Wednesday, January 27, 2010

Week 5: Irrigation

The first irrigation in week 2 was 7 mm, and this water went all the way down to the 40 cm depth detector. In weeks 2 ands 3 I gave 10 mm and 14 mm. These amounts reached the 20 cm detector, but not the 40 cm depth. This is understandable. The growing crop dries the soil, so each subsequent watering does not goes as deep. This week I estimated that around 20 mm of drip irrigation should reach 40 cm. But there was no response from the deep detector. I kept watering – 25 mm, 30 mm, 40 mm… By now water was starting to run off the beds into the furrows. Finally, after 46 mm had been added, the 40 cm wetting front detector collected a sample. The reason? Salt in the washing machine water has made the soil less permeable. Since the water cannot infiltrate as fast it spreads sideways, and therefore does not go as deep. The end result was that my irrigation ratio was just over 1. This means I applied just over the maximum amount of water I expect a mature crop could use in a week.