| Abstract |
The objective of the present work is to investigate possibilities of enriching soil organic carbon (SOC) and humus in fruit orchards as an ecosystem service. Results are presented from a 50-year long-term fertiliser trial at Klein-Altendorf near Bonn, Germany. The location (50 degrees N) is exposed to westerly Atlantic winds buffered by the mild Rhine valley. The temperate zone climate is characterised by ca. 600mm annual precipitation and 9.6 degrees C annual temperature. The soil is a fertile luvisol with 90 (out of 100) soil fertility points on loess currently planted with cherry cv. 'Kordia' on GiSelA 5. The grass mulch from the alleyways and the cuttings/prunings remain in the orchard. The four (out of eight) selected treatments, comprising 40 trees each, for this contribution were (1) control trees without additional fertilisation; (2) lime (1t CaO/ha and 10 years to stabilise the pH near the optimum for stone fruit; (3) lime as above plus organic fertiliser; and (4) lime with inorganic NPK-all applied to the tree herbicide strip only-with the following results: (1) control trees without any additional fertilisation grew well without any nutrient deficiency symptoms or yield depression, (2) occasional lime (1t CaO/ha in 10 years) over 50+ years increased soil pH from pH 6.3 to pH 6.7 within the optimum soil pH for stone fruit orchard, whereas the pH in the unfertilised plot dropped to pH 5.7-5.9, thereby confirming the slow soil acidification in the herbicide strip proposed in the literature, (3) lime as above plus organic fertiliser (in the form of pig manure at 3t dry matter/ha) in the first year and then green compost (average 10t DM/ha and year) in the last 12 years increased humus 2.5-fold from 1.8% in 1968 to 4.3% in 2021, equivalent to a 0.03% increase in soil humus content per year, (4) similarly, SOC more than doubled from 1% to 2.5% doubling with 37.5 t CO2/ha carbon sequestration over 50+ years or 0.7 t CO2/ha and year in the plot with organic fertiliser, (5) lime as above plus inorganic NPK fertiliser (40kg N/ha and year) increased both pH and soil nutrient content. These results are discussed with respect to a dual-purpose use of fruit orchards. Under the Bonn soil and climate conditions, humus enrichment in the soil, carbon sequestration and increase in SOC were only achieved with frequent supply of organic matter. |