Getting the most from autumn nitrogen

In the early autumn, there is a lot of pressure on trying to build pasture feed reserves while you increase grazing round lengths. This can affect your ability to build cow condition or extend milking.

The good news is autumn is still a great time to grow grass. Soil moisture and temperatures are generally good (often warmer than early spring), and nitrogen can effectively boost growth to provide the quality feed needed at this critical time.

These five levers can help improve autumn nitrogen use efficiency (a measure of the nitrogen taken up by plants relative to what’s available). It’s about optimising production while minimising environmental impacts.

1. Optimal base soil fertility

To maximise potential pasture growth, make sure base soil fertility (pH, phosphorus, potassium, sulphur and magnesium) is within optimal ranges. Apply maintenance and/or capital fertiliser as needed to ensure pasture growth isn’t limited by base fertility.

2. Clover herbage testing

Diagnose and correct any deficiencies in clover to ensure pasture has everything it needs to grow to its potential. Potassium, molybdenum and sulphur are important for clover and other legumes.

3. Timing of nitrogen fertiliser

Time autumn nitrogen fertiliser applications so that pasture growth response isn’t limited by weather conditions. Autumn nitrogen fertiliser needs to be applied well before the soil temperature drops below 6°C, so pasture not only takes up nitrogen but there is sufficient time for a good pasture response from it (and nitrogen isn’t lost via leaching over winter).

4. Minimise volatilisation losses

Timing applications around adequate moisture to minimise nitrogen lost to the air as ammonia gas (volatilisation) can be tricky. To minimise volatilisation losses, at least 5–10mm of rain or irrigation within eight hours after urea is applied is critical. This moves the nitrogen into the soil profile, and less ammonia gas is produced than if it were to remain on the soil surface.

A more convenient and reliable way to reduce volatilisation losses is by using a urea fertiliser with a urease inhibitor. SustaiN is a urea fertiliser coated with the urease inhibitor AGROTAIN^®, which reduces the rate at which the urea converts to ammonium, which in turn reduces volatilisation. Compared to standard urea, SustaiN may cut nitrogen volatilisation losses upwards of 50%. It also provides increased nitrogen efficiency, with research showing over a wide range of conditions the average increase in pasture yield is 5% when using SustaiN instead of urea¹.

5. Varying nitrogen rate by block

A soil Total Nitrogen test can help identify areas of the farm that may be more responsive to nitrogen fertiliser, so nitrogen application rates can be tailored accordingly. Total Nitrogen results can vary across the farm due to variations in soil type, topography and farm management, and in general low total nitrogen level areas will have a larger pasture growth response to nitrogen fertiliser than areas with high total nitrogen levels.

The Total Nitrogen test can be incorporated into a regular soil testing regime every four to six years, as the total nitrogen in the soil changes slowly over time if land management has not changed significantly.

Other levers to improve nitrogen use efficiency include pasture renewal (as new pastures provide a greater response to nitrogen than damaged, poorer condition pastures), pasture measurement (the rate of pasture growth dictates the size of the response to nitrogen), and legumes in pastures (more legume content can reduce your farm’s reliance on nitrogen fertiliser).

Your Ballance Nutrient Specialist can provide advice on making the most of every kilogram of nitrogen applied, helping you boost productivity and profit and reduce environmental losses, while meeting regulatory requirements. Contact your Farm Source TSR or talk to your Ballance Nutrient Specialist.

Article supplied by Ballance

1. 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.