Escória de siderurgia e a nutrição fosfatada de milho inoculado com fungos micorrízicos arbusculares

Abstract

To evaluate the use of steel basic slag as a corrective of soil acidity and its effect on phosphorus availability and mycorrhyzal symbiosis, they were applied to an Rhodic Udox soil four corrective for pH, being: steel basic slag (4 Mg.ha-1), lime (4 Mg.ha-1), mixed 50% lime with 50% slag (2 Mg.ha-1 slag and 2 Mg.ha-1 lime), and a control without pH correction. The dosages of each material were determined by means of calibration curves of soil maintained at 80% field water capacity for 59 days. For each treatment there were applied 5 doses of P (0, 42, 95, 231 and 480 mg dm-3 of soil), as triple super phosphate. The corrective and P treatments were combined with the presence or absence of inoculums of arbuscular mycorrhyzal fungi (AMF) (containing about 100 spores.mL-1 of each species, Glomus clarum and Gigaspora margarita), forming a 4x5x2 factorial with five replicates, in pots of 3 kg of soil. Maize (Zea mays, variety Eldorado) plants were cultivated in the pots, with one plant in each pot after thinning. The height and diameter of the plants were measured weekly, and it was taken a disk of 8 mm from the 2nd leaf, expanded every 15 days, to analyze phosphorus content. Seventy-seven days after planting, the plants were harvested, separated the shoots and roots (by sieving the soil in the pots). The rate of roots colonization and the number of spores contained in 50 mL soil of pots, the leaf area, dry mass of roots and shoots, and the nutrient content in shoots (P, Si, Ca, Cu, Mg, Mn, Zi e Al) were evaluated. There were also tests for the content of heavy metals (Cr, Co, Ni, Cd and Pb) in the shoot, although they were not detected in the plants. The spore density increased with the increasing levels of P up to 95 mg dm-1, and then reduced in the highest P dosages. The fungi colonization was highest in plants without phosphorus and treated with 95 mg P dm-1 soil, in the presence of limestone, slag and in the control; and for the dosage of 42 mg P dm-1 soil in the mixed limestone and slag treatment. It was observed the greatest plant growth in height, diameter, leaf area, and dry weight of shoots and roots of plants inoculated with AMF, with interaction between inoculation and phosphorus levels in leaf area and dry mass of shoots and roots. In general, the highest dosage of phosphorus (480 mg P dm-3) inhibited the growth of inoculated plants that exhibited, in this condition, lesser growth in dry mass of roots then the non-inoculated. The P in the leaf disc at 75 days showed a significant interaction between inoculation and P levels, where non-inoculated plants showed a linear increase in P content with increasing doses, and they showed decrease in P content at the highest dose of P applied to soil. For the nutrients in shoots, inoculated plants grew faster and they exhibit a dilution effect of the content. When comparing the total nutrient content in shoots, inoculated plants had highest absolute amounts of nutrients up to the dose of 213 mg P dm-1 soil, and the beneficial effect of mycorrhyzal inoculation disappeared at the highest P dosage. There was no effect of the different corrective in plant development.