J.M. Steyn

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.

Water and nutrient retention by Aquasoil® and Stockosorb® polymers

Water retention and hydration rate of Aquasoil and Stockosorb polymers, the effects of these polymers on the water, ammonium and nitrate retention of a pine bark growth medium and the response of the polymers to fertilizer solutions were investigated. Aquasoil retained 129 g of distilled water g−1 of polymer, whereas Stockosorb retained 216 g−1 of polymer. Both polymers reached their maximum capacity in about one hour. The polymers when combined with 1 or 2 g 500 g−1 of pine bark, improved the water retention capacity of the growth medium. However, longer time was required in the growth medium for the polymers to reach maximum capacity than in the distilled water. All polymer-amended pine bark media retained more ammonium, compared to non-amended media. The 2 g polymer treatment retained greater amounts of NO3 than the lower rates. Retention of water by the Aquasoil® and Stockosorb® polymers was reduced to 88% and 86% of capacity compared to distilled water, whereas fertilizer solution reduced water retention to 53% and 42% of capacity. Soaking in distilled or tap water improved water retention of the polymers over fertilizer solutions.

Comparison between traditional and scientific irrigation scheduling practices for furrow irrigated potatoes (Solanum tuberosum L.) in Ethiopia

Traditional irrigation schemes constitute about 40% of the total irrigated land in Ethiopia. Despite this, the sector has been overlooked and not supported by improved water management technologies. A survey conducted on one of the schemes, Godino, indicated that farmers apply the same amount of water regardless of crop type and growth stage. In view of this, an experiment was established at the Debre-Zeit Research Centre in Ethiopia with the objective of comparing the performance of two traditional irrigation management practices to two scientific scheduling methods namely an Irrigation Calendar generated with the Soil Water Balance (SWB) model and a neutron probe (NP) based scheduling method. The four irrigation regimes were applied to furrow irrigated potatoes. Plant sampling for dry mass determination was undertaken on a weekly basis. Results of leaf, canopy and total dry matter, as well as fresh tuber yields, indicated that the NP and SWB schedules were superior to the traditional scheduling methods. Leaf dry matter was the most responsive parameter to irrigation treatments. The overall results revealed that traditional irrigation practices did not meet the full potato crop water requirements to ensure acceptable yield, which emphasized the need for introducing better and more efficient practices. Since the best performing treatment, N P, is capital and skills intensive, site specific SWB calendars, which performed similarly to NP and are simpler to use, are to be recommended for farmers at the Godino scheme.

Liming improves herbage yield, essential oil yield and nutrient uptake of rose-scented geranium (Pelargonium capitatum×P. radens) on acidic soils

A field experiment was conducted on rose-scented geranium (Pelargonium sp.) in Pretoria, South Africa, to evaluate plant response to liming on acidic soils. Treatments were dolomitic limestone at 0 (control), 2, 4 and 6 t/ha, laid out as a randomized complete block design. Soil pH was not influenced by liming for any of the treatments at the first harvest, whereas at the second, third and fourth harvests an increase in pH was observed for all the limed treatments. At the time of the first harvest, plants did not respond significantly to 2 and 4 t/ha of liming, but responded positively to 6 t/ha, with higher herbage yield compared with the control and 2 t/ha lime treatments. At the second, third and fourth harvests fresh herbage and essential oil yield increased significantly due to liming. The differences among limed treatments were not significant for fresh herbage and essential oil yield. Cumulative fresh herbage and essential oil yields of all harvests were higher on the limed treatments than the control. Soil pH above 5.5 and soil base saturation above 55% increased fresh herbage and essential oil yield (per ha), which corresponded in this case with 2 to 6 t/ha of lime application. Oil content (%) was not affected by application of lime or an increase in soil pH but was more dependent on air temperature fluctuations. Similarly, no clear differences were observed in the composition of the essential oil throughout the experimental period due to liming. The ratio between citronellol and geraniol correlated with seasonal differences in maximum temperatures and not with liming. The implication of this study is that optimum growth of rose-scented geranium can be achieved by application of lime when plants are grown on acidic soils (pH (H2O) <5.5) but without any effect on oil content and essential oil composition.

Frodo and Darius: South African potato cultivars with good processing quality

Two newly released South African potato cultivars, Frodo and Darius, were compared with two foreign processing cultivars, Pentland Dell and Shepody. The cultivars were grown under sprinkler irrigation and evaluated for external and internal tuber characteristics and processing quality. The experiment was conducted at Bronkhorst-spruit, South Africa. Results indicated that Frodo had significantly higher tuber form index values (long tuber shape) for all tuber sizes, a desired characteristic for french fry processing. Pentland Dell and Shepody exhibited more vascular discolouration, while Frodo had the highest occurrence of tuber brown spot. These physiological disorders probably resulted from unfavourably high temperatures and water stress during the late growing season. Shepody had the lowest specific gravity, followed by Pentland Dell. Reducing sugar levels for both the foreign cultivars were also relatively high and only marginally within the ranges required for french fry processing. Frodo and Darius, on the other hand, had high specific gravities and low reducing sugar levels, which are desirable characteristics for long-term storability and the production of quality frozen fries. Tuber yields of these two cultivars were also similar or higher than those of the foreign cultivars. Frodo and Darius can, therefore, successfully compete with Shepody and Pentland Dell as processing cultivars under local conditions.