Strategies for Enhanced Protection of Agricultural Produce in Outdoor Storage

Introduction: Agricultural produce that are stockpiled in the field are generally covered with a waterproof tarp made of polyvinyl chloride (PVC) or polypropylene material to protect them from rain. A disadvantage of these materials is that moisture is trapped under the tarp and condensation drips back into the stockpile. The higher moisture content in turn promotes microbial growth. Tarps that are waterproof yet able to liberate moisture from agriculture produce are needed to reduce the risk of microbial contamination.

Purpose: The purpose of this study was to evaluate the performance of a breathable waterproof tarp (BWT) for protection of almond stockpiles.

Methods: The performance of a new and a reused piece of BWT was compared with a standard PVC tarp (STD) during the 2015 and 2016 seasons. Relative humidity (RH) and temperature at various depths in stockpiles were monitored using an array of smart sensors connected to a data logger. Tests were conducted on samples, in triplicate, collected at trial set up and six to nine weeks after storage to determine: (i) moisture content; (ii) microbial levels; and (iii) the incidence of spoilage.

Results: In comparison with almond stockpiles covered with an STD, those protected by the BWT had lower RH and less diurnal fluctuations. Consequently, almonds in the surface layers of stockpiles under the BWT, which were most at risk from condensation run-off, had significantly lower moisture contents; lower levels (36x) of spoilage fungi; lower levels (143x) of bacteria; and lower incidence (8x) of moldy kernels. The reused BWT was, also, able to limit microbial growth in almond stockpiles.

Significance: The BWT has ensured almonds remain dry during storage, with little increase in the level of spoilage. The BWT provided effective protection when reused for a second season, thereby improving its cost-effectiveness.