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Conventional thinking has made autumn the most popular time to phosphate and potash shortfalls by applying straights. But there’s a growing body of... How autumn P and K applications reduce yield

Conventional thinking has made autumn the most popular time to phosphate and potash shortfalls by applying straights. But there’s a growing body of evidence suggests this is far from ideal in many situations.

Sajjad Awan, head of agronomy at CF Fertilisers, says the practice could lead to lower Nitrogen fertiliser use Efficiency (NfUE), reduced spring plant growth and ultimately poorer yields. But he believes there could also be environmental implications too.

“P and K are traditionally applied in autumn but many trials have shown that the timing of these applications is critical to yields, particularly on soils with P and K indices of one and below.

“Applying P and K in the spring so these vital elements are used quickly as crops are growing is potentially a better approach than leaving them in cold soils over the winter at the mercy of the weather.

“Furthermore, spring applied true granular NPKS compounds ensure P and K are available alongside both Nitrogen and Sulphur at the same time so all four nutrients can work together to promote growth.”

Significant benefits

But meeting crop nutrient requirements in this way has significant other benefits, he points out.

“The single application approach with NPKS fertilisers means you’re eliminating potentially two autumn applications using heavy machinery at a time when soils are not in their best condition for load bearing.

“With a typical fertiliser application estimated at around £6/ha, the savings in labour, fuel and machinery resulting from the single application approach are substantial.

“Independent trials have also shown CF true granular NPKS compounds can be reliably and accurately spread up to 36m in properly set up and calibrated fertiliser spreaders.”

There is a growing range of results supporting the use of spring NPKS fertilisers over separate autumn P and K applications from both formal trials and practical farm scenarios, Dr Awan says.

“Work carried out at the Royal Agricultural University shows that wheat yields 1.0t/ha more with spring-applied CF Heartland Sulphur (24-8-8 + 8SO3) compared to when P and K were applied in the autumn.

“In most situations you would probably use a conventional nitrogen source such as Nitram (34.5%N) or a true granular NS compound alongside the NPKS fertiliser in the spring, but it all depends on individual requirements.

Improved crop resilience

NPKS compounds could also help crop resilience, particularly with regard to better drought tolerance, he says.

 “Spring-applied K, in particular, supports nitrogen uptake considerably, which stimulates healthy growth of both the plant and its roots so this can also help with drought tolerance.

“Highly soluble phosphate in NPKS compound fertiliser also encourages optimum root development so plants are better able to find water when drought conditions prevail.

“These nutrients working in conjunction with the nitrogen and sulphur improve growth, maximise nitrogen utilisation and deliver the highest final yield and grain quality.”