16th National Crop Improvement Conference Part II

Abstract

Depending on the soil physical and chemical properties, added phosphorus may become essentially unavailable in the soil, when slightly soluble or insoluble phosphorus compounds are formed in the soil. This is why soils are often classified by their phosphorus fixing capacity (Pox, 19725 Sanchez, 1975; Uost, 1978)? snd many placement methods have been tested to determine efficiency and availability of applied phosphorus to the growing crops. Crops may respond much bettor to banded than broadcast phosphorus, especially on soil testing low phosphorus or on soils where high phosphorus fixing capacity precludes easy amanipulation of phosphorus level (Roy, 1980) Where soils are built up to medium or high levels broadcast or banded phosphorus may be equally effec+ive (Barber, 195^? Albosal, 19797 Peterson et.al, 1982; Murphy, ( 1982). The methods of phosphorus fertilization influence the amount of phos phorus needed for good yield (Abed et.al, 1978^ Turkhede and Prasad, 19^0), and phosphorus must be applied early, showing that young roots absorbing pnosphorus much more rapidly than old roots (Hagen^ieker, 195^5 Duncan and Ohlrogge, 1958; Reith, 1959; Lawton and Davis, 1960; Duell, 19645 King and Skogley, 1969? Foote, 1969; Barber 1977, Foud et.al 1979? Lamond, 1981). This type of result is a function of the plant and fixation capacity of the soil; a different plant might require a different width of band, and on a soil with a low fixation capacity broadcasting and ploughing in mi^it be better (Ez.edinma* 19^5i Meptu, 1973). Placement' and type of fertiliser are inter-related and the needs of a plant for phosphorus could be met either by placement of a readily soluble phosphorus source or by spreading and mixing a slowly soluble source such as rock phosphate (Singh and Black, 196a; Roy et.al, 197-? Arrogavel, 1979; Lamond, 1981). As it is impossible to saturate all the soil fixation capacity, it is necessary to ensure that enough fixation site is saturated so that intensity is no longer a limiting fa.ctor (De Datta et0al, 1965? Engoumendies and Pichot, 1975)• The method of application is a compromise between the volume of soil in which the fertilizer is placed (and where the roots can find it) and the fixation capacity of the soil (Sadaphel and Singh, 1971; Pieri, 1975).