Jandeilson Alves de Arruda

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.

Amostragem para avaliação da fertilidade do solo em função do instrumento de coleta das amostras e de tipos de preparo do solo

The measures of the average and variability of soil fertility indexes can vary with the sampling tool and soil tillage type. Soil sampling methods must be developed that are more reliable to represent the real conditions of soil fertility. This study aimed at an evaluation of the effects of the cutting shovel and hand auger on measures of average and variability of the soil fertility index (a) under no-tillage (NT) and conventional tillage (CT), (b) to estimate the minimum number of simple samples to form a composite sample and (c) to test the hypothesis that the arithmetic average of simple samples is equal to the result of the chemical analysis of the composite sample. Chromic Luvisol samples were collected in a control experiment of soil tillage type, planted with corn. In a 81 m2 plot under NT 48 simple soil samples were collected, 24 with a cutting shovel (perpendicularly to the furrow and in-between two furrows) and 24 with auger hole, in controlled sampling (four samples collected in the planting furrow, 8 to 10 cm away from the furrow and 12 in-between the furrows), close to the points of sampling with the cutting shovel. The procedure was repeated in a second plot under CT. Composite samples of different numbers of simple samples (4, 8, 12, 16 and 24 simple samples/composite samples), with three repetitions were prepared for each combination of soil tillage type - collection tool. The pH and the contents of P, K+ Ca2+, Mg2+ and organic matter (OM) were determined in all simple and composite samples. The variability of the evaluated characteristics in samples collected with auger hole was greater than with the cutting shovel, independent of the soil tillage type. For both collection tools, the decreasing order of variability was: P > Mg2+ > K + > Ca2+ > OM > pH. The medium fertility of a field under NT or under CT after the crop and before subsequent soil preparation can be evaluated with the auger hole, substituting the cutting shovel, if the composite sample consists of 17 % of simple samples collected in the planting furrow, 33 % at a distance of 10 cm from the furrow and 50 % in the middle between the furrows. The mean fertility of a field under NT or CT after the crop and before the subsequent soil preparation, evaluated by the chemical analysis of the composite sample, is similar to that evaluated by the arithmetic average of the chemical analyses of the simple samples collected with cutting shovel or with auger hole in a controlled manner, as used here. In general, a minimum of eight simple samples collected with cutting shovel or hand auger would be enough to form a representative composite sample for evaluation of the soil fertility of a unit of seemingly homogeneous sampling. However, the higher the number of collected simple samples, the more reliable or accurate is the medium fertility estimate.

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.

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.

Produtividade e acúmulo de nitrato nos frutos de abobrinha em função da adubação nitrogenada

Despite Zucchini nutritional and commercial importance, few studies have been carried out with the nitrogen fertilization of the culture. The objective of this research was to evaluate the zucchini yield (cv. Caserta) and nitrate accumulation in the fruits as a function of the nitrogen fertilization. The experiment was set in a randomized block design with five rates of mineral N (0; 50; 100; 200 and 400 kg ha-1), with four replications. The number of fruits per plant, average fruit mass, fruit yield and nitrate accumulation in the fruits were significantly affected (p<0.01) by N rates. The maximum number of fruits per plant (7.7 units), mean fruit weight (240 g fruit-1) and fruit yield (29.88 t ha-1) were obtained with 323, 265 and 331 kg ha-1 of N, respectively. The maximum economical efficiency rate of N for the culture of the zucchini was 322 kg ha-1, resulting in a fruit yield of 29.86 t ha-1. The nitrate content in the zucchini fruits presented linear increment as a function of N rates. At the highest N rate, the nitrate content in the fruit fresh matter was 162 mg kg-1. This nitrate contents value does not represent risk for human health.

Amostragem para avaliação da fertilidade do solo em função da variabilidade de suas características químicas

The aim of this study was to evaluate the variability of chemical attributes of soil, to define the number of single samples required to form a composite sample and to evaluate if the mean fertility values obtained from the composite sample is the same as obtained from the arithmetic mean of single samples. Three series of sampling, each one with 36 samples collected in an Oxisol, were carried out. Samples of the first series were taken 15 m apart from each other, the second one 2.5 m, and the third one 0.42 m. Composite samples were formulated with samples of first series by a homogenous mixture of 4, 8, 14, 20, 28 e 36 single samples, with three replications. The variability of soil chemical attributes did not vary when the area size decreased from 8,100 m2 to 225 m2. Doses of lime and fertilizer may have the same recommendation, independently if soil fertility was evaluated by chemical analysis of a composite sample or obtained from the arithmetic mean of single sampling. At least eight single samples were necessary to compose a representative sample of the area.

Formas de potássio em solos representativos do Estado da Paraíba

Os solos do Estado da Paraiba apresentam grande diversidade de caracteristicas quimicas, fisicas e mineralogicas, acarretando em variacoes nos teores e formas de K disponiveis no solo. Objetivou-se com este trabalho avaliar os teores de K nao-trocavel, K trocavel e K soluvel em doze solos do Estado da Paraiba, na ausencia e na presenca de fertilizacao potassica, e correlaciona-los com as caracteristicas quimicas, fisicas e mineralogicas desses solos. O estudo constou de 60 tratamentos, sendo 12 solos e cinco doses de K (0; 50; 100; 200 e 300 mg dm-3) na forma de cloreto de potassio, com tres repeticoes. Apos receberem os tratamentos, os solos foram incubados por um periodo de 21 dias, e em seguida, uma sub-amostra de 0,2 dm3 de cada solo foi retirada para determinacao dos teores de K nao-trocavel, K trocavel e K soluvel. Os solos formados sob clima semiarido foram os solos que apresentaram as maiores reservas de K nao-trocavel. Solos com maior proporcao de mica e minerais do tipo 2:1 na fracao argila apresentaram os maiores teores de K nao-trocavel e K trocavel. Independente do grupo de solos, os teores de silte apresentaram correlacao elevada com os teores de K nao-trocavel e de K trocavel. Nos solos mais desenvolvidos, nao foi evidenciada fixacao de K proveniente do fertilizante. Porem, nos solos menos desenvolvidos, a fixacao de K ficou evidenciada pela pequena quantidade de K recuperada pelo extrator acetato de amonio nos solos mais argilosos e, principalmente, naqueles com predominância de minerais do tipo 2:1 e mica.