Inorganic nitrogen in soil green manured with biocidal crops

Summary

The knowledge of the dynamics of inorganic N in soil may help to establish the most suitable timing for green manure (GM) incorporation, which leads to the improvement of crop N use efficiency in conventional as well as organic agriculture. The practice of green manuring with crop species belonging to the Brassicaceae family has recently expanded, in Italy and abroad, due to their demonstrated biocidal effect against soil-borne pathogens. In this plot-scale study we monitored the release of soil inorganic N in 3 soil types (1 clay and 2 loams), in the months following late-spring green manuring with plant material from Brassica juncea, Sinapis alba, and Raphanus sativus species. Soil inorganic N content increased and reached a maximum 2 months after GM incorporation (+14.4 mg N kg1 dry soil, on average, over the initial inorganic N content), and subsequently declined. The inorganic N accumulation was higher in soil amended with R. sativus. We did not observe any significant influence of the soil type on the variation of inorganic N content in the period after GM incorporation. The inorganic N released after late-spring green manuring with Brassicaceae species may become available in the early growth phase of subsequent summer-autumn crops.