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  • 1
    Electronic Resource
    Electronic Resource
    Effects of gypsum on the uptake, assimilation and cycling of 15N-labelled ammonium and nitrate-N by perennial ryegrass (1992)
    Springer
    Plant and soil 143 (1992), S. 19-31 
    Details
    ISSN: 1573-5036
    Keywords: ammonium ; calcium ; carboxylate/organic nitrogen ratio ; 15N isotope ; nitrate ; nitrogen cycling ; perennial ryegrass
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Solution culture studies have shown that plant uptake of NH4 + and NO3 - can be improved by increasing the concentration of Ca2+ in the root environment: the same may be true for grass grown in soil culture. An experiment was set up to see whether gypsum (CaSO4 2H2O) increased the rate at which perennial ryegrass absorbed 15NH4 + and 15NO3 - from soil. The results demonstrated that gypsum increases the rates of uptake of both NH4 + and NO3 - by perennial ryegrass. However because there was little potential for mineral-N loss from the experimental system, either by gaseous emission or by N immobilization, long term improvements in fertilizer efficiency were not observed. Nitrogen cycling from shoots to roots commenced once net uptake of N into plants had ceased. Labelled N transferred thus to roots underwent isotopic exchange with unlabelled soil N. It was suggested that this exchange of N might constitute an energy drain from the plant, if plant organic N was exchanged for soil inorganic N. The fact that the exchange occurred at all cast doubt on the suitability of the 15N-isotope dilution technique for assessing fertilizer efficiency in medium to long term experiments. There was evidence that the ‘extra’ NO3 --N taken up by plants on the all-nitrate treatments as a result of gypsum application, was reduced in root tissue rather than in shoots, but to the detriment of subsequent root growth and N uptake.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00009125
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  • 2
    Electronic Resource
    Electronic Resource
    A re-examination of phosphorus-lime interactions in perennial ryegrass (1991)
    Springer
    Plant and soil 135 (1991), S. 185-196 
    Details
    ISSN: 1573-5036
    Keywords: calcium ; critical phosphorus concentration ; gypsum ; lime ; perennial ryegrass ; root membranes ; soluble carbohydrate ; zinc
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The results of a previous study had suggested that under conditions of limited P availability, Ca may be able to compensate for P in the shoot tissue of perennial ryegrass. To verify this preliminary finding, a factorial experiment was set up which simultaneously tested the effects of Ca and P fertilization on the yield and chemical composition of perennial ryegrass. Calcium was supplied as either lime or gypsum in order to differentiate between the effects of Ca and pH on the response of perennial ryegrass to P fertilization. In the final stage of the experiment a Zn treatment was included, to see whether altering the P/Zn ratios of plant shoots had any influence on the purported interaction between Ca and P. The results demonstrated that the P-sparing effect of lime occurs, at least partly, because Ca application improves the efficiency of absorbed P for DM production. However, it was reasonably clear that the site of the interaction between Ca and P was the soil-root interface, and not shoot tissue. It was suggested that under conditions of limited P supply, Ca stablizes root membranes and thereby minimizes both the efflux losses of nutrients from root tissue, and the compensatory flow of photosynthates from shoots to roots. No interaction was observed between P and Zn treatments in this study. Instead, a positive interaction was found between lime and Zn treatments, which suggests that the stabilizing action of Ca on root membranes requires Zn as a co-stabilizing factor. It is proposed that chemical analysis of shoot tissue alone may not be sufficient to accurately diagnose the P, Ca or Zn status of whole plants, since the critical levels of these elements in shoots appear to bear little relation to their requirements in the rhizosphere.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00010906
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  • 3
    Electronic Resource
    Electronic Resource
    The Diagnosis and Recommendation Integrated System (DRIS) for diagnosing the nutrient status of grassland swards: III Practical applications (2000)
    Springer
    Plant and soil 222 (2000), S. 255-262 
    Details
    ISSN: 1573-5036
    Keywords: basaltic soils ; DRIS ; perennial ryegrass ; phosphorus recommendations ; soil P test ; soil type
