Urea should only be apply in oxidized zone. After irrigation, when soil reached at field capacity level of moisture, urea should be top dress.

You may find this link helpful. https://water.unl.edu/documents/Section%20D.pdf

We typically used soil scientists to test for the specific fertilizer needs, but also suggest timing. We often used to fertilize from February to April, just before or during active spring growth flush. Nitrogen tends to be mobile in soil, especially sandy soils and during heavy rain. Unless the fertilizer was Pelletier, we tried to apply just before a rain event of maybe 0.1 to 0.3 inches, enough to mobilize the nitrogen into the soil, but not so much as to encourage overland flow and/or deep soil flushing. If you have some wells monitored, you want to avoid rain events which rapidly and substantially raise the depth in the wells of the vicinity. If you monitor enough storms and well data, you will be able to see how much rain delivers a small response, suggesting most of the rain is retained in the soil, and how much rain produces rapid water level response and flushing. In many cases, if the plants are not growing and actively taking up moisture, the nutrient additions may be lost or not fully effective. In some cases, pelletizing fertilizers can provost time release over several rainfall events. We used soil scientists to test soils relative to their fertilizer needs to avoid applying fertilizer when not needed. We sometimes included legumes and other nitrogen fixing plants in our seed mix, which was mostly pine forests and wildlife food plots, stabilization of roads, barrens and gullies.

@ Udit, I think it is better to apply before irrigation as urea needs to be watered or tilled into the soil within two days to make sure the plants can access as much nitrogen as possible. Urea initially breaks down as ammonium, then turns into nitrate. This breakdown begins immediately after spreading the urea, which is why you must work fast to incorporate it into the soil.

@ J C Tarafdar sir,

Application of urea before irrigation is always beneficial? In clay soil after applying urea irrigation water can wash out the fertilizer as urea is very much soluble in nature, then?

@ William F Hansen sir,

In India most of the areas coming under Rainfed, so the amount of rainfall is not in our hand then how the time of urea application differ from sandy soil and clay soil? Is there any specific consideration of urea application in clay and sandy soil?

@ Udit, in clay soil you incorporate urea into the soil during a tillage operation that's why I mentioned you can tilled into the soil. You can also blend it into the soil with irrigation water.

@J C Tarafdar sir,

Thank you.

Urea is rapidly hydrolyzed to ammonium (this process is completed in about 5 days), which can be potentially lost through ammonia volatilization. But if urea is placed at a depth (even 1-2 cm below the soil surface), losses of urea-N via ammonia volatilization are greatly reduced or are minimal. The application of urea before or after irrigation is linked with ammonia volatilization losses rather than the issues discussed above by different colleagues. In coarse-textured soils where water percolation rates are high, it is recommended to apply urea before the irrigation event as the percolating water carries urea to a depth in the soil and urea-N does not remain prone to losses via ammonia volatilization. But one should make sure that the time between urea application and irrigation is kept to a minimum. Urea lying on the dry soil before application of irrigation water can also be hydrolyzed to ammonium though to a limited extent. We need to keep in mind that that urea is very hygroscopic.

In heavy-textured soil, the best way to apply urea is to incorporate it into the soil at a depth. But when urea is to be topdressed while the crop is in the field, apply urea immediately after the irrigation water has percolated down the soil surface. Due to the heavy texture of the soil, water slowly keeps moving down and transports urea to a depth where it is safe from ammonia volatilization losses.

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@Bijay singh sir,

Thank you sir for your answer.

Udit.

La urea se puede usar bien en suelos francos y arcillosos tanto para riego de gravedad como para riego de goteo en cualquier cultivo, pero usarla en suelos arenosos es una perdida total por la escases de coloides sea arcilla o materia orgánica, y la falta de la enzima Ureaza la cual transforma la urea a amonio. Con ello se acelera el proceso de volatilización

As urea is easily soluble fertilizer, it is better to apply after the irrigation in both sandy and clayey soil. However, if the light irrigation water is applied, then urea can be applied in the clayey soil as in that case water would be just sufficient to wet the soil and water would not infiltrated through the soil profile. Further, urea is applied before full irrigation after part urea is lost down the soil profile and a part volatilizes. Thank you for the useful question which is very relevant to food producers and land managers.

siendo la urea un producto no iónico no tiene la capacidad de adherirse a ningún coloide del suelos por lo tanto , no recomiendo su uso en suelos arenosos, solo en los de textura media y pesada. mejor en el fertirriego, para cultivos perennes o de de largo periodo vegetativo. pero para cultivos anuales de rápido desarrollo es mejor los nítricos y los amoniacales.

@Bijay singh sir,

As per you said we have to apply urea in clay soil after the irrigation, but sir I hve a doubt that if we apply urea after irrigation then some urea will lost by volatilization as urea will hydrolyzed and produce ammonia as well ... But sir as per you said urea will slowly go through soil profile by irrigation ... In this slow time some urea will lost by volatilization no?

Please clarify my doubt...

To increase NUE if urea is applied just after irrigation when there is thin layer of standing water on soil surface i.e. just to dissolve and carry the fertilizer to the rootzone depth.

The timing of Urea application before the irrigation or after the irrigation means top dressing of urea. It is not the application of urea during the final land preparation. Usually top dressing is done before intercultural operation of a standing crop. Different seed treatments are used alone or in combination to address or prevent a number of pests, diseases and nutrient deficiencies and to enhance plant growth. ... Fertilizers: These types of treatment are used to enhance fertilizer performance or supply micronutrients to the soil, which helps plant growth.

Fertilization or fertilizer application is the supplemental application of plant nutrients to crop plants to augment the supply from natural sources. This consists of applying nutrient-containing materials, called fertilizers, generally into the soil in proximity to receptor plants. Urea or Urea super granules can applied at the time of seeding after that one or two times urea can be applied. Conventional N fertilizers are highly soluble and may be lost easily from the soil-plant system. The N recovery by crops from the soluble N fertilizers such as urea is often as low as 30–40%. In order to improve urea-N recovery and reduce its loss, many forms of slow-release urea fertilizers have been developed and such slow-release urea fertilizers can increase the efficiency of urea-N and are environmentally friendly because their N release is in synchrony with plant N uptake, and can provide sufficient N to satisfy plant N requirements while maintaining very low concentrations of mineral N in soil throughout the growing season.

Urea fertilizer is highly soluble and volatile particularly in a sandy soil. hence, it is best applied after irrigation so that it can be absorbed by the crops immediately without much loss to either leaching or volatilization.