Crops Notes March 2007

The key determinant of spring barley yield is sowing date. One month’s delay in sowing often leads to a yield reduction of around 2 t/ha.

Sowing should take place as soon as a good seedbed can be created. The chosen seed rate, calculated from the thousand-grain weight, should lie between 350 and 400 grains per square metre. The lower rate should suffice for March-sown barley drilled into a good seedbed, however in poorer conditions, or if sowing later, the higher rate is preferable.

Normally one third of the total nitrogen (N) top dressing should be applied to all winter cereals during late tillering (late February/early March in winter barley, mid/late March in winter wheat). The remainder can then be applied during early stem extension, Growth Stage (GS) 30-32, which, for winter barley, is reached in early/mid April and by winter wheat in late April/early May.

Due to ideal sowing conditions in the autumn many winter cereal crops have established well producing crops with high plant numbers. Densely tillered wheat crops, (those with more than 1000 shoots/m²⁾, are at increased risk of lodging later in the season and nitrogen top dressings should be delayed until after GS 30.

Crops at risk from take-all, for example second wheat’s on light land, may benefit from a little extra nitrogen at late tillering.

Since 1985 atmospheric deposition of sulphur (S) has fallen by more than 25 percent in Northern Ireland.  Risk of deficiency is highest where soils are light and rainfall is low. Winter cereals should receive 20 KG S /ha (50 KG SO3 /ha) in the spring before GS 32. This is most conveniently applied as ammonium sulphate which will also add nitrogen.

Attention to detail during the handling and preparation of seed prior to planting can result in an increased early tuber yield, while optimising fry colour and skin quality.

Results from hot box testing at Greenmount of once grown home saved seed have shown that the skin blemishing diseases silver scurf and black scurf are prevalent. Seed should be treated with a fungicide pre-planting with the aim of reducing disease transmission and maximizing marketable yield.

Germination or sprouting ability of all seed lots has been good, indeed with the relatively mild winter conditions, management of sprout growth will be essential to ensure short, strong green sprouts are produced.

A number of systems are available for pre-sprouting including tray and bag systems. Systems must ensure adequate temperature control and ventilation (to control sprout growth and protect against frost) and light (to control sprout growth).

Seed of early potato varieties should be set up in sprouting boxes with the aim of promoting apical dominance i.e. producing one strong sprout per seed tuber, one stem and a small number of large tubers early. The opposite holds for maincrop potatoes where multiple sprouting is encouraged to produce many tubers which can increase in size over a longer growing season.

Maincrop seed potatoes should be set up to sprout 4-8 weeks prior to planting depending on variety and target market.

The aim in pre-sprouting late maincrop varieties such as Navan would be to accumulate 250-300 day degrees prior to planting. Working back from a target planting date of say 20 April, and allowing seven days for dormancy to break, seed set up on 1 March assuming an average daily temperature of 10 ^oC, would accumulate 264 day degrees, that is, 44 days x (10^oC - 4 ^oC ).

This system of seed preparation aims to produce seed tubers with sprouts no more than 2 mm long. Seed is stored at 3-4 ^oC until close to planting time. The refrigeration unit is then turned off for seven to ten days to allow chitting to occur.

Once sprouts of 1-2 mm have formed evenly, the seed should be cooled down again to 3-4 ^oC to prevent further sprout growth up to planting. Mini-chitting, whilst not having the benefits of earlier harvesting associated with pre-sprouted seed, produces a crop that emerges quickly and evenly.