Soil organic matter and soil quality - lessons learned from long-term experiments at Askov and Rothamsted

Summary

The various elements of an arable cropping system, such as crop type and cultivar, soil tillage, crop protection measures, use of mineral fertilizers and animal manure, crop-residue disposal, and addition of town-derived organic refuses all interact in a complex manner with basic soil properties (texture and mineralogy), and this interaction determines the general productivity of the cropping system. The same elements also influence soil organic matter (SOM) turnover, some more than others. The SOM holds large pools of organically bound plant nutrients, which, through mineralization, may become available for crop uptake or loss from the soil-plant system through leaching or gaseous losses. Additionally, SOM is important to both soil structure and the potential for soil erosion, to sorption of mobile plant nutrients and retention of pesticides, and to the CO2 balance between agroecosystems and the atmosphere. Thus SOM levels and turnover rates are intimately linked to soil properties of importance in maintaining an economically and environmentally sustainable agricultural production, and thereby also to soil quality.
Based on results from long-term field experiments conducted at Askov and Rothamsted experimental stations, we present in this chapter some of the lessons learned in relation to the role of SOM. We focus on the effects of cropping, applications of mineral fertilizers and animal manure, and crop-residue disposal on SOM levels, and on the effect of SOM on crop yields and certain soil properties. The presentation is by no means exhaustive but exemplifies the research potential of long-term experiments.