0508 AGRIMAGIC (247 462 442) info@agrimagic.co.nz

Using more of OVERSEER’s horse power to plan for nutrient constraints

by | Feb 1, 2016 | News

Having access to a computer model like OVERSEER and then only using it to run one retrospective budget annually to spit out a number for compliance, well, it’s just a waste!

It’s like having one of these:


And only using it to pull one of these:



In a time when farmers must reduce nutrient loss, it is crazy that the emphasis has been on the use of OVERSEER nutrient budgets for compliance purposes. In fact, when used well, with the context and understanding of the farm resources, system and business, OVERSEER is a phenomenal tool to help highlight the aspects of the production system that can be altered to improve nutrient loss in a sustainable way for the farm business. It has so much more horsepower that most are even aware of.

This article hopes to highlight some things farmers (or those directing farm businesses) can consider when you are ready to use more of OVERSEER’s horse power to extract value beyond compliance.

Use OVERSEER to compare scenarios, not to just run one nutrient budget in isolation

At the very least if you are asked to provide a baseline nutrient budget (representing the seasons 2009-2013) then you should also run a current budget for the same farm and compare the results. An additional scenario that models future options provides the most powerful comparison. This allows you to really see which management options your farm or parts of your farm may be sensitive to.

Please note that each farm is a unique mix of resources, soil types, climate, topography, irrigation opportunity and of course management. I don’t know a person good enough to be able to consider how each of these aspects integrate with the dynamic soil processes to estimate nutrient loss accurately and to just know where you should prioritise your actions in detail– that is why the OVERSEER model is so good. Once I have run the model I can check the output for sensibility, but I have stopped trying to guess what the nutrient loss estimate might be in advance. Your situation is likely to be different to your neighbour. This issue absolutely requires a customised approach. We know that aspects such as improving irrigation water use efficiency and reducing drainage from soils will reduce nitrogen loss, this generalisation is useful but in a world of emerging rules you need to know where you get the biggest impact in the context of your own farm and plan your changes to match your other farm and business objectives. The next level of detail can be very insightful – and that insight can lead to more valuable decisions and timing of action.

It is imperative that you only compare OVERSEER outputs that have been calculated from the same version of the model. People get their knickers in a knot about the fact that “the number keeps changing” as the versions of OVERSEER change– take your focus off the number. To get value from this process it is the relative difference and the drivers of the difference that you need to understand. It would be simpler to interpret but far less effective if the versions didn’t update and the calculation didn’t improve – To use another Tractor analogy… if we got cranky because Tractor versions kept changing we would all still be farming with Red Spot Fordson Majors!! It’s progress and we need to let that part happen. Try not to let “the number” of your nitrogen loss estimate be your only focus.

Use many of the OVERSEER output reports

These reports help you make sure the budget actually reconciles and is accurate. They help the modeller know if the scenarios are realistic and which aspects of the system are the most sensitive to losses. The following are the ones I use the most

  1. The overall nutrient budget for the farm
  2. The individual block N loss reports (and P loss risk report)
  3. Estimated pasture production
  4. Other values (particularly to check the annual depth of irrigation OVERSEER estimated and the drainage)
  5. Effluent summary – reconcile the area and nutrient loading

Invest in the “Tool that drives the tool” (!!)

Use qualified people that understand you, the business of farming (cross-sector), the rules and planning process and who are also certified nutrient management advisors. If you can’t find those skills in one person or business then employ a team to work together for you. It’s just like driving machinery, the more of the horsepower you use, the more skill the driver should have, or they become dangerous!

Feel particularly alarmed when someone sends you a template to fill in to then processes your budget in an office with inexperienced “data input” people – NEVER use such a nutrient budget for compliance, strategy, due diligence or planning unless the inputs and outputs are also checked by someone who understands more about you, your farm business and the physical resources you are working with and is certified as a nutrient management advisor. It only costs a little bit more to get the job done properly. It is a complex business and could have a big impact on your future.

  • Recognise that we are going through a time of change and make sure you have a plan for your business for the future. This is not going away.
  • Understand that farming is a complex business and that “effects based policy” is a powerful opportunity for you to continue to innovate to manage your own nutrient reductions. If you don’t make plans to understand and manage this you may lose the privilege and be forced by input controls. I back NZ farmers to be better than that!
  • Learn what nutrient constraints might mean in the context of your farm business and then get stuck in to influence your future.

Once you know the aspects of your farm business that are more risky from a nutrient loss perspective you are far more valuable at contributing to industry and catchment level planning processes. Farmers are the best advocates for their own businesses but these issues have become complex, academic and detailed and allowed you to let others advocate on your behalf. Once you see nutrient constraints in the context of your own farm business you become a far more effective advocate.

Invest in more of OVERSEER’s horsepower to gain insight and help position your farming business to better manage nutrient constraints and protect our future.

By Charlotte Glass – AgriMagic

Featured in: ATS / Ruralco – Real Farmer
February/March 2016