Sulfonated nitrogen and added-sulfur sources influence productivity, quality, and nutrient acquisition of soybean-wheat cropping system

Soybean-wheat is the predominant cropping system covering >2.5 Mha area in India. The lower productivity of soybean-wheat cropping system (SWCS), remains a serious concern primarily due to inadequate nutrient management. Increasing sulfur (S) deficiency is widespread, especially under oilseed-based cropping system. Hence, to standardize the S requirement through customized fertilization, an experiment was conducted in completely randomized block design (RBD) comprised of 12 nutrient sources, replicated thrice. The study aims to evaluate the agronomic performance of sulfonated nitrogen (SN) in comparison to conventional S nutrient sources in SWCS. The maximum soybean productivity was recorded under NPK + S through 40-0-0-13 (SN1), although NPK + 50% S (15 kg/ha) as basal and 50% (15 kg/ha) as top dressing through SN2 10-0-0-75 produced maximum wheat grain yield. When compared with no nitrogen (control), the application of 30 kg S ha^-1 to both crops increased the productivity of the soybean-wheat cropping system up to 39%. The maximum system (SWCS) productivity (8.45 tha^-1) was obtained with the application of 50% S as basal and 50% as top dressing (SN₂-based), remaining N through urea. The highest sustainable yield index of soybean (SYIS), i.e. 0.90 was under SN1+ remaining N through urea and likewise highest sustainable yield index of wheat (SYIW) was under S splitting. The application of SN also improved the nutrient acquisition and grain quality of soybean and wheat with a positive nutrient balance in the soil. The protein content and yield of soybean and wheat grains also improved. The higher gluten content in wheat grain was produced with 60 kg S ha^-1 applied. The agronomic efficiency of N and S (AE_N and AEs) were highest under SN₁ and SN₂, respectively (32.8 kg grain/kg N applied; 15 kg grain/kg S applied) in soybean, however in wheat, S splitting and urea application resulted in highest agronomic efficiency (AE_N and AES) of N and S (17.1 kg grain/kg N applied; 22.3 kg grain/kg S applied respectively). Hence splitting of S doses of SN along with urea and recommend P, K was found efficient for the soybean-wheat cropping system.