Soil seed bank characteristics in relation to land use systems and distance from water in a semi-arid rangeland of southern Ethiopia

AbstractThe size and species composition of the soil seed bank of southern Ethiopia rangelands were examined under three land use systems (communal land, a government ranch and traditional grazing reserves) and along a distance gradient (near, middle and far) from water sources. Soil seed bank sampling was carried out at the end of the growing season from 0.25 m−2 quadrates 30 mm deep. The aboveground species composition was also compared. Of the total plant species identified in the soil seed bank in the greenhouse, 25% were grasses and 75% non-grasses. The near, middle and far sites from water was dominated by Leucas glabrata, Verbesina encelioides and Lintona nutans, respectively. Lepthotrium senegalensis made up 67% of the total composition of the soil seed bank in the traditional grazing reserve. Graminoid seedling density at the traditional grazing reserve (798.8 seedlings m−2) was higher (P<0.01) than that of the ranch and communal sites, but did not vary significantly along the distance gradient from water (average 239.2 seedlings m−2). Non-graminoid seedling density did not vary much (P>0.05) between the land use systems (average 128.9 seedlings m−2) and along the distance gradients from water (average 183.7 seedlings m−2). Sorensen's similarity index of the aboveground vegetation and the associated seed bank was low at all the sites. Difference in grazing pressure between the land use systems was one of the most likely causes of variations in the soil seed bank density and botanical composition of graminoids. The non-significant differences in the graminoid seed bank density along the distance gradients from water were due to similar population of grasses and may not explain the levels of grazing impact and disturbance. Regeneration from the soil seed bank may have a profound effect in restoring the composition of the grass layer in the degraded Borana rangelands if sustainable management practices are applied and sufficient rest periods followed. By translocating seed rich topsoil from the grazing reserves to degraded grazing areas, the soil seed bank can be used to develop valuable grass species at small community level

Root distribution with changes in distance and depth of two-year-old cactus pears Opuntia ficus-indica and O. robusta plants

AbstractOpuntia is a drought tolerant crop and even the smallest amount of water is absorbed efficiently through the shallow and horizontally spread root system. However, there is a lack of knowledge on the root dynamics of cactus pear for sustainable production of fodder and fruit in the drier areas. This study, conducted during the 2003/2004 growing season on two-year-old Opuntia ficus-indica (L.) Miller (cultivar Morado–green cladode) and O. robusta Wendel. (cultivar Monterey–blue cladode) plants in the field was therefore aimed at quantifying root distribution with distance and depth from the stem. Root growth was expressed in terms of both mass and length, and water-use efficiency (WUE) was defined as the cladode dry mass production per unit of evapotranspiration. In both species most roots were concentrated in the first 150 mm soil layer. After only two growing seasons the roots spread as far as 2.5 m from the stem for both species. The total root dry weight production calculated per plant up to a depth of 1200 mm, was 239 and 316 g per plant or kg ha−1 for O. ficus-indica and O. robusta respectively. The thickest roots developed directly from the planted cladode and were 9.1 mm thick for O. ficus-indica and 6.3 mm for O. robusta. Opuntia robusta showed a finer root system than that of O. ficus-indica. After two growing seasons 3407 and 2702 kg ha−1 aboveground dry mass was produced by O. ficus-indica and O. robusta respectively. The WUE of O. ficus-indica (6.52 kg ha−1 mm−1) was significantly higher than that of O. robusta (5.39 kg ha−1 mm−1). The roots comprised only 11% of the total biomass for O. robusta and 7% for O. ficus-indica. Such root adaptations of this species are in addition to the classical physiological and structural modifications of CAM plants to tolerate prolonged drought

Evapotranspiration and water use efficiency of different grass species in the central Orange Free State.

Evapotranspiration (Et) and water use efficiency (WUE) were determined for each of seven grass species during the 1986/87 seasons. The highest and lowest mean daily Et of 2, 39 and 1, 66 mm were recorded respectively for Themeda triandra and Sporobolus fimbriatus. Between species, the average Et for the two seasons did not differ significantly. On average the highest and lowest WUE of 7, 83 and 4, 72 kg/ha above-ground phytomass produces for each mm water evapotranspired, were recorded respectively for Cymbopogon plurinodis and Panicum stapfianum. The average WUE of C. plurinodis, Digitaria eriantha and T. triandra was 38% (P < 0, 01) higher than that of the other four species. Under conditions of moisture stress the WUE of the above-mentioned three species was the lowest and that of Eragrostis chloromelas the highest.Keywords: above-ground phytomass; cymbopogon plurinodis; digitaria eriantha; eragrostis chloromelas; eragrostis lehmanniana; evapotranspiration; grass; grasses; hydraulic non-floating lysimeters; moisture stress; orange free state; panicum stapfianum; phytomass; south africa; sporobolus fimbriatus; themeda triandra; water use efficienc

Short-term effect of severe drought on veld condition and water use efficiency of grassveld in the central Orange Free State.

