The limited water holding capacity of sandy soils (4-8% by volume) represents a management challenge in vegetable production – especially when growers are attempting to produce shallowed rooted crops like onions or crops with high rates of moisture use like tomatoes. The standard approach to managing these crops on sandy soil is to irrigated heavily and frequently – resulting in poor water use efficiency and the leaching of valuable soil nutrients. As supplies of water become more limited and