1. Ensure that cuts will be sufficiently deep to prevent cutting the tubers.
2. Lifts enough quantity of ground so potatoes will not be not ruined in their journey.
3. Maintain stable slow cropper speed along the furrow to evade violent agitation of of elevator chains. Reduce the speed more when the ground is dry.

These damages are largely reduced in mature potatoes, because just peelings are the critical points where more damages take place quickly.

Exposure from sun heat causes rotting. This happens in only 2 or 3 days. These damages can take place as a result of direct contact with the sun at the time of being harvested. This may also occur before harvesting when the plant is dead or cut.

• The damages are proportional at the time of sun heat exposure after potatoes are harvested.

• If after sun damage the potato is stored in temperatures from 10 to 15.5° C it will not rot. At 21°C, there is little rotting. At 32° C, there is more rotting.
• In storage, the incidence of rot is higher for potatoes exposed to higher temperatures on the surface.
• Potatoes harvested in hot weather rot more than those removed in more temperate days.
• A half hour or an hour of sun is more dangerous before noon than between 2 to 4 of the afternoon.
• Rottenness is found in cuts, contusions, peelings or sites of secretions.
• When air temperature is 32°C or higher, it is not advisable to dry potatoes. Air temperature of 26.5°C or less is correct.
• It is recommended not to expose potatoes to air and sun for more than 15 minutes on days when temperatures hover near 32°C in shade.

It should be completed rapidly to avoid sun damage.

The containers that are recommended are the bottom rigid and flat baskets, padded wire baskets, or padded pails. Transferring tubers in sacks generate a larger percentage of damages unless the work is done very carefully.

Thus crop handling inside the field or transport to exterior with trucks or trailers has great importance. There are mechanical damages to potatoes before leaving field. These damages will become evident later at storage. To avoid mechanical damages in all these operations, it is necessary to convince the personnel to utilize proper handling:

The use of soft linings is recommended in trailers and trucks that transport potatoes. A straw bed should be used in trucks, or pads can be made with sewn sacks half filled with straw. These pads go first to line the truck platform, where the crop will be laid.The impact bruising during the transfer will be significantly reduced.

It is also necessary to securely tie the load to avoid movement of sacks, resulting in bruising.

Another point is that potatoes should be handled the absolute minimum number of times possible. Clearly, damage often proportional to the number of times that potatoes are transferred.

All labour involved with potato handling should be supervised carefully to guarantee an appropriate operation.

Frequent detailed inspection is needed at different process steps, to detect and to correct damages that take place.

 Figure 17:Potato Truck Transport

During sorting, ground, stones, vegetal wastes, cut or rotten tubers are separated. Sorting of harvested tubers consists of selecting tubers that show symptoms of plague or illness. Sorting is achieved manually or with sorting machines. The second case offers better advantages as for efficiency and economy. Whichever method is chosen, potato contusions or bruising are avoided. The quality of stored tubers is the most important factor that affects technical output of any storage system. To carry out this practice, potato tubers should be mature or previously cured.

 Figure 18:Potato Sorting and Grading

Potato tuber curing consists of conditioning them during a period of several days (1 to 2 weeks) in a warehouse or deposit with good ventilation and appropriate temperature. This allows wound healing or lesion suberization.

Curing is an indispensable requirement for successful tuber conservation. It is appropriate to apply curing after harvest. This is carried out by maintaining tubers at temperatures from 16°C to 21°C with 90 percent relative humidity during approximately 10 to 15 days. During this phase healing of wounds caused by potato handling will take place while avoiding water loss and fungous invasion. This wound healing is effected by the production of new layers of cells under wounds. The cell layers will become corklike. When healing is finished, the wound area will have a thick film than will serve as a protective layer.

Temperature, humidity and curing duration period should be modified for sick or damaged potatoes. Suberization temperatures will promote microorganisms development of rotten and tuber soft rupture. The potatoes affected with rotten and bacterial soft freeze will decay and will increase warehouse humidity. In this case, the relative humidity should be maintained as low as possible to prevent additional rupture.

There is no consensus regarding the ventilation regime that should be used during the curing period. Softening or condensation in the exposed tubers happens when they are fresher than those inside the pile. A small quantity of free water is generally harmless, but any excess of humidity will propitiate soft rotten areas. Continuous ventilation is recommended when condensation is present.

