Fiber quality, oil seed composition and fatty acid profiling of cotton (Gossypium hirsutum L.) seed as influenced by sub-surface drip-irrigation and foliar-fertilization strategy in semi-arid agro-ecology of south-Asia

Abstract

Under climate-change, micro-irrigation practices like sub-surface drip-irrigation (SSDI) coupled with optimized-fertigation and foliar-nutrition, may improve crop-productivity and quality. Hence, current study in cotton (Gossypium hirsutum L.) comprised of three SSDI-regimes [60, 80, 100 % ET_c], two N-fertigation levels [80, 100 % RDN] and two nutrient-application methods [foliar-spray of KNO₃ & MgSO₄ (M_foliar) versus fertigation (M_fert)] in factorial randomized-complete-block-design besides three additional controls (surface-drip + N₁₀₀ + M_foliar; surface-drip + N₁₀₀ + M_fert; flood-irrigation + soil RDN + M_foliar). The results indicated that SSDI at 80%ET_c enhanced seed-cotton-yield by ∼5.3 and 9.9 %, ginning out-turn (GOT) by ∼2.1 and 4.8 %, fiber-length by ∼5.7 and 7.6 %, lint-index by ∼5.8 and 11 % and protein-yield by ∼7.8 and 11.6 %, over 60%ET_c in 2019 and 2020. Oil-content, oil-yield, cake-content, and cake-yield varied significantly with increased irrigation from 60 to 100%ET_c, underscoring the importance of adequate water for oil-synthesis in cottonseeds. Fatty-acid composition was sensitive to irrigation-levels, with significant reduction in saturated-fatty-acid (SFA) and unsaturated-fatty-acid (UFA) by ∼5.4 and 5.5 %, and monounsaturated-fatty-acid (MUFA) and polyunsaturated-fatty-acid (PUFA) by ∼2.9 and 5.9 % at 60%ET_c over 80%ET_c during 2019 and 2020, respectively. Polyunsaturated:saturated (P/S) index, vital for human cardio-vascular health, increased by ∼5.2 and 7.1 % under 60%ET_c. To harness higher yield with better quality fiber, protein, oil-yield and cottonseed-cake, SSDI at 80%ET_c proved optimal, with no-additional benefits beyond this level. Enhancing fertigation from 80 to 100%RDN slightly enhanced UFAs and reduced SFAs. Higher UFAs is desirable for reducing low-density lipoprotein (LDL) cholesterol-levels. Foliar-spray of KNO₃ & MgSO₄ enhanced GOT, lint-index, UFAs, MUFA:PUFA and P/S index over fertigation. SSDI improved both fiber and seed-composition over flooding. Overall, SSDI at 80%ET_c, combined with fertigation at 80%RDN and foliar-fertilization offers substantial benefits for cotton-productivity and quality in water-scarce agro-ecologies. These practices improve water-use-efficiency and sustainability, hence, enhancing resilience and economic-viability of cotton-industry amidst environmental-challenges.