摘要:

In South Africa there is widespread reliance on kikuyu grass as a source of summer forage for intensive dairy, beef and sheep enterprises. There is, however, a dearth of reliable information on the fertility requirements of kikuyu pastures. Responses of previously productive and unproductive kikuyu pastures in the Mistbelt and Highland Sourveld of KwaZulu‐Natal to top‐dressed nitrogen (N) and phosphorus (P) fertilizers were studied infield cutting trials conducted during two consecutive seasons. Significant dry matter (DM) yield responses accompanied incremental N applications of up to 500 kg ha−1. First‐season DM yields of previously productive pastures at zero applied N were in the range 6 to 9 t ha−1, while yields of previously unproductive pastures at zero N were 0 to 2 t ha−1. By the second season, yields at zero N were uniformly low on the various pastures, reflecting the limited extent of plant‐available N reserves in soils under productive kikuyu. In both the Mistbelt and Highland Sourveld, efficiency of response to applied N in seasons when rainfall was similar to the long‐term mean was approximately 30 kg DM per kg N over the N application range of 0 to 250 kg N ha−1. When rainfall was substantially below average, N efficiencies decreased markedly. Application of N in six rather than three dressings during the growing season resulted in the N efficiency increasing by 3.5 kg DM per kg N. In contrast to the enormous responses to N, there was little or no response to P in the various trials. An optimum P test (NH4HCO3/ NH4F / EDTA) for high clay content (>50% clay) Mistbelt soils of approximately 10 mg L−1is suggested from yield‐soil test calibrations. Data highlighting the impact of soil sampling depth on P test values are presented, and this information serves to underline the importance of standardizing sampling procedures in the soil testing of pastures for fertility purposes.

ISSN:1022-0119    

DOI:10.1080/10220119.1997.9647911

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The influence of micro‐site (shaded, exposed, buried) on the seed longevity and seedling emergence of Themeda triandra was tested using experimental seed banks. Deep shade considerably reduced soil surface temperature. Seeds did not persist in any micro‐site for longer than one year. The fate of most seeds in the first year was to germinate but most buried seeds died before emergence; <20% of seed decayed. Greatest seedling emergence occurred with seed on the surface, particularly if shaded. The temporal pattern of emergence depended on micro‐site, with implications for seedling risk. Limited seed longevity may render T. triandra, an obligate seed‐reproducing species, vulnerable to failure of seedling recruitment.

ISSN:1022-0119    

DOI:10.1080/10220119.1997.9647912

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

This research was conducted in the Mamora cork oak forest of Morocco to describe the impacts of sheep grazing (no use, 35% use, 70% use) in March, April, May and June of 1987 and 1988 on seasonal changes in forage quality of the herbaceous vegetation. The study showed that trends in herbage quality were related mainly to plant maturity. As more species mature, forage quality declines and falls below animal nutritional requirements, especially for young animals. With declining forage quality, the manager has the option of moving stock to areas of less‐mature forage, supplementing the forage or modifying the demand placed upon it.

ISSN:1022-0119    

DOI:10.1080/10220119.1997.9647913

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The widespread drought of the early 1990s resulted in considerable stock losses in the semi‐arid savanna of KwaZulu‐Natal. We compared the influence of four drought response strategies on herd number, milk yield, cost and net present value for a communal cattle herd over the period 1983 to 2001 using a simulation modelling approach. The strategies were (1) no reaction to drought; (2) moving stock to areas not affected by drought; (3) purchasing replacement stock after the drought; and (4) supplementing stock during the drought with sugar‐cane residues. Moving, buying or feeding stock generated greater milk yields and net benefits relative to no drought response, but at considerably greater cost. Cost:benefit was greatest where a small proportion of female stock (10 percent) were moved. By doing nothing in the face of regional drought, communal graziers may be acting rationally, given the constraints under which they operate. The study reveals that simulation modelling may provide a useful basis from which to assess the outcome of various management strategies for communal graziers, and for integrating the disparate suite of influences which drive decision‐making on communal lands.

ISSN:1022-0119    

DOI:10.1080/10220119.1997.9647914

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The resilience of rangeland soils and vegetation to different levels of grazing is still poorly understood. A study was conducted to determine the recovery of a rangeland grazed at different intensities and allowed a two‐year rest period. The following treatments were applied to 0.5 hectare plots: 0, 4, 8 and 16 heifers per hectare, hereafter referred to as CL, X, 2X and 4X respectively. At the end of the grazing period, the highest stocked treatments (2X and 4X) had lower herbage biomass, higher soil bulk density, lower soil moisture and lower herbaceous cover than the lower stocked treatments (CL and X). Drought in the rest period caused an increase in bulk density and decline in soil moisture in all the treatments. Even after the two‐year rest period, the more heavily grazed treatments had higher bulk density and lower soil moisture than the more lightly grazed treatments. Similarly, the herbaceous biomass in the 2X and 4X treatments did not recover after the two‐year rest period and was lower (P < 0.05) than the CL and X treatments. At the end of the recovery period a trend of declining herbaceous cover with stocking density was still evident. The relative cover of forbs in the 4X treatments increased more than in the other treatments, while the cover of perennial grasses did not recover in the 4X treatments after the rest period. Thus, stocking above 2X produced negative soil and vegetation responses which did not recover during the two‐year rest period. This study also indicated that drought can cause vegetation and soil responses similar to those of overgrazing.

ISSN:1022-0119    

DOI:10.1080/10220119.1997.9647915

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

ISSN:1022-0119    

DOI:10.1080/10220119.1997.9647916

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

ISSN:1022-0119    

DOI:10.1080/10220119.1997.9647910

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor