RESUMO
In the conilon coffee tree, the stress caused by high light can reduce the photosynthetic rate, limit the development and also reduce the yield of beans. Considering that the quality of a sunscreen spray can influence photosynthetic performance, the goal was to understand the iterations between the quality of the spray and the variation of the chlorophyll a fluorescence when applying sunscreen on conilon coffee trees. The parameters coverage, volumetric median diameter, density, droplet deposition, and the variation of the chlorophyll a fluorescence were evaluated. The nozzle and application rate factors did not show direct effects in the physiological responses of the plants. Plants with no sunscreen application showed high values of energy dissipation flux. The photosystem II (PSII) performance index and PSII photochemical maximum efficiency indicate that the use of sunscreen for plants promotes better performance of photosynthetic activity and that it provides photoprotection against luminous stress, regardless of the application rate and spraying nozzle; however, we recommend using the application rate of 100 L ha-1 and the cone jet nozzle type because they provide lower risks of product loss due to runoff.
RESUMO
Growth regulators have been widely employed as maturation inducers in the sugarcane crop, as an agricultural strategy. However, the response of varieties to the use of these compounds has been poorly studied, mainly in cerrado (savannah-like biome) areas occupied by the crop. This study was carried out to examine the effects of trinexapac-ethyl on important morphological characteristics of sugarcane varieties. The experiment was set up as a randomized block design with a 4 × 2 factorial arrangement consisting of four varieties (RB83-5054, SP80-1816, RB96-6928, and RB85-5156) associated or unassociated with application of trinexapac-ethyl (375 g L1 of the a.i. ha1), with four replicates. The ripener was applied at 126, 178, and 228 days after planting (DAP) the first-cycle sugarcane, using the dose of 125 g L1 a.i. ha1 per application. Upon harvest, which occurred at 243 DAP, we determined the number of stalks per meter, weight of 30 stalks without top, internode length, number of internodes per stalk, and yield of sugarcane stalks. Ripener application increased the number of stalks in varieties RB96-6928 and RB83-5054 and the weight of 30 stalks in varieties RB96-6928 and RB83-5054 and SP80-1816; reduced internode length in varieties RB85-5156 and RB83-5054; and increased stalk yield per hectare in varieties RB96-6928 and RB83-5054, but did not increase the number of internodes per stalk in any of the tested varieties. The variables number of stalks, stalk weight, internode length, and stalk yield responded in a genotype-dependent manner to the application of trinexapac-ethyl.
O uso de reguladores de crescimento como indutores da maturação em cana-de-açúcar tem sido uma prática agrícola bastante empregada. Entretanto, a resposta das variedades à utilização desses compostos tem sido pouco estudada, principalmente em áreas de cerrado ocupadas pela cultura. O objetivo deste estudo foi avaliar os efeitos do trinexapac-ethyl em características morfológicas importantes para a produtividade de variedades de cana-de-açúcar. O delineamento experimental utilizado foi o de blocos casualizados em esquema fatorial 4 x 2, sendo quatro variedades (RB83-5054, SP80-1816, RB96-6928 e RB85-5156), combinadas com e sem aplicação de trinexapac-ethyl (375 g L-1 do i.a. ha-1) e quatro repetições. A aplicação do maturador ocorreu aos 126, 178 e 228 dias após o plantio (DAP) da cana planta, com dose de 125 g L-1 i.a. ha-1 por vez. Por ocasião da colheita, realizada aos 243 DAP, foram avaliados o número de colmos por metro, massa de 30 colmos sem ponteiro, comprimento de entrenós, número de entrenós por colmo e produtividade de colmos de cana-de-açúcar. Verificou-se que a aplicação do maturador incrementou o número de colmos para as variedades RB96-6928 e RB83-5054, a massa de 30 colmos para as variedades RB96-6928 e RB83-5054 e SP80-1816, maior redução no comprimento de entrenós para as variedades RB85-5156 e RB83-5054 e maior aumento na produção de colmos por hectare para as variedades RB96-6928 e RB83-5054, mas não aumentou o número de entrenós por colmo nas variedades testadas. A resposta das variáveis: número de colmos, massa de colmos, comprimento dos entrenós e produtividade de colmos à aplicação do trinexapac-ethyl mostrou-se genótipo dependente.
