Raunira da Costa Araújo

Nitrate production and accumulation in lettuce as affected by mineral Nitrogen supply and organic fertilization

Lettuce is one of the leading vegetables in Brazil. However, studies concerning its fertilization for the Northeastern region of the country are still scarce. This work was carried out to evaluate the effects of mineral Nitrogen supply and organic fertilization on the production and nitrate accumulation in lettuce, cultivar Elba, in the semi-arid zone of Paraiba, Brazil. A randomized block design, with four replications, was used to test five doses of cattle manure (30; 60; 90; 120, and 150 t ha-1), five doses of N supplied as urea (30; 60; 90; 120, and 150 kg ha-1), and a control without fertilization. Along with mineral N, the other nutrients were also supplied using mineral sources. No additional nutrients were supplied where organic fertilization was used. Lettuce yield was significantly higher when organic fertilization was used, compared to the mineral nutrient supply. Taking into account most of the fertilization doses recommended for growing lettuce in the Brazilian Northeastern States, N mineral fertilization in sandy soils with low organic matter contents can be fully replaced by organic fertilization with cattle manure. Plant total (PTY) and commercial yield (PCY) as affected by the mineral N supply fitted into a quadratic model, in which the doses 94.5 and 95.7 kg ha-1 corresponded to respectively the highest PTY (381.9 g plant-1) and PCY (321.6 g plant-1). Where organic fertilization was used, PTY and PCY fitted into a linear model. Therefore, the highest PTY (523.9 g plant-1) and PCY (449.48 g plant-1) were observed at the highest manure doses. Nitrate content on roots, stems, and leaves increased linearly with Nitrogen and manure application. In roots, the nitrate content (mg kg-1 of fresh matter) reached 93.96 (N mineral (Nm)) and 65.09 (organic fertilization (OF)); in stems, 183.45 (Nm) and 98.22 (OF); and in leaves, 121.98 (Nm) and 75.62 (OF). The maximum nitrate content observed in leaves was far below the risk level for human health.

Absorção e distribuição de chumbo em plantas devetiver, jureminha e algaroba

SUMMARY : ABSORPTION AND DISTRIBUTION OF LEAD IN VETIVER,MIMOSA AND MESQUITE PLANTS The use of plants for phytoremediation of metal-contaminated areas is an emergingtechnology, and studies concerning heavy metal tolerance, absorption and distribution inplants are essential for the success of such programs. This study was carried out to evaluatethe tolerance, absorption and distribution of lead (Pb) in vetiver grass [ Vetiveria zizanioides(L.) Nash], mimosa [ Desmanthus virgatus (L.) Willd] and mesquite trees [ Prosopis juliflora(SW) DC] subjected to increasing lead doses in solution. The experiment was conductedunder a screenhouse, at the DSER/CCA/UFPB, Areia-PB, Brazil. The species were grownin nutrient solution containing increasing Pb levels (0, 50, 100 and 200 mg L -1 ) during a 45-day exposure period. An entirely randomized split-plot design was used with threereplicates. The main plot was represented by the plant species and the subplot by Pblevels. The increased Pb levels caused significant reductions of dry mass of the root, shootand whole plant (root + shoot) in the three species under study. Based on critical toxicitylevels, the tolerance of vetiver to Pb contamination was higher than in the other species. Invetiver and mesquite plants, the roots were the component most sensitive to Pbcontamination, whereas a similar response to Pb by all plant components was observed formimosa. Total Pb concentrations and content in plant compartments were significantlyaffected by the increasing Pb levels in solution, and a higher accumulation of this elementwas observed in the roots of the three species under study. The highest Pb concentrationand content were found in all compartments of vetiver, which suggests a high potential ofthis grass for phytoremediation of Pb-contaminated areas.Index terms: pollution, heavy metal, phytotoxicity, tolerance, phytoremediation.

Crescimento e produção do maracujazeiro-amarelo em resposta à nutrição potássica

Avaliaram-se os efeitos da nutricao potassica sobre o crescimento e a producao do maracujazeiro-amarelo (Passiflora edulis Sims f. flavicarpa Deg.) cultivado em solucao nutritiva. O experimento foi conduzido em casa de vegetacao na Universidade Federal de Vicosa, Minas Gerais, de janeiro a outubro de 1999, utilizando-se do delineamento experimental em blocos casualizados, com cinco tratamentos e quatro repeticoes. Os tratamentos foram constituidos por cinco doses de K (1; 2; 4; 6 e 8 mmol/L), na solucao nutritiva de Hoagland e Arnon, modificada. A unidade experimental foi constituida por um vaso plastico de 20 L, contendo uma planta/vaso, tendo como substrato areia lavada. O sistema hidroponico utilizado foi do tipo circulante, e as readicoes dos nutrientes foram baseadas na condutividade eletrica da solucao e no teor de K. O aumento da concentracao de K na solucao nutritiva resultou em aumentos lineares no comprimento dos ramos, vingamento e diâmetro equatorial de frutos. A producao de frutos por planta e o peso medio de frutos aumentaram com o aumento da concentracao de K na solucao, com pontos de maximo correspondente a 6,43 e 6,24 mmol/L de K, respectivamente. O tempo transcorrido entre a fecundacao da flor e a maturacao do fruto foi reduzido com o aumento da concentracao de K na solucao nutritiva. O aumento da concentracao de K na solucao nutritiva nao exerceu efeito sobre o comprimento medio dos frutos de maracujazeiro-amarelo.

Doses de nitrogênio no acúmulo de nitrato e na produção da alface em hidroponia

Lettuce production in hydroponic system presents growing expansion in Brazil, but still there are problems of quality and risk of nitrate accumulation. This work was carried out to evaluate the lettuce production and nitrate accumulation in hydroponic system depending on the increasing levels of nitrogen in the nutrient solution. The experiment was conducted in greenhouse of the Universidade Federal da Paraiba, Brazil. The lettuce plants were grown in nutrient solution containing increasing levels of N (11, 13, 15, 17, 19 and 21 mmol L-1) during a 25-day period. An entirely randomized design with four replications was used. Plant total yield (PTT), plant commercial yield (PCM) and nitrate contents in the fresh matter of roots, stems and leaves of the lettuce were evaluated. There were no significant effects of increasing levels of N in nutrient solution on PTT and PCM, average values of 357.3 and 352.5 g/plant being observed, respectively. The increased levels of N in nutrient solution increased linearly nitrate content on all lettuce parts. The nitrate content reached 659, 623 and 615 mg/kg in the fresh matter of roots, stems and leaves, respectively, at the highest N level. Nevertheless, the maximum nitrate content observed in leaves was far below the risk level for human health.