Mobilização de fósforo e crescimento de leguminosas submetidas a diferentes níveis de adubação com fosfato de rocha.

Abstract

Green manuring is a strategy of ecological management of soil that aims the reestablish the original conditions of fertility of degraded enviroments. The most use species for this purpose are legumes, due to their association with nitrogen-fixing bactéria. Some legumes used as green manuring can also solubilize organic P.This not only increases N availability, but also P. This research was carried out with the objective of evaluating the potential of four legumes species \Miiciina aterrima (Black Mucuna), Cajanus cajan (Pigeon Pea), Crotalaria juncea (Sunnhemp) and Pueraria phaseoloides (Tropical Kudzu)] to mobilize organic P through fertilizing with natural phosphate of slow solubilization and to use this P for their growth, and make available to subsequent crops. The experiment was carried out in the period of 30 (thirty) days, in a green house at Embrapa Amazônia Oriental, Belém, Pará. Tive fertilization leveis were tested using rock phosphate of Morocco (0 kg.ha"1, 46 kg.ha"1, 92 kg.ha"1, 183 kg.ha"1 and 366 kg.ha"1). The substratum used was a mixture of distrophic Oxisol (0 20 cm), washed sand and clay (horizon B) in the proportion of 2:1:1 (v:v:v). The experimental design was entirely randomized and analyzed according to a design 4 (species) x fertilization leveis). The aerial and root biomasses; relative growth and net assimilation rates; leaf macronutrient contents; total volume root, EMA colonization rate; acid phosphatase of the rhizosphere; macronutrient contents of the substratum, available, organic and total P contents of the substratum; carbon and phosphorus of the microbial biomass and quantification od spores of indigenous AM fungi were evaluated. Mucuna aterrima was the most productive specie and that accumulated more leaf nitrogen were Crotalaria juncea, Pueraria phaseoloides and Cajanu cajan species; Cajanus cajan, Crotalaria juncea and Pueraria phaseoloides were more efficient in the association with indigenous AM funji; were more sensitive to P deficiency; induced larger activity of the acid phosphatase in the rhizosphere; showed the highest ne assimilation rates in response to fertilization with rock phosphate, wich resulted in dry mass increase. Also these species showed a larger effectiveness in solubilization and absorption of P and essential macronutrients, being the most suitable species for improvement of soil fertility and quality of degraded and intensive traditional cultivation arcas than the species Mucuna aterrima.