Análises fisiológicas em cana-de-açúcar em resposta a diferentes manejos de adubação.

Abstract

Sugarcane (Saccharum spp.) It is a species of plant that belongs to the Poaceae family, a perennial culture that presents erect and slightly decumbent growth in its initial phase, being classified as monocot. As it is the main raw material for the production of alcohol, sugar cachaça and many other derivatives, this culture becomes one of the most important in the tropical world, in addition to generating a large number of direct and indirect jobs. The objective of this work was to evaluate gas exchange and chlorophyll levels at different times of fertilizer application in sugarcane. The work was carried out at the Experimental Farm Chã de Jardim, belonging to the Center for Agrarian Sciences, of the Federal University of Paraíba, in the municipality of Areia-PB. The design used was randomized blocks (DBC), in a 2x (4+1) factorial scheme, with 2 sugarcane genotypes (RB867515 and RB041443) x 4 times of application of the products (0 + 90 + 120 DAP, 0 + 90 + 150 DAP, 0 + 120 + 180 DAP, 0 + 90 DAP + period in which the leaf +1 dries completely) plus the absolute control, referring to the absence of application of the products, thus containing 10 treatments with 4 repetitions and a total of 40 experimental units. To collect gas exchange data, the following measurements were taken: photosynthesis rate (A) (µmol m-2 s-1), CO2 internal concentration (Ci) (µmol m-2 s-1), transpiration (E ) (mmol of H2O m-2 s-1), stomatal conductance (gs) (mol m-2 s-1), instantaneous water use efficiency (EiUA - W/E) calculated relating it to net photosynthesis with transpiration [(µmol m-2 s-1) / (mmol of H2O m-2 s-1), and the instantaneous carboxylation efficiency (EiC - A/Ci) [(µmol m-2 s-1)/ (µmol m-2 s-1)]. The fluorescence of chlorophyll “a” was measured and the following parameters determined: minimum fluorescence of the dark-adapted leaf (FO), maximum fluorescence of the dark adapted leaf (Fm), maximum variable fluorescence (Fv = Fm – FO), quantum efficiency FSII potential (Fv/Fm) and the Fv/FO. Chlorophyll a + b. The results indicate that the use of fertilizers at different application times and sugarcane genotypes promoted better crop development. Fertilizer application as a function of different application times and sugarcane genotypes showed better responses for maximum fluorescence, variable fluorescence, variable fluorescence ratio and initial fluorescence (Fv /F0), maximum quantum yield of photosystem II ( Fv/Fm), Chlorophyll “a”, chlorophyll “b” and total chlorophyll. The use of fertilizers at different times of application in sugarcane promoted a higher concentration of CO2, approaching results found in the literature.