20 March 1998

Define objective before you choose your variety….

Maize variety selection is

not easy with so many to

choose from. Robin Turner,

convenor of the British

Society of Plant Breeders

maize crop group, offers

some advice to help make

the decision easier

CHOOSING a variety is the most common difficulty reported by maize growers despite there being no shortage of choice.

There are 53 varieties on the current NIAB Descriptive List and many more not listed but commercially available. Each comes with a range of information detailing performance and extolling individual features and benefits.

The first step in selecting which one to grow is to decide your main objective in growing maize. Is it starch content or high forage yields? Is maize a replacement for poor grass growth? Is dry matter intake and therefore dry matter content most important? Priority for one objective is likely to mean a compromise on others and will affect variety choice.

Maize is not a natural crop for the UK. The main limitations to growth are a low temperature – both in spring and total accumulated heat – water stress and exposure to wind. It is important to understand how these factors affect growth and how they can be reduced by correct variety choice.

Low spring temperatures restrict germination and prevent early leaf development. Without this leaf the plant cannot use the available sunlight and fails to grow. This phase can last for the first six to eight weeks after drilling, accounting for a loss of up to one third of the growing season. Differences in variety scores for early vigour are therefore important. Real differences exist between varieties of a similar maturity level and across maturity groups (see table) allowing positive selection.

Variety growth is influenced by the amount of heat accumulated during the season. There is a strong relationship between variety maturity and the heat needed to reach this. Variety requirements range from 2200 to 3000 OHU (Ontario Heat Units) for early to medium maturing varieties. Heat accumulated in the UK varies with season, location and height above sea level. Average temperature in May decreases by 1C for every 91m (300ft) increase in elevation. Varieties also differ in the heat required for each phase of growth – early vegetative growth, pollination, grain fill and maturity. Distribution maps are available that show the pattern of accumulated heat within the UK.

Pay more attention to the accumulated heat figures for your own farm (and fields) and use this to determine the latest maturing variety you can safely grow. Later maturing varieties produce significantly more yield without penalising starch if harvested at the same dry matter content. Maize accumulates dry matter at 2%/week as maturity progresses. A grower harvesting a variety of maturity class seven in mid September could alternatively harvest a variety of maturity class five in early October at a similar dry matter and starch content but with extra yield and a lower cost/t.

Water stress can also be a major limitation to maize growth. It occurs more often and in more locations than is generally recognised. Moderate stress during early growth can reduce total yields whereas a moderate to severe water deficit – for one to seven days, during pollination can reduce grain content by 20-50%.

Exposure to wind is mainly recognised as a risk of lodging. However, constant exposure reduces the average temperature, increases moisture loss through transpiration and the risk of lodging or brackling. Varieties differ significantly in their standing ability and should be selected accordingly.

Decide what you want from maize. Then make a realistic appraisal of the limitations to growth on your farm in an average and a difficult season – the worst case scenario. Then set targets for yield, dry matter content, quality – starch and digestibility – and all the main agronomic characters.

Variety choice is your responsibility; it should not be handed over to anyone else. Ideally, selection should begin by ranking characters in order of importance and setting minimum target levels for each. Choose what is important and select a variety with the best combination of characters to match this most closely. Do not assume early maturity is essential. Many other varieties are capable of reaching 30-32% dry matter content and with higher total yields. Those that offer good cob ripeness scores will also produce acceptable starch levels. Look for varieties that offer additional yield or quality but at least risk. Remember even a small difference in digestibility can make a big difference to animal performance.

EXAMPLES OF DIFFERENT VARIETY PROFILES WITHIN MATURITY GROUPS

________________________________________________________________________Maturity Variety Relative Yield Early Vigour Cob Ripeness Lodging

Group % of 14.17t/ha Score Score Score

________________________________________________________________________9/10 Nancis 93 8.4 9.8 6.7

7 Reinold 97 8.6 6.7 6.0

________________________________________________________________________5 Manatan 99 9.1 8.1 8.2

Sovereign 93 9.1 9.0 5.0

________________________________________________________________________Minimum 4 0.3 0.35 0.5

meaningful

difference

Varieties differ in pollination, grain fill and maturity, says Robin Turner.

Examples of different variety profiles within

maturity groups


Maturity Variety Relative yield Early vigour Cob Ripeness Lodging

group % of 14.17t/ha score score score

9/10 Nancis 93 8.4 9.8 6.7

Reinold 97 8.6 6.7 6.0

7 Husar 100 8.1 8.5 8.3

Lincoln 103 8.9 8.3 6.4

5 Manata 99 9.1 8.1 8.2

Sovereign 93 9.1 9.0 5.0

Minimum 4 0.3 0.35 0.5

meaningful

difference