Edemar Joaquim Corazza

Sensibilidade do clorofilômetro para diagnóstico nutricional de nitrogênio no milho

A obtencao de altas produtividades de milho (Zea mays L.) torna-se dificil, dentre outros fatores, pela complexa quantificacao dos requerimentos de nitrogenio (N) da cultura do milho ao longo do seu ciclo, o que dificulta o seu dimensionamento, ainda mais, considerando a variada capacidade de suprimento de N em solos brasileiros. Nesse sentido, os teores relativos de clorofila surgem como uma opcao para o manejo do N. Objetivou-se, neste estudo avaliar a sensibilidade do clorofilometro em indicar o estado nutricional do milho em resposta ao N, em solos com teores de argila contrastantes e sob diferentes condicoes de suprimento de N. Para isso, foram realizados experimentos em condicoes controladas e de lavoura. Em condicoes controladas, foram testados tres solos com teores de argila contrastantes e cinco doses de N, sendo avaliados, aos 55 dias apos a emergencia (estadio previo ao VT), os teores relativos de clorofila, de N foliar e a producao de materia seca da parte aerea. Em condicoes de lavoura foram avaliados seis tratamentos, resultantes da combinacao de tres doses de nitrogenio em cobertura, na presenca e ausencia de calcario, sendo a maior dose de N correspondente a condicao na qual nao haveria limitacao de disponibilidade quanto ao suprimento do nutriente. A nutricao nitrogenada foi monitorada semanalmente com uso do clorofilometro. Foram avaliados tambem os teores de N na folha e no grao, o N mineral no solo, a materia seca da parte aerea e a produtividade de graos. Os resultados permitiram concluir que ha sensibilidade do clorofilometro em detectar diferencas no estado nutricional do milho em resposta a diferentes caracteristicas de solo e de suprimento de N, servindo como indicador da necessidade de adubacao nitrogenada de cobertura.

Clorofilômetro no ajuste da adubação nitrogenada em cobertura para o milho de alta produtividade

The evaluation of the chlorophyll relative content in the leaves provides an indirect measure of the plants nutritional status and can help farmers to adjust the quantity of nitrogen (N) to be applied as top dressing fertilization for corn. The aim of this work was to validate the use of chlorophyll meter for detection and correction of N deficiency during the crop vegetative growth. The experiment was carried out in plots under commercial crop conditions and the corn nutritional status was monitored weekly with the chlorophyll meter. Six treatments of top dressing N included a check (0kg ha-1) and four doses (45, 90, 135 and 180kg ha-1), considering the nitrogen sufficiency index (NSI) of 0.95 monitored with the chlorophyll meter based on a reference treatment (500kg ha-1). The chlorophyll meter indicated top dress N application for corn up to 180kg ha-1, exceeding the quantities required to maximize the technical (144kg ha-1) or economic (105kg ha-1) efficiency. The establishment of reference plots makes the chlorophyll meter an useful indicator of the need of N top dressing during the corn growth, however, the use of the 0,95 NSI value throughout the crop cycle may not be the most appropriate strategy.

Variabilidade de nutrientes em plantas de milho cultivado em talhão manejado homogeneamente

The knowledge of variability of plant nutrition and grain productivity in cultivated areas may provide important information for rational use of fertilizers and soil amendments. The objective of this case study was to determine the corn plant mineral nutrition variability through the fractionation of a commercial grown corn field into small management cells. The study was carried out at the farm Alto Alegre in Planaltina, Goias State, Brazil, on a Typic Dystrarox soil in 373 ha area of corn crop during the crop year of 2003/2004. After outlining a polygon of area it was divided into 80 management cells of 4 ha each. The leaf sampling followed a diagonal with twelve points to constitute a representative composite sample within each cell. The leaf samples were analyzed for macro and micronutrients. Yield for each cell was obtained through grain yield monitor of a combine harvester equipped with GPS. For data variability analysis descriptive statistic parameters were considered. Test for correlation coefficients were accomplished considering the significance level of 5%. The variability of nutrient content in the diagnostic leaves were considered low for N, P, K, S and Mg content; and medium for Ca, Cu, Fe, Mn e Zn. Yield variability showed yield differences among cells. Linear correlation coefficients between nutrient content and grain yield were significant and negative for Cu, Mn and Zn.