A nutrient use efficiency experiment and effect of different phosphate fertilizer forms on coffea grown

Since 1996 with the assistance and support of PPI/PPIC/IFA, the NISF started to conduct field experiments on the efficiency of nutrients, rates and ratios of nutrients as well as efficiency of phosphorus fertilizer forms on Arabica coffee grown in 3 upland soil areas of Northern Vietnam (in Phu Tho, Yen Bai and Son La) and two long term field experiments on fertilizer nutrient efficiency and phosphorus fertilizer forms efficiency on Robusta coffee on ferralitic soils derived from basalts at the Dak Lak site (Central Highlands). The research results again affirmed the finding recorded in previous: N, K and P were the most important nutrients to Arabica coffee and it was followed by S and Mg. Recently in the Arabica coffee growing areas, the dropping of coffee bean price together with the damages caused by severe hoarfrosts in late 1999 leading to the compulsory cutting of about 1/3 of production coffee area in Son La province has made some of farmers become disheartened to continue growing coffee. However, the good results of on farm demonstrations on balanced fertilization for Arabica coffee carried out by NISF (one of which gained a yield increase of 126 percent compared with farmers' practice) have contributed to consolidating the farmers' confidence in advanced fertilization technologies. All studied fertilizer nutrients N, P, K, Ca, Mg, S, Zn, B and Cu had effects on growth and development to form yield of Robusta coffee, in which N, P, K were most essential. On the base without FYM application, their omission from the full nutrient combination led to decrease in node forming rate, increase in dried branch rate, decrease in fruit weight, increase in unfilled fruit rate thus leading to decrease in Robusta coffee bean yield of 46.2percent 67.9 percent compared with full nutrient application. On the base with FYM application the respective yield decrease was 40.8 percent 57.3 percent. The application of P fertilizers increased growth and development of Robusta coffee plants thus leading to increase in coffee yield. It also increased nutrient contents in soils and plants. Application of SSP or DAP in the first years resulted in rather high yields, but the continuous application of these P fertilizer forms in the last years led to yield decrease compared with FMP application.