Soil health and local recirculation ensuring organic cucumber cultivation in Norway.

Summary

New European organic regulation claims cultivation directly in soil in greenhouses. Cultivation practises in accordance with organic principles imply application of sustainable growing media and compost added for soil improvement. Local resources may be preferred. The goal of soil improvement is good soil health, including biological soil activity, nutrient availability, and physical properties. Only a few studies are done on biological soil health in greenhouses.
Biological soil activity was monitored in a greenhouse cucumber experiment on organic soil enriched with biochar and addition of local (1) compost, (2) solid digestate after biogas or (3) imported organic peat. Effects of silage mulching was tested. Biological activity was measured in soil by different indicators, and above soil, plant growth was followed.
Results indicated that the mixture with compost contained more organic matter than mixtures with solid digestate and peat. Biological activity in the compost mixture was lower and started later than in the two other mixtures and was in all mixtures more pronounced where silage mulch was added. Respiration rates and fungi content classified all three mixtures as stable growth media.
Nitrogen content and pH in all three mixtures were similar at the start of the experiment. The peat mixture needed most amendments, while phosphorous content was highest in solid digestate and lowest in peat. Plant nutrient turnover to plants was appropriate except lack of micronutrients. Yields performed well.
Preliminary conclusion is that although compost is based on microbial activity and taken for a protagonist in soil health, the results showed lower biological activity that started later than in the other mixtures. Balance between fungi and bacteria were in all three mixtures similar and equal to measurements in Norwegian, organic managed soil. Indicators were useful on farm level but could be diversified more. Local compost and digestate functioned as good as peat.