Lupines-Invaded Pine Forest and Cultivated Scrublands in Volcanic Ash Soils in Mexico: Dry-Sieved Aggregation and Instability Indices

A field study was conducted to investigate the effectiveness of wild lupines invasions and planted pastures on improvement of soil structural aggregation and to determine the macroaggregate instability indices for environmental impact assessment on the sustainability of traditional cropping management practices. Dry aggregate size distribution (ASD), macroaggregate instability indices (CoES), soil-water retention (SWR), total organic carbon (TOC), soil pH and particle size distribution were determined from air-dried soil under the long-term intensive cultivations (CA), natural oak forest (VN), lupines invaded disturbed pine forest (BL), planted pastures (PP), lupines invaded meadows (PL), lupines invaded fallows (SDL) and freshly-tilled lupines invaded fallows obtained by converting SDL to CA (BRDL). The higher moderate-acid pH and total clay content increased with depth, except for the SDL soils. The lowest amount of microaggregates (MicAg) at 0-20 cm depth was observed for the SDL soils than for the VN and BL soils. The small macroaggregation (SmMag) was the highest for the CA and VN soils at 20-40 cm depth, but the lowest for the SDL and PL soils at 0-20 cm depth. The VN soils caused higher medium macroaggregation (MeMag) at 0-20 cm depth as compared to the BL soils. The large macroaggregation (LaMag) was the highest for the BRDL soils at both depths and for the CA soils at 0-20 cm depths while was the lowest for the BL soils at both depths. The macroaggregate instability (CoES) indices for the TMag, SmMag and MeMag size classes were the lowest for the SDL soils and for the LaMag for the PL soils at 0-20 cm depth, while were the lowest for all the macroaggregate size classes for the VN soils at 20-40 cm depth, but were the highest for all microaggregate size classes for the BL soils at both depths. The linear regression analysis indicated strong negative association between CoES, pH and total clay content, but a positive relationship was observed between CoES and TOC. High yielding grain lupines genotypes could be considered for future inclusion in the cropping management practices to improve the physical soil fertility and socio-economic sustainability of the traditional farming systems.