October 3, 2014
Raising the Wheat Performance Bar with Nutrition
Wheat nutrition needs to go well beyond conventional N, P and K thinking if yields are to be cost-effectively pushed ahead, according to Agrii head of crop science, David Langton.
The latest information from our Best of British Wheat 15 Tonne Challenge, involving parallel field-scale studies on commercial farms and small plot trials across the research network, highlights the fundamental importance of the best-balanced nutrition throughout the growing season to consistently raise the yield bar.
Nutrition is the first essential for yield-building. We don’t have all construction plans yet. But our own work, together with contributions from some of the country’s leading crop experts, is pointing the way ahead in a number of exciting ways.
Our target for a 15t/ha crop is essentially 500 ears/m2 carrying 55 grains/ear with a 1000 grain weight of 55g. For this we need to build and maintain sufficient tillers, ensure the best possible grain set and preserve the most efficient crop canopy to support grain fill. We cannot do this without getting sufficient N, P and K into our crops. Nor can we achieve it if other essential nutrients are limiting. And the balance between them needs to remain as optimal as possible through each stage of crop development.
We know, for instance, that access to phosphate is often one of the most limiting factors at establishment, potash demand peaks at more than 300 kg/ha K2O at flowering, and extra nitrogen uptake at any time increases the demand for every other nutrient.
P and K indexes of 2 and 250 kg/ha of N may be sufficient for yields of 8-10 t/ha. Equally, at these levels there may not be much need for extra sulphur, magnesium or micro-nutrients. But for 15t/ha it’s another story. So, as we raise the performance bar we need to raise our whole nutritional game.
Clear evidence of the extent to which this is required and indications of ways it can be achieved are emerging from the past two seasons of our studies investigating a whole range of nutrient interactions on a downland site.
Here, we see classic diminishing returns from extra nitrogen above around 270 kg/ha as other limiting factors kick in. Where we apply 300 kg/ha of N or more, though, we find worthwhile responses to higher levels of P and K.
In the same way, we see insufficient sulphur limiting responses to N, P and K and vice-versa. Lack of magnesium has also limited responses to sulphur, with Kieserite (25% MgO) delivering valuable yield advantages over ammonium sulphate (with no Mg).
Particularly impressive have been the yield responses we’ve found from foliar trace elements. Interestingly, our most recent work showed no response to individual applications of zinc, copper or boron but an extra 0.5 t/ha from a mixture of the three. And this has clearly been linked to better green leaf retention during grain fill.
This underlines the importance of eliminating all the nutritional limitations if we are to make the most of every nutrient we apply. More than anything else, we’re convinced it has to be the single most important nutritional key to pushing yields towards the 15t mark.”
Our research into the timing of nitrogen applications and compost application to improve the physical and chemical properties of soils is also providing valuable contributions to the wheat performance improvement road map.
Early in the spring we want to drive tiller production and survival. Into mid-season and we’re after building the most efficient canopy and ensuring the greatest ear fertility. And later on our key objective is to sustain that canopy for as long as we can for maximum carbohydrate transfer into the grain.
Depending on crop growth and soil nitrogen supply, upwards of 325 kg/ha of fertiliser N is likely to be required to support 15t/ha. To minimise the potential for N loss through leaching, de-nitrification and lock-up by soil microbes, this is likely to mean four splits. But we need to take particular care with mid-season applications. Too much N at this stage can easily produce lush floppy canopies which are inefficient at capturing light and more prone to lodging and disease; especially so if not balanced with other nutrients.
Of course, raising the efficiency of fertiliser N from the 60% generally achieved on medium soils to say 80% by improving soil health and condition will have a major effect on the amount of N we need to apply. Which is where our work on compost application, showing valuable increases in organic matter, P & K indexes and soil condition, is proving very instructive.
We mustn’t forget either the contribution varieties with greater nutritional efficiency can make towards our 15t/ha objective. Nor the importance of complementing improved nutrition with appropriate PGR and fungicide programmes in ensuring the most efficient and robust canopies.