The effects of different cutting heights, mulching and burning on the control of bellyache bush (jatropha gossypifolia L.) applicable in East Timor

Abstract

Since bellyache bush invaded to East Timor it has significantly reduced crop and animal production and consequential loss of income from farm enterprises. Methods of control of bellyache bush chosen should be appropriate to the poor economic position of the farmers. An integrated method of controlling bellyache bush involving slashing combined with mulching and or burning is low cost and is widely used by the Timorese farmers. Although these practices are commonly used to control weeds, there are still many problems that appear in the field during and after weed control. For instance, rapid regeneration of cut stems and production of less fuel than mixed stands to support burning management.Therefore, the objective of this study is to investigate mechanical control such as cutting stems at different heights and cutting stems at different heights in combination with mulch, handpulling and mulching of small plants and mulching of seedlings. This study also investigates bellyache bush properties as a fuel for burning management in the late dry season to control its infestations.Mechanical control of bellyache bush plants was undertaken south of Darwin at Acacia (12º45’S, 131º09’E) which has an annual average rainfall of 1588.1 mm and Channel Island (12º33’S, 130º51’E) which has annual rainfall of 1713.9 mm. This study was conducted from January 2007 to February 2008. All bellyache bush plants were cut off at different heights according to treatment 0cm (ground level), 10cm, 20cm, 30cm, 40cm and uncut plants considered as a control.The results indicated that all cutting treatments achieved 100% mortality under low canopy cover, irrespective of season. While, under high canopy cover bellyache bush plants only achieved 100% mortality if cut at 0cm and 10cm height. Stems cut at 20cm, 30cm and 40cm heights re-sprouted in the dry season. Hand-pulling completely killed small plants while mulching did not. Mulching achieved a partial kill of seedlings however it stimulated seedling emergence in the wet season, irrespective of site.The use of bellyache bush as a fuel for burning management was studied. The study was undertaken at Channel Island, Acacia and Katherine (14º22’S, 132º09’E). The latter has a mean annual rainfall of 875 mm. All bellyache bush plants in the plot were cut in May. Five 1m x 1m quadrat samples were selected within a 10m x 10m plot to measure wet weight and dry weight for the curing rate calculation. In addition, 15 of the cut stems were randomly selected to measure re-sprouting. From five randomly selected 25cm x 25 cm quadrat samples were taken to calculate the weight of fine fuel (less than 6mm in diameter), medium (6mm-25mm) and coarse (greater than 25mm). Heat yield of fuel combustion of this material was calculated by using a bomb calorimeter (As 10-38.5 leco 350 calorimeters).The results indicated that cut stems of bellyache bush from a low canopy cover site had 7 percent moisture content while stems from a high canopy cover site had a 66 percent moisture content by the end of the dry season. The proportion of these stems in the site with low canopy cover re-sprouted significantly less than those in the high canopy cover site. The fuel load at bellyache bush monoculture had less fine, medium and coarse fuel compared with tropical savanna fuel. However, results from this study indicated that it had a similar heat yield of combustion to other plants in the tropical savanna.A study of the use of fire as a control tool for bellyache bush was undertaken at Acacia and Katherine from May 2007 to February 2008. This study was carried out on established plants of bellyache bush. The experiment was undertaken in three 10m X 10m plots at each of the two sites. The experiment consisted of three treatments namely: cutting stems at 30 cm and followed by burning, uncut plants plus burning and unburnt plants considered as a control. Each of 20 pieces of bellyache bush stems were randomly selected for fine 0-6 mm, medium 6-25 mm and coarse 25 mm fuel. All these pieces were weighed before and after fire to calculate fuel consumption. Fire intensity was calculated by using Byram’s fire intensity equation. Fifteen soil temperature sensors were buried under uncut plants before burning. After burning all soil temperature sensors were dug out the temperature read and used to calculate fire temperature. Plant mortality was calculated by counting live bellyache bush plants before and after fire. Seed germination and seed recruitment was calculated by counting all seedlings within five 1m x 1m randomly chosen quadrats.The results show that fire consumed all bellyache bush stems in the late dry season burning. Fire intensity of bellyache bush fuels was quite low compared to other tropical savanna fuel. Soil temperatures ranged between 54.17ºC to 126.13ºC. All bellyache bush plants were completely killed by the fire treatment, but fire stimulated seedling emergence in the following wet season. It was concluded from the results of the experiments that mechanical control slashing system may provide a suitable fuel for the burning management if cut early in the dry season. By late in the dry season bellyache bush plants cut early in the dry season have a low moisture content are completely cured and able to support fire spread of adequate intensity to destroy the plants.