Everything you need to learn about growing potato in Australia:- 1. Introduction to Potato 2. Botany of Potato 3. Climate 4. Breeding 5. Supply of Nutrients 6. Management 7. Diseases.
Introduction to Potato:
The potato (Solarium tuberosum) is a food crop of great importance in the world. In 1974, the total area under potatoes was 22 000 000 ha. Seventy-five per cent of the world production is grown in Europe, Russia being the greatest producer. Germany and Poland have large areas of potatoes, but the United States of America has only 600 000 hectares, and Australia had only 34 000 hectares in 1976-77.
Potatoes were discovered in Peru by early Spanish explorers and taken to Europe in the year 1535, but were not grown widely until 1750. Because they are easy to grow, potatoes have become the chief carbohydrate food of millions of people.
Consumption of potatoes per head of population varies between 180 kg in European countries with a low standard of living, to 45 kg in countries with a high standard of living like Canada and the United States. Australian consumption is 49 kg per head of population.
In Australia potato production is not a big industry and most crops are grown as a sideline. The bulk of the Australian potato crop is grown in Victoria and Tasmania because these states have a more suitable climate for the crop.
Botany of Potato:
The potato belongs to the family Solanaceae. It is an annual with erect stems possessing ridges. The compound leaves are slightly hairy and stipules occur where the petiole joins the stem. Each leaf has one terminal leaflet, and two or more pairs of oval pointed leaflets. Smaller leaflets are often paired with the larger ones.
The flowers are carried in cymes at the end of the stems. Each flower bears five sepals, five petals fused at the base, five stamens and a bicarpellate ovary. The petals may be white, rose or purple. The flowers usually drop off without setting seed, but sometimes the green potato “apples” will be formed.
The potato tuber is really the swollen tip of an underground stem. From the potato stem immediately below ground level branches called stolons arise which are five to ten cm long. The ends of these stolons swell with stored starch and become tubers.
The outside of the tuber is covered by cork, and the buds or eyes have the same spiral arrangement as the leaves upon the stem. Just under the cork layer is the thin cortex layer which may carry red, brown or purplish pigments. The tuber grows in size through the activity of the cambium cells, which lie very close to the skin.
If a tuber is cut and the exposed surface left to dry, a layer of protecting cork cells is formed. Thus when large potatoes are cut into “sets” for planting, the pieces should be left until corking or tuberisation is completed.
If tubers are exposed to sunlight they will turn green. Greened potatoes contain a poisonous glucoside called solanin. Most of this dangerous layer is removed by peeling, but any which remains is rendered harmless by cooking.
Climate Required for Cultivating Potato:
Potatoes are cool climate plants. They do best where the mean summer temperature is 21°C or lower. The soil temperature governs the production of tubers. Tuber formation is greatest when the soil temperature is 17°C, and is retarded at soil temperatures above 20°C.
When the soil temperature reaches 28°C no tubers are formed, because the food made by the leaves in daytime is used up by respiration during the night. This explains why in Queensland and northern New South Wales one sometimes sees very large potato bushes with very small tubers under them.
Attempts by the farmer to keep the soil cool will result in bigger tubers. Hilling potatoes keeps the soil cool. It is for this reason that Tasmania and Victoria have more suitable climates for potatoes than New South Wales and Queensland. In New South Wales the chief potato areas are on the cooler highlands—Dorrigo, Batlow, Guyra, Red Range and Crookwell.
Potatoes need adequate soil water to grow well. An annual rainfall of 760 mm is satisfactory provided that 300 to 380 mm falls during the growth of the crop. 500 mm during growth is needed to produce a really good crop.
Irrigation of potato crops was not widely practised in the past because of the danger of second growth, but the newer potato varieties do not have this fault. The best time to apply irrigation is early to build a good plant, and then at flowering when tuber formation is rapid. If irrigation is used, potatoes are planted closer together, more fertilisers are added but a more careful watch must be kept for signs of disease.
Potatoes will grow on a wide variety of soils, such as sandy loams, silt loams, peaty soils and clays. Sticky clay soils are not suitable, but the self-mulching red loams of Batlow, Guyra and Red Range are satisfactory. In New South Wales the early crops do best on the alluvial soils of the coast, but the main crops do best on the red soils of the tablelands.
Breeding of Potato:
New potato varieties have been of grejat benefit to the industry. All the old varieties like Factor and Manhattan have now gone and their place taken by varieties like Sebago, Sequoia, Kennebec, Exton, Kurrel, and the red varieties Krana and Pontiac.
