The Effect of Humic Acid and Phosphorus Fertilizer on Phosphatase Enzymes, Active Carbon and Available Phosphorus in Sugarcane Rhizosphere

Soil enzymes are considered as a measure of soil biological status. Phosphatase enzymes (alkaline and acid) are very important because of their role in converting organic to inorganic phosphorus and improving plant nutrition. Various factors such as organic compounds and phosphate fertilizers affect the activity of these enzymes. In this study, the effect of humic acid and phosphorous (P) fertilizers onsoil rhizosphere phosphatase enzymes, active carbon and P uptake by sugarcane was investigated, conducting a greenhouse pot experiment in south west of Iran. The experiment was performed as a factorial based on complete randomized design, in three levels of P application as triple super phosphate (0, 50% and 100 % of recommended phosphorus application, 250 kg.ha-1, in the region), four humic acid treatments (three immersion levels of setts in 0, 0.3 and 0.5% solution of humic acid as well as application of 30 mg humic acid per kg soil treatment) and two harvesting time (45 and 90 days after planting). The results showed that in non-fertilized treatment, the use of humic acid (especially in the form of cuttings immersion) increased P uptake by about twice at the first harvest and by 30% at the second harvest compared to the control treatment. Improvement of P uptake in the soil with deficit P was due to changes in activated carbon in the rhizosphere and also the impact on density and activity of microorganisms and the activity of enzymes such as phosphatase, which increases the availability of P in the vicinity of the plant root. By increasing the phosphorus application, the activity of the alkaline phodphatase enzyme decreased and reached to the minimum measured value dry soil (17% Less than the control).