Can Urea Be Used As A Fertilizer?

Last updated on October 23rd, 2023 at 08:59 pm

Urea is known mainly from cosmetics as an ingredient in creams, but also from agriculture and horticulture.

But can you use urea as fertilizer?

Here I explain whether and if so, how you can use urea fertilizer.

Urea can be easily used in the garden as a nitrogen fertilizer. Urea fertilizer contains 46% pure nitrogen and thus in the long term mainly ensures better plant growth and yield and photosynthesis (leaf greening).

What is urea fertilizer?

Urea fertilizer is a slow-release nitrogen fertilizer that has a nitrogen content of 46%, so it can be used to fertilize fruits, vegetables, lawns or other plants with high nitrogen needs.

The nitrogen contained in urea fertilizer* contributes to plant growth, promotes yield and stimulates metabolism and leaf greening of plants.

Compared to other nitrogen fertilizers, urea fertilizer usually contains more total nitrogen and is therefore much more concentrated.

When used properly, urea fertilizer can be more effective than other nitrogen fertilizers, but the higher nitrogen content also means there is a much greater risk of overfertilization.

Since urea fertilizer is a pure nitrogen fertilizer, it does not contain other nutrients, such as potassium or phosphorus, which are contained in complete fertilizers.

Urea is also known as urea and, in addition to its use in fertilizers, is also processed into other industrial products such as cosmetics or animal feed.

In addition, urea is also used in AdBlue*, the agent used for diesel exhaust gas aftertreatment for cars.

More precisely, AdBlue contains 32.5% pure urea in addition to water and can therefore also be used for fertilizing the garden.

If you want to learn more about this, that is, how to fertilize with AdBlue, check it out right here.

Can you fertilize with urea?

Urea can be used for fertilizing in professional agriculture as well as in home gardens. When used properly, urea guarantees rapid nitrogen availability yet long-term fertilizing effects.

Urea can be used in different forms for fertilizing. In general, urea is a purely natural, organic compound that occurs naturally (for example, in liquid form as part of urine) but can also be produced chemically as a crystalline solid.

With all kinds of urea (yes, theoretically also with urine) the garden can be fertilized. However, depending on the concentration, different amounts are needed to produce a sufficient fertilizing effect.

Urea fertilizer ingredients

Urea fertilizer consists of 46% nitrogen in the form of amide nitrogen and otherwise contains no other ingredients. Thus, urea fertilizer is a pure nitrogen fertilizer.

Amide nitrogen is in contrast to ammonium nitrogen or nitrate nitrogen not immediately available for plants and must first be decomposed in the soil through various conversion steps to finally be available as nitrate to the plants.

Urea fertilizer effect
Urea is a slow-release fertilizer (and available here, for example*) and consists of 46% pure nitrogen, which is why its main effect on plants is increased growth or yields, as well as increased photosynthesis and thus leaf greening.

Because of the increased photosynthesis, turfgrass, when fertilized with urea, normally forms a lush and dense green.

Urea works in a similar way to liquid manure, i.e. the nitrogen is converted to nitrate in various intermediate steps, which in turn is absorbed by the plants through the roots and used for metabolism or the build-up of protein. Due to this boosted metabolism, the plants grow or yields are increased.

How quickly does urea act as a fertilizer?

Depending on the soil temperature, urea* acts at different speeds: at a soil temperature of 20°C, urea acts within about a week after fertilizing, and at a soil temperature of 2-5°C, urea acts after about 6-7 weeks.

Soil temperature is one of the most important factors in the application and effect of urea.

At a soil temperature of about 20°C, the amide nitrogen in urea is converted to ammonium nitrogen within only 24 hours. Ammonium is already available to plants but will still be further converted to nitrate within about a week as part of the nitrification process.

If the soil temperature is sufficiently high (20°C), the nitrate will be available within about one week after the urea fertilization.

At a low soil temperature of about 2-5°C the metabolism of urea takes a little longer, because at low temperatures the particle movement and thus the reaction rate is lower.

More precisely, urea hydrolysis, i.e. the conversion of amide nitrogen to ammonium at 2°C, takes about 4 days. It then takes another 6 weeks at about 2-5°C to produce nitrate by nitrification.

Thus, after urea fertilization at soil temperatures of about 2-5°C, pure nitrate is available after 6-7 weeks.

