27 August 2020
Overseer Limited is always looking to represent proven farming practices or technologies in OverseerFM to ensure farmers have more options to assess when looking at their nutrient management systems.
The Tonic variety of plantain has been used as a pasture for some time with purported benefits for reducing nitrate leaching.
The DairyNZ-led research programme Forages for Reduced Nitrate Leaching (FRNL) – a cross sector approach from 2013-2019 - aimed to provide new scientific knowledge, tools and technologies for forage production that reduces nitrate leaching.
Research undertaken as part of the FRNL programme assessed the impact of Tonic plantain on nitrate leaching and assessed how this might be incorporated into the Overseer science model.
Overseer Limited partnered with FRNL to translate this research into the software.
This document sets out the FRNL recommendations and how they have been implemented into the Overseer science model. It does not justify or comment on the FRNL science research findings, which have been through a research panel set up by the programme and published.
The reports listed below outline the process undertaken in FRNL to recommend changes in the Overseer science model for reflecting plantain. The reports can be downloaded from www.dairynz.co.nz/frnl.
- Evaluation of FRNL data against Overseer (April 2019)
- Recommendations for implementation of plantain-based pasture in Overseer (Feb 2020)
- Plantain sensitivity analysis (April 2020)
- Testing of the Overseer plantain block model (July 2020) - also attached as a PDF.
Recommendations from FRNL
FRNL identified the following effects that could be modelled from feeding animals plantain:
- Adjust the proportion of N in urine
- Adjust the urine patch N load.
Based on the finding from FRNL, these effects are evidenced for plantain in the diet up to a maximum of 60%. Any plantain above 60% in the diet are assumed to have the same effect as 60%.
Proportion of Nitrogen allocated to urine
Overseer calculates the nitrogen in excreta and proportions this to urine and dung using an equation based on the concentration of nitrogen in the diet.
FRNL research identified that where animals are fed plantain the proportion of nitrogen allocated to urine should be adjusted by multiplying it by 1-PP/3, Where PP is the proportion of plantain in the diet.
So, at 60% plantain (proportion of 0.6), the proportion allocated to urine will be 80% (1-0.6/3) of the existing proportion.
Urine patch N load
The Nitrogen load of a urine patch currently used in the urine patch model is 750 kg N/ha. FRNL research identified that where animals are fed plantain, this should be set to 750-(PP*500), Where PP is the proportion of plantain in the diet.
Proportion of plantain in the diet (PP)
Where animals are grazing a pastoral block that contains plantain, the percentage of plantain in the pasture for that block can be entered by the user. The calculation of the percentage of plantain in the diet needs to consider the pasture proportion and any supplements fed to animals as well.
Where supplements are harvested from a block that has plantain and it is fed directly to the animals (Direct Feeding category type for the supplement) it is assumed that the effects of the plantain are consistent with grazing and so PP is calculated for this type of supplementary feed.
The FRNL research did not find an effect on urine N concentration or partitioning from silage. As such, no PP is calculated for supplements containing plantain that are stored (silage). Further research is identified to test this current thinking.
Implementation into OverseerFM
To implement these findings in OverseerFM we have made the following changes.
Plantain is included as a pasture type on pastoral and cut and carry blocks.
If the user selects plantain, they must enter a percentage of the pasture that is plantain. They can enter any percentage between 5 and 100%. Anything above 60% is treated as if it is 60 for the effect on urine load and proportion.
Percentage of plantain in the diet (PP)
The model calculates the total dry matter eaten by animals for each enterprise and month. The dry matter from supplements is calculated first with the remainder coming from pasture. This dry matter (for each enterprise and month), is allocated out to blocks via the inter block model.
The model now records the amount of dry matter fed as plantain for supplements harvested from a plantain block and fed directly. It does this by multiplying the proportion of plantain for the block being harvested multiplied by the total dry matter of supplement.
The model rolls up all supplements to the enterprise level and so is calculated per enterprise and month.
The total proportion of plantain in the diet is calculated for each enterprise and month using:
PP = (DMSupplementsPlantain + DMPasturePlantain)/DMTotalFed
DMPasturePlantain is the DM from grazed pasture on the block multiplied by the plantain proportion of that pasture.
PP is limited to a maximum of 0.6 (60%) and so if it is calculated as grater then 0.6, 0.6 is used instead.
Proportion of urine
For each enterprise and month, the nutrient distribution model calculates the amount of nitrogen in excreta using the nutrient intake minus the nutrient loss in product.
This is proportioned into urine and dung using the following equation:
(11.9 * NutrientDietConcentration * 100 + 29.9)/100.0
NutrientDietConcentration is NutrientIntake/DMIntake
This is used to allocate N from excreta into N from urine and dung for each enterprise and month. This is then allocated to blocks based on consumption and area in the inter block model.
A change has been made to the model, to allow it to calculate a different urine proportion for each block. This is now calculated based on the plantain proportion (for each enterprise, block and month) and applied in the inter block model.
The proportion of urine is now adjusted by 1-PP/3.
Urine patch N load
The N loading for a standard urine patch is 750 kg N/ha.
For animals eating plantain this is adjusted by using the proportion of plantain in the animals diet in the equation 750-(PP*500).