As the spring fungicide campaign approaches, leading agronomy firm Hutchinsons is reminding growers of the need to support chemistry with well balanced crop nutrition to maximise plant health.
Disease control invariably focuses on fungicides, but while they are the primary tool for tackling existing disease and protecting crops from infection, nutrition has a big impact on plant health.
As with human fitness, well-nourished crops will be healthier and less susceptible to infection, although excessive amounts can cause problems too.
Fit, healthy crops can also better tolerate stress conditions, such as those caused by weather or spray applications, which reduces the likelihood of health problems developing, says Hutchinsons fertiliser manager Tim Kerr.
All macro and micro nutrition should be well balanced, although certain nutrients are of particular importance earlier in the season.
Potash is the nutrient with the greatest uptake demand of all arable crops, peaking at 50 kg/ha per week. Growers should note this when assessing fertiliser requirements for high yielding crops, as standard RB209 recommendations are based on an 8t/ha yield.
Potash has a major role in several plant functions, notably cell extension and maintaining the water content and turgidity of cells, says Mr Kerr.
“Turgid cells give plants a more rigid and upright structure that reduces the likelihood of lodging and physical damage, which creates a point for infection. Plants with adequate K are also better equipped to handle drought stress and maximise photosynthesis”
A high potassium concentration in the plant also increases its resistance to parasites.
Plants cannot store large amounts of potash, so enough must be available from the soil when required through peak growth periods.
“We recommend applying potash from the beginning to end of March, which gives fertiliser time to get into the soil solution in time for peak uptake.”
Nitrogen has a particular influence on green tissue development and is of similar importance to plant health as potash.
Extremes of availability can cause health issues, Mr Kerr says. For example, when insufficient nitrogen is available plants start to “cannibalise” themselves, using nitrogen from within cell walls, which increases susceptibility to infection and reduces yield potential.
Equally, excess nitrogen produces flushes of lush, soft growth and/or dense canopies that are more prone to infection and disease spread. Evidence also suggests excess nitrogen supply can increase severity of Septoria, rust and mildew.
Mr Kerr says it is essential to tailor fertiliser applications to yield potential, Green Area Index of individual crops and available soil nitrogen, especially given the propensity of nitrogen to be leached over winter. Soil mineral nitrogen testing is usually carried out in January or February, but tests can be done into early March if necessary.
“Little and often is the ideal for nitrogen fertiliser applications, but this has to be balanced with practical economic considerations.”
North Yorkshire agronomist Sam Hugill says foliar phosphite sprays, such as Advance 66 or Phorce, are a particularly good way of getting key nutrients into young crops early in the season ahead of the main fertiliser timings.
There are benefits for both tiller survival, ear numbers and overall plant health, plus the relatively low concentration of nutrients poses less potential environmental threat than bagged fertilisers can when conditions are very wet, he says.
“A relatively small volume of foliar nutrients applied early can have a comparatively big impact on crops by keeping tillers alive, which in turn increases final ear number and yield.”
Benefits differ depending on soil type, he continues. “Nutrients leach very quickly on light land, so a top-up foliar product before solid fertiliser is applied helps to kick-start growth. On heavy land tillers are often sat in standing water, or ground is too wet to put bagged fertiliser on, so slow-release products that help keep plants going and retain tillers is worthwhile.”
Sam Hugill Northallerton Summer 2017