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Articles by N. PERSAUD
Total Records ( 2 ) for N. PERSAUD
  N. Persaud , G. Hassan , W.D. Joshua and D. Lesolle
  The purpose of this study was to use mechanistic modeling of soil-plant-atmosphere hydraulics to develop quantitative measures of post-establishment agricultural drought for subsistence sorghum production under soil and rainfall conditions typical of semi-arid Eastern Botswana. Daily AET/PET ratios were calculated for 120 days following each of 15 growing period start dates over 9 growing seasons (1981/82 through 1989/90). The resulting series for each start date were used to calculate values for the total occurrences when AET/PET ≤ 0.3 for 2, 4 and 6 consecutive days and values of agricultural drought days using baseline AET/PET ratios reported in the literature. These two agricultural drought measures were compared over 3 the high-rainfall seasons (1983/84 to 1985/86) and 3 low rainfall seasons (1987/88 to 1989/90) for the 15 start dates. The mean occurrences when AET/PET ≤ 0.3 over the dry seasons were markedly higher and tended to be more variable for all growing period start dates. The mean occurrences for the 3 dry seasons showed the same pattern over the 15 start dates for all durations, but the values decreased with increasing duration in a non-linear manner. The same was true for the wet season occurrences. Agricultural drought day means were always < 0 and were more negative for the dry seasons for all start dates. Although the patterns for all measures contained low mean values, there were no well-defined minima for either the dry or wet seasons.
  The primary objective of this study was to investigate the impact of observation scale on the estimation of soil thermal properties. Transients are usually filtered out and ignored when classical Fourier approaches are used to deconstruct and model temperature time series. It was hypothesized that examination of such transients may be more important in identifying and quantifying short-term perturbations in internal soil heat transfer induced by agronomic disturbances. Data-logged temperatures were collected at 10-minute intervals from thermistor probes installed at 10 and 25 cm depths in isolated areas of two grassed plots. One plot (6T) had been treated twice with 6 Mg ha−1 composted turkey litter as received. The other plot (NPK) was fertilized at the same time with NPK fertilizer. Various methods were used to analyze the series to obtain apparent soil thermal diffusivity (D-value) at various time scales. Results supported the hypothesis that short-term differences in internal soil heat transfer between the 6T and NPK plots were more manifest and effectively captured by estimated D-values calculated from the monthly and daily partial series. The 6T plot had higher soil organic matter content than the NPK plot and had lower apparent soil thermal diffusivity. Diurnal soil temperature amplitudes, required to calculate the mean D-values from partial series, were more effectively obtained using a temperature change rate method. The more commonly used Fourier analysis tended to be effective for this purpose when the partial series reasonably presented well-defined diurnal patterns of increasing and decreasing temperatures.
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