Importance of phosphorus application in Acacia mangium plantation

Fertilizers (nitrogen/N, phosphorous/P, and potassium/K) have been widely applied to increase the productivity of forest plantation, especially in poor soils. This study was to test the effects of fertilization at planting and additional fertilization in the following two years on growth and aboveground biomass (AGB) of a 30-month old plantation of Acacia mangium in Northeast Vietnam. There were four treatments including (1) 1 kg compost/tree at planting and 0.2 kg NPK (16:16:8)/tree/year in the following two years (IC-A-NPK), (2) 1 kg compost/tree at planting and 0.2 kg P (16.5% P₂O₅) + 0.1 kg K (60% K₂O)/tree/year in the following two years (IC-A-PK), (3) 1 kg compost + 0.2 kg NPK/tree at planting and 0.2 kg NPK/tree/year in the following two years (IM-A-NPK), and (4) 1 kg compost + 0.2 kg NPK/tree at planting and 0.6 kg P + 0.1 kg K/tree/year in the following two years (IM-A-PK). The results indicated there was no significant effect of fertilization at planting and additional fertilization on diameter at breast height (DBH), basal area, and AGB between IC-A-NPK (DBH of 8.9 cm, basal area of 7.4 m² ha^-1, and AGB of 37.8 Mg ha^-1) and IM-A-NPK (DBH of 10.1 cm, basal area of 9.2 m² ha^-1, and AGB of 47.5 Mg ha^-1). Meanwhile, DBH (9.6 cm), basal area (8.6 m² ha-¹) and AGB (44.2 Mg ha^-1) in IM-A-PK were significantly higher than that in IC-A-PK (DBH of 8.4 cm, basal area of 6.4 m² ha^-1, and AGB of 31.6 Mg h^-1). It was concluded that fertilization at planting of both compost and NPK is not required for A. mangium plantation. While additional fertilization of phosphorus should be applied for higher productivity.