Eyob Tesfamariam

Exporting large volumes of municipal sewage sludge through turfgrass sod production.

The nutrient content of sludge produced by municipal water treatment works often far exceeds the requirements of nearby crops. Transporting sludge further afield is not always economically viable. This study reports on the potential to export large volumes of anaerobically digested municipal sewage sludge through turfgrass sod production. Hypotheses examined are that sludge loading rates far above recommendations based on crop nutrient removal (i) are possible without reducing turf growth and quality, (ii) do not cause an accumulation of N and P below the active root zone, (iii) can minimize soil loss through sod harvesting, and (iv) do not cause unacceptably high nitrate and salt leaching. An 8 Mg ha(-1) sludge control (the recommended limit) was compared with sludge rates of 0, 33, 67, and 100 Mg ha(-1) on a loamy, kaolinitic, mesic, Typic Eutrustox soil near Johannesburg, South Africa. Sludge application rates up to 67 Mg ha(-1) significantly improved turfgrass establishment rate and color. The ability of sods to remain intact during handling and transport improved as the sludge application rate increased to 33 Mg ha(-1) but deteriorated at higher rates. A sludge application rate of 100 Mg ha(-1) was needed to eliminate soil loss, but this rate was associated with unacceptably high N leaching losses. All our hypotheses were accepted for application rates not exceeding 33 Mg ha(-1) on the proviso that some soil loss was acceptable and that the leaching fraction was carefully managed during the first 2 mo after sludge application.

Mobility and uptake of zinc, cadmium, nickel, and lead in sludge-amended soils planted to dryland maize and irrigated maize-oat rotation.

Sludge application to agricultural lands is often limited mainly because of concerns about metal accumulation in soils and uptake by crops. The objective of the study was to test the following hypotheses: (i) in the short to medium term (5-10 yr), the application of good-quality sludge according to crop N requirements will not lead to significant accumulation of water-soluble metal fractions in soil, (ii) mobility and uptake of metals is higher under irrigated than dryland systems, and (iii) metal concentrations in plant tissue could reach phytotoxic levels before the soil reaches environmental threshold levels. Field plots were arranged in a randomized complete block design comprising four replications of three treatments (0, 8, and 16 Mg ha yr anaerobically digested municipal sludge) planted to dryland maize and irrigated maize-oat rotation. Soil and plant samples were collected after 7 yr of treatment application for selected metal analyses. A large fraction of the Zn, Ni, and Pb in the soil profile was ethylenediaminetetraacetic acid extractable (46-79%). Saturated paste-extractable fractions of Cd and Pb were <1 mg kg. Plant uptake of Cd, Pb, and Ni under irrigation was double that for dryland systems. Concentrations of the metals considered in plant tissue of both cropping systems remained well below phytotoxic levels, except for Zn under dryland maize, which received 16 Mg sludge ha yr. Metal concentrations in the soil remained far below total maximum threshold levels. Therefore, hypotheses 1 and 3 were accepted for the metals considered, and hypothesis 2 was rejected for Zn.

Long-term impacts of grazing intensity on soil carbon sequestration and selected soil properties in the arid Eastern Cape, South Africa.

BACKGROUND Little is known about how basic soil properties respond to contrasting grazing intensities in the Karoo biome, South Africa. The aim of this study was to investigate impacts of long-term (>75 years) grazing at 1.18 heads ha(-1) (heavy; CGH), 0.78 heads ha(-1) (light; CGL), and exclosure on selected soil properties. Soil samples were collected to a depth of 60 cm from the long-term experimental site of Grootfontein Agricultural Development Institute, Eastern Cape. The samples were analyzed for C, N, bulk density and infiltration rate, among others. RESULTS Generally, heavy and light grazing reduced soil N storage by 27.5% and 22.6%, respectively, compared with the exclosure. Animal exclusion improved water infiltration rate and C stocks significantly (P < 0.05), which was 0.128, 0.097, and 0.093 Mg ha(-1) yr(-1) for exclosure, CGL and CGH, respectively. Soil penetration resistance was higher for grazing treatments in the top 3-7 cm soil layer but for exclosure at the top 1 cm soil surface. CONCLUSION Although livestock exclusion has the potential to improve C sequestration, a sufficient resting period for 1-2 years followed by three consecutive grazing years at light stocking rate would be ideal for sustainable livestock production in this arid region of South Africa.

Yield, resource use efficiency and trace metal uptake of weeping lovegrass grown on municipal sludge‐amended soil

BACKGROUND There are concerns that fertilization using sludge in semi-arid areas, where water is limiting, will compound the effect of drought, resulting in the decline of yield from potential salt accumulation. This study investigated impacts of annual sludge application at 0, 4, 8 and 16 Mg ha-1 on weeping lovegrass hay yield, crude protein (CP) content, rainfall use efficiency (RUE), nitrogen use efficiency (NUE) and trace metal uptake over eight consecutive years. RESULTS Both hay yield and RUE increased by 5-53% as the sludge rate increased. Hay yield was highest (13.3 Mg ha-1 ) during the wet season and RUE (27.1 kg mm-1 ) during the dry season. RUE was highest at sludge rates of 16 Mg ha-1 and NUE at 4 Mg ha-1 . Similarly, municipal sludge application increased CP content as well as crop Cr and Zn uptake from the 16 Mg ha-1 treatment. CONCLUSION Results from this study indicated that eight consecutive years of treated municipal sludge application increased weeping lovegrass hay yield, CP content and RUE. Similarly, trace metal uptake by crop did not differ between the zero control and the 16 Mg ha-1 treatment, except for Zn and Cr, which showed a slight increment. Nonetheless, all trace metals remained well below the maximum tolerable dietary concentrations for domestic animals.

Modelled impacts of extreme heat and drought on maize yield in South Africa

Abstract. This study assessed two versions of the crop model CropSyst (i.e. EMS, existing; MMS, modified) for their ability to simulate maize (Zea mays L.) yield in South Africa. MMS algorithms explicitly account for the impact of extreme weather events (droughts, heat waves, cold shocks, frost) on leaf development and yield formation. The case study of this research was at an experimental station near Johannesburg where both versions of the model were calibrated and validated by using field data collected from 2004 to 2008. The comparison of EMS and MMS showed considerable difference between the two model versions during extreme drought and heat events. MMS improved grain-yield prediction by ∼30% compared with EMS, demonstrating a better ability to capture the behaviour of stressed crops under a range of conditions. MMS also showed a greater variability in response when both versions were forced with scenarios of projected climate change, with increased severity of drought and increased temperature conditions at the horizons 2030 and 2050, which could drive decreased maize yield. Yield was even lower with MMS (8 v. 11 t ha–1 for EMS) at the horizon 2050, relative to the baseline scenario (∼13 t ha–1 at the horizon 2000). Modelling solutions accounting for the impact of extreme weather events can be seen as a promising tool for supporting agricultural management strategies and policy decisions in South Africa and globally.