Polímeros hidrorretentores na produção e no plantio de mudas de Enterolobium contortisiliquum (Vell.) Morong e Paubrasilia echinata Lam

Abstract

Agriculture is the activity that most demands fresh water from the planet, largely due to its inefficient use during the irrigation process, generating great waste. In forest nurseries, irrigation is performed in an empirical way, causing significant waste. Hydroretentive polymers have the potential to reduce the amount of water used in irrigation, but there is a lack of studies in the production of forest species, besides the variation in characteristics of the commercial products available. The study aimed to evaluate the use of water-retaining polymers in the production and planting of seedlings of Enterolobium contortisiliquum and Paubrasilia echinata, analyzing morphological characteristics and survival. The water uptake of three water-retaining polymers: Hydroplan®, Forth® and UPDT® was also evaluated, as well as the effect of the electrical conductivity of water with potassium chloride and calcium chloride salts on their uptake, and the influence of polymers on the physical properties of the substrate. Adopting an entirely randomized design, three independent experiments were conducted aiming at seedling production, using three doses of the hydroretentative polymer Hydroplan® (2,0; 4,0 and 6,0 g L-1) added to the commercial substrate MecPlant®, plus a treatment without the presence of the polymer, in 280 cm³ tubes. To quantify the volume of water applied, a low cost semi-automated drip irrigation system was used. The seedlings were planted in pots, simulating field conditions. A 4x4 factorial scheme was used, with factor 1 being the seedlings produced in the previous treatments and factor 2 the application of polymers at planting (0; 1,5; 3,0 and 6,0 g planting hole-1) in an entirely randomized design. The polymers Hydroplan® and Forth® had a higher water absorption capacity between 349 and 374 g of water per g of product, than the plant-based polymer (78 g). A significant reduction in water absorption was observed as a function of increasing electrical conductivity of the water. Even at a lower conductivity, 1,0 dS m-1, the reduction was approximately 50% of the water uptake capacity, calcium chloride being more harmful than potassium chloride. No changes occurred in the physical properties of the substrate with the addition of the hydroretentive polymer. Considering the morphological variables, in general, Enterolobium contortisiliquum seedlings had similar growth and quality among treatments. For Paubrasilia echinata seedlings, a negative effect was observed for some variables with higher polymer doses, but with no difference in quality. Due to the absorption capacity and gradual release of water from the hydroretentive polymer, the reduction was 51,6% and 42,9% of water consumption for the species Enterolobium contortisiliquum and Paubrasilia echinata, respectively, in the treatment of 6,0 g L-1 compared to the treatment without addition of the polymer. There was increased survival of seedlings produced with increasing doses of hydroretentive polymer in pots, even at lower doses, on average 59 versus 41 days.