Desenvolvimento e produção do milho e alterações químicas em diferentes solos com aplicação de manipueira

Abstract

Wastewater use in agriculture, when properly administered, provides organic matter and nutrients to plants, and also shows soil physical and chemical properties improvement. Cassava wastewater is a residue from manioc (Manihot esculenta) processing to obtain flour or starch. It has favorable attributes for agricultural use as source of nutrients, such as potassium, nitrogen, magnesium, phosphorus, calcium and, also, micronutrients to plants; in contrast, it may cause soil and plant depletion when application criteria are not taken into consideration. On the other hand, maize crop (Zea mays) stands out by its economic agricultural and industrial importance, and for presenting physiological response to the excess and lack of nutrients. Nevertheless, proper nutrition will depend on the nutrient amount plants can extract from the soil, being necessary understanding the nutrients uptake and accumulation as function of plant development stages. The present study had as objective to evaluate the development, nutritional and enzymatic content of maize plants subjected to different cassava wasterwater dosages and the effects on soil fertilization under different incubation periods. For this purpose, two experiment were carried out, one under greenhouse and other under field conditions. The crop used in both experiments was maize cultivar AG 1051; while the cassava wastewater was from a flour mill house located on the municipality of Pombos, PE. For the first experiment, soil from Itambé, PE was used in 20-liter pots. it was used a completely randomized design in a factorial 5 x 3 arrangement, with four replications, totalizing 60 experimental plots. The factors of the study were: cassava wastewater dosages (5 levels) 0, 12.6, 25.2, 50.4, 75.6 m3 ha-1 and planting periods, at 20, 40 and 52 days. The second experiment, under field conditions, was carried out at Vitória de Santo Antão IPA Station; in a complete randomized blocks design with five treatments: 0, 32, 64, 128, 256 m3 ha-1 and six replications. The experimental unit consisted in an area of 203 m2, composed of six blocks, each one with 11 cultivation lines, being used the 5 central lines for measurements. The lines were cultivated with 12 plants; with 0.80 m within-row, 0.40 m within-plant and 0.40 within-block spacing. On both treatments, it was carried out the determination of the following parameters: plant height, stalk diameter, number of leaves, fresh leaf matter, fresh stalk matter, dry leaf matter, and dry stalk matter, in addition to nutritional content determination of nitrogen, phosphorus, potassium, calcium, magnesium, sulfur and sodium on plant leaves and stalk. Forty days after sowing, harvesting of leaves were executed in order to determine enzymatic activity of catalase, ascorbate peroxidase and total soluble proteins. Soil chemical attributes characterization was performed by determining the following parameters: electrical conductivity of the saturation extract, pH in water and phosphorus, potassium, calcium, magnesium and sodium concentrations. Obtained data were subjected to variance analysis using the statistical software SAS, with 5% significance levels for F test. Some parameters did not show adjustable models for regression (linear and quadratic), thus Tukey test was performed. Based on the results, under the first experiment conditions, cassava wastewater showed a good macronutrient input, which demonstrates its suitability as a fertilization source for maize crop, as long as under proper dosages. It was found that the studied nutrients presented maize aerial part accumulation, in decreasing order: K, N, P, Mg, Ca, Na and S, not presenting visual nutrient deficiency. Cassava wastewater use alternatively to mineral fertilizers promoted increase in pH, Cees and soluble P, K+, Mg2+ and Na+ soil contents. Cassava incubation periods significantly affected pH, Cees and soluble K+ soil content. For field conditions, although it was observed low content for the examined nutrients, nutritional deficiency was not noticed visually.