Fall Nitrogen Fertilization Strategies in Prairies

The selection of a nitrogen fertilization strategy in autumn for rainfed meadows should consider the state of the plants as a central point, which is largely dependent on climatic conditions and the grazing management carried out during the summer-autumn.

Considering a normal or dry summer, in which the meadows dry up as a result of high temperatures and lack of humidity, The suggestion is to wait 1 or 2 important grazings to make the first application with some nitrogenous source., since the soil will have nitrogen above what is required as a result of the mineralization of organic matter, which can only be used with the regrowth and growth of the meadows.

Therefore, Nitrogen (N) should be avoided before or immediately after the first rains, since there would be an excess of available nitrogen, without obtaining additional growth, but it will result in an excessive content of protein in the pasture, reducing consumption due to lower palatability and decreasing milk production as a consequence of lower consumption and energy expenditure by the cow to remove excess nitrogen consumed.

In addition, there is the risk that dairy cows suffer from a number of problems, such as; reproductive failure, laminitis, risk of poisoning by nitrites and risk of poisoning by ammonium.

Added to this and considering the current cost of nitrogenous fertilizers, an application earlier than suggested has no technical justification.

In irrigated meadows, there is a more constant and less abrupt release of nitrogen from the soil, so a balanced and environmentally sustainable supply of nitrogen must be maintained, which considers the contribution of mineralization, of other species such as clovers, the recycling that can be produced by the contributions of urine during grazing and the contributions of manure applications.

What strategies can I follow to make nitrogen contributions that have a positive impact on the grasslands and that are economically viable, considering the current cost of fertilizers?

At the beginning of the important rains, which should normally occur in March, the suggestion is to use only the contribution of the soil (Diagram 1).

As an alternative to the above, the contribution of mineralization can be complemented with products that help reactivate the growth of the meadows (nutrients and growth promoters; example 2 L/ha of NanoEnergy). It is important to note that the application of this type of product must be carried out on a meadow that has already sprouted, since it must have green and growing leaves that can absorb the product.

Diagram 1. Strategies for the use of nitrogen in regrowth of meadows.

Once 1 or 2 important grazings have been carried out, it is possible to take different alternatives of external nitrogen supply (April-May), according to what is exposed in Diagram 2.

Diagram 2. Nitrogen use strategies after the first grazing.

Strategy 1: consider traditional management, applying for example 60 kg/ha of urea or 100 kg/ha of Can27 or similar nitrogen fertilizer; also considering as an alternative the N units that a mixture may contain.

Strategy 2: the nitrogen contribution that can be made through the application of manure (and other similar) is important, with a range of 0.16% to 5.25% of total N (0.02 to 2.11 of soluble N ), depending, among other factors, on the dry matter content, which will normally be higher in autumn, due to less rainwater entering the slurry well.

Taking this into consideration, an application in autumn of approximately 25,000 to 35,000 L/ha would cover a complete dose of N, with additional units of N to be delivered in the medium or long term (organic N that must be transformed into soluble N and available for plant).

Consider that slurry, in addition to being a resource available in all dairies, allows internal recycling of nutrients within the farm at low cost; providing other nutrients such as potassium, phosphorus, sulfur, calcium, magnesium and microminerals in general.

It is suggested to apply slurry before or during rains to reduce N losses due to volatilization.

Nitrogen should ideally be applied immediately after grazing, since the absorption of the meadow is rapid and the maximum occurs between 5 and 12 days post-application, so it is necessary to allow enough time between the application and the following grazing.

The application of N in autumn should be carried out only until there are favorable temperature conditions, and therefore adequate growth rates of the meadow.

If you have any comments or queries, do not hesitate to request the support and advice of the COLUN agricultural department team.