Association of sulla and atriplex shrub for the physical improvement of clay soils and environmental protection in central Italy

Improved land-use practices are needed for difficult to manage marginal cla y soils in the Mediterranean region. A field experiment was carried out in the Era valley (Pisa, Italy), an clay soil marginal areas. The aim was to e valuate the effects of a Sulla (Hedysarum coronarium L.)+Saltbush (Atriplex halymus L.) perennial agri-forestry system in improving the physical chara cteristics of the soil and to provide environmental protection by controlli ng runoff and reducing soil erosion on slopes. The experimental results sho wed that the Sulla/Atriplex shrub soil Management System (SAMS) was capable of increasing, over a period of about 4 years, the mean weight diameter (M WD) of stable soil aggregates from 1 to 6 mm, compared to the MWD (i.e. 1 m m) for a soil ploughed every year for continuous wheat (Triticum durum L.) cultivation. The improved soil structure was similar to that under a natura l sod ecosystem. Soil total porosity was also improved in the SAMS. Of part icular interest was the increase in large elongated bio-pores (from 400 to 1000 mum) left in the soil by the decay of Sulla roots. The average yearly runoff amount was reduced to 5% under SAMS in comparison to continuous whea t cultivation. It was inferred that the canopy of the Sulla/Atriplex shrub plant association dissipated the storm kinetic energy, reducing consistentl y the detachment of soil particles by raindrop impact, reduced runoff veloc ity and prolonged lag-time of peak discharge. The overall integration of the above mentioned processes, facilitating wate r infiltration into the soil, increased the storage of water available to p lants. In addition, SAMS reduced the average yearly soil loss of about 7%, in comparison to continuous wheat cultivation. Thus, SAMS has the potential to reduce the contributions of pollutants from slopes to stream and river systems, with the general effect of decreasing the overall environmental im pact down-slope. (C) 2001 Elsevier Science B.V. All rights reserved.