Evaluation of the DNDC Model for Estimating Growth of Perennial Ryegrass and Identification of Its Regulators

Abstract

Plant available nitrogen (N), typically supplied through organic and inorganic fertilisers for managed grazed grasslands, can be lost from the soil into the environment with negative impacts on ecosystems, human health and the economy. To optimise plant uptake and mitigate the potential negative impacts of N loss, while at the same time maintaining or enhancing grass yields, it is necessary to account for the impact of management and interactions between soil and atmospheric conditions. In this research, we investigated the scope of employing the DNDC (DeNitrification-DeComposition) model, a site-specific process-oriented biogeochemical model, as a tool to support more geographically refined N management, at field and farm scale, considering soil and atmospheric conditions. However, a key limitation in utilising the model in this context is associated with the input data requirements. To address this, we evaluated the model's performance in estimating the growth rate and yield of perennial ryegrass (PRG) at an intensively managed dairy farm. In recognition of the paucity of detailed site-specific soil information, model estimates of yield were generated using both directly measured and commonly available soil and management information as well as more generalised farm level information. The results indicated that DNDC could reliably simulate the growth rate and annual yield of PRG, at both paddock and farm level, using both detailed and more generalised model inputs for soil, when the model parameters relating to the crop phenology are specified, and using regional atmospheric chemistry measurements.