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

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 NONH yearly at the rate of 70-130 kg ha); 3. compost application at a rate of 5 Mg DW ha yr; 4. compost application at a rate of 10 Mg DW ha yr. 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 yr 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.