Pre-storage Treatment of Potatoes and Several Practical Storage Methods Explained

1. Pre-storage treatment

Pretreating the tubers before storage can inhibit potato sprouting and plays a very good role in ensuring storage results.

(1) Sun-drying After harvesting, potato tubers can be spread out in the field to dry briefly, releasing some moisture to facilitate storage and transport. Generally, sun-drying for 4h can significantly reduce the incidence of disease during storage. If sun-drying lasts too long, the tubers will lose water and wilt, which is unfavorable for storage.

(2) Pre-storage Potatoes harvested in summer coincide with the hot season; after harvest, the potato tubers should be piled in a cool, ventilated room, cellar or shade shed for pre-storage. To facilitate ventilation, heat dissipation and turning for inspection, the pre-storage pile should not be higher than 5cm or wider than 2m, and ventilation pipes should be placed in the pile to allow ventilation and cooling. To avoid sunlight, coverings can be placed over the potato pile to block light.

(3) Sorting After pre-storage, sorting should be carried out, removing tubers with pests, diseases, mechanical damage or wilting, and care should be taken to handle them gently.

(4) Chemical treatment Proper treatment with chemical agents can inhibit tuber sprouting and also has a certain sterilizing and preservative effect. Spraying the leaves with maleic hydrazide (MH) at a concentration of 0.2% within 2 weeks to 4 weeks before potato harvest can inhibit sprouting of the tubers during storage, but if rain occurs within 48h (spring crop) or 72h (autumn crop) after spraying, the effect will decline markedly, and the spraying should be repeated.

For potatoes harvested in summer and autumn in the south, treating the tubers with methyl α-naphthaleneacetate or ethyl α-naphthaleneacetate can also prevent sprouting. The method is to take 150g to 250g of the commercially available 98% formulation of the above agent, dissolve it in 300mL of alcohol or acetone, mix it into 10kg to 12kg of powdery fine soil, and evenly scatter it over a 5000kg pile of tubers. For long-term winter storage of potatoes in the north, treatment should be carried out in the middle of dormancy; if applied too late, the effect will be poor.

2. Storage methods

(1) Indoor pile storage In some areas, tubers are directly piled indoors, on bamboo floors or other floors, and some are put into bags made of palm and then piled or hung on the floor. This method is simple and easy to carry out, but it is difficult to control sprouting; if combined with chemical treatment or radiation treatment, the storage effect can be improved. Covering to block light can also be used to inhibit sprouting, and this method is relatively ideal for storing potatoes harvested in the rainy season. In relatively cold regions such as Northeast China, pile storage is also quite successful for storing potatoes. If large-scale storage is to be carried out, a warehouse with good ventilation and a dry site can be selected, fumigated and disinfected with a mixture of formalin and potassium permanganate, and then the sorted and pretreated potatoes can be put into the warehouse and piled, with the surroundings enclosed with wooden boards, etc. To improve space utilization, indoor rack storage, box stacking, etc. can also be used.

(2) Cellar storage In a light-blocking, cool, ventilated, dry room or outdoor shade shed, build a rectangular cellar with bricks, leaving holes in the pool walls to form a lattice-wall style for ventilation and heat dissipation, then cover with 10cm to 15cm of fine sandy soil and press it down slightly; this method is suitable for warm southern regions.

In the northwest region, where the soil is clayey and firm, well cellars or cave cellars are mostly used for storage. These two types of cellars can store 3000kg to 3500kg, and because only the cellar opening is used to ventilate and regulate temperature and humidity, the insulation effect is relatively good, but it is not easy to lower the temperature in the early storage period, so pre-cooling treatment should be carried out.

In northern Liaoning, Jilin, Heilongjiang and other places, shed cellars are mostly used for storage. The height of the potato pile in the cellar should not exceed 1.5m, otherwise the temperature inside the pile will rise in the early storage period and the tubers will easily sprout and rot.

