Mitigating effects of various phosphorus sources on arsenic toxicity under anaerobic conditions for rice and aerobic conditions for sunflower and maize plants

Arsenic (As) contamination is one of the major factors that contribute to environmental pollution, and it plays havoc with sustainability of crop production. Nano-hydroxyapatite (nHAP) can be an effective phosphorus (P) source to cope with As toxicity. The mitigating effects of variable P sources on As toxicity in rice, sunflower, and maize grown in an alkaline soil were evaluated. Arsenic was applied at 0 and 20 mg kg-1, and P was applied at 0, 50, and 500 mg kg-1 in the forms of triple superphosphate (TSP) and nHAP. In addition, the same amount of phosphoric acid was also used in the sunflower and maize experiments with the other P sources. The structural and functional properties of nHAP were determined by Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. Stunted growth was observed in rice, and less in sunflower; maize remained unaffected by As toxicity. In the presence of As, TSP and nHAP at their high doses (500 mg kg-1) significantly increased the rice dry weight compared with the control (0 mg kg-1). The As concentration in rice was decreased by approximately 25% in the presence of 50 mg kg-1 TSP and 500 mg kg-1 nHAP. The P treatments had no significant effect on the As concentration in sunflower, whereas the As concentration in maize was increased by 500 mg kg-1 TSP. In the absence and presence of As, nHAP at 50 mg kg-1 significantly increased rice P concentration, whereas in the presence of As, 500 mg kg-1 TSP significantly increased P concentration in rice compared with the control. Arsenic had no significant effect on sunflower P concentration, while the maize P concentration was decreased in the 0 mg kg-1 P treatment. It can be concluded that TSP and nHAP were effective in alleviating As toxicity in rice and sunflower. Comparative studies are further needed to determine the long-term effects of TSP and nHAP on prevention of As toxicity in field conditions.