Effects of sewage sludge application on unfertile tropical soils evaluated by multiple approaches: A field experiment in a commercial Eucalyptus plantation.

Sewage sludge (SS) reuse in forest plantation as soil fertilizer/amendment has tremendously increased in recent years. However, SS may have high concentrations of potentially toxic elements (PTE), representing a potential risk for soil and the whole ecosystem. This paper was aimed to assess the toxicity of PTE in unfertile tropical soils amended with SS in a commercial Eucalyptus plantation, with an integrated multiple approaches combining: i) the use of a battery of bioassays (Daphnia magna, Pseudokcrichirella subcapitata, Lactuca sativa, and Allium cepa); and ii) the evaluation of some PTE (Cd, Cr, Cu, Fe, Mn, Ni, Pb, and Zn) and their availability into the pedoenvironment. Differences in total and available PTE between SS doses and time of treatments were evaluated using ANOVA; correlations between PTE and bioassays by a sparse partial robust M-regression (SPRM), while multiple correlations among parameters were performed by principal factor analysis (PFA). Results show that PTE contents in soils tended to increase with SS application doses. However this cannot be assumed as a general rule since in all the investigated treatments the PTE concentrations were consistently below both soil natural background concentrations and quality reference values. Bioassays showed a generalized low eco- and genotoxicity of SS with an increase in toxicity at increasing SS doses but with a clear decreasing trend as time went by. A. cepa was the most sensitive bioassay followed by P. subcapitata > D. magna > L. sativa. Overall, the results indicate that in realistic open field conditions SS risk may be lower than expected due to dynamic decrease in PTE toxicity with time after application. This study has an important implication that open-field trials should be strongly encouraged for evaluating environmental risk of SS application in forestry.

Short-term usage of sewage sludge as organic fertilizer to sugarcane in a tropical soil bears little threat of heavy metal contamination.

A field experiment was carried out to study the effect of application rates of sewage sludge and mineral nitrogen and phosphate fertilizers on As, Ba, Cd, Cr, Cu, Ni, Pb, Se, and Zn concentration in soil, cane plant, and first ratoon (residual effect) in a Typic Hapludult soil. To allow an analysis by means of response surface modeling, four rates of sewage sludge (0, 3.6, 7.2 and 10.8 t ha(-1), dry base), of N (0, 30, 60 and 90 kg ha(-1)) and of P(2)O(5) (0, 60, 120 and 180 kg ha(-1)) were applied in randomized block design, in a 4 × 4 × 4 factorial scheme, with confounded degrees of freedom for triple interaction, with two replications. To evaluate the residual effect of the sludge applied to cane plant on the cane ratoon growth, mineral NK fertilizers were applied at the rates of 120 kg ha(-1) N and 140 kg ha(-1) of K(2)O, on all treatments. The application rates of mineral nitrogen and phosphate fertilizers did not affect statistically the heavy metal concentration in the soil and in the sugarcane plants. Sewage sludge application increased As, Cd, Cu, Ni, Pb, and Zn concentrations in soil, but values did not exceed the quality standard established by legislation for agricultural soils. Although the concentrations of metals in the plants were very low, the uptake of heavy metal by sugarcane plants was generally increased by sewage sludge doses. The use of sewage sludge based on N criteria introduces a small amount of heavy metal into the agricultural system, however it poses no hazard to the environment.

Composição mineral de frutos de quatro cultivares de quiabeiro / Mineral composition of four cultivars of okra fruits

Este experimento foi realizado na Universidade Federal de Viçosa e teve como objetivo avaliar a composição mineral dos frutos de quatro cultivares de quiabo. O delineamento utilizado foi em blocos casualizados, sendo os tratamentos constituídos pelas cultivares Amarelinho, Red Velvet, Star of David e Mammoth Spinless, com cinco blocos. Os maiores teores de cálcio, fósforo, enxofre e magnésio foram encontrado na Cultivar Red Velvet. Os maiores teores de nitrogênio total, amônio e manganês e menor teor de fósforo foram encontrados na cultivar Mammoth Spinless, enquanto nas cultivares Red Velvet e Star of David foram observados os menores teores de nitrogênio total, amônio e manganês. Menores teores de cálcio, enxofre e magnésio foram verificados em conjunto nas cultivares Amarelinho, Star of David e Mammoth Spinless.

This experiment was carried out at Universidade Federal de Viçosa and had the objective to evaluate the mineral composition of four cultivars of okra fruits. The experimental design was in randomized blocks, where the treatments were composed by the cultivars Amarelinho, Red Velvet, Star of David and Mammoth Spinless, with five blocks. The cultivar Red Velvet had the highest content of calcium, phosphorus, sulfur and magnesium. The cultivar Mammoth Spinless had the highest content of total nitrogen, ammonium and manganese and the lowest content of phosphorus. The cultivars Red Velvet and Star of David had the lowest contents of total nitrogen, ammonium, and manganese. Lower contents of calcium, sulfur and magnesium were present in the cultivars Amarelinho, Star of David and Mammoth Spinless.