Sensibilidade do clorofilômetro para diagnóstico nutricional de nitrogênio no milho

Abstract

RESUMOA obtenção de altas produtividades de milho (Zea mays L.) torna-se difícil, dentre outros fatores, pela complexa quantificação dos requerimentos de nitrogênio (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 opção para o manejo do N. Objetivou-se, neste estudo avaliar a sensibilidade do clorofilômetro em indicar o estado nutricional do milho em resposta ao N, em solos com teores de argila contrastantes e sob diferentes condições de suprimento de N. Para isso, foram realizados experimentos em condições controladas e de lavoura. Em condições controladas, foram testados três solos com teores de argila contrastantes e cinco doses de N, sendo avaliados, aos 55 dias após a emergência (estádio prévio ao VT), os teores relativos de clorofila, de N foliar e a produção de matéria seca da parte aérea. Em condições de lavoura foram avaliados seis tratamentos, resultantes da combinação de três doses de nitrogênio em cobertura, na presença e ausência de calcário, sendo a maior dose de N correspondente à condição na qual não haveria limitação de disponibilidade quanto ao suprimento do nutriente. A nutrição nitrogenada foi monitorada semanalmente com uso do clorofilômetro. Foram avaliados também os teores de N na folha e no grão, o N mineral no solo, a matéria seca da parte aérea e a produtividade de grãos. Os resultados permitiram concluir que há sensibilidade do clorofilômetro em detectar diferenças no estado nutricional do milho em resposta a diferentes características de solo e de suprimento de N, servindo como indicador da necessidade de adubação nitrogenada de cobertura. Termos para indexação: Adubação nitrogenada, SPAD, Zea mays. ABSTRACTHigh corn yields are conditioned by the different factors involved in the quantification of nitrogen requirements for the crop throughout its cycle, which becomes difficult considering the varying capacity of Brazilian soils to supply N. In this sense, the relative contents of chlorophyll are a tool which helps to improve soil N management. The study aimed to evaluate the sensitivity of the chlorophyll meter to predict the nutrient status of corn in response to N applied in the soil with contracting clay contents and under different conditions of N supply. To that end, experiments were carried out under both controlled and field conditions. Under controlled conditions, three soils with contracting clay contents and five doses of N were tested. 55 days after emergence (before the VT period), the relative contents of chlorophyll, leaf N and the weight of the dry matter of the shoot were evaluated. Under crop conditions, six treatments, resulting from the combination of three doses of nitrogen topdressing, in the presence and absence of limestone, were evaluated, the highest dose of N corresponding to the ideal condition of N supply for corn. Nitrogen nutrition was monitored weekly with a chlorophyll...

Chlorophyll relative index for diagnosing nitrogen status in corn hybrids

“…In this particular case, the organ in consideration is the leaf, being therefore incorporated into the membranes of the thylakoids as reaction centers called components of photo systems II and I (Taiz and Zeiger, 2013). Mean values of CRIL 03 V 5 (46.87) and CRIL 05 V 5 (55.69) were to be very close to that one obtained by Hurtado et al (2010) at V 4 to V 5 phenological stages, causing the maize crop to reach yields of 11.300 kg ha -1 found by such scientists, as well as by the current research (roughly corresponding to 11.684 kg ha -1 ). However, either CRIL 05 V 5 or mean yields were similar to the outcomes obtained by these authors.…”

“…Average values obtained for the hybrids P30R50 and AG8025 was higher and similar to a CRI of 45.4% as cited by Argenta et al (2003) at the stage V 3 to V 4 , indicating that the content of N in the plant is quite adequate. The reading CRIL 03 V 4 did not correlate with the N content in the leaf, as well as with yield (Table 3), corroborating with Argenta et al (2002) and Hurtado et al (2010).…”

“…CRIL 03 V 5 correlated positively with leaf N content and yield, showing coefficients equivalent to 0.42 ** and 0.36 * , respectively, as opposed to the CRIL 05 V 5 (Table 3). Similarly, Hurtado et al (2010) observed a positive correlation between CRIV 4 -V 5 with yield.…”

“…The estimated value for the hybrid P30R50 was superior to the mean value of 59.7, a fact that was evidenced also by Hurtado et al (2010) between V 7 and V 8 .The correlation of CRIL 07 V 7 with leaf N content and yield was of 0.39 ** and 0.33 ** , respectively, being therefore quite below the one for CRIL 05 V 9 (Table 3).…”

Spacing, population density and nitrogen fertilization in corn grown in an Oxisoil

“…Amaral Filho et al (2005) also observed increases in leaf N content and in estimates of chlorophyll content and yield. Nevertheless, Hurtado et al (2010) evaluated the nutritional status of corn using a chlorophyll meter and found a need for up to 180 kg ha -1 N, exceeding the amount required to achieve maximum yield with 150 kg ha -1 (Souza et al, 2011).…”