Agrochemical characterization, net N mineralization, and potential N leaching of composted olive-mill pomace currently produced in southern Spain

TY - JOUR

T1 - Agrochemical characterization, net N mineralization, and potential N leaching of composted olive-mill pomace currently produced in southern Spain

AU - Gómez-Muñoz, Beatriz

AU - Hatch, David J.

AU - Bol, Roland

AU - García-Ruiz, Roberto

PY - 2013

Y1 - 2013

N2 - In S Spain, the Andalusian olive oil industry generates annually 2.5-3.0 million tons of olive mill pomace, a by-product which is comprised of the residues from the two-phase oil-extraction process. The agricultural policies of the EU have led to widespread interest in recycling these agricultural by-products. Olive mill pomace might be evaluated as an organic fertilizer after composting, however, before wider use of composted olive mill pomace is advocated, characterization of the final product is needed. In this study, the physico-chemical characteristics, net N mineralization, and the potential for N leaching of 7 out of the 11 olive-mill-pomace composts currently produced in the Andalusian olive mills were investigated. Compost of olive mill pomace differed in the proportions of raw materials co-composted with the olive mill pomace, such as olive leaf material, manure, and straw. In all the composts tested, organic matter, total C and K were high with 60.5%, 30.7%, and 1.7% on average, respectively, whereas total P was low (0.4%) and with intermediate levels of N (1.5%). Compost pH (8.03), electrical conductivity (2.85 dS m-1), and germination index (65% on average) were adequate for agricultural use. Furthermore, principal component analyses revealed a clear relationship between the quality of the composts and the proportion of manure mixed with the raw materials. Net N mineralization was negative on average (-20 μg IN g-1) after 1 y, but positive after 2 y of incubation with up to 94% of available N from the total N added and the short-term potential N leaching after compost application was negligible (less than 3.9% of added N) and much lower than the other N fertilizer with up to 80% added N leached. Overall, results of this study clearly show that these currently produced composts of olive mill pomace are suitable as soil improvers for agricultural purposes, but may not contribute significantly as a N fertilizer for up to 2 y after application.

AB - In S Spain, the Andalusian olive oil industry generates annually 2.5-3.0 million tons of olive mill pomace, a by-product which is comprised of the residues from the two-phase oil-extraction process. The agricultural policies of the EU have led to widespread interest in recycling these agricultural by-products. Olive mill pomace might be evaluated as an organic fertilizer after composting, however, before wider use of composted olive mill pomace is advocated, characterization of the final product is needed. In this study, the physico-chemical characteristics, net N mineralization, and the potential for N leaching of 7 out of the 11 olive-mill-pomace composts currently produced in the Andalusian olive mills were investigated. Compost of olive mill pomace differed in the proportions of raw materials co-composted with the olive mill pomace, such as olive leaf material, manure, and straw. In all the composts tested, organic matter, total C and K were high with 60.5%, 30.7%, and 1.7% on average, respectively, whereas total P was low (0.4%) and with intermediate levels of N (1.5%). Compost pH (8.03), electrical conductivity (2.85 dS m-1), and germination index (65% on average) were adequate for agricultural use. Furthermore, principal component analyses revealed a clear relationship between the quality of the composts and the proportion of manure mixed with the raw materials. Net N mineralization was negative on average (-20 μg IN g-1) after 1 y, but positive after 2 y of incubation with up to 94% of available N from the total N added and the short-term potential N leaching after compost application was negligible (less than 3.9% of added N) and much lower than the other N fertilizer with up to 80% added N leached. Overall, results of this study clearly show that these currently produced composts of olive mill pomace are suitable as soil improvers for agricultural purposes, but may not contribute significantly as a N fertilizer for up to 2 y after application.

KW - Agrochemical characterization

KW - Composted olive mill pomace

KW - N mineralization

KW - Olive orchards

KW - Potential N leaching

KW - Recycling by-products

U2 - 10.1002/jpln.201200421

DO - 10.1002/jpln.201200421

M3 - Journal article

AN - SCOPUS:84884984556

SN - 1436-8730

VL - 176

SP - 655

EP - 664

JO - Journal of Plant Nutrition and Soil Science

JF - Journal of Plant Nutrition and Soil Science

IS - 5

ER -