Compost boosts soil life in practical test with shrubs

18 July 2022 - Published by Hanne Lakkenborg Kristensen

Written by Esther Hessel.

In Boskoop, with soils very rich of organic matter and peat, a grower of shrubs and confers applied compost. Application was part of a practical trial of Delphy.  In 2020, the grower added the compost before planting the prunus. In a layer of approximately 35 centimetre. In Boskoop replenishing the fields with specific soil is needed because of the extreme settling of the soils. The compost was mixed with additives. Based on the Soil Balance Analysis (BBA). A soil sample were the cation exchange capacity is examined together with the calcium, potassium and magnesium levels on this complex. In these analysis also spore elements are examined. Smeets Agroconsultancy developed for Delphy the tailor made compost. Greencompost was mixed with the following elements and products:

  • Lignite or braun coal; addition leads to more water holding capacity and binding of nutrients.  
  • Actionine; a potassium rich rock flour;
  • Lava; also a rock flour, but containing more calcium and spore elements;

Products with spore elements like cupper, zinc were added, together with Dolokal supra and magnesium because of the lack of magnesium in the field.



Why adding different products in the compost? In optimizing soil quality, application of a strategy is key.  Objective of applying compost with additives is to improve the chemical balance in the soil and to eliminate shortages of elements which are crucial for soil health and plant growth. But also to improve soil structure and biology in the soil. These three objectives influence each other and are connected. For example, by using compost the organic matter content of the soil increases, soil structure is improved. And the organic matter is the substrate were the soil life is multiplying and feeding.


First results in Prunus

Using compost, is applying organic matter to the field. In the peaty soils of Boskoop, the percentage of peat is already high, approximately 14-21%. Looking at the organic matter content there was, unexpected, no difference between 2020 en 2021.  The Cation Exchange Capacity, however, increased. Addition of compost leads to an increase in soil binding capacity of nutrients and water. The strategy resulted also in more plant available calcium, potassium, magnesium and phosphate. The pH of the soil increased also from 5,2 to 6. Both compost and lava are responsible for this increasing pH levels.


Boosting soil life

Soil life is crucial for mineralisation and making nutrients available for the plants. Increasing organic matter contents, adding lignite and also the rock flours are measures leading to an increase in soil life. In case of this trial investigation of soil life was made by using a PLFA. In which the phospholipid fatty acids of different organisms are measured.

The PLFA showed large increases of:

  • Gram + and gram- bacteria, respectively 115% and 122%. Gram negative bacteria are responsible for dissolving of phosphate. They improve the uptake of iron and other minerals.  Gram positive bacteria play a role in soil resilience.
  • Mycorrhizae: 218%
  • And 300% of the protozoa Protozoa eat bacteria and release nitrogen for the plants. Interesting what the addition of this specific compost is leading to in the soils.

Both the number and diversity of bacteria and fungi increased. By addition of this tailor made compost the three pillars of soil, chemical, biological and soil structure, improved. Fundamental for a healthy cultivation.


Added value in crop

As seen, the condition of the soil improved, looking at the soil life and availability of nutrients. Of course the improvement must be seen in the crop also. Therefore we assessed the crop growth. The crop was assessed by three experts in the tree nursery cultivation. Assessment was carried out in autumn 2020 and in summer 2021. We can conclude that the compost with additions leaded to steady growth of the plants. Possibly because of the large amount of compost applied.  In the second year the plants were in a better condition than the untreated plants. And crop length was comparable or better than the untreated plants.