If you have ever wondered what really goes on after you apply urea, you are not alone. We’ve put together a simple diagram to show the two main routes urea can take once it is out of the fertiliser shed either sprayed as a foliar application or spread as granular urea. The science is fascinating (and useful), but the end story is all about speed, waste, and looking after your soil.
Why Compare the Two Pathways?
Knowing how urea travels through your pasture matters if you want to get the best bang for your buck. Many have seen foliar-applied urea give crops a fast green-up and a kick into gear, while soil-applied urea is slower, sometimes feels “wasted”, and can drop your soil’s pH. There is solid science under these differences:
Foliar Urea Pathway (Leaf)
- Leaf Entry
Fine urea spray lands on the leaf and quickly moves in through stomata and cuticle. - Leaf Urea Conversion
Leaf urease enzymes turn urea straight into plant‑ready ammonium inside the leaf. - Fast Protein Build
That ammonium is rapidly built into amino acids and proteins to drive growth with less energy cost.
Granular Urea Pathway (Soil)
- Soil Surface Application
Dry urea granules sit on the soil surface after spreading. - Soil Urea Hydrolysis
Soil urease converts urea to ammonia, which becomes ammonium in soil moisture. - Ammonium to Nitrite
Nitrifying microbes first oxidise ammonium into nitrite in the soil. - Nitrite to Nitrate
Other microbes then convert nitrite into nitrate, completing nitrification. - Root Uptake from Soil
Roots absorb ammonium and nitrate from the soil solution. - Energy‑Costly Protein Build
The plant uses more energy to turn soil‑derived nitrate and ammonium into amino acids and proteins.
As you can see, same fertiliser – but different process. Less energy required through foliar uptake and less risk of losses to volatilisation and leeching.
Granular Urea – Soil Applied The Long Way Round
Spreading solid urea kicks off a longer process. The urea is first broken down by soil microbes to ammonia, then quickly changes to ammonium. From there, different soil bacteria change it into nitrite, then nitrate. Plants mainly absorb ammonium and nitrate, but every stage offers chances for urea to be lost through leaching, runoff or conversion to gas. Rain can wash nitrate deep into the soil, while wet soils can turn it into nitrogen gas, either way, these are losses paid for but not utilised. Sometimes granular urea can be a more practical application method when conditions are too wet, or windy to spray, but the losses are still high.
Foliar Urea Application Direct and Fast
When dissolved urea is sprayed onto leaves, the plants quickly absorb it through small pores called stomata. Once inside, the plant’s enzymes break it down to ammonia, and this is almost immediately fixed into amino acids like glutamine and glutamate. Because the process barely involves the soil, there is little loss on the way, and plants can use the urea almost straight away for growth and repair.