Targeting Nutrition with tissue testing – Farmers Guardian – Tim Kerr
More crops could be at risk from nutrient deficiencies this season,so growers are being urged to use plant tissue testing ahead of the main fungicide timings to avoid problems through...
Excessive winter rainfall has exacerbated losses of leachable nutrients such as nitrogen, sulphur and boron, from some soils in the wettest areas.
Many crops have also experienced variable establishment and poor rooting, reducing their scavenging ability and increasing the risk of deficiencies.
However, soil nutrient status is site-specific and while soil testing in February or March provides a useful indicator of nutrient levels coming out of winter, it can be hard to tell what proportion of these nutrients are available to crops, especially if rooting is restricted.
The most effective solution is to measure what is actually getting into the plant, and do so before any deficiency symptoms become visible, says Hutchinsons fertiliser manager Tim Kerr.
In winter wheat, tissue tests should be conducted around a fortnight before the main fungicide timings, as this allows time for samples to be sent for analysis, results to come back (usually within a week) and any nutrient products to be ordered in time for application with a fungicide.
Mr Kerr says: “Testing a wheat crop three times in a season is ideal, but if you’re only going to do it once, then around growth stage 31 is an important time in cereals.”
Testing every crop on the farm is unlikely to be feasible, so he advises growers to select representative crops across the main soil types to provide a benchmark, prioritising areas where there are potential nutrient concerns.
Crop requirements for individual nutrients fluctuate through the season. To help growers tailor nutrition more accurately, Yara has introduced new growth stage-specific critical values into its testing analysis.
Tissue test reports give the actual amount of each nutrient found in the plant sample, together with a guideline target figure.
However, the guidelines for wheat and oilseed rape are now dynamic, changing depending on the growth stage of the crop due to the levels changing throughout the crop’s growth cycle.
These guideline values are based on analysis of multiple years of data compiled by Yara Analytical Services, which conducts thousands of tests each year.
A traffic light system is used to provide a visual indicator of the status of each nutrient analysed, while reports give product recommendations to rectify any issues.
Yara arable agronomist Natalie Wood says: “Given the weather and crop growth in many areas, I expect we could see a lot more nutrient deficiencies this season.”
The period around TO and Tl fungicides (GS30-32) is often when deficiencies occur, as crops are growing quickly and putting on a lot of biomass.
But problems can develop at any point in the growing season if crop requirements are not being adequately met, she says.
Yara analysis shows 63 per cent of wheat samples tested last year were deficient in magnesium and copper, while 86 per cent were deficient in boron and 73 per cent lacked adequate zinc. In oilseed rape, 87 per cent of samples showed a magnesium deficiency, while 56 per cent had a molybdenum deficit.
“Year-on-year, we find that magnesium, boron and zinc are the key nutrients where deficiency is likely in winter cereals,” Ms Wood adds.
This backs up similar research by FMC Agro and its key customers, including Hutchinsons, last year, which found magnesium and zinc to be the micronutrients most frequently below the optimum level in more than 100 plant tissue samples analysed as part of a nationwide survey.
Some 65 per cent of samples lacked sufficient zinc, while magnesium was sub-optimal in 71 per cent.
The cost of testing and correcting nutrient deficiencies should be easily outweighed by the benefits to crop health and final yield, says Ms Wood. Yara trials in winter wheat last year found an application of boron costing about £3/hectare (£1.21/ acre) gave a 0.2-0.3 tonnes/ha (0.08-0.12t/acre) yield response, worth £30-45/ha (£12-18/acre) at a grain price of £150/t.
TISSUE TESTING TIPS
Tissue testing allows deficiencies to be identified before symptoms are seen or yield is affected. It should be used in conjunction with regular soil testing, not as a replacement.
Additionally, when sampling:
- Pick the youngest, fully emerged leaves for testing. Do not use partially unfurled or old leaves
- Avoid picking leaves with disease infection
- Take a representative sample for the field/soil type
- A good handful of fresh leaves is required for testing as leaves are dried and milled for analysis in the lab
- Results are typically available within a week
- Tests vary from a nitrogen-only test, to a basic leaf analysis for N, P, K, Mg, or a broad-spectrum leaf analysis for 12 key nutrients, including N, P, K, Ca, Mg, S, B, Cu, Fe, Mn, Mo and Zn
- Be prepared to act on results and advice from a professional FACTS qualified adviser