Tuesday, June 25, 2019

Assess soil nitrogen reserves now to ensure crop success

January 2, 2019 by  
Filed under Crops

Producers are advised to pay particular attention to soil nitrogen testing over the next few weeks to make the correct decisions regarding fertiliser use later this spring.

Challenging conditions during 2018 are likely to have left a legacy of variable soil nitrogen reserves that will be difficult to estimate without accurate testing, says CF Fertilisers arable agronomist Allison Grundy.

“If ever there was a time to invest in good quality soil nitrogen testing then spring 2019 is it. Many growers were unable to apply their full amount of fertiliser last year due to the very wet conditions in the spring and in these cases, it is likely soil reserves will be low.

“Conversely, for those who did manage to get their full application on, subsequent dry weather and lower yields are likely to have resulted in less nitrogen being recovered and utilised by the crop.

“Much of this could have remained in the soil since autumn so reserves are likely to be higher than typical, especially so if we have a dry winter.”

Growers who have chosen to apply organic manures to the land before establishing their autumn crops also need to understand how much organic nitrogen is likely to be contributed to crops in the spring, she adds.

Soil reserves

“All in all, there’s a very mixed bag of indications on how all these factors will have affected the soil nitrogen supply for the 2019 crop and the only way growers will be able to make the right decisions for their own particular situation is to test the soil for nitrogen.”

But a simple analysis of Soil Mineral Nitrogen (SMN) will be insufficient to give the true picture of N reserves, Ms Grundy believes.

“SMN gives you a snapshot of what nitrogen is available at the moment in time the test is taken but fails to address the amount of nitrogen that will be mineralised and made available to the plant as the growing season progresses.

“This can be a sizeable quantity and if you don’t factor it into calculations, you could end up applying more nitrogen from the bag than the plant can use.

“This can not only result in a negative impact on the farm’s economic performance, it can also cause potential problems from an environmental perspective.”


CF’s patented and proven N-Min analysis is the only commercially available soil nitrogen test that includes Additionally Available Nitrogen (AAN), a measure of organic nitrogen mineralisation, together with SMN to give a true picture of the amount of nitrogen the soil contains, she says.

“Only by knowing what is currently available in the soil, what is likely to become available and what the plant already has taken up can you make the right decision about how much extra N to apply in any individual situation.

“Where weather conditions have been difficult, on land new to combinable crops, or where organic materials are applied, the CF N-Min test is the only practical way of working out exactly what Nitrogen you have available and what the most economic application rate is.”

Soil temperature in the spring has a profound effect on soil nitrogen mineralisation with soil moisture governing the overall uptake of soil nitrogen, she says.

“If we have a cold spring, AAN mineralised in the soil is unlikely to be available until later in the spring whilst warmer conditions, especially on lighter soil types, make soil nitrogen available earlier, so plants have the opportunity to get away quicker.

Fertiliser trials

“When you consider CF Fertiliser trials in wheat have shown yield improvements of 1.0t/ha and improved farm profitability from using CF N-Min, it is very difficult to argue against it – especially taking into account the low cost of performing the test.”

With growing concern over agriculture’s contribution to greenhouse gases and the developing Clean Air Act singling out urea fertilisers as contributing significantly to ammonia emissions, correct product choice and fertiliser management will be critical in the years ahead, she says.

“While there’s a genuine case for N-Min testing this year, in the future it will become even more important in making sure Nitrogen is used efficiently by crops and as little as possible is left unused in the system.

“One of the best ways of achieving this is to use a high quality source of ammonium nitrate (AN) such as CF Nitram (34.5%N) or an AN-based true granular compound where the N contained is directly available to the crop and is utilised with optimum levels of efficiency.”


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