Spatial variability in soil properties on slow-forming terraces in the Andes region of Ecuador

Due to severe land degradation problems, soil conservation is a matter of major concern in the Ecuadorian Andes. Slow-forming terraces, a variation of hedgerow agro-forestry systems composed by contour grass barrier strips, can be considered as the most frequently used technique in Andean rural communities of Ecuador. However, due to shallow soils, terrace development often has the disadvantage causing gradients in soil properties from the upper to the lower elevations within the terrace. The main objectives of this study were to assess (i) spatial variability in soil properties on slow-forming terraces in the Andes and (ii) implications of variability for the management of this soil conservation technique. In order to measure spatial variability, soil sampling (0–15 cm) was carried out in bands following the contour, which were located every 1m beginning at the highest point of elevation and including the lowest point on the terrace. Soil properties, such as pH(H2O), pH(NaF), organic carbon, total nitrogen, NO3 −, P, K, exchangeable aluminium, P fixation, exchangeable bases, cationic exchange capacity, base saturation and texture, were monitored on eight terraces, having slopes from 15 to 30%, a length of 4–8m and soils ranging from Cambisols to Phaeozems, in the Ecuadorian Andes (Gima, Azuay). Terraces, which were 2–4 years, were managed in a traditional or more intensified way (i.e. without or with the application of organic manure). Bufferstrips were composed by (i) Pennisetum clandestinum and Lolium multiflorum or (ii) Phalaris tuberosa. Spatial variability was analysed by stepwise multiple regression analysis, where position on the terrace was the independent variable and soil property was the dependent variable. Factor analysis was carried out in order to compare spatial variability patterns of the terraces and formulate management strategies. High spatial variability in soil properties was found. Although spatial variation was site dependent, it was clear that soil fertility increased from the upper to the lower part of the terraces. The present study shows that management strategy could influence the pattern and magnitude of spatial variation. Site-specific soil fertility improvement is suggested as means to combat variation caused by tillage erosion in slow-forming terraces.