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  • 2000-2004
  • 1990-1994  (3)
  • 1990  (3)
  • 1
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    Unknown
    London : Periodicals Archive Online (PAO)
    Journal of adolescence. 13:2 (1990:June) 185 
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Journal of mathematical biology 29 (1990), S. 77-90 
    ISSN: 1432-1416
    Keywords: Population dynamics ; Age-structure ; Harvesting
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract Here we investigate the optimal harvesting of an age-structured population. We use the McKendrick model of population dynamics, and optimize a discounted yield on an infinite time horizon. The harvesting function is allowed to depend arbitrarily on age and time and its magnitude is unconstrained. We obtain, in addition to existence, the qualitative result that an optimal harvesting policy consists of harvesting at no more than three distinct ages.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1573-0867
    Keywords: Phosphorus ; P-efficient ; P-availability ; P-placement ; P X management interactions ; nutrient balance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Phosphorus interactions with various management practices and inputs are complex and vary from physiological to inorganic in nature. Awareness of these interactions can have significant effects on decisions to apply P, can influence rates of applied P and should be seriously considered in decisions on method of P application. Recognizing that combinations of climatic and tillage system factors can influence short-term P availability may lead to the decision to apply fertilizer P even when soil P tests are high. Nutrient balance is one of the most important factors in P response. The interaction of N, P and K are of special significance, often determining whether responses to additions occur and the extent to which they are efficient and profitable. Phosphorus-micronutrient interactions can have significant effects on plant growth and yield but often are of more academic than practical interest for most crops. Soil testing and plant analysis to detect levels of micronutrient deficiency followed by applications of appropriate amounts of micronutrients can offset detrimental P-micronutrient interactions commonly reported for metals such as Zn, Fe and Cu.
    Type of Medium: Electronic Resource
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