Trials show just how low you can go

2 March 2001

Trials show just how low you can go


funded sector challenge

project aims to boost UK

wheat-growing efficiency by

improving farm practice. In

this second article profiling

the project on an Essex

farm, Andrew Swallow

reports on establishment

and nitrogen plans

SECTOR challenge trials on an Essex farm are proving to local growers just how low you can go with seed rates and why it will be vital to count tiller numbers this spring.

"The clear message to me is we do not need to encourage these crops too much and that I have got to be out there counting plants and tillers," says Robert Davidson, of Brickhouse Farm, Peldon.

He has two demonstration wheat crops in the project on his farm. Recently 15 local farmers plus project agronomists Sara Osborne and Andrew Gilchrist of ADAS walked the crops to see for themselves how the three seed-rates used had established.

Then it was back to the warmth of The Plough in Peldon to discuss how these and other crops should be managed this spring using the concept of canopy management.

"We are aiming for an increase in yield, with savings in seed, agrochemical and fertiliser costs," says Mrs Osborne.

To achieve that, counting how many plants and tillers a crop has coming up to GS30 is essential. Nitrogen and, to a lesser extent, pgrs, can then be managed accordingly.

Counts on Mr Davidsons farm reveal that both the 50kg/ha (0.4cwt/ acre) and 100kg/ha (0.8cwt/acre) seed-rate strips have produced an adequate stand. But the highest seed-rate, 150kg/ha (1.2cwt/acre), seems set to be a problem with too many plants and tillers already, says Mrs Osborne (see table 1).

Because the trial aims to demonstrate the effect of seed-rate, all three strips will be managed identically this spring. That is not how growers should approach their own crops, she stresses.

"Look at each crop as an individual management opportunity because there is no such thing as an average crop out there."

With wheat, nitrogen should be the main tool to fine-tune tiller numbers.

"Early applications are used to increase tillering so you must monitor the Green Area Index and tiller numbers before making an application," advises Mr Gilchrist. "If crops are too thick it is most important not to apply N too early. All you will end up with is a mass of surplus tillers that will be lost later."

How much nitrogen to apply is based on building a GAI of 6 at GS61, plus 40kg/ha to sustain the canopy through grain-fill. Each GAI unit contains 30kg/ha of nitrogen, making a total crop requirement of 220kg/ha of N.

But N content of the crop coming out of winter needs to be taken into account, again on the basis of each unit of GAI containing 30kg/ha. Soil mineral nitrogen (SMN) availability must also be deducted from the fertiliser requirement.

"Most soil mineral nitrogen tests are in the 50-100kg/ha range, but some can have over 500kg/ha of nitrogen available, and the ADAS record reading is 1400kg/ha."

Soil N is taken up 100% efficiently by the crop so the total SMN in the top 90cm of soil is taken off the fertiliser requirement. Testing to 90cm will be especially important this year as there could be large reserves at depth, but little near the surface, says Mrs Osborne.

Once crop content and SMN have been allowed for, the remaining nitrogen needed to build and sustain the target GAI 6 canopy must be delivered as fertiliser. But fertiliser N is only 55-70% efficient, depending on soil type.

"So for example at 60% efficiency 50kg/ha of fertiliser N is needed to produce 30kg/ha of crop N," says Mr Gilchrist.

Unlike in barley, it is difficult to manipulate tiller numbers with plant growth regulators such as chlormequat, says Mrs Osborne. Their use should be targeted at decreasing crop height to reduce the leverage on crop roots and stem bases that causes lodging.

Pgr stem strengthening and rooting effects are often overstated, she maintains.

"Stem strength and rooting is mainly determined by variety and plant population. There is no magic chemical you can spray on despite what you may read."

But in a thin crop, an application of 5C Cycocel (chlormequat + choline chloride) at the end of tillering can reduce the apical dominance, allowing secondary tillers to catch up. Waiting for mild weather before spraying is important.

"Where I would split the Cycocel, probably in two half rates, is where conditions are not perfect at the time of application. The chemical has only a very short half life in the plant."

An adjuvant such as Li700 can help get more of the Cycocel into the crop, but Mr Gilchrist sees little reason to go for more sophisticated pgr formulations.

If crops are deemed to be in danger of lodging, either because of poor root anchorage or weak stem strength, then further reducing the height of the crop will help, she says. "In these thicker crops Terpal, usually at GS33-37 shortens the top internode. It can go on with cleavers herbicides or the T2 if you are prepared to go early, but the Terpal timing is not that critical. The aim is simply to shorten the plant at a time of rapid growth."

But if canopy management has been correct, the Terpal (2-chloroethylphosphonic acid + mepiquat chloride) should not be needed, and in well established, late drilled crops, even the chlormequat could be left out, she says. &#42

Table 1: Establishment

Third wheat after grass

Shamrock drilled

Sept 29 @ (kg/ha) 50 100 165

Target November

plant pop (/sq m) 75 150 250

Actual January

plant pop (/sq m) 102 198 330

First wheat after grass

Marshall drilled

Oct 5 @ (kg/ha) 52.5 105 173

Target November

plant pop (/sq m) 75 150 250

Actual January

plant pop (/sq m) 97 159 239

Table 2: Plants and tillers

Drilling Target Target

date plants tillers

Early 100/sq m 800/sq m

Late 300/sq m 1,200/sq m

Tiller counting

To count the tillers in a crop, simply measure a metre length of row and count the shoots. Then multiply by the number of rows in a meter width. "Do that at least three or four times across the field," says Mrs Osborne. Counting points must be chosen at random to avoid biased results. "I throw my trowel and start counting where it lands." Plant counts are a little more tricky, especially in thick crops, as individual plants can be hard to identify where two or more seeds are bunched.

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