Potatoes are the world's most widely grown tuber crop and the fourth largest crop in terms of fresh produce — after rice, wheat, and maize ('corn'). Potatoes are grown in over 150 countries throughout the world. In many of these counties, it is considered a staple food. Despite recent changes in the diets of some economically developed countries, worldwide consumption of potatoes continues to increase. Potassium (K) and Sulfur (S) play an integral role in affecting the production quantity and quality of potatoes. Sulfate of Potash is a dual-nutrient that combines a high potassium content (50%) with 17% sulfur to maximize potato yields and profits.

Potato Harvest and Production

Between 2004 and 2005, the harvested acreage of potatoes grew almost 12%. And in the past 10 years, harvested acreage worldwide has grown more than 17%. Production has also increased at an annual average rate of 4.5% over the last 10 years and exceeded the growth in production of many other major food commodities in developing countries, particularly Asia. Consumption of the potato has increased in the developing world, from less than 10 kg per capita in 1961-63 to 21.53 kg in 2003 (FAO, 2007). While still less than the consumption of developed countries, all evidence suggests it will increase strongly in the future. Over the next decade, it is expected that most of the world's potatoes will be grown in Asia, Africa and Latin America.

History

The potato (‘papa’) was first grown by the Inca Indians in the Andes Mountains of South America over 6,000 years ago. Archaeologists have discovered potato remains in ancient ruins of Peru and Chile that date back to 500 B.C. In addition to growing and eating potatoes, Incas also worshipped them and buried potatoes with their dead. The Spanish Conquistadors were the first Westerners to discover potatoes when they invaded Peru in the 1530’s. Potatoes soon became a basic supply on Spanish ships, and sailors noticed that those who ate them did not suffer from scurvy - caused by lack of Vitamin C.

The popularity of the potato was slow to grow, however. The Spanish considered it a food for the underclass and used it primarily to feed hospital inmates. Illnesses related to Solanine, caused when potatoes are left too long in the light and the skin turns green, and causing the potato to taste bitter were another drawback. At the time, these perceptions and disadvantages outweighed the benefits.

It took nearly three decades for the potato to spread to the rest of Europe. The Irish adopted the potato as a food staple in the 1780s and its appeal then extended to France.

Value

The potato quickly replaced other crops as a food staple because it was a more reliable crop than wheat, which was adversely affected by Europe’s damp climates. Potatoes are easy to plant and have an exceptionally high yield per acre, many times that of any grain crop (Burton, 1969). Potatoes have a wide variety of table, processed, livestock feed and industrial uses.

Potatoes are high in dietary fiber, fat free, cholesterol free, sodium free and saturated fat free. The benefits of which have been shown to protect against long-term health problems like coronary heart disease, obesity, diabetes and some types of cancer. They are also high in vitamin C and potassium and are a great source of vitamin B6. A plain, seven-ounce baked potato provides nearly 50 percent of vitamins C and B6 recommended for adults each day, as well as 20% potassium and nearly 5 grams of fiber for about 220 calories. Potatoes are also an excellent source of complex carbohydrates that help keep the blood sugar levels steady and provide energy on a long-term basis.

Growing

The part of the plant we call a potato grows underground. It grows on a unique underground stem called a stolon. Although potatoes grow underground, they are stems, not roots, and are known as "tubers." Potatoes grow best in cooler temperatures (50-70 degrees F) in deep, loose, well-drained, moisture retentive loam.

Potatoes are grown from special potatoes called "seed potatoes" which are cut into pieces (sometimes left whole) and planted in the ground. These pieces of potato grow stems and roots from the "eyes." Because they are able to feed off the energy in the seed piece, potato plants grow very fast right from the start. Just two pounds of seed potatoes can yield 50 lbs of potatoes.

Potato plants emerge from the ground 2-6 weeks after planting, depending on weather, location and time of year. The plants grow quickly, and will begin to grow tubers just a few weeks after emergence.

Fertilization Requirements

The following fertilizer recommendations are for Russet Burbank potatoes either for the fresh market or for processing (French fries). The yield goal is 600 cwt/acre. The amounts include the vines and the tubers for nutrient removal.

• Nitrogen – 350 units per acre
• Phosphorus – 105 units per acre (expressed as P₂O₅)
• Potassium – 437 units per acre (expressed as K₂O)
• Sulfur – 60# per acre (expressed and sulfate sulfur)
• Calcium – 50# per acre
• Zinc, Manganese, Iron, Copper, and Boron in very small amounts per acre depending on soil tests. Some of these micronutrients may not be added to the fertilizer mix if soil levels are adequate.

These amounts of fertilizer would be applied if there were no nutrients in the soil, so these amounts would vary based off a soil sample.

The potato is water-stress sensitive crop. Potato plants are more productive and produce higher quality tubers when watered correctly. Potatoes are more sensitive to water stress than most other crops because they have a shallow root system. Soil moisture must be checked often. If potatoes are over-irrigated there is yield reduction, more disease problems and leaching of nutrients.

Sulfate of Potash is the recommended potassium source for potatoes because of the lack of chloride in the fertilizer mix. If a farmer were to apply 437 units of KCl to the potato field he would also apply 291# of chloride (almost as much chloride as nitrogen. Although the vines will not show any adverse effect to the chloride, excess chloride in the soil displaces nutrients and interferes with nutrient uptake resulting in reduced quality and yield.

Benefits of Sulfate of Potash – SOP

While potatoes have a relatively short growing season, they have a very high potassium (K) demand. Potassium is involved in many of the important metabolic processes, including: stimulating early growth, disease resistance, drought and frost resistance, strengthening cells, improving water-use efficiency, carbohydrate formation and storage, and photosynthesis. Potassium, of all the nutrients, is the one which is taken up in the largest amount and an adequate supply of potassium is critical throughout the entire growth process.

Potassium deficiency symptoms appear first on blades of young, fully expanded leaves as a glossy sheen with pronounced crinkling and slightly-black pigmentation. A severe deficiency causes marginal leaf scorch which eventually turns to dead tissue and final loss of leaves. (see figure A)

Sulfur, often called the fourth major nutrient, is essential for a number of critical functions, including: efficient use of nitrogen, increasing yield potential, stress and pest resistance, seed development, chlorophyll production, carbohydrate formation and vitamin synthesis. Numerous experiments in Germany, Switzerland, France, Russia, England, United States, etc. have led to the conclusion that the sulfur component of fertilizer can be responsible for appreciable increases in yield (Beaton, JD, 1966; Bertrand, D and Wolf, A, 1964; Gisiger, L, 1962). The tubers and stems have relatively high S contents, up to 0.3 and 0.5% in the dry matter respectively, indicating the high sulfur requirement of potatoes.

Like plants suffering from a lack of nitrogen, potato plants suffering sulfur deficiency turn a light green, except that the entire plant, including the younger leaves, remains light green. Severely deficient plants remain yellow and in time curl upward. (see figure B)

SOP Benefits:

• Increased Yields
• Less Shrinkage in Storage
• Higher Specific Gravity
• Improved skin set and russeting
• Low chloride content
• Reduced disease incidence
• Reduced bruising