Kenaf (Hibiscus cannabinus L.) is a highly productive crop that is cultivated
worldwide for its fibre content which may be used to produce various
commodities. The kenaf crop was commercially cultivated in South Africa in the
1950’s, but production was discontinued from the 1960’s up to the mid 2000’s.
Production commenced again and kenaf emreged as a “new” fibre crop with the
first kenaf processing factory in the country going into production in 2006 in
KwaZulu-Natal. Due to the importance of kenaf in manufacturing of various
commodities, there was a need to investigate the agronomic practices thereof to
ensure sustainable yield. Therefore a two year study (2008/09 and 2009/10
summers) was conducted in Pretoria to investigate the influence of nitrogen,
plant population, row spacing and water treatments on kenaf growth, yield,
chemical quality and microscopic analysis of the fibre. In total, four field trials
were conducted at the Hatfield Experimental Farm of the University of Pretoria.
In 2008/09 a trial was conducted to investigate effects of plant population
(200,000; 300,000 and 400,000 plants ha-1), nitrogen level (0, 50, 100 and 150 kg ha-1) and row spacing (0.17, 0.34 and 0.50 m) under rainfed conditions. Sampling
for growth parameters were done at 85, 113 and 126 days after planting (DAP).
The biomass and chemical analysis of bark fibre were conducted only at or after
the final harvest, at 126 DAP. In general, no clear effect of different treatment
was observed on either parameter studied.
During 2009/10 three experiments were conducted. The first two had the same
nitrogen levels as in the previous season, but were grown either under rainfed or
irrigated conditions. The nitrogen was applied as two dressings of 0 and 50 kg
ha-1 at planting and 0, 50 and 100 kg ha-1 at thinning (35 DAP). The third
experiment investigated combinations of plant population (main plots) and row
spacing (sub plots) under rainfed conditions. Due to increasing stem yield with
increasing plant population during 2008/09, the lowest population of 200,000
plants ha-1 was left out and 500,000 and 600,000 plants ha-1 were added. The
same three row spacings as in 2008/09 were used. Nitrogen was applied at 150
kg ha-1, with 50 kg ha-1 at planting and 100 kg ha-1 at thinning. Growth and
biomass parameters, water use efficiency (WUE) (nitrogen trial only) were
subsequently measured up to the end of the growth cycle. The chemical
characteristics of bark fibre and nutrient removal (nitrogen trial only), nutrient use
efficiency as well as the nitrogen contents of leaves and stems were determined
only once at final harvest. The number of fibre rings and fibre bundles were
assessed only once during the growth cycle.
Growth and biomass parameters, WUE and both nutrient removal and nutrient
use efficiency generally tended to increase with increase in nitrogen level under
both rainfed and irrigated conditions. On the other hand, increasing plant
population tended to result in a decrease in all growth parameters, while it
increased biomass yield per hectare. Finally, the effect of row spacing was
inconsistent for the same parameter from one sampling to another one, and from
one parameter to another. The chemical characteristics of bark fibre showed
inconsistent responses to all agronomic practices. The number of fibre rings and
fibre bundles increased with increasing nitrogen level, decreased as plant
population increased, but did not show clear trends with regard to row spacing. In
general the plants grown under irrigated conditions performed better than those grown under rainfed conditions. The results of this study revealed that under the
environmental conditions of Pretoria, nitrogen levels above 100 kg ha-1 applied in
two dressings should result in best plant performance, but most benefit could be
obtained under irrigated conditions. A plant population of 500,000 plants ha-1 or
higher and row spacing wider than 0.34 m proved to be most suitable for both
growth and biomass parameters.
Dissertation (MScAgric)--University of Pretoria, 2015.