The Effect Of Pesticides Dichlorodiphenyl Trichloroeyhane (d.d.y) And Benzene Hexachroride (bhc) On The Microflora Of The Three Types Of Soil

CHAPTER ONE
INTRODUCTION
According to crupta and Daroren (2003) soil is that portion of the surface of the land which is essential for plant growth. Plant are anchored in the soil by their root, which spread in all direction and which by holding on to the soil keep the plant in position plant draw all their water and  most of their food or nutrient from the soil. Soil is therefore the source of food for plants, animals and man. Soil is of different types, sandy, clay and loamy soil. Sandy soil has or size range of 0.2 to 2mm diameter. They are free draining and do not retain any appreciable amount of soil water. It is brown loose and dry. While clay soil range in size from 0.002mm and lower and contains more than 40% of clay particles. They are sticky, plastic and  easily moldable into  shape. Another type is loamy soil which contains a fair balance of clay , silt and sand particle and it is the best  soil for agriculture, as it has a high proportion of organic matter or content soil organic malter represents on accumulation of  partially decayed and animal residues. Such material is continually being broken down as a result  of the  work of soil micro –organism consequently. It is a rather  transitory soil constituent and must be renewed constantly by the additionb of plant residues. The organic matter content of a soil is small, only 3-5 percent by weight in a representative minerals topsoil. It is a major soil source of two important mineral elements namely phosphorous and suefur and essentially the sole source of nitrogen. Through its effect on the physical condition of soil, organic matter also increase the amount of water a soil can hold and the proportion of water available for plant growth. Further more   organic matter is the main source of energy for soil microflora. Without it biochemical activity would come practically to a stand still soil organic matter consist of two groups (a) Original tissue and its partially decomposed equivalent and (b) the humus. The original tissue include the under composed roots and the tops of higher plants. The materials are subject to vigorous attack by soil organism and both plant  and animal which use them as sources of energy and tissue building material. The gelatinous, more resistant products of this decompository both the synthesized by the micro organisms and those modified from the original plant tissue are collectively known as HUMUS. This material, usually black or brown in colour is coloidal in nature. Its capacity to hold water and nutrient ions greatly exceeds that of clay, its inorganic counterpart. Small amount of humus thus augment remarkably the soil capacity to promote plant production.