Soil Moisture Deficits

Press, Volume CIII, Issue 30568, 10 October 1964, Page 8

Soil Moisture Deficits

A GAIN this year on these pages it is proposed to advise farmers who irrigate of the soil moisture deficit at the Winchmore irrigation research station.

This year this will consist of the weekly deficit for an area not irrigated, compared with the deficit at the same time last season. In addition it is proposed to include the deficit information for a farm which can Irrigate every 14 days. This calculation will be based on the automatic irrigation unit on the research station. Irrigation is applied when the deficit is 100 points, or one inch, at each fortnight after September 14. On the roster date a decision as to whether or not to irrigate is made dependent on whether the deficit has reached 100 points or not. A tolerance of plus or minus half the average daily moisture loss is allowed. For the months of the season these tolerances are:

September, plus or minus three points; October, plus or minus four points: November, plus or minus five points; December, January and February, plus or minus six points;

March, plus or minus five points; April, plus or minus three points.

For example, if the weather is fine and the deficit has reached 95 points in the November-March period irrigation can be applied. If rain is considered likely and the deficit did not exceed 105 points in the same months irrigation could be postponed for 24 hours. However, if the deficit was less than 95 points irrigation could not be applied or if it was more than 105 points irrigation could not be delayed. On September 14 the deficit was 28 points and on September 28 it was 81 points so no irrigation was applied. The next roster date will be October 12. Until irrigation is applied the deficit on this unit will be about the same as on the non-irrigated area. The deficit advised by the station yesterday was 175 points compared with 96 at the same time last year.

Forms which will enable farmers to calculate their own deficits may be obtained free of charge from the Winchmore irrigation research station, Private Bag, Ashburton. i