An alternative stage that the peasants carry out prior to potato storage is placing the tubers on a straw and muña bed in a walled place. Tubers are exposed to environment for two weeks to enable the worms collected with the harvest to fall and die after contacting the penetrating scent emanated from muña.

Also, Andean uplands climate conditions are at or near the range of temperature and relative humidity that allow appropriate wound healing or curing. These are parameters corresponding to temperatures from 15 to 21°C and humidity measurements between 85-95 percent during approximately 10 to 15 days.

Grading refers to the process of classifying tubers according to its size. The size of grading tubers will agree with the specifications dictated by seed potato standards of each country. These are the same guidelines that also establish norms for pack characteristics and for pertinent information contained on the label.

The purpose of grading for quality is to facilitate marketing, simplifying for product selection for wholesalers..

Among the benefits that grading provides to the producer are:

• It stimulates production of potato superior qualities of more economic value;
• It facilitates product concentration;
• It allows establishment of price differences in function of quality;
• It reduces marketing costs when suppressing product movement of low quality and smaller price;
• It simplifies sales based on quality. In case of potato seed, the quality should not only be judged by appearance, but rather its antecedents should be known detailing identity, sanity, origin and handling.
• In the Peru, potato for its sale will be classified as white potato, potato colour and yellow potato.

The white potato and the potato colour are classified in turn into A and B grades, according to their dry matter content.

1. White Potato: Has white or creamy peel, can have blue or rosy stains, white, blue or reddish eyes, white or creamy pulp and a rounded or snub form. The varieties considered as White Potato are:

3. Yellow Potato:

• Extra grade
• First grade
• Second grade

Potatoes for their classification in grades that are indicated next, will belong to the same variety and to be in an appropriate maturity stage (verdant won't be), not being accepted potatoes that present rotten neither scents or flavours strange (residuals from insecticides, fertilizers, etc.)

1. Extra Grade: Minimum sizes

a. White Potato 8 cm wide

b. Colour Potato 7.5 cm wide

c. Yellow Potato 6 cm wide

Aspect and Sanity: In this grade, potatoes won't present perforations or galleries, wounded or courts, neither cracks. Verdant potatoes won't be accepted with sprouting beginning or deform. It will be accepted until 5 percent of potatoes with contusions.

2. First Grade:Minimum sizes

a. White Potato 5.5 cm wide

b. Colour Potato 5 cm wide

c. Yellow Potato 4 cm wide

Aspect and Sanity: In this grade 5 percent of potatoes will be allowed with perforations or galleries, 5 percent with deformations, 3 percent with wounded or courts and 10 percent with contusions. Potatoes verdant or in sprouting won't be allowed.

3. Second Grade:Minimum sizes

a. White Potato 8 cm wide

b. Colour Potato 7.5 cm wide

c. Yellow Potato 6 cm wide

Aspect and Sanity: In this grade, 10 percent will be allowed with perforations or galleries, 5 percent with wounded or courts, 10 percent with healing and 15 percent with contusions. It will be allowed 5 percent verdant, 3 percent of sprouted potatoes and 10 percent with deformations.

In Table 12 permissible tolerances are shown for different types of damage observed in potatoes.

Table 12: Tolerances for Different Types of Damage According to Potato Grade.

Complementary rules:

1. It will be allowed that 10 percent of product weight is of size different to suitable for each grade.

2. Tolerances allowed for different damages or defects are refereed to product weight percentage.

3. It will be considered that a potato can present damages and different defects that will be graded individually.

4. Product grade qualification that has been stored will be made with the same requirements settled down in the present norm.

5. Potato grade commercial value considered in each type, it would be larger, for the extra grade potatoes.

6. The potatoes that cannot be classified in the suitable grades will be considered outside of Standard, and their sale will be carried out according to agreement between Wholesaler and Buyer, should be lower price than second grade.

a. By weight:

Extra : Tubers of 81 g or larger

First : Tubers among 60 to 80 g

Second : Tubers among 40 g to 59 g

Third : Tubers among 20 g to 39 g

b. For their form and diameter, it corresponds to their biggest traverse dimension expressed in millimetres:

For long and long oval tubers:

Extra : Tubers of 80 mm or bigger

First : Tubers among 60 to 70 mm

Second : Tubers among 45 to 59 mm

Third : Tubers among 28 to 44 mm

Please refer to Section 2.4.1.2 Curing or conditioning for details on reduction of moisture content for potatoes. Actual drying of tubers for food processing is addressed under secondary products discussed in Section 1.4.

