Exploring the depths: Uncovering the contribution of deep water and nutrient uptake by chicory
Research output: Book/Report › Ph.D. thesis › Research
Deep-rooted agricultural crops can explore subsoil resources that more shallow-rooted crops do not have access to. This gives deep-rooted crops the potential to utilize deep water and nutrient pools and reduce periods where growth is limited by unfavourable conditions in the topsoil. The question is how much of an advantage this gives deep-rooted crops, and under what circumstances deeper rooting is beneficial? Chicory (Cichorium intybus L.) is known to be deeprooted and able to reach more than 3 m depth, but the contribution of deep roots to water and nutrient uptake under well-watered and drought conditions and when exposed to competition in the topsoil has not been studied. This dissertation presents results from a central experiment carried out in 2016 and 2017, where chicory was grown in 4 m tall soil filled rhizotrons. Root development was observed through transparent surfaces and with the use of ingrowth cores. Water and nutrient uptake under various conditions was studied using water content sensors and hydrological and nutrient tracer techniques. Water uptake from 1.7 m depth in 2016 and 2.3 m depth in 2017 contributed significantly to chicory water use. However, contrary to expectations neither drought nor intercropping increased the deep water uptake. It was concluded that though chicory benefits from being deep-rooted when topsoil resources are limited, the deep water uptake cannot compensate for the reduced topsoil water uptake during drought. Chicory also acquired trace element tracers applied at 2.3 m depth and 15N labelled nitrogen applied at 3.5 m depth. The trace elements Li, Rb, Cs, Sr, and Se were used as nutrient analogues to trace nutrient uptake activity. Tracer uptake from all tested depths tended to be lower in chicory exposed to drought than when well-watered. This in accordance with the observations of water acquisition, where no compensatory uptake from deeper soil layers was observed. However when chicory was intercropped with shallow-rooted species, the results gave indications of a compensatory tracer uptake from 2.3 and 2.9 m depth. The study also tested the use of multiple trace element tracers to be used interchangeably as root activity tracers. Furthermore this project contributed to a study using coloured roots to distinguish intercropped species and to a study on the automatization of root observations in soil. Reviewing the use of hydrological isotope techniques to study water uptake dynamics, revealed an inclination in the literature to draw conclusions, which data does not deliver evidence for. This dissertation discusses the limitations of studies only observing changes in the relative distribution of water uptake, and call attention to the risk of confirmation bias.
|Publisher||Department of Plant and Environmental Sciences, Faculty of Science, University of Copenhagen|
|Publication status||Published - 2019|