Nutrient Management Research for Eggplant in Hainan

Due to high economic returns in vegetable production, over-application of fertilizers is a common practice in vegetable-growing regions of China. The objective of this study was to determine the optimal fertilizer rates for eggplant, one of the most widely grown winter vegetables in Hainan Province. The experiment consisted of treatments including six N application rates (0, 150, 225, 300, 375, and 450 kg N/ha) and six K rates (0, 75, 150, 225, 300, and 375 kg K₂O/ha) with a fixed P rate (150 kg P₂O₅/ha). Nitrogen was used as urea (46% N), P as SSP (12% P₂O₅) and K as KCl (60% K₂O). Nitrogen and K fertilizers were split-applied four times, viz., basal application (30%) at seedling, transplanting and topdressings (70%) at seedling stage and after every other fruit harvest of eggplant as drip fertigation. Phosphate was applied only once as a basal application.

Eggplant yields significantly increased with an increase in N and K application rates, but leveled off at 300 kg N/ha and 225 K₂O/ha. This N and K combined treatment produced 17,218 kg/ha (119%) more eggplant yield and US$11,067 more return than the N omission treatment. It also resulted in 6,725 kg/ha (26%) more eggplant yield and $4,201 more economic return than the K omission treatment. The agronomic efficiency was 57.4 kg fruit/kg N applied and 30 kg fruit/kg K₂O applied. Nevertheless, fertilizer recovery rates were rather low for both N and K, measured at 19 and 31%, respectively. Preliminary results suggest that the optimal N and K rates for eggplant production in this region are around 300-150-225 kg N-P₂O₅-K₂O/ha. More studies will be conducted to validate this optimum fertilizer rate before it is extended to large areas.