Wednesday, 5 August 2020

Liquid nitrogen as an option


Following on from Dr Ants Roberts article titled ‘Surviving spring’, applying nitrogen (N) in liquid form can provide an alternative and convenient option for sprayer or irrigation applications.

Advantages of applying nutrients in liquid form include better use of existing on-farm application equipment (sprayers and/or irrigators), flexibility with timing (especially at times of year when spreading trucks are busy) and potential accuracy (reduced overlaps) when applied with well-calibrated sprayer or irrigation equipment.

Ravensdown has two liquid products available (currently in the South Island only), one of which contains just nitrogen (N) and the other nitrogen (N) + sulphur (S). Both can be applied using either spray or irrigation equipment and if sprayed, are compatible with gibberellic acid and some pesticides and herbicides.

From an agronomic perspective, plants cannot tell the difference between nutrients supplied in granular or liquid form once the nutrients enter soil solution. One kg of N applied is the same in both liquid and granular forms, and all else being equal, will grow the same amount of dry matter (DM) regardless of state, form or application method. Plant leaves can absorb liquid urea, but the effective amount that diffuses this way depends on how much remains on the leaf surfaces, rather than drips onto the soil.

"Plants cannot tell the difference between nutrients supplied in granular or liquid form once the nutrients enter soil solution."

Losses of N due to ammonia volatilisation can still occur with liquid N products as the amount of water applied with the urea may not be enough to completely prevent the rise in pH during urea hydrolysis by the urease enzymes.

The two critical factors in determining losses (NH3) following N applications are the amount and timing of irrigation (or rainfall) during and/or immediately following the N application. As a general rule of thumb, 10mm of rainfall/irrigation is required within eight hours of any urea (granular or liquid) application to significantly reduce volatilisation risk. Nitrogen applied through fertigation does however have the benefit of being applied with water so can reduce the risk of volatilisation if enough water is applied with the application.

As always, any advantages will need to be balanced against any additional costs of liquid products and their application.