The following content is based on a HyFarm Spudcast episode featuring COO Mohammad Arif and Tjaart Hofman from PUM Netherlands, where they discussed ways to support small and medium-sized cold store owners, especially those using bag storage for potatoes.
Bag cold storage represents a widely adopted and cost-effective method for preserving harvested potatoes, particularly in regions like India and Pakistan where smaller-scale farming is prevalent. This approach, utilizing individual bags to store potato lots, offers distinct advantages in terms of traceability and cost-effectiveness, enabling farmers to manage their produce separately and reducing the need for extensive infrastructure associated with bulk storage. However, effectively maintaining the quality of potatoes within these bag cold stores for extended periods requires careful attention to various factors, from post-harvest handling to in-store management practices.
Advantages and Context of Bag Cold Storage
The primary appeal of bag cold storage lies in its practicality for smallholder farmers. Each bag can be traced back to its respective farmer, simplifying inventory management and potentially facilitating fairer returns. Furthermore, the initial investment and operational costs associated with bag cold stores are significantly lower compared to bulk storage facilities. This cost-effectiveness makes it a viable option for a larger segment of the agricultural community. While bag cold stores are widely used for storing potatoes intended for table consumption, they can also be utilized for processing potatoes for a period of six to seven months. However, for storage durations exceeding eight to ten months, bulk storage might be considered more suitable.
Challenges in Ventilation and Air Movement
A key challenge inherent in bag cold storage systems is achieving uniform air movement throughout the stored potato mass. Unlike bulk stores, where air can circulate more homogeneously, bag stores often experience restricted airflow, particularly in the central areas of stacked bags. While the open spaces between rows and along the sides of the stacks allow for some air movement, the densely packed interiors can suffer from poor ventilation.
This lack of uniform air movement poses several risks. Inadequate ventilation can lead to the build-up of carbon dioxide (CO2) produced by the respiring potatoes, as well as the accumulation of heat generated by their metabolic activity. These conditions can negatively impact potato quality, potentially leading to spoilage and reduced shelf life. Furthermore, the uneven distribution of cold air can result in temperature variations within the store, creating localized “hot pockets” where deterioration might occur more rapidly.
To mitigate these issues, the stacking arrangement of the bags becomes crucial. Maintaining sufficient space around blocks of potato bags is essential to facilitate better air circulation. Proper layout, considering the placement of ventilation shafts and cooling units, also plays a significant role in ensuring a more uniform distribution of cold air throughout the storage facility. Ideally, cooling units should be positioned in a way that aligns with the direction of air movement to maximize their effectiveness.
Temperature Management: A Cornerstone of Quality Preservation
Temperature is a critical determinant of potato quality during storage. Effective temperature management is essential not only for preserving the inherent quality of the tubers but also for controlling respiration rates, minimizing moisture loss, and inhibiting the development of diseases and sprouts.
The initial phase after potatoes are brought into the cold store is known as the curing period. During harvesting, potatoes often experience minor injuries and wounds. The curing process, typically lasting around a week or sometimes longer, involves maintaining a relatively higher temperature (around 16-18°C) to allow these wounds to heal and form a new, protective skin layer. This suberization process is vital as it reduces evaporation and provides a barrier against pathogens.
Once the curing period is complete, the temperature within the cold store should be gradually reduced, typically by about half a degree Celsius per day. This slow cooling helps to acclimate the potatoes and maintain their quality.
CIPC Application for Long-Term Storage and Sprout Control
For extending the storage life of potatoes beyond a few months, the application of Chlorpropham (CIPC) is a common practice to inhibit sprouting. CIPC is a cell division inhibitor, and therefore, its application should only occur after the curing period is complete, as applying it prematurely would interfere with the wound healing process.
The timing of the first CIPC application is crucial for its effectiveness. It is generally recommended to apply CIPC within three weeks after the store is closed. Earlier application at lower dose rates tends to provide better sprout control compared to delaying the treatment until sprouts become visible. Dealing with established sprouts is significantly more challenging and reduces the overall storage potential of the potatoes.
However, achieving uniform CIPC distribution within a bag store presents a specific challenge. CIPC is typically applied as a very fine mist of particles that settle on the potato tubers. In a bag store setting, it can be difficult for these particles to penetrate into the center of individual bags and the core of densely stacked bag lots. This uneven distribution can lead to inadequate sprout control in the inner regions, even if the outer layers appear satisfactory.
Proper spacing between bag stacks is not only essential for ventilation but also for facilitating better penetration of the CIPC mist. The method of application, whether it’s hot fogging or fumigation, also needs to be carefully considered to maximize coverage.
Additional Considerations for Maintaining Potato Quality
Beyond ventilation, temperature, and CIPC application, careful handling of the potato bags is paramount in preserving quality. Bruising during harvesting, transportation, and loading into the cold store can create entry points for diseases and accelerate deterioration. It is recommended to minimize the falling height of tubers during field handling (ideally to a maximum of 30 cm) and to handle the bags gently throughout the entire process to avoid mechanical damage. The height of stacking bags within the store (typically around eight bags high) also presents a potential risk for pressure bruising on the lower layers, although this is often a fixed constraint in many stores.
The Importance of Training and Guidance
Given the complexities involved in managing bag cold stores effectively, providing comprehensive training and detailed guidance to farmers and cold store operators is crucial. This training should cover all aspects of post-harvest handling and storage management, including best practices for ventilation, temperature control, humidity management, and CIPC application. Tailored advice that considers the specific conditions and challenges of bag cold storage is essential for ensuring the long-term preservation of potato quality and minimizing losses. Initiatives aimed at educating stakeholders on these best practices can significantly benefit the agricultural community by enabling them to maintain the health and quality of their potato harvests for extended periods.
While bag cold storage offers a practical and cost-effective solution for potato preservation, particularly for small-scale farmers, successful long-term storage hinges on a thorough understanding and diligent implementation of best practices. Paying close attention to ventilation, maintaining optimal temperature regimes, applying CIPC judiciously, and handling the produce with care are all critical elements in ensuring the quality and extending the shelf life of potatoes stored in this manner. Continuous learning and the dissemination of detailed, practical advice are vital for empowering stakeholders to maximize the benefits of bag cold storage.
