USE OF BIOENERGY RESIDUES AS AMENDMENTS: IMPLICATIONS ON SOIL FERTILITY AND SOIL CARBON SEQUESTRATION

Abstract

The increasing use of renewable energy sources as substitutes to fossil fuels has provoked an increase in the production of bioenergy residues. These residues could

be effectively used for the recovery and conservation of soil fertility. However, the

effect of the organic residues on the soil ecosystem is different depending on their

physico-chemical characteristics and, particularly, the knowledge of the impact of

bioenergy residues on soil quality is still limited. The aim of this work is to study

the effects of different bioenergy residues on C and N mineralization and soil

microbial content and activity. A degraded soil (clay 49.7%, pH 7, OC 0.37%)

from Southern Spain was amended (0.5% w/w) with four different bioenergy

residues (anaerobic digestate, rapeseed meal from biodiesel production, bioethanol

residue and biochar) and three other organic residues commonly used as organic

amendments (wastewater sludge and two composts). The amended soil was then

incubated for 30 days at 20 ºC. During incubation soil CO2 evolution was measured

every 4 hours by means of an automatic chromatographic system. After 2, 7 and 30

days of incubation the following parameters were also analysed: K2SO4-extractable

C, N, NO3 -, NH4 + and P, microbial biomass C and some enzymatic activities involved in the cycle of the main nutritive elements (β-glucosidase, arylsulfatase,

esterase, alkaline and acid phosphatase and leucine aminopeptidase). Soil addition

of the different residues led to a general increase in C and N mineralization, in the

availability of nutrients and in the microbial content and activity, but with remarkable different values and dynamics. The only exception was represented by biochar that did not cause any significant variations of the measured parameters with respect to the control. The obtained results demonstrate that bioenergy residues may represent an effective alternative to usual amendments for the recovery and conservation of soil quality. The different physico-chemical characteristics of the residues suggest different uses. Rapeseed meal, bioethanol residue and anaerobic digestate are more suited to improve soil biological fertility, while biochar is more appropriated for the enhancement of soil organic matter content and to promote soil C sequestration.