A phyto-sociological survey of weeds was conducted on a Jatropha curcas plantation in University of Ilorin, Ilorin, Kwara state with the aim of determining the most relatively frequent weed species on the plantation. A quantitative method was employed for the enumeration of weeds which involved mapping of ten plots and laying of quadrants of 50 by 50m along w-shaped pattern. Individual weed species in each quadrant were counted and identified to species level. The relative frequency of each species were estimated and a total number of 35 weed species belonging to 16 families were identified across the Jatropha curcas plantation. Tridaxprocumbens was the most relatively frequent specie on the plantation with the relative frequency of (38.0%) and the least dominant specie is Vernonia amygdalinawith relative frequency of (0.003%) followed by Ipomoea trilobawith relative frequency of (0.005%). The result showed that adequate removal of Tridaxprocumbens could limit the adverse effect of weed infestation.
1.1 BACKGROUND TO THE STUDY
Jatropha curcas is a species of flowering plant in the spurge family, Euphorbiaceae, that is the native to American tropics, most likely Mexico and Central America (Janicket al., 2008). The name is derived from the Greek words ‘’jatros’’ meaning ‘’physician and ‘’trophie’’ meaning nutrition, hence the common name is Jatropha plant.
Sub Kingdom: Tracheobionta
Species: Jatropha curcas
Binomial: Jatropha curcas
Jatropha curcas is a plant that produces seeds with high oil content. Seed is toxic and in non-edible. Jatropha curcas gained prominence because of its added features like excellent adaptability to various habitats, large fruits and seeds, high oil yield, soil conservation capabilities and thriving well as live fence.
Jatropha (Jatropha curcasL.) is a drought resistant monoecious large shrub or small tree 5(-8)m tall, belongs to the genus Jatropha which has over 170 species, and is a member of the Euphorbiacaeae family. The leaves appear alternately with a petiole (3-20cm long) and a blade broadly ovate in outline, usually shallowly 5-lobed. The inflorescences are terminal or axillary umbel-like cymes, often paired, with solitary female flower terminating each major axis and many male flowers on lateral branches. The flowers are unisexual. Since only female flowers produce seed flower ratio is an obvious target for yield improvement. Fully female genotypes exist, which offers the opportunity of creating pure hybrid varieties. The fruits are broadly ellipsoid capsule 2.5-3cm*ca. 2cm, smooth-skinned, initially fleshy green, turning yellow and eventually dry and black and are 3-seeded. The seeds are ellipsoid,1-2cm long, mottled black and coarsely pitted (Henning, 2000).
All parts of the plant exude sticky, bitterly pungent and astringent latex, which can be used as making ink. The bark contains tannin, wax, resin and saponins for industrials purposes. The kernel, which forms 60-68% of the seed weight, contains 46-58% of oil of the kernel weight and 30_40%of the seed weight. Seed oil is used for illumination without smoke, substitute of diesel, kerosene, lubricants, soaps and candle manufacturing. It can be used as hair oil and livestock against sores. As an excellent source of organic manure, the oil contains 3.2% nitrogen, 1.4e% phosphorus and 1.2% potassium. Although, Jatropha plant can grow easily from fully matured seeds, it can be propagated by nursery and stem cutting. In some cases Jatropha plant naturally forms a symbiosis with soil mycorrhiza that increases the nutrients and water plant uptake from the soil by plants. The presence of mycorrhiza increases the plant tolerance to drought and shortage of nutrients. The symbiosis relationship occurs sometimes under natural conditions but never occurs in plantations, unless artificially introduced.
The stem of haat (Jatropha cuneata) is used for basket making by seri people in Sonora, Mexico. The stems are roasted, split and soaked through and elaborate process (Ilangoet al., 2015). The reddish dye that is often used is made from the root of another plant species which is called Krameria gayi. The oil from jatropha curcas family is mainly converted into biodiesel. The cake resulting from oil extraction, a protein rich product, can be used for fish or animal feed (if detoxified). It is also a biomass feedstock to power electricity plants or to produce biogas and a high quality organic fertilizer. Jatropha curcas is also being studied for use as a carbon sequestration plant in arid regions (Becker et al 2013).
In agriculture, the term weed is applied to any plant that grows or reproduces aggressively or is invasive outside its native habitat (Janicket al., 1979). Weed occasionally is applied to the species outside the plant kingdom, species that can survive in diverse environments and reproduce quickly (David, 1998) when a plant is found in an unwanted place and at an unwanted, time it is considered invasive or a weed Examples commonly are plants unwanted in human-controlled settings, such as farm fields, gardens, lawns and parks. Taxonomically, the term “weed” has no botanical significance, because a plant that is a weed in one context is not a weed when growing in a situation where it is in fact wanted. The term “weed” also applies to any plant that grows or reproduces aggressively or is invasive outside its native habitat. (Janick, 1979).
Nature has bestowed the following qualities on weeds:
- Produces larger number of seeds compare to crops.
- Most of the weed seeds are small in size and contribute enormously to the seed reserves.
- Weed seeds germinate earlier and their seedlings grow faster.
- They flower earlier and mature ahead of the crop they infest.
- They have the capacity to germinate under varied conditions, but very characteristically, season bound. The peak period of germination always takes place in certain seasons in regular succession year after year.
- Weeds seeds possess the phenomenon of dormancy, which is an intrinsic physiological power of the seed to resist germination even under favorable conditions.
- Weed seeds do not lose their viability for years even under adverse conditions.
- Most of the weeds possess C4 type of photosynthesis, which is an added advantage during moisture stress.
- They possess extensive root system, which go deeper as well as of creeping type.
Weeds have both positive and negative impacts. Some of the impacts are:
Weeds cause reduction in crop yield through competition for light, nutrient, water and space.
They can also reduce the yield of crop through the release of toxic substances or exudates which inhibit crop growth, this is called allelopathy. Uncontrolled weed infestation can lead to 95% yield loss in cassava, 40% in maize, 53% in cowpea, soya bean and pigeon pea.
Weeds can reduce the quality of harvested agricultural products.
Weeds interfere with harvest operations and increase the cost of harvesting in both small holder and large scale farms.
The cost of controlling weeds is high.
The presence of weeds can impede water flow in irrigation canals.
The presence of weeds in lakes and reservoir can increase loss of water by transpiration.
Weeds serve as alternate hosts to many plant diseases and animal pests e.g insects, rodents, birds etc that attack crops.
The presence of weeds imposes a limit on farm size.
The presence of weeds can also reduce the economic value of lakes by preventing or limiting fishing activities.
Weeds such as Imperatacylindrical become fire hazards in the dry season throughout the savanna vegetation zone
Weeds affect health of humans, stinging nettle can cause skin rashes and the flowers of some other weeds can be associated with allergies in humans
Weeds impair visibility along roads and railway lines.
Uncontrolled weed growth reduces the value of real estate
Beneficial Effects of Weed
While the term ’’weed’’ has a negative connotation, many plants known as weeds can have beneficial properties. A number of weeds, such as dandelion (Taraxicum) are edible and their leaves or root maybe used for food or herbal medicine (Baker, 1974). Some weeds attract beneficial insects, which in turn can protect crops from harmful pests. Weeds can also prevent pest insects from finding a crop because their presence disrupts the incidence of positive cues which pests use to locate their food. Weeds may also act as living mulch providing ground cover that reduces moisture loss and prevents erosion, weed also improve soil fertility, dandelion for example, bring up nutrients like calcium and nitrogen from deep in the soil with their tap root (Preston et al., 2002).