摘要:

The effect of defoliation during wilting on the production ofThemeda triandraandEragrostis lehmannianawas studied over four years (1977 to 1980). Defoliation whilst the plants were at temporary wilting point in the early growing season (before 1 January) decreased production from both species in the subsequent season (P≤0.01). Defoliation over the last half of the growing season, during wilting, had little effect on growth in the following season (P≤0.05). The effect of a defoliation treatment on production was not necessarily neutralised after one season's rest.Themeda triandraproduced more (P≤0.01) thanE. lehmannianafor each defoliation. The seasonal soil‐water extraction pattern in the soil profile was also determined. As the season progressed, plants showed visible signs of wilting at lower soil‐water content than earlier in the season. Most water extraction over the season takes place to a soil depth of 600 mm.

ISSN:1022-0119    

DOI:10.1080/10220119.1993.9638336

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

ALolium multiflorumcv. Midmar pasture and ninety individual plants (both Italian and Westerwolds types), from 15 differentLolium multiflorumcultivars in a spaced‐plant trial, were assessed for total nonstructural carbohydrate (TNC) content, TNC yield, dry matter (DM) content, DM yield and nitrogen (N) content. Maximum TNC values in the plants were reached after 12h00. The TNC content was positively correlated with the DM content of the plant, but this was probably environmentally induced. The negative relation between TNC and N content appeared to be genetically controlled. Diploid Italian types had the highest mean seasonal DM content. Cultivars with the highest mean DM yield over the growing season rated poorly in terms of TNC content. However, the coefficients of variation for the seasonal DM yield and TNC content were high. Coefficients of variation for mean DM content over the growing season were much lower than for TNC content and DM yield. It was concluded that the variation within and between cultivars was sufficiently large for successful manipulation in a breeding programme. The cultivars Exalta, Exalta × Lemtal, Moritz and ex Matador ranked high in both TNC yield and DM content.

ISSN:1022-0119    

DOI:10.1080/10220119.1993.9638337

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The effects of a cutting trial, conducted to study the combined influence of defoliation and competition from surrounding vegetation on the vigour ofThemeda triandraandAristida junciformis, were evident after the single season of treatment implementation.Aristida junciformiswas more sensitive to defoliation thanT. triandra, whereas competition reduced yield to a greater extent inT. triandrathan inA. junciformis. The two species differed in their ability to tolerate defoliation under competition. Defoliation reduced the yield of A.junciformis, at all levels of competition, to a greater extent thanT. triandra. Aristida junciformiswas particularly sensitive to a combination of severe defoliation and full competition. It is suggested that manipulation of grazing patterns may shift the competitive balance between palatable (e.g.T. triandra)and unpalatable (e.g.A. junciformis)components of the sward.

ISSN:1022-0119    

DOI:10.1080/10220119.1993.9638338

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

A step‐wise approach was followed towards the design of a monitoring system for the herbaceous layer on the escarpment of the Drakensberg mountains in the Transvaal, South Africa. The parameter of concern was proportional species composition. In a first phase, the plot size and number of point observations required to achieve a repeatable assessment of a single plot at a predetermined precision level were investigated. The Chapman‐Richards three‐parameter model was fitted to similarity values obtained from comparisons between successively larger sets of points. This resulted in 140 points being required within a 30 × 30 m plot in order to recover 95% of the internal association of the composition data. In a second phase, the number of plots required for a repeatable assessment of a large stratum was determined. Successively larger nested areas were sampled. Monitoring of a large stratum at 95% of asymptotic replicate similarity would require sets of 21 randomly selected plots. The third and final phase was concerned with the development of a procedure for detecting change. A similarity test made it possible to detect change between successive surveys with a known degree of precision.