In Washington State (USA), there was an experiment with potatoes that passed directly from harvester-loader machine to a truck provided with a tank full of sodium hypochlorite solution that washed them, whitened, and avoided impact bruises damage.

It has been that potatoes harvested in water have less blue stains and they are much more faded that tubers bulk harvested in cars or trucks; water harvest also reduces external damage. Water potato unloading when arriving at the warehouse reduces damages and eliminates the necessity to move transporters and cranes.

The tubers once arrived to the reception area they pass to conveyor belt that drive them until washing machines.

The washers consist on a tank system in which potatoes are sunk so soon arrive from field, or wash by means of a fine rain or pressure rain that avoids the soft rottenness contamination that frequently happens in tanks. This machine gives better appearance to the tubers and facilitates sorting.

From the washer potatoes pass through in a conveyor belt through an air current at 65°C for 4 minutes to remove excess humidity. If atmosphere relative humidity is lower than 70 percent, it is possible to pack still humid tubers.

 Figure 19:Potato Mechanical Washing

For potato conservation, whether under refrigeration or by using sprouting inhibitors, it is necessary to utilize packages that allow good air circulation and easy handling. It is recommended to use 50 kg sacks of open weft where superior air circulation is achieved.

Boxes of 50 kg or 100 kg capacity are recommended to pack the potato sacks featuring lateral openings for a good airflow.

 Figure 20:Potato Hand Packing in Propylene Sacks

 Figure 21:Potato Mechanical Packing

Storage is only part of total production system. The losses that are presented in this stage are affected by numerous previous factors, at harvest and pre-harvest that influence considerably tuber preservation.

Potato varieties present diverse resistance characteristics to mechanical damage in at harvest and by handling, as well as plague resistance, and rest period length and sprouting.

The different cultural practices affect physical conditions, and physiologic stage and sanitary of tuber at harvest time.

To reduce lesions risk and illnesses, it is advisable to eliminate foliage 2 or 3 weeks before harvest. It is preferable to use a contact herbicide, because cutting is not able to eliminate whole foliage, and it can propitiate appearance of some illnesses that ending affecting to tubers.

If foliage is not eliminated, it is necessary to delay harvest until tubers are very mature.

After harvest, it is necessary to protect tubers from sun exposition, since intense sunlight became tubers verdant, diminishing quality for consumption.

It is requirement for a good preservation that potatoes are dry. If they are humid, fungi and bacteria that cause illnesses and rottenness will easily attack them. For this reason, humid potatoes should be dried, by means of a quick circulation of environmental air.

It is necessary tuber selection to only store products of more quality, without impurities neither illnesses.

In storage preparatory phase, it is indispensable requirement that potato been cured.

The seed that will be stored should be disinfected after being cured and selected.

For potato preservation for direct consumption, sprouting inhibitors should be applied to extend potato shelf life of the product. Usually No Brotan is used in a dosage of one kilo per tuber tonne.

It is convenient to use a repellent against plagues. In the Andean uplands, it is common to use muña. A layer of this grass is placed under potato pile, and is continued with intercalated layers each 30 cm.

Healthy potatoes should only be stored, without damages neither decay visible signs. The potatoes dedicated to direct consumption or elaboration processes should be stored in the darkness to avoid that become green. Those for sowing are stored with diffuse light to promote the development of several vigorous sprouts in each tuber.

Due to the lack of warehouses for potato harvest preservation, most producers are forced to sale immediately their products after harvest, loosing their profits with rising economic detriment.

Appropriate facilities for good preservation of this tuber, will allow a regular supply to wholesale markets and a better product use by producers.

