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Estimate Plant Available Water Capacity (PAWC) from an apsimx file

Source: R/soil.R
get_pawc.Rd

This function calculates the Plant Available Water Capacity (PAWC) from soil properties in an APSIM Next Generation (.apsimx) file. PAWC represents the amount of water that can be stored in the soil and is available for plant uptake.

Usage

get_pawc(l, soil_path = NULL, crop = NULL, depth = NULL)

Arguments

l

The list of apsimx file

soil_path

The path to the soil model. If NULL (default), searches for the first Soil model. Can be a character string specifying the soil name.

crop

The crop name for crop-specific lower limit (LL). If NULL (default), uses LL15 and does not apply XF. If provided, uses the crop-specific LL and XF values from the SoilCrop parameters.

depth

The depth (in mm) to which PAWC should be calculated. If NULL (default), calculates for all layers. If specified, applies proportional weighting to layers that are partially or completely beyond this depth.

Value

A numeric value of PAWC in mm

Details

PAWC represents the soil's water storage capacity between field capacity (DUL) and the permanent wilting point (LL). It is a critical parameter for:

PAWC is calculated for each soil layer using the formula:

**When crop = NULL and depth = NULL:** $$PAWC_i = (DUL_i - LL15_i) \times Thickness_i$$

**When crop is specified:** $$PAWC_i = (DUL_i - LL_i) \times Thickness_i \times XF_i$$

**When depth is specified (with or without crop):** $$PAWC_i = (DUL_i - LL_i) \times Thickness_i \times [XF_i] \times Weight_i$$

Where:

  • DUL (Drained Upper Limit): The volumetric water content (mm/mm) after the soil has drained under gravity, typically 2-3 days after saturation

  • LL (Lower Limit): The volumetric water content (mm/mm) below which plants cannot extract water. This can be either:

    • LL15: Generic lower limit at 15 bar suction (used when crop = NULL)

    • Crop-specific LL: Lower limit specific to a crop type, accounting for different rooting characteristics

  • Thickness: Layer thickness in millimeters

  • XF: Exploration factor (0-1), representing the fraction of a layer explored by roots. Only applied when crop is specified; represents the proportion of the layer volume that roots can explore

  • Weight: Depth weighting factor (0-1), only applied when depth is specified:

    • 1.0 for layers completely within the specified depth

    • Proportional fraction for layers partially within the depth

    • 0.0 for layers completely beyond the specified depth

The total PAWC is the sum across all layers: $$PAWC_{total} = \sum_{i=1}^{n} PAWC_i$$

Examples

wheat <- read_apsimx(system.file("extdata/wheat.apsimx", package = "rapsimng"))

# Get total PAWC using LL15 (generic)
pawc <- get_pawc(wheat)
pawc
#> [1] 361.23

# Get PAWC for wheat crop (uses crop-specific LL and XF)
pawc_wheat <- get_pawc(wheat, crop = "Wheat")
pawc_wheat
#> [1] 246.015

# Get PAWC to 1200 mm depth
pawc_1200 <- get_pawc(wheat, depth = 1200)
pawc_1200
#> [1] 256.41

# Get wheat PAWC to 1500 mm depth
pawc_wheat_1500 <- get_pawc(wheat, crop = "Wheat", depth = 1500)
pawc_wheat_1500
#> [1] 244.125