African Journals Online
African Journal of Range & Forage Science

VOLUME 19 (2) (2002)
Abstracts

African Journal of Range & Forage Science 2002, 19: 79–80

Printed in South Africa — All rights reserved

Presidential Address — 2002: The Grassland Society of Southern Africa should be striving for greater synergy with the farming community

DCW Goodenough

ARC — Range and Forage Institute, PO Box 1055, Hilton 3245, South Africa

e-mail: [email protected] 

Delivered at Congress 37, Christiana, North West Province, 13 May 2002

African Journal of Range & Forage Science 2002, 19: 81–91

Printed in South Africa — All rights reserved

Response to elevated CO₂ from a natural spring in a C₄-dominated grassland depends on seasonal phenology

SJE Wand¹*, GF Midgley² and WD Stock³

¹ Department of Horticultural Science, University of Stellenbosch, Private Bag X1, Matieland 7602, South Africa

² Ecology and Conservation, National Botanical Institute, Private Bag X7, Claremont 7735, South Africa

³ Department of Botany, University of Cape Town, Private Bag, Rondebosch 7700, South Africa

* Corresponding author, e-mail: [email protected] 

Received 20 February 2002, accepted 10 June 2002

A South African C₄-dominated grassland was exposed to twice-ambient atmospheric CO₂ concentration using gas emitted by a natural CO₂ spring and distributed over a 7m x 7m plot. A similar control plot was established 20m away at near-ambient CO₂ concentrations. Photosynthetic CO₂ response curves were performed on three C₄ and one C₃ grass species under both treatments, in spring (post-fire), mid-summer and autumn. Photosynthetic efficiency of the post-fire dominants, Alloteropsis semialata subsp. eckloniana (C₃) and Andropogon appendiculatus (C₄) was significantly enhanced in high CO₂ only during the early season, when photosynthetic capacity was high. Thereafter, photosynthetic capacity decreased with advancing season in both species, and positive responses to high CO₂ were lost or reduced. In the mid- to late-season dominant Themeda triandra (C₄), photosynthetic capacity was maintained in elevated CO₂ during the mid- to late-season, while decreasing in ambient CO₂ relative to high CO₂. Eragrostis racemosa (C₄), a slow grower, showed no significant responses to high CO₂ during the late season. CO₂-responsiveness in the field generally followed the seasonal phenologies of each species, being greatest during the most active growth period.

Keywords: climate change, gas exchange, photosynthetic regulation, stomatal conductance

African Journal of Range & Forage Science 2002, 19: 93–105

Printed in South Africa — All rights reserved

The influence of various types and frequencies of rest on the production and condition of sourveld grazed by sheep or cattle. 2. Vigour

KP Kirkman

Grassland Science, School of Applied Environmental Sciences, University of Natal, Private Bag X01, Scottsville, Pietermaritzburg 3209, South Africa

e-mail: [email protected] 

Received 3 September 2001, accepted 11 June 2002

Treatments involving a full growing season rest in alternate years, half a growing season rest (late season) in alternate years and no rest were applied to veld grazed by sheep or cattle at similar stocking rates. Residual effects of the treatments on veld vigour were determined by measuring species regrowth during the season following treatment application, compared to ungrazed controls. The vigour of veld grazed by sheep declined rapidly relative to veld grazed by cattle. The vigour of palatable species was severely impacted, vigour of intermediate species was variably impacted and vigour of unpalatable species increased dramatically on veld grazed by sheep. Similar trends occurred in veld grazed by cattle, but to a lesser degree. Resting was beneficial for vigour recovery in both sheep and cattle treatments but it seems that the grazing treatment between rests has an over-riding influence on veld vigour. The veld grazed by sheep remained at a lower productivity level than veld grazed by cattle. Principles related to resting and the impacts of sheep and cattle grazing are briefly discussed with a view to formulating management strategies.

Keywords: veld management, livestock type, livestock movement, dry-weight-rank

African Journal of Range & Forage Science 2002, 19: 107–116

Printed in South Africa — All rights reserved

Patch grazing of Tall Grassveld by cattle after a spring burn

CD Morris

Grassland Science, University of Natal, Private Bag X01, Scottsville 3209, South Africa

Present address: Range and Forage Institute, Agricultural Research Council, Private Bag X01, Scottsville 3209, South Africa e-mail: [email protected] 

Received 13 February 2002, accepted 10 June 2002

Patterns of herbage removal by rotationally stocked cattle (at a density of 4.85AUE ha^-1) on initially structurally homogenous Tall Grassveld were examined over a single season. Three unreplicated camps were stocked early (29 days), at the recommended `10–15cm' sward height (44 days), and late (80 days) after a spring burn. Temporal change in the spatial distribution of herbage in each treatment was described by intensive measurement of compressed sward height (CSH) with a disc pasture meter and analysed with parametric and spatial statistics. Grazing pressure at the start of the grazing was highest in the early graze, intermediate at the recommended, and least in the late graze treatment because of variation in initial herbage mass related to period of deferment after the burn. The early graze paddock was most spatially uniform and the late graze paddock the most uneven and patchy before grazing. Such initial conditions significantly affected subsequent herbage removal patterns: the greater the amount and spatial variability of herbage accumulated before grazing, the greater the chance for patches to develop through area-selective grazing. The early graze paddock was utilised non-selectively during the first two grazing periods but similar to other treatments, became patchier with time. Spatial pattern, a mosaic of short, intermediate and tall patches, peaked in late summer and was most pronounced in the late graze treatment. Intensive, early stocking after a burn is recommended for minimising intraseasonal development of patches and efficient use of high-quality forage available after a burn.

