Soil quality recovery and crop yield enhancement by combined application of compost and wood to vegetables grown under plastic tunnels

• We assessed the effects of combined compost–wood application on two agricultural soils.
• Use of compost–wood mixtures allowed a rapid recovery in soil organic C.
• Organic amendment enhanced crop yield in 12 out of 14 cropping cycles.
• Organic amendment positively affected microbiological and enzymatic parameters.
• Increases in electrical conductivity and Na+ content were recorded in amended plots.

Vegetable cultivation under plastic tunnels is a steadily growing agricultural sector but concern developed over environmental sustainability of this farming system. Our aim was to identify organic amendments with a biochemical quality that effectively balance the trade-off between organic carbon recovery, in terms of increasing soil organic C stock, and nutrient mineralization. A three-year field experiment was carried out in two farms of southern Italy characterized by plastic tunnel cultivation and contrasting soil characteristics. Two compost–wood mixtures were used, with final C/N ratio of 15 and 25, and supplied in two doses (30 and 60 Mg ha−1). Vegetable yield was assessed by monitoring 14 cropping cycles, and soil quality by determining 18 soil parameters including chemical and biological properties. Crop yields were significantly higher in amendment plots, compared to unamended control plots under plastic tunnel, for 12 out of 14 cropping cycles. Combined application of compost and wood allowed an effective recovery of soil C content within three years. Soil amendments improved soil biological functions as revealed by a general trend of positive effects on dehydrogenase, phosphatase and β-glucosidase as well as on soil respiration. The higher C/N ratio mixture determined only a short-term restriction of mineral nitrogen availability. Organic amended plots showed a significant increase in soil exchangeable Na+ and electrical conductivity compared with untreated controls. Compost–woody combination can be used to recover soil carbon stock and fertility and, at the same time, to support vegetable production under plastic tunnels. However, the possible increase of soil salinity after compost amendment may negatively affect soil quality in the long-term.

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