Boost nitrogen to optimise strob use in spring barley
4 February 2000
Boost nitrogen to optimise strob use in spring barley
GROWERS of spring malting barley need to boost nitrogen inputs to make the most of the extra yield potential provided by strobilurin fungicides.
The danger is that extra yield following strobilurin use can dilute grain nitrogen levels, taking them below the threshold levels now specified by maltsters, warns Peter Gould, UAPs Dorset-based regional technical adviser for the west.
"Use of strobilurin on a spring malting crop provides an opportunity to boost yields, but if grain N levels are to be maintained the crop needs extra nitrogen," he says.
Most malting contracts now specify a minimum grain N level of 1.55 or more, so the amount of applied N needs to be stepped up to offset the dilution effect as well as to lift yield.
On chalkland farms of the south and west Optic used to get 100kg/ha (80 units/acre). But over the past two to three seasons, this has risen steadily to 125kg/ha (100 units/acre). Now, depending on the state of the crop and prevailing conditions, UAP is advising nitrogen rates of 150kg/ha (120 units/acre).
When the crop is growing strongly and there is no shortage of moisture this tactic is considered to be safe, but not if growth is slow and soil dry.
"We tried this out for the first time in 1999 and consistently ended up with 7.5-8t/ha crops of spring barley with 1.6-1.7N. Where we had stayed on 125kg and jacked up the yield with the fungicide the grain Ns might have slumped to below the saleable threshold. On thin soils the 125kg rate gave good yields, but grain Ns were too low for comfort."
The effects of strobilurin on winter barley are very different to the effects on the spring crop, Mr Gould notes. "On winter barley the yield response is related to the control of net blotch and late occurring brown rust. In trials on farms we have seen an extra 0.5-1t/ha in disease susceptible varieties like Halcyon in brown rust seasons.
"On spring barley yield responses to the fungicide are more related to its greening effect and longer leaf retention. This is particularly noticeable in Optic and Chariot, where we have seen a consistent yield increase of 0.6-0.7t/ha over normal fungicide treatments. But for this to be achieved the strobilurin has to be added in as an extra component to conventional triazole/morpholine treatments."
While winter barleys Fanfare and Regina are grown as feed-plus types and frequently given up to 165kg/ha (132 units/acre) on the chalks, a more cautious approach is needed with the malting type Halcyon. Where the new fungicide is used in programmes with Unix (cyprodinil) rhynchosporium is controlled so more consistent yields with a reduced level of screenings can be harvested.
"It is still possible to secure premiums of £20/t for a 1.55 or 1.6N sample, and if strobilurin is used this can be achieved together with yields of 6.8-7t/ha where 130kg/ha of N is applied," Mr Gould says. *
MATCH N TO STROB USE
• Extra yield diluting N.
• N% could miss spec.
• Boost N rate.
• Spring and winter crops respond differently.