P50: Half-viability period

In aravind-j/viabilitymetrics: Seed Viability Calculations and Curve Fitting

Description

P50 computes the half-viability period, which is the time taken for 50% of the seeds to lose viability. \loadmathjax

Usage

P50(initial, vcindex, vcdirect, mc, temp, years = FALSE)

Arguments

initial	The initial viability (%).
vcindex	An integer value indicating the index of seed viability. constants to be used from the viabilityconstants dataset in the package.
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 TRUE, returns the output period in years instead of days.

Details

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.

\mjsdeqn

v=K_i-\fracp\sigma

or

\mjsdeqn

v=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.

\mjsdeqn

P_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.

Value

The half-viability period in days or years (according to argument years).

Note

For initial viability percentage values of 100%, adjust it according to sample size using the PercentAdjust function to avoid infinity values in output.

References

\insertAllCited

See Also

Sigma, PercentAdjust

Examples

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)

aravind-j/viabilitymetrics documentation built on May 15, 2021, 9:10 a.m.