Browsing by Author "Loaiza, George"

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Animal-powered tillage erosion assessment in the southern Andes region of Ecuador
(2007-06-01) Dercon, Gerd; Govers, Gerard; Poesen, Jean; Sánchez, Henrry; Loaiza, George; Vandenbroeck, E.; Rombaut, K.; Deckers, Jozef
While water erosion has been the focus of past research in the Andes, former studies show that soil erosion could also be related to the methods used in cultivating the fields. The main objective of the present study was to assess (i) tillage erosion caused by the traditional animal-powered “yunta” or ard plough in the Andes and the factors controlling the process and (ii) the implications for soil conservation. Erosion rates were experimentally measured on 27 sites, having slopes from ca. 0% to 60% and soils ranging from Andosols to Cambisols, in the Andes region of Ecuador (Gima, Azuay). Different tillage methods were assessed: (i) tillage parallel to the contour lines (‘Paralelo’) and (ii) tillage at an angle with the contour lines. Statistical analysis points out that erosion caused by animal-powered tillage is gravity-driven. A strong correlation exists between slope and downslope displacement: furthermore, tillage depth and initial soil condition are important. For the ‘Paralelo’ tillage method the tillage transportation coefficient (k) is below 100 kg m− 1 Tillage Pass− 1, for the combined ‘Arado’–‘Cruzado’ tillage method k may exceed 300 kg m− 1. Tillage erosion is responsible for the reduction of the slope between the contour strips over a relatively short time period of 20 years, resulting in the formation of terraces and therefore the reduction of the water erosion risk. However, at the same time it may negatively affect soil quality.
Spatial variability in crop response under contour hedgerow systems in the Andes region of Ecuador
(2006-03) Dercon, Gerd; Deckers, Jozef; Sánchez, Henrry; Ramírez, Marco; Vanegas, Raúl; Tacuri Espinoza, Víctor Eduardo; Loaiza, George; Govers, Gerard; Poesen, Jean
Land management practices on tropical soils have been studied extensively during the past decades. However, assessments of their impact on field-scale spatial variability in crop performance are rare. A case of practices affecting spatial crop response at field level in a systematic way is the contour hedgerow system, a widespread soil conservation technique on steep lands in the tropics. The objectives of this study were to assess: (i) spatial variability in crop response under contour hedgerow systems in the Andes and (ii) implications for management of steep land alley farming. In order to measure spatial variability in crop response, Triticum aestivum was sown in rows following the contours, placed every 25 cm along the slope direction. Grain yield was monitored on eight alleys, having slopes from 15 to 30%, a length of 4–8 m and soils ranging from Dystri-Vertic Cambisols to Haplic Phaeozem, in the Andes region of Ecuador. In order to relate crop response with soil fertility, soil sampling was carried out in bands following the contour. Top soil properties, such as organic carbon, NTotal, NO3−, P, exchangeable Aluminium, P fixation, exchangeable bases, CEC and texture, were analysed. The barrier strips of the contour hedgerow systems were composed of: (i) Pennisetum clandestinum and Lolium multiflorum or (ii) Phalaris tuberosa. Spatial variability in crop response was described by fourth-order polynomial equations, where position in the alley was the independent variable and plant characteristics were the dependent variables. Grain yield ranged from 0.8 to 4.0 t ha−1 (net area). Clear and significant patterns of spatial variability in crop response were found in all alleys, with R2 varying from 0.55 to 0.90. Crop response was strongly and positively correlated with NO3−, P, exchangeable bases or organic carbon, dependent on the management, age and soil conditions of the alleys. Tillage erosion and soil accumulation on respectively the upper and lower elevations of the alleys were the main causes for a tendency to a significantly increased crop response along the slope direction. However, according the type of grass used in the barrier strip, competition for soil fertility and soil moisture occurred and influenced in negative way crop productivity in the lower elevations of the alleys. An index is proposed to assess the effect of contour hedgerows on crop response. The present study shows that contour hedgerow systems cannot always be evaluated as completely positive. Soil fertility improvement on the upper part of the alleys and a better management of the barrier strip are suggested to enhance crop productivity of contour hedgerow systems.
The impact of environmental change on the intensity and spatial pattern of water erosion in a semi-arid mountainous Andean environment
(2003-04-01) Vanacker, Veerle; Govers, Gerard; Poesen, Jean; Deckers, Jozef; Loaiza, George
Aerial photographs taken in 1976 and 1989 and a field survey in 1999 showed that land use in a 900-ha catchment in the southern part of the Ecuadorian Andes is highly dynamic. Over 23 years, ca. 83 ha of arable land was abandoned and ca. 70 ha was taken into agricultural production. Changes in land use were not spatially homogeneous. Parcels on unstable geologic formations and close to village centres were preferably set-aside. Land taken into cultivation was preferably located on gently sloping areas close to newly built sites and arterial roads. The area with bush vegetation increased by regeneration of natural vegetation on fields set-aside in the late 1970s and early 1980s. There was a complex interaction between water erosion and environmental change in the study area. Land taken into production was levelled for furrow irrigation: this led to a net reduction in the area susceptible to water erosion. However, one quarter of the area affected only by sheet and rill erosion 23 years ago has since become incised by deep gullies. This increase in gully density was related to inadequate construction and management of irrigation infrastructure, rather than to change in vegetation cover and/or soil erodibility caused by agricultural practices. This factor is often overlooked in studies of the effects of environmental change on geomorphologic processes.