oa Agrochemophysica - Effect of contact time of labelled fertilizer with soil on the estimation of labile phosphate

Volume 3, Issue 4
  • ISSN : 0302-7112



Plants were grown for periods ranging from 4 to 12 weeks in different soils intimately mixed with a labelled fertilizer. Although the plants absorbed up to several times greater mounts of ? in the longer than in the shorter growing period, only relatively small increases in L value were observed. The increase in L value was highest for orchard soils or soils stored for 25 months after enrichment with different phosphatic fertilizers but the change in L for growing periods shorter or longer than 7 weeks was less than 20% and therefore negligible from a practical standpoint. When the labelled fertilizer was mixed with the soil for periods of up to 8 weeks prior to planting, the maximum increase in L was less than 10%. The constancy of the L values, irrespective of time of contact of the labelled fertilizer with the soil is considered to be caused by the efficient mixing of the 3 2P with the soil and the fact that the plant roots could integrate over small areas of non-uniform distribution of 3 2P in the small pots used. Of the two possible factors that could result in increased L values with growing period of a plant, namely non-equilibrium or release of non-labile P, the latter is considered to be more important but not of great practical significance. As a general rule a seven week growing period was found to ensure isotopic equilibrium, and sufficient ? uptake to facilitate seed ? corrections but not to induce secondary effects.

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