The role of lysimeters in the development of our understanding of soil water and nutrient dynamics in ecosystems
This paper considers the development of lysimeters and their role in the evolution of our understanding of the dynamics of water and plant nutrients in ecosystems. Lysimeters are delineated volumes of soil. They can be divided into those filled with repacked soil, and those enclosing an undisturbed monolith. The original repacked lysimeter was developed to investigate the concept that all life stems from water, and is considered to be the first quantitative experiment in history. It focussed on the growth of a willow tree and how much of the increment was derived from the soil solids. From this start some 360 years ago lysimeters quickly contributed to the quantification of the transpiration stream and the differentiation of water loss by evaporation from the soil from loss via the leaves of plants. Chronologically, further development began about 210 years ago with the exploration of whether precipitation could account for all the water moving from the land to the oceans, and was the origin of springs. In part, this required a careful quantification of soil evaporation, runoff and deep drainage. This in turn led to the quantification of the soil water balance. As a result, we are able to predict indices, such as crop water use efficiency, drainage and irrigation requirements, contributions to stream flow, groundwater recharge and nutrient loss by leaching. Recognition that the quantification of drainage and leaching required soils of natural structure and profile integrity resulted in the building of the first monolith lysimeter and the development of ‘pan’ or ‘Ebermayer’ lysimeters. Improved technology allowed a better understanding of the role of soil in the regional water balance through the development of small diameter lysimeters that could be transported to a central location subject to the same climatic variables. In contrast, other technological changes allowed the impact of typical soil management operations carried out using regular machinery to be applied on field-scale lysimeters. The contribution of the different types of lysimeter to the development of our understanding of soil use and management is considered.