Should You Lime and Manure at the Same Time?

I was asked about adding lime and manure to the soil by a newsletter reader, so I thought a detailed answer might be helpful for my readers.

In the traditional vegetable growing 3 year rotation, liming and manuring were basically undertaken once every three years and not in the same year. So there would always be a gap around a year between them.

In my book, Vegetable Growing Month by Month, I say this:

If you have ever had a pee (slightly acid) into a toilet with bleach (very alkaline) in it, you will have noticed there is an unpleasant reaction, Just the same if you mix your lime and fertilizer. They will at best cancel each other out in an unpleasant, to the soil, reaction. So never lime at the same time you fertilize.

This article goes into more detail.

Nitrogen Loss

Manure, especially fresh manure, contains a high level of ammonium nitrogen (NH4+). This has that distinctive ammonia smell. It’s a product of bacterial action on urea formed from the kidneys excreting excess protein, which is contained in urine.

Applying lime and manure at the same time will raise the soil pH, making it more alkaline, which causes the NH4 to become NH3, ammonia gas. This escapes into the air, so the nitrogen is lost from the manure and soil.

Applying both together on the surface, the high pH from lime can cause ammonia loss within hours.

Microbial Balance and Action

Lime temporarily changes the soil’s microbial environment. Normally this is effect calms down over a short period as rain mixes the lime down through the soil.

When manure is applied at the same time as the lime, the increased pH disrupts the microbial action and normal decomposition. This reduces the plant available nutrients from the manure.

How to Break the Rotation Rule

I’m a great believer in crop rotation, a system developed by trial and error over many years and codified by horticulturalists whose livelihood depended on getting it right. But there are times when rules have to be bent or broken.

Moving my brassica cage is a difficult and time-consuming task, so one of the instances of my breaking the rotation rule.

NB – if I had a build up of soil-borne disease, especially clubroot, then I’d have to revert to moving the cage to rotate down the severity of the problem.

To keep the cage in situ, I amend the soil pH by liming and increase the nutrient levels by adding manure or compost. Incidentally, I could just use Nitro-chalk fertiliser but this has become very hard to find and expensive for gardeners. Apparently it can be used to make an explosive, so a lot of retailers have just stopped stocking it. The regulations came into effect in 2023.

Regardless, I prefer using manure as it is a complex of macro and micro nutrients along with microbes enabling conversion to plant usable nutrients in one package.

How to Lime and Manure in the Same Season

It’s possible to lime and manure in the same season, so if you want to both increase the nutrients in the soil whilst amending the pH with lime, it is possible. Not ideal, but gardening is often about compromise rather than slavish adherence to the rules.

The way to do it is to first apply the lime. Rake it into the top of the soil. If it’s a dry period, water to wash the lime down into the soil and improve contact between the lime particles and soil particles.

Leave things for as long as you can, ideally for a number of months, but practically four weeks will be long enough for the soil fauna to settle down and stabilise. Even two weeks will make a significant difference.

If you have months to play with, then feel free to manure in late autumn and lime in late winter. This enables you to check the manured soil’s pH and, therefore, lime required to achieve the desired final pH level.