Determining the best ISUM (Improved stock unearthing Method) sampling point number to model long-term soil transport and micro-topographical changes in vineyards

Abstract

Advances in soil erosion measuring tools and micro-topography modelling will contribute to our understanding of land degradation processes and help to design correct erosion mitigation measures in agricultural fields. Vineyards being one of the most degraded agricultural landscapes, it is necessary to accurately predict soil erosion levels within them. One possible method to achieve this goal in vine plantations is ISUM (improved stock unearthing method). To apply ISUM, it is necessary to detect the graft unions which are recognised as passive bioindicators of the original micro-topography at the time of planting. In this paper, we propose a methodology to determine: (i) how many measuring points are necessary to reach the best estimate of soil erosion for developing current soil surface level maps; and (ii) which spatial interpolation method is the best to map the micro-topographical changes. ISUM was applied in the Ruwer-Mosel valley vineyards (Germany) using 18 measuring points at 10 cm intervals between opposite pair graft unions of 1.7 m inter-row distance. Several interpolation methods were used to map the micro-topography changes and anisotropic ordinary kriging (OK) emerged as the best as judged by the performance statistics of the coefficient of determination and the root-mean-square-error. Our findings demonstrated that soil erosion rates were 40.1, 39.4, 25.0, 38.9, 37.9, to 64.8 Mg ha−1 yr−1 over the 40 years since the establishment of the vineyard studied, when using 18, 15, 10, 7, 5 and 2 measuring points, respectively. We propose that ISUM can be standardised as using measuring points at 10 cm intervals.