Nitrogen volatilisation from urea in oil palm: why so much applied N disappears into the air

Urea (46% N) is the dominant nitrogen fertiliser used across Malaysian oil palm plantations, on both estates and smallholdings, because it is the cheapest per unit of nitrogen and is readily available through the subsidised supply chain. Yet research in Malaysia shows that a substantial fraction of applied urea never reaches the oil palm root system, because part of its nitrogen is lost to the air as ammonia.

When losses are high, a large part of the money spent on nitrogen fertilises the air, not the crop. Reducing this loss is one of the most direct routes to improved fertiliser efficiency and reduced input cost in Malaysian plantation agriculture.

The chemistry of urea volatilisation

When urea granules are applied to the soil surface, the enzyme urease (produced by soil bacteria and present in plant residues) rapidly hydrolyses urea into ammonium carbonate and then ammonium (NH4+) and bicarbonate ions. This reaction raises the pH locally around each urea granule, shifting the ammonium-ammonia equilibrium strongly toward the volatile gas form, ammonia (NH3). Ammonia gas diffuses from the soil surface into the air: this is volatilisation.

The rate of loss depends on surface temperature, wind speed, soil moisture, and the time between urea application and rainfall or irrigation. The highest volatilisation rates occur when urea is applied to a dry or moist (but not wet) soil surface under warm, windy conditions. Warm Malaysian daytime temperatures during dry weather create near-optimal conditions for rapid urease activity and ammonia escape. Most of the loss occurs in the first few days after application, before a rain event can dissolve and carry urea into the soil.

When volatilisation is worst in Malaysia

Malaysian rainfall patterns are highly seasonal in some regions and episodic everywhere. Dry spells are common, particularly during the southwest monsoon in Peninsular Malaysia and during El Nino-influenced dry periods in Sabah and Sarawak. These are often exactly the periods when urea applications are most needed (to support bunch development ahead of the seasonal harvest peak) and exactly when volatilisation losses are highest.

Urea applied during drought tends to perform poorly, through a combination of poor uptake from dry soil and high volatilisation under dry conditions. The paradox of fertilising during drought for harvest preparation, and losing much of it to the air, is a structural inefficiency in conventional oil palm nutrition programmes that organic nitrogen sources can partially address.

Slopes and terraced plantations face an additional nitrogen loss risk from surface runoff. When rain finally arrives after a dry period, it often falls intensely, washing urea granules that have not yet dissolved off terraces and down drains before they can enter the root zone, compounding the air loss with water loss.

Mitigation strategies: timing and formulation

The most accessible volatilisation reduction strategy requires no input change: apply urea shortly before forecast rain or after rainfall when soil is moist but not waterlogged. Moist soil accelerates urea dissolution and movement into the soil profile before hydrolysis produces volatile ammonia. Malaysian plantation managers with reliable weather monitoring can time applications to capture this window consistently and reduce volatilisation losses substantially.

Splitting annual nitrogen applications into more frequent, smaller rounds reduces the concentration of urea on the soil surface at any one time, lowering peak ammonia flux. While it increases application labour, splitting also improves synchrony between nitrogen supply and crop demand, particularly around bunch development cycles.

Urea treated with a urease inhibitor slows the hydrolysis reaction, and polymer-coated urea slows the release of urea into the soil; both extend the window between application and volatilisation. These products can reduce ammonia loss; whether their higher cost per unit N pays back depends on how much nitrogen you are losing now and on your prices, so compare them on your own figures.

Organic nitrogen sources: a complementary approach

Organic nitrogen (from compost, cover crop biomass, POME and biological conditioners) behaves fundamentally differently from inorganic urea. Organic nitrogen is mineralised from complex organic compounds by soil microorganisms at rates controlled by soil temperature, moisture, and microbial activity. This slow-release, soil-mediated supply is inherently less susceptible to volatilisation because it does not produce the surface ammonium flush that drives ammonia escape from urea.

CSB Organico provides nitrogen in organic-bound forms that mineralise progressively over the growing season. Used alongside a soil conditioner such as SoilBoost EA, which may support soil biological conditions, organic nitrogen sources can supply part of oil palm's nitrogen requirement, reducing the amount of urea needed and with it the volume of nitrogen exposed to volatilisation risk.

Leguminous cover crops including Mucuna bracteata and Pueraria javanica fix atmospheric nitrogen through their Bradyrhizobium symbiosis and add it to the soil organic nitrogen pool. This nitrogen enters the crop system via microbial mineralisation of cover crop residues, again through the slow-release, low-volatilisation pathway. On fields with well-established cover crop systems, part of the crop's nitrogen can come by this route; change urea rates only on the basis of leaf and soil analysis.

The business case for nitrogen efficiency

The value of reducing volatilisation is simple to estimate with your own figures: multiply your annual urea spend per hectare by the share of nitrogen you expect to lose under your conditions, then by your planted area. Timing optimisation, split applications and partial organic nitrogen substitution can recover part of that loss without changing the hectarage, crop variety or other inputs. Nitrogen efficiency is one of the most direct agronomic improvements available. To discuss organic nitrogen inputs or cover crop seed for your blocks, request a quote.