...et al 2014, Preliminary results of soil biol and chem prop

来自 : www.researchgate.net/publicati 发布时间：2021-03-25

696 samples as well as the buffer capacity of local soils. A different behavior was observed with EC levels which were significantly higher in alperujo amended soils than in control ones; nevertheless, it is interesting to highlight that despite the observed increase, EC levels remained within normal values for local soils being insufficient to adversely affect the normal growth of olive groves. Interestingly, a long-term assay performed under Mediterranean conditions indicated that the increase in EC levels after alperujo applications is a cumulative effect, and that consecutive applications to the same soil can raise EC to undesired levels (Lopez-Pineiro et al., 2011). In this sense, despite of the differences between Mediterranean and Argentinean conditions, non-consecutive application to the same soil could be an interesting alternative to prevent EC increases. Organic Matter and Soil Nutrients Even though the dry fraction of alperujo is mainly composed by organic matter (Table 1) no differences were observed in OM content of 0-20 cm soil samples between control and alperujo amended soils (Table 2). This result does not agree with previous reports indicating that amendment with olive mill wastes increased OM content in soil (Lopez-Pineiro et al., 2007, 2008, 2011; Altieri and Esposito, 2008; Kavdir and Killi, 2008; Aguilar, 2009; Monetta et al., 2012), however, it could be due to slight differences on assay conditions. In the present study alperujo was spread in soil surface without subsequent land incorporation provoking the formation of a dry crust in soil surface that allowed only water-soluble compounds to infiltrate into the soil helped by the irrigation water, while major non-soluble components such as hemicelluloses, lignin and cellulose remained on surface. According with this hypothesis, both N and available K levels were highly increased in soils amended with alperujo (Table 2). The observed increase in N and K was also reported by others authors (Lopez-Pineiro et al., 2008, 2011; Monetta et al., 2012) and is of real agronomic interest since these elements are the main players in olive fertilizing programs. Regarding to P levels no differences were observed between control and amended soils (Table 2), this being explained by the low P content of alperujo combined with the low mobility of this element in alkaline soils. Biological Indicators Microbial diversity and stability determine the ability of a given soil to react under external changes such as agricultural practices (Kautz et al., 2004). Therefore, determination of biological indicators can show the effects of agronomic practices before it can be detected by traditional chemical parameters (Lupwayi et al., 1999). In this sense, abundance of cultivable microorganisms, content of microbial biomass carbon and OM degrading enzymes were evaluated and compared between control and amended soils. As shown in Table 3 no differences were observed in the abundance of cultivable soil microorganisms neither in the activity of organic matter degrading enzymes nor in content of microbial biomass carbon. Reported data about the effects of olive mill wastes application on biological indicators is highly variable. A recent work showed that surface application of alperujo increased the activity of key enzymes related to N, K, P, C and S soil cycles indicating a beneficial effect on microbial communities given by the high organic supply to soils (Lopez-Pineiro et al., 2011). On the other hand it is reported that due to the high content of phenolic compounds olive mill waste water application negatively affected soil microbial communities decreasing mycorrhizal root association and affecting olive tree photosynthetic rates (Mechri et al., 2007, 2008). These data indicate that the impact of olive mill residues on soil biological properties is the result of complex effects depending on both the relative amounts of beneficial and toxic compounds, as well as on other factors such as agro-ecological conditions, type and dose of olive mill residue applied and crop management system. In the present study the lack of differences in microbiological and enzymatic parameters analyzed is interesting because it may suggest that resident microbial populations involved in OM degrading processes was conserved, and main nutrients soil cycle was unaffected. This observation was expected since OM and phenolic compounds content did not present differences