西南地区小农户种薯储藏技术要点(Carah potato team)
Recommendations to improve storage in the two pilot storage warehouses in Wuxi
Pilot storage warehouse of Li Jingyou in Dabao village, JianShan Zhen
Description of current situation
This warehouse can store 50 T of potato. The farmer stores potato seeds from late May to late December. During this period, temperatures can raise to 36 °C during August and decrease to minimum -5 °C in December.
Figure 1: Monthly average temperatures and precipitations of the last 4 years in DaBao
Figure 2: Li Jingyou inside his storage warehouse
The building seems to be well insulated. The floor is cement and very clean. When the door is opened, we smell mold. It seems that there is a humidity problem. Temperature is 8 °C (Figure 3) and there is no humidity sensor. The temperature sensor is on the ceiling and not near or inside potato bulk. Potatoes are stored in bulk (50 cm high) and in bags (only one bag high). They are stored directly on the ground (Figure 2). Potatoes seems healthy and of good quality. However, we find potatoes with very thin skin and with cuts and wounds (Figure 5).
Potatoes are directly stored at low temperature without drying or healing period after harvest. This is due to different periods of harvest for potatoes that are stored together. Potatoes are directly planted after they take them out of the fridge. This could provoke condensation on the potatoes and a delay in germination.
In front of the building, we saw a lot of waste and of old rotten potatoes (Figure 4).
Figure 3: Temperature is 8°C
Figure 4: Many waste In front of the warehouse
Figure 5: On the left, damaged potato and on the right potato without good skin
Pilot storage warehouse of Xie Jinxuen in Zishu village
Xie Jinxuen has two storage buildings, a traditional one, without refrigeration and insulation, and a modern one, with insulation and refrigeration unit. The modern building was build two years ago and was used for the first time last year. The insulation seems of good quality. We did not see the temperature sensors. However, Mr Xie does not use the refrigeration unit since temperatures can drop up to -10 °C in winter. Temperatures in summer are not as hot as in Dabao, because it is on higher altitude. So he stores in his traditional storage building, which is more ventilated, until temperature drops and then stores in the new building to use the insulation to prevent potatoes to freeze. Here, the summer storage enable the healing of the potatoes. Potatoes are stored from the end of July to the end of February in bags piled on 1.5 to 2 meters height. Before storage, buildings are cleaned with a disinfectant.
Figure 6: Mr Xie in front of his refrigerated warehouse
Figure 7: Monthly average temperatures and precipitations of the last 4 years in Zishu
Figure 8: Inside Mr Xie refrigerated warehouse
Figure 9: Inside Mr Xie other warehouse
Figure 10: Potatoes are rotting in the modern storage unit. Many of these potatoes are rotten. Even after cleaning the building,, these rots may infect newly stored potatoes.
Improvements that we recommend
1. Cleanliness of the storage building and surroundings
At the time of plantation, directly after the storage building is emptied of potato seeds, the inside of the warehouse must be emptied from all remaining potatoes and cleaned with a disinfectant. At all time, the outside of the warehouse must be clean, free of potatoes, especially old abandoned ones.
This is important because diseases such as Potato Late Blight and Rhizoctonia survive in vegetal tissue such as old potatoes. If you don’t take them out, they might contaminate your tuber seeds, which will then contaminate your field with the disease. Moreover, Rhizoctonia and other diseases can subsist on or in the soil and on all surfaces on the building. So it is important to clean and disinfect the ground and walls after utilization. The surroundings of the building are also important because you pass by these surroundings every time you enter the warehouse and you can then transport some diseases inside.
In Belgium, we use thermonebulization (Figure 11) to clean the warehouses. This allows to reach all the surfaces of the building. Different products exist. Another solution is to use ozone, with a special machine.
Figure 11: Thermonebulizer
2. Quality of the potatoes that enter the storage warehouse
Potatoes must have thick skin before they are put inside storage. In Figure 5, you can. This can be obtained by killing the leaves 2 weeks before harvest. This can be done by spraying an herbicide such as diquat (bipyridilium). When potatoes have thick skin, they are less sensitive to transpiration, to diseases and will keep a better germination quality.
Potatoes with bruises, cuts or wounds due to harvest (Figure 5) must be sorted out before storage because they can be easily contaminated by diseases and can then contaminate other potatoes.
It is also important to keep the potatoes at more less 20 °C for two weeks before storing them at low temperature. We do this for the healing of potatoes that have bruises due to harvest that could not be detected and sorted out. This also prevent diseases to attack potatoes. In situation such as Dabao village, the healing could be achieved with a temperature of 20 C° in the storage building during the harvest period. In the future, new building could be compartmented in order to be able to keep potatoes in different temperatures, so that the newly harvested potatoes could be stored at healing temperature and the older one stored at a normal storage temperature (4C°).
3. Store the potatoes on wooden pallets or in wooden crates
In order to prevent humidity accumulation on the bottom of the bag, it is important that potatoes are not in contact directly with the soil and to enhance ventilation. If you choose to use wooden crates, be careful not to pile too much of them without an adapted ventilation system, or you could have some humidity problems inside crates and rotten potatoes.
Figure 12: pallets and wooden crates
4. Have a strict control of temperature and humidity parameters
It is important to monitor temperature inside the potato bags/crates/stack. We recommend to use good quality sensors. These sensors can be in a first time manually checked and therefore be very simple. We remind you that the optimal temperature is 4 °C for potato seeds conservation. If you have higher temperature, you risk having germination before planting period (Figure 14). At more than 8 °C, you risk the development of diseases.
Figure 13: temperature sensor in potato stack
Figure 14: Early germination due to too high storage temperature
Concerning the Relative Humidity, we recommend the installation of some good quality sensors, at least one inside the building. Potatoes must be dry before they enter the storage building. If they are not, you must ensure that dehydrating air is pulsed inside the building to dry the potatoes. When potatoes are dry, you must ensure that Relative Humidity is about 90 % in order to prevent both rotting and dehydration of potatoes. Mollier diagram can be used to ensure that the external air you use will not bring to much humidity and condensate on potatoes or dehydrate them. Although it is possible to manage this manually, computer based controls are more efficient. So we recommend this approach that in the future.
5. Take out potato seeds two weeks before planting
In order to have a good germination and to avoid humidity on tuber (which can lead to the development of diseases such as rhizoctonia), we recommend that you take out potato seeds two weeks before planting and leave them at external temperature on a small layer (Figure 15).
Figure 15: Heat and dry potato seeds before planting
If you have any questions or require more precisions on some topics, please do not hesitate to contact us
For the Carah potato team:Pierre and Maxime