Physio-morphological and agronomic responses of cotton (Gossypium hirsutum L.) to fertilizer management and water stress at different reproductive growth stages

Two experiments were carried out in which the first one was pot experiment conducted at the Crop Science Cluster, UPLB [University of the Philippines Los Baños, College, Laguna, Philippines] from January to May, 2010 and second one was field experiment conducted at the Central Experimental Station (CES), UPLB from October, 2010 to February, 2011 to investigate the morphological, physiological, and agronomic responses of cotton to water stress and to evaluate the effect of water stress on cotton at reproductive growth stages with different fertilizer management. The cultivar used was CRDI 1 for both experiments. The pot experiment was laid out using a split-split plot in randomized complete block design with three replications. In pot experiment, 20 days water stressed plants had significantly reduced plant height, total dry matter (TDM), relative growth rate (RGR), functional leaf area, leaf water potential (LWP) and relative water content (RWC) as compared to control. Fertilizer application did not show significant effect on yield and yield components. Among reproductive stages, the flowering stage was very sensitive to water stress and resulted in reduction of TDM, harvest index (HI), RWC and functional leaf area. The plants, wherein the water stress was imposed at flowering stage for 20 days had lower yield and this was associated with lower number of sympodial branch and number of boll per plant resulting from low TDM, functional leaf area, RGR and HI as compared to control (no stressed) plants. Path coefficient analysis showed that yield components such as number of sympodial branch and number of boll per plant, boll weight and 1000 seed weight had positive and significant contribution to yield in both control and water stressed plants (10 days stressed and 20 days stressed). In the field experiment, water stress at flowering stage reduced TDM, crop growth rate (CGR), leaf area index (LAI) and root length (RL), HI and root shoot ratio as compared to well watered plants (control). Among fertilizer management, FYM [farmyard manure] + NPK application gave the highest in CGR, net assimilation rate (NAR), root volume (RV), and the lowest value was obtained by FYM alone. No significant difference between FYM + NPK and NPK was recorded in plant height and TDM. Seed cotton yield was lowest in FYM fertilized plants which were subjected to water stress at flowering stage. On the other hand, the highest yield was obtained from well watered plants applied with FYM + NPK. Path coefficient analysis revealed no significant correlation between yield and yield components in control plants. However, in stressed plants, number of boll per plant and number of sympodial branch per plant were positively and highly correlated with seed cotton yield.