computing stuff:

NOTES: WLEF is 37% sand, 15% clay acc. to Pridhoko
http://biocycle.atmos.colostate.edu/Prihodko.et.al.pdf

from:
http://www.pedosphere.com/resources/texture/worktable.cfm

Saxton, K.E., W.J. Rawls, J.S. Romberger, and R.I. Papendick. 1986. Estimating generalized soil-water characteristics from texture. Soil Sci. Soc. Am. J. 50(4):1031-1036

percent_sand = 0-100
percent_clay = 0-100
percent_silt = 1-total of the above

    sand_2 = percent_sand * percent_sand
    clay_2 = percent_clay * percent_clay

  acoef = Math.exp(-4.396 - 0.0715 * percent_clay -
                4.88e-4 * sand_2 - 4.285e-5 * sand_2 * percent_clay)

    bcoef = - 3.140 - 0.00222 * clay_2 - 3.484e-5 * sand_2 * percent_clay


;saturation cm3 water / cm3 soil = THETA_MAX
    SAT = 0.332 - 7.251e-4 * percent_sand + 0.1276 * log10(percent_clay)


;field capacity (cm3 water / cm3 soil)
      FC   = Math.pow((0.3333/ acoef),(1.0 / bcoef))

;wilting point (cm3 water / cm3 soil)
      PWP  = Math.pow((15.0  / acoef),(1.0 / bcoef))

;saturated hydraulic condoc (cm/hr)
   KSAT =
        Math.exp((12.012 - 0.0755 * percent_sand)  +
            (- 3.895 + 0.03671 * percent_sand -
                       0.1103  * percent_clay +
                       8.7546e-4 * clay_2)
            / SAT)


;p available water (cm3 water / cm3 soil)
    PAW = (FC - PWP)

;bulk density (g/cm3)
  BD = (1 -  SAT) * 2.65