Influence of Intensive and Super-Intensive Olive Grove Management on Soil Quality-Nutrients Content and Enzyme Activities

Agricultural soil quality is an issue that has been widely debated in the literature in recent decades. Three olive grove areas (one in Lisbon and the others in Santarém, Portugal) with different management techniques (intensive and super-intensive) were selected. Nutrient concentrations and enzyme activities of soils were determined, as well as the C and N of litter and pruning waste (mulch) to estimate the influence of management techniques on the quality of olive grove soils and to assess the extent to which they are affected by organic covers and different cultivation intensities. Organic C and total N concentrations in soils of the intensive olive grove in Lisbon were the highest when compared with those in the intensive and super-intensive olive groves soils of Santarém. The concentrations of Ca, Mg, Na, and K were the main differences between the Lisbon olive groves and the other two from Santarém. Phosphatase, cellulase, and urease activities were related to the Na, extractable K, extractable P, Zn, Mn, organic C, and total N soil concentrations. Soil management and agricultural practices are determining factors for these enzymatic activities of Santarém olive groves, although climate conditions and soil properties play an important role in the soil enzymatic activities.

Pinus halepensis in Contaminated Mining Sites: Study of the Transfer of Metals in the Plant-Soil System Using the BCR Procedure

The study aimed at evaluating the geochemical fractions of Zn, Pb, Cd and their bioavailability in soil in-depth and around the root of Pinus halepensis grown on heavily contaminated mine tailing in south-western Sardinia, Italy. The contaminated substrates were partly investigated in a previous study and are composed of pyrite, dolomite, calcite, quartz, gypsum, barite, iron-sulfate and iron-oxide. The geochemical fractions and bioavailability of Zn, Pb and Cd were measured through the BCR extractions method. Cadmium in the superficial contaminated substrates was mainly found in the exchangeable BCR fraction. Zinc and lead were often found in the residual BCR fraction. PCA confirmed that the uppermost alkaline-calcareous layers of mine waste were different with respect to the deeper acidic layers. We demonstrated that Pb and Zn were less present in the exchangeable form around the roots of P. halepensis and in soil depth. This can be due to uptake or other beneficial effect of rhizospheres interaction processes. Further studies will shed light to confirm if P. halepensis is a good candidate to apply phytostabilization in mine tailing.

Trade-Off between Facilitation and Interference of Allelopathic Compounds in Vegetation Recovery: The Case of Rosmarinus officinalis in Degraded Gypsum Habitats

Rosmarinus officinalis advantageously competes with other species in restored gypsum outcrops, and further research is needed to understand the causes. Specifically, we focus on the potential allelopathic effects derived from its terpenes on the emergence of gypsum species. To this end, we established 120 circular subplots in a previously restored gypsum outcrop, and randomly applied four different treatments based on the presence/absence of rosemary plants and their leaves on the soil. Afterwards, we conducted an experimental sowing of native gypsophiles. All subplots were monitored to estimate seedling emergence, and soil and leaf samples were analysed for terpenes. The results show that the treatments had significant effects on the overall emergence of seedlings, and terpenes were found in rosemary leaves and soils, with no significant differences in terpene composition. In particular, we identified a clear negative effect in the treatment where rosemary plants were eliminated but its leaves were left along with allelopathy (2.57 ± 0.54 individuals/subplot). Unexpectedly, the presence of rosemary plants seems to facilitate the emergence of gypsum species (9.93 ± 1.61 individuals/subplot), counteracting the effects of the allelopathic substances in the soil. Consequently, we do not suggest removing rosemary plants in early stages to encourage the emergence of gypsum species in restored areas.

Implications of afforestation vs. secondary succession for soil properties under a semiarid climate

Afforestation or secondary succession after cropland abandonment are different strategies to restore soil ecosystem services such as nutrient cycling, soil conservation, and carbon sequestration. However, the studies on the effects on soil-property dynamics after land-use changes are limited in semiarid regions. In this context, an experimental area with a semiarid climate allowed the assessment and comparison of physicochemical soil properties (soil organic C [SOC], soil total N [TN], available P [AP], available K [AK], cation-exchange capacity [CEC], bulk density [BD], pH, available water-holding capacity [AWHC], and C:N ratio) after Pinus halepensis afforestation and secondary succession following agriculture abandonment in 1994. The impact of 12 soil-preparation treatments for planting on soil properties was also evaluated. For this, soil samples (0-10 cm deep) from the afforestation were taken in 1998, 2002, 2007, 2010, 2013, and 2016, and from abandoned cropland in 2010, 2013, and 2016. In afforestation, soil-preparation treatments did not alter differentially the soil properties after 22 years. Significant differences among years were found in SOC, TN, AP, AK, CEC, pH, and C:N. BD changes were detected neither in afforestation nor in abandoned cropland. After 22 years, only SOC, AK and the C:N ratio proved significantly higher in afforestation than in abandoned cropland. In general, soil properties improvement (i.e. SOC, TN, AP, AK, and CEC) was slow after afforestation and abandoned cropland likely due to the legacy of the previous land use (cereal crops) and the semiarid climate influence.