ISSN:1022-0119    

DOI:10.1080/10220119.1993.9638339

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Leucaena leucocephala, Clitoria ternatea, Macroptilium atropurpureumcv. Siratro,Cassia rotundifoliacv. Wynn,Macrotyloma axillarecv. Archer,Stylosanthes guianensisvar.guianensiscv. Graham,S. guianensisvar.intermediacv. Oxley,S. hamatacv. Verano and 5.scabracv. Fitzroy and cv. Seca were screened for their ability to establish at five coastal sites of Maputo province, Mozambique. Three grazing treatments were imposed in strips: continuous access, dry‐season‐only access and an ungrazed control. Grazing pressure was dependent on the movement of communal cattle and goat herds. Mean seedling emergence ranged from a low of 28% for Graham to a high of 78% for Siratro. First season mean seedling vigour (1–10) differed (P=0.01) among entries and ranged from 4.0 for Graham to 8.0 for Seca. First‐year dry season individual plant vigour showed an interaction (P=0.1) between grazing treatment and entry with Siratro and Seca plots averaging 3.0 or better. Dry season plot cover likewise showed an interaction (P=0.002) between treatment and entry with Siratro and Seca averaging over 20%. Second rainy season vigour showed differences (P=0.03) among species only, with Siratro and Seca having values over 7.0. Plot cover was likewise differentiated only among species(P=0.0006) with Siratro and Seca both covering 59% of their plots, superior toC. ternatea(19%),L. leucocephala(9%), Archer (7%), Verano (16%), Fitzroy (28%), Graham (29%), and Wynn (4%). Oxley (36%) was undifferentiated from either group. Overall, Siratro and Seca had the best establishment whilst Oxley showed promise. Deferred grazing generally appeared to have little effect on establishment.

ISSN:1022-0119    

DOI:10.1080/10220119.1993.9638340

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Sheep were used in two investigations to study factors which could limit voluntary intake ofPennisetum clandestinum(kikuyu) pasture. Possible reasons for the low intakes were found in the high soluble nitrogen and nitrate content of the pasture, its high oxalate content, and its considerable potential for foaming, the latter suggesting the presence of sapbnins. The high fibre content of the material could also have limited intake in wilted, dry or stemmy kikuyu. The relative importance of these factors appears to change with growth stage, the amount of nitrogen fertilizer applied, stocking rate and moisture supply. The factors which are detrimental to forage quality such as oxalates and nitrates are higher in the young and actively growing material than in older material, while thein vitroproduction of foam seems unrelated to forage quality and remained high, despite changes in other factors which detrimentally affected forage quality.

ISSN:1022-0119    

DOI:10.1080/10220119.1993.9638341

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Two experiments designed to establish possible reasons for the often‐observed low voluntary feed intake of animals grazing kikuyu pastures were conducted at two widely differing locations. Low digestibility and low rate of digestion limited feed intake only when sheep were grazing dry, wilted kikuyu. At other times, rumen contents were relatively low, and voluntary intakes appeared to have been controlled by other factors. The foaminess of the rumen under circumstances of a low rumen fill seems to suggest that a high saponin content could have limited intake. However, the fact that a high rumen fill coincided with a highin vitrofoam production in one instance may imply that a high saponin content was not instrumental in limiting intake. Only the rumen ammonia concentration and the total nitrogen content of the leaves showed a consistent relationship with voluntary intake.

ISSN:1022-0119    

DOI:10.1080/10220119.1993.9638342

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Acacia tortilis, A. karrooandDichrostachys cinereasubsp.africanatrees were divided into nine height classes, with increments of 0.5 m. The abundance ofP. maximumgrowing under their canopies was estimated by scoring on a scale of 0 (noP. maximum)to 3 (P. maximumpredominates). Presence ofP. maximumwas mainly associated with larger trees of all three species, and ranged from virtual absence under small trees to pure stands under larger trees. Spearman's rank correlations between tree height and the abundance ofP. maximum(median score) were positive and significant.Panicum maximumattained pure stands (score 3) under smallerA. tortilistrees than under eitherA. karrooorD. cinerea. A median score of 3 was attained underA. tortilis, A. karrooandD. cinereatrees of >2.0 m, >4.0 m and >4.5 m, respectively. Tree height therefore represents a simple index of conditions favourable toP. maximum.

ISSN:1022-0119    

DOI:10.1080/10220119.1993.9638343

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

ISSN:1022-0119    

DOI:10.1080/10220119.1993.9638344

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

ISSN:1022-0119    

DOI:10.1080/10220119.1993.9638335

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor