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  • 1
    Electronic Resource
    Electronic Resource
    Equations for describing sigmoid yield responses and their application to some phosphate responses by lupins and by subterranean clover (1990)
    Springer
    Nutrient cycling in agroecosystems 22 (1990), S. 181-188 
    Details
    ISSN: 1573-0867
    Keywords: Sigmoid curves ; phosphate response ; substitution rate ; relative effectiveness ; lupins ; subterranean clover
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Responses to nutrients are sometimes sigmoid. A series of equations is proposed to describe such curves and to test whether the sigmoid component is significant. These equations are then applied to responses to freshly applied, and to incubated, phosphate by three species of lupin and by subterranean clover. The responses byLupinus angustifolius, and especially by subterranean clover, were sigmoid on a log scale; the response byL. luteus was not significantly sigmoid and the sigmoid component of the response byL. cosentinii was small and only barely significant. The sigmoid response by subterranean clover occured even though it was strongly infected with vesicular arbuscular mycorrhiza. Including the sigmoid component enabled a closer description of the response and therefore a more precise estimation of the effectiveness of the incubated phosphate relative to that of fresh phosphate. This produced increased confidence in the conclusion that there was no statistically significant differences (P 〈 0.01) in the relative effectiveness of incubated and fresh phosphate amongst the four species of legume.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01120393
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  • 2
    Electronic Resource
    Electronic Resource
    Incubating superphosphate in ‘dry’soil can reduce its effectiveness (1995)
    Springer
    Nutrient cycling in agroecosystems 44 (1995), S. 205-215 
    Details
    ISSN: 1573-0867
    Keywords: Incubation of phosphorus in soil ; relative effectiveness ; superphosphate ; ×Triticosecale ; Triticum aestivum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Single superphosphate was incubated for six months at 25°C in soil which had been subject to one of three moisture treatments. These were: dried in a glasshouse, dried at a constant temperature of 25°C, or moist soil. Phosphorus (P) effectiveness was then compared with effectiveness of P from freshly-applied superphosphate using yields of wheat (Triticum aestivum) and triticale (×Triticosecale) tops in pot experiments. Incubation in soil which had been dried at 25°C did not decrease the effectiveness of the P. Incubation in moist soil decreased it to about 20% of the effectiveness of freshly-applied P in one case and to about 50% in the other case. Incubation in soil which had been dried in a glasshouse also decreased its effectiveness. The decrease varied with conditions, but in two cases the P was 70% as effective as freshly-applied P, and in one case only 45% as effective. Presumably sufficient moisture was present in the soil dried in the glasshouse to enable water-soluble P present in the fertilizer to react with the soil.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00750927
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  • 3
    Electronic Resource
    Electronic Resource
    A comparison of methods for measuring the effect of level of application on the relative effectiveness of two fertilizers (1990)
    Springer
    Nutrient cycling in agroecosystems 26 (1990), S. 1-10 
    Details
    ISSN: 1573-0867
    Keywords: Response curves ; relative effectiveness ; substitution rate ; rock phosphate ; Calciphos
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The effectiveness of a slowly soluble source of phosphate relative to a soluble source may decrease with increasing levels of application. This may cause yields to approach a lower asymptote. Four methods for measuring this effect are compared using field experiments in which a calcined rock phosphate (Calciphos) was compared with superphosphate for growth of subterranean clover. The methods were: subjective estimates using a hand drawn calibration curve; objective estimates using a fitted calibration curve; objective estimates using the fit of separate response curves; and objective estimates from the fit of a common response surface in which relative effectiveness was related to level of application. The role of these four methods differs. The first method, though often informative, is suitable only for an initial inspection of the data. The other three methods may all be useful for analysis but the fourth method was the most general. It gave the most sensitive statistical test and had the further advantage that it was a direct test of the hypothesis. All four methods showed that the relative effectiveness of Calciphos decreased with increasing levels of application.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01048739
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