Crop residues module

author: young

At the end of the growing season AFO has the option of harvesting or baling each crop, which leaves stubble for stock consumption, or crops can be left standing for fodder grazing. Stubble and fodder are modelled in the same ways, as follows.

Stubble and fodder are a key feed source for sheep during the summer months. In general, sheep graze crop residues selectively, preferring the higher quality components. They tend to eat grain first, followed by leaf and finally stem. To allow the optimisation of the proportion of the stubble grazed - which is optimising the trade-off between quantity and quality of the feed consumed - the total crop residues are divided into ten categories (A, B, C … J). Each category is a defined quality, which is the same across all crop types. The higher categories are better quality but generally lower quantity. Lower quality categories can’t be consumed until some higher quality categories have been consumed. This reflects the reality of selective grazing and ensures the model can’t defer all the high quality stubble categories until late in the autumn while grazing lower quality categories earlier in summer. If feed in a given category is not consumed then it deteriorates in quality and quantity due to adverse effects of weather and the impact of sheep trampling.

The total mass of crop residues at first grazing (harvest for stubble and an inputted date for fodder) is calculated as a product of the biomass, harvest index and proportion harvested (see f_biomass2residue below). The total mass of the residue is allocated between the categories using the AFO’s residue simulator which leverages the AFO stock generator (see Livestock for more information).

The proportion of total residue in each category is estimated with the Crop Residue Simulator using trial data of sequential animal liveweights grazing crop residue of a crop with known yield. See Crop Residue Simulator for more details.

The energy provided from consuming each crop residue category is calculated from DMD. Like pasture, crop residue FOO is expressed in units of dry matter (excluding moisture), therefore feed energy is expressed as M/D (does not require dry matter content conversion). The volume of each crop residue category is calculated based on both the quality and availability of the feed.

Work with farmers suggested that hay residue is treated just as any other crop residue. However, there are small differences between hay and a normally harvest crop. Hay is cut earlier therefore there is no split or spilt grain but there is some higher quality regrowth. The model captures the difference in quality through the Crop Residue Simulator and the impact on residue volume is handled through adjusting the harvest index and proportion harvested inputs.

Farmers often rake and burn crop residue in preparation for the following seeding. This is represented as a cost see Phase.py for further information.

Stubble grazing optimisation in AFO includes:

  • The time to start grazing of each stubble

  • The class of stock that grazes the stubble

  • The duration of grazing

  • The amount of supplementary required in addition to stubble (to meet alternative LW profiles)

Stubble definitions:

  • Total Grain = HI * (above ground) biomass

  • Leaf + Stem = (1-HI) * biomass

  • Harvested grain = (1 - spilt%) * Total grain

  • Spilt grain = spilt% * Total grain

  • Stubble = Leaf + Stem + Spilt grain

  • Spilt grain as a proportion of the stubble = (HI * spilt %) / (1 - HI(1 - spilt%))

AfoLogic.CropResidue.crop_residue_all(params, r_vals, nv, cat_propn_s1_ks2)

Calculates the crop residue available, MD provided, volume required and the proportion of the way through the feed period that crop residue becomes available.

AfoLogic.CropResidue.f_biomass2residue()

Residue produced (Stubble or standing fodder) per kg of biomass.

The total mass of crop residues at first grazing (harvest for stubble and an inputted date for fodder) is calculated as a product of the biomass, harvest index and proportion harvested.

Note

Residue production can be positively impacted by frost because frost during the plants flowering stage can damage cell tissue and reduce grain fill [ZCC+15]. This results in less grain and more residue due to not using energy resources to fill grain. However, this is not currently captured in the calculation of residue as it is challenging to represent and isn’t a significant error.

This is a separate function because it is used in residue simulator.