1.   Purpose and objectives

     To describe methods monitoring soil water under drip-irrigated crops, using soil physical techniques, with a view to improving irrigation scheduling using only tensiometers.

2.   Description

     This report describes experiments carried out in drip-irrigated sugar cane in Mauritius directed at understanding all processes involved so that the efficiency of irrigation could be increased. The emphasis was on saving water without reducing crop yield. Details of the site, its climate and soil are given together with a description of the instrumentation, which included a neutron probe and arrays of tensiometers. The importance of measurement in the soil as well as above ground in assessing an
irrigation system is stressed.

      An explanation of techniques developed for the analysis of data from irrigation schemes is given. These include diagrams showing the two- dimensional distribution of water potential in the plane at right angles to the drip line, and the concept of soil water Status - a method of summarizing large quantities of data from tensiometer arrays. There is detailed analysis from the sugar cane experiments of water movement under different irrigation regimes and hence of irrigation efficiency.

      Situations are identified where inappropriate regimes might be used on crops if determined solely by observation of the crop itself without measurements in the soil. In order to prevent this, a method for
scheduling irrigation directly from measurements in the soil is proposed using 'index' tensiometers. The results of experiments applying this technique are described and the method compared to normal water budgeting.  There is a discussion on the circumstances of climate, crop type and layout which would be best suited to each of these methods, with both simplicity and efficiency in mind. Suggestions and recommendations are made as to how index tensiometers might be used in commercial practice.

      One of the Appendices gives an outline of soil physics theory and terminology as it applies to this report.

3.   Input

     Not applicable.

4.   Output

     Not applicable.

5.   Operational requirements and restrictions

     Applicable to drip-irrigation schemes. Not restricted to sugar cane, but possibly less appropriate for crops whose yield is significantly affected by short periods of water shortage.

6.   Form of presentation

     Report in English.  67 pages, 31 figures, 7 tables.

7.   Operational experience

     Some knowledge and experience of soil physics are necessary in order to appreciate fully the details of this report and make use of its conclusions.

8.   Originator and technical support

     Institute of Hydrology, Wallingford, Oxon OX10 8BB, UK.

9.   Availability

     From HOMS National Reference Centre for the United Kingdom.

10.  Conditions on use

     Free of charge.