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Perennial ryegrass is the most important species of forage grass in both continental Europe and the British Isles. An investigation was carried out to see if the DRIS model developed for this species was able to diagnose crop nutrient sufficiency status, at harvest time, using data for herbage samples collected 2 weeks earlier. A re-evaluation of P fertiliser recommendations for silage, based on the ‘Olsen’ soil P-test, was then carried out using DRIS diagnoses of P sufficiency status as the criteria with which to judge if swards had been adequately, under, or over-supplied with fertiliser P. The results confirmed that reliable (DRIS) diagnoses of N, P, K and S sufficiency statuses of silage swards may be made from herbage clippings taken 2 weeks prior to harvest. Current P recommendations for silage swards proved to be excessive for non-basaltic sandy textured soils at first cut, correct for this group of soils at second cut, and more or less correct for non-basaltic clay textured soils at both cuts. For basaltic soils, however, P recommendations at both cuts appeared to be unrelated to plant P status, and it was concluded that the ‘Olsen’ soil P-test had provided an erroneous assessment of plant available P in these exceptionally iron-rich soils.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1004827206618
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  • 4
    Electronic Resource
    Electronic Resource
    Estimating true scores in kinship data (1987)
    Springer
    Behavior genetics 17 (1987), S. 487-491 
    Details
    ISSN: 1573-3297
    Keywords: true scores ; measurement error ; kinship data ; twins
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Psychology
    Notes: Abstract Estimated true scores are occasionally used to provide an estimate of scores which would be obtained if measurement error could be removed from fallible measures. When one knows only a test's relibility and an observed score for each subject, true scores are estimated by regressing observed scores toward the group mean. When relatives' observed scores are also available, estimates of true scores can be improved by using the additional information. Observed scores of subjects and relatives can be used as predictors of subjects' true scores in a multiple regression. The resulting formula is presented for the case in which only one relative's score per subject is known. Estimation of true scores for the general case ofN relatives per subject is also discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01073115
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  • 5
    Electronic Resource
    Electronic Resource
    Sexual orientation, sexual identity, and sex-dimorphic behaviors in male twins (1991)
    Springer
    Behavior genetics 21 (1991), S. 75-96 
    Details
    ISSN: 1573-3297
    Keywords: sexual orientation ; twins ; heritability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Psychology
    Notes: Abstract Sexual orientation, sexual identity, and sex-dimorphic behaviors were assessed concurrently and retrospectively, for childhood, in 95 pairs of male monozygotic (MZ) twins and 63 pairs of dizygotic (DZ) twins. There was a significantly higher rate of adult homosexuality among the MZ than among DZ twins. We employed a model-fitting approach using LISREL to test for genetic and environmental influences on variation for each trait singly and on the covariation among all six traits (three for childhood and three for adulthood). Univariate analyses confirmed the presence of familial factors for five of the six variables but were generally unable to distinguish shared environmental from genetic influences. Hierarchial tests of multivariate models supported the existence of an additive genetic factor contributing to the covariance among the variables. More restrictive multivariate models yielded a significant genetic influence on sexual orientation. Because of the different rates of orientation by zygosity and because of the restrictive nature of some of the multivariate models, our results are best considered tentative but do suggest that further biometrically oriented studies of sexual orientation and its correlates would be worthwhile.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01067668
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  • 6
    Electronic Resource
    Electronic Resource
    Measurement Models for Sexual Orientation in a Community Twin Sample (2000)
    Springer
    Behavior genetics 30 (2000), S. 345-356 
    Details
    ISSN: 1573-3297
    Keywords: Homosexuality ; sexual orientation ; heritability ; twins
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Psychology
