Alternative sugar beet production using shallow tillage and municipal solid waste fertiliser

The application of conventional agricultural practices, e.g. deep soil tillage and repeated, plentiful mineral fertilisation, can lead to a progressive deterioration of soil fertility, especially in Mediterranean environments characterised by scanty rains and high summer temperatures. As a consequence, to maintain high levels of both crop productivity and soil organic matter and to improve some soil properties, a reduction of agricultural inputs and a greater supply of organic material are needed. In the light of these considerations, we carried out a two-year field experiment in Southern Italy to determine the effects of reduced soil tillage and municipal solid waste compost application on growth parameters, production and quality of sugar beet crops, and on both soil chemical characteristics and mineral nitrogen deficit. Two soil tillage depths were compared: conventional tillage, till 40–45 cm and shallow tillage, at 15–20 cm. Within each soil tillage, the following N-fertilising strategies were tested: (1) mineral fertilisation, with 100 kg N ha−1; (2) organic fertilisation with municipal solid waste compost at 100 kg N ha−1; (3) mixed fertilisation, with 50% of organic N as municipal solid waste compost, and 50% of mineral N; and (4) slow-release organic-mineral N fertiliser, at 100 kg N ha−1. All these treatments were compared with a lower level of mineral fertiliser at 50 kg N ha−1, and with an unfertilised control. Our findings show first the absence of a significant difference in root and sucrose yields between reduced tillage and deep tillage; as shown by roots (36.02 t ha−1) and sucrose (3.41 t ha−1) yields for reduced tillage and 35.76 and 3.51 t ha−1, respectively, for the deepest tillage. Secondly, among the N treatments, the mixed organic-mineral N fertilisation gave productions statistically not different from mineral N fertilisation; as shown by root yields (36.38 versus 36.40 t ha−1) and sucrose yields (3.56 versus 3.65 t ha−1). Third, the mixed organic-mineral N induced a reduction of 13.2% in α-amino N content by comparison with the mineral treatment of 100 kg N ha−1. Fourth, our results showed that the applications of the municipal solid waste compost increased the extracted and the humified organic carbon by +27.7 and +25.4%, compared with the mineral fertiliser, and did not raise the content of heavy metals. These findings highlighted that in Southern Italy it is sustainable to adopt alternative sugar beet production, safeguarding crops' quantitative and qualitative performance, decreasing the production costs and using the natural resources better.