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Aquaponic Nitrogen Calculator – What is it?

The primary concern we have in these integrated systems is the retention and management of the nitrogen inputs. Nitrogen is the simplest measure however it is also very expensive when using fish feed as your Nitrogen source compared with other synthetic and organic sources.   So in aquaponic systems we have to manage it as a precious resource and be sure our designs make the best use of it.  This calculator is part of that solution. The above image gives you a basic outline of the path nitrogen takes in an aquaponic system.  The changes in oxygen in the system is the most critical point of optimum use.  You will note in a low oxygen environment, even at a microscopic level such as the layers of bacteria, the loss of nitrogen is great.  Keeping the system clean and oxygen rich is the key to maintaining optimum use of nitrogen in the system and preventing, as much as possible the nitrogen gas losses. Failure to make the best use of our farm inputs, see our cost of production increase through losses or wastes of these fertilizer inputs.  This is no different to any other agriculture farm.  Agriculture generally employ an agronomist to help make decisions on the farm about their fertilizer inputs to increase the soil productivity and increase the nutritional value of the crops grown. Agriculture has to use caution with their fertilizer applications to avoid under and over use and miss use of fertilizer programs to get the best out of their soil and their crops.  Integrated systems are no different, especially when you are competing in the same market.  If your inputs are higher, it will be reflected in your cost of production and obviously either your sales margins will be lower, or your price higher than your competitors. It is a key part  of the designers role to act like an agronomist and advise on the best system design to get the most control and use of fertilizer programs on your farm in your particular climatic conditions.  There is no “ad hoc” approach to this and at the same time there is no one size fits all.   Some may think there is not enough data out there to make these determinations, however there is a substantial amount of information you can use from horticulture, specifically hydroponic that will get you remarkably close to the positive outcomes you need. This information is no different for aquaculture.  If you are using a low quality feed, extremely low numbers of fish, poor system design and management, your cost of unit production will be higher than those around you and you will be forced to try and slash a new market path while the competition is selling their fish profitably.  If your fish system is not making you money, there is no justifiable argument to consider aquaponics.  This is why we design systems to achieve the maximum output for the investment and it must be sustainable both financially and ecologically. Sidebar on Aquaponics Feed Input: There are a few basic feed application formulas out that make it a very simple task to calculate how much plants to support the feed input and visa versa.  Some of these are below: 60 grams of feed per square meter of plants (Rackocy) 13 grams of feed per square meter of plants (Lennard) There is some criteria around these numbers that lacks crispness.  They both run at 25 plants per square meter and one runs a protein feed level of 32% the other has not been clear on the protein percentage in the feed.  However, we can assume the comparison was made using the same input parameters. As you can see above the difference between the two is significant and can be a little confusing.  Which one should you use?  Both of these comparisons are very different system designs.  One does single loop inline nitrogen control and the other (latter) does separate offline mineralization. You can use either one of these quite simply by determining the amount of square meters of plants (and their density) and calculate the amount of feed you need (adjusting for protein percentage).  However this is a bit like throwing darts at a board blindfolded. An example: You have 1000 m2 of plant growth at 25 plants per square meter (assuming lettuce or a similarily light nitrogen feeder).  Just multiply one of the two (13 or 60grams) by the square meters.  1000 x 13 grams = 13kg or 1000 x 60 grams = 60 kg of feed per day.  A vast difference indeed that will see one with an increase in production costs compared to the other by a factor of 4.6!.  Looks easy and it does work sometimes.  However it lack crispness in application because of the vast differences in system design. This is the second release of the aquaponic nitrogen calculator has been developed to assist the small grower and home grower to estimate their nitrogen use through their systems.  It is not suitable for detailed large commercial systems simply because there  is a great deal of variation in the design process from different consultants which have various preferences for system design.  However, will work within reason for a boutique farm, but we are not able to offer any guarantee.  We know it works for us in our designs but it does not mean it will work for everyones designs. The Aquaponic Nitrogen Calculator estimates the losses and uses of the nitrogen you put into your system through all of the interesting processes to eventually indicate the amount of plants you can grow from the fish wastes.  Later in this series we will reverse the process so those wanting to set up a farm from the plant side can estimate the amount of fish required.  We covered the basics of that method in this post. The numbers and calculations within the calculator are very loose or soft. Meaning, there are quite a number of variables and external changes, such as climate and fish species and health that will affect the end result. However, it is a good estimation tool for basic design parameters and production capacity based on available date and research conducted on a commercial aquaponics farm by the author. It is important to recognize any changes to a system design, will affect the end result. This is something the author cannot account for in the formula. For example, you may have a small system using a blue drum with aeration as your mineralization or you could be using just a media filled grow bed for all of the filtration processes. These smaller systems will present much higher nitrogen losses than system with independent process equipment. The purpose of this calculator is the guide you in design decisions on your farm.  It will also show you where their may be improvements in your fertilizer use.  Understanding when we talk about fertilizer we are talking about the fish feed inputs.   Removing as many points of denitrification is a good start.  Some of the process consumption can not be avoided, but most (not all) degassing of nitrogen can be. It will help you understand some of the impacts on the path the nitrogen input (protein in fish feed) takes through the system.  This is not the “be-all-and-end-all” but it is a great start for the budding designer. In our next article we will start by taking a broad look at the feed inputs to the fish farm. Some of this we covered last week however this will be the quick calculations to determine the nitrogen input and its value before another other processes start….

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