Effect of compost application on the dynamics of carbon in a nectarine orchard ecosystem

Highlights: • Compost at 5 and 10 t ha^-1 yr^-1 were compared with control and mineral fertilization for 14 years in a nectarine orchard • Compost at 10 t ha^-1 showed a plant growth and yield, similar to mineral fertilization • Compost application increased soil organic C, microbial and extractable C • The rate of compost application of 10 t ha^-1 showed a C storage in soils 3 times higher than the rate of 5 t ha^-1fold The aim of the present study was to compare the quantity and the type of carbon (C) stored during the 14-year lifetime of a commercial nectarine orchard ecosystem fertilized with mineral or organic fertilizers. The study was carried out in the Po valley, Italy, in a nectarine orchard of the variety Stark RedGold, grafted on GF677 hybrid peach × almond. Since orchard planting in August 2001, the following treatments were applied in a randomized complete block design with four replicates per block and compared: 1. unfertilized control; 2. mineral fertilization (including P and K at planting and N applied as NO₃NH₄ yearly at the rate of 70–130 kg ha⁻¹); 3. compost application at a rate of 5 Mg DW ha⁻¹ yr⁻¹; 4. compost application at a rate of 10 Mg DW ha⁻¹ yr⁻¹. Compost was obtained from domestic organic wastes mixed with pruning material from urban ornamental trees and garden management after a 3-month stabilization period. Application of compost at the highest rate increased C in the soil; the amount of C sequestered was approximately 60% from amendment source and 40% from the net primary production of trees and grasses with a net increase of C compared to mineral fertilization. Compost application was found to be a win-win strategy to increase C storage in soil and, at the same time, to promote plant growth and yield to levels similar to those obtained with mineral fertilization. The rate of C application is crucial, indicated by the fact that compost supply at the rate of 10 Mg ha⁻¹ yr⁻¹ was the only fertilization strategy of the ones tested that resulted in higher C sequestration. This shows that compost amendment may stimulate an increase in the net primary production of plants.