Yield-limiting nutrient response of lowbush blueberry grown in recent and ancient alluvial soils of the Mekong Delta

The blueberry yield in AA soil was only 81% of that in RA soil. In both RA and AA soils, N omission caused foliar N content deficiency (10.42 g kg^-1), resulting in the content of foliar P (0.84 g kg^-1) and K (3.78 g kg^-1) to fall below the Trevett threshold. In both RA and AA, N omission resulted in reduced fruit yield (47% and 39%, respectively) as well as reduced weight of the stem (70% and 42%, respectively) and leaf (59% and 46%, respectively). Increased crop yields in soils were mainly related to nitrogen fertilizer. The indigenous nutrient supply (INS) of RA, which is fertile, was high but its apparent nutrient recovery efficiency (ARE) index was low, whereas the INS of AA, or the level of degraded soil, was low but its ARE index was high. In alluvial soils, the higher the INS level, the less positive the impact on the ARE index. In AA soil, the indigenous N and K supplies can be improved through fertilizer investment; however, a balance must be achieved considering economic efficiency.