Is Bat Guano a Sustainable & Environmentally Friendly Fertilizer?

Many of us who choose to grow organically do so, at least in part, because we want to grow in a way that is sustainable and more environmentally friendly. But just because a product is certified organic, doesn’t mean its use is sustainable or good for the environment. One such product I would personally not use is bat guano. Today I’ll talk about why. What is bat guano? It is simply bat droppings that have accumulated and decomposed over a very long period of time in bat caves. These aged droppings are then mined from the caves and used as fertilizer. Insect eating bats produce high nitrogen guano while bats that eat fruit produce guano that is high in phosphorus. Both types of guano are excellent fertilizers when used to address actual deficiencies. Bat guano also contains micronutrients and fresh guano contains beneficial microbes. Now let’s look at high phosphorus bat guano, which is produced by fruit eating bats. Organic gardens that are amended annually with compost probably won’t have a phosphorus deficiency, so I wouldn’t use a high phosphorus fertilizer, unless a soil test showed an actual deficiency. Adding more phosphorus than needed won’t stimulate blooms or produce sweeter fruit, but it can contribute to water pollution, inhibit mycorrhizal associations, and create nutrient deficiencies by preventing plants from absorbing other nutrients. So, unless there is a known phosphorus deficiency, it is a good idea to avoid fertilizers with a high “P” value in the “NPK” ratio. Even when there is a deficiency, there are alternatives that are more sustainable and environmentally friendly than bat guano. High nitrogen bat guano produced by insect eating bats, on the other hand, is more likely to be useful in an organic garden. This is because nitrogen moves through the soil more quickly than phosphorus, so there is more likely to be a nitrogen deficiency than a phosphorus deficiency. Even so, I wouldn’t use bat guano because there are alternatives that are more sustainable and better for the environment. I’ll elaborate more on this point later. Bat guano is also sought after because of its micronutrients and beneficial microbes. However, nutrients and beneficial microbes are available everywhere, and there is no reason to go to exotic locations like bat caves to find them. I’m also very skeptical that these products have anywhere near the diversity of beneficial microbes that you can find in good homemade compost. Why? Because there is a very good chance that the microbes in bat guano are dead on arrival when they reach your door. Think of it this way; how likely is it that microves that have evolved to thrive in a cave would survive the extreme and foreign conditions encountered in processing, packaging, shipping, and storage? Temperature extremes alone could kill them. If you want to add nutrients and beneficial microbes to your soil, it’s hard to beat homemade compost. No let’s consider the sustainability of bat guano. Bat droppings become bat guano after accumulating, decomposing, and aging in bat caves over a long period of time – sometimes decades, sometimes centuries. Guano beetles and microbes play an important role in this transformation. This very long aging process is often featured in bat guano marketing. In fact, some companies boast that their guano comes from ancient bat guano deposits. The downside of this very long process is that bat guano is not a rapidly renewable resource. As a result, if it is harvested for worldwide widespread use, it clearly is not sustainable. Harvesting bat guano also has a negative impact on the environment. Fragile ecosystems have developed inside bat caves that are entirely dependent on guano as the main energy input from the outside world. Many unique species have evolved in bat caves and and depend on guano as a food source. And some of these species exist only in specific caves. Harvesting guano threatens these fragile ecosystems and species. But the greatest damage caused by harvesting guano is to the bat colonies themselves. Bats are highly vulnerable to regular disturbances, which can disrupt feeding, roosting, and reproduction and lead to starvation, loss of pups, abandonment of caves, and even loss of bat species. Research in Jamaica has found that mining bat guano is the greatest threat to bat caves on the island and directly responsible for the loss of bat species and other organisms dependent on fragile bat cave ecosystems. This discussion is not complete without talking about the important role bats play in the environment. In addition to supporting bat cave ecosystems, it is estimated that bats provide billions of dollars in ecosystem services, including seed dispersal, pollination, and insect control. Their role in insect control is vital to human and animal health and to agriculture. They reduce populations of insects that spread disease and pests that damage agricultural crops. Given pressures already faced by bat populations, including white nose syndrome, which killed 5.7 million bats in North America in 2012 alone, I personally would not recommend a product that potentially further puts bats at risk. While bat guano is a very good fertilizer, there are other alternatives that are more sustainable and better for the environment. And there is no reason to go to exotic locations like bat caves in search of beneficial microbes and nutrients. Though our soil currently has nutrient surpluses, if a soil test showed deficiencies, I’d first turn to nitrogen fixing cover crops and compost and mulch from free local resources. If further fertilzation was required, I would turn to sustainable organic fertilizers like alfalfa meal, cottonseed meal, soybean meal, and livestock manures. I would do my best to avoid mined products, and I would definitely avoid bat guano. So, just because a product is certified organic does not mean its use is sustainable or good for the environment. In the future, I hope to take a closer look at more organic products that I would avoid for these reasons. As I’ve said before, nitrogen fixing cover crops and compost and mulch from free local resources are a great way to start building your soil, and over time you might discover that you do not need anything else. Well, that’s all for now. Thank you very much for watching, and until next time remember you can change the world one yard at a time.

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