    Notes: Abstract Multivariate structural equation modeling techniques have been applied to examine the causes of individual differences in responses to several items concerning sexual orientation. To minimize potential ascertainment and response biases, the study sample involved a large (N = 4901) community-based cohort of Australian twins aged 18–52 who answered an anonymous questionnaire on sexual behavior and attitudes. The statistical power of the analysis was increased by the availability of multiple measures of sexual orientation (behaviors, attitudes and feelings), providing stronger evidence for the existence of additive genetic influences on this phenotype than in a previous analysis (Bailey et al., 2000). Estimates of the heritability of homosexuality in this sample ranged between 50 and 60% in females but were significantly lower (heritability of approximately 30%) in males.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1026557719181
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  • 7
    Electronic Resource
    Electronic Resource
    A source of variance in IQ unique to the lower-scoring monozygotic (MZ) cotwin (1986)
    Springer
    Behavior genetics 16 (1986), S. 509-516 
    Details
    ISSN: 1573-3297
    Keywords: twins ; heritability ; environment ; intelligence
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Psychology
    Notes: Abstract Environmental factors more common in twins than singletons appear to be disadvantageous with respect to intelligence. If these factors contribute to within-pair differences in IQ, the effect should be found more in the cotwin lower in IQ (the low twin) than in the cotwin higher in IQ (the high twin). In this case, the variance of the low twins should exceed that of the high twins. This hypothesis was tested for five samples of monozygotic (MZ) twins and three samples of dizygotic (DZ) twins but was confirmed only for the MZ samples. These results suggest that there are disadvantageous environmental factors unique to MZ twins which contribute to within-pair variability. Such factors will cause heritability coefficients obtained using MZ twins to be underestimated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01066337
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  • 8
    Electronic Resource
    Electronic Resource
    Increased heritability for lower IQ levels? (1991)
    Springer
    Behavior genetics 21 (1991), S. 397-404 
    Details
    ISSN: 1573-3297
    Keywords: twins ; heritability ; environment ; intelligence
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Psychology
    Notes: Abstract Dettermanet al. (1990) presented evidence based on twins that the heritability of IQ may be higher in the lower part of the IQ range. We first offer an alternative test for differential heritability across the IQ range, based on the analysis of absolute intrapair differences of monozygotic versus dizygotic twins. We then review two previous studies, each containing more twins than the sample of Dettermanea al., which examined the distribution of intrapair absolute differences. In contrast to the study of Dettermanet al., both yielded results more compatible with higher heritability in the upper range of IQ. We discuss various interpretations of these findings and show how our proposed test might aid in distinguishing among them.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01065975
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  • 9
    Electronic Resource
    Electronic Resource
    Empirical Models for Predicting the Dry Matter Yield of Grass Silage Swards Using Plant Tissue Analyses (2000)
    Springer
    Precision agriculture 2 (2000), S. 131-145 
    Details
    ISSN: 1573-1618
    Keywords: empirical models ; perennial ryegrass ; silage swards ; tissue analyses ; yield mapping
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Quantifying spatial variability in forage grass yield within individual fields is hampered by the lack of accurate yield monitoring equipment. Here, it is shown how dry matter (DM) yield of silage swards can be predicted on the basis of their mineral composition. This empirical method of predicting yield enables diagnoses of sward nutrient status to be made simultaneously from the tissue test information, and provides a unique opportunity for identifying the nutritional and non-nutritional factors responsible for variability in sward productivity at sub-field scales. Maps of sward DM yield at first, second and third cut silage stages in 1999, and at first cut silage stage in 2000, on a large (7.9 ha) grassland field were produced using two different yield models: one model for first cut and a separate model for second and third cuts. The maps indicated that DM production varied considerably across the field, particularly at first cut, but that the pattern of yield variability at this cut was consistent from 1999 to 2000. The results of the plant tissue tests suggested that N deficiency had been responsible for limiting DM production on the lower yielding parts of the field.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1011421613409
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