Fungos micorrízicos e superfosfato no crescimento e acúmulo de nutrientes em plantas herbáceas em solo degradado

Abstract

The effects of increasing P rates (0, 50, 100, 200 and 400 mg.kg"1 supplied as triple superphosphate) and inoculation with a misture of arbuscular mycorrhizal fungi (AMF) on plant growth and N and P accumulation were studied during three cuttings in a degraded soil under glasshouse conditions. Soil material was collected from a borrow pit site and plant species studied were: braquiária (Brachiaria decumbens Stapf), stylosanthes (Stylosanthes guianensis (Aubl.sw.)), capim gordura (Melinis minutiflora Beauv) and a mixture of capim gordura and stylosanthes. Shoot and root mattertotal dryyield and accumulated N and P in three cuttings were enhanced by AMF inoculation and by P application. Treatment effects were highly differentiated among species. AMF inoculation reduced the externai P-requirement from >400 to 90 mg.kg"1 for stylosanthes, from 90 to 20 mg.kg"1 for braquiária, from >400 to 215 mg.kg"1 for mixture of capim gordura and stylosanthes, and had no effect on capim gordura. Considering P doses for 90 % of maximum shoot yield, it was found that AM inoculation enhanced shoot and root yields, N and P accumulations by 129, 38, 160 and 168 %, respectively over control for stylosanthes and by 30, 63, 5 and 24 % for braquiária grass. Capim gordura did not respond to AMF inoculation, gavethe highest dry matter yield and exhibited high externai P-requirement (335 mg.kg"1 soil). Spore density in the soil was more abundant after stylosanthes than after any other plant species. Inoculation with selected AMF and application of the appropiated amount of soluble P may enhancegrowth and nutrition of cover plants in degraded low-fertility soils.