We haven’t been on the orchard for a long time. It is about time that we are in March and it is an intense month in the gardens and orchards. Today we are going to talk about manure, specifically horse manure. It is a manure that must be mixed, it is not perfect but it is very good and properly mixed and composted, it can be a fertilizer element for the garden and garden of high quality . Let’s see what can and cannot be done with horse manure.
COMPOSITION OF HORSE MANURE
Manure depends fundamentally on the type of metabolism of the animal and secondly on the type of feeding. In general, herbivores generate a large amount of manure and the horse is one of them. Each animal can generate around 8-9 tons of manure each year . Having a horse is a guarantee of manure to compost all year round.
It is considered a good manure, balanced , somewhat lax in some nutrients. However, it is a manure with a high dry fraction, more than cow manure but less than sheep and goat manure. It has a little nitrogen shortage although the relationship with carbon is not bad. Others such as sheep are more aggressive, stronger due to the nitrogen content and considered better. Still, it is considered good manure.
Here is a detailed analysis of a horse manure analysis. As we can see, the C / N ratio is fine, around 20. This analysis has been extracted from Germán Tortosa’s website at compostandociencia.com . It’s worth taking a look at the general composting topics on their website.
Note: Data expressed on dry matter, pH and EC in a 1:10 aqueous extract, nd: not detected.
All these amounts have to be taken with a grain of salt because the absolute amount of nutrients is not the same as the amount of nutrients available . Potassium, phosphorus, and even nitrogen are found in chemical forms not available to the plant . This availability is achieved over time. So the question we ask ourselves now is:
CAN HORSE MANURE BE APPLIED DIRECTLY TO CROPS?
Absolutely not. Neither that of a horse nor that of any other. Manure comes with very unstable biochemical conditions that do not benefit from entering the crop, including ammonia nitrogen. In fact, it can burn the roots due to fermentation processes that can increase the temperature of the soil, damaging and even burning the roots. Remember that in the maturation and composting processes, temperatures can easily reach 60-75ºC.
You need what is called a maturation or stabilization process . This stabilization can be considered a form of composting , although the latter practice requires other factors and other elements in the mix. If it is only 100% manure without any other matter, it is not usually considered composting, but a simple stabilization. They share transformation processes such as fermentation but it is not the same.
The other unpleasant point of not letting it stabilize is the strong, unpleasant smell of fresh manure . You have to compost it.
If you want to know more about how to compost, consult the compost section of Gardenprue.
HAVING MADE THIS POINT CLEAR, HOW DO WE STABILIZE HORSE MANURE?
It can be added to the usual compost and it works very well, it can be mixed with grass cut from the garden for example or with green remains . We could even mix it with so-called green manures to achieve very good stabilization and balances. There are numerous practices and studies that evaluate the suitability of manure stabilization with different materials. In a 2019 study (references at the end of the article) the stabilization of horse manure mixed with rice husk was evaluatedand the horse’s own urine. At the end of 16 weeks, different parameters observed during that time led to the conclusion that it was a good way to stabilize the manure. The change in the C / N ratio is mainly attributed to the microorganisms adhering to the rice husk, which are the ones that acted by fixing the nitrogen.
If the manure is to be applied directly to the cultivation land, it is advisable to allow between 1 and 4 months to pass until the crop is planted to allow time for it to mature and stabilize together with the soil. And if it is a little longer, better for the nitrogen to mineralize.
THE PROBLEM OF LEACHATE SEEPAGE WITH N: CONTAMINATION OF AQUIFERS AND RUNOFF.
This problem is not just horse manure. It is a problem of management of all livestock waste and fertilizers from agriculture that can generate many problems and its use and application must be controlled. In fact there are limits established in Spain for the application of fertilizers precisely for this reason that come from a European directive. A maximum of 170kg / ha of Nitrogen is allowed to avoid groundwater and surface water contamination problems.
A large amount of nitrogen in the water causes the excessive growth of algae and microorganisms, a process known as eutrophication . This imbalance causes a decrease in oxygen in the water, unbalancing entire ecosystems and killing fauna and flora. Analytical parameters such as BOD5 (biological oxygen demand) or COD (chemical oxygen demand). show the state of eutrophication.
In addition, the nitrogen in the aquifers of the waters that we later drink also has a limit established by a public health issue. We will not go into detail, but surely nitrites and nitrates sound like potentially carcinogenic elements when they are transformed into nitrosamines by the flora of our digestive tract. An underground water with more than 50mg / l of NO3-, is considered contaminated and not suitable for consumption.
THE CHEMICAL FORM OF NITROGEN
Alluding to the previously exposed composition, we see that the total nitrogen content is 15.3 g / kg of manure. This is 1.5% . Roughly speaking , we could dump up to 11 tons of fresh manure per hectare per year on the ground. (170 /0.015 = 11.333 kg)
Although it seems little, we have to differentiate between compost from horse manure and fresh manure. It is not the same in terms of the amount of nitrogen and especially its chemical form:
- The mineral nitrogen is the only assimilable by plants. the fraction of mineral nitrogen in manure is low. Almost everything is in organic forms.
- The organic nitrogen . This can be divided into mineralizable in the short term (1 year) and mineralizable in the medium long term (more than one year) or non-mineralizable.
Mineralization rates are slow, and therefore we cannot set the above calculations based on fresh manure analysis as a limit for composted manure application. The nitrogen present in composted manure remains fundamentally organic and its mineralization will be gradual for years.
In fact, in many crops (fruit trees for example) the amounts of fresh manure in relation to the nitrogen that is contributed would be insufficient as an amendment. In composted manure fertilizers the amounts are higher, doubling the doses per hectare. It must be taken into account that the assimilable nitrogen for the plant from horse manure does not exceed 50% during the first year. That is, of the initial calculation of nitrogen discharged to the soil, the plant will only be able to take advantage of half or less during the first year.
On the other hand, the calculation of agronomic dose is an important point to avoid excesses. There are other sources of nitrogen that also affect the global balance such as:
- Mineralizable nitrogen already present in the soil in the form of humus.
- Mineral nitrogen already available. It is therefore necessary to do a soil analysis.
- Nitrogen present in irrigation water. An analysis of irrigation water is necessary.
- Nitrogen that we are going to contribute with the organic manure amendment
OTHER USES OF HORSE MANURE
In addition to using it as an organic and nutrient amendment to the soil of our crops, horse manure has been used or is at least investigated for other purposes such as:
- Obtaining biogas from equine manure in Batch-type digesters
- Studies have been carried out in which it has been used as a bioremediation method for soils contaminated with oil.
- Combustion to obtain heat energy . In this case, high NOx emissions were analyzed due to the presence of nitrogen. Not everything can be good.