Validation of fertilizer recommendations for soybean under high yielding crop production systems in Central and South of Russia

Field experiments were conducted on leached chernozem, ordinary chernozem, and meadow chernozem soils in three locations of Krasnodar Krai. Soils had a fine texture, a near neutral pH (6.6 to 7.0), low organic matter content (2.9 to 3.6%), high concentrations of Olsen P (16 to 26 ppm), and very high levels of exchangeable K (272 to 505 ppm) in the top 20 cm layer. The following six treatments (kg/ha) were applied in 2014: 1) unfertilized control; 2) 18 N; 3) 9-39 N-P₂O₅; 4) 9-39-60 N-P₂O₅-K₂O; 5) 18-78 N-P₂O₅; 6) 18-78-60 N-P₂O₅-K₂O. Potassium fertilizer was broadcasted prior to spring cultivation and other fertilizers were applied at planting (2 cm below and to the side of the seed). Inoculation and Mo seed treatment were done in each treatment. A medium maturity soybean variety (115 to 118 days) was grown in each location.

Soybean yield ranged from 1.3 to 2.0 t/ha depending on the location. In 2014, both high temperatures and zero precipitation in August negatively affected soybean development during the R4 to R6 stages. The highest yields were obtained on meadow chernozem soil under a rice-based cropping system. Macronutrients (N, P and K) did not result in a significant yield increase based on these first year findings. Another preliminary conclusion is that the Vilana variety used in this experiment may be sensitive to salt concentrations because in two of three locations seed yield decreased in a treatment providing 18-78-60 kg N-P₂O₅-K₂O/ha

In Central Russia, field experiments were conducted in Belgorod Oblast on large industrial farms in two locations (i.e., a grey forest soil site and a typical chernozemic soil site). The following six treatments were studied: 1) control; no fertilizers; 2) 18 N; 3) 9-39 N-P₂O₅; 4) 9-39-60 N-P₂O₅-K₂O; and 5) 18-78-60 N-P₂O₅-K₂O. All fertilizers were broadcasted pre-plant prior to spring cultivation. Two different soybean varieties were tested, namely Horol (Canadian) and Lantzentnaya (local variety).

At the chernozem site, seed yield varied from 1.2 to 1.4 t/ha. The highest yield (1.4 t/ha) was achieved with 18-78-60 N-P₂O₅-K₂O, or 15% above the control. At the grey forest site, seed yield was higher and varied from 2.1 to 2.5 t/ha. The highest yield (2.5 t/ha) was achieved by adding 9-39-60 kg N-P₂O₅-K₂O/ha, which was 20% higher than the unfertilized control. Both sites had low grain S concentrations, thus next season an additional S treatment will be included in order to study soybean responses to S fertilization.