Soybean yield under different systems of nitrogen fertilization, use of nitrapyrin and seed inoculants

The use of mineral fertilizers to achieve maximum soybean yield involves specific considerations regarding the forms of applied nitrogen, its transformation into various compounds harmful to the environment, and the response of the symbiotic apparatus of this leguminous plant to mineral nitrogen. Field experiments were conducted in the Male Polissya area within the Western Forest-Steppe zone. The research aims to determine the impact of mineral fertilization systems, the application of the nitrification inhibitor N-LokTM, and seed inoculants on soybean grain yield. The soil is deep gley, sandy-loamy in texture. Traditional field research methods and laboratory analysis techniques were applied. It has been established that nitrogen rates, forms of nitrogen fertilizers, and nitrogen stabilization with nitrapyrin significantly impact the loss of gaseous nitrous oxide into the atmosphere and nitrates into the lower soil layers. Including seed inoculation in the fertilization system significantly conserves mineral fertilizers, ensures maximum yield, and enhances the environmental safety of production. On deep gley, sandy-loamy soil, the highest yield over the period from 2022 to 2024 was achieved in 2023 with the application of N30P60K60 (ammonium sulfate) combined with seed inoculation using HiCoat Super Soy (produced by BASF), which contains nitrogen-fixing bacteria Bradyrhizobium japonicum, resulting in a yield of 4.12 tons/ha. The grain yield increase compared to the N30P60K60 control (ammonium sulfate) was 0.43 tons/ha (LSD05 = 0.16 tons/ha). The application of nitrapyrin with ammonium sulfate, both at the lower N30 rate and the higher N60 rate in two applications, resulted in a more significant yield increase compared to similar treatments with ammonium nitrate, yielding 0.11–0.35 tons/ha and 0.04–0.24 tons/ha respectively. With the N30P60K60 treatment (ammonium sulfate) and seed inoculation using HiCoat Super Soy (produced by BASF), which contains the nitrogen-fixing bacteria Bradyrhizobium japonicum, the soybean yield was 0.35 tons/ha. When combined with the phosphorus-mobilizing product Rhyzo P (produced by Agriteam), containing Bacillus amyloliquefaciens bacteria, the yield increased further to 0.40 tons/ha. The fertilization system for soybeans, using minimal and double nitrogen rates in the form of ammonium sulfate with a nitrification stabilizer and bacterial inoculants, significantly reduced nitrate accumulation in the arable and subsoil horizons (by 21.1 % compared to the N30P60K60 control treatment with ammonium sulfate). Applying the nitrogen-fixing inoculant HiCoat Super Soy in this system did not significantly alter the nitrate reserves in the arable soil layer. Doubling the nitrogen fertilization rate from N30 to N60 increased nitrous oxide emissions into the atmosphere by 25 %. The N30P60K60 fertilization system with ammonium sulfate and N-mobilizing bacteria controlled gaseous nitrogen emissions at the level of the control system N30P60K60 (ammonium sulfate) without inoculant. The research confirms the effectiveness of the improved soybean fertilization system in preserving environmental quality within the agricultural sector.