 Figure 22:Potato Traditional Storage

The potato is a living tissue that is subject to physiologic processes which induces to quantitative and qualitative changes in its physiologic behaviour. Among these processes, have the following:

• Transpiration: Quantitatively it is the most important and it depends on the gradient of temperature between potato pile and environmental air, relative humidity in the warehouse and tuber peel permeability.
• Respiration: It is affected mainly by pile potato temperature. Because of the respiration, potato tuber gets lost dry matter, that is to say that it diminishes the quality of the tuber.
• Sprouting: It contributes to weight and quality losses. A high temperature will favour sprouting beginning when finishing dormancy period.
• Illnesses: The illness occurrence in the storage depends on degree of initial contamination and temperature conditions, relative humidity and storage length.

The storage objective is to control these processes to maintain quality and to minimize losses tubers weight. Factors that should be controlled in storage are the followings:

• Temperature
• Relative humidity
• Ventilation
• Light

It should be executed in dark atmospheres, on a ground of muña, with good ventilation, low temperatures (6 to 8 centigrade degrees) and high relative humidity (85 to 90 percent).

To achieve tuber preservation by 5 to 6 months, it is recommended to use the product No Brotan, to the dosage of 100 gr./tonne of potato, applied to each layer 10 centimetres high of potato stored. Storage should not overcome 2 meters height.

The potato tuber is a living tissue, with such physiologic actions as the respiration and transpiration. For respiration, effect tubers consume oxygen, dry matter, producing carbon dioxide, water and heat. For transpiration effect that is proportional to the deficit of pressure of vapour (VPA), tubers become dehydrated.

An increment of temperature produces higher transpiration and respiration, what favours a quicker dehydration, quick sprouting and favourable environment for proliferation of microorganisms. From this point the importance, that heat produced by stored tubers should be extracted permanently via natural or forced ventilation, with the purpose to reduce physiologic processes velocity and to minimize losses by dehydration, sprouting and rottenness.

It is made in warehouses with diffuse light, with good ventilation, low temperatures (4 to 5 centigrade degrees) and high relative humidity (85 to 90 percent).

Basically, it consists on storing potato seed in platforms or bookcases or boxes, in such a way that the tuber doesn't receive direct light but in indirect or diffuse way. It must allow appropriate greening and good ventilation.

The main effects that produce diffuse light in tubers are the following:

• Greening

The skin and pulp of the tubers form a green coloration, being of production of chlorophyll and solanin, those that are of bitter flavour and they can end up being toxic. This is achieved with storage process to diffuse light.

• Break of apical dormancy

The vast majority of potato varieties have a positive response to break apical dormancy. This consists in that young buds from apex begin to grow while growth of old buds is suspended. In consequence, a tuber stored on diffuse light system will have higher bud number that tuber stored under darkness conditions.

• Production of small, strong and vigorous sprouts

For darkness storage system is necessary a break of sprout apical before sowing. However, in diffuse light system, it is not necessary to carry out the disbuding before sowing

• It favours the appearance of radicle primordia.

The basic knowledge of these factors will allow an appropriate storage handling.

Consequently, it can have a vigorous seed for effect of diffuse light.

There is not a storage method that is the most effective for potato handling. Method selection depends on technical, social, economic and financial factors.

In general, the simple or rustic warehouses are cheaper and in many cases can tolerate a higher losses level that in more expensive storage systems.

For selection of storage method should be considered in addition technical and economic aspects, their acceptance by consumer and producer.

• A classification of storage methods based on their physical location is considered: In field ground, by means of harvest delaying.
• In simple piles or heaps covered with straw and ground.
• In specially built or multiple purpose warehouses.

Harvest delaying or storage into ground, consist on leaving potato into ground after foliage has been eliminated by a natural process, or are induced by cutting or by using herbicides. It is the simplest method and can be used for 3 months, depending on variety, climate, ground, illnesses and plagues.

They can only be considered varieties that have a period of rest of at least three months.

The climate should be cold, with a temperature that fluctuates between 0 and 15°C.

The ground should be loamy or sandy. It should not remain humid for several hours, because it could propitiate tuber rottenness.

The main advantages of the storage into ground are:

• Low cost
• It allows a careful harvest
• Potato has a fresher appearance that potato stored in warehouses.

They are simple structures that can be employed to store potato in field. It is useful when one doesn't want to invest in infrastructures and when the labour cost is not very significant.