Potatoes stored in cellars easily sweat on the surface of the tuber pile; therefore, in severe cold seasons, straw curtains can be spread on the surface of the potato pile to shift the sweating layer and prevent sprouting and rotting. Potatoes stored in cellars are generally not turned after being put in, but in southern Northeast China, because the cellar temperature is higher and the storage period is longer, they may be turned 1 to 2 times as appropriate to remove diseased and rotten tubers and prevent spread.

(3) Trench burial The trench runs east-west, about 1m deep, 1m wide at the top opening, slightly narrower at the bottom, with an inverted trapezoidal cross-section; the length can be determined according to storage volume. After digging a drainage ditch on each side, let it dry thoroughly, then put in the potato tubers. The lower layer of tubers should be piled to a thickness of about 40cm, with 15mm to 20mm of dry sandy soil filled in the middle, and the upper layer of tubers should be about 30cm thick, lightly covered with fine sandy soil. Set up a temperature measuring tube about 20cm from the ground and insert 1 thermometer. When the air temperature drops below 0°C, add covering soil in stages to form a roof-ridge shape, just enough not to freeze through, and keep the trench temperature at about 4°C. When the air temperature rises in spring, cover the ground with straw, wheat straw and other materials that conduct heat poorly, to prevent the temperature in the burial trench from rising sharply.

(4) Ventilated storehouse storage In cities, ventilated storehouses are mostly used to store potatoes. The tuber pile should be no more than 2m high, and ventilation towers should be placed in the pile to do a good job of cooling in the early stage. They can also be put into baskets and stacked; where conditions permit, special wooden-slat cabinets can also be set up in the storehouse to hold the tubers for ventilation, and the storage capacity is also large, but the cost is relatively high.

(5) Cold storage Where cold storage conditions are available, the tubers can be put into baskets or wooden-slat boxes and pre-cooled first in a pre-cooling room; when the tuber temperature approaches the storage temperature, they are then transferred to the cold storage room for storage, and the storage temperature should be kept within the range of 0°C to 2°C. When stacking baskets (boxes), appropriate ventilation passages should be left so that the temperature and humidity inside the pile are uniform and consistent. During storage, regular inspections should be carried out, and diseased tubers should be removed in time to prevent spread.

(6) Chemical storage In various places in the south, it is difficult to obtain a low-temperature environment in summer and autumn; after the tubers' dormancy ends, sprouting losses are severe, so some chemical treatments can be used to inhibit sprouting. According to reports from Shanghai, Guangdong and other places, treatment with methyl α-naphthaleneacetate or ethyl α-naphthaleneacetate has a clear sprout-inhibiting effect. For every 5000kg of tubers, 100g to 150g of the agent is used, mixed with 7.5kg to 15kg of fine soil to make a powder and scattered in the pile; the application time is about the middle of dormancy, and if too late, the efficacy will be reduced. Maleic hydrazide also has a good effect on inhibiting potato sprouting, but it must be sprayed in the field during the tuber bulking period, with a mass fraction of 0.2%; applying it too early or too late will make the effect insignificant.

(7) Radiation treatment It has been reported that irradiating potatoes with 2.06C/kg to 3.87C/kg of γ rays has a clear sprout-inhibiting effect, and it is currently one of the techniques with relatively high sprout-inhibiting effectiveness for potato storage. Experiments also show that under the same dose, the higher the dose rate, the more obvious the effect. Usually, at an irradiation dose of 12.9C/kg, the cells still have vitality; at an irradiation dose below 25.8C/kg, DNA synthesis in the cells of the growth point can be blocked, and the protein colloid undergoes changes, the cell sap transforms from acidic to alkaline, the activity of enzymes in mitochondria is clearly inhibited, and the respiration intensity of the bud eyes decreases markedly.

Potatoes are prone to rotting during storage due to ring rot and late blight. Higher doses of γ ray irradiation can inhibit the growth and reproduction of these pathogens, but it will also damage the tubers and reduce their resistance. After inoculating such tubers with the pathogen, the pathogen multiplies rapidly, but this adverse effect can be eliminated by raising the storage temperature, because when the temperature is raised, cell lignification and periderm tissue formation accelerate, thereby reducing the chance of pathogen infection.