Farm Economics - Part II: Hidden Costs of Synthetic Fertilizers


Water flushing reservoir hydroponic systems

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 Written by Riyana Razalee

This is Part II of a 3-part article series on the topic of farm economics for soilless (hydroponic) farms

In Part I of our farm economics series, we shared a high level analysis of the typical costs that can be expected from a hydroponic farm growing lettuce or tomatoes. We then showed that if these farms choose to grow organically, they can expect a profit margin of 60% and 66 – 82% for lettuce and tomatoes respectively in most markets. However, this assessment does not take into consideration other externalities involved at a hydroponic farm. In this article, we will explore why farms should consider shifting away from synthetic mineral salts as a nutrient source for plants.

Synthetic Mineral Salts & The Environment: Greenhouse Gas (GHG) Emissions

The fertilizer industry is currently dominated by synthetic mineral salts which have a significant adverse environmental impact. However, what does this mean for a farm in terms of GHG emissions and why does this matter?

Using a baseline technology of a widely-commercialized synthetic mineral fertilizer 4-18-38 for lettuce, a lifecycle analysis was carried out to measure its environmental impact. For the purpose of this article, this fertilizer will be referred to as “Fertilizer X”.  

Fertilizer X’s specification details the amount needed per “set”, where one set is sufficient for 19 liters of water and includes:

  • 10 grams of Fertilizer X
  • 10 grams Calcium Nitrate, Ca(NO3)2
  • 5 grams Magnesium Sulfate, MgSO4d

The results showed that GHG emissions from Fertilizer X, using 100 year global warming potential values (GWPs) (IPCC, 2013), ranged from 0.008  - 0.071 kg CO2e for every pound of produce grown using Fertilizer X. For commercial farms, this value can add up significantly and very quickly.

Customers care about these numbers now more than ever, demanding companies to step up and provide more sustainable solutions at every point of their production line. A Deloitte report confirms that the market for sustainable and health-focused products grew at an unprecedented rate, making up almost 50% total consumer products sales growth between 2013-2018, at a CAGR of 5.2%, 4x higher than conventional products. If farms honor their role in this move towards sustainable agriculture systems, they could also benefit from the estimated 2/3 of US consumers who are willing to pay a premium for sustainable brands. It’s also important to look forward and realize that as the world starts to move further towards enabling carbon cap-and-trade programs across various industries, it would be safe, if not wise, to say that at some point, farms may need to thoroughly assess every aspect of their production chain’s GHG emissions. Fertilizer usage will undoubtedly be a key area of focus.

Water Flushing: Wasting Resources and Money

A general rule of thumb when it comes to growing large plants with a hydroponic system, such as tomatoes, is that it needs approximately three gallons of water volume per plant. This of course decreases as the size of the plant gets smaller. However, an experienced hydroponic farmer also knows that more water is always better. For a large-scale farm, this leads to a significant cost in the form of water bills. But what is it exactly that makes the water bills especially high?

No hydroponic system is perfect and problems are bound to occur. However, a smart grower will look for ways to avoid these problems. Synthetic mineral salts are able to produce crops at a rate that is necessary for commercial farms to be able to get their product to market in a timely manner. Unfortunately, it comes at a price – the creation of unnecessary issues in a hydroponic system:

1. Flushing – This is a crucial step in hydroponic farms and must be done regularly. The entire contents of the nutrient tank needs to be flushed out in order to remove any chemical imbalances which develop over time that could potentially lead to plant stress. For commercial farms, this can be a very costly aspect of the production process – not just from a water flushing perspective, but also in terms of time, energy, and manpower.

2. Clogging – Debris from synthetic mineral salts is something that a farm needs to be cognizant of. Once again, this necessitates flushing of the reservoir.

3. Municipal Monitoring – For many municipalities, if the nitrate levels of water discharged from a hydroponic system exceeds a set limit, these farms are then susceptible to fines and additional costs. On average, hydroponic wastewater solutions contain highly concentrated nitrate (200 – 300 mg L − 1 ) and phosphorus (30 – 100 mg L − 1 ) levels.

While testing for Total Dissolved Solids (ppm) in the reservoir could help a farm monitor when the water needs to be flushed, it becomes close to impossible to measure the composition of the mixture after a few days or weeks. There is the option to hire third-party testing labs, but this will come at a cost. As such, the best choice for farms goes back to frequent flushing of the reservoir.

Now if we look at the numbers, typically a farm needs to top up its nutrient tank every 2-3 days, and to then eventually change the water in its entire reservoir every 2-3 weeks. This could cost up to thousands of dollars worth of unnecessary expenses which the farm could have used for other expenses. For example, in a 75-gallon reservoir, you may lose and replace about 15-25 gallons a week. Within five weeks, you would have replaced 75-125 gallons of water just through topping up. This number then increases when the entire reservoir is flushed out. Is there a better way?

Can Organic Hydroponic Nutrients Really Reduce Help?

Yes and no. Organic hydroponic nutrients on its own will undoubtedly reduce GHG emissions. However, will it completely solve the issue of water flushing and crop growth comparable to synthetic mineral fertilizers? No.

To complete this puzzle, technology is needed. Firstly, the nutrient mix of the organic hydroponic nutrient needs to be perfected. Secondly, and perhaps more importantly, a nutrient delivery system that allows farms to fully utilize the organic hydroponic nutrient in a way that optimizes its solubility, concentration, and minimizes a farm’s wastage of water is key. This is where Re-Nuble comes in. 

We will explore how Re-Nuble has cracked this code in Part III of this series. In the meantime, if your farm could potentially benefit from an organic hydroponic nutrient that will reduce the need for unnecessary resource wastage, speak to us here