General Rules for Managing Nitrogen on Your Farm

1. Practice smart use of N with a proactive mindset.

Use N in a smart way, not in a set way. Before each N application, figure out how much N will be used and compare the cost of the extra pasture to other feed options that can be bought. Other management concerns around nitrogen use include.

1. Managing ammonia losses
2. Manure and urine management
3. Animal health and welfare
4. Nitrate leaching and denitrification
5. Surface runoff loses.

Each of these concerns makes for its own articles, for now, let’s get into the general rules for managing nitrogen on your farm.

2. Get your game on with suitable timing and use of N.

As a general rule, only apply N when the pasture is growing and can use the N. A good rule of thumb: Make sure that there is enough soil moisture to sustain the regrowth, that there will be enough rain during the growing season, that the temperature is right for good pasture growth, there is a good mix of species, and that other major soil nutrients are not limiting.

Apply N as soon as possible after grazing, because this is when plants need the most N for regrowth. As a general rule, you can lose 1% of the N response every day you wait to apply N after grazing.

If you want to graze, wait until the grass has at least 2.5 leaves, or until the canopy has closed for grasses like ryegrass. Or the three-leaf stage for grasses like kikuyu and paspalum that grow in tropical places. Grazing at these targets will make the most of the nitrogen that is used, the energy:protein ratio in the diet, and the amount of N that is excreted or lost.

When the soil temperature is above 4°C, grasses like ryegrass like to get N fertiliser. As long as soil temperatures are above 10°C, grasses like kikuyu can use N fertiliser. Remember that this is the average temperature of the soil at 10 cm over the regrowth period, not just on the day that the fertiliser was put on the soil.

Soil moisture is very important for dryland pastures in the fall and summer. Without adequate soil moisture, you are literally volatilizing money!

3. Know what you’re doing with an appropriate N application rate.

In a typical dairy farming scenario, apply N at rates of 20 to 50kgN/ha per application, no closer than 21 days apart at the lighter rates and at least 28 days apart at the heavier rates. It can be a handy calculation to multiply the daily equivalent rate of N by the number of days between N applications (e.g. 1.2 kg N/ha per day by 21 days = 25 kg N/ha applied).

For a single grazing rotation in spring, raising the maximum rate to 60 kg N/ha may be possible for good soil fertility and newer pasture breeds.

The most effective pasture growth responses occur when N fertiliser is applied at rates ranging from 20 to 50 kg N/ha at a time. This is due to the fact that the strongest reactivity to N occurs at these rates and decreases as rates climb.

Do not apply more than 50kgN/ha in a single application, and do not apply N within 21 days of each other, since this will increase N losses tenfold and may endanger animal health. The exception may be on very productive pastures at their peak growth phase, with a newer cultivar, and where soil moisture is not a constraint, in which case pastures may respond to rates of 60 kg N/hectare per treatment for a single grazing rotation in spring.

Applying less than 20kgN/ha in any one application may result in unexpected N responses, for example, 20 kg N/ha on 2ha may generate less than 40kgN on 1ha. Similarly, applying 80 kilogramme N to 1 hectare (80 kg N/ha) is projected to produce less pasture than applying 80 kilogramme N to 2 hectares (40 kg N/ha) because of decreased N responses on the flat region of the curve.

4. Maximise your pasture growth response with the best timing of N.

Use the extra pasture that you grow, either by grazing or harvesting it for forage, to make it more profitable to use N. In the same way, overgrazing a pasture can make the next grazing rotation take longer to respond to N.

N should be applied to pastures with a high density of desirable species. Ryegrass and kikuyu pastures will respond to N better than other less appealing pasture kinds or weedy pastures.

N should be applied to pastures that have a good ground cover. Gaps or dry areas in pastures will result in increased N loss due to leaching, denitrification, runoff, and volatilisation.

N should be applied to pastures that have no constraints on the principal soil nutrients. Soil testing on a regular basis will assess the nutritional health of the soil, and if other key nutrients or pH are impeding growth, these issues may be addressed before or at the same time as the N treatment.

N should not be applied to drought-stressed or water-logged pastures, such as when water is pouring off the surface. Or when grazed at less than 2.5-leaf renewal stage or canopy closure for temperate grasses like ryegrass and 3-leaf stage for tropical grasses like kikuyu and paspalum.

Because cows migrate N towards the gate, consider placing less N in the front of a paddock than in the back.

Avoid applying N to high-traffic areas for animals, such as gates, water troughs, shelterbelts, and stock camps. These areas have significant N loading and are suitable N loss sites on dairy farms.

5. Summarising general rules around managing nitrogen

Spring and summer grazing rotations benefit from nitrogen treatment at the appropriate rate to increase soil fertility and fodder quality - provided that soil moisture is not a limiting factor. As a general rule, every day that you delay applying N after grazing costs you 1% of the N response.

Other nitrogen-related management challenges include. Management of manure and urine; animal health and wellbeing; and surface runoff.

Apply nitrogen at rates ranging from 20 to 50kgN/ha per application in a typical dairy farming situation. This is because the largest sensitivity to N occurs at these rates and declines as rates increase. Overgrazing a pasture may delay the following rotation's response to N.

You'll get the most bang for your money from grasses like kikuyu, which may benefit from N fertiliser if soil temperatures are over 10°C. Nitrogen should be supplied to pastures where desirable species, such as ryegrass and kikuyu, are abundant.

Regular soil testing will determine the nutritional status of the soil. If other critical nutrients or pH levels are hindering plant development and growth, these concerns may be addressed before or concurrently with the N applications.