Storage of excess root crops

 By JAMES LARAKI

STORING excess food for extended periods can contribute significantly to reducing food shortages, particularly during droughts, when it is uncertain when rain will fall. Modern cooling facilities could easily do the job. In developed countries with access to refrigeration technology, food is kept for long periods of time. However, it is the way around for our rural farmers as they do not have access to refrigeration or even electricity. They have to resort to other storage methods. 

Main staple foods such as sweet potato (kaukau), yam, taro and cassava have poor storage qualities. Unlike grains, these are perishable. They are susceptible to microorganisms, pests, and physical damage during harvesting and handling. As such these staples are not generally stored for extended periods following harvest. This becomes a major barrier for their optimal use and could lead to wastage. 

As diets of most of our people consist of these staples, poor storage qualities could easily lead to food shortages, making our efforts to reducing food shortages during droughts difficult. Apart from few less common traditional storage techniques, little is known of any storage methods.

Storage qualities depends on a number of factors including; respiration, senescence (dominant or plants go to sleep), and chemical processes. The following describes storage qualities of the main staples, and what could be done to improve any traditional storage techniques.

Sweet potato tubers

Sweet potato is considered as the number one staple in PNG, especially in the highlands, providing for food as well as feed for livestock. 

Most users of sweet potato do not have a storage technique of any kind. The common practice is continuous planting and sequential harvesting (selective harvesting of mature tubers from growing plants and leaving other tubers to mature). This to some extend decreases the need for storage. However, it was reported during the 1997/98 drought sequential harvesting became impossible because the soil became very dry and weevils were found to be destroying tubers stored in the soil. 

While less common, some simple methods of storage exist. These include pit and indoor storage among others, which may extend the storage of sweet potatoes by some degree. For most, however, could extend storage for only up to a month. Otherwise, not much is known of any methods for storage. 

Maintaining proper storage temperature is considered to be the most significant barrier to good storage. This could also be true for the other root crops.

Insect pests like sweet potato weevil do not help either. Thus weevil control becomes very important as it is the worst pest of sweet potato. 

The weevil bores holes in the tubers, causing them to taste bad and to rot quickly. Weevils can cause the loss of up to half of the sweet potato produced and sometimes total produced, especially during dry seasons.

Taro corms

Taro is harvested after six months and some traditional storage practices exists, but like sweet potato, taro can only be stored for a short period. Again not much is known for any storage methods.

Yams tubers

Unlike the other root crops, yam becomes senescent (dominant or sleep), and is storable for several months. Yams in many parts of the country are traditionally harvested around May to July and could be stored till October/November before replanting. For yams to be stored for extended period the following must be considered:

• Physical damage during harvesting and handling must be minimised; 
• yams must be stored in traditional yam houses or other dry shelters; and, 
• Shoots must be removed a number of times to extend the dominancy.

Cassava tubers

While production and consumption is not too popular like other root crops, cassava can survive in the soil longer. Cassava’s swollen roots unlike the other tuber crops roots that bud, act simply as carbohydrate stores that may be used by the plant, enabling it to survive during periods of drought. Storage properties of cassava can be improved by:

• Leaving tubers in the ground until need arises. This probably is the best place to store cassava during a drought;
• avoiding detachment of roots from the plant;
• pruning of all branches from the plant up to three weeks before harvest. This causes changes in the tubers that improve storage;
• reducing exposure of roots to air and moisture loss; and, 
• Sugar content may increase during storage and cassava tubers stored in the soil during a drought may become more fibrous but remain edible.

While little is known for any storage methods for most of staple crops, rural communities must use whatever techniques known to ensure enough food is available during droughts and reduce wastage as much as possible. 

Rural communities need to take ownership and do what they can in such situations rather than rely on help from outside alone. At the same time efforts must be made to develop techniques to improve storage qualities of our main staples.