Is it okay to grow root vegetables in soil enriched by manure?

Question

I have a few raised beds where I grow vegetables every year (organically). Vegetables I grow include root vegetables (carrots, beets), leafy (kale, lettuce), tomatoes, zucchini, cucumber, etc. Every year I enrich the soil by mixing in some steer manure and chicken feed that I get from my local big box store. Then as the plant starts growing and bearing vegetables, I will add some organic fertilizer (Jobes).

I recently read on one of these posts that root vegetables don't take manure enriched soil very well (not sure what that means). That prompted my question and more generically, does the method I am using sound reasonable for growing the types of vegetables I am growing?

Answer 1

There are two possible problems that could come from using manure on root vegetables, one of which only applies to fresh manure and the other is more applicable to fresh manure also.

The first, and the most obvious, is the potential for contamination. If you're putting the manure into the soil, the part of the vegetable you eat is growing in direct contact with potential manure-borne bacteria, like E-Coli. If those bacteria enter into the root they can make you very sick. But, if the manure has been composted properly those bacteria should be dead from composting heat.

The second complication comes down to how root vegetables grow. For root vegetables like carrots, radishes and beets you want one straight tap-root. If the root branches early it leads to a misshapen vegetable. If the manure has high enough nutrient density, the plant may fork, sending off feeder roots to the side to grab that manure nutrition. The result is an oddly shaped vegetable. Not exactly the end of the world, but it can sometimes make them harder to work with in the kitchen. For example, washing dirt out of all the odd creases a branched carrot has.

Answer 2

There is a big difference between manure from ruminants (e.g. cows) and non-ruminants (e.g. horses, chickens, etc).

Non-ruminant herbivores produce poo which is relatively bulky and contains a lot of undigested plant material. This material is degraded rather quickly by bacteria, but until that happens the manure is traditionally described as "hot", and indeed if it is stored in bulk it can become physically very hot because of the biological processes going on in it. In the 19th century horse manure was the standard way to grow tropical plants in "hot-beds" or "hot-houses" in temperate climates - just plant them into neat horse-manure that would easily heat up to 50 degrees C or more.

Using it in that state is not a good idea for root veg, because it may cause cosmetic surface damage to the roots. Also it is releasing a big rush of easily absorbed nutrients which can cause distorted growth (e.g. forked roots), or induce the plant to flower (bolt), set seed, and die while there is a lot of food available for its seeds to germinate, instead of slowly storing up food reserves in its roots which is what you want it to do.

Manure from ruminants has already been "reprocessed" several times before it leaves the animal, and is therefore less bulky, often has a high water content until it has dried, and has a lower nutrient value - but it is still useful as a soil conditioner.

Aside from any issues with pathogens, you can use cow manure for root veg pretty much "straight from the cow," but horse manure needs to be stored (which is effectively the same as composting it) until the bacteria have finished doing their thing with it, and it has (literally) cooled down. Most of the pathogens will have been killed by the heat.

Using "chicken feed" as manure seems a rather strange idea - unless you are letting some chickens process it first, of course!

Answer 3

For pathogen concerns, stock/standard advice often enshrined in regulations is "not less than 120 days before harvest." So if you are adding fresh steer poop (which you should not, in most cases) do so a minimum of 4 months before your planned harvest date.

As an instance where you might actually do this, consider the "compost in place" approach where you'd build a compost pile on the garden in the fall, possibly using fresh manure. By the time you are harvesting spring crops, more than 120 days has passed (in most climates that have a winter to speak of), all is good. If the manure has been composted for 120days or more, you can apply it whenever you like. If what you actually apply is "bagged composted steer manure" you have little if anything to worry about here.

The primary reason to "avoid heavily manured plots for root vegetables" is that some will react to abundant nitrogen by growing a lot of leaves, and not so much roots; branching/forking (as already mentioned by GardenerJ) is another possible negative side effect. This will apply whether or not the manure is composted, and for other, non-manure sources of nitrogen.

Answer 4

Root vegetables should be just as fine as any other root plant in my mind. They will take in those nutrients and everything like any other. I say they will be fine and that is that. Maybe they were talking about fresh manure, which would burn the plant/root.