Karbon til bondens beste

Summary

In the last 20 years, the investigated farms have had either solely arable farming or crop rotations with grassland included. We do also present simple methods for assessment of soil quality for agricultural advisors and farmers. More carbon storage in soil is wanted to both remove CO2 from the atmosphere and enhance organic matter content, which improves the agronomic characteristics of the soil when it is low in organic matter. Crop rotations with grassland and fertilization, particularly with manure has been seen upon as measures to enhance the content of organic matter and thus carbon storage in soil. However, there have been done few investigations on this in silty and sandy soils. We have chosen Surnadal and Sør-Østerdal and Solør areas because there are farms with silty sand in both those areas and because they are placed in two different climatic zones (coast and domestic climate). Both places have farms with solely arable farming and farms with grasslands in the crop rotation. We selected eight farms in each of two areaes. In Surnadal there were four arable farms and four farms with also grasslands in the crop rotation. In Sør-Østerdal and Solør there were less differences in the crop rotations between farms with solely arable land and crop rotations with grassland included. The farms were fertilized with mineral fertilizer and animal manure, mainly slurry from cattle or pig. On the farms with grassland included in crop rotation there were none that only used mineral fertilizer. On each farm two fields with cereals 2020 were chosen. On each of these fields two sample areas were selected where we investigated soil physical, biological, and chemical parameters. The period of sample collection lasted from August until October 2020, and it was in all farms done shortly after the cereal was threshed.
We observed a clear trend with more organic carbon, better soil aggregate formation and aggregate stability, more rapid transformation of organic matter and more earthworms with grasslands included than by solely arable farming. Isolated, many of these factors are not significantly different, but together they showed a pattern with better soil conditions when grassland is included in crop rotations. For the factors root depth, penetration depth, soil infiltration, soil pore volume, POXC-carbon and soil respiration, the difference between solely arable farming and when grassland is included, is not so clear. One could assume that a part of the differences between farms with and without grassland in crop rotation could be explained by more manure used in farms with grassland, but that is not the case. Contradictory, on some of the arable farms larger quantities of animal manure was used than on the farms with grasslands included. However, we observed that fertilization with animal manure increased carbon storage, improved aggregate stability, and enhanced soil respiration on arable farms.
We recommend the spade as the best tool to judge soil structure, dense layers, root growth, content of earthworms and degradation of plant material from last year. This can be supplemented with various simple methods like digging down a piece of cotton cloth, or a tea bag and then examining how much is left a few months later. Penetrometers and infiltration measurements can provide valuable information, but moisture conditions and soil type must be considered in the assessments. Bouncing tails and other small insects can be caught in a trap and counted. There are several simple microbiological tests under development such as Pasco CO2 sensor, Solvita basal CO2 and Microbiometer. We will gather more experience before we make recommendations on them.