Crop grazing module

Author: Young

Crop grazing is an option that allows stock to graze green crops, by default, from June until August (user customisable range). Green crops have a high energy content and grow erect allowing for easier grazing. Therefore, crops can meet livestock energy needs at a lower FOO than an equivalent pasture. However, for every kilogram of crop biomass consumed yield is reduced by 150 grams per hectare (user customisable), with a corresponding effect on stubble production. Trials have recorded varying yield penalties from -15% to +15%, but the consensus is that the yield penalty is minimal if the crop is grazed early and lightly. The level of the yield penalty is an input which can be easily changed.

AfoLogic.CropGrazing.crop_md_vol(nv, r_vals)

Energy provided and volume required from 1t of crop grazing.

p5 axis exists because sowing time influences crop DM which impacts ME and vol.

AfoLogic.CropGrazing.f_cropgraze_DM(r_vals=None, total_DM=False)

Calculates the dry matter (DM) available for grazing on crop paddocks and the total DM used to calculate relative availability.

The total DM is calculated from the initial DM plus growth minus the consumption. The initial DM is an inputted amount which represents germination and first growth over an establishing period. No grazing can occur during the establishing period. After the establishing period, the crop grows at an inputted rate per day and a proportion of this growth becomes available for consumption. Total DM (used to calc relative availability) is calculated assuming that all the crop available for grazing is consumed. Depending on grazing management this may underestimate DM however, crop grazing has high availability at low DM levels (due to upright growth) so this limitation is likely to be minor.

If DM is not consumed in the period it grows it is transferred to the following feed period. Currently, it doesn’t incur a growth rate (e.g. 1t that isn’t consumed in fp0 transfers to 1t in fp1). A possible improvement would be to include growth in the transfer activity.

Crop growth rate is an input for each feed period, LMU and land use. There are two main limitations of the representation:

  1. Impacts of rotation are not included in the estimation of crop growth.

  2. Growth rate is independent of selected grazing management (e.g. if the crop isn’t grazed in the first period then the subsequent growth rate does not change).

Both DM parameters are built with a z8z9 axis. This is because provision of crop grazing is hooked up to the seeding activity which is not transferred to future periods and thus doesn’t uncluster but seeding provides crop DM in future periods which may be in nodes. Therefore, a z8z9 axis is required so that seeding in z[0] provides crop grazing in z[1] and other children.

P5 axis is required to represent sowing time. Sowing time impacts the DM provided in each p6 period.

Parameters:

total_DM – boolean when set to True calculates the total crop DM used to calculate relative availability.

AfoLogic.CropGrazing.f_cropgraze_biomass_penalty(r_vals)

Biomass penalty associated with the amount of crop consumed.

The yield penalty is an inputted proportion of the dry matter consumed. Below it is converted to a biomass penalty.