The effect of sewage sludge application on soil phosphatase activity and nutrients uptake by maize plant inoculated with symbiotic fungi

Due to the low amount of rainfall and vegetation and the low use of organic fertilizers, Iran's soils have a low amount of organic matter, which affects the quantity and quality of agricultural products. Sewage sludge is an organic waste that is used as fertilizer in agriculture in some areas and can both improve the physical and chemical properties of the soil and increase the concentration of macro- and micro-nutrients that are essential for plant growth. Maize, Zea mays, is a tropical and subtropical four-carbon plant that is one of the most important grains in the world and has high nutritional requirements. Plant inoculation with symbiotic microorganisms, especially roots symbiotic fungi, could increases the ability of plants to better absorb water and nutrients, fight against environmental stresses, and improve plant growth and health. Therefore, in the present study, the effects of sewage sludge application adjust by inoculation with root endophytic fungi in maize cultivation on the uptake of some micronutrients and phosphorus was investigated.

A surface soil sample (0 to 30 cm) was prepared from the agricultural farm of Lorestan University. A factorial experiment in the form of a completely randomized design including soil microbial inoculation at three levels (no inoculation, inoculation with Rhizophagos intraradices, and inoculation with Serendipita indica) and sewage sludge (zero and 2 percent; w/w) was performed in three replicates under greenhouse conditions. Maize seeds were grown in 4 kg pots and after 3 months, the concentration of phosphorus, copper, zinc, iron and manganese elements in the shoot and root of the plant were measured. Also, some microbial characteristics (respiration, microbial carbon biomass, and acid and alkaline phosphatase activity) were measured in the soil.

The results showed the positive effect of both applications of sewage sludge and microbial inoculation on the concentration of elements in the plant. Biological parameters significantly increased (p< 0.05) with the application of 2 % sewage sludge: soil respiration (33 %), microbial carbon biomass (38 %), acid phosphatase (35 %), and alkaline phosphatase (6.5 %). Also, fungal inoculation significantly increased the concentration of phosphorus and micro-nutrients in the roots and shoots of the plant. There were no significant differences between the applications of the two symbiotic fungi; the only exception was the Zn concentration of root that was higher in treatments inoculated with R. intraradices than in treatments inoculated with S. indica. There was a positive correlation between available phosphorus with soil organic matter, plant biomass, and acid and alkaline phosphatase activity.

The results showed the positive effect of using purified sewage sludge at the level of two percent and inoculation of root endophytic fungi in the uptake of phosphorus and micronutrients by the plant, improving plant growth characteristics, and improving soil biological characteristics such as microbial carbon biomass and phosphatase enzyme activity. Inoculation with both symbiosis fungi was similar, but regarding this point that reproduction of S. indica is simpler, so it is recommended as a plant-promoting fungi that could reduce the application of P fertilizers and help the plant to uptake more P from soil. In this research, refined sewage sludge was used in low content (2 %), so it is essential to pay attention to the application of unrefined or higher amounts of sewage sludge that may result in microbial contamination or future problems.