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.


22 May 2017

2016 Annual Interpretive Summary

This five 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 subsequent crops in rotation. The single application of KCl was only 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 was studied. The effect of four increasing KCl rates (from 30 to 280 kg K2O/ha) was studied on the background of optimal nitrogen and phosphorus (NP) rates and absolute control (without fertilizers). The project objectives were: 1) to determine the optimal application rates of KCl based on crop response to K application, crop quality, K balance, and economic parameters; and 2) to assess the suitability of the existing routine soil K test methods for predicting the soil K supply for crops.

In the soil samples collected at the beginning of the experiment (2012) and the next four seasons (2013 to 2016), exchangeable (1 M NH4OAc), mobile (0.5 N HAc or in 1% (NH4)2CO3), and easily exchangeable (0.01 M CaCl2) forms of K were determined. The results (2012 to 2016) showed that on chernozems with increased and medium soil K levels, the maximum yield increase due to K was for sugar beet (7.5 to 9.2 t/ha), followed by maize (1.3 t/ha), spring rape (0.2 t/ha), and soybean (0.1 t/ha). Average contribution of K to the yield increase was maximum for grain maize (18 %) followed by sugar beet (14 %), spring rape (13 %), and soybean (6 %). Significant residual effect of KCl applications resulted in substantial yield increase of the next crop in crop rotation – cereals, grain maize. or soybean. Potassium fertilization also substantially improved crop quality and profitability of crop production. The calculation of optimal application rates of K fertilizers using multi-criteria estimations shows that the optimal rate for sugar beet in Voronezh is 140 kg K2O/ha, with a possible increase to 210 kg K2O/ha in favorable years for crop development. In Lipetzk, optimal K fertilization for sugar beets is 280 kg K2O/ha. For the grain maize, the optimal rate is 120 kg K2O/ha (Voronezh).

In chernozem soils, the crop K supply can be predicted from the exchangeable K pool. In Central Russia (Lipetsk, Voronezh, and Belgorod) the 1 M NH4OAc soil test is the most predictive of sugarbeet and maize response to application of K fertilizers.