EUROPEAN JOURNAL OF SOIL SCIENCE
Volumen: 68, Numero: 3, Páginas: 1-10 pp.
Agriculture in the temperate zone of the Midwestern USA has removed most riparian buffer zones from the landscape, which impairs the soil functioning of the soil in these ecosystems. The objective of this study was to assess soil degradation in a non?buffered riparian zone with an annual row crop (ARC) and in a longer established (more than 85 years) riparian cool season grass (CSG) buffer in central Iowa, USA. To achieve our objective, we compared the functioning of the target system, ARC, with a system that has been undisturbed since 1990, CSG. We measured the aggregate size distribution and stability of macroaggregrates, aggregate?associated soil organic carbon and particulate organic matter (POM). The categorization of aggregates by size and water stability (slaking resistance) showed a significantly larger (P < 0.05) proportion of water?stable macroaggregates (> 250 µm) under CSG (53%) than under ARC (26.3%). On the other hand, soil under ARC had the larger proportion of large and small water?unstable macroaggregates. The results indicate that the concentration of organic C associated with the total water?stable aggregates is 1.9 times greater under CSG (23.9 mg C g?1) than for the ARC (12.4 mg C g?1). The concentration of carbon in light particulate organic matter (LPOM?C) under CSG accounted for 12% of total soil organic carbon (TSOC), but only 6% under ARC management. The chemical composition of LPOM in the ARC soil had a large alkyl?C/O?alkyl C ratio, which suggests more organic matter decomposition than with the CSG. Electronic micrographs showed evidence that under CSG roots and fungal hyphae form an extensive network around the large macroaggregates (> 2000 µm), and thus maintain the stability of the macroaggregates. Preserving the CSG buffer reduces soil erosion and the processes associated with nonpoint source pollutants, which improves water quality in an intensively managed agricultural system.