on the metabolic processes of the crop resulting in lower yields. However, the environment can be artificially modified to meet the crop requirements. Modifying the environment artificially can be very expensive. Therefore, it is done only when it is highly profitable or for experimental purposes. The weather also determines when to undertake farm operations, such as land preparation, weed control, fertilizer application, harvesting and irrigation. Certain vegetable varieties can be bred to grow well in regions where the species is not adapted. Thus, there are now varieties of vegetables that are heat or drought or salt or shade-tolerant. Some ecological factors influencing vegetable production include: 1. Soil The soil holds up the plant and acts as a reservoir for water. It is also the main source of plant nutrients. It should therefore be the best for that particular crop. Its physical and chemical characteristics greatly influence the nature and rate of plant growth. The soil mineral status should be optimum. It should be free from diseases and pests. Soil properties can be altered by fertilizer application, liming, manure application and through tillage and drainage. Soil characteristics influencing vegetable crops include: a.Soil depth-shallow soils tend to be water logged and therefore affect vegetable production negatively. Shallow soils also restrict root penetration. b.Soil drainage-soil should be well aerated and drained. The mineral particles tend to group together so that there are spaces (the pore spaces within the soil which are partly occupied by air and partly by water). Poorly drained soils leads to water logging conditions which might kill some vegetable crops. Extreme draining soils can be mixed with organic manure to improve water retention.
7 c.Topography-refers to the levelness or roughness of the earth surface, the degree of slope on hillsides, and the general form of the earth surface. An example of the modifying effect of topography on climate is the greater amount of sunlight received by aslope facing the sun compared to that facing away from it. Steep soils lead to erosion and at lower levels there is washing away of crops and water logging conditions. d.Texture-the solid part of the soil which is composed of a mixture of broken down rocks (mineral particles) of different sizes and the remains of plants and animals at different stages of decomposition (organic matter). The organic matter is a very small portion of the soil. The mineral particles are: clay (0.002 mm or less), silt (0.05 to 0.002 mm) and sand (0.05 mm or more). The relative proportion of these particles determines the soil texture which include sandy, loamy sand, silty clay, loam, light clay, and heavy clay. Those with sand are described as coarse textured and those with clay as fine-textured or heavy. Those with no predominant particle size are called moderately coarse-textured. Sandy soils are best suited for the root, bulb and tuber vegetables provided rainfall is adequateor irrigation is available. Crops like onion, garlic, carrot, radish, turnip, sweet potato and cassava do well in lighter soils. It allows fast development and easy harvesting of storage