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 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.

Olive pulp and its effluents suitability for soil amendment.

Olive pulp (OP) and its effluents produced after digestion processes were characterised and their suitability as soil amendment materials were investigated. Results showed that OP and its effluent for hydrogen (EH2) and methane production (ECH4) contain high amount of organic matter, remarkable concentration of nutrients and negligible content of heavy metals. Decreasing concentrations of low molecular weight phenols (monomeric phenols) and increasing amount of humic-like materials were found passing from OP to EH2 and ECH4. The effects on both wheat seed germination and seedlings growth were also investigated. Addition of OP at the highest doses delayed both seed germination and seedling growth. These effects decreased when the OP and its effluents were incorporated into the soil. On the contrary an enhancement of seedlings growth was detected by addition of EH2 and ECH4. Enhancement effects also were found out by addition of lower OP concentrations. The phytotoxic effects decreased when the products were incorporated into the soil.

Effects of aluminum sorption on calcium-polygalacturonate network used as soil-root interface model.

The objective of this study is to determine the influence of aluminum sorption on a calcium-polygalacturonate (Ca-PG) network used as a soil-root interface model. The Ca-PG network is exposed to aluminum solutions at different concentrations (25-800 microM) at pH 3.50. High concentrations lead to a release of calcium (80%) and aluminum becomes the predominant reticulating cation of the polygalacturonic chains. The FTIR spectra show how aluminum sorption induces shifts of the characteristic bands of carbohydrates in the spectral regions of 1700-1400 and 1200-800 cm(-1), which are enhanced by decreasing intensities. This might be induced by a weakening of the metal-PG complex through conformational variations of the structure. Scanning electron micrographs also show a collapse of the fibrillar structure of Ca-PG that is due to aluminum sorption. This structural rearrangement suggests that the soil-root interface could modify its functionality, affecting the transport of metal ions (nutrients) across the interface and consequently through the cell membranes.