Recipientes e fontes orgânicas em substratos na produção de mudas de gravioleira

Abstract

Soursop (Annona muricata L.), family Annonaceae, is a fruit of great economic value, commercially cultivated in many tropical and subtropical countries. In Brazil, its cultivation is scattered in several states, and Bahia appears as the major producer. Soursop cultivation represents an attractive alternative income source, especially for small farmers. The acceptance of the fruit by the consumer market has steadily increased in recent years. Its economic importance is not only based on consumption of fresh fruit, but mainly in the consumption of processed food products often found as juice, ice cream, pulp, jelly, and also by the pharmaceutical industry that uses the fruits of this species in homeopathic medicine. Soursop seedling production occurs predominantly through sexual propagation, using the seed as propagation material. There are few reports in the literature about containers, substrates and fertilizers to be used in the seedling production process and, oftentimes, fertilizer recommendations are adopted from other species, thus limiting the expansion of this crop in the country. Soursop seedling development was evaluated in different containers with different sources and levels of organic material, in a nursery, at the Fruit Crops Sector in Água Limpa farm, at the Federal University of Uberlandia. Two experiments, both in randomized block design with five replicates of six plants per plot, the first one as a 2 x 3 factorial (containers x doses of poultry litter) and the second, as a 3 x 4 factorial (sources and levels of organic material), were done. In the first experiment, the results showed that container size and poultry litter proportion had significant and independent effects on plant height, while stem diameter was affected only the factor proportion of poultry litter. The seedlings produced in smaller containers were taller (16.07 cm) than those grown in larger containers (14.29 cm). The use of 20% v/v of poultry litter in the composition of the substrate showed higher values for plant height (16.43 cm) than the proportion of 40% v/v (15.18 cm) and 30% v/v (13.93 cm). Similarly, soursop seedling stem diameter also showed the greater values (3.12 mm) on the substrate containing 20% v/v poultry litter than in the other concentrations, thus demonstrating that there is no need for large amounts of organic material in soursop seedling production, thereby reducing production costs. Foliar concentrations of sulfur (S) were affected by the proportion of poultry litter, with greater values observed with 30% v/v of this material in the composition of the substrate, whereas the concentration of zinc (Zn) showed the greatest values when the seedlings were grown in larger containers, regardless of the substrate used. Thus, smaller plastic bags promoted better development of soursop seedlings giving them greater plant height and thicker stem, while the substrate containing 20% v/v of poultry litter in its composition are presented seedlings visually more attractive, with greater height and thicker stems. In the second experiment, the sources of organic matter affected the variables studied, with the greatest values for plant height (4.18 cm), stem diameter (1.98 mm), dry shoot mass (1.28 g), when cattle manure was used in the composition of the substrate; however, such values were not statistically different from those observed when poultry litter was used in the composition of the substrate. The greatest ratio of root dry mass and shoot dry mass was observed in seedlings with earthworm humus in its composition, which was statistically different from poultry litter. Foliar concentrations of macro and micronutrients were not affected by treatments. Thus, it can be concluded that the use of cattle manure or poultry litter in the composition of the substrate for soursop seedling production promotes better seedling growth.