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Potential of a Root Bioassay for Determining P-Deficiency in High Altitude Grassland

A. F. Harrison, K. Taylor, J. C. Hatton, J. Dighton and D. M. Howard
Journal of Applied Ecology
Vol. 28, No. 1 (Apr., 1991), pp. 277-289
DOI: 10.2307/2404129
Stable URL: http://www.jstor.org/stable/2404129
Page Count: 13
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Potential of a Root Bioassay for Determining P-Deficiency in High Altitude Grassland
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Abstract

(1) The significance of phosphorus deficiency in limiting sward production was assessed in an altitudinal sequence of Agrosto-Festucetum grasslands at the Moor House National Nature Reserve. (2) A 32P root uptake bioassay was applied both to sand-culture grown plants of Agrostis capillaris and Festuca ovina and to roots of tillers collected from field experiments, to indicate the potential value of this method for determining the P status of the hill grasslands. (3) The two species grown in sand-culture showed negative relationships between 32P uptake in pg P mg root-1 15 min-1 and (a) a range of P concentrations (0.4-40 mg P litre-1) supplied in the culture solution, and (b) the total P content (mg P plant-1). (4) Both the total annual dry matter production (g m-2) in the four altitudinal grassland sites and total P in the annual sward production (mg m-2) were negatively and asymptotically related to 32P uptake by excised roots of Festuca ovina, the most common component species in the swards. (5) Sward production differed significantly in the 2 years of observations relating to the degree day values above 6 ⚬C for the respective growing seasons. The 32P root uptake values derived from the bioassay reflected the differences in the P demand by the swards between these two years with the results forming a single regression. (6) In a field fertilizer experiment, the bioassay was able to detect the effects of site, applied P fertilizer and site x fertilizer interactions only 2 weeks after fertilizer application. (7) The results of the bioassay appear to provide integrated assessments of (i) the demand for P, (ii) the P supply in the soil, and (iii) likely responses of sward production to fertilizer applications, in high-altitude grasslands.

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