Changes in soil chemical parameters and organic matter balance after 13 years of ramie [Boehmeria nivea (L.) Gaud.] cultivation in the Mediterranean region

The introduction of perennials in the Mediterranean crop rotations can have a positive effect on soil organic matter (SOM) concentration, thus improving the long-term sustainability of cropping systems, affected by the progressive degradation in soil fertility. Ramie [Boehmeria nivea (L.) Gaud.], a perennial herbaceous species used for its high quality bast fibre, has recently received renewed attention for production in Europe due to the increasing natural fibre demand globally. Little attention has been focused on the ramie cultivation management and on its effect on soil chemical characteristics. A long-term field experiment was carried out in Pisa (Central Italy, 43°40′ N; 10°19′ E) since 1996, with the aim to assess the long-term environmental sustainability of ramie in terms of productivity, nutrient balance, soil fertility and SOM pool. The fertiliser management of ramie consisted of 150–100–100 kg N–P–K ha−1 in the establishment year and 150–65–165 kg N–P–K ha−1 year−1 from the second year onwards. Plant nutrient uptake was analysed to optimise the crop mineral nutrition and to evaluate the nutrient balance and the efficiency of fertiliser management. The SOM dynamic was evaluated using the actual investigated data and Hénin–Dupuis's equation in order to estimate the organic requirements for SOM equilibrium. Over the 13-year cultivation period, a mean value of 14 Mg ha−1 year−1 of total above-ground dry biomass was obtained. In the 0–30 cm soil depth, SOM, total nitrogen (N), available phosphorus (P), exchangeable potassium (K) and pH varied significantly throughout the cultivation period. SOM increased significantly, from 13.4 g kg−1 to 25.3 g kg−1. A significant correlation between the measured SOM and the cumulative organic matter (OM) inputs (r2 = 0.908; P = 0.012) was found. The average annual N and P balances were positive (equal to 14 kg ha−1 and 38 kg ha−1, respectively), while the K balance was negative (−57 kg ha−1). The results show that ramie crop has a positive effect on SOM pool, thus representing an interesting sustainable fibre crop for the Mediterranean area.

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► The effects of ramie, a new interesting fibre crop, on soil fertility are assessed.
► Stocks of SOM, N and P significantly increase after 13 years of cultivation.
► Measured SOM is positively related to the above and below-ground crop residues.
► Hénin–Depuis's equation accurately predicts SOM pool.
► Ramie can represent an alternative crop in rainfed Mediterranean cropping systems.