The system consists on to accommodate tubers in heaps and to cover them with potato layers and ground. Numerous modifications of the method exist. Method main advantages are their low cost and their adaptability to numerous situations. It is used so much by small farmers, as for farmers that work to great scale.

The excessive losses of this storage system come from rottenness, resulting from humidity penetration in heaps.

It is necessary to use sprouting inhibitors if tubers will be stored by for higher time to natural rest period.

Among method variations, one has heaps holes or piles type, covered with straw, or straw and ground, with or without ventilation duct, etc.

Premises of multiple purposes are constructions commonly used to store potato. They should maid used for other purposes, and for it are found less efficient for storage. They can be from one or several rooms of farmer's house, to general deposits of multiple purposes, inclusive with refrigeration. They are always less effective than specific buildings to store potato.

For the design of a warehouse specifically for potato, it should be defined the size that will be in function of potato quantity of potato that will store at first. It should be decided if it will consist of a single or several rooms, if the ventilation will convection or forced air and if it will provide refrigeration.

Inside warehouse, the tubers can be stored to bulk, in boxes or sacks.

The boxes are particularly useful when are stored in one room several harvests. The best thing is to use boxes of 1/2 tonne or 1 tonne of capacity. It is required of a mechanical handling.

The sacks don't offer bigger advantages with regard to the storage to bulk or in boxes. The sacks of lighter material and fabric that is more open are better than those of heavier material and stronger fabric do.

In the storage to bulk should take care about pile height that will be in function of room temperature, and ventilation conditions and refrigeration, if there were them.

Another important element in warehouse design is the relationship area/volume that affects heat transfer flow.

Specially built warehouses vary from small rustic warehouses of low cost, going by warehouses intermediate with natural ventilation, to warehouses of great capacity with forced ventilation and refrigeration.

Potato storage system in silos is one of the most traditional. It is used thoroughly in the South region of Argentina and Chile, it has been taken to Europe it is of common use in Great Britain, Ireland, Germany, Poland, among others.

The silo, in general, gets ready especially in a land site in that has been the crop to avoid transport, in the extensive farms. The potato is deposited in a gutter, or on ground surface, being the latter system more in use. It is built an array of potatoes of more or less 2 m base, 1 m high and of a length variable, 15, 20, 30 or more meters. Once deposited potatoes are cover with some protective vegetable material-canes and straw of corn or of wheat-with a thickness of 5-10 cm covering later with ground; each 2 to 5 m portholes are placed to allow certain air circulation. In Balcarce potatoes stay under these conditions until the next sowing. It is considered losses of 10-30 percent during preservation period.

In Europe, the great technological changes occurred in the last decades in agriculture and social field conditions gradually conduce to silo elimination.

Wages that are used to keep the potato in silos are not very expensive, but guard's method in warehouses allows a quicker selection and this doesn't depend on the conditions of time; besides giving permanent labour to agricultural workers of a farm in rainy periods.

The silo used in the potato main region Argentinean, the southeast of Buenos Aires County, is the pile; a simple potato heap on ground surface and that is covered with a straw layer. It has been introduced certain modifications to this low cost and primitive system, for example silos semi-underground with respiration portholes.

This is the most frequent method used in Latin America. Potatoes are placed up to a height from 1.5 to 3 m; the storage conditions depend mainly on local temperature.

With a temperature higher than 15°C of potato is not preserved more than 3 months because shows general sprouting by ending rest normal period of tubers. When choosing a warehouse for potatoes it should be considered the readiness, that can offers this for load and unload operations. It is preferable to make load from the roof or from a second floor, taking advantage of some land difference, by means of belt conveyors from the cars or trucks, and unloading from first floor.

Potato culinary quality, palatability and composition are influenced markedly by storage temperature.

In general, storage at +4°C or fewer give for result an increase in the sweet flavour and changes in consistency and colour.

a. Enough ventilation through barn, from bottom to top, to extract corrupted air and excess of humidity.

b. To avoid the light for potato-direct consumption, in order to prevent the solanin development.

c. The tubers should stay dry and mud free. A humidity or mud excess increases heat quantity on recently stored potatoes and it causes the black heart.

d. All damaged and sick potatoes should be eliminated before storage.

e. Not to store potatoes in barns of more than 4 m depth and to provide them of ventilation grills, not only lateral but on the ground.

f. Barclay and McNair (1974) studied the loss of weight of two potato varieties stored under the best conditions. It was experienced with a potato lot of variety Kennebec and another lot similar of the variety Netted Gem, placed in boxes and fixed in a design of blocks not matched in two warehouses, during 8 months.

