Effect of no-tillage on nutrient content and organic matter of the soi, Pratique du semis direct en grandes cultures: effets sur la structure du sol

In the long-term field trial “Oberacker” at Zollikofen (Switzerland) the content of organic matter and macro-nutrients in the soil was analysed to determine the effect of no-tillage without any soil disturbance and conventional tillage with mouldboard plough.The amount of nitrogen mineralised during the year was similar in both treatments. However, nitrogen mineralisation in spring was delayed due to lower soil temperature and higher soil water content in no-tillage plots. As a consequence, spring-planted crops showed a slower plant development during their early growth stages. Under these conditions an application of a starter fertiliser may help to promote early plant development, as root growth may be reduced also by the higher bulk density of no-tillage soils. In contrast, under winter cereals, soil content of mineral nitrogen in spring was almost the same for both treatments, implying that no special nitrogen fertilisation strategy is required.Five years after the start of the field trial, the amount of organic matter in the top-soil (0 – 20 cm) with no-tillage had increased by 6.8 t*ha-1 or 10 % compared to conventional tillage. This augmentation was mainly observed in the top 10 cm of the soil, whereas in the 10 – 20 cm soil layer, the content of soil organic matter in no-tillage did not increase. Nevertheless, there is still a lack of information whether the combined effects of increased content of organic matter and nitrogen in the soil result in a higher nitrogen mineralisation, which would allow a reduction of nitrogen fertilisation in no-tillage compared to conventional tillage.