Population growth and high demand of food has led to increases in the cultivated areas at the expense of restorative bush fallow. In the process, the resource base is depleted as many tropical soils are fragile, quickly losing organic matter and nutrients when intensively cultivated. Therefore there is an urgent need to replace this destructive cycle with economically and ecologically farming practices. It is justified that inorganic fertilizer has been responsible for sustained increases for food production. Organic inputs are needed to maintain the physical condition of soil (Hsieh and Hsieh, 1996). As soil fertility depletion is the single most important constraint to food security in Nigeria there is the need to adopt practices that can help sustain crop production while maintaining sol fertility.

The objective of the study was to find out the influence of Tithonia diversifolia, NPK fertilizer and poultry manure on the growth and yield of water melon. The treatments consisted of control, Tithonia diversifolia, NPK fertilizer and poultry manure. These were applied in sole applications as well as in varying combination of different treatment as shown in the table below.

One of the greatest challenges in agriculture is the need to develop viable farming for increase and sustained crop production with minimum soil degradation. For instance, in 1992 the population in Nigeria was 8million, and in 2000 it was 18.9 million later in 2010 it increased to 25million. Much of the agricultural land in developing countries used for traditional farming is based on shifting cultivation and bush fallow systems. This is a biologically stable system and with long fallow period, can sustain agricultural production for many generations (Kang and Wilson, 1987).

However, because of increasing land pressure resulting from rapid population growth and other uses, it is no longer possible in many areas to maintain the long fallow periods crucial for soil fertility regeneration. This has resulted in the breakdown of the natural soil fertility replenishment system, to the point where large tracts of land are becoming degraded and left out of cultivation. This has led to the practice of continuous cultivation on low fertile soils resulting in inadequate food production or decline in crop yield. This is because shorter fallow periods are less effective in restoring soil fertility (Ruthenberg, 1971).

The traditional system, which is known to be stable and biologically efficient, operates effectively only when there is sufficient land to allow for long fallow periods to restore soil productivity (Kang et al., 1989). Today, however, because of rapid demographic and economic changes, the cultivated area has expanded onto marginal land and fallow periods are being reduced, resulting in systematic reduction of major areas of land leading to declining yield (Matlon and Spencer, 1984). Research results obtained at International Institute of Tropical Agriculture (IITA) (1992) Ibadan, Nigeria and elsewhere indicate that soil degradation can be halted or retarded by maintaining a crop cover or continuous incorporation of organic residue on the soil surface. Soil fertility depletion is the single most important constraint to food security in West Africa. Though the use of organic resources such as farmyard manure and compost have been in use for several years for improving soil fertility (Sridhar and Adeoye, 2003) and more recently use of inorganic fertilizers, varying constraints still make the use of these traditional and conventional methods of soil fertility improvement inadequate to meet the challenges of soil fertility depletion in the region. Such constraints include high procurement cost for mineral fertilizer sources, insufficient quantities to meet farmers’ needs especially in less developed countries, and relatively low nutritive content of traditional crop residues or animal manure used for soil improvement.

Inorganic fertilizer has been the major means of achieving higher yield of crop. Even though Government subsidizes the cost of fertilizer, these inputs have become so expensive that small scale farmers who constitute about 80% of the farming population cannot buy and apply them. Though inorganic fertilizer contributes largely to soil fertility, it does not improve soil physical properties, such as soil structure, water retention capacity and aeration for crop production. Many legume species, both herbaceous and shrubs are well adapted to the infertile soil of the tropics and therefore, their ability to improve the soil fertility status needs to be investigated.

There is, therefore, the need to develop alternative or integrated low input soil fertility management strategies based on maximum use of local biological nutrient sources and supplementation with chemical input when available.

Inorganic nitrogen compounds tend to increase the leaf, stem and the roots. The higher the rate of application of nitrogen to a plant, the more rapidly will the synthesized carbohydrate be converted to proteins. Leaves which are low in nitrogen often have a pale yellow or light green colour. However when nitrogen is present in excess, it increases the growing periods and delays maturity of fruits (Akinyosoye, 1985). The ripening of grain for instance is retarded by too great a proportion of nitrogen in the medium of growth. In addition to nitrogen, phosphorus is an essential component in the reaction of carbohydrate synthesis and also for carbohydrate degradation enabling energy to be liberated. When a crop such as water melon is deficient in phosphorus, growth is retarded and the formation and, ripening of seeds may be retarded, plants develop a stunted root system and leaf development is reduced.

Potassium is absorbed in fairly large quantities by plants. The response of plants to potassium intake depends on the concentration of nitrogen and phosphorus present in the soil. Potassium starvation becomes obvious, usually resulting in the premature death of the leaves. Fruits and seed become poor in quality and of reduced size and weight (Akinyosoye, 1985). All crops which produce large quantities of carbohydrate use fairly high levels of potassium.

In addition to inorganic fertilizer use, another means of improving soil fertility involves incorporating green manure into the soil. This releases nutrients and provide farmers with viable and ecologically sustainable alternative to shifting cultivation. Green manuring supplies nutrients and organic matter from the decomposing material (Lal, 1975) and may be useful for farmers where external inputs for crop production are less likely to be available and the cost exceeds farmers cash on hand.

