Strange MWCON values in Medium clay (Mona Park No820)

[BrianCollinss]

This profile has a value of 0.02 only for the 4th layer, which causes soil water to back up under heavy irrigation. This can lead to significaitnly large amunts of denitrification (Table 2 in Thorburn et al., 2011; see denitrification values in 'Mona Park'). I wonder if this is correct/intended.

[KirstenVer]

This was the parameterisation used in the publication to reflect a soil susceptible to waterlogging. These days we use Ksat to regulate (tipping bucket) flow above SAT instead of MWCON, but as this parameterisation is linked to a published paper it was left as is. The MWCON can be adjusted for local conditions, or changed into 1.0 with Ksat added to the APSoil record to reflect the waterlogging nature of the local soil to be simulated. It is usually used to reflect a constriction to flow (very low Ksat) or to mimic a local/regional water table. Without a low Ksat or MWCON in the old parameterisation soils would never waterlog, and we know that some soils in the sugarcane area do (whether that's due to soil's properties or a water table rise due to its position in the landscape.

[BrianCollinss]

Thanks @KirstenVer. May I know whether this specific soil was characterised/created by via field measurements or via adoption of knowledge of the soil types in the region abd based on other soil profiles? As you mentioned that the 0.02 value was to mimic waterlogging, does it mean that this soil type could be used without this characteristics as well? Would that be still a representtative soil for the Burdekin Region?

[KirstenVer]

I don't know more than what's in the comments field, which I think refers to published papers. But in general, APSoils reflect a specific soil (often in a specific location), so that when you want to use it elsewhere you need to consider whether the conditions are similar enough or you may need to adjust it. E.g. in dryland agriculture where PAWC (DUL-CLL) is critical, we may need to adjust the CLL depending on depth and strength of subsoil constraints like salinity (as indicated by chloride levels). In this case you can adjust the MWCON, but removing it may make it a more permeable soil than clay soils in the area might be. You can adjust that by adding Ksat, based on e.g. texture. The other thing to check (e.g. with locals) is how often the soil will waterlog and for how long. That gives some guidance. Waterlogging drives denitrification loss. A more permeable soil will have more leaching loss.