Subsoil loosening in a crop rotation for organic farming eliminated plough pan with mixed effects on crop yield

Summary in the original language of the document

Compacted subsoil may reduce root growth with resulting effects on plant uptake of water and nutrients. In organic farming systems subsoil loosening may therefore be considered an option to increase nutrient use efficiencies. We investigated the effect of subsoil loosening with a Paraplow to c. 35 cm depth in an organic farming experiment at Foulum (loamy sand) and Flakkebjerg (sandy loam) in Denmark. In each of the years 2000 to 2004 one half of four plots per site were loosened in the autumn in a young grass-clover crop established by undersowing in spring barley. The grass-clover was grown for a year as a green manure crop and followed by winter wheat, lupin:barley and spring barley in the following three years. On-land ploughing was used for all these crops. Penetration resistance was recorded in all crops, and the results clearly showed that subsoil looseling had effectively reduced the plough pan and that the effect lasted at least 3.5 years. Measurements of root growth at Foulum in 2002/03 did not show marked effects of subsoil loosening on root density in the subsoil. Subsoil loosening resulted in reduced growth and less biological nitrogen (N) fixation of grass-clover crop in which the subsoil loosening was carried out. This had a marked effect on the growth of the succeeding winter wheat. Negative effects of subsoil loosening on the yield of winter wheat was observed without manure application and in years with high winter rainfall, whereas small positive yield effects of subsoil loosening was observed in crops with a good N supply. There were no marked effects of subsoiling on yield of the spring sown crops, although subsoiling had a tendency to increase crop growth and yield of spring cereals and pulses during dry summers. The results suggest that subsoil loosening can only be recommended under Danish conditions in case of severe subsoil compaction.