Note: This page is no longer being maintained and is kept for archival purposes only. For current information see our main page. Kurtz-Fernhout Software Developers of custom software and educational simulations. Home ... News ... Products ... Download ... Order ... Support ... Consulting ... Company
Garden with Insight
Product area
Help System
Contents
Quick start
Tutorial
How-to
Models

#### Garden with Insight v1.0 Help: Plant Growth - Phosphorus

Crop use of P is estimated with the supply and demand approach described in the N model. The daily demand is computed with equation 276 written in the form [Equation 291] where UPD is the P demand for the plant in kg/ha, UP is the actual P uptake in kg/ha, and c(PB) is the optimal P concentration for the plant.

Equation 291

UPD = c(PB) * B - (sum with k from 1 to i-1 of) UP(k)
Code:
same
Variables:
UPD = PlantPhosphorusDemand_kgPha
c(PB) = plantOptimalPConc_kgPkg
B = totalPlantBiomass_tPha
UP(k) = plantPUptake_kgPha
sum of UP(k) = lifeTotalPlantPUptake_kgPha (summed daily)

As in the case of N, the optimal plant P concentration is computed with equation 277 written in the form [Equation 292] where bp(1), bp(2), and bp(3) are parameters calculated from crop-specific optimum P concentration at the seedling stage, halfway through the season and at maturity.

Equation 292

c(PB) = bp(1) + bp(2) * exp(-bp(3) * HUI)
Code:
c(PB) = (bp(1) - bp(3)) * (1.0 - HUI / (HUI + exp(bp(1) - bp(2) * HUI))) + bp(3)
Variables:
c(PB) = PlantoptimalPConc_kgPkg
bp(1) = plantOptimalPConcParams[0
bp(2) = plantOptimalPConcParams[1
bp(3) = plantOptimalPConcParams[2
HUI = heatUnitIndex

Soil supply of P is estimated using the equation [Equation 293] where UPS is the amount of P supplied by the soil in kg/ha, LF(u) is the labile P factor for uptake, RW is the root weight in layer l in kg/ha, and RWT is the total root weight on day i in kg/ha. The constant 1.5 allows 2/3 of the roots to meet the P demand of the plant if labile P is not limiting. This approach is consistent with studies suggesting that roots of P-deficient plants (or plants whose root systems have been pruned) can absorb P faster than the roots of normal plants (Andrews and Norman, 1970. DeJager, 1979. Jungk and Barber, 1974).

Equation 293

UPS = 1.5 * UPD * (sum with l from 1 to M of) LF(u) * RW / RWT
Code:
LF(u) is for layer of interest only, not summed
if UPS > labile p in layer, UPS = 0.9 * labile p in layer
GWI change: this was P uptake, but since we added a nutrient competition component
where the soil patch partitions N and P to its plants, what the plant calculates
as uptake is actually now a request made to the soil patch.
Variables:
UPS = PSupplyForLayer_kgPha
UPD = pDemand_kgPha
LF(u) = labilePUptakeFactor_frn
RW = rootWeight_tPha (layer)
RWT = totalRootWeight_tPha

The labile P factor for uptake ranges from 0.0 to 1.0 according to the equation [Equation 294] where c(LP) is the labile P concentration in soil layer l in g/t. Equation 294 allows optimum uptake rates when c(LP) is above 20 g/t. This is consistent with critical labile P concentrations for a range of crops and soils (Sharpley et al., 1990). Sharpley et al. (1984, 1985) described methods of estimating c(LP) from soil test P and other soil characteristics.

Equation 294

LF = 0.1 + 0.9 * c(LP) / (c(LP) + exp(8.01 - 0.360 * c(LP)))
Code:
same except if c(LP) > 30, LF = 1.0
Variables:
LF(u) = LabilePUptakeFactorForLayer_frn
c(LP) = labilePConc_gPt

 Home ... News ... Products ... Download ... Order ... Support ... Consulting ... Company Updated: March 10, 1999. Questions/comments on site to webmaster@kurtz-fernhout.com. Copyright © 1998, 1999 Paul D. Fernhout & Cynthia F. Kurtz.