Sulphur demand, uptake and fertilization of Vicia faba L. under field conditions

Abstract

In order to gain a better understanding of the Sulphur (S) supply required by faba bean (Vicia faba L.) under field conditions, field trials were conducted at several sites in Germany on long-term (>10 years) organically cultivated arable land in the years 2012–2014. These field trials investigated the effects of the sulphate-containing fertilizers kieserite (MgSO4), gypsum (CaSO4), epsom salt (MgSO4 × 7 H2O) and elemental sulphur on the S uptake, yield, yield structure and Nitrogen (N) accumulation in faba bean. Additionally, the field analysis observed recovery levels of fertilized S.Under the given environmental conditions, fertilizing the faba bean did not influence seed yields. S accumulation in the shoots of plants from different sites only ranged from 9 to 11 kg S ha−1, whereas the seeds accumulated the bulk of the absorbed S (average S harvest index: 0.65). Optimal growth in the youngest open leaf at flowering was achieved with a N:S ratio of about 20.5 and a corresponding S concentration at 0.29% in the leaves’ dry mass. Obviously, the content of plant-available S in the soil combined with the atmospheric S deposition at the testing environments fulfilled the beans’ S requirement as the additional S fertilization did not produce any effects in yield. The apparent S recovery from the kieserite, gypsum and epsom salt fertilizers - which generally provide plant-available S - was comparatively low, exhibiting values of 3.16%, 5.35% and 8.94%. However, these three fertilizers still generated noticeable increases in S accumulation in parts of the plant. Kieserite and gypsum significantly increased the S concentration in the seeds and straw while narrowing the crop’s N:S ratios. Foliar fertilization with epsom salt exhibited the most apparent S recovery among the tested fertilizers. This analysis deems it unlikely that Elemental S will increase S concentration in faba bean in the year of application or narrow the plant’s N:S ratio. These results show that fertilizing faba bean with S does not currently appear to be necessary when cultivated under conditions similar to the tested environments.