Response of seedbed physical properties, soil N and cereal growth to peat application during transition to conservation tillage

In the short term, discontinuation of mouldboard ploughing (MP) in clay soils may cause yield decrease because of coarse seedbed and poor crop establishment. This study evaluated the role of partly decayed peat in improving soil properties at the soil surface during the transition to conservation tillage. Moderately decomposed peat was spread on the soil surface (0.02 m, 50% of field area). Since 1995, the field was either (1) tilled each September with a mouldboard plough, (2) tilled each September with a field cultivator, or (3) not primary tilled (NT). Oat (1996, 1998, 2000) and barley (1997, 1999) were sown in May, after a shallow secondary tillage. Discontinuation of MP created a coarser seedbed with subsequent yield reductions. Peat delayed the drying of the soil surface in early seasons. Plant growth was enhanced even 5 years after the application. Peat did not, however, significantly improve the aggregate stability of this clay soil in 1996–1998. Within 1 year after application, peat and/or MP increased risk for N leaching. Overall, mineral N contents were low in all the tillage practices, with or without peat application. This appeared to be a response to a low N fertilisation rate (90 kg ha−1) and sufficiently high soil C/N. Mineral N contents after harvest were related to previous plant growth and N uptake. Peat application offers a means to minimise the risk of poor growth, and hence nutrient leaching. Peat did not, however, improve aggregate size distribution after the tillage change.