How is the potato sown? When is it harvested?

Potatoes are grown in more than 100 countries, in temperate, subtropical and tropical climates. It is essentially a "temperate climate crop", for whose production the temperature represents the main limit: temperatures below 10 ° C and above 30 ° inhibit decisively the development of the tuber, while the best production occurs where the daily temperature maintains on average 18 ° to 20 ° C.

For this reason the potato is planted in the early spring in temperate zones and at the end of winter in the warmer regions, and in places of hot tropical climate it is cultivated during the cooler months of the year. In some subtropical highlands, benign temperatures and high solar radiation allow farmers to grow potatoes year-round, and harvest the tubers 90 days after planting them (in colder climates, such as in northern Europe, they can be necessary up to 150 days).

The potato is a plant that has a great capacity for adaptation and it is good without the soil or the cultivation conditions being ideal. However, it is also the victim of a series of pests and diseases. To prevent the accumulation of pathogens in the soil, farmers avoid growing potatoes on the same land every year. Instead, they rotate the crops in cycles of three or more years, alternating for example with corn, beans and alfafa. It avoids producing other crops that are vulnerable to the same potato pathogens - such as tomatoes - in order to interrupt the development cycle of pests.

With good agricultural practices, including irrigation when necessary, one hectare of potatoes in the temperate regions of northern Europe and North America, can produce more than 40 tons of fresh tubers four months after planting. However, almost all the developed countries average production is much lower, from scarce 5 to 25 tons, due to the lack of good quality seeds and improved cultivars, to a lower use of fertilizers and irrigation, and to problems of plagues and diseases.

The seed potatoes

Seed potatoes are usually the most expensive input in potato production, accounting for 30% to 50% of production costs. In parts of the developing world where there is no official seed supply system, farmers have created their own methods of selecting seed tubers: they sell the largest potatoes for cash, they consume medium-sized potatoes at home and they conserve the smallest as future planting material.

The soil and the preparation of the earth

Potatoes can grow on almost all soil types, except where they are saline or alkaline. Soils naturally soils, which offer less resistance to the growth of tubers, are the most convenient, and soils clay or sand with clay and abundant organic matter, with good drainage and ventilation, are the best. A pH of 5.2 to 6.4 in the soil is considered ideal.

The cultivation of potatoes requires a great preparation of the soil. It is necessary to rake the soil until all the roots of the brush are removed. It is usually necessary to plow three times, rake frequently and apply the roller, so that the soil acquires the proper condition: soft, well drained and well ventilated.

Planting

It is usually not carried out with seeds, but with "seed potatoes", which are small tubers or fragments of these, which are introduced to a depth of 5 to 10 centimeters in the earth. The purity of the cultivars and the health of the seed tubers are essential to obtain a good harvest. The seed tuber must be free of diseases, have good shoots and weigh 30 to 40 gr. The use of commercial seed of good quality can increase production from 30% to 50%, compared to the farmer's seed, but the expected profits must offset the higher cost.

The density of each row of potatoes depends on the size of the tubers, and the space between the rows (see below) should allow the hilling of the crop. In general, about two tons of seed potatoes are planted per hectare. In dry rainfed areas, potato cultivation in flat soils produces more abundant crops (thanks to better moisture retention in the soil), while under irrigated conditions potatoes are grown mainly in ridges.

Stages of crop development

1. Sown seed tuber 

2. Vegetative growth 

3. Start of tuber production 

4. Growth of tubers

Care of the crop

During the growth of the potato foliage, which takes about four weeks, it is necessary to fight the weeds so that the crop has a "competitive advantage". If the brush is large, it must be removed before starting to form the ridges. These are formed by piling earth, taken from between the rows, around the main stem of the potato. The ridges, or hops, serve to keep the plant vertical and the soil is loose, prevents insect pests, such as the tuber moth, reaches the tubers, and helps prevent the growth of weeds.