Keywords: deferment, grazing pressure, selective grazing, spatial heterogeneity, sward structure

African Journal of Range & Forage Science 2002, 19: 117–122

Printed in South Africa — All rights reserved

Statistical power of commonly used point methods in grassland monitoring

BK Reilly and MD Panagos*

Department of Nature Conservation, Technikon Pretoria, Private Bag X680, Pretoria 0001, South Africa

* Corresponding author, e-mail: [email protected] 

Received 22 January 2002, accepted 14 July 2002

It has become almost universally accepted that the management of conservation areas and game ranches be subject to pre-determined sets of objectives and goals. Key to management decision making are the results of vegetation monitoring protocols that are designed to indicate changes in vegetation status. These changes are frequently measured as a proportional species composition and measure of basal cover and based on samples of 100–200 points in specific fixed sites. Minor changes of the magnitude of the order of single percentage points often form the basis of a management decision relating to herbivore stocking rates. These values are often quoted sans confidence limits or any other measure of dispersion. This paper investigates the statistical power of within stand replicates of three commonly encountered point methods, replicated within the same stand on Suikerbosrand Nature Reserve, Gauteng Province, and shows unacceptably high Type II error probabilities.

African Journal of Range & Forage Science 2002, 19: 123–128

Printed in South Africa — All rights reserved

Effect of plant height at cutting, source and level of fertiliser on yield and nutritional quality of Napier grass (Pennisetum purpureum (L.) Schumach.)

T Zewdu¹*, RMT Baars² and A Yami³

¹ Adet Agricultural Research Centre, PO Box 8, Bahir Dar, Ethiopia

² Alemaya University, PO Box 138, Dire Dawa, Ethiopia

³ Ethiopian Agricultural Research Organisation, PO Box 32, Debre Zeit, Ethiopia

* Corresponding author, e-mail: [email protected] 

Received 31 January 2002, accepted 20 May 2002

Napier grass (Pennisetum purpureum (L.) Schumach.) was studied using a 5 x 3 factorial experiment arranged in a randomised complete block design with three replications. The treatments were five fertiliser applications (0kg ha^-1 N, 46kg ha^-1 N and 92kg ha^-1 N, 1t ha^-1 and 2t ha^-1 cattle manure) and three plant heights at cutting (0.5m, 1m and 1.5m). The mean dry matter (DM) yield was 8.21t ha^-1 per cut but increased when the plant height at cutting increased and when the level of N fertilisation increased (P<0.05). Neutral detergent fibre (NDF), acid detergent fibre (ADF), acid detergent lignin (ADL), cellulose, calcium, in vitro dry matter digestibility (IVDMD) and metabolisable energy were significantly (P<0.05) affected by plant height at cutting while total ash, crude protein (CP), ADF-ash, hemicelluose and phosphorus were affected by both plant height at cutting and fertiliser level. As plant height at cutting increased from 0.5m to 1.5m, IVDMD declined from 71.74% to 61.03% (P<0.05). Correlations between IVDMD versus CP, NDF, ADF, ADL, cellulose and hemicellulose were high with r = 0.92, -0.94, -0.96, -0.98, -0.83 and 0.74, respectively. CP yield per hectare per day of growth was highest for the 0.5m height at cutting, whereas the digestible DM yield was highest at both the 0.5m and 1.0m cutting height. The results of the present study suggest that Napier grass could be categorised under medium to high quality forage if cut at 0.5m or 1.0m height.

Keywords: cattle manure, digestibility, elephant grass, forage, nitrogen fertiliser

African Journal of Range & Forage Science 2002, 19: 129–130

Printed in South Africa — All rights reserved

Research Note

The effect of prolonged heavy grazing pressure on the regrowth of two perennial grass species in a semi-arid communal rangeland

W Twine^1,2*, V Gray² and N Owen-Smith²

¹ Wits Rural Facility, Private Bag X420, Acornhoek 1360, South Africa

² School of Animal, Plant & Environmental Sciences, University of the Witwatersrand, PO Wits 2050, South Africa

* Corresponding author, e-mail: [email protected],  [email protected] 

Received 7 February 2002, accepted 16 July 2002

We tested the hypothesis that initial above-ground regrowth of defoliated grass tufts would be reduced in sites which have been exposed to prolonged heavy grazing. The regrowth of Themeda triandra and Urochloa mosambicensis tufts was compared between three heavily grazed sites close to a village and three relatively lightly grazed sites far from a village, in a semi-arid communal rangeland in the South African lowveld. A clipping experiment was done in the field using T. triandra and U. mosambicensis tufts. Regrowth was lower (P_0.01) in the heavy grazing sites for both species. This was more a function of tiller production rate, in terms of numbers of tillers, than of tiller extension rate. Rate of regrowth was not strongly affected by tuft size.

Keywords: clipping experiment, savanna, stocking rate, Themeda triandra, Urochloa mosambicensis