EFFECT OF MINERAL FERTILIZERS ON THE GROWTH AND DEVELOPMENT OF SOYBEAN CULTIVARS UNDER LIGHT SIEROZEM SOIL CONDITIONS OF THE FERGANA REGION: A NARRATIVE REVIEW

Abstract

Soybean (Glycine max (L.) Merr.) is an increasingly important second crop in the irrigated Fergana Valley, where it is sown after winter wheat on soils that are low in humus and nitrogen. Mineral fertilizers are the main tool for improving its growth, development and seed yield, yet region-specific evidence for light sierozem (light gray) soils is scarce. This narrative review integrates verified evidence on (i) the agrochemical properties of light gray and meadow-gray soils of the Fergana region, (ii) the nitrogen, phosphorus and potassium requirements of soybean, and (iii) the interaction of mineral fertilizers with Bradyrhizobium/Rhizobium inoculation and micronutrients. The evidence indicates that biological nitrogen fixation supplies roughly half to 60% of soybean nitrogen demand, that fertilizer nitrogen rarely increases yield in the absence of a high yield potential, and that phosphorus and potassium stimulate nodulation and yield, with potassium often having the stronger effect. In the Fergana Valley, Rhizobium inoculation of the cultivar Orzu raised seed yield from 1.43–1.54 to up to 2.12 Mg/ha under irrigation. No published field trial that factorially tests N, P and K on soybean cultivars in the light sierozem soils of Fergana was identified. A hypothesis-driven experimental design is therefore proposed, and priorities for future research are outlined.