Elly M. Hansen, Department of Agroecology, Aarhus University, DK-8830 Tjele, Denmark, Ingrid Kaag Thomsen, Department of Agroecology, Aarhus University, DK-8830 Tjele, DENMARK and Rodrigo Labouriau, Department of Mathematics, Aarhus University, DK-8000 Aarhus C, Denmark
The use of nitrate catch crops is part of the Danish regulations to reduce nitrate leaching during autumn and winter. Fodder radish (Raphanus sativus) can be used as one such catch crop and must be followed by a spring-sown crop. However, due to their higher yield potential farmers often want to grow winter cereals instead. In such cases early-sown winter cereals may substitute for nitrate catch crops. During 2015-16 field experiments were carried out on two sandy loam soils, Foulum and Flakkebjerg, in Denmark. Nitrate leaching was measured by ceramic suction cups. At Foulum, leaching from early-sown winter rye (Secale cereale) and from fodder radish, both sown early September (3th-4th) and both following spring oat (Avena sativa), did not differ significantly (15 and 17 kg N/ha, respectively). In comparison, leaching from timely sown winter rye (September 28th) was significantly higher (37 kg N/ha) but differed significantly from bare soil after spring oat (45 kg N/ha). At Flakkebjerg, fodder radish broadcast on August 6th before harvest of the main crop (August 18th) reduced leaching significantly more than early-sown (September 2nd) winter wheat (Triticum aestivum) with leaching of 10 and 20 kg N/ha, respectively. In comparison, leaching from timely sown winter wheat (September 29th) was significantly higher (34 kg N/ha), while leaching from bare soil after spring oat was 47 kg N/ha. The provisional conclusion is that early-sown winter rye may reduce nitrate leaching to the same level as fodder radish when sown at the same time. With earlier sowing of the fodder radish, the radish appeared more effective at reducing nitrate leaching than winter wheat. The experiment continues.