P. J. Pieterse

The breaking of seed dormancy of guayule (Parthenium argentatum Gray.) by treatment with gibberellic acid and smoke water solution

Guayule seed exhibits poor germination due to natural dormancy that can last from six- to twelve months after seed-set. In an attempt to stimulate seed germination, four guayule seed lines (AZ101, AZ-3, N565 and 11591) were treated with smoke water as well as gibberellic acid, both separately and in combination. The split-plot analyses of variance showed no significant interaction between cultivar and treatment factors (P = 0.71), but when the time factor was included interaction was highly significant (P < 0.0001), indicating that some treatments influenced the rate of germination. Seeds of cultivar AZ-3 treated with the smoke water-gibberellic acid mixture required the shortest number of days for maximum germination to occur. However, treatment of seeds with gibberellic acid resulted in the highest germination of seeds of all four cultivars. These results showed that guayule seed can be stimulated to germinate faster and better by treatment with gibberellic acid and/or smoke water solutions.

An effective technique for breaking the seed dormancy of Acacia longifolia

The effect of different pre-treatments on the dormancy of the hard-coated seeds of Acacia longifolia Andr. Willd. was determined. A final germination figure of 100% could be obtained with hot water treatments, acid scarification and manual scarification. However, if germination rate was taken into consideration, acid scarification proved superior to all other treatments.

Quality as a factor influencing the possible utilization of eight exotic legume species as mulches

Invasive exotic legumes need to be controlled by amongst others, mechanical control methods. Residues such as twigs and leaves of felled trees can possibly be utilized as a low cost, organic fertilizer. The quality of the organic materials influences their behaviour as mulches. In this study eight exotic legume trees were compared in terms of quality parameters such as C:N ratio, lignin, polyphenol, cellulose and hemicellulose contents. Additionally, a decomposition trial in pots was executed and three selected species were compared in terms of in vitro mineralization of C and N. Clear distinctions in terms of mulch quality could be drawn. Paraserianthes lophantha and Chamaecytisus palmensis produced mulch of a high quality, whilst Acacia pycnantha, A. saligna and A. melanoxylon produced mulch of a low quality. The mulch quality correlated well with the decomposition rates of the species in the pot experiment. The in vitro mineralization experiment supported the results of the other experiments and showed that mulch of a poor quality has an extended initial immobilization period. However, it can be used to protect soil against erosion, soil moisture depletion and weed establishment. The application of a mixture of low and high quality mulches will probably result in the most positive response by crop plants.

Vegetative growth of Amaranthus hybridus and Amaranthus tricolor under different watering regimes in different seasons in southern Mozambique

Drought-tolerant crops with high nutritional value such as amaranth leafy vegetables have the potential to improve the diet of rural communities in dry semi-arid areas of southern Mozambique. A study was conducted aiming to assess the vegetative growth and leaf nutritional content of Amaranthus hybridus and A. tricolor when subjected to different watering regimes (80%, 50% and 20% of total available water) during the rainy and dry seasons, and ascertain the relationship between temperature and day length affecting the leaf yield of the two species. Six field trials were conducted in a randomised complete block design with 2 × 3 factorial layout with six replications in Maputo. Vegetative growth was sensitive to soil water at 50% and 20% of available water. However, the leaf and side-shoot number, leaf area and yield were less sensitive to short-interval water deficits during the rainy season. Leaf calcium and crude protein contents were higher at low water levels. Leaf yield was significantly affected by temperature and day length, where total leaf yield increased during the rainy season, and decreased during the dry season. Both species have the potential for sustainable leaf production during rainy and dry seasons.

Effect of varying degrees of plant residue cover from different crops on annual medic pasture re-establishment and production

Annual medics can play an important role as a pasture crop in short-rotation pasture-cropping systems in the Overberg district of South Africa. Permanent soil cover, an important aspect of conservation agriculture, and different crops in rotation may be, amongst other factors, detrimental to annual medic re-establishment and production. A field study was conducted to test re-establishment and subsequent production of medic pasture under varying degrees of cover (0%, 25%, 50%, 75% and 100% cover) from wheat, barley, oats and annual medic residues. Medic pastures showed the highest re-establishment and production if following wheat in a cropping system. The re-establishment and production of annual medics did not differ significantly from 0% to 75% cover, whilst 100% cover decreased re-establishment and production significantly.

