Organic vs Synthetic
Organic is all the rage. Understandably, organic growing techniques are beneficial. Personally, I'm a big proponent of organic produce. But the term "organic" casts a very wide net. It excludes the use of GMOs. It forbids many types of pesticides and herbicides, while encouraging safer more natural methods for disease and pest management. Most people like to avoid pesticide and herbicide exposure.
But "organic" also entails very strict guidelines when it comes to nutrient inputs. According to current standards, synthetic fertilizers are not compatible with organic growing. This puts the two approaches at odds. Looking specifically at fertilizers, it's important to understand the advantages of both organics AND synthetics. Some will call them "inorganic" fertilizers or even "chemical." In general, the word chemical carries a bad stigma, often being used to invoke an emotional response. So instead, let's call them synthetics.
- Pros & Cons: Synthetic vs Organic Fertilizer
- What Are Synthetic Fertilizers?
- Does Synthetic Fertilizer Harm the Soil?
- Is Synthetic Fertilizer Bad?
- Are There Benefits to Synthetic Fertilizers?
- Where Do Organic Fertilizers Come From?
- Is Organic Fertilizer Safe?
- Is Organic Fertilizer Better?
SYNTHETIC FERTILIZERS - are mostly or entirely man-made in origin. Despite what some alarmists might claim, synthetic fertilizer is not made from petroleum. Rather, depending on the macronutrient being synthesized, various chemical reactions are used to create inorganic compounds. For example: phosphate rock can be mined, then treated with acid to extract water-soluble phosphate salts. This results in a phosphate fertilizer that is more potent than an organic source. Similarly, potassium fertilizer is made from naturally occurring potash rock which is mined and processed.
Nitrogen-based fertilizers are produced differently, using the Haber–Bosch process. This is done by combining atmospheric nitrogen(N2) with hydrogen (H2) to produce ammonia (NH3). That ammonia can then be converted into other products like urea, ammonium nitrate (AN) or area ammonium nitrate (UAN). The process is energy intensive and involves the use of natural gas.
There is a flawed generalization that synthetic fertilizer harms soil biology. In some very specific instances, this can be true. For example, commercial farmers may inject anhydrous ammonia directly into the soil. This causes a cascade of reactions as the nitrogen converts into the stable form of ammonium. In this process, microorganisms and plant roots or seedlings can be damaged. Such fertilizer applications are not what consumers and home gardeners think of when they consider using synthetic nutrients.
The most common synthetic fertilizer amendments for consumers come in the form of time release pellets or water soluble liquid feeds. These are not the same as injecting toxic ammonia gas (a compound which is corrosive to tissues). Common consumer-grade synthetic fertilizers release their nutrients into the soil when dissolved in water. These nutrients are immediately ready for plant absorption as various ions. The nitrate (NO3-), ammonium (NH4+), phosphate (P2O5) or potassium (K+) ions are chemically identical to the ones produced from organic sources.
These compounds are not lethal to bacteria or other micro-organisms. This has been well studied and scientifically demonstrated. Compared to a control soil, adding synthetic nutrients does not decrease bacterial or fungal populations. In fact, researchers observed an increase in soil biology compared with untreated soil. This should come as no surprise considering the fact that microorganisms require fertilizer ions to survive. That's why compost piles won't heat up if they are deprived of nitrogen. You can actually add synthetic nitrogen to a high carbon cold compost pile and it will heat up as microbial activity increases!
Although there is plenty of variability in composition, consumer grade synthetic fertilizers do not contain toxic levels of harmful chemicals or heavy metals. They will not directly kill soil biology. Compared to organic fertilizers, they build less microbial biomass carbon and can result in lower organic carbon content. But when applied properly, they won't kill your soil, harm your plants or make your food unsafe to eat.
Some critics claim that synthetic fertilizers only contain macronutrients (NPK) and that they do nothing to address the micronutrient needs of plants. This is not necessarily true. It's easy to find synthetic fertilizers that also contain micronutrients. Each product should be examined on a case-be-case basis.
That being said, synthetic fertilizers do have their drawbacks. The creation of nitrogen fertilizers is energy intensive. The production of synthetic fertilizers has had negative environmental impacts. The Piney Point phosphate fertilizer plant disaster is a grim example. In 2021 a reservoir on the property leaked 215 million gallons of polluted water into Tampa Bay, threatening groundwater, soil and municipal water supplies.
Synthetic fertilizers are not bad for your garden. They won't turn your land into a sterile toxic waste dump. But the manufacturing of them has had negative consequences. And the over application of fertilizers at the commercial scale has damaged air and downstream water quality. Aquatic wildlife has been devastated by large "dead zones" in water bodies caused by runoff.
So yes, an argument can be made that synthetic fertilizers are "bad." They are bad when poor management practices are used. But when used judiciously, they offer benefits as well.
