摘要：Most corn planted on tropical acidic soils suffers substantial yield loss caused by low crop phosphorus (P) uptake. Humic acid is recommended to increase crop P uptake since it is capable of competing with P to be bound to soil adsorption complexes. Humic acid extracted from composted manure (MHA) is a good alternative to humic acid because it is more reactive and has a higher complexation ability compared with leonardite. Therefore, the effectiveness of soil-applied MHA combined with P was evaluated to improve corn yields in acidic soils from the aspect of crop nutrient uptake efficiency and crop physiological performance. Two high-yielding corn cultivars that are highly accepted by Indonesian farmers and resistant to downy mildew disease were subjected to five different types of MHA and P combinations. The amount of P fertilizer was equivalent to 120 mg P2O5 kg−1 soil. The H10P1 produced the most significant result p < 0.05 in terms of total crop dry weight, grain dry weight, and corn yield. The highest efficiency for P uptake in the leaves and grains was found with H10P1 and H5P1, respectively. Although chlorophyll content was not substantially improved, the stomatal apertures 7 weeks after planting (WAP) were significantly increased p < 0.05 with H10P1 and H15P1. The photosynthetic rate and nitrate reductase (NR) activity at 10 WAP were significantly increased p < 0.05 with H5P1 and H10P1, respectively. The results clearly indicated significant increases in the efficiency of crop P uptake and physiological performance for stomatal aperture, photosynthetic rate, and NR activity can highly contribute to higher corn yields.
