Simulating Biomass and Grain Yields of Barley and Oat Crops with the Sirius Wheat Model

Abstract

Mechanistic crop models have been used widely to simulate wheat crop responses to the environment. In contrast, there have been few attempts to model barley or oat responses using crop simulation models. This study used Sirius to simulate barley and oat crops from a range of sowing dates under good growing conditions. Simulations were conducted using Sirius, a crop model that was originally conceived for wheat but has a mechanistic framework that is sufficiently robust to be applied to other temperate cereals. The objective of this research was to test the processes operating within the model rather than simply applying it to predict final yields. Therefore, data sets were chosen that had intensive within-season measurements of leaf area index (LAI), biomass and grain yield.

All observed crops were grown at Lincoln, New Zealand, with water and nitrogen supply presumed to be non-limiting. The barley cultivars grown were ‘Triumph’, ‘Dash’, and ‘Valetta’ at five sowing dates and the oat cultivar grown was ‘Drummond’ at seven sowing dates. Sirius requires a small set of cultivar-specific parameters. Cultivar parameters for the phenology of ‘Drummond’ oats were taken from a previous experiment. A single cultivar description for ‘Triumph’ was used for all barley simulations. This cultivar description was based on wheat but with a more rapid phyllochron and a slightly modified LAI relationship with thermal conditions. Otherwise no modification was made to the model structure.

Time courses of crop and grain growth were generally well simulated by Sirius. Root mean squared deviations for final grain yield were 1.3 t ha⁻¹ for barley and 1.0 t ha⁻¹ for oats. Although there were some small errors in the simulation of LAI, these had only minor effects on simulated biomass and grain yields. However, for late autumn and early spring sowings of ‘Drummond’ oats LAI and biomass were over-predicted and for a mid spring sowing these parameters were under predicted. This error suggested that there is an aspect of phenological or canopy development not accounted for in Sirius. Overall, Sirius gave good predictions of biomass and grain yield of barley and oat crops under good growing conditions with little or no modification.