Measuring changes in soil nutrient availability at the root surface using ion-selective electrodes in Advanced Technologies for Measuring Nutrient and Water Availability to Plants

AJ Miller, J Borras, SJ Smith & DM Wells

For research on crop nutrition, in order to control nutrient supply to roots, plants have been usually grown in hydroponic culture. There are some disadvantages in growing plants under these conditions because this is an artificial situation due to the lack of a normal rhizosphere at the root/soil interfaces. The rhizosphere and associated root morphology may have important consequences for nutrient acquisition by roots. The aims of this research were to investigate more fully nutrient availability in the soil/root interface by developing a method for growing roots in rhizoboxes containing soil. This method allows direct access to the root surface and we have been able to directly measure potassium and nitrate availability at the root surface using microelectrodes. These measurements showed that gradients can develop along the length of the root. The microelectrode measurements led to the idea that this methodology can be used for direct evaluation of nutrient availability in the soil. In agriculture the efficient use of fertiliser by crops is achieved by matching supply to demand but in practice this is very difficult to achieve, particularly as the nutrient requirements for each type of crop are different and change throughout the season. Regular and accurate measurement of soil nutrient status is very important in all agricultural systems. The ability to manage soil nutrient supply to match the changing crop demand depends on these measurements. However, soil nutrient status is dependent on a range of different factors such as soil type, weather conditions (particularly temperature and rainfall), and previous cropping regimes. Measurements of nutrient status are also complicated by the heterogeneity of soil as each method gives a value at one point in the field. Soil heterogeneity can be both spatial and temporal, but usually soil measurements are taken shortly before a fertiliser treatment so that application rates can be adjusted to account for what is available. The development of nutrient soil sensing probes makes it possible to measure changes in soil nutrient availability throughout the year that can be used to advise on future fertiliser applications.

Available online before publication in Proceedings of the Dahlia Greidinger Symposium