Efeito de micorriza comercial na biodisponibilidade de nutrientes no solo e crescimento de plantas jovens de oliveira

Abstract

The olive (Olea europaea) tree is one of the most important crops of the Mediterranean basin. It represents a great economic importance for Portugal, being Trásos-Montes the second most important producing region of the country. For maintaining high levels of production, it is necessary to have a fertile soil, capable of fulfilling the nutritional needs of the crop. Microfauna of the soil can helps in this purpose, because it is responsible for organic matter mineralization and immobilization of the nutrients. A good example is the association between the roots and a type of fungi, named as mycorrhizal. In this context, a growing range of commercial biofertilizers has emerged on the market. Thus, the aim of the study was to evaluate the effect of a commercial mycorrhiza on: (i) soil properties, in particular on the bioavailability of the nutrients; (ii) photosynthetic performance of the young plants; (iii) their nutritional status during the growing season; and (iv) dry matter yield. The experiment was conducted in a greenhouse of the Polytechnic Institute of Bragança (IPB), located in the northeast region of Portugal. Seven treatments (control, mycorrhiza, 3% NPK; 3% NPK + 3% N, 3% NPK + 3% P, 3% NPK + 3%K, 3% NPK + micro) were arranged in a completely random design with three replicates. Young rooted plants (-20 cm height) were used in this study and grown in pots of 3 kg soil for a year. During the growing season, it was evaluated the photosynthetic performance of the plants. The plants were destroyed one year after had been plantated and separated into roots, stems and leaves. The plant's parts were dried in an oven, weighted, ground and analyzed for the elemental composition. From a soil sample they were determined several soil properties. There were not detected significant differences among treatments on the photosynthetic performance of the plants. For the biomass, it was possible to record significant differences among treatments for the roots. Phosphorus concentrations in the stems and roots were significantly higher in Mycorrhiza treated plants than in the other treatments. In Mycorrhiza pots were recorded the higher pH values. Soil phosphorus and potassium availability in Mycorrhiza pots was similar to the treatments receiving an addition of those elements. Mycorrhiza gave soil organic matter values similar to the treatments which maximized this parameter. For the phosphatase activity, the mycorrhiza (487,51 ug nitrofenol g'h) showed twice the value of the treatment with phosphorus addition (280,70 ug nitrofenol g' h ). In view of the above, the commercial mycorrhiza appears as a good fertilizer since it may contribute for the maintenance of the plants nutritional status at satisfactory levels.