Urea fertilizer application

To make the application of urea as a fertilizer* as efficient as possible, certain general conditions should be met:

Soil pH: when applying urea as fertilizer, the soil pH should not be greater than 7.5. Otherwise, urea should be incorporated into the soil after application to avoid nitrogen losses

Temperature: urea should be applied at a soil temperature of 20°C for effective application or metabolism, but the temperature should not exceed 25°C

Weather: urea is best applied under overcast skies and before rain, so ideally the urea will penetrate directly into the soil
Incorporate urea fertilizer
As of February 1, 2020, there is a new fertilizer ordinance that states urea fertilizer must be incorporated into the soil within four hours of fertilizing at the latest, so that nitrogen losses or ammonia emissions are avoided.

Although this fertilizer regulation applies primarily to agriculture, it should also be applied to home gardening. This is because nitrogen losses can occur especially when the soil pH is above 6.5 or when the soil is alkaline, temperatures are above 25°C and there is drought and wind.

Urea should be incorporated as even when applied in your own garden immediately after application, because the first conversion form of urea – gaseous ammonia – is highly susceptible to loss.

So, although you should always make sure that the weather and conditions are optimal when applying urea, urea should be lightly worked into the soil directly after fertilizing with a rake or rake.

If this is not possible, for example when fertilizing lawns, you should moisten the soil with a watering can after applying urea fertilizer.

Urea fertilizer dosage

In the home garden, you should not use more than 5-10 grams of urea per square meter for fertilizing. 1 kg of pure urea fertilizer* is thus sufficient to fertilize approximately 100-200 m² of area.

The lower range of urea, i.e. 5 grams per square meter, should be used especially when fertilizing with urea for the first time or by gardeners who have little experience with pure nitrogen fertilizers.

The upper range, i.e. 10 grams of urea per square meter, can also be used during the first fertilizing of the vegetation phase, provided that experience has already been gained with pure nitrogen fertilizers or, more specifically, urea.

The following table shows the dose of urea that can be used for different garden sizes or areas:

When to fertilize with urea?

Normally, urea* is fertilized in spring, either at the beginning of the growing season between February and May or at sowing. Especially high-yielding vegetables, such as potatoes, tomatoes or cabbage, can be re-fertilized one or more times during the growing season.

Re-fertilization with urea can take place one or more times during the growing season, i.e. between March and October.

Especially lawns or vegetables with a high nutrient requirement, such as tomatoes, potatoes or cabbage, but also fruits can be fertilized with urea several times.

If fertilizing is done not only once but also during the year, it is recommended to use only the lower range of urea for fertilizing.

Urea as a fertilizer for tomatoes

Urea as a pure nitrogen fertilizer is very suitable for fertilizing tomatoes, as they are heavy growers and therefore have a high nutrient or nitrogen requirement.

To fertilize tomatoes with urea, you should follow the generally applicable dosage of urea, that is, spend between 5-10 grams per square meter. So, for example, if there are on average 2 tomato plants per square meter, then they can be fertilized with 5-10 grams of urea.

Urea as a fertilizer for vegetables

Urea fertilizer* is generally suitable for all vegetables, which can be fertilized both at sowing and once or several times during the growing season.

In particular, heavy growers such as potatoes, cabbage, broccoli, tomatoes, carrots or peppers can be fertilized with urea fertilizer several times a year.

If vegetables are to be fertilized with urea several times a year, however, it is recommended that fertilizer be applied more frequently but a little less each time. When fertilizing with urea several times, each fertilization should contain only about 5-7 grams of urea per m².

Is urea good for the lawn?

Urea is an excellent fertilizer for lawns, because urea fertilizer* contributes to vigorous growth of lawns and strong photosynthesis due to its high nitrogen content.

Fertilizing with urea can thus lead to strong, dense growth and lush, green colors in lawns in particular.

Especially when lawns have been heavily used or dethatched, urea is an inexpensive substitute for special lawn fertilizers.

Urea fertilizer ban?

Since February 1, 2020, a new fertilizer ordinance has been in effect in with the goal of reducing ammonia emissions. However, this regulation does not include a urea fertilizer ban, but states that urea must be incorporated into the soil within four hours of fertilizing to minimize ammonia losses.

If the fertilizer cannot be incorporated due to frozen soil, for example, a urease inhibitor must be used along with the urea fertilizer.

This urease inhibitor ensures that the urea (Latin name: urea) is converted into ammonia two to three weeks slower and thus has more time to penetrate deeper soil layers.

There is therefore no ban on urea fertilizers, but there are more restrictions on the use of urea in agriculture.

Although hobby gardeners:inside use far less urea in the home garden, they too should follow the regulations and lightly work urea directly into the soil after fertilizing is best.

Since home gardening involves much smaller areas than farming, this should not be a problem.