CONTINUITY OF PRODUCTION - A REVIEW OF THE PART PLAYED BY THE VARIETY
The National Institute of Agricultural Botany is a centre for giving advice to growers concerning suitable varieties. In the past we have usually been asked to suggest one good variety. Now, the more usual request is for a series of varieties to provide a continuity of supply to fulfil a contract throughout the season either with a processing factory, or with a prepacking company, or with a chain of multiple shops.
In some cases we have to advise that there is very little scope for using varieties to extend the season of production and the grower must rely upon a series of dates of sowing. Generally, a grower prefers to have a succession of varieties so that the whole field can be cultivated, fertilised and drilled in one operation. It is not economical to have to take cultivators, fertiliser distributors, seed drills and so on, to the field to be used for sowing one small strip only. Also, under English weather conditions it is very difficult to keep to a strict schedule - even if it is not raining, the soil may be too wet or too dry. Again, with a 5-day working week, Saturdays and Sundays have to be avoided in the programme.
For Lettuce, we do advise successive sowings, firstly because there are too few varieties available to give a continuity of cropping (see Table 1), and secondly, because most lettuce growers have irrigation and light soils which enable them to obtain good field establishment at any time in the season.
Perhaps it should be mentioned here that continuity of production usually includes uniformity of product too. A home gardener may sow butterhead, crisp and cos types of lettuce to give a succession of crop which may be acceptable for home use, but for commercial production the series of varieties must be so similar to one another that the final product is consistent throughout the season.
In addition to Lettuce, Broad Beans and Runner Beans are other crops in which sowing date is of greater importance than variety for providing a succession of crops.
Tables 2, 3, 4, 5 and 6 illustrate the range of maturity in some other crops and tend to show that a grower may be able to use a series of