Urea Deep Placement

What is the Urea Deep Placement technology?

Urea Deep Placement (UDP) is when farm laborers strategically bury urea (fertilizer) supergranules near the root zone of crops. This practice is most frequently used for lowland rice crops. Although the practice is labor intensive, UDP enhances the efficiency of nutrient delivery to crops and reduces Nitrogen (N) losses from agricultural fields. Globally, most of the fertilizer applied on rice crops is broadcasted on top of the soil. When plants are not able to absorb available nutrients, nitrogen is rapidly lost from the soil surface to the atmosphere through a process called ammonia volatilization, or it is washed off fields during flooding or heavy rains. Fertilized rice fields also emit nitrogen oxides (N20, NO), which are greenhouse gases that are widely implicated in climate change. Burying UDP granules in rice fields can greatly reduce N losses, conserve soil nutrients, and mitigate climate change, as well as enhance yields and plant health.

How and where is UDP currently used?

UDP has been widely adopted in lowland paddy rice production systems in South Asia, such as Bangladesh (see map). Under UDP, fertilizer in the form of a supergranule, or briquette, is hand-buried 7 to 14 centimeters deep between every four rice plants about a week after transplanting. This better synchronizes the availability of nutrients with the nutrient demands of the crop, which in turn, strengthens nitrogen balances, increases soil fertility, and boosts rice yields—all with less fertilizer. Reportedly, UDP occupies more than 2 million hectares of farmland in Bangladesh, approximately 12 percent of the nation’s annual irrigated rice crops. UDP can increase rice yields by at least 15 percent and decrease N consumption by one third. However, in most of the approximate x million hectares of lowland rice growing areas of Africa south of the Sahara (SSA), UDP is still a novel technology. Scientists and development practitioners have recently promoted the potential of UDP in a select number of African countries, mostly in West Africa where the XX percent of African-grown rice is cultivated.

Where is the UDP technology biophysically suitable for use?

Critical determinants for UDP success are soil and climate characteristics and farm management practices. UDP is most likely to succeed in rice growing areas that are prone to Nitrogen (N) loss through surface water runoff and ammonia volatilization (i.e. the loss of N into the atmosphere from the soil surface), which occur under conditions of high and intense rainfall in areas with nonacidic soil (>pH 5.4). These losses – unmitigated by broadcasting urea on the soil’s surface – decrease the amount of N available to crop plants. The potential of UDP success also depends on soils that are structurally appropriate for deep placement of urea and water retention. In clay and silt soils that have a higher capacity to hold water, concentrated N from UDP is released slowly to roots and plants are able to uptake most of the nitrogen as the season progresses (around 60 percent). Lighter-textured and sandy soils are vulnerable to leaching and poorly retain the N released by deeply place urea briquettes. UDP is not recommended, therefore, in dryer areas with low or infrequent rainfall, acidic soils, and light-textured soils, particularly if the soil is low in organic matter and cation-exchange capacity (i.e. ability of the soils to retain and release nutrients).

Using the soil and rainfall criteria mentioned above, we can thus map the spatially-explicit suitability of UDP anywhere. The included maps show the extent of biophysical suitability for UDP in rice growing regions in Ghana (below) and Senegal (interactive map), as well as Bangladesh (previous map). These are based primarily on soil suitability characteristics noted above. Although most of the rice growing area in Bangladesh is suitable for UDP (77 percent), the area of suitability makes up less than half of the current extent of rice in Ghana and Senegal and is spatially disconnected with a patchy distribution. When the two African countries are compared, the extent of suitability is, however, noteworthy in Ghana (39 percent), especially in the more productive rice growing regions of Northern and Upper East, where more than 40 percent of the area is biophysically suitable for UDP. The area of suitability is much lower in Senegal (23 percent with the highest concentration in the northern region of Saint Louis) despite large yield potential under UDP adoption in several regions of the country .

What are the benefits of UDP if adopted?

Inefficient nitrogen (N) management impacts global food security, farmer livelihood, and contributes to widespread pollution, the degradation of water quality and aquatic ecosystems, and climate change. UDP helps manage the application and loss of N and in turn contributes to higher yields, fewer nitrogen-based greenhouse gas emissions, and a more resilient rice production system.

Rice yields are reportedly capable of increasing 5-30 percent under UDP in different regions of Asia and Africa. Here we estimate yield increases in lowland rice production systems of Ghana and Senegal under UDP technology (previous map and current map). Across regions in Ghana, simulated increases in rice yields under UDP range from 2 to 10 percent under low rate of N fertilization. Yields more than doubled under a doubled (intensified) rate of N application via UDP. Much higher yield increases were estimated across regions in Senegal (10 to 76 percent) since baseline yields in this country are generally lower than those in Ghana. The largest yield increase (27 percent) under the higher N scenario is expected in the Western region of Ghana, where more than 15,000 hectares of rice are currently grown, yet according to the suitability map, only 5 percent of the region is suitable for UDP technology.

In addition to increasing yields, UDP is also an effective means of decreasing the amount of nitrogen-based GHGs that are released from fertilized fields (Gaihrea et al, 2015). Up to 70 percent of nitrogen is lost with broadcast fertilizer application leading to both water pollution and increased emissions. UDP ensures a slower release of fertilizer near the roots of the plants, therefore increasing the nutrient uptake and limiting N losses. This reduction in leached nitrates decreases the likelihood nitrous oxide emissions (FAO 2013). UDP additionally increases the resilience of agricultural systems as they are less susceptible to economic changes such as a sudden increase in the price of fertilizer.

What are the constraints, risks and/or tradeoffs of adopting UDP?

Suitability of UDP is constrained by, among other things, the soil. Many of West Africa’s soils are sandy, acidic, and low in organic matter and cation-exchange capacity, which limits the ability of a soil to hold onto essential nutrients. For this reason, the geography of UDP suitability in the rice growing regions of Ghana and Senegal has a patchier, less-connected spatial distribution than in Bangladesh where the soils are more consistently suitable. The potential of UDP in Ghana and Senegal, and presumably in other West African countries, may be limited at scale due to the nature of the soils. The availability and affordability of extra labor is also particularly important and a major constraint to adoption, despite potential savings in the cost of Nitrogen fertilizers. Scaling will also rely on the establishment of a reliable supply chain of UDP briquettes and the appropriate machinery and tools for UDP manufacturing and burial. The potential success of UDP scaling, therefore, depends on a complexity of events and requires a comprehensive value-chain approach.

Learn More about UDP

  • UDP on Map Journal: http://arcg.is/1f5utZn
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