Biossólido como fonte de nutrientes para o algodão herbáceo e seu efeito residual no milho.

Abstract

The research aimed the evaluation of UASB sludge use on the growth and development of the green herbaceous cotton BRS and hybrid corn AG 1051. The experiments were conducted in EMBRAPA-Algodão, (Campina Grande, Paraíba-Brasil). The experiment was conducted in randomized blocks design, with the treatments distributed in factorial scheme [(5x2)+3], represented by five sludge concentrations (70, 140, 210, 280 and 350kgN/ha), two sludge consistencies (dry and lime treated) and three controls (absolute - soil; mineral fertilizer - NPK; and organic fertilizer - cow manure), with four repetitions. The experimental unit was represented by 21L plastic buckets, totalizing thirteen treatments and fifty two buckets. The lime treatment was accomplished at 50% sludge dry weight (total solids) while sludge air drying was conducted in green house during 20 days at 26-38ºC. Cow manure was incorporated to the soil at 20t/ha dosage. The mineral fertilizers used were: ammonium sulphate (20% of N), triple super-phosphate (45% of P2O5) and potassium chloride (60% of K2O). In the first experiment (green cotton BRS), plant height and diameter, plant biomass (aerial and root), number and weight of boll, total yield and seeds yield, weigh of hundred seeds, root length, fibre percentage and technological qualities of the fibre were evaluated. The second experiment was carried out to evaluate the sludge residual effect on the hybrid corn AG 1051with initial monitoring of the variables: plant height and diameter, leave total area, plant biomass (aerial and root) and root length. After 55 days of cultivation, the experiment was finish and diagnosis analysis of leaf (nitrogen, phosphorous, potassium, calcium and magnesium content) and soil (pH, organic matter, nitrogen, phosphorous, potassium, calcium, magnesium, sodium and aluminum) was made for the different treatments. Soil, sludge, cow manure and drained liquid were submitted to physical, chemical, microbiological and parasitological characterization. Lime treated sludge removed 100% of faecal indicators (Escherichia coli and faecal streptococci), while drying only removed 99,7% of total coliforms, 98,9% of faecal coliforms, 82,4% of Escherichia coli and 92,5% of faecal streptococci. The heavy metals concentrations in the sludge samples were below the permissible maximum values for agricultural use (USEPA, 1992), allowing its use. The drainage liquid was classified as highly saline particularity due to the presence of sodium and chloride ions, increasing the risks of soil salinization and deterioration of underground waters. For the cotton crop there was significant response of the interaction consistency x sludge doses for variables: boll numbers per plant, total yield and seed yield and aerial biomass. The incorporation of dry sludge to the soil, for each dose studied, provided an increase on the above mentioned variables. The maximum production for dry sludge was: 12 boll/plant (243kgN/ha), total yield of 47g/plant (300kgN/ha), seed yield of 12g/plant (231,5kgN/ha) and aerial biomass of 108g (316kgN/ha). When the contrast factorial versus controls was analysed for these variables the superiority of the factorial was found for each analyzed controls. Among the controls, the plants cultivated with cow manure and mineral fertilizer, in a general, overcame the those cultivated in soil (absolute control) in all variables studied. There was a positive effect of dry sludge on cotton growth (height and diameter) and root biomass. The increase of dry sludge doses promoted reduction of some technological qualities: length uniformity, resistance, lengthening, fiabilidade index and increased the index of short fibres. On the other hand, residual effect of dry sludge was observed on corn plants, with a larger concentrations of nutrients to the leaves, and providing a better growth (height and diameter), increasing leaf area (per leaf and plant) and biomass (aerial and root), mainly after 210kgN/ha of dry sludge. Some soil proprieties were better in treatments which received dry sludge. Concerning the potassium determination in the corn leaves, the highest concentration occurred in treatments which received the limed treated sludge (210 and 280kgN/ha). On the other hand the increase of sludge doses, contributed to reduce the concentration of this macronutrient in the soil. The results of the contrast factorial versus controls, the factorial stood out in all variables, except for potassium in the soil, where plants cultivated in soil (absolute control), with mineral or organic fertilizer stood out of the factorial. The agricultural use of the sludge is viable, safe for humans, animals and environment, since requirements of sanitary monitoring are accomplished, particularity to helminth eggs viability and total and faecal coliforms presence in the soil.