The feasibility of utilizing kenaf (Hibiscus cannabinus L.) as a fibre crop and potential source of paper pulp is being investigated. This paper is the first in a series which develops and validates a simulation model of kenaf, and applies it to assessing the potential for dryland production in regions of tropical Australia. The duration from sowing to flowering is an important determinant of fibre yield in kenaf. Accordingly, the effect of temperature and photoperiod on the phenology of kenaf was examined. Data were collated from sowing-date experiments on kenaf cultivars Guatemala 4 and Everglades 71 at six locations in tropical Australia, ranging in latitude from 12� 54'S. to 19� 32'S. Data from one site, Kununurra, W.A. (15� 39'S.), was used to develop a model which described the duration from sowing to flowering in kenaf based on four stages: (1) sowing to emergence; (2) emergence to the end of the basic vegetative phase (BVP); (3) a photoperiod-induced phase (PIP) which ends at floral initiation; and (4) a flower development phase (FDP). Both kenaf cultivars responded as qualitative short-day plants where flowering did not occur above a critical photoperiod of 12.9 h. Assuming a base photoperiod of 12.0 h, the thermal time required to complete the BVP for the two cultivars was similar. However, photoperiod sensitivity during PIP, and the thermal time required for FDP, were greater for Guatemala 4 than for Everglades 71. Validation of the model against independently observed data for both cultivars at other sites resulted in close predictions in the thermal time required for flowering. This phenological model for kenaf can be used to assess the effect of sowing date on phenology at different locations in tropical environments, and is a key component of a crop growth simulation model to assess the environmental constraints to productivity in these regions.
The recent history of dryland farming in the Australian semi-arid tropics is discussed briefly against the background of national and state policies, established following World War II, aimed at increasing the population and development of northern Australia. Some reference is also made to irrigation as a means of overcoming limitations imposed by rainfall and to complement dryland farming systems. The environmental and socio-economic constraints whch have so far limited commercial agriculture in the Australian semi-arid tropics are highlighted. Efforts, particularly in north-west Australia, to develop sustainable farming systems based on legume pasture leys and livestock production in conjunction with annual cropping, as a basis for closer settlement, are reviewed. These attempts, which began in the 1960s and stemmed from earlier post-war agricultural research in the region, initially relied on a pasture legume (Stylosanthes humilis cv. Townsville stylo) and conventional tillage. Farming system development continues today using new legume species (e.g. Stylosanthes hamata cv. Verano and Centrosema pascuorum cv. Cavalcade) and no-tillage cropping technology. This paper documents the history of agricultural and research development, and commercial practice in the Australian semi-arid tropics.
During the wet season of 1964-65 two trials were established near Darwin to determine if Townsville lucerne (Stylosanthes humilis H.B.K.) could be established in undisturbed annual sorghum (Sorghum intrans F. Muell. ex Benth.) pastures after wet season burning had controlled grass growth. In the first trial, plots were burnt at intervals throughout the wet season. Townsville lucerne pods were broadcast immediately after burning. Grass control and Townsville lucerne establishment were satisfactory in plots burnt after December 6. The second trial examined the effect on Townsville lucerne establishment and S. intrans control of burning, seeding rate, superphosphate, and weedicide treatments. Burning had the most important effect ; seeding rate had little significant effect and superphosphate none. The weedicide treatment was ineffective. The trials indicate that provided wet season burning is used to control S. intrans, Townsville lucerne can be established cheaply over wide areas of the higher rainfall region of the Northern Territory.
Field experiments were conducted at Berrimah, Douglas Daly and Katherine in the Northern Territory (NT) during the 1987-88 and 1988-89 wet seasons to obtain yield data for kenaf (Hibiscus cannabinzis L. cv. Guatemala 4) grown under rainfed and irrigated conditions. Under rainfed conditions, maximum stem yield was obtained from sowings early in the wet season. Yield decreased with delay in sowing until the late-December-January period. The maximum rainfed stem yield at Katherine in an above-average rainfall season was 18 400 kg/ha. The maximum yield in a below average rainfall season was 11 700 kg/ha at Katherine, 9200 kg/ha at Douglas Daly and 9400 kg/ha at Berrimah. The applicability to the NT of growth and yield relationships established for irrigated kenaf in the Ord Irrigation Area (OIA) was assessed. The yield potential under irrigated conditions in the NT (21 600 kg/ha at 131 days after sowing) was higher than that reported elsewhere in Australia for the same growth period, but similar to that reported elsewhere for longer growth duration (180-300 days). In the NT, in contrast to the OIA, stem yield showed little or no response to N fertilisation. Stem yield was not related to N uptake, and at high levels of N application, there was marked N accumulation in the stem. Kenaf was able to accumulate up to 110 kg N/ha from the soil reserve where no N was applied. The yield response to plant density varied with the yield level and was similar to that in the OIA. Bark and core yield could be estimated directly from biomass, and indirectly from stem length and plant density, over a wide range of yield levels and cultural conditions. It was concluded that data relating to yield potential and response to N fertilisation cannot be transferred directly from the OIA to the NT.
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