As fertiliser prices increase, so do the number of reasons to make sure you're not using more than you need.
Arable growers, concerned about rising fertiliser prices, are being advised to invest in thorough soil testing to ensure they are not spending any more on fertiliser than is necessary.
FAR Environmental Researcher, Dirk Wallace, says this is particularly the case for nitrogen (N), where over application can result in undesirable environmental and financial impacts.
“We strongly recommend growers to carry out soil nitrogen testing before applying N fertiliser. Over application of N isn’t just a waste of money, it also results in increases farm nitrous oxide emissions and increases the risk of N losses to freshwater.”
Dirk says the soil mineral N test measures how much plant available nitrogen (nitrate and ammonium) is available to your crops right now, for free, and the results can be used to adjust N fertiliser input using the following equation:
Fertiliser N (kg N/ha) = Crop N requirement (kg N/ha) – Soil mineral N (kg N/ha).
It is best to run a soil mineral N test as close to fertiliser application as possible. This is because soil N supply is driven by temperature and moisture, so as the season progresses more N is made available. The new hot water extractable organic nitrogen test can be used to predict how much nitrogen might become available from the soil over a three month period (called potentially mineralizable nitrogen), however, this test does not include a measure of what is there right now (mineral N). Our advice is that if you are interested in measuring potentially mineralizable N, make sure you also include a measure of soil mineral N – this way you know what you’ve got in the bank to start off with and an indication of much you may get over the season.
He adds that as the season progresses, the Nitrate Quick Test and the Quick Test Mass Balance Tool can be used to adjust in season N applications to meet current soil and growing conditions.
“This DIY test takes 30 minutes and costs just $2 per test, which is pretty good, considering that recent FAR research showed that using it can increase your dollars returned on dollars spent on N fertiliser by 290%.”