Long term impact of organic amendments on forest soil properties under semiarid Mediterranean climatic conditions

摘要

Soil degradation affects more than 52 million ha of land in countries of the European Union (Hueso-Gonzálezet al., 2016). This problema is particularly serious in Mediterranean areas, where the effects of anthropogenicactivities (tillage on slopes, deforestation, and pasture production) add to problems caused by prolonged periodsof drought and intense and irregular rainfall (Martínez-Murillo et al., 2016). Depending on the scale of study,soil organic carbón (SOC) dynamics in Mediterranean forests have been found to be particularly sensitive tofactors related to seasonal changes in temperature and soil moisture (Casals et al., 2000; Eaton et al., 2008;Hueso-González et al., 2014). During dry periods in theMediterranean area, the lack of water entering the soilmatrix reduces organic contributions to the soil (Parras-Alcántara et al., 2016). These processes lead to reducedsoil fertility and soil loss (García-Orenes et al., 2010). Restoring the native vegetation is one of the most effectiveways to control soil degradation in Mediterranean areas, especially in very degraded areas. In the initial monthsafter afforestation, vegetation cover establishment and soil quality could be better sustained if the soil wasamended with an external extra source of organic matter (Hueso-González et al., 2016).The goal of this study was to test the effect of various organic amendments on select soil properties over a54-month period. Five amendments were applied in an experimental set of plots: straw mulching (SM), mulchwith chipped branches of Aleppo Pine (Pinus halepensis L.; PM), sheep manure compost (SH), hydroabsorbentpolymers (HP) and sewage sludge (RU). Plots were afforested following the same spatial pattern, and amendmentswere mixed with the soil at the rate 10Mg ha-1.Soil from the afforested plots was sampled in the following: (i) spring 2012 (6 months postafforestation);(ii) spring 2013(18 months postafforestation); (iii) spring 2014 (30 months postafforestation); (iv) spring 2015(42 months postafforestation) and; (v) spring 2016 (54 months postafforestation). The sampling strategy for eachplot involved the collection of four disturbed soil samples taken from the surface (0 to 10-cm depth). The soilproperties analyzed were as follows: (i) soil organic carbon (SOC); (ii) pH; (iii) electrical conductivity (EC); (iv)aggregates stability (AS) and; (v) texture (TE).Regarding to soil aggregate stability, 54 month after the afforestation, the percentage of stable aggregateshas increased slightly in all the treatments (HP, RU, PM, SM and SH) in relation to control. Specifically, thedifferences were recorded in the fraction of macroaggregates ( 0.250 mm). The largest increases have beenassociated with SM, PM and RU treatments. Although the SM, PM and RU treatments helped to maintain the SOCat high levels in the 54 months following application. Conversely, not significant differences relative to the controlplots were found for the pH, EC or texture, 54 months following afforestation. To conclude, these results showedan increase in the SOC and the stability of the macroaggregates when soil is amended with sludge, pinus mulchand straw much. This fact has been due to an increase in the number cementing agents due to: (i) the applicationof pinus, straw and sludge had resulted in the release of carbohydrates to the soil; and thus (ii) it has favored thedevelopment of a protective vegetation cover, which has increased the number of roots in the soil and the organiccontribution to it.