Most modern varieties have two great advantages; they are resistant to some of the worst fungus diseases, and they do not show second growth when irrigated.
The breeding of potatoes is carried out by specialists. New varieties are produced by crossing older varieties. Most potatoes do not set seed because the food made in the leaves is stored in the tubers.
However if the tubers are removed as soon as they form, flowers and seeds will be produced. The tubers to be used in crossing are placed on bricks which have been set into the soil. The tubers are then covered with sand. The plants which develop are supported by trellis.
The potato roots go down through the sand into the soil below, but the tubers are formed in the sand layer and can be removed as they form. When the flowers open, pollen from one plant can be transferred to flowers of another variety.
The green potato “apples” will contain seeds from which new varieties will grow. If the new cross produces well and is disease resistant, it will be multiplied from its tubers.
Supply of Nutrients in Potatoes:
Potatoes respond to the presence of available nitrogen and phosphorus in the soil. In most districts they do not respond to potassium. The most economical way of maintaining soil nitrogen and fertility is to use a rotation.
No land should be planted to potatoes more often than once in three years or yields will suffer. A rotation must include legumes either as green manures or pasture leys.
Although soil nitrogen will be increased by the legumes, it is desirable to add more in the form of ammonium sulphate. On the tablelands a mixture of three parts of superphosphate and one of ammonium sulphate is applied at the rate of 500 kg per ha. On poor coastal soils much heavier applications are needed.
General Management of Potato:
Potato lands must be well cultivated in order to remove weeds, to conserve water and to loosen the soil. It is usual to begin soil preparation for potatoes some months before planting. If a green manure crop is grown, it should be ploughed under about a month before planting.
If potatoes are to be kept for seed next year, they should be stored in a cool dry place. Prior to planting it is usual to sprout the tubers by spreading them out on a floor and exposing them to light.
Seed which has been sprouted emerges from the ground quicker, enabling early tuberisation while the soil is still cool. If seed potatoes are bought, they should be certified seed which is guaranteed to be free of serious diseases.
Tubers may be planted whole or cut into pieces or sets. The ideal seed is whole potatoes of small size, 40 to 55 grams in weight. If scab diseases are common, it is usual to dip the seed potatoes into a weak mercuric chloride solution (use a wooden vat) for ten minutes and then spread them in a thin layer to dry.
If there is difficulty in getting potatoes to break their dormancy and sprout, as for instance with an autumn crop, seed may be treated with acetylene gas which causes sprouting to occur.
Potatoes may be planted by hand or by using a potato planter. The distance apart of the rows varies between 68 and 90 cm and may be as much as 100 cm in drier areas. The distance apart of the sets in the rows is by custom 30 to 45 cm but good results are now coming from a much closer planting. Not only does production per hectare increase, but there is a reduction in size of tubers to a product which is more popular with the housewife.
During the growth of the crop irrigation water may be applied. The area of irrigated potatoes in Australia is increasing and yields of up to 50 tonnes/ha has been obtained. One disadvantage is that irrigated crops cannot be sold as certified seed, because irrigation tends to cover up the signs of disease.
Potatoes should be hilled properly as this not only reduces soil temperature around the tubers but also helps to keep out the potato moth.
Vine killing is the practice of killing off the tops of the plants before harvesting. This is now done by using rotobeaters or by spraying with an herbicide such as hydrochloric acid or a substance called DNO. This practice hardens off the tubers quickly and leads to earlier harvesting.
Potatoes may be dug out, ploughed out or harvested mechanically. The rotary spinners result in some damage to the tubers, and a more satisfactory machine is the elevator type harvester which digs and lifts the tubers.
Advances are now being made in marketing potatoes in an attractive condition.
Diseases of Potato:
Fungi, viruses and insect pests result in loss of production. Probably the worst insect pest is the potato moth. This pest can be controlled by hilling properly and by the use of Azinphosethyl. This insecticide is applied at the rate of one kg/ha.
In wet seasons, attacks by the late and early blight fungi may be expected. The early blight fungus only attacks the above-ground parts, but the late blight fungus also enters the tubers. Some varieties are resistant to these diseases.
Thus Sebago, Monak and Adina are resistant to late blight. Varieties which are susceptible to these diseases may be protected in a wet season by spraying with Zineb or Bordeaux mixture.
The potato virus diseases often cause severe losses, the worst being the potato leaf-roll disease. These diseases usually occur because a farmer has planted infected tubers. Provided that certified seed is planted, virus diseases should not be a great problem.