http://dx.doi.org/10.5007/2175-7925.2009v22n4p225O objetivo deste trabalho foi caracterizar quimicamente os frutos de biri-biri (Averrhoa bilimbi L.) coletados em diferentes estádios de maturação. Foram avaliadas as seguintes características morfométricas e químicas do fruto: peso, número de sementes, comprimento, largura maior e menor, pH, sόlidos solúveis totais, acidez titulável e vitamina C. Os teores de sόlidos solúveis totais variaram de 2,35 a 3,23o. Brix, sendo maiores em frutas de biri-biri maduras, assim como os valores de acidez, que variam de 1,15 a 1,66g/100g-1, em frutos verdes e maduros, respectivamente. Entretanto os níveis de vitamina C foram mais elevados nos frutos verdes, porém não apresentaram diferença significativa entre os três níveis de maturação avaliados.
Alterações no arranjo de plantas na cultura do milho permitem maiores populações e exigem adequações nas doses de nitrogênio fornecidas. Objetivou-se avaliar o efeito de doses de nitrogênio em cobertura no desenvolvimento e desempenho produtivo do milho de segunda safra em diferentes densidades de plantas. O experimento foi conduzido em duas safras com o híbrido AG9010 YG, em blocos casualizados e parcelas subdivididas, com quatro repetições. Nas parcelas, alocaram-se as populações de plantas (40, 60, 80 e 100 mil plantas ha-1) em espaçamento de 0,45 m entre linhas e, nas subparcelas, as doses de nitrogênio (ureia 45%) em cobertura (0, 50, 100, 150 kg ha-1). Foram avaliados o diâmetro de colmo, a altura de inserção de espiga e de plantas, a massa da folha seca, o teor de nitrogênio na folha e nos grãos e a produtividade de grãos. A produtividade de grãos é influenciada pela interação entre população de plantas e doses de N em cobertura. A população de 80.000 plantas ha-1 aliada à aplicação de 120 kg ha-1 de nitrogênio cobertura proporciona maior rendimento.
The objective of this work was to evaluate the influence of isolated or combined roots and straw of black oat and wheat, as previous crops in autumn/winter, on the performance of soybean in succession. The experiment was carried out in the 2017/2018 and 2018/2019 crop seasons in a randomized complete block design, with four replicates. The following seven treatments were applied in the autumn/winter of 2017 and 2018, before soybean planting: fallow; straw of black oat or wheat, distributed on plots kept under fallow during autumn/winter, without roots; plots only with roots of black oat or wheat, without straw; and plots with straw and roots of black oat or wheat. Soybean crop performance was estimated using the following variables: plant density, leaf area index, soil plant analysis development (SPAD) index, shoot dry matter, grain yield, and yield components. In comparison with fallow, the cultivation of black oat or wheat, as previous crops during the autumn/winter, increases soybean grain yield. The impact of the roots of black oat or wheat on soybean yield is similar to that of straw. Soybean agronomic performance is improved in the combined presence of roots and straw of black oat or wheat.
Second-crop maize-ruzigrass (Urochloa ruziziensis) intercropping, nitrogen (N) fertilization, and high maize plant densities enhance biomass production and N cycling, which may favor soybean growth and yield in the following season. This study aimed to assess the effects of second-crop maize-ruzigrass intercropping, N top dressing, and maize plant density on straw production in autumn/winter, N cycling, and agronomic performance of soybean crops grown in succession. Field experiments were installed in the 2018/2019 and 2019/2020 seasons using a randomized complete block design with split-split plots and four replications. The following factors were investigated: cropping system (sole maize and maize intercropped with ruzigrass), N top dressing (0 and 80 kg ha-1), and maize plant density (40, 60, 80, and 100 thousand plants ha-1). Maize-ruzigrass intercropping improved straw yield (2,365 kg ha-1) and N cycling (50 kg ha-1), and increased soybean yield in the following season (232 kg ha-1). N fertilization of maize increased soybean grain yield by 180 kg ha-1. Maize plant density did not influence the performance of succeeding soybean crops, regardless of the growing season.
Topdressing nitrogen (N) rates may alter the second-crop corn performance, and this response may vary if the corn is grown single or intercropped with grass or leguminous species. This study aimed to evaluate the effect of topdressing N rates on the growth and productive performance of second-crop corn grown single or intercropped with ruzigrass (Urochloa ruziziensis) or showy rattlebox (Crotalaria spectabilis). The experiment was carried out in a randomized block design, with a split-plot arrangement and four replications. The plots consisted of corn grown single or intercropped with ruzigrass or showy rattlebox, while the subplots consisted of N rates (0, 60, 120, 180 and 240 kg ha-1). The evaluated variables were: SPAD index at R1; normalized difference vegetation index at V4 and V7; leaf area at R1; leaf and total corn dry mass at R1; grain and total corn dry mass at R6; number of ears per plant and grains per ear; 1,000-grain mass; and grain yield. In the absence of N fertilization and with topdressing of 60 kg ha-1 of N, the intercropping with U. ruziziensis reduces the growth and productive performance of second-crop corn. The topdressing N fertilization for second-crop corn intercropped with U. ruziziensis minimizes the forage competition on corn growth and provides a productive performance similar to monocropping from 120 kg ha-1 of N. The intercropping with C. spectabilis does not change the corn growth and productive performance, as well as the response to the topdressing N rates, when compared to monocropping, in the second crop cultivation.
An appropriate combination of plant density with nitrogen (N) fertilization can optimize corn growth and increase grain yields. This study evaluated the effects of nitrogen topdressing rates and plant density levels on the agronomic performance of corn. The early hybrid DKB 240 YG, with high yield potential and stability, was evaluated in two summer crops in Mauá da Serra, Paraná (950 m asl), in a Cfb climate, on a Rhodic Eutrudox. The experiment was arranged in randomized complete blocks and subdivided plots with four replications. The plant densities (60,000; 75,000; 90,000 and 105,000 plants ha-1) were assessed in the plots and the nitrogen (ammonium nitrate 32% N) topdressing rates (0, 60, 120, 180 and 240 kg ha-1) in the subplots. The stem diameter, plant height, ear insertion height and grain yield were evaluated. The stem diameter, plant height, ear insertion height and grain yield were influenced by the interaction between plant density and nitrogen topdressing under the tested high-altitude edaphoclimatic conditions. The stem diameter of corn plants decreased due to the increase in plant density whereas nitrogen topdressing attenuated this reduction. Maximum plant height was observed at a density of 75,000 plants ha-1 associated with a topdressing of 169 kg ha-1 of N, and highest ear insertion at 60,000 plants ha-1 and 168 kg ha-1 of N. Corn yield was highest at a density of 105,000 plants ha-1 associated with a topdressing of 185 kg N ha-1 of N.
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