Vincent de Leijster

38 Chapter 3 they give a broad view of the potential decomposition processes in the soil, as they are indicators for the breakdown of cellulose (glucosidase), the P-cycle (phosphatase), N-cycle (urease) and C-cycle (dehydrogenase) (Das and Varma, 2011). Dehydrogenase activity was measured according to the methodology described by García et al. (1997). To assess phosphatase and β-glucosidase activity we used the methodology described by Ramos et al., (2011). Urease activity was determined using the method described in Kandeler and Gerber (1988). Soil organic matter, carbon and chemical properties Soil organic matter (OM) content was determined using the method described by Walkley and Black (1933). Soil organic carbon (SOC) content was calculated by multiplying OM content by 0.5, as proposed by Pribyl (2010). Total nitrogen content (N) was determined using the Kjeldahl method (Bremner, 1960). Extractable phosphorus content (P) was determined using the ascorbic acid Olsen method (Watanabe and Olsen, 1965). Extractable potassium (K) was determined with the ammonium acetate method (Pratt, 1965). The pH was determined in a 1:2.5 (w:v) aqueous solution. 3.2.3.2 Understory properties We sampled the understory in the second and third week of May 2017 as in this period the herbaceous vegetation is fully developed (Ramos et al., 2010). All plant species that grew underneath and in between almond trees were considered the understory. Plant species richness and cover The understory plant species composition was assessed using the point-intercept method, modified as proposed by Ruiz-Mirazo and Robles (2012) for natural grasslands in the same territory. We assessed six 10 m long transects that were laid out in each plot, going diagonally from one row of almond trees through the middle to the next row of almond trees. Each transect consisted of one hundred points at intervals of 10 cm. At each point of the transect, a pin 30 cm long and 2 mm of diameter was thrust into the ground. All plants that touched the pin were identified to the species level. When there was no plant touching the pin, we recorded bare soil or litter. From these data, we calculated species richness and percent understory cover.