It's great to have the reference section and detailed listing of so many potatoes as it is not easy to get this information in books generally, or even by searching the web. I can see that I'll be referring to this section regularly to get more information about the potatoes I grow, or might grow in the future.
The book also contains some wonderful tips for growing potatoes and increasing yields. It goes beyond general advice you usually get, such as remembering to earth up your potatoes and when to dig them up. Below is a summary of some of the key points (in my opinion) from the book that should help increase your potato yields.
1. The most productive potato plants are those produce a good leaf canopy, and the longer the leaves remain, the higher the potato yield. I found this interesting as we are often told you shouldn't feed potatoes nitrogen as it will just encourage leafy growth at the detriment of the potatoes in the ground. BUT, as the book says, a good leaf canopy means there is more area to intercept light, which via photosynthesis is turned into energy for the plant. This helps it develop good roots systems that extract the water and nutrients needed to increase yields.
2. Stem numbers are key. That is, the more stems that come direct from the ground and form a leaf canopy, the higher the yield. Stems that grow direct from the seed potato you planted are 'main stems' and these usually produce tubers. So the more main stems, the more tubers. Stems that branch off from the main stem are 'secondary stems' and these don't usually produce tubers unless the branching point is close to the seed potato. That is, the branching out happens quite low down at the base of the plant.
3. Watering. The key growth stage for potatoes is usually 3-4 weeks after a plant has first emerged from the ground. The plant sets tubers at this early stage, so a lack of water or soil moisture at this point will effect the yield. Potatoes of course need watering throughout their growth cycle, particularly in hot weather if you are to maintain yields. But it's particularly important that they are well watered at this point if you want your potatoes to set more tubers. And don't forget that the more organic matter your soil has, the more moisture and therefore the better chance of increased yields.
4. Foliage die back. When the foliage starts to die back, the plant is coming to the end of its life cycle. But where the foliage starts to die back is very important. If the dying back starts at the base of the plant and moves up the leaf canopy, you should have healthy tubers. However, if the lower leaves are healthy but the upper leaves are turning yellow, it may be the plant is suffering an attack from a pest or disease, or lacking nutrition.
5. Digging up. Don't start digging up all the tubers as soon as foliage starts dying, unless you intend on eating them all fresh! As the plants die back, tubers start to form a skin, called setting a skin. This helps the tubers to develop a protective layer, which is particularly important if you want to store your potatoes for any length of time. You need to allow 2-4 weeks from when die back begins before digging up the crop that you intend on storing. Allowing the tubers to set their skin helps prevent water loss, stops tubers from going soft, and reduces the risk of disease. So, for fresh earlies, harvest whilst the leaves are still green. To store, wait for the skin to set.
6. Inside the potato. Generally, though not always, lower dry matter (i.e. less than 20% starch) is typical of earlies, and usually (but not always) produces smooth waxy potatoes that are good for salads. Potatoes with a higher dry matter content (more than 22% starch), produce more floury roast/baking potatoes. For boiling potatoes, avoid using high dry matter varieties. Or if you do boil them, do so for less time, so they don't break up.
The book goes into more detail than I have here, but hopefully it gives an indication of it's usefulness. I learned a lot of new things about how to grow potatoes, and also the reasons why you should do things a particular way.
I recommend this book to anyone who enjoys growing and eating potatoes. It's intelligent and engaging, and I expect my yields will be increasing this year. And that makes for a happy belly.