Representativeness of Scholander chamber measurements as a function of time after leaf removal.

The objectives of the study were to determine the maximum tolerable period between leaf removal from a plant and the determination of leaf water potential (Ψ l ), and to evaluate different ways of packing leaves after their removal from a plant (LR). Two experiments (Exp) were conducted in a randomized complete block design with four replicates, using bean, maize, and soybean crops. The predawn leaf water potential (Ψ PD ) (Exp1) and the minimum leaf water potential (Ψ min ) (Exp1 and Exp2) were determined. The maximum tolerable period between LR varied among species, ranging from 80 to 90 min for bean and soybean, and from 40 to 60 min for maize. A box with low interior air temperature and capable of blocking the effect of solar radiation reduced variation in leaf water potential. These results indicate that the determination of the Ψ l in bean, soybean, and maize crops does not need to be carried out immediately after leaf removal.

Interception of solar radiation by the productive structures of spring canola hybrids / Interceptação de radiação solar pelas estruturas reprodutivas de híbridos de canola de primavera

ABSTRACT: The objective of this study was to adjust parameters related to the interception of photosynthetically active radiation (PAR) by reproductive structures of spring canola, with different nitrogen levels and hybrids. Two field experiments were conducted, being one with different sowing dates and hybrids (Hyola 61 and Hyola 432) and another with doses of 10, 20, 40, 80, 160kg ha-1 of N, applied in top dressing. They were conducted in Passo Fundo and Coxilha, RS, Brazil, in 2011 and 2014, respectively.The evaluated variables were: area index of reproductive structures, interception efficiency and extinction coefficient of these structures for PAR. PAR interception increased by increasing the reproductive structures volume. Interception efficiency of PAR by reproductive structures ranged from 45 to 80%. It was higher in the Hyola 61 hybrid and at the highest dose of N. The extinction coefficient of reproductive structures for PAR was 0.44 in non-limiting doses of N.

RESUMO: O objetivo deste estudo foi parametrizar a interceptação de radiação fotossinteticamente ativa (RFA) pelas estruturas reprodutivas de canola de primavera, em função de doses de nitrogênio e híbridos. Dois experimentos de campo foram conduzidos, sendo um com diferentes híbridos (Hyola 61 e Hyola 432) e outro com doses de N de 10, 20, 40, 80, 160kg ha-1, aplicadas em cobertura. Eles foram conduzidos em Passo Fundo e Coxilha, RS, Brasil, em 2011 e 2014, respectivamente. As variáveis avaliadas foram: índice de área de estruturas reprodutivas, eficiência de interceptação de RFA e coeficiente de extinção dessas estruturas. A interceptação de RFA aumentou com a elevação do volume das estruturas reprodutivas. A eficiência de interceptação de RFA pelas estruturas reprodutivas variou de 45 a 80%, sendo maior no híbrido Hyola 61 e na maior dose de N aplicado. O coeficiente de extinção de estruturas reprodutivas foi de 0,44 em doses não limitantes de N.