Effect of Rice Bran Biochar, Mixed and Enriched with Triple Superphosphate, on the Availability of Phosphorus andGrowth of Corn

Application of organic fertilizers such as biochar is one of the most effective techniques to avoid immobilization of P chemical fertilizers in soils. In order to evaluate the effect of rice bran biochar (produced at 550º C) alone, biochar mixed with P, and that enriched with P on some chemical properties of soil and yield of corn plant, a field experiment was conducted based on a completely randomized design with 7 treatments and 3 replications. The treatments included a control, triple superphosphate (350 kg ha-1 TSP), biochar at 2 levels (2 and 4 t.ha-1), biochar enriched with TSP (2 and 4 t.ha-1 biochar enriched with, respectively, 350 and 700 kg TSP), and 2 ton ha-1 biochar mixed with 350 kg TSP. To determine the chemical properties of soil and yield of corn, soil sampling was done three times during the growing season while plants were sampled 120 days after sowing. The results revealed that pH value decrease and soluble and available phosphorus increased in almost all treatments including biochar. The biochar with TSP was the best treatment (soluble and available P increased by 190% and 105%, respectively, compared to the control).  Grain yield was the lowest in the control (9.1 t.ha-1) and the highest in 4 t.ha-1 biochar enriched with TSP (15.9 t.ha-1). The treatment including 4 t.ha-1 biochar showed the highest P concentration in corn root (0.47%) and grain (0.79%). It is concluded that although TSP alone was able to increase available P in the soil, but its effects will decrease in longer times. Application of biochar mixed with TSP had the best effect on the P availability and its uptake by the plant. In general, for soils with low content of  P and organic matter, treatment of 4 t.ha-1 biochar enriched with 700 kg TSP is recommended to obtain the highest grain yield. However, environmental issues caused by the overuse of phosphorus fertilizers and the costs imposed on farmers must be considered.