In Table 13, the results of the experiment are shown.

Warehouse N°1 was equipped with automatic ventilation with circulation of lateral air by walls, temperature was constant at 5.6° C with 92 percent relative humidity, achieved by wetting cement floor continually. Warehouse N°2 were equipped with automatic ventilation, with air circulation by means of ducts opened up in the floor and with an automatic humidifier that maintained relative humidity in 92 percent. Temperature was 4.4°C. Each box was weighed for intervals of one month and half. Losses were calculated in percentage for the storage period and the mean difference was compared by Student t test.

It was registered a loss of 5.8 and 5.1 percent for Kennebec and 3.6 and 2.7 percent for Netted Gem in the warehouse N°1 and in the warehouse N°2, respectively. It is seen that losses in warehouse N°1 went higher to those happened in N° 2, in both potato varieties.

If one makes an economic estimate with this 5.8 percent weight loss to 100 boxes of 1/2 tonne of capacity each with potatoes prices of US $250 tonne on tonne farm, one will have a loss of 2.9 tonne, that is to say of US $725.00.

This system developed in Holland (Potato Preservation) it is based in that, during the coldest hours (night), it is possible to blow external cold air by means of fans through stored potatoes.

External heat influence should be the less possible thing to retain low temperatures that can be reached by means of warehouse night cooling.

At warehouse floor, ducts are made that are covered with wood. Channel is communicated with external air by means of a hole of fan diameter size. Through ventilation channel, there are wooden laths grills, each one of which are of an appropriate length to be lift easily and has a separation so that potatoes that are deposited above don't pass through holes while the air can circulate by them. In roof, exist several holes for air exit that can close in their inferior part by some small wooden floodgates.

The interior height of these warehouses is about 4 m. To make ventilation the external shutters and roof sliding doors open up, corresponding to air escape holes located there. Fan is started and cold air goes by feeding channel and by wooden lath grills through potatoes.

Theoretically this cold air ventilates each potato tuber, since 1/3 part of potato heap is empty space and 2/3 parts are potato mass. In fact, thousands of small channels through which air finds its road from bottom to top; air lightly heated is liberates later in potato heap superior parts and abandons warehouse through roof openings and top windows. In addition, it is continued this way with ventilation until potato temperature is equal to exterior ambient.

In Europe glass warehouses are used, similar to greenhouses, specially built to store the potatoes, high quality seeds during winter time; walls and roof parts are made up of lined glass wired in double layer; air that exists between both walls serves as insulator. To avoid that temperature increase too much, it is also applied isolation material.

In glass warehouses, you can only preserve potatoes in trays, since light should penetrate through tubers. For such a reason not very deep trays are used, as well as among trays piles. It is also necessary not to fill them until border, because this would also impede air penetration. If tubers of small size are stored, it only suits to put thin layers in trays.

It can happen that in spite of preservation to light it has excessive germination; in this case, it is necessary to pour trays content in other trays, so that bottom tubers change place and be up. From time to time, it will be necessary to change interior piles and external ones to each other.

This preservation system is one of the most expensive because potatoes occupy a great volume being in trays. Only are used by farms specialized in seed production.

The potato tubers for consumption deposited in warehouses refrigerators or in warehouses to ambient temperature, predominant in potato Latin American regions (10 to 25°C), can be treated with sprouting inhibitors chemicals to prolong storage period.

In Table 14 most common potato, sprouting inhibitors are shown.

For many years, potato storage in the Andean uplands is carried out according to farmers' uses. The potato that is harvested is sold for direct consumption and, at its time, as seed; each small or medium farmer preserve himself potato that would use by family consumption and as seed for next sowing. In addition, a small part of the crop can be used by small farmers to pay labourers or to sell whenever they need cash for purchases. This reserve could also cover demand that occurs in other producer areas when harvest time is ending, allowing continuous supply of regional markets. The storage for sale in the future is not given. This alternative is risky due to probability that it doesn't happen a enough potato price increase so that it covers storage cost, weight and quality losses occurrence, besides the farmer's necessity of paying its debts, or having cash liquidity at harvest time.

