Physical properties of technosols as evapotranspiration covers on potash tailings piles.

The covering of potash tailings piles with technosols (artificial soils) is a modern and promising method for decreasing the saline drainage of these piles. In this context, it is important to determine whether technosols have appropriate physical properties for crop growth. In evapotranspiration covers, physical properties, such as bulk density, particle size distribution, total porosity, proportion of large pores, and available water are particularly important because they allow for robust crop growth, which subsequently determines the evapotranspiration capacity. However, few studies have been performed to assess the physical properties of technosols and their ability to act as evapotranspiration covers on potash tailings piles. Therefore, the present study aims to evaluate the physical properties of four different technosols made of municipal solid waste incineration bottom ash and coal combustion residues installed on a potash tailings pile located in Heringen, Germany. The total porosity, infiltration capacity, particle size distribution, bulk density, wettability, water retention curve, pH, electrical conductivity, and water content were determined. The pH of the technosols averaged 8.5, the electrical conductivity varied from 2.8 to 3.3 mS/cm, the mean bulk density was 1.21 g/cm³, the total porosity was 52.8%, and the rate of medium pores was 13.9% of the technosol volume. On average, the coarse fraction accounted for 42% of the technosol mass, whereas the fine fraction accounted for 52% of the sand-size particles, 43% of the silt-size particles and 5% of the clay-size particles. Likewise, no wetting restrictions for the technosols were found. To conclude, the different technosols present no limitations for crop growth, although the heavy metal contents of municipal solid waste incineration bottom ash and coal combustion residues should be considered in future studies.

A modification of a traditional Ethiopian maize store for solar powered ambient drying to reduce post-harvest losses.

A gombisa is a traditional Ethiopian structure widely used for maize storage over several months. It lacks adequate ventilation for timely moisture removal, which promotes mold development and aflatoxin production. In this study, a traditional gombisa was compared to one modified by installing a solar powered fan to provide forced ambient air ventilation during daytime. Approximately 900 kg of moist ear maize were loaded into each structure and samples from selected locations were weighed periodically to monitor moisture loss. Temperature and relative humidity of ambient air and inside the maize bulk were continuously recorded. Significantly faster drying was achieved in the modified gombisa, where drying occurred from bottom to top. In the traditional store, drying was much faster at the surface, with drying rate declining sharply with increasing depth in the bulk due to more limited air exchange. Relative humidity in the bulk center of the traditional structure remained above 90% for more than 4 weeks while in the modified gombisa it decreased progressively from the beginning of the trial. The results are promising and the modifications simple to implement, with the potential to effectively reduce post-harvest losses of maize. Field tests in Ethiopia are recommended.

Water balance assessment of different substrates on potash tailings piles using non-weighable lysimeters.

Water balance is an important tool to evaluate water deficit or excess in crop systems. However, few studies have evaluated the water balance of vegetation grown on the residues from potash mining because the high sodium chloride levels of the residues hinder agricultural development. Therefore, this study aims to measure the water balance components in eight non-weighing lysimeters installed on a potash tailings pile in Heringen (Werra), Germany. These lysimeters were filled with different mixtures of household waste incineration slags and coal combustion residues, resulting in 4 different substrates with two repetitions. Manual seeding was performed using 65% perennial ryegrass (Lolium perenne L.), 25% red fescue (Festuca rubra L.) and 10% Kentucky bluegrass (Poa pratensis L.). Environmental conditions were monitored using an automatic weather station; ground-level and 1-m-high rain gauges. Precipitation and drainage were recorded weekly following the initial saturation of the lysimeters. Water balance components were determined for two hydrological years based on the expression: ET (mm) = P - D, where ET = evapotranspiration, P = precipitation and D = drainage. In addition, evapotranspiration was studied using the standard FAO Penman-Monteith equation and Haude's method. The lysimeter water balance measured in 2014 revealed an actual evapotranspiration rate of 66.4% for substrate 1, 66.9% for substrate 2, 65.1% for substrate 3 and 64.1% for substrate 4. In 2015, evapotranspiration ranged from 65.7% for substrate 4 to 70.2% for substrate 1. We observed that the FAO Penman-Monteith and Haude's evapotranspiration models generally overestimated the water use of the green coverage by 67% and 23%, respectively. Our study suggests that an evapotranspiration cover for potash tailings piles may decrease brine drainage from these piles and reduce soil and water contamination.