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04Mar

SustaiN principles (SustaiN vs urea)

Words and image supplied Ballance Agri-Nutrients

Up in the air

There’s a convenient, cost-effective way to keep your nitrogen investment in the ground for plant use.

“People generally attribute nitrogen (N) losses to leaching, but a significant proportion of N can be lost in the form of ammonia gas,” says Ballance Agri-Nutrients Science Extension Officer Jess Hollever.

Research shows that in pastoral situations as much as 42 per cent of the total N applied can be lost as the greenhouse gas ammonia, with losses typically between 10 and 20 per cent1.

“Volatilisation, the loss of N as ammonia gas, can happen at any time of year, including in cooler weather. Moist conditions are particularly problematic.”

The volatilisation process starts soon after urea fertiliser is applied to the soil surface. As the granules start breaking down they are ‘attacked’ by urease (an enzyme produced by soil bacteria) which converts urea into ammonium. As the urea granules dissolve, the pH of the soil in the immediate area increases, which promotes the conversion of ammonium to ammonia gas.

“Moist soil or dew after application can increases volatilisation losses. The moisture breaks down the urea granules and starts the conversion into ammonium, but doesn’t actually wash any N into the soil profile, where volatilisation losses are greatly reduced.” 

The longer the urea granules remain on the soil surface, the longer they are exposed to the urease enzyme, and the more N is lost in gas form. Ammonia gas losses peak one to three days after urea application.

Will rain protect your N?

“Sufficient rainfall will wash the N into the soil profile, which can reduce volatilisation losses by around 50 per cent. There needs to be at least 5-10 mm in the March Real Farmer article it states at least 10mm  of rain or irrigation within 8 hours of fertiliser application.” I feel that both need to be the same.

This amount of rainfall or irrigation moves the N into the soil profile, where it disperses, reducing the change in soil pH, and producing less ammonia gas compared to when on the soil surface. Only between 5 and 10 per cent of the applied N is likely to be lost as ammonia gas if this occurs2.

“Rainfall isn’t always reliable, and there’s also the inconvenience of timing urea application around adequate rainfall, so that’s why SustaiN is convenient.”

A convenient, cost-effective alternative

“A urease inhibitor on urea fertiliser reduces volatilisation losses without the need for adequate rain. It can be applied when it suits you, or when the crop or pasture needs N.”

SustaiN, a urea fertiliser coated with the urease inhibitor AGROTAIN®, cuts N volatilisation losses by around 50 per cent (compared to standard urea).

When SustaiN is broadcast, the coating dissolves into the soil with the urea and temporarily blocks the urease enzyme, reducing the amount of ammonium formed, and the amount of N lost as ammonia gas.

SustaiN provides increased N efficiency, with research showing over a wide range of conditions the average increase in pasture yield is 5 per cent when using SustaiN instead of urea3.

“It costs about 10 per cent more than standard urea, but in a regulatory environment where every kilo of N counts, SustaiN is a convenient, cost-effective way of protecting your N fertiliser investment and the environment,” says Jess.

For more support, talk to your Ballance Nutrient Specialist or Ruralco Representative.

1 Theobald PW, Ball PR 1984. Nitrogen lost by ammonia volatilisation, and the effectiveness of urea and ammonium sulphate fertilisers, Proc. NZ Grassland Assoc. 45: 236-8

2 Saggar S, Singh J, Giltrap DL, Zaman M, Luo J, Rollo M, Kim D-G, Rys G, Van der Weerden TJ 2013. Quantification of reductions in ammonia emissions from fertiliser urea and animal urine in grazed pastures with urease inhibitors for agricultural inventory: New Zealand as a case study, Sci. Total Env. 465: 136-46

3 Stafford A, Catto W, Morton JD 2008. Ballance Agri-Nutrients approach to sustainable fertiliser use. Fertiliser and Lime Research Centre, Massey University, Occasional Report No. 21: 197-205

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