Agricultural intensification without adequate restoration of soil fertility may threaten the sustainability of agriculture. Quantitative estimation of plant nutrient depletion from soils is useful for comprehending the state of soil degradation and for devising corrective measures. Nutrient-balance exercises serve as instruments to provide indicators of the sustainability of agricultural systems.
Nutrient-balance studies have used a variety of approaches and methods for different situations. However, the information has remained scattered in several publications. In order to address this issue, the Land and Water Development Division (AGL) of FAO organized an electronic conference on ‘Assessment of soil nutrient depletion and requirements - approach and methodology’ from September 2002 to July 2003. The electronic conference enabled institutions, agencies and scientists to share information and exchange ideas, views and experiences on the subject. A background document reviewing known approaches and methodologies was made available to the participants as a starting point for discussion.
This publication is the outcome of an amalgamation of the technical contents of the background paper, the inputs of the electronic conference, and further reinforcement through the latest literature and analysis. The publication presents a state-of-the-art overview of nutrient-balance studies. It brings out the evolution of the various approaches and methodologies, provides for comparisons among them, and highlights the improvements made and the issues that are still to be addressed. It categorizes case studies into macrolevel, mesolevel and microlevel classes. The macrolevel is used for national, continental and global farming-system levels. The mesolevel coincides with the level of the province, district and agro-ecological zone. The microlevel is largely defined as the farm or village level. For each case, the study explains the methodological approaches, the elements of the nutrient balance, and the calculation of the nutrient flows. Furthermore, it also discusses knowledge gaps and caveats that warrant attention.
The intention is for this publication to help bridge the scientific knowledge gap and to provide updated information on nutrient-balance approaches and methodologies to the scientific community, higher level extension workers, decision-makers, non-governmental organizations and other stakeholders concerned with agricultural development.
