• Variogram investigation of covariance shape within longitudinal data with possible use of a krigeage technique as an interpolation tool: Sheep growth data as an example

      Chalh, A.; El Gazzah, M. (Teagasc (Agriculture and Food Development Authority), Ireland, 2014)
      Most quantitative traits considered in livestock evolve over time and several continuous functions have been proposed to model this change. For individual records (longitudinal data), it is evident that measures taken at close dates are generally more related than these further apart in time. Since milk production involves several parities, the covariance structure within this trait has been analysed by time series methodology. However, the covariance structure within traits that are not repeated during life, such as those linked to growth, has not yet been formally modelled by considering time lags as is done in time series analysis. We propose an adaptation of the variogram concept to shape this structure; which gives the possibility of kriging missing data at any particular time. A new parameter, the halftime variogram, has been proposed to characterise the growing potential of a given population. The weight records of a Barbarine male lamb population were used to illustrate the methodology. The variogram covering the whole growth process in this population could be modelled by a logistic equation. To estimate the missing data from birth to 105 days of age, a simple linear interpolation was sufficient since kriging on a linear model basis gives a relatively more accurate estimation than kriging on a logistic model basis. Nevertheless, when both known records around the missing data are distant, a krigeage on the basis of the logistic model provides a more accurate estimation.
    • Visual drainage assessment: A standardised visual soil assessment method for use in land drainage design in Ireland

      Tuohy, P.; Humphreys, James; Holden, N.M.; O'Loughlin, James; Reidy, B.; Fenton, Owen T. (Teagasc (Agriculture and Food Development Authority), Ireland, 20/08/2016)
      The implementation of site-specific land drainage system designs is usually disregarded by landowners in favour of locally established ‘standard practice’ land drainage designs. This is due to a number of factors such as a limited understanding of soil–water interactions, lack of facilities for the measurement of soil’s physical or hydrological parameters and perceived time wastage and high costs. Hence there is a need for a site-specific drainage system design methodology that does not rely on inaccessible, time-consuming and/or expensive measurements of soil physical or hydrological properties. This requires a standardised process for deciphering the drainage characteristics of a given soil in the field. As an initial step, a new visual soil assessment method, referred to as visual drainage assessment (VDA), is presented whereby an approximation of the permeability of specific soil horizons is made using seven indicators (water seepage, pan layers, texture, porosity, consistence, stone content and root development) to provide a basis for the design of a site-specific drainage system. Across six poorly drained sites (1.3 ha to 2.6 ha in size) in south-west Ireland a VDA-based design was compared with (i) an ideal design (utilising soil physical measurements to elucidate soil hydraulic parameters) and (ii) a standard design (0.8 m deep drains at a 15 m spacing) by model estimate of water table control and rainfall recharge/drain discharge capacity. The VDA method, unlike standard design equivalents, provided a good approximation of an ideal (from measured hydrological properties) design and prescribed an equivalent land drainage system in the field. Mean modelled rainfall recharge/drain discharge capacity for the VDA (13.3 mm/day) and ideal (12.0 mm/day) designs were significantly higher (P < 0.001, s.e. 1.42 mm/day) than for the standard designs (0.5 mm/day), when assuming a design minimum water table depth of 0.45 m.
    • Yield losses caused by late blight (Phytophthora infestans (Mont.) de Bary) in potato crops in Ireland

      Dowley, L.J.; Grant, Jim; Griffin, D. (Teagasc, Oak Park, Carlow, Ireland, 2008)
      Field experiments, using foliage blight susceptible cultivars, were conducted at Oak Park, Carlow from 1983 to 2007 to determine the loss in potato production caused by crop infection with Phytophthora infestans. In each of the 25 years an untreated control was compared with protectant and with systemic fungicide programmes to determine the effect of late blight on the defoliation percentage at the end of the season, the area under the disease progress curve, marketable tuber yield, total tuber yield and yield of blighted tubers. The earliest date of first recorded late blight was 22 June and the latest was 15 September, but in 15 of the 25 years, blight was first recorded between 17 July and 13 August. Disease reached epidemic proportions in all but 4 of the years. Yields varied considerably among years. The mean loss in total yield from not using a fungicide was 10.1 t/ha. Differences in yield were significant across the 25 seasons. No overall increase in aggressiveness of the pathogen could be detected over the 25-year period.