New challenges in organic fertilization: soil quality indicators under long-term sewage sludge application

Abstract

Soils represent a fundamental part of life on Earth and represent a crucial player on climate change action, for their capacity to sequester atmospheric carbon (C) through organic matter stabilization, constituting one of the largest C-reservoirs. The management of soil organic matter (SOM) seems highly relevant for maintaining or improving soil function in Mediterranean agricultural areas. Mediterranean soils face several threats that increase soil susceptibility to degradation processes, hampering soil ecosystem services. Under the framework of the European Green Deal, and the need to promote circular economy, the use of sewage sludge (SS) as a fertilizer seems a good solution. When properly managed, it can be a way to prevent environmental pollution, recycle nutrients, and decrease the need for commercial fertilizers. Long-term experiments (LTE) can provide valuable data for soil science. The main objective of this work is to make a holistic assessment to the state of the soil after 28 years of continuous fertilization with sewage sludge. To be resilient with future challenges on food security, soil needs to be addressed according to its importance on the planet wellbeing. The work carried out in this thesis provides a functional assessment of the continuous use of sewage sludge as an organic fertilizer in agricultural land in the region of Navarra. It is important to consider the multiple soil functions and de-centralize crop-production from health indicators. Soils are not good and not bad, management yes. The results provided by this thesis highlight the importance of a healthy management of the soil and the bias provided by small-set of indicators. Agricultural soils provide important services that should be valued, not only those related to food production, but also to other key functions such as the control of soil degradation and vulnerability or climate regulation. The scientific community must coordinate and collaborate with politicians, policy makers, and stakeholders to explore these services, and to guide a transition to sustainable agriculture to address the challenges of the future.