Nutrient omission plots in spring wheat in Russia: Omsk Oblast and Republic of Bashkortostan

The following fertilizer treatments were applied in the Republic of Bashkortostan (N-P₂O₅-K₂O in kg/ha): 1) control, 2) 10-10-10, 3) 150-25-28, 4) 150-25-0, 5) 150-0-28, 6) 6-25-28. Spring wheat was the third crop after fallow in this location (after winter rye and buckwheat). The highest grain yield of 3.49 t/ha was obtained with recommended application of N, P, and K (treatment 3). N, P, and K fertilizer use increased grain yield by 0.52 (18%), 0.28 (9%), and 1.09 (45%) t/ha, respectively. Initial soil properties indicate low nitrate level in the soil. It was assumed that favorable conditions (temperature, rainfall) for N mineralization from soil organic matter occurred during 2011 growing season resulting in the moderate efficiency of N application. Somewhat low response to P fertilizer was likely because of “increased” content of P extracted by a routine soil test (0.5 M acetic acid [CH₃COOH]) and also high content of Olsen P according to soil test interpretation classes proposed by researchers in Russia. This leached chernozem in the Republic of Bashkortostan had an “increased” content of K extracted by a routine soil test (0.5 M CH₃COOH) but a low content of exchangeable K. Thus, K fertilizer application was very effective in increasing yield.

The fertilizer scheme in Omsk Oblast was as follows: 1) control, 2) 10 kg N, 3) 96-82-30 kg N-P₂O₅-K₂O, 4) 96-82 kg N-P₂O₅, 5) 96-30 N-K₂O, 6) 82-30 P₂O₅-K₂O. The third spring wheat after fallow was grown in this location. The highest yield of grain of 3.09 t/ha was again obtained with the recommended application of N, P, and K (treatment 3). Nitrogen, P, and K fertilizer use increased grain yield by 0.98 (46%), 0.04 (1%), and 0.06 (2%) t/ha, respectively. The effect of P and K applications was not significant. This leached chernozem in Omsk Oblast had a medium content of P extracted by a routine soil test (0.5 M CH₃COOH) but an “increased” content of Olsen P. The latter may explain why P fertilizer application to spring wheat was not effective at increasing crop yield at this experimental site. K fertilizer use was also not effective at increasing yield because of the very high content of K extracted by a routine soil test (0.5 M CH₃COOH) and also a very high content of exchangeable K. IPNI-32