Uncultivated margins in agricultural landscapes: effects on soil functioning

Background/Question/Methods

Agricultural intensification is a major cause of habitat degradation in terms of biological diversity and nutrient contents. In agricultural lands of Argentina, continuous cropping has reduced landscape heterogeneity and altered the provision of ecosystem services such as biodiversity and carbon sequestration. In this scenario, empirical evidence has shown that uncultivated, permanently vegetated areas (uncultivated margins) imbedded in the agricultural matrix play a critical role on plant and animal communities with respect to the usual situation of crops surrounded by other crops (cultivated margins). However, the potential impact of the uncultivated margins on their own soil functioning and on that of their neighbouring cultivated areas remains unknown. We investigated the role of woody and herbaceous uncultivated margins on soil carbon dynamics and soil biota. We compared these two spontaneous vegetation-crop interfaces with the usual cultivated margin situation (crop-crop interface). We selected pairs of soybean paddocks surrounded by crops (control) and by either herbaceous or woody margins and sampled transects from the neighboring situation (margin) towards the center of the soybean paddock  (n= 5). At each sample point, we quantified litter and soil carbon contents in the top soil layer, litter decomposition and soil biota abundance and diversity (arthropods and bacteria).

Results/Conclusions

Woody margins differed from controls and herbaceous margins and had the greatest influence on the adjacent cultivated area. Herbaceous margins differed from controls and woody margins but had no effect on the adjacent crop. Woody margins had the greatest litter accumulation, soil carbon contents, and functional diversity of its bacterial biota (p≤0.05). Besides, these properties decreased as the distance from the margin increased. The herbaceous margins had the lowest litter accumulation and the most decomposable litter (p≤0.05). The decomposition rate of common substrates, used to isolate the effects of litter quality from micro-environmental effects, was insensitive to margin type and position along the interface. Arthropod abundance and diversity were highly variable and statistically similar among margin types or position. The centers of the cultivated fields resulted similar in all the studied properties, irrespective of margin type. These findings suggest that woody margins represent the single current landscape element with a spatially limited though effective potential to mitigate soil carbon and bacterial functional diversity losses in the cultivated land. On the contrary, the low production of highly decomposable litter of herbaceous margins reveals the urgent need to re-think current management strategies of these margins.