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Publication Date
1981
Description
Quantitative measurements of the amount of soil phosphate available to plants were made by an isotopic-dilution technique (L-value). Following very thorough mixing and equilibration of 32P with soil P, sequential harvests of perennial pasture species were used to monitor the available P pools in two alkaline clay soils. In initial experiments with Cenchrus ciliaris (buffelgrass), an apparent increase was noted in the size of the available P pool over a number of sequential harvests during a 3-month period. This finding suggested that P was being transferred from a previously unavailable pool to the available pool during the experimental period. Planting buffelgrass after various periods of incubation of 32P with soils established that the apparent increase was not driven by P removal from the soil by growing plants since it also occurred in the absence of plants. The increase was linearly related to time. It may represent a natural cycling of P that is occurring continuously in the soils. A further experiment was run to determine whether species that differ in their efficiency of using soil P may influence·this rate of transfer. The tropical legumes Stylosanthes hamata, Stylosanthes gui,a,nensis, Macroptilium atropurpureum, and Desmodium intortum were used in addition to buffelgrass. Measurements of the initial sizes of the available P pools were similar with all species. Furthermore, the apparent rate of increase in size of the available P pools was the same for all species in spite of large differences in both the rates of P removal and the total amounts of P removed by the various species. Differences between these species in their efficiency in taking up and using soil P were therefore due to differences in their ability to exploit th same pool of available P. Differences were not due to a capacity of any of the species to expand this pool during their growing period by increasing the rate of transfer of P from previously unavailable sources.
Citation
Smith, F W., "Availability of Soil Phosphate to Tropical Pasture Species" (1981). IGC Proceedings (1981-2023). 2.
(URL: https://uknowledge.uky.edu/igc/1981/section3/2)
Included in
Agricultural Science Commons, Agronomy and Crop Sciences Commons, Plant Biology Commons, Plant Pathology Commons, Soil Science Commons, Weed Science Commons
Availability of Soil Phosphate to Tropical Pasture Species
Quantitative measurements of the amount of soil phosphate available to plants were made by an isotopic-dilution technique (L-value). Following very thorough mixing and equilibration of 32P with soil P, sequential harvests of perennial pasture species were used to monitor the available P pools in two alkaline clay soils. In initial experiments with Cenchrus ciliaris (buffelgrass), an apparent increase was noted in the size of the available P pool over a number of sequential harvests during a 3-month period. This finding suggested that P was being transferred from a previously unavailable pool to the available pool during the experimental period. Planting buffelgrass after various periods of incubation of 32P with soils established that the apparent increase was not driven by P removal from the soil by growing plants since it also occurred in the absence of plants. The increase was linearly related to time. It may represent a natural cycling of P that is occurring continuously in the soils. A further experiment was run to determine whether species that differ in their efficiency of using soil P may influence·this rate of transfer. The tropical legumes Stylosanthes hamata, Stylosanthes gui,a,nensis, Macroptilium atropurpureum, and Desmodium intortum were used in addition to buffelgrass. Measurements of the initial sizes of the available P pools were similar with all species. Furthermore, the apparent rate of increase in size of the available P pools was the same for all species in spite of large differences in both the rates of P removal and the total amounts of P removed by the various species. Differences between these species in their efficiency in taking up and using soil P were therefore due to differences in their ability to exploit th same pool of available P. Differences were not due to a capacity of any of the species to expand this pool during their growing period by increasing the rate of transfer of P from previously unavailable sources.
