摘要:

Satellite‐derived vegetation indices were used to identify a geochemical mound of higher active greenness in the Karoo National Park, Beaufort West, South Africa. We determined whether this mound was occupied by plants with higher CO2assimilation rate. Plant cover on and off the mound was determined. Three woody species with high cover were selected for further investigation. Two deep‐rooted species,Rhigozum obovatumBurch. andEriocephalus ericoides(L.f.) Druce, showed greater net CO2assimilation rates on the mound. Net CO2assimilation rates for the third species,Pentzia incana(Thunb.) Kuntze were similar both on and off the mound. In an attempt to find a mechanistic basis for the elevated CO2assimilation rates, the relationships between soil factors, foliar nutrients and CO2assimilation capacity were also examined. Our results suggest that the elevated net CO2assimilation was not mediated via improved soil or plant water relations on the actively greening mound, nor through a difference in nitrogen levels in the soil or plant material, but possibly by way of the higher sub‐soil phosphorus levels measured from the geochemical mound. Genotype and cover cannot alone be used for rangeland condition assessment since localized elevated soil nutrient status (patchiness) contributes to greater photosynthetic carbon gain which may confer superior browsing responses to plants occurring on these mounds.

ISSN:1022-0119    

DOI:10.1080/10220119.1997.9647925

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The productivity ofTrifolium repensL. cv. Ladino, under irrigation in the subtropical region of Gauteng, South Africa, is unknown. The performance ofT. repenswas determined over five years (1981/1982 to 1985/1986), at two defoliation frequencies, four levels of nitrogen (0, 400, 800 and 1 600 kg N ha−1‐ total applied over five years), and either the removal or recycling of harvested material. Frequent, compared to infrequent defoliation, resulted in higher dry matter (DM) yields from the second year onwards. Dry matter yields were positively affected by the recycling of material, compared to no recycling. A mean DM yield of 191 ha−1in the first year and 12 t ha−1in the final year, was obtained. The highest DM yields occurred during October for all years and lowest DM yields from January to March. The first and final year showed similar peaks (late October) and troughs (March till April). Crude protein (CP) content of the herbage was influenced more by frequency of defoliation than recycling of material, where the highest CP content in any year was obtained from frequent defoliation. Nitrogen fertiliser applied up to a total of 1 600 kg N ha−1over five years had no effect on either DM yield or crude protein content. This study has shown thatT.repenscould be a productive pasture for at least five years in the subtropical region of Gauteng, South Africa. Productivity and quality ofT. repenswere enhanced by a defoliation interval of less than five weeks and when soil high fertility was maintained by recycled plant material.

ISSN:1022-0119    

DOI:10.1080/10220119.1997.9647926

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Species density and grass density were measured using a small‐quadrat method in eight plant communities in the Nylsvley Nature Reserve, South Africa. The presence of new species in each additional quadrat was used to calculate sample size. A sample size of 20 quadrats of 0.25 m2per site was found to be sufficient to measure species richness and density, and grass density in most plant communities in Mixed Bushveld. A sample size of approximately 30 quadrats was found to be necessary to survey plant communities with a relatively high species richness.

ISSN:1022-0119    

DOI:10.1080/10220119.1997.9647927

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

In the past, veld condition in the Karoo was assessed according to the ecological index method. This has recently been replaced by the grazing‐index method. The principles governing the method of botanical survey remain the same, but this methodology has not been described in detail. The objective of this paper is to address this shortcoming. The method is based on canopy‐spread‐cover strikes, and these strikes are assumed to represent mass as well as number of the species. Through the application of the individually estimated grazing‐index values of the different species, the index of veld condition is computed from either line‐point or clipped‐quadrat data. With appropriate data management, both the line‐point and the clipped‐quadrat data yield acceptable indices of veld condition, from which values, current grazing capacities, can be estimated for assessed sites.

ISSN:1022-0119    

DOI:10.1080/10220119.1997.9647928

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Livestock and wildlife share much of their respective ranges throughout the semi‐arid ecosystems of the world. As the profitability of livestock production becomes more marginal and wildlife values increase, there is a need to understand the interactions between livestock and wild large mammalian herbivores (and other indigenous biodiversity). To address this, we have established a long‐term multi‐species herbivore exclusion experiment in the Laikipia ecosystem in Kenya. Using a series of semi‐permeable barriers, we are differentially excluding various combinations of cattle, large wild mammalian herbivores, and mega‐herbivores (giraffes and elephants) from a series of replicated four‐hectare plots. We are monitoring soil, plant, and animal responses to these treatment characteristics. This multi‐disciplinary project is one of the first to include controlled, replicated exclusion of combinations of multiple guilds of rangeland herbivores in the same place at the same time. We report here (1) the first quantitative vegetation analysis of this important grazing ecosystem; (2) details of the experimental design; (3) evidence of the effectiveness of the herbivore exclosures; and (4) a summary of some preliminary results.

ISSN:1022-0119    

DOI:10.1080/10220119.1997.9647929

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Making good quality hay from Eragrostis curvula is a risky operation in many areas in South Africa due mainly to unfavourable weather conditions. Ensiling should therefore be considered as an alternative method for conserving the forage. The aim of this study was to determine if the use of a lactic acid bacterial inoculant when ensiling E. curvula is beneficial in terms of the fermentation dynamics during ensiling and the aerobic stability of the silage. The composition of the fresh chopped grass was 37.8+0.1% dry matter, 50.8±2.3% in vitro organic matter digestibility, 5.8±0.3% crude protein, and 79.2±0.34% neutral detergent fibre on a dry matter basis. Eragrostis curvula was ensiled in eighteen mini silos (three replications x six periods) for each of the control and inoculated treatments to follow the fermentation dynamics during ensiling. The pH of the control silage on day 1, 2, 4, 8, 16 and 122 of ensiling was 5.90, 5.08, 4.81, 4.76, 4.67 and 4.33, and that of the inoculated silage was 5.12, 4.34, 4.24, 4.30, 4.14 and 4.0 respectively. The ammonia nitrogen as percentage of total nitrogen of the control and inoculated silage differed (P<0.05) and was 14.4% and 10.9% respectively. The butyric acid content of the control and inoculated silage was 2.77% and 0.16% (P<0.05), and the lactic acid content 2.22% and 3.15% (P<0.05) respectively. Addition of the lactic acid bacterial inoculant to E. curvula at ensiling resulted in a more rapid drop in pH and better preservation compared to the control silage. Both silages were stable when exposed to air for five days.

ISSN:1022-0119    

DOI:10.1080/10220119.1997.9647930

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

In the past, veld condition in the Karoo was assessed using the ecological index method. This recently changed to the grazing‐index method on account of the differently estimated grazing‐index values being used. The principles governing the method of survey remain the same. The method employs canopy‐spread‐cover strikes to record the species composition of different sites. By appropriate management of these line‐point data, different sites can be compared with one another by employing the Z‐index of agreement (similarity).

ISSN:1022-0119    

DOI:10.1080/10220119.1997.9647931

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

ISSN:1022-0119    

DOI:10.1080/10220119.1997.9647924

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor