Analysis of Yield Gap and Limiting Factors for Cassava on the Farmland

Purpose Our aim was to analyze the cause of yield gap and its limiting factors of cassava, and then to explore measures to narrow the gap.Method The yield gap of cassava both in Wuming and Hepu Counties of Guangxi Province was studied in this research.Results The results showed that average planting density and continuous cropping years of 25% the lowest yield farmer were significantly higher than those of other farmers. Only 25% the highest yield farmers' N, P₂O₅, K₂O ratios were fitted for recommended fertilization ratio of long-term fertilization trial, and the other farmers' N, K₂O ratios were lower than this ratio, also 25% the highest yield farmers' K₂O applications were significantly higher than those of the other farmers. More than 45% farmers had excessive fertilization, the average saving amount of fertilizer was 127.50 kg/hm², the saving potentials of phosphate, potassium and nitrogen fertilizer were 43.58%, 16.26%, 15.00%, respectively. The fertilizer efficiency was low, only 4.26%- 6.32% farmers reached a high yield and high efficiency. The investment/yield ratio reached the maximum when the yield reached 79.63 t/hm², after that, it showed diminishing returns with the increasing of yield. The cost of labor, especially spending on the harvest and management was the main limiting factors for yield gap.Conclusion Therefore, we have four suggestions for narrowing the yield gap of cassava.(1) Reasonable planting density.(2) The years of continuous cropping should not be more than three years.(3) The principles of fertilizer application should be in accordance with "tiny adjustment based on fertilization formula" and "if that longer continuous year of cropping is, the ratio of nitrogen and potassium fertilizer is higher", it recommending that, more nitrogen fertilizer and potassium fertilizer in basic fertilization, less nitrogen fertilizer and more potassium fertilizer in top-dressing fertilization, and to decrease phosphorus fertilizer and control nitrogen fertilizer and also potassium fertilizer in total could be effective nutrient management.(4) The input-output ratio should be promoted, and advanced mechanization replacing for labor should be spread in all cassava production.