Soil supply and nutrient demand (SSAND): A general nutrient uptake model and an example of its application to forest management

Models of soil nutrient bioavailability and uptake assist in nutrient management and lead to a better understanding of nutrient dynamics in the soil-plant system. SSAND (Soil Supply and Nutrient Demand) is a steady state, mechanistic nutrient uptake simulation model based on mass flow and diffusive supply of nutrients to roots. It requires user inputs for soil and plant parameters to calculate a nutrient's concentration at the root surface and the subsequent uptake by a plant root and/or extrametrical mycorrhizal hyphae. It can be considered a sub-model linked to hydrological or plant growth models. SSAND provides a basis for simulating nutrient uptake under different soil-plant scenarios, including multiple soil compartments, net mineralization inputs, changing root growth, changing mycorrhizal hyphae growth, changing soil water content and multiple fertilizer events. It incorporates uptake from roots and mycorrhizal hyphae, including the potential competition between these entities. It should be useful for simulating the effects of climate change on soil nutrient bioavailability. It should also be a useful tool for managers in evaluating fertilizer regime options.