The impact of an intensive drought (1982/1983 and 1983/84-growing seasons) on botanical composition, basal cover, mortality of grazing plants and water use efficiency (WUE) of veld in good, moderate and poor condition was identified. Increaser II species were apparently more capable of surviving drought than the Decreaser species. Under optimal soil moisture conditions the Decreaser species increased and the Increaser II species decreased. During the drought extensive grass mortality took place. Veld condition plays an important role in determining mortality during drought. Decreaser species have a high water requirement for optimal WUE, while Increaser II species can reach maximum WUE with less water. Under water stress conditions Increaser II species significantly (P < 0.01) do not use the water as efficiently as do Decreaser species. The WUE under water stress conditions for veld in good, moderate and poor condition was on average, during the study period, 0.90; 0.90 and 0.40 kg ha -1mm -1, respectively, and towards under optimal water conditions, 2.47; 1.67 and 0.23 kg ha -1mm -1, respectively.Keywords: afrikaans; basal cover; botanical composition; botany; composition; decreaser species; drought; efficiency; free state; grasses; grazing; increaser ii species; mortalities; mortality; soil moisture; south africa; species composition; stress; sydenham; veld condition; water use efficienc

Influence of bioregion and environmental factors on the growth, size and reproduction of Bonsmara cows

A better understanding of the influences of the bioregion (production environment) and environmental factors on the productivity of beef cows is vital in the pursuit of improving beef production. The influence of bioregion and important environmental factors in South Africa (temperature, rainfall, soil pH, soil cation exchange capacity, soil organic carbon content, soil phosphorus (P) concentration, and grazing capacity) on production and reproduction traits of Bonsmara cows were analysed by means of cluster analysis and analysis of variance (ANOVA). Stepwise regression analyses were used to determine the influence of the different environmental factors (and possible non-additive genetic effects) on the production and reproduction efficiency of the cows. Results of the effects of bioregion and non-additive genetic effects (the contribution of which was not quantified per se) on beef cow productivity indicate that bioregion influenced production and reproduction traits of cows, while significant farm effects were also noted. Bonsmara farm influenced the production efficiency of cows through the implementation of management practices and breeding objectives. Environmental factors significantly influenced all production traits measured for Bonsmara cows. The extent of the effects of the combined influences of environmental factors on cow productivity depended on the physiological stage of animal growth and reproduction. Environmental effects on production efficiency were buffered by maternal effects at birth, but became more significant after weaning (9%) to yearling age (10%) and maturity. Most environmental factors studied influenced the production traits of cows, with rainfall and temperature having the largest influence. The negative influence of rainfall on cow productivity was attributed to its negative influence on grazing quality, through effects on soil pH, phosphorus and soil organic carbon content. The small negative influence of temperature on the productivity of cows indicates that this breed is well adapted to the main South African beef production regions. It should be noted that in this study the non-additive genetic component was not separated from the environmental components.Keywords: Beef cattle, bioregion, geographic location, growth curve, production efficienc

The influence of nitrogen and defoliation on the nitrogen content of Lolium multiflorum cv. Midmar

The response of the nitrogen content in ryegrass (Lolium multiflorum cv. Midmar) to a variation in applied nitrogen (0kg N ha-1, 150kg N ha-1, 300kg N ha-1 and 450kg N ha-1) and defoliation intervals (every 2, 4, 6 and 8 weeks, as well as twice a season) was determined. In a field trial, the four nitrogen levels were combined with the five defoliation intervals. The quality of the dry matter (DM) was determined by Near Infrared Spectroscopy (NIRS). Total nitrogen, non-protein nitrogen and true protein were significantly (P&le;0.01) influenced by nitrogen level, defoliation interval and the interaction between these two factors. The total nitrogen content varied from 0.68% to 3.38%, the true protein from 0.57% to 2.74% and the non-protein nitrogen from 0.11% to 0.65%. Nitrogen assimilated in the aboveground material ranged from 9.8kg N ha-1 to 423.0kg N ha-1. Linear relationships (P&le;0.01) between total nitrogen, true protein and non-protein nitrogen (NPN) respectively were found. Keywords: NPN, nitrogen content, ryegrass, true protein African Journal of Range & Forage Science 2002, 19(3): 167-17

Hydrological cycle and water use efficiency of veld in different successional stages.

Hydraulic non-floating lysimeters were used to determine the evapotranspiration (Et) and water use efficiency (W.U.E.) of veld in different successional stages for the period September 1978 to June 1979. In addition runoff of the various successional stages was recorded on runoff plots.Averages of 1,018 litres, 1,258 litres and 1,771 litres of water were lost by evapotranspiration from climax, subclimax and pioneerveld respectively for each gram D.M. produced during the second half of the growing season. The highest Et-losses were recorded during the last week of November, when the grasses were in the reproduction phase.The runoff from the pioneer-runoff plots was 171 percent higher than that of the climax runoff plot. A computer programme was used to fit harmonic curves to the weekly Et/Eo relationship of each successional stage for the 1978/79 growing season.Keywords: afrikaans; botany; evapotranspiration; grass; grasses; hydraulic non-floating lysimeters; lysimeter; orange free state; runoff; season; south africa; sydenham; university of the free state; veld; water use efficienc

Ranking of grass species according to visible wilting order and rate of recovery in the central Orange Free State.

A number of grasses were ranked according to the order in which they wilted with diminishing moisture availability, and according to their ability to recover after water replenishment. Digitaria eriantha and Digitaria argyrograpta were the most sensitive to moisture stress, whereas Sporobolus fimbriatus and Panicum stapfianum were last to show signs of wilting. The latter two grass species were the first to recover from wilting during optimum soil water conditions. The leaf water potential and soil water content at which each grass species wilted were recorded.Keywords: availability; digitaria argyrograpta; digitaria eriantha; grasses; leaf water potential; moisture stress; neutron probe; orange free state; panicum stapfianum; soil water; soil water content; soil water potential; south africa; sporobolus fimbriatus; stress; water use efficiency; wiltin