New fertiliser recommendations based on predicted yield Fertiliser use recommendations are set for change when published in the revised edition of the RB209 Fertiliser Manual in May 2017, and this was the main subject of discussion at CropTec’s Crop Nutrition seminar. Dominic Kilburn writes. AHDB’s revised edition of RB209 – called the Nutrient Management Guide – will be available in May 2017 and key changes include fertiliser rate adjustments (for wheat and winter and spring barley) being made on the predicted yield of the crop, as well as updated nitrogen rate recommendations across arable, and other, crops. That was the main message from ADAS senior research scientist Sarah Clarke (right), speaking at the CropTec event’s Crop Nutrition session. She explained that since the 8th edition of RB209 had been published in 2010, as much as £11m had been spent on relevant research and, consequently,
a considerable amount of data needed adding to the new edition – reviewed by ADAS and funded by AHDB.
Adjusting for yield Dr Clarke said that adjusting nitrogen rates according to predicted yield was already the case in oilseed rape nitrogen calculations and, based on data available, it was also worth doing in wheat and barley. “To do this growers need to be confident of achieving the expected yield and any limiting factors such as poor soil structure, disease and weed pressure or supply of other nutrients, need to be dealt with,” she suggested. “Crops shouldn’t be fertilised for high expected yield if this is unlikely to be achieved due to
other factors. Up to seven years of yield data is necessary for growers to be confident of adjusting rates according to predicted yield,” she added. Dr Clarke highlighted ADAS winter barley trials at High Mowthorpe in 2015 where adjustments in rates according to yield prediction, across a range of varieties, had resulted in much closer economic optimum rates achieved compared with current RB209 recommendations.
Urging caution Also at CropTec, Yara’s Mark Tucker (right) urged grower caution regarding the guidance to use yield as a basis for calculating nitrogen applications. The new guidance seeks to simplify what is a complex calculation and so must be used with care, he advised. “Yara has long supported the ‘measure to manage’ approach which enables farmers to achieve a level of accuracy with nitrogen applications that achieves a healthy harvest while avoiding over fertilisation to keep costs in check and protect the environment. “Unfortunately, to achieve this level of accuracy, the calculations can be complicated. RB209 is seeking to over simplify them.” Mr Tucker is worried that if applied without great care, farmers who follow the guidance may experience big disappointments come harvest time.
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Yara analytical services’ business development manager, Jonathan Telfer added that if nitrogen rates are to be pushed higher then more analysis must be used to identify limiting factors to nitrogen reaching its full potential. He said that half the UK’s arable soils were below pH 6.5 and soil deficiencies of P&K were widespread and variable. Meanwhile, it was well known that sulphur levels
were exhausted and tissue testing revealed persistent deficiencies of key micronutrients. “Only 13.5 per cent of winter wheat growing soils in the UK have adequate supplies of key nutrients and only 7 per cent of OSR soils are fit for purpose. Therefore we need to invest in soil analysis to identify the limiting factors of nitrogen usage,” he stressed.
Other changes Aside from adjustments to rates according to predicted yield, updated N rate tables will recommend a small increase (about 20kg N/ha) for wheat grown on light sands and silts, while a lack of data for spring wheat meant no change in recommended rates. Small increases for winter feed barley (10–20kg N/ha) will be seen in the new guide on light sand, silts and shallow soils. Rates for winter malting barley are set to see small rises on sands but there will be reductions for other mineral soils, as analysis had shown that a greater reduction was needed from the economic optimum to meet the 1.8 per cent grain N target. There will be rate increases of 20–30kg N/ha for spring feed barley on sands, small increases for spring malting barley on sands, and falls for other mineral soils. Other crop recommended changes included oats increased by 40kg N/ha (although not in a high lodging situation), while rye rates remain unchanged due to a lack of data. Dr Clarke pointed out that triticale now has the same recommended rates as winter wheat except that there should be a reduction by 40kg N/ha if lodging risk is high, and a reduction should occur according to crop price differential where the economic threshold to apply nitrogen to triticale is lower than wheat. ■
Adjusting N rates for expected yield in wheat and barley
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N rates should be adjusted up or down by 20kg/ha, per t/ha increase or decrease from: 8.0t/ha in winter wheat (up to 14t/ha) 6.5t/ha in winter feed barley (up to 12.0t/ha) 5.5t/ha in spring barley (up to 10t/ha) OSR remains the same at 30kg N/ha per 0.5t/ha above 3.5t/ha
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