The Effect of Phosphorus, Mucuna, and Nitrogen on the Biomass, Leaf Area Index, and Foliar Nutrient Content of Maize on a Depleted Sandy Loam Soil in Zimbabwe

Sufficient nutrient levels in leaves of crops have substantial effects on plant growth, development, and grain yield, as it is a fundamental constituent of many leaf cell components. The effect of phosphorus (P), mucuna management options, and nitrogen (N) on the biomass, leaf area index (LAI) and leaf nutrient content of maize on a depleted sandy loam soil in Zimbabwe were investigated. The experimental design was a split-split-plot with two P rates, four mucuna management options, and four N treatments (applied to a subsequent maize crop). Biomass, LAI, and foliar N, P, potassium (K), calcium (Ca), and magnesium (Mg) in the subsequent maize crop were determined. A significant three-way interaction (P < 0.05) between mucuna management options, N rates, and time was observed in terms of biomass production and all nutrients in the leaves of the subsequent maize crop.

Effects of Artemisia afra leaf extracts on seed germination of selected crop and weed species

Herbicide resistance in weeds is a phenomenon threatening sustainable cereal production in the winter rainfall region of South Africa. Every possible weed control measure that may be used to complement chemical weed control measures should be investigated. The effect of aqueous leaf extracts of the aromatic shrub African wormwood (Artemisia afra) on germination of selected crop and weed species were investigated. The selected plant species included wheat (Triticum aestivum L.), herbicide resistant and non-resistant ryegrass (Lolium spp.), canola (Brassica napus) and lucerne (Medicago sativa). Various dilutions were investigated and the original extract was the most effective in inhibiting seed germination as compared to the inconclusive results from further dilutions. The original extract that completely inhibited seed germination in canola, had no significant negative effect on seed germination of wheat and lucerne. The reduction in seed germination of both the resistant and non-resistant ryegrass was highly significant, although there was no significant reduction in rate of germination. The different seed germination responses of the test species to an aqueous leaf extract of African wormwood raises the possibility of developing a bioherbicide from the extract.

Improving seed germination of Stylosanthes guianensis by means of warm water treatment.

The effect of different warm water treatments on the dormancy of hard-coated Stylosanthes guianensis seeds was investigated. Light and dark coloured seeds were placed into water at different temperatures. Warm water treatments induced a large number of soft-coated seeds. The optimum treatment for increasing germination percentage and germination rate was immersion in water at 60°C. Temperatures higher than 60°C led to a rapid decrease in germination due to loss of viability. Dark coloured seeds appeared to be more dormant than light coloured seeds.

Amaranth grain production as affected by watering regimes and day length in southern Mozambique

The high nutritional value of amaranth grain makes it attractive for the diet of rural people living in dry semi-arid areas of southern Mozambique. A study was implemented with Amaranthus hybridus and A. tricolor in sandy soil aiming to assess (1) the effect of different watering regimes (80%, 50% and 20% of total available water) on reproductive stage and grain crude protein content of the two species during the rainy and dry seasons, and (2) the effect of day length and minimum temperature on the time to flowering. Six field trials were conducted in Maputo in a randomised complete block design with a 2 × 3 factorial layout with six replications. This study revealed that panicle and internode lengths as well as straw and grain yields of both species decrease when the soil water content decrease. Conversely, the time to flowering and the grain crude protein contents were unaffected by the water deficit. The onset of flowering was significantly delayed by long days. The highest grain yield and harvest index were produced by A. tricolor under day lengths above 12u2005h d−1. When irrigation was applied to maintain soil water content at 80% of total available water, both species produced all year long.

Effect of soil- and foliar-applied nitrogen fertiliser on growth, yield and protein content of spring wheat (Triticum aestivum L.) under glasshouse conditions

Foliar application of nitrogen (N) can be essential in improving yield and grain protein content of wheat. Limestone ammonium nitrate and calcium nitrate solution were used as two N top-dressing treatments applied at three growth stages to evaluate their effect on growth, yield and yield parameters, and protein content of wheat under glasshouse conditions. At stem extension, plants treated with soil applied N performed significantly (p<0.05) better than plants treated with foliar applied N in terms of all measured vegetative growth parameters except for leaf area and leaf area index. At early heading stage, soil applied N performed significantly better for all the parameters studied except for number of leaves pot–1. After harvesting, all the studied parameters gave significantly better results from soil N applications compared to foliar N applications with the exception of number of ears pot–1. A protein content of 11% was found in plants treated with foliar N compared to 10% obtained from plants treated with soil N. Soil applied top-dressing appears to be superior to foliar applied top-dressing although the positive effects of foliar top-dressing on protein content need to be investigated further.