PhD A. W. Flegmann MA’s research while affiliated with University of Bath and other places

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Publications (5)


The Management of Soils for Horticultural Crops
  • Chapter

January 1975

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6 Reads

PhD A. W. Flegmann MA

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Raymond A. T. George BSc, NDH, MIBiol

Any operation involving the soil, whether done mechanically or by hand can be regarded as a cultivation. Traditionally tasks such as ploughing, digging, seed-bed preparations and hoeing are included as cultivations. Whatever we do to or on a soil, whether or riot in the presence of a crop, is likely to have some effect on the physical conditions of that soil. Possibly the effect is only temporary; on other occasions it may affect the physical structure for a long time. In this section some of the effects of different cultivation operations will be discussed.


Macroscopic Structure and Properties of Growth Media

January 1975

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1 Read

A knowledge of the macroscopic properties of soils is essential to the scientist working in the field and to the commercial grower. When an assessment is made in the field, an impression of the soil’s origin, texture and structure is obtained; this information will subsequently provide a useful guide as to the ‘workability’ of a particular field soil and its suitability for particular crops. Similarly, if the land is to be used for amenity, the assessment must indicate its usefulness for particular purposes, such as sports turf.


The Molecular Environment of Plant Roots

January 1975

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3 Reads

Having reviewed the microstructure of soil materials, we shall now consider the pore space in growth media. Apart from the roots of plants this pore space contains the soil solution and the soil air. The components, to a first approximation, are water and the common atmospheric gases nitrogen, oxygen, water vapour and carbon dioxide. The solution in the pore space is of course not pure water but contains ions, some of which serve as nutrients for plants. For the purposes of this chapter, however, the presence of dissolved ions can be neglected except in so far as they affect the osmotic pressure of the soil solution, which is the case in saline soils. The pore space of a good growth medium allows the simultaneous presence of water and oxygen in adequate quantities around the roots of plants and it permits the movement of water and air at adequate rates in the plant root environment. There also are requirements with regards to the energy with which a good growth medium retains water over the widest possible range of moisture contents. The energy of water retention should not be excessive, because plants would then be unable to utilize the soil water. Nor should it be too small to prevent undue drainage by gravity. In the soil air the component of primary interest for plant roots is oxygen; the partial pressure of oxygen in the soil air should therefore be adequate for the requirements of plants.


The Ionic Environment of Plant Roots

January 1975

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4 Reads

In the previous chapter the solutes contained in the water that fills the soil pore space were neglected, except for their effect on the soil moisture potential. Soil water, even in nonsaline soils is, however, not pure water but an electrolyte solution. This solution is dilute: the sum of the concentrations of all the ions is usually in the molar range 10−3 to 10−2 whereas the concentration of the most abundant ions are commonly of the order of 10−4 to 10−3 molar. The composition of the solution is very different not only among soils, but also varies with time and depth of sampling within any one profile. The composition of the soil solution of a wide range of soils is shown in table 3.1. Apart from carbon, oxygen and hydrogen, which occur in the plant environment as carbon dioxide and water respectively, thirteen elements are known to be essential for higher plants (nitrogen, phosphorus, sulphur, potassium, calcium, magnesium, iron, manganese, zinc, copper, boron, molybdenum and chlorine). All these elements occur in ionic form in the soil solution. Among those listed in table 3.1, calcium, magnesium and potassium are cations, whereas chloride, sulphate and phosphate are anions; nitrogen occurs in the soil solution either as the ammonium cation or as the nitrate anion. The remaining six elements not listed in the table are usually present and are required by plants only in trace quantities.


Microstructure of Soil Materials

January 1975

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3 Reads

It is a matter of common observation that all growth media are heterogeneous, consisting of solid, liquid and gaseous phases. A heterogeneous system is said to be disperse when its constituent phases are thoroughly intermixed. One of the phases of disperse systems is usually continuous in the sense that it is possible to move from any point to any other point within that phase without leaving it; in the remaining phases this is not possible. In growth media, water can be regarded as the continuous phase and the discontinuous phases are the soil solids and the soil air. This may at first seem paradoxical, but soil particles are always covered by thin water films even when air dry. Particles of soil solids are therefore never in direct contact. In a field soil the particles are nevertheless close enough to form loose networks and are prevented from free, unrestricted motion; such systems are known as gels. When mixed with a larger amount of water, the soil-water system is referred to as a suspension.