Comparison of four low-technology composting methods for market crop wastes.

Four methods for composting, pit-cover (PC), pit-open (PO), above ground-open (AO) and above ground-covered (AC), were compared for their effect in accelerating compost maturity using market crop waste (MCW). The composting process was monitored through determining changes in temperature and pH, with compost maturity indices measured in terms of variations in water-soluble carbon (WSC), ammonium-N (NH(4)(+)-N) and nitrate-N (NO(3)(-)-N), and C/N, NH(4)(+)-N/NO(3)(-)-N, WSC/organic N and WSC/total N (TN). Total organic carbon (TOC), nitrogen (TN), potassium (TK) and phosphorus (TP) were also determined. Temperature rapidly increased from mesophilic to thermophilic and gradually reduced through maturation phases. A similar pattern was recorded for pH, which reached a slightly alkaline level at maturity. Composting significantly (p<0.05) decreased the concentrations of TOC, TN, TP, TK, NH(4)(+)-N and WSC and increased that of NO(3)(-)-N. All four low-technology composting methods used in this study produced mature composts within 63 days. Suitable maturity indicators for MCW compost were C/N ratio<12, WSC<1%, NH(4)(+)-N<400 mg kg(-1), NH(4)(+)-N/NO(3)(-)-N<0.2, WSC/TN, WSC/organic-N<1. On the basis of these indicators, the AC method generally enhanced maturity faster than the AO, PC and PO methods. Pit methods require less investment and are recommended for the smallhold farmers.

Root establishment of perennial ryegrass (L. perenne) in diesel contaminated subsurface soil layers.

The efficiency of rhizosphere biodegradation of petroleum hydrocarbons heterogeneously distributed in soils is dependent on the ability of plant roots to prospect into contaminated zones. Rhizobox experiments were conducted to study the influence of diesel contaminated layers on the spatial distribution and the development of the roots of perennial ryegrass. Root distribution and root and shoot development were monitored over time. The final root and above ground biomass and the final TPH concentration were determined. The spatial distribution of the contaminant as well as the irrigation method used affected root distribution, plant development and TPH degradation and therefore ryegrass remediation potential. The results show that roots colonise fully uncontaminated soil and grow preferentially between zones of contamination. Conversely, when no immediate uncontaminated soil is available, roots grow through contaminated zones in order to prospect for uncontaminated soil.

Effects of sewage sludge on pH and plant availability of metals in oxidising sulphide mine tailings.

A field study was conducted adjacent to the tailings deposit of the Aitik copper mine in the north of Sweden to investigate the effects of sewage sludge on pH and plant availability of Al, Mn, Cu, Zn, Ni, Pb, As, Cr and Cd in the oxidising sulphide tailings. One treatment was supplied with sewage sludge, while the control received NPK-fertiliser. The tailings samples were collected at the beginning and the end of the growing season and extracted by NH(4)NO(3), NH(4)Ac-EDTA and HNO(3). Plant tissue concentrations of the elements were determined in the above-ground parts of barley (Hordeum vulgare) and red fescue (Festuca rubra). The application of sewage sludge resulted in higher crop yields compared to the control, although the buffering capacity and the metal immobilising effect of the sludge were limited. The pH decreased from 6.6 to 4.3 in the control and from 6.4 to 4.8 in the sludge-treated tailings during the growing season, probably due to sulphide oxidation in the tailings. This resulted in increased levels of soluble elements in all treatments studied. Application of sewage sludge resulted in elevated levels of soluble Zn and lower values of soluble As and Cd in the unaltered tailings but increased levels of specifically adsorbed Cu, Ni and As in the oxidised tailings. This was partly reflected in the plants, as the application of sewage sludge resulted in 67 mg Zn kg(-1) in barley grains and 60 mg Zn kg(-1) in red fescue shoots, both values twice as high as the corresponding values in the control, but lower As contents in both straw (0.3 mg kg(-1)) and grain (0.06 mg kg(-1)) of barley compared to the control (0.6 and 0.2 mg kg(-1), respectively). In addition, red fescue grown in sludge-treated plots contained significantly higher levels of Al, Cu, Pb, As and Cr compared to the control. The levels of several metals in barley and red fescue grown in both treatments exceeded background values found in the literature. The Cu content in barley straw exceeded 100 mg kg(-1) in both treatments and might be toxic to grazing animals. Thus, this study suggests that adding sewage sludge to the mine tailings at Aitik would not counteract the effects of the sulphide oxidation in the tailings. Furthermore, using a sequential extraction technique proved preferable to using total metal analysis in order to predict plant uptake of the elements in the tailings.

Bamboo as bioresource in Ethiopia: management strategy to improve seedling performance (Oxytenanthera abyssinica).

Seedling emergence and subsequent survival and growth are vital for natural forest restoration or plantation establishment by means of seeds. Such information is lacking for the African bamboo species. Two experiments were carried out in a greenhouse to evaluate the influence of seed orientation and sowing depth of the lowland bamboo Oxytenanthera abyssinica on seedling emergence, survival and growth. A randomised complete block design was used. Seedling emergence in the seed orientation experiment followed the order embryo-end-up>lay-flat>embryo-end-down. Survival rate after 62 days decreased in the order lay-flat>embryo-end-down>embryo-end-up. Mean seedling height and number of leaves per seedling followed a similar pattern. Seeds sown on top of the soil surface and at 2.5 mm depth achieved faster and higher seedling emergence than those sown at 5 and 10 mm depths. However, mean seedling height and number of leaves per seedling were higher in 5 and 2.5 mm depths than surface and 10 mm depths. There were significant quadratic relationships between sowing depth and seedling height (p=0.034) as well as number of leaves per seedling (p=0.032), both peaking around 5 mm soil depth. Lay-flat orientation, which is the most frequent position in broadcast sowing, is recommended at 5 mm sowing depth for the lowland bamboo based on overall performance in seedling emergence, survival and growth.