Soil deficiencies with manure

1

I had a conversation recently with a person that had heard from a scientist that if you only use animal manure, your soil might develop some deficiencies over time.

That got me thinking. This could actually be true, especially with manure from grazing livestock (cows, sheep), as they eat mainly grasses, which are low in nutrients. It probably is less of a problem with browsers (goats, camels), as these rely on a more varied diet of bushes and trees.

So, any thoughts on how to prevent or remedy such soil deficiencies? My personal idea was to utilize the bat manure that gathers in our roofs. Bats are carnivores, and their manure is very nutrient-rich. The only drawback is that one needs to deal very cautiously with this manure, as it is filled with pathogens that are potentially harmful to people.

2

I don’t think the use of manure would create actual deficiencies in the soil. The nutrient content in manure is dependent on the kind of animal the manure is from and what that animal’s diet is, and the nutrition in the diet depends on the soil the feed is grown in. If you use manure from animals that only eat feed grown on your farm, you aren’t going to change the soil makeup much at all, except to add organic matter, which is always a good thing. Plants and animals can’t create minerals, they can only get them from the soil, and so whatever is in the manure is already present or lacking in the soil.

My guess is that what this person meant is that adding manure would create nutrient accessibility issues by way of lowering the pH. When the pH drops too far towards acidic (or the opposite, too alkaline), you start seeing nutrient deficiencies in plants. However, this would be following the common assumption that manure is very acidic. It isn’t. Manure, especially from ruminants, tends toward a neutral pH, slightly less that 7.0. This is because the animals’ bodies need to be between 6 and 7. They have ways of regulating their internal pH, and the pH of the manure correlates with that (urine is the body’s way of disposing of acid wastes). Animals raised on high-grain diets have slightly more acidic manure, as low as 5.5, but even then you would have to apply illogical amounts of manure to the soil to make any real alterations.

Fresh manure, obviously, will “burn” your plants, but this is due to high levels of ammonia in fresh manure that are too high for the plants to deal with, not due to general acidity. Composted manure should be a safe additive.

When it comes down to it, most soils have the necessary nutrients for growth, especially for plants adapted to that area. Making more nutrients available is very dependent on soil microorganism activity, organic matter, CEC, etc. That’s the hard part, especially in the tropics. Try to put in as much or more than what you are getting out; in that sense, using only manure, or only anything, is not as beneficial as using varied inputs. The more good stuff you can put back in your soil, the better off you will be.

If you can do it safely, I’m sure the bat manure would make a great soil additive!

3

I am no expert in manure by any means, but growing up in a Pennsylvania farming community that relies on it as a main source of fertility, I have never heard of problems with animal manure, except with chickens.

In one case, a farmer renting ground had used only chicken manure on a field for several years. Chicken manure is really high in nitrogen and also potassium (N and K). The result was that potassium accumulated in levels that were too high and affected the nutrient balance in the soil, which inhibited the growth of plants and took several years to resolve. So as Seth said, varied inputs are important:)

I would second your caution with bat manure- I have heard of many diseases associated with them, including lung conditions (histoplasmosis), just from breathing too much in.

4

Maybe he was talking about trying to maintain fertility for vegetable production by using only manure? Some vegetables are very nutrient-demanding…

Other than that, I totally agree with you all that biology is more important than chemistry when it comes to soil (except for some extreme cases like extreme accidity or severy lack of certain nutrients). We do composting, mulching, re-distributing manure, rain water harvesting etc. on our farm in Central Tanzania to work on this. Pretty much everything except EMO and Compost teas (Elaine Ingram stuff - too complicated to be a solution for small scale farmers, so we don’t do it either. And composting etc. does the same thing, just more slowly).

Someone replied to your post.





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Seth_Phillips



August 10

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I don’t think the use of manure would create actual deficiencies in the soil. The nutrient content in manure is dependent on the kind of animal the manure is from and what that animal’s diet is, and the nutrition in the diet depends on the soil the feed is grown in. If you use manure from animals that only eat feed grown on your farm, you aren’t going to change the soil makeup much at all, except to add organic matter, which is always a good thing. Plants and animals can’t create minerals, they can only get them from the soil, and so whatever is in the manure is already present or lacking in the soil.

My guess is that what this person meant is that adding manure would create nutrient accessibility issues by way of lowering the pH. When the pH drops too far towards acidic (or the opposite, too alkaline), you start seeing nutrient deficiencies in plants. However, this would be following the common assumption that manure is very acidic. It isn’t. Manure, especially from ruminants, tends toward a neutral pH, slightly less that 7.0. This is because the animals’ bodies need to be between 6 and 7. They have ways of regulating their internal pH, and the pH of the manure correlates with that (urine is the body’s way of disposing of acid wastes). Animals raised on high-grain diets have slightly more acidic manure, as low as 5.5, but even then you would have to apply illogical amounts of manure to the soil to make any real alterations.

Fresh manure, obviously, will “burn” your plants, but this is due to high levels of ammonia in fresh manure that are too high for the plants to deal with, not due to general acidity. Composted manure should be a safe additive.

When it comes down to it, most soils have the necessary nutrients for growth, especially for plants adapted to that area. Making more nutrients available is very dependent on soil microorganism activity, organic matter, CEC, etc. That’s the hard part, especially in the tropics. Try to put in as much or more than what you are getting out; in that sense, using only manure, or only anything, is not as beneficial as using varied inputs. The more good stuff you can put back in your soil, the better off you will be.

If you can do it safely, I’m sure the bat manure would make a great soil additive!

5

Good morning. Having some knowledge of farming and organic farming. I want to say soil deficiencies is normal not from the manure applied. You could have it test before applying it.

The Amish have built soil using manures and crop rotation. So they have done these practices for several hundred years. Seems to me it works.

Deficiencies have really showed up in the last 50 years or so. With herbicide use. And chemical fertilizer. In the teaching Farming God’s way. They teach building the soil. In a zone. Year after year. Yes compost is more stable then fresh manure.

I hope these thoughts help. Plant on, Kevin Fall

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6

That’s an interesting topic. It really depends on the animal source used and the load introduced to the soil. Take poultry manure, for example—it provides a small fraction of phosphorus, but the manure must be treated first. Two issues can arise: the displacement of elements due to pH instability, and salinity (since certain compounds can increase the load). It is a complex subject regarding the specific elements involved. You could use composting, but be careful there; I’ve observed that large volumes of organic matter can acidify the soil, turning a good practice into a critical mistake. Also, remember the most important factor: the soil type. Each type has different characteristics and, consequently, different problems. If a soil is already acidic, adding certain amendments could make it even more acidic. You have to look at the results across different soil types to establish a baseline. Bat guano can be a good option, but again, it depends on the soil type. Dr. Jose Gabriel from Northern Arizona University is an expert on bats—he’s a young man from Nicaragua who is approachable and always willing to help—so perhaps he could discuss which species provides the best contribution. Best regards!

7

Thanks for your reply.

I don’t think we can overdo it with compost/organic matter at our place. The average organic matter content here is between 0.3-0.6%

Soil is rather acidic, from 5.9-6.3. Any healthy compost (enough green matter) should be higher than that. But adding more alcalic stuff is not easy for small scale farmers, that’s why we don’t do it either (except for ashes, which everyone here has).

The only place where we might have problems (we don’t do soil testing for the same reason as adding stuff - most small scale farmer could never afford this) is our vegetable area, where we plant a lot of nutrient-demanding stuff which we then sell off. Most of our farm is different types of agroforestry systems.

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