Reduced fertilizer rates enhanced yields of vegetables grown on fertilizers overdosed vegetable soils in Yunnan
IPNI-2008-CHN-YN11
09 Jan 2009
2008 Annual Interpretive Summary
Reduced Fertilizer Rates Enhanced Vegetable Yields in Yunnan, 2008
Dianchi Lake, near Kuming City, was once a pristine, 300 km2 water body. However, over the past two decades the quality of this lake has fallen due to pollution, mainly caused by sewage sludge discharge into the lake from the surrounding phosphate industry and urban residences. Nutrient losses induced by improper fertilization from surrounding vegetable- and flora-growing farmlands are also blamed for eutrophication of the water. This study investigated soil nutrient status and farmer fertilization practices (FP) in order to better assess their contribution to the problem. Fertilizer use surveys and past soil test typically revealed soil nutrient accumulation from over-application of fertilizer to vegetables and flowers because they are high value crops. In the first year, three vegetables including lettuce, chili pepper, and celery were targeted. Treatments included: lettuce–450-180-0 kg N-P2O5-K2O/ha (FP), 85%, 60%, 50%, or 40% of FP plus 300 kg K2O/ha; celery–1,067-943-0 kg/ha (FP), 60%, 35%, 25%, or 15% of FP plus 450 kg K2O/ha; and chili pepper–670-650-0 kg/ha (FP), 65%, 45%, 40%, or 35% of FP plus 450 kg K2O/ha.
Results showed that vegetable yields were significantly improved with correctly reduced N and P rates plus added K. The optimal treatment for lettuce was 50% of the current farmer rate for N and P plus the test K rate (225-90-300 kg/ha) which increased lettuce yield by 21 t/ha (30%) compared to FP. For chili pepper, 30% of the FP treatment plus K (200-195-300 kg/ha) produced the highest pepper yield of 23.6 t/ha, which was 89% above FP. Optimal fertilizer reduction for celery amounted to 60% of FP plus K (640-390-450 kg/ha) slightly increased celery yield by 450 kg/ha (0.2%). All the other treatments with reduced fertilizer rates significantly reduced celery yield. This may be due to the fact that celery produced a much higher yield of 182 t/ha, about 3.6-fold that of chili pepper and 2-fold the yield of lettuce.
Besides yields, nitrate contents in the vegetables were also significantly reduced by correctly reducing N and P and adding K. Vegetable fertilization in fields surrounding Dianchi Lake has been unbalanced and needs to be adjusted for better yields, quality, income, and environmental protection. Yunnan-BFDP-08