Studies on Suitable NPK Fertilizer Dosage and N:P:K Ratio for Dien Pomelo (Citrus grandisL.) Growing on Acrisols in Chuong My District, Hanoi City

The aim of this study was to determine the appropriate dosageand N:P:K ratioof fertilizer for Dien pomeloduring the production cycle on Acrisolsin Chuong Mydistrict, HaNoi. Ten experiments with different formulaswereconducted in2 years on 20-year-old Dien pomelo orchard. The efficiency of fertilizer was determined on the basis yield, quality and economic efficiency. The results showedthat the two formulas withthe highest yield and quality of pomelo were CT4formula(30kg Manure + 0.6kg N + 0.4kg P2O5+ 0.54kg K2O)/tree/year, with NPK ratio of 1:0.65:0.90 and CT6formula(30kg Manure + 0.75kg N + 0.38kg P2O5+ 0.56kg K2O)/tree/year,withNPK ratio of 1:0.50:0.75. The net yield in CT4 formula was28,425 (in 2020)and28,536 (in 2021) fruit/ha and in CT6formulawas28,074 (in 2020)and28,326 (in 2021) fruits/ha (average increase in 2 yearsfor CT4 and CT6 formula was 38.8% and 35.9%, respectively compared to that of the control). CT4 and CT6 formula also gave the best fruit quality with an average fruit height of 11.75cmand11.73cm,and averagefruit diameter of 13.74cm;averagedry matter content of 11.41%and 10.65%;average vitamin Ccontentof 80.0mg%and 73.1mg% and average Brix level of11.15%and 10.93%. In bothyears,2020 and 2021, CT4 yieldedthe highest economic efficiencywiththe averageprofit ofVND427.16 million/ha/year.