Nitrogen is the most limiting nutrient in crop production in tropical Africa. The inclusion of nitrogen-fixing leguminous species in the production system can help to meet the nitrogen requirement for crop production. In addition to a greater capacity to fix nitrogen in soil, legumes to be used should have large mass of tissue and high nitrogen concentration. Kang (1988) estimated the effective nitrogen contribution from Leucaena leucocephala and Gliricidia sepium pruning to alley cropped maize to be about 40 kg N/ha. Mulongoy and Vander der Meerch (1988) reported a lower nitrogen levels of 4.4 – 23.8 kg N/ha from L. leucocephala pruning to the associated maize crop, the nitrogen contribution representing less than 30% of nitrogen yield of the pruning. This low efficiency in the crops use of N from pruning probably results from the lack of synchronization between release from the pruning and nitrogen demand, volatilization of nitrogen from pruning, and leaching, (Mulongoy and Akobundu, 1990).

In addition to inorganic fertilizer as a method to regenerate soil fertility and improve productivity, poultry manure is an excellent source of nutrients and can be incorporated into most fertilizer programmes. It is therefore, used as an alternative method of improving soil and crop yield besides the conventional inorganic fertilizer that has become expensive.

Legume species can also be used in cropping system to improve soil fertility in Nigeria Legumes used as green manure can,

• Provide biologically fixed nitrogen
• Increase soil organic matter.
• Provide protection against soil erosion.
• Improve soil structure.
• Make other nutrient such as phosphorus, calcium more available.

Among the various shrubs and forage, legumes used as a biological nitrogen fixation for soil productivity, Tithonia diversifolia, a legume shrub, has been selected as an alternative option for improving agriculture productivity (Jama et al., 2000). Tithonia mulch, apart from being rich in nutrients including calcium, nitrogen and phosphorus can also increase the soil moisture retaining capacity (Jama et al., 2000).

Research further indicates that the ability of Tithonia to decompose quickly makes it the best way to replenish soil fertility. However long term benefits of the organic matter storage can be achieved only when there is continuous application of the organic resource. Liasu and Atayese, (1999) reported that, the concentration of nutrients in Tithonia is highest in young plants and before the plant flowers. It is further reported that Tithonia has shown a great improvement in crop yield of 46 farms in western Kenya where the yield of green beans increased when the biomass was applied (Liasu and Atayese, 1999).

Tithonia has also been reported as a nutrient source for maize in Kenya, Malawi and Zimbabwe (Jama et al., 2000). Stems and leaves of Tithonia have been reported to contain sesquiterpene lactones such as tagitinins that prevent attack by termites, and possess antimicrobial properties (Adoyo et al., 1997).

• WATER MELON (Capsicium fructescens) USED AS TEST CROP
The crop selected as the test crop for the study is hot water melon (Capsicium fructescens). Water melon is one of the most widely used foods in the world. Hot water melon, a member of the family solanaceae is more important as a spice than a vegetable in the tropics. It originated from Mexico and Central America. Christopher Columbus encountered water melon in 1943 and because of its pungency, thought it was black water melon, Piper nigrum which is actually a different genus. He introduced the crop to Europe and it subsequently spread into Africa and Asia. The bulk of water melon produced in countries such as U. S. A is sweet water melon but hot water melon dominates in other countries such as Nigeria. Water melons are important crop for Nigerian farmers, but successful water melon production is not easily achieved. However water melon production has increased in recent years partly because of its high consumption rate by most people and for its nutritional value.

Water melon production requires highly intensive management and marketing skills. Per- acre cost of production is high and yield can be severely limited by pest problem or environmental problems. A phenolic compound called capsicin is responsible for pungency in hot water melon, and various cultivars markedly differ in their content of this chemical. Water melon is a herbaceous perennial plant and will survive and yield for several years in the tropical climate provided there is moisture in the soil.

The crop can withstand temperatures as high as 38 °C but cannot withstand low temperature below 18°C. The ideal temperature range for good plant growth is 18°C - 32°C. Fruit set is greatly influenced by low humidity and high temperature. These conditions of very low humidity and very high temperature results in poor fruit set due to dropping of flower buds.

Water melon can be produced on a wide variety of soil types but it grows best in deep, medium textured sandy loam and well-drained soils. It grows well in soil within the pH range 5.0-7.0.

Soil rich in organic matter tends to promote excessive vegetative growth resulting in poor yield of the crop. The nursery period may range from 4 – 6 weeks depending on the fertility of the nursery soil. Compound fertilizer (N.P.K, 15-15-15) applied at the rate of 250 kg/ha 10 days after transplanting and top dressed with sulphate of ammonia at the rate of 60 kg/ha two weeks after first application is recommended. The ideal time of planting is about mid or latter part of the rainy season, that is minor season, so that harvesting period falls in the dry season.

Water melon requires about 75 days from transplanting to first harvest and can be harvested for several weeks before production wanes. The potential for extending the duration of fruiting period in order to improve yield output lies generally on genetic quality of plant but most importantly in soil conditions, as early growth termination is often caused by soil nutrient depletion, moisture stress, pest and diseases and root infection resulting from buildup of soil pathogens (Muller-Saman and Kotschi, 1994a).

To help the plant support continuous fruiting it is advisable to give a top dressing of compound fertilizer (NPK 15-15-15 or 20-20-0) as soon as the first flowers open, using 15 g per plant in a ring of 15 cm from the stem.

Inorganic fertilizer use has been the major means of achieving higher crop yield. They are fast acting and effective. However, with the removal of subsidy in agricultural inputs these inputs have become so expensive that small scale farmers cannot afford to buy and apply them. Hence the need to develop alternative farming systems, which could build up organic matter levels to improve the physical conditions of soil and at the same time supply the essential plant nutrients for sustainable agriculture at affordable cost. Organic manuring seems to provide a possible solution to this problem.

Water melon responds to both organic and inorganic fertilizer. But the high cost of inorganic fertilizer that limits affordability has made water melon production less encouraging among Nigerian farmers. It is therefore necessary to explore other sources of material for use to regenerate soil fertility to improve crop production.

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