Maize (Zea mays) cropping has greatly increased in Southeast Asia since the mid-1990s, mainly by expanding its production into steep forested uplands. This led to severe erosion, soil degradation, and strong environmental impacts. This study aimed at assessing the magnitude of erosion in maize and the mitigation potentiality of soil conservation measures in such environments. Bounded experimental plots established in two catchments of the Son La province of Northwest Vietnam were monitored during 2009-2011. Three soil conservation measures represented by Guinea grass (Panicum maximum) barriers, minimum tillage with Pinto peanut (Arachis pintoi) as a cover crop, and minimum tillage with relay cropping of Adzuki beans (Phaseolus calcaratus) were compared against the current farmers' maize cropping practice based on slashing, burning, and ploughing. Additional on-farm measurements of soil loss on maize fields were made using sediment fences on six convergent unbounded fields in 2010 and 2011. Under farmers' practice, annual soil losses of experimental plots reached up to 174 t ha(-1), being higher than those from sediment-fence plots (up to 111 t ha(-1)). The pattern of erosion events, however, was similar in both methods. Most of the soil loss occurred in the first weeks after sowing or under maize mono cropping when high rainfall intensities coincided with a low percent ground cover of fields. Under the prevailing conditions (1270 mm rainfall, inclination 53-59%), a very high ground cover is required to keep erosion rates low, which is hardly achievable by maize mono-cropping. Conservation measures had no effect on soil loss in the year of trial establishment as rainfall was low and erosive rains fell only when ground cover by plants was already high. From the second year after establishment of soil conservation measures, erosion was reduced by 39-84% in grass barriers or by 93-100% in simultaneous cover crop treatments. Maize yields, however, decreased by 26% in grass barriers or up to 35% in cover crop plots if Pinto peanuts were not cut on time. Both of these options provided animal feed, up to 5.5 t ha(-1) yr(-1) dry grass or 1.8 t ha(-1) yr(-1) dry biomass of Pinto peanuts. Guinea grass even yielded higher in 2010, a dry year with erratic rainfall distribution. Minimum tillage with relay cropping reduced soil loss by 94%, while providing similar maize yields as the controls. This latter practice is a win-win situation and, hence, attractive to farmers fostering its acceptance. (C) 2013 Elsevier B.V. All rights reserved.
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