Dry weather makes challenging work for crop nutrients
Dry weather makes challenging work for crop nutrients
Maintaining the correct
nutrient status of crop
plants is a challenge,
particularly in a dry spring.
Our latest baseline article
provides some pointers
WHY wait until crop symptoms appear before diagnosing a trace element deficiency, asks Gidon Bahiri, foliar and sap manager with Omex.
With the right test programme and a good knowledge of soils, most deficiencies can be avoided before they cause damage.
"Doing a sap test at the appropriate time gives you two weeks advance notice of any likely shortfall. Checking the nutritional status of a crop at key times of year is a good insurance, especially with high value crops, where quality issues and visual appearance are so important."
Cereals
Manganese is the trace element most likely to be in short supply in cereals, particularly on high pH soils. "There are soils which have a manganese problem year on year," he says. "These situations dont need testing – growers will be applying manganese as a matter of course."
Where deficiency is identified elsewhere it is cheap to put right, costing less than £2.50/ha (£1/acre) to apply manganese. "Even growers with deficient sites, who have to spray 5-6 times in a season, wont be out of pocket."
Magnesium and copper are the other two trace elements that show up at low levels in many tests. "These are more difficult, in that they dont appear every year. So a test helps to get them right."
Mr Bahiri believes there are two critical stages for testing winter cereal and oilseed rape crops. "The first is in the autumn, either October or November, just before the plant shuts down for the winter.
"If certain trace elements are lacking, it makes plants less winter hardy. Anything that needs correcting can be co-applied with the BYDV spray."
Seven elements should be tested for in the autumn – nitrogen, phosphate, potash, sulphur, magnesium, manganese and copper, plus boron in oilseed rape.
The second timing is from late March, during stem extension. "The crop goes through very rapid growth and theres a high demand for nutrition. Although the days are warmer, often the soils are still cold."
Testing is simple. Send around 50 leaves in a bag to a laboratory and the results will come back within 48 hours, he says.
Potatoes
Both potato yield and quality are at risk if trace elements are deficient. "Tuber number, tuber size and skin finish can all be affected. So it is worth doing three tests over the five month growing season," Mr Bahiri explains.
Do the first test 2-3 weeks after emergence, as cold soils may struggle to meet crop requirements. The second test is done at tuber initiation, when growers should check phosphate and calcium levels in particular.
"If phosphate is too low, the crop wont produce as many tubers, which can be critical with some varieties. And calcium is important to prevent rust spot developing, as well as for skin finish and skin set."
The third test is done at mid-bulking, in June or July, to check the crop has enough to sustain it. "A common deficiency at this time is nitrogen," reveals Mr Bahiri. "If its been very wet, nitrogen may have been lost." *
TRACEELEMENTS
1Sap Testing Appropriate testing programme gives 2 weeks advance notice of any problems.
2 Manganese The most common deficiency in winter cereals.
3 Copper and Magnesium Other regular deficiencies in cereals.
4 Boron Oilseed rape very responsive, so include in test.
5Timing Check cereals and oilseed rape in autumn and at stem extension in spring.
6Test Requirements Collect 50 leaves and send to lab.
7 Potatoes Test 3 times in growing season; 2-3 weeks after emergence, at tuber initiation and at mid-bulking.
8 Phosphate Levels determine tuber number.
9Calcium Affects tuber quality.
10Nitrogen Common deficiency in potatoes in wet season.
Nutrient testing
There are big differences between tissue and sap tests, says Mr Bahiri. "With a sap test, the leaves are frozen so that the cells burst. This then shows what nutrients are contained in the xylem and phloem transport systems, indicating what is available for the plant to use." A tissue test is different because although it shows the nutrients in the plant, it doesnt tell growers what is available to the plant. "Some nutrients are locked in, so the plant doesnt benefit," Mr Bahiri comments.