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effect of environmental factorssome lower organisms though the genetic determiners of the sexes are present the ambient environment plays a decisive
sexual reproductionyou must be aware that reproduction is one of the distinguishing features of living beings reproduction is basically of two types
homozygous and weterozygousin an individual two identical alleles may exist or a given character and hence the individual is referred to as
genes and allelesthe inheritance of any character can be studied only when thcre are two contrasting conditions such as yellow versus green seed
birth of geneticsmodern genetics originated with gregor mendels work it is based on this paper entitled experiments in plant hybridisation published
development of genetics-a historical perspectas systematic study of genetics began answers were sought to questions such asi why are we like our
genetics genetics is the study of heredity it is an ancient discipline at least 4000 years ago in sumeria egypt and other parts of the world farmers
improvement of soil aerationsoil organisms greatly improve soil structure and facilitate aeration root decay leaves the soil riddled with channels
soil mixingthe larger soil organisms are responsible for considerable mechanical mixing and weathering of soil the wedge-like action of roots and
nitrogen fixationnitrogen is an essential constituent of living organisms and there is an inexhaustible supply of it in the atmosphere in the free
decay and nutrient cyclingsoil organisms are the chief agents of decay of organic matter decomposition and mineralisation of organic matter results
influence of associated ionsthe second important factor influencing the plant uptake of a given cation is the effects of the ions held in association
cation saturation and nutrient absorption by plantsthe availability of adsorbed cations is not always so easy as the above explanation might suggest
nutrient availabilityyou have seen that cation exchange plays an important part in nutrient availability to plants cation exchange functions in two
cation exchange capacitythe adsorption of a cation by a colloid nucleus or micelle and the accompanying release of one or more ions held by the
aerationa well-aerated soil is one in which gases are available to plant roots and other soil organisms in sufficient quantities and in proper
permeabilitypermeability is the ability of a soil to transmit water or air permeability or infiltration rate is measured in terms of the rate of
available and non-available wateryou have seen above that water is present even in the apparently dry soils but it is of not much use as far as the
hygroscopic coeflicientto have a more complete picture of soil moisture relations let us take a soil sample and oven dry it for 24 hours at 11oc now
retention of soil moisturethe movement of water into and within the soil moisture storing capacity of soils and the availability of moisture to
forms of soil watergravitational water or ground water after a heavy rain or irrigation much of the water drains or sinks downwards this is called
soil watersoil water relationship is very important in the fist place the supply of large quantities of water is necessary to satisfy the
light and heavy soilsthe presence of silt and especially clay in a soil imparts to it a fine texture and a slow water and air movement such a soil is
aeolianwind transported materials constitute this category this can be further divided into dunes or loess dunes are found in thramp types of
alluvialmaterials of this categoya re deposited by running water in the form offroodplains river terraces deltas and alluvial fans these deposits