S15 - Session O4 - Acidification, N-mineralisation and carbon sequestration in an orchard soil at Klein-Altendorf after 50 years

Authors: Achim Kunz, Michael Blanke *

In the strive for sustainable and resilient horticulture, the objective of this study was to investigate long-term (60 years) effects of different fertilisation viz orchard management strategies at Klein-Altendorf, University of Bonn (50°N), Germany (ca. 600 mm annual precipitation; 9.6 °C; fertile luvisol on loess). Both the grass mulch from the alleyways and the cuttings/prunings remain in the orchard. The four treatments of 40 trees each were 1) control trees without fertilisation; 2) lime (1 t CaO /ha/10 years to stabilise the pH near the optimum for stone fruit; 3) lime as above plus organic fertiliser; 4) lime with inorganic NPK n on the herbicide strip - with the following results after 60 years: 1) Control apple and cherry trees without fertilisation grew well without nutrient deficiency symptoms or yield depression; 2) lime (1 t CaO/ha/10 years) increased soil pH from to pH 6.3 to pH 6.7, whereas the pH in the un-fertilised plot dropped to pH 5.7-5.9, thereby confirming the proposed slow soil acidification in the herbicide strip; 3) lime as above plus organic fertiliser (3 t DM pig manure/ha) in the first and then green compost (ø 10 t DM/ha) in the last 12 years increased humus and nitrogen mobilisation in spring; 4) lime as above plus inorganic NPK fertiliser (40 kg N/ha/year) increased both pH and soil nutrient content; 5) lime as above plus organic fertiliser accumulated the largest total nitrogen (Nt) with the largest nitrogen mineralisation (28 - 55 kg Nmin/ha) in spring, double that of the other plots (18-28 kg Nmin/ha) primarily as NO 3 and also as NH 3 . 6) lime plus organic fertiliser increased the humus content by 2.5 fold from 1.8 % (in 1968) to 4.3%,in 2021, i.e. a rate of 0.03% humus/year and potential for carbon sequestration, of 0.7 t CO2/ha/year, if organic matter was continuously supplied.