Abstract

The primary, major elements, N, P and K play a promi- nent part in relation to the principles and practices of plant nutrition. Ironically enough, due to their 'fixation in the soil to a certain extent, the availability of these elements to the crop is also affected to a certain extent by their fixation-release pathway, that is characteristic of a given soil. The ability to fix and release nutrients coexists in any soil although there may be marked degree of variation between soils. Studies of fixation of elements is of interest in clay mineralogy from the standpoint of structure and alteration of minerals and in soil-plant relationships in connection with their availability to plants. The factors affecting the fixation of nutrients are both intrinsic and extrinsic. The parent material of the soil, clay content and its mineral make up, degree of saturation, pH and the organic matter level are some of the intrinsic factors. Some of the extrinsic factors which influence the determined fixing capacity of a soil are the type of salt added, the nature of coions, the concentration range employed, time of equilibration, temperature, moisture level and operations such as complete drying, alternate wetting and drying or drying and heating. The variation in fixing capacity of P and K by two contrasting soil types is discussed in this paper.

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