Opportunities for soil carbon sequestration under old and new grazed grassland in the Netherlands.

Abstract

Soil carbon sequestration under agricultural soils is mentioned by the IPCC as a mitigation method to withdraw carbon-dioxide from the climate system of the earth. Grasslands could contribute to the withdrawal. In the Netherlands some grasslands are historically an important source of fodder for ruminants. Besides these relatively old soils the Netherlands has also relatively new soils, that are reclaimed from the sea. In a phosphorus (P) field trial that started in 1997, two old sandy soils, with an estimated agricultural use of 800 years, and a young clay soil, reclaimed in the 50s and in use from the 70s of last century, were part of the trial. In the trial the grassland use was a mixed grazed and mown system, as is usual on grazed farms in the Netherlands. Organic manure was annually applied, at a legally allowed dosage of balanced P fertilisation. On the two sandy soils the trial was running for 16 and 17 years, and on the young marine clay for 20 years and is still running. Soil organic carbon (SOC) was measured in this field trial, in 0-5, 5-10, 10-20, and 20-30 cm below surface.On the old sandy soils the SOC did not change over the trial period. On one sandy site, were the botanical composition was changed to a more clover-based sward, the division over the layers changed slightly: the SOC in the top soil decreased and increased in the two lower layers. On the other sandy site the SOC did not change. In the young marine clay, however, the SOC increased in all layers except on a field were no organic manure was applied and was not grazed.Assumed is that the old grasslands were saturated with SOC and that the clay soil could still sequester more carbon. The saturation level of this site is not known yet.