Plant development, nitrogen dynamics and nitrate leaching in plot cultivated with mouldboard ploughing and no-tillage techniques

How do "mouldboard ploughing" (PF) and "no-tillage" (DS) cultivation techniques influence plant development, soil nitrogen dynamics and nitrate leaching? What influence do "mineral nitrogen fertilisation" (MIN) and "slurry fertilisation" (GUL) have on plant development and soil nitrogen dynamics? In Tänikon near Aadorf (Switzerland), these issues were investigated under practical conditions in a field trial lasting several years. The soil was a luvisol with 22 % clay, 34 % silt and 1.6 % organic carbon. Crop rotation was maize (1999) _ winter wheat (2000) - maize (2001). Two years before the trial, the plot was covered by a temporary pasture. Plant biomass development and nitrogen absorption were recorded using intermediate harvests. Mineral nitrogen was measured at various depths using Nmin-analysis for the soil and suction cups for soil water. Where ploughing and no-tillage with mineral nitrogen fertilisation were carried out, monolithic lysimeters with a 1 m2 surface and a depth of 1.5 m were installed to record the volumes of percolating water and leached nitrate-nitrogen. Even with the lysimeters in place, all soil cultivation, management and harvesting was carried out with commonly used agricultural machinery. In the first two years, the yields of wheat and silage maize were significantly lower with DS than with PF. Especially in 1999, there was a 50 % lower yield with DS, attributed to severely retarded early growth. No clear reasons could be found for this unsatisfactory growth. The high bulk density of the soil, low macroporosity (5 %), low air conductivity combined with high rainfall in May/June 1999 had caused waterlogging in the no-tillage seed drills, doubtless creating poor growing conditions for the maize. In most of the plant parameters recorded, e.g. biomass yield and weight per thousand seeds, the values of the various fertilisation methods followed the sequence MIN GUL "no nitrogen fertilisation" (0N). Nitrogen utilisation in mineral fertilisation was higher than the mineral nitrogen utilisation (NH4) of slurry. The ammonia losses following slurry spreading must have caused this poorer nitrogen utilisation by the plants despite the fact that a trailing hose spreader was used and attention was paid to the weather conditions. The various parameters recorded only showed significant interaction between the tillage and fertilisation techniques in exceptional cases. The fertilisation methods had a uniform effect on both tillage regimes. After the first year of maize cultivation, 1999, 70 kg NO3-N/ha were leached beneath the winter wheat between September 1999 and May 2000 with DS. This figure was 40 kg NO3-N/ha with PF. The remaining organic carbon and nitrogen from the temporary ley preceding the maize very probably caused increased nitrogen mineralisation in the no-tillage regime. In the second year of maize cultivation, approximately 30 kg NO3-N/ha were leached in each of the tillage regimes between September 2000 and September 2001. The amounts of percolating water did not differ here. After infiltrating Vitasyn-Blue dye solution into the topsoil, approximately 30 % more profile area was dyed blue in PF than in DS, indicating flow through a greater soil volume. Despite these differing flow structures, it is impossible to prove effects such as a reduction in nitrate leaching. In both techniques, soil nitrate concentrations recorded using Nmin samples and suction cups showed a similar pattern in the course of the year. Except between September 1999 and May 2000, both tillage systems in this trial affected soil nitrogen mineralisation and nitrate leaching to ground water in much the same way.