Potash rules for potatoes - OK?
Grown in practically every country of the world, Irish potatoes are now enjoying unprecedented and accelerating success, especially in Asia. Production in China, the world's largest producer, has increased by an average of more than 6% a year in the last decade whereas Indonesia's growth has increased even faster at more than 10% and Nepal's by nearly 9%. From 4.5 million tonnes in the seventies, India is now producing well over 20 million tonnes today. Potatoes are feeding more and more people every year but potatoes need feeding too. Better quality nutrition for potatoes means better quality potatoes for growers, consumers and the processing industry.
As production increases, storage becomes more important. India, for example, has been building cold storage for potatoes since 1938 and even though there are now over 1,400 cold stores this is sufficient for only about one-third of total produce. Potatoes are a high value cash crop grown in the north of the country between November and March. The season for the fresh vegetable is short because as soon as the soil temperature rises, tuber growth stops. Growers are then faced with the major problem of storage. Often their only option is to sell the crop which means that markets overflow at harvest time and prices plummet. If growers could keep their potatoes, even for a few weeks, the price they could obtain would increase well beyond the level required to cover the inevitable losses that would occur in store. Anything that could be done to increase shelf life, would be of great benefit to farmers, processors and consumers. Potash is the nutrient that is critical for better storage quality.
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levels of potash deficiency |
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Mild |
Severe |
None |
| credit: Dr J.P Singh International Potash Institute |
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In many countries, India included, potash is often neglected. The reasons are many but cost is undoubtedly a factor. Whereas India has its own factories for producing nitrogen, potash must be imported. Furthermore, unlike nitrogen, plants do not respond immediately to applications of potash. With potatoes, tuber growth, and therefore yield, are reflected in the leaves. Plants that are grown in potassium-deficient soils show early senescence of the shoots, bronzing and scorching of the leaves and increased risk of late blight. Without balanced fertilization, which means potash as well as nitrogen, there will be no bumper yield.
The International Potash Institute (IPI) has supported an extensive programme of field trials in India (as elsewhere) to investigate the effect of balanced nutrition with potash on yield and quality. Results show that yields in West Bengal could be increased to almost 30 t/ha with application of 100 kg/ha of K2O, compared to the NP control of 12 t/ha. Growers' net income could be boosted by an additional Rs 15,000 per hectare with such a yield. Potash also increases the proportion of 'A' grade tubers a clear indication of improved quality. At the time of the trials, potash use was repaid by a profit of between 14 and 19 rupees per rupee invested. In Simla, Himachal Pradesh, moderate levels of N, combined with 150 kg/ha of K2O, increased yields by 5 t/ha and net income by more than Rs 4,000/ha.
Another major development in recent years has been the growth of the potato processing industry. Again, potash has an impact on processing quality because sufficient K allows the plant to convert sugars to starch. Without sufficient K, the sugars remain and chips made from such potatoes are darker and more bitter in taste after processing. With K, yields increase, storage quality is better, dry matter content increases - and chips are a better colour and taste. All these factors please the growers, the processors - and the consumers.