Synthetic fertilizers often require less volume by weight during application. The upfront costs for the fertilizer may be less than an organic alternative. Soluble liquid fertilizers provide a quick release of nutrients to plants that are showing signs of malnutrition. Granular or pelletized fertilizers may have a special time release coating that supplies a low, constant supply of nutrients over a long period of months. A very popular application of synthetic nutrients is through the use of hydroponic growing systems.
Video: Synthetic Hydroponic Nutrients vs
Organic Worm Casting Nutrients
Using synthetics allows for the replenishment of a single macronutrient if soil tests reveal a deficiency. For example, a soil might be high in phosphorus and potassium while being deficient in nitrogen. Synthetic formulations can be selected that target nitrogen specifically.
A big benefit of synthetic fertilizers is that they work. They can be applied consistently to achieve predictable results. In a healthy growing environment, properly balanced synthetic nutrients will nurture strong, vigorous plants. Rather than appearing sickly or diseased, well nourished healthy plants are able to fight off pathogens and resist many pests.
A first time gardener may find initial success using synthetics. This is good! With success, comes a continued desire to garden and to learn more. However, sole reliance on synthetics does not allow a gardener to experience any measure of self-sufficiency. For long-term sustainability, many gardeners choose to incorporate organic composts for both structure as well as nutrition.
ORGANIC FERTILIZERS - are derived from natural sources such as minerals, animals or plant by-products. Through the decomposition or breakdown of organic matter, nutrients are released for plant consumption. Microbes, including beneficial bacteria and fungi are a vital part of this system. This is because the nutrients that are tied up in organic matter are not immediately available for uptake. The decomposition or mineralization process is what reduces organic compounds to their inorganic forms. These ions are then transported in water to the root systems and thus absorbed by the plant.
This process could be likened to the extraction of a refined metal from a metal ore. It takes 2 tons of iron ore to make 1 ton of pig iron. Similarly, organic fertilizers are much like that unrefined ore. They still need to be processed. That's why a larger volume of fertilizer may be needed to reach NPK values that rival synthetics.
Organic fertilizers sold to consumers are tested for various contaminants and can be considered safe for use in the garden. However, the general practice of using organic amendments will not free a gardener of contamination concerns. Just because a nutrient input is considered organic, that doesn't make it free of pollutants like heavy metals or pesticide residues. In one study, researchers reduced the application of synthetic fertilizers on a field and replaced it with organic amendments. After 10 seasons had elapsed, they found that organic fertilizer introduced higher levels of cadmium and chromium than synthetic nutrients.
Chicken manures are popular additives in organic fertilizer blends. But if the chicken feedstock was contaminated with metals like arsenic, then it passes into the manure. Naturally occurring mineral deposits like rock phosphate could also contain high concentrations of cadmium or arsenic. Even the very basic process of composting is not without risks. If the source organic materials used in the compost contain heavy metals, then those metals can become hyper concentrated as the end product reduces in volume. Pesticides and herbicides can also accumulate in compost, if it was made from contaminated plants or manures.
This does not mean organic fertilizers are inherently bad or unsafe. It merely underscores the fact that this is a nuanced issue. Just as synthetic fertilizers can pose serious risks to humans and the environment, poorly managed organic practices can be detrimental as well. Factors that are concerning to commercial farmers, might not apply to a home gardener. If you only compost plant materials that originated on your site, then you can ensure that they are free of pesticide or herbicide residues. If you select organic fertilizers that have been tested for heavy metals, then you can safely use them without needing to worrying.
Utilizing organic fertilizers can be very beneficial in the long-term. The incorporation of organic matter into soils can improve texture as well as water retention. Using organic fertilizers can be a simple process if you're willing to buy a pre-blended, balanced commercial supplement. Or for the adventurous, you could acquire base components and blend them yourself. I've done that in the past, making custom blends from rock phosphate, green sand, kelp meal, alfalfa meal, blood meal, bone meal, etc. But these days I'm completely satisfied with all purpose organic fertilizer blends from companies like Jobe's or Espoma.
Having said that, I'm not very impressed with most organic liquid feeds. Things like liquid seaweed meal or fish emulsion smell pretty bad. They are overpriced, while offering very little in the way of macronutrients. In this regard, I was say a synthetic water soluble like Miracle-Gro Plant Food is vastly superior. It's an exceptional value. Lab testing has shown it to be extremely low in heavy metals. And it is very effective, especially on late season plants that show signs of nitrogen deficiency.
Some gardeners will turn their noses up at a synthetic fertilizer, making baseless generalizations designed to scare people. But both types of nutrient sources can be potentially harmful if poorly sourced or improperly applied. When it comes right down to it, there's no reason why a gardener can't use both synthetic AND organic. The one won't nullify the other. The best fertilizer is the one that you've taken time to research and to apply properly.