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The minimum of these two estimates is the actual biomass production for the day.ĭelta_drymatter_transpiration = soil_ water_ supply * transpiration_efficiency eqn 1. Biomass accumulation (Photosynthesis)Įach day two estimates of the daily biomass production are calculated, one limited by available water for transpiraton (eqn 1), and the other limited by radiant energy (eqn 2). Table 2 gives phenology parameters currently available in the sorghum module. There are cultivar-specific fixed thermal time durations for the subsequent phases between flowering and the start of grain fill, between the start and end of grainfill, between the end of grainfill and maturity, and between maturity and harvest ripe. The model assumes that sorghum, as a short day plant, will have a longer phase (dependent upon cultivar) between the end of the juvenile phase and initiation if photoperiods exceed the base photoperiod. Between the end of the juvenile phase and floral initiation the thermal development rate is sensitive to photoperiod (calculated as a function of day of year and latitude) if the cultivar is photoperiod sensitive. The phase between emergence and floral initiation is composed of a cultivar-specific period of fixed thermal time, commonly called the basic vegetative or juvenile phase. Hence the timing of floral initiation will determine the total leaf number and the timing of the appearance of the flag leaf and flowering.
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Apsim sorghum plus#
The total number of leaves is equal to the number in the seed at germination (4) plus the number subsequently initiated at a rate of 21 o Cdays per leaf, until floral initiation is reached. The duration between emergence and flag leaf appearance is determined by the total number of leaves destined to appear on the plant, and the rate at which they appear, which is determined by temperature (see below). The phase between germination and emergence includes an effect of the depth of sowing on the thermal time target. The thermal time between sowing and germination is dependent upon soil water status. Table 1: Phenological stages simulated in the sorghum module. In the sorghum module different relationships are used for development before and during grainfilling. Between the stage of emergence and flowering the calculated daily_thermal_time is reduced by water or nitrogen stresses, resulting in delayed phenology when the plant is under stress.įigure 2: Relationship between temperature and thermal time accumulation. These daily thermal time values are cumulated into a thermal time sum which is used to determine the duration of each phase. Different thermal time relationships are used for development before and during drain-filling. Thermal time is calculated using the relationship in Figure 1 with the eight 3-hour estimates averaged to obtain the daily value of thermal time (in growing degree days) for the day. Each day the phenology routines calculate today’s thermal time (in degree days) from 3-hourly air temperatures interpolated from the daily maximum and minimum temperatures.
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There are 11 crop stages and nine phases (time between stages) in the sorghum module (Table 1), and commencement of each stage (except for sowing to germination which is driven by soil moisture) is determined by accumulation of thermal time. Sorghum Module Structureįigure 1: Order of key simulation steps in the sorghum module. The sorghum module was originally developed from the QSORG model (Hammer and Muchow 1991) with features of the AUSIM model (Carberry and Arbrecht 1991) but has been extensively revised and improved since then. Sorghum stover and root residues are ‘passed’ from sorghum to the residue and soiln module respectively at harvest of the sorghum crop.Ī list of the module outputs is provided in the ‘Sorghum module outputs’ section below, but basically the module will predict leaf area development, N% and biomass of stover depth, N% and biomass of roots grain N% and biomass grain yield and N%, grain size and grain number all on a daily basis. Information on crop cover is also provided to the soilwat module for calculation of evaporation rates and runoff. The sorghum module returns information on its soil water and nitrogen uptake to the soilwat and soilnmodules on a daily basis for reset of these systems. Sorghum growth in this model responds to climate (temperature, rainfall and radiation from the met module), soil water supply (from the soilwat module) and soil nitrogen (from the soiln module). The sorghum module simulates the growth of a sorghum crop in a daily time-step (on an area basis not single plant).