Description Usage Arguments Details Value Note References See Also Examples
P50
computes the half-viability period, which is the time taken for
50% of the seeds to lose viability. \loadmathjax
1 |
initial |
The initial viability (%). |
vcindex |
An integer value indicating the index of seed viability.
constants to be used from the |
vcdirect |
A numeric vector of length 4 with the four viability constants viz.: \mjseqnK_E, \mjseqnC_W, \mjseqnC_H and \mjseqnC_Q. |
mc |
Moisture content. |
temp |
Temperature in °C. |
years |
If |
The period to lose 50% viability (\mjseqnP_50) is computed according to the relationship between probit percentage viabilities and time of storage described by \insertCiteellis_improved_1980;textualviabilitymetrics as follows.
\mjsdeqnv=K_i-\fracp\sigma
or
\mjsdeqnv=K_i-\left ( \frac1\sigma \right )\cdot p
Where, \mjseqnv is the probit percentage viability at storage time \mjseqnp (final viability), \mjseqnK_i is the probit percentage viability of the seedlot at the beginning of storage (seedlot constant) and \mjseqn\dfrac1\sigma is the slope.
Germination percentages plotted against storage times yield a sigmoid seed survival curve which is converted to a linear relationship by the probit transformation with slope \mjseqn\dfrac1\sigma.
When \mjseqnv = 0 (equivalent to 50% viability), \mjseqnP_50 can be computed as follows.
\mjsdeqnP_50 = K_i \times \sigma
If the initial viablity (initial
) is beyond limits (0-100 %, an error
is issued.
The value of this computation is appropriate for temperature between -20 to 90 °C and seed moisture content between 5 to 25%. For values beyond this range, a warning will be displayed.
The half-viability period in days or years (according to argument
years
).
For initial viability percentage values of 100%, adjust it according
to sample size using the
PercentAdjust
function to
avoid infinity values in output.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 | P50(initial = 98, vcindex = 24, mc = 5, temp = -20)
P50(initial = 98, vcindex = 24, mc = 5, temp = -20, years = TRUE)
# With intial viability of 100%
P50(initial = 100, vcindex = 24, mc = 5, temp = -20)
P50(initial = 100, vcindex = 24, mc = 5, temp = -20, years = TRUE)
# With intial viability of 100%, use of PercentAdjust() to avoid Inf
P50(initial = PercentAdjust(100, n = 50), vcindex = 24, mc = 5, temp = -20)
P50(initial = PercentAdjust(100, n = 50), vcindex = 24, mc = 5, temp = -20,
years = TRUE)
## Not run:
# Error if initial viability is beyond limits (0-100 %)
P50(initial = 110, vcindex = 24, mc = 5, temp = -20)
## End(Not run)
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