Soil carbon, pH and yield development in a long-term humus balance trial
Agriculture has to be performed in a sustainable way in order to sustain high yields and to support a globally growing population. Functional soil properties are fundamental for high yields and in order to achieve good soil conditions sustainable management is a key. Loss
of soil organic material and increased soil acidity are problems associated with degradation of soils and hence less sustainable agriculture. In this thesis, the effect of different agricultural systems on soil organic matter, pH and yield was examined. The systems examined are a cereal system with straw removal or returning and a ley system, all with different nitrogen levels. In order to compare the results and to get a wider understanding of the subjects a literature review has been performed. The systems are located in Sweden on four different sites from South to North; Lönnstorp, Lanna, Säby and Röbäcksdalen.
Assumptions were that the ley system should give more carbon to the soil then the cereal system and if straw was removed carbon content should decrease more. Further, the systems with nitrogen fertilizer should result in higher soil carbon. As for pH there was an assumption that ley should be more acidifying than cereals and that non fertilized ley system should be more acidifying than the system which received fertilizer.
The results showed that soil C contents decreased less when nitrogen was applied to the cereal treatments as compared to the no N treatment. Further straw management, return vs
removal, gave different effects on soil C contents. The cereal system reduced soil carbon more than the ley system. In unfertilized leys, pH decrease was more pronounced compared to fertilized ones indicating the acidifying effect of biological nitrogen fixation. The main conclusion from the yield results showed that application of N fertilizer increases yield. Nitrogen fixation in the legumes did not compensate for an application of 150 kg
N/ha in the ley systems. No correlation between yield development and soil C content was found as suggested by literature. Initial carbon content has a greater influence than management over an increase or decrease in soil carbon content.