Indices for quantitative evaluation of soil quality under grassland management

• As grassland management intensified soil quality deteriorated.
• The best soil quality index was calculated from a minimum dataset of OC, CN and BD.
• Non-linear scoring produced the index most sensitive to management.
• Weighted addition improved the efficiency of the most sensitive index.

ObjectiveThe objectives of this study are to determine appropriate indicators, the most appropriate scoring function (linear or non-linear) and integrating procedure (additive and weighted additive) for a soil quality index for typical temperate, maritime grassland management (e.g. livestock grazing and silage production).MethodsThe study was conducted on twenty grassland sites classified by three levels of management intensity. Twenty-one soil properties were measured as potential indicators of soil quality, and the visual evaluation of soil structure was applied to select indicators responsive to management and for the validation of the indices. Indices were calculated using linear and non-linear scoring, followed by additive and weighted additive integration. Principal component analysis used with the total dataset of indicators sensitive to management to determine a minimum dataset.ResultsSoil organic carbon (SOC), total nitrogen, aggregate size distribution, bulk density, bulk density of ≤ 2 mm fraction, extractable potassium and carbon–nitrogen ratio (CN) were the indicators that comprised the total dataset, while SOC, CN and bulk density of ≤ 2 mm fraction were the minimum dataset. The management intensity influenced each indicator in different ways, and the index calculated using minimum dataset and nonlinear weighted additive integration had the best discrimination ability.ConclusionsThe average soil quality index values were lower under higher intensity management, and indicated that management intensification was tending toward an adverse impact on soil quality under grassland systems in Ireland.PracticeThere was no evidence that current grassland management was having a long-term detrimental effect on soil quality for grassland production, but the trend suggested that increasing intensity might cause management difficulties due to soil limitations in the future.ImplicationsThe indexing approach in this study provides a practical, time and cost effective method for quantitative evaluation of soil quality under temperate maritime grassland management.