Potato weight or quality losses have relationship with tubers placement in heaps or barns and with environmental conditions that are presented inside and outside of warehouse. It is known that a tonne of tubers prepared in heaps or piles has near 0.5 m3 of air into them.

The tubers in the barn or heap should not have ground because can affect internal heat transfer rate toward air (resistance to the current of air could increase); on the other hand, sprout growth among tubers spaces also increases resistance to airflow. Air circulation (natural or forced), it is necessary to remove heat, to evacuate CO2, water and to supply oxygen. Ventilation that increases necessary air exchange will increase water loss inevitably.

Next, it is a detailed description about storage ways used by peasants in the Peru Andean uplands:

Troques, is quite employed in Cusco; it consists on storing potato on straw in dark and fresh rooms.

Taqe: Also used to store grains; it is a warehouse of circular form of 1.5 m diameter by 1 m height woven of wheat or barley straw. The taqe generally settles in dark rooms.

Kawito is a warehouse type frequently used in Paucartambo-Cusco; this is made with shelves of eucalyptus branches and straw or with adobes in which potato seed and for direct consumption is stored covered with straw at bottom part; in the top part is stored grains.

Suncho is a variation of the kawito in which shelves are wooden.

Chaclanka is a warehouse used in Mantaro valley. The chaclanka is a specially built platform through room beams on first floor. It is made of Eucalyptus trunks on which potato covered with a straw layer is spread. In this warehouse, it is only stored direct consumption potato.

The llutasca used in Corata-Puno, is a warehouse in which potato is gathered supporting it on wall then covered it with straw and ground storing it by 4 or 5 months.

The pinakancha, used in the department of Cusco; consists on placing potato among wall fences forming heaps that cover with straw. The pirhua is a pinakancha variation; it is a circular warehouse made of straw tied with ropes and where potato can be stored in the bleakness from May through November.

The qoto, is another variant of the pinakancha where seed potato is placed in heaps and covered with straw. Each heap contains only 30-50 kilos of potato.

In the pampasc'a, potato tubers stay underground in a 4x 1.5 m rectangular hole and whose depth is a man height; bottom is covered with stones on which ichu is placed. The ichu is also placed between wall and tubers; at the end, tubers are covered with ichu and ground levelling with soil. This storage form is called pogullo or huaco in Mantaro valley.

A variant of pampasc'a is montonasq'a which consists on forming large tuber heaps that are covered with ichu and ground, that resembles the pitra and that it is used in Mantaro valley.

The shunto is used at higher altitudes, a method that consists on extending potato on field covering with ichu straw. Superficial potatoes possibly freeze, appear black and dry off forming a waterproof cover that protects those underneath.

Another form of storing potato in Matachico (Jauja, Junín) it is the trojasystem. The troja is a weave of wheat shafts with ichu ropes that closes in cylinder form placing alternately in its interior muña layers and potato; at the end a layer of muña is placed.

Storage in holes is used in Chamis-Cajamarca. The entrance of a hole is narrower in this warehouse. It consists of placing ichu straw and branches of hanca(muña) at the bottom and along the walls. It is filled alternately with layers of potato and chanca branches until contents are covered at the end with straw and soil arriving at the ground level. Elder, marco and molle branches are also used. If the potato risks attack by pests, ash is sprinkled.

In Chamis-Cajamarca, named troja to seeds storage in a small house built of adobe or quincha with a straw roof of straw of three floors or levels. First underground level or semiunderground level is used as a ventilation chamber and to store tubers or firewood. Second level or intermission presents two dark chambers to store up to 80 arrobas, the third level is a house entrance, which communicates with the second level.

Losses during the storage are affected so much by physiologic tuber condition, mechanical damage suffered during harvest and handling, as well as by storage conditions

Mechanical damage (cuts and contusions) facilitates invasion and development of microorganisms that cause illnesses and rottenness.

In Table 15 weight and rottenness, losses are shown during storage of Russet Burbank potato variety, considering different physical damage characteristics when entering warehouse.

The physical damage causes a tuber stress condition, what originates an increment in potato tuber respiration activity, with a weight loss increase.