Soil Moisture Monitoring with Special Reference to Irrigation Management

Abstract

Inspite of the importance of soil moisture in the hydrological cycle and to the economic development of mankind, it has received relatively little attention from research workers. This study emphasizes the need for reliable soil moisture monitoring in both agriculture and water engineering, and attempts to improve existing monitoring methods especially those concerned with irrigation management. A review of the existing direct and indirect monitoring methods is presented and details are given of a field study based upon neutron probe practice and involving the establishment of a small network of monitoring sites.  Data obtained from the field study is used to investigate the spatial and temporal variability of soil moisture both within sites and between sites. Comparisons are made between the measured variations in soil moisture deficit and those estimated by the computer system operated by the Meteorological Office and the hand method proposed by the Ministry of Agriculture Fisheries and Food. A cost-effectiveness study of soil moisture networks based upon neutron probe practice is presented and recommendations are made concerning the design and operation of such networks. A computer model of the soil-moisture-plant system, incorporating simulation of the principal physical processes involved, is developed, calibrated and proven. The model is shown to provide reliable estimates of the soil moisture deficits in each of three soil layers when tested against field data, and is also shown to provide a means of irrigation scheduling based upon the crop's state of stress as opposed to the moisture deficit of the soil. Finally, proposals are made for the improvement of existing monitoring Systems and the developments of new systems for on-farm use, and recommendations are made for further research.