Improvement of Winter Wheat Mineral Nutrition on Calcareous Common Chernozems

This project assessed the spatial variability in soil fertility parameters using 27 soil samples (0 to 20 cm soil depth) collected from the experimental area of 39 ha prior to starting the field experiment. The experiment comprised of two demonstration plots of 19.5 ha each. Soil test results showed that the nitrate-N concentration varied from very low to low (average 4.8 ppm), ammonium-N averaged 22.3 ppm, available P extracted with 1% ammonium carbonate at soil to solution ratio of 1:20 (AC-P) was low to medium (average 7.2 ppm), and available K extracted with ammonium carbonate solution (AC-K) was medium to ‘increased’ class (average 241 ppm). AC extraction is a routine method in Russia to assess available P and K in calcareous soils, including chernozems and chestnut soils. Olsen-P and exchangeable K extracted with ammonium acetate solution were also measured and averaged 15.7 and 277 ppm, respectively. Soil pH averaged 7.7.

Soil ammonium and nitrate concentrations were found to be the most variable parameters with coefficients of variation (CV) of 25 and 46%, respectively. Both Olsen-P and AC-P had moderate variability (CVs of 11% and 19%, respectively), while exchangeable K and AC-K were less variable parameters (CVs of 8 and 9%, respectively). Soil pH was quite consistent in the experimental area (CV of 1%). A noteworthy fact is that variable rate fertilizer application may be a profitable placement method when spatial variability exceeds 20%. A very strong correlation was found between exchangeable K and AC-K (R = 0.99), because cation exchange reactions between K and ammonium occur during both extraction procedures. Similarly, Olsen-P was strongly correlated with AC-P (R = 0.88). Thus, routine soil testing methods may provide adequate assessment on the availability of soil P and K to plants in calcareous chernozems.

Dry conditions prevailed during winter wheat planting and then during spring-summer season too. The farmer used reduced tillage and applied fertilizers (monoammonium phosphate, potassium chloride) before planting to the surface soil layer. Ammonium nitrate was topdressed at early spring. The farmer harvested 2.75 t/ha yield in K-omission or farmer's fertilizer practice (54-52 kg N-P/ha) plot. Application of 40 kg K₂O/ha had practically no effect on grain yield as only a nonsignificant yield increase of 0.04 t/ha (or 1.5%) was observed in the field.