Tolerancia a toxidez de aluminio por leguminosas tropicais utilizadas em adubação verde

AUTOR(ES)
DATA DE PUBLICAÇÃO

2003

RESUMO

Cover crops or green manures are widely cultivated plants for the conservation and recovery of soils, employing mainly herbaceous leguminous crops. Due to its economic and environmental benefits in agricultural productions, there has been a significant increase in the adoption of the green manuring technique in Brazil. However, there is no scientific information about the reaction of the main tropical species to aluminum (Al) toxicity. The present study aimed at the evaluation of aluminum tolerance among tropical leguminous species usually grown as green manure or cover crops. This comparison was done in experiment 1. In a second experiment, the influence of phosphorus nutrition on Al tolerance was assessed in the leguminous cover crop Lablab purpureus L. In the former experiment, conducted under greenhouse conditions, it was possible to verify that there was a great difference among the 17 species tested, when compared by the following parameters: evaluation of the degree of Al toxicity, relative root elongation and critical Al activity to reduce 50% of root elongation. Based on these parameters and on the comparison of two tropical maize genotypes differing in Al tolerance, it was possible to establish the following classification for the plant materials tested: highly tolerant, for Mucuna nivea, M aterrima, M deeringiana, Vigna unguiculata and Lablab pwpureus, tolerant for Glycine max cv. IAC 13, Cajanus cajan cv. Fava larga, Calopogonium mucunoides, G. max cv. IAC 9, Canavalia brasiliensis, C. cajan cv. IAPAR 43; moderately tolerant for Crotalaria mucronata, C. 5pectabilis, Zea mays cv. Taiúba tolerant, Canavalia ensiformis, C. ochroleuca, G.max cv. Biloxi and sensitive for Neonotonia wightii, C. breviflora, Z. mays cv. Taiúba sensitive and C. juncea. Among the total Al thresholds employed in the study (111, 222, 333 e 444 ?mol/L), 111 ?mol/L Al in nutrient culture solution was the best to separate the materials as for root elongation. Shoot and root dry matter were not good variables to compare the Al tolerance among the species after 9 days of growth in nutrient solution culture, and root elongation was a better parameter for A1 screening in these species. The results obtained in experiment 1 allowed to conclude that the cover crops grown in Brazil are generally well adapted to A1 toxicity, which is one of the main nutritional limitations found in Brazilian acid soils. In the second study, carried out under greenhouse conditions, the effect of phosphorus nutrition on AI tolerance by the lablab specie was evaluated, employing the split-root technique with complete nutrient culture solution. The root system was divided in two parts, combing two concentrations of P (20 and 230 ?moI/L; P1 e P2, respectively) and/or three concentrations of A1 (111, 278 and 412 ?mol/L; AL1, AL2 and AL3, respectively), formed by the following treatments: P1/PI1 P2/P1, P2/P2, P1/AL1, P2/AL1, AL1/AL1, P1/AL2, P2/AL2, AL2/AL2, P1/AL3, P2/AL3 e AL3/AL3. The solutions with AI had the same P concentration as P1 treatment. After 30 days from sowing, growth and development parameters as well as chemical composition of shoots and roots were assessed. 11 was verified that the partial supply of A1 to half of the roots significantly shifted the root system grow1h to the other half without A1, independently of the P concentration on the other half the shoot of the plants grown with high P (230 ?mol/L) in half or the whole root system was greater than the low P treatments (20 ?mol/L), which was even greater than the shoot of plants grown with AI in both sides of the system. There was an increase in P concentration in roots under A1 stress, which increased with A1 concentration in the nutrient solution. This increase was even higher in the roots that were under A1 stress in one side of the system while high P was applied to the other half Even though, A1 tolerance, assessed by the growth of root under AI stress, was not significantly changed. However, in P2/AL1 treatment A1 toxicity symptoms were alleviated in AL1 roots, when compared to roots grown in AL1/AL1 or P1/AL1 treatment. Inner cycling of P in lablab seemed to be efficient, demonstrating the importance of the insertion of this specie in crop rotation on acid soils, by the possibility of greater redistribution of P fertilizer applied locally in soil

ASSUNTO(S)

hidroponia metabolismo mineral adubação verde

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