Long-term residual effects of the management of cover crop biomass on soil nitrogen and yield of endive (Cichorium endivia L.) and savoy cabbage (Brassica oleracea var. sabauda)

There is a lack of information regarding the long-term residual effects of winter cover crops on the following cash crops. Two 2-year field experiments (from 2009 to 2012) were carried out in the Mediterranean environment of Central Italy in a Typic Xerofluvent soil. Endive (Cichorium endivia L.) and savoy cabbage (Brassica oleracea var. sabauda) were grown following a winter cover crop-pepper (Capsicum annum L.) sequence. We hypothesized that some cover crops and their residue management can have a long-term effect on the availability of soil nitrogen. The objectives were to quantify the: (i) nitrogen remaining in the soil and in the residues of cover crops after pepper cultivation; (ii) endive and savoy cabbage response due to the residual effect of cover crop residues, and (iii) mass of inorganic nitrogen required for obtaining a similar effect to that obtained with the residues of cover crops. The treatments consisted in three cover crop species [hairy vetch (Vicia villosa Roth.), oat (Avena sativa L.) and oilseed rape (Brassica napus L.)], three managements of the aboveground biomass of cover crops [incorporated into the soil 30 cm depth (conventional tillage, CT), incorporated into the soil 10 cm depth (minimum tillage, MT), left on the soil surface in mulch strips (no-tillage, NT)] plus a control without cover (no cover) fertilized with three levels of nitrogen (none, medium, high). At transplant of vegetables, the nitrogen in the cover crop residues ranged from 60 kg ha1 in hairy vetch NT to 9 kg ha1 in oilseed rape CT, while the soil inorganic nitrogen (NO3-N + NH4-N) was about twice in hairy vetch (20.9 + 7.4 mg kg1 dry soil, respectively) compared with oat and 1.5 times compared with oilseed rape. The marketable yield of endive and savoy cabbage was approximately tripled in hairy vetch compared to oat, oilseed rape and the unfertilized control (20.4 and 18.6 vs. 6.7 and 5.2 t ha1 of FM, respectively). The endive and savoy cabbage yield was higher in NT and MT than in CT hairy vetch and similar to no cover fertilized with 50 and 75 kg ha1 of N, respectively. Results confirm the hypothesis that some cover crops, such as hairy vetch, can have a long-term effect on the availability of soil nitrogen which exceeds the cultivation period of the following summer vegetable crop and can be profitably used by a second cash crop transplanted in close sequence.