Evaluation of almond shells as cover material and minor component of substrates for young plants

Almond trees are grown in southern Italy, mainly in Sicily and Apulia. It is estimated that every year no less than 100,000 m3 of almond shells (AS), the ligneous material forming the thick endocarp or husk of almond fruit, incur as byproduct which is mainly used for domestic or greenhouse heating. Sometimes almond shells are used in mixtures with other organic materials to prepare green compost. This study investigates the physical and chemical features of crushed AS and their behavior when used in vegetable nurseries. High air content, low shrinkage, low water retention, moderate swelling capacity, low EC, sub-acid pH and an appreciable lignin content are some of the observed peculiarities. Trials were carried out using a granulometry fraction of 1-2 mm, in order to evaluate the suitability as cover material for plugs, and as minor component (5% v/v) in substrates for vegetable seedlings. Data from cultivation trials showed encouraging results when AS were used as covering material. In comparison with vermiculite, AS influenced foliage growth in many cases reducing plant height, improving seedling compactness, dry matter and final quality. Moreover, an improvement in seedling quality was observed when AS were added to peat based substrates. Likewise, when used as a cover material, seedlings look more compact, and showed a higher dry matter and chlorophyll content compared to the control.