Let’s Talk Nitrogen application with Charlie Walker
Seasons come in many shapes and sizes and can vary significantly from one year to the next. One common denominator from year to year is that you will be applying Nitrogen in one form or another.
In-season applications of nitrogen are generally decided by a sensible and realistic estimation of the expected yield, the crop demand and the anticipated soil nitrogen supply to make up the difference between demand and supply. But, it isn’t always this easy and every application involves risk which eventuates to economic losses if not treated properly. These risks come in the form of losses through wet seasons or lack of water and therefore demand in dry seasons. A timely, appropriate rate of nitrogen applied in the right form can be the difference between a profitable return on investment and seeing a loss.
Hear from Charlie Walker at Incitec Pivot on the best strategies, or read below to learn more about nitrogen application.
Soil Available Nitrogen
A big factor on determining how much nitrogen to apply is knowing how much nitrogen is already there. Finding out how much nitrogen is available in the soil is highly dependent on what crop was in that paddock the year before.
A general rule of thumb is that a cereal stubble will leave 50 kg N/ha and a legume will stubble will leave at least 80 kg N/ha. Although, this can vary greatly from a range of factors such as last year’s yield, soil type, stubble load, soil moisture and geography. By having a rough idea of what nitrogen is left in the soil it can help make the decision of how much to apply.
Timing of a nitrogen application is arguably one of the most important factors when fertilising and will be the major causes to an increase or decrease in losses. Common practice is for growers to apply urea ahead of a rainfall event, this will help reduce volatilization.
Soil texture, wind speed, stubble load, soil organic matter, crop height and temperature can all affect the rate of volatilisation. If there is low volatilisation for some reason but still no moisture to wash it in, the urea will be trapped in the top soil and therefore be inaccessible to the root system.
Most early applications of nitrogen to wheat will result in a yield increase whilst most late applications of nitrogen will result in an increase of protein. Although this is not the case when dealing with canola, even very late applications of nitrogen on canola can result in yield increases.
The rate of nitrogen can be put down to a basic sum.
Supply at seeding + mineralisation of crop – any potential losses = rate
The difference between the supply of the soil nitrogen and the crop requirement needs to be met with the right rate of nitrogen. A general rule of thumb is that wheat will require roughly 40 kg of nitrogen for every tonne of grain produced and canola will require 80 kg of nitrogen for every tonne of seed produced. This is why it is so important to sensibly and realistically estimate the potential yield of the crop.
When applying nitrogen it is very important to avoid any potential losses. Part of avoiding losses is applying the right form of nitrogen. While it is very common practice to apply urea studies have shown losses of up to 23% for urea and 12% for liquid UAN and sulphate of ammonia over a 9 day period with a light rainfall event. Although, losses of urea will be significantly reduced if there is a rainfall event within 24 hours of application. It is important to consider your losses when estimating your yield to calculate your supply and demand.
For more information contact your local Elders agronomist.
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