In large-scale experiments with intermittent irrigation of rice fields, extending over four years, it has been found that the rice does not suffer in quantity or quality, under this practice. On the contrary there is usually some increase in yield, and the physical qualities are slightly improved. However, the effect on some varieties and in some soils may be somewhat variable.
In addition, it has been found that the amount of water used with intermittent irrigation is less than with continuous flooding.
Under ordinary field conditions, there was a reduction of over 80 per cent in the number of anopheline larvae found, while with good conditions breeding of anopheles was entirely controlled.
Intermittent irrigation requires special preparation of the fields and of the irrigation and drainage systems, and needs close supervision, which makes it somewhat more expensive than the ordinary method. However, once the fields are set up for this practice, the economic advantages resulting from an increased yield, and better conditions for labor, stimulate interest on the part of the growers, and the practice is spreading slowly.
It is concluded that intermittent irrigation is the only feasible method so far evolved for the control of anopheles breeding in the rice fields of Portugal.