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Bob Morton, Warwickshire

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The re-sowing decision and making a plant population calculator

Cereal production in Britain in 2013 has been heavily affected by adverse weather. Farmers have been unable to sow their normal acreage of the higher yielding winter hardy varieties: there has been a 25% decline in autumn drilled wheat; 19% fewer acres of winter barley sown, and a 30% reduction of winter oats. The unsown land means there will be much more to do this spring, and the resulting yield will be significantly lower.

Stubble in mid-March                                              Recently ploughed land                       

In addition to the unplanted acres, oil seed rape has suffered with pigeon damage, floods etc, and there will be a far higher level of crop abandonment than normal.

Adding crop abandonment to the extension of winter into April caused one leading grain trader who I Interviewed on March 28 to say he was expecting a total UK grain crop 20 per cent lower than normal. The consequence of a smaller domestic crop on prices should give uplift - but the market is global, both in terms of demand as well as supply.

Pigeons, slugs and snow and Siberian temperatures and wind chill have hit crops in many parts of the country. Seedlings in some areas are weak and look like they have little life in them. Every farmer with a crop in this condition has to decide whether to persist with what is there or grub up and replant - assuming that seed can be found and bought at a reasonable price.

The decision is based on a number of factors: one of which is knowing the number of plants you have per acre or hectare.  Plant numbers are a major deciding factor for re-sowing or not.

If only the decision was a matter of counting plants! It involves much more than this. There's a lot to think about: like the farm cropping and rotation and impact of livestock; expected sales prices, and most crucially, forward selling contracts that may have been made. Other costs such as rent or mortgage payments impact on the potential returns. The calculations are always difficult to make, and re-sowing is decision fraught with difficulty.    

                Water logged for months                       Not forward for late March, but all there          

Crop assessment and re-sowing opportunities

The number of plants you have is just one factor. Plants which are just surviving may never really recover. Land which has been heavily waterlogged or is capped has soil that needs moving for it to function at all. If the soil condition is poor and the crop looks very backward, it may well be economic to re-sow, even if the plant population itself is satisfactory.

If plant condition and population is reasonable, but the soil itself is capped, using a very light Einbock, preferably with some rows of tines removed, should break the surface and allow the soil to breathe without damaging too many plants, but some will be sacrificed in the process. There is also the problem of wheelings, unless a special wide machine is created in the workshop. (A challenge for workshop enthusiasts - send me the ideas and/or pictures!)

Plant population is an important measure. Agronomists provide figures for the ideal crop, but farmers know that a viable number of plants can be a good deal less. Oil seed rape is one that can make a decent crop with as few as 10 - 12 plants per sq m, especially if they are well distributed.
Wheat plants with space around them will tiller to compensate, but this late season there may well be less tillering than normal. Spaced out plants suffer disease less acutely, so there may be a small saving in spraying.

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Re-sowing opportunities

Despite the extension of winter into April, there's still time to get spring sown crops drilled. Spring wheat can go in right through April, Spring Rape in early April, Sugar Beet and other roots by mid May, Spring Barley up to the end of April - Cardigan has the traditional 'Barley Saturday' at the end of the month. There's time to get things planned and done - provided the weather decides to look kindly on farmers for a month or so.

  Re-sowing the headlands where there is greatest damage - soil capping will need addressing

Population calculator

Here’s a simple way to make a circular calculator using alkathene pipe. The circular shape is far superior to the square or rectangle often used, because it cuts through drill lines. Figures obtained with a square will vary considerably, depending on the way it’s positioned, even when placed on a diagonal to the drill. The circle gives you the smallest border for any given area.

Easy calculation
The clever part of this tool is that the area it describes makes it easy to find out the plant population either per hectare or per acre - or per sq ft or sq metre. Complicated? This piece makes it very simple to make and use. All you do is count the plants inside the circle, do the simple calculation which mainly consists of adding four zeros, and you have the population per acre.  The hoop is tossed onto the field so it lands randomly.  There’s no need to make any adjustments for crop rows.  


In-built maths makes it easy to calculate

A circle with a radius of 14.13 inches (dia = 28.3ins, circumference = 88.78ins) describes 1 / 10,000 of an acre.  Make your hula hoop this size and you have a plant counter that does the calculations for you – all you do is add up the plants which are growing within the circle. The metric variety is more complicated. The ring needs a radius of 56.4cm, or a width from side to side of 112.8 cm (44.3 inches) which is perhaps not the most convenient size. A hoop which represents a half hectare is almost as useful, and with a diameter from side to side of 79.6 cm or 31.3 inches, it's easier to handle, quicker to do the plant count.

Calculator dimensions

                            Hoop Diameter       Hoop area*                                Calculation                                   
                              Inches  Cms        Sq ft / sq m
(plants per acre)    28.3        71.9        4.36 sq ft        Add four noughts: so 75 plants in the hoop is 750,000 plants/ac                   
(plants/ha)             31.3        79.6        0.46 sq m        Add four 0s and x 2: so 75 plants in the hoop is 150,000 pl/ha               
*To calculate the number of plants per sq ft or sq m divide the plant number counted in the hoop by the factor shown.

Armed with the population figure, you can see how your crop compares with the ideal. Recommended sowing rates of 260 seeds per sq metre for wheat should result in a population in excess of 200 plants per sq m, and this, according to one advisor should not go lower than 150. However the cost of re-sowing in terms of seed and drilling costs need taking into account, and it might be more economic to accept a thinner crop than a more costly replacement. Recommended seed rates and plant populations do vary.

The HGCA Topic Sheet No. 36 suggests the following for winter wheat:

Target plants per sq metre - winter wheat            Plants per acre       Plants per hectare
62 plants/m2 for crops sown by late September            250852              620,000          
90 plants/m2 for crops sown by mid-October                 364140              900,000
140 plants/m2 for crops sown by mid-November           566440           1,400,000

Source: HGCA

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