Soil structure breakdown following land use change from forest to maize in Northwest Vietnam

Conversion of forest to agricultural land for maize cultivation is known to negatively affect soil fertility. However, limited knowledge is available of the impact on aggregate stability and interconnected soil properties. The aims of the present study were to (1) quantify soil aggregate stability, (2) assess aggregate stability changes after land use change, and (3) determine the interactions of aggregate stability with clay, soil organic carbon (SOC), exchangeable Ca2+ and Mg2+, and soil erosion rates. The topsoils of three soil types in Northwest Vietnam were analyzed in chronosequences (0-18 y after land use change from forest to continuous maize) by two methods: Wet sieving and sonication. By differentiation of these aggregate stability measurements, the impact of both methods on aggregate size distribution could be quantified separately and compared. The sonication method indicated a more homogeneous disaggregation whereas the wet sieving method was more suitable to detect low aggregate stabilities. Soil aggregate stability declined simultaneous with a decrease of SOC and exchangeable Ca2+ and Mg2+, which both declined with increasing time since land use change. The Alisol and Luvisol chronosequences were 1.9 times more stable under primary forest than under maize (shown by sonication) whereas the Vertisol chronosequence was 2.5 times more stable under primary forest (shown by wet sieving). Over the 18 y chronosequence the topsoils had 1.6 kg m(-2) lower SOC and 3.2 g kg(-1) lower Ca2+ contents. This study highlights the destabilization of soil in interaction with a degradation of relevant chemical soil properties with differentiated aggregate stability methods. (C) 2016 Elsevier B.V. All rights reserved.