Once the ridges are formed, the weeds that grow between the potato plants and on the ridge are eliminated mechanically or with herbicides. The ridges should be formed two or three times, with intervals of 15 to 20 days. The first time will be done when the plants have reached 15 to 25 cm in height, the second time is often carried out to cover the tubers.

Application of fertilizer and fertilizer

The use of chemical fertilizers depends on the amount of nutrients present in the soil (volcanic lands, for example, usually lack phosphorus), and for commercial irrigation production a large amount of fertilizer is usually used. However, the potato thrives with the application of organic fertilizer at the start of each new rotation, because it offers a good balance of nutrients and maintains the structure of the soil. The application of fertilizers must be correctly calculated according to the expected crop, the potential of the variety and the expected use of the crop.

Water supply

The soil must maintain a relatively high moisture content. The best harvests, in crops of 120 to 150 days, are obtained with 500 to 700 mm of water. In general, the lack of water reduces production when it occurs halfway through or late in the development period, rather than if it is missing at the beginning. When there is little water, it concentrates on obtaining the maximum production per hectare instead of applying it to a larger area.

Due to the shallowness of the roots of the potato, the productive response to frequent irrigation is considerable, and very abundant crops are obtained with automatic irrigation systems that substitute daily or every third day the water lost by evapotranspiration. In temperate and subtropical irrigated climate conditions, a crop of about 120 days produces crops of 25 to 35 tons per hectare, while in the tropics it is 15 to 25 tons per hectare.

Plagues and diseases

To combat diseases, some basic precautions can help avoid major losses: crop rotation, the use of tolerant varieties and healthy and certified seed tubers. There are no chemicals to fight bacterial and viral diseases, but they can be controlled by constant monitoring (and spraying when necessary) of the aphids that are their vectors. The severity of fungal diseases, such as late blight, depends mainly, after the first infection, on the climate. The persistence of favorable conditions, if not fumigated, can promote the rapid spread of the disease.

Insect pests can quickly destroy a potato crop. The recommended measures to combat them are the constant vigilance and protection of the natural enemies of pests. Even the damage caused by the Colorado potato beetle, an important pest, can be reduced by destroying the insects, their eggs and their larvae when they appear at the beginning of the season. Health, crop rotation and the use of resistant potato varieties help prevent the spread of nematodes.

Harvest

When the leaves of the potato plant turn yellow and the tubers come off easily from their stolons, it means that the potato is ripe. If the potatoes are to be stored instead of being consumed immediately, they are left on the ground so that the skin becomes thicker, because a thicker skin prevents the diseases that occur during storage and prevents the potato from shrinking due to loss of Water. However, if the tubers are left in the soil too long, it increases the chance that they will contract the fungal disease called potato pox.

To facilitate harvest, the foliage of the potato plant should be removed two weeks before removing the tubers from the soil. According to the volume of production, the potatoes are harvested with trident, plow or with commercial potato harvesters that extract the plant from the soil and eliminate the soil from the tubers by vibration or application of air. During the harvest, it is important not to injure or produce any type of lesion in the tubers that may serve as an input to the diseases during storage. To facilitate the harvest, potato climbers should be removed two weeks before removing the tubers from the ground.

Storage

Since the newly harvested tubers are living tissue and, therefore, susceptible to decomposition, it is essential to store them correctly, both to prevent post-harvest losses of potatoes intended for fresh consumption or for industry, and to ensure an adequate supply of seed tubers for the next agricultural season.

The objective of storage both in the case of potatoes for fresh consumption and for industry, is to prevent them from becoming green (chlorophyll accumulates under the skin, which is associated with solanine, which is a potentially toxic alkaloid) , and lose weight and quality. The tubers should be kept at a temperature between 6 º and 8 º C, in a dark and well ventilated environment, with a relatively high humidity (85% to 90%). The seed tubers, on the other hand, are stored under diffuse light to maintain their germination capacity and to encourage the formation of vigorous shoots. In some regions, such as northern Europe, where there is only one agricultural season and it is difficult to store the tubers from one season to the next without the use of costly refrigeration.