The availability of P in acid soils may be raised through the application of phosphatesolubilizing fungi (PSF). Coal fly ash (CFA) that has a high pH and contains a relatively high P may also be used to raise the availability of P in acid sois. The purpose of this study was to explore the possible use of CFA and PSF in a biochar-compost carrier to improve the availability of P and plant growth in acid soil. Combined applications of two PSF isolates (Aspergillus oryzae = F1, and Neosartorya fischeri = F2) carried in three levels of biochar-compost (80% biochar + 20% compost = B1, 70% biochar + 30% compost = B2, and 60% biochar + 40% compost =B3), and two doses of CFA (60 t/ha = C1, and 80 t/ha = C2) were tested in this study through two experiments. The results of experiment 1 (laboratory experiment) showed that the application of N. fischeri carried in 70% biochar + 30% compost combined with 80 t CFA/ha (F2B2C2 treatment) significantly increased the available P more than other treatments. In comparison with control, the increase of soil available P content ranged from 13% in the F1B1C1 treatment (A. oryzae in 80% biochar + 20% compost combined with 60 t CFA/ha) to 101% in the F2B2C2 treatment (N.fischeri in 70% biochar + 30% compost combined with 80 t CFA/ha). The results of experiment 2 (glasshouse experiment) showed that the highest dry weight of maize shoot was obtained by the F2B2C2 treatment that increased 123% compared to control. The highest P uptake by maize was obtained by the F2B2C2 treatment (N. fischeri in 70% biochar + 30% compost combined with 80 t CFA/ha).

The potential of Ultisols, especially in East Kalimantan for the development of food crop agriculture is faced with constraints on phosphorus availability due to low soil pH and high solubility of aluminum (Al). The purpose of this study was to elucidate the effect of a combination application of coal fly ash (CFA) and oil palm empty fruit bunches (OPEFB) on the availability of phosphorus in an Ultisol from East Kalimantan and its impact on the production of maize. The combination of CFA and OPEFB consisted of seven treatments with three replications. The research was carried out in two steps. The first experiment (incubation in the laboratory), was carried out under non-leaching condition for 42 days. Parameters observed included soil pH, available soil P, total soil P, and soil exchangeable Al. The second experiment (growth experiments in a glasshouse), was were carried out by growing maize plants with the same treatment as for experiment 1. The plant height and leaf area were observed every week. At the harvest time (age 12 weeks), dry weight of shoots and roots, maize weight with cobs, and maize weight without cobs were observed. The results of soil incubation showed the decrease in the soil exchangeable Allevel, the increase in soil total-P, and soil available-P. The combination application of CFA and OPEFB did not have a significant impact on soil pH, and soil organic-C. The results of the glasshouse experiment showed that CFA and OPEFB were not significantly different in the parameters of plant height, leaf area of 12 weeks, weight of shoots and roots, maize weight with cobs, and maize weight without cobs.