PRELIMINARY RESULTS OF SOIL BIOLOGICAL AND CHEMICAL PROPERTIES AFTER LAND SPREADING ALPERUJO IN INTENSIVELY-MANAGED OLIVE ORCHARDS IN SAN JUAN, ARGENTINA

Abstract

Utilization of olive oil mill wastes as olive groves soil amendment represents a simple option to recycle the residues and restore organic matter to soils. This practice has been widely evaluated in Mediterranean countries, however, there is still little consensus about the effects that it may produce on soil quality indicators. Substantial differences on climatic, soil, irrigation and management conditions as well as in the type of olive waste applied and the application method prevent to formulate wide-ranging conclusions and force to evaluate each single situation. The aim of this work was to evaluate under local conditions the use of alperujo (semi-solid by-product of two-phase olive oil mills) as soil amendment on high-density drip-irrigated olive groves. A surface layer of alperujo was applied in soils under olive trees at doses of 40 t/ha without subsequent land incorporation and soil biological and chemical parameters were evaluated after one year of the application. The results showed that alperujo amendment increased soil nitrogen (N) and available potassium (K) without affecting the levels of available phosphorous (P), water-soluble phenolic compounds (PC), C/N ratio and soil pH. Electrical conductivity (EC) was significantly increased but presenting values insufficient to adversely affect the normal growth of most crops. Regarding to biological indicators, no differences were observed in the total number of culturable soil microorganisms neither on the activity of organic matter degrading enzymes nor on the germination index of Medicago sativa seeds. Together the results indicate that soil application of alperujo under local conditions may constitute an interesting alternative to reuse this residue and supply essential nutrients to soil. Undoubtedly special attention must be taken on the increase on EC levels, therefore further long term assays must be performed.