (higher than medium) content of routinely extracted potassium. Crops - sugar beet, grain maize, rapeseed, soybean.


14 May 2018

2017 Annual Interpretive Summary

This 5-year project located in Lipetsk, Voronezh, Belgorod, and Rostov oblasts has a special focus on the efficiency of the direct and residual effects of potassium chloride (KCl) for three consecutive crops in rotation. The project includes short-term field experiments conducted on large industrial farms located in Central Russia (Lipetskaya, Voronezhskaya, Belgorodskaya oblast) and South of Russia (Rostovskaya oblast) on Chernozem soils.

The single application of KCl was applied to the first crop in rotation (sugar beet, grain maize, rapeseed, or soybean). For the next two crops in rotation, the residual effect of KCl has been monitored and studied. The effect of four KCl rates (from 30 to 280 kg K2O/ha) was studied on the background of optimal nitrogen (N) and phosphorus (P) rates and absolute control (without fertilizers).

The project aims were to: (1) determine optimal application rates of KCl based on crop response to K application, crop quality, K balance, and economic parameters; and (2) assess the suitability of the existing soil K testing methods with a view to predict soil K supply. In soil samples collected at the beginning of the experiment (2012) and over the next five seasons (2013-2017), exchangeable (in 1 M NH4OAc), mobile (in 0.5 N HAc or in 1% (NH4)2CO3), and easily exchangeable (in 0.01 M CaCl2) K forms were determined.
Summarized results for 2012 to 2017 showed that on chernozems K supply depends on the exchangeable K pool. In the Central Russia region (Lipetsk, Voronezh, Belgorod) for sugar beet and grain maize grown on chernozems, exchangeable K (in 1 M NH4OAc) in the soil test is the most sensitive to predict crop response to application of K fertilizers.

Results for 2012 to 2017 also showed that on chernozems with increased and medium soil K levels, maximum yield increase due to K was for sugar beet (7.5 to 9.2 t/ha), followed by grain maize (1.3 t/ha), spring rapeseed (0.2 t/ha), and soybean (0.1 t/ha). The average contribution of K to the yield increase was maximum for grain maize (18%), followed by sugar beet (14 to 15%), spring rape (13%) and soybean (6%). After one year of K fertilizer application for the first crop in rotation, residual K resulted in substantial yield increase for the subsequent second crop in rotation – cereals, grain maize, and soybean. Moreover, residual K improved crop quality and profitability of crop production. However, after the second year after K fertilizer application, residual effect on yield and quality of the third subsequent crop in rotation was not significant.