N-utilization in non-inversion tillage systems

When changing from ploughing to non-inversion tillage, N rates are of particular importance both for farmers and the environment. A tillage and fertilizer experiment was established in Denmark under temperate coastal climatic conditions to evaluate the N fertilizer responses on yields and N uptake of six crops in different crop rotations, three winter wheat crops (Triticum aestivum L.), one winter barley (Hordeum vulgare L.), one winter oilseed rape (Brassica napus L.) and one spring barley crop during the years 2003–2005. The experiment was established in autumn 2002 on a loamy sand with 92 g clay kg−1. The tillage treatments were stubble cultivating to 8–10 cm or 3–4 cm, direct drilling, or ploughing to 20 cm. Five different fertilizer N treatments were included: 1:50% (0.50N), 2:75% (0.75N), 3:100% (1.00N), 4:125% (1.25N) of recommended N rates, respectively, and 5: application of 15–30 kg N ha−1 of the total fertilizer N amount in autumn to autumn-sown crops (1.00NAut). In all the crop rotations, straw was chopped and retained after harvest. Different types of N fertilizer responses were observed in the six crops, but generally yields were lower with non-inversion tillage than with ploughing. On two occasions, yields in ploughed plots were significantly (p < 0.05) higher than yields with direct drilling as an average of N treatments. Increasing the fertilizer application was generally not able to offset the growth reduction, which resulted from poor growth in patches probably caused by soil compaction in plots with non-inversion tillage. Applying some of the N allocation in autumn cannot be recommended for stimulation of growth of winter cereals or winter oilseed rape with either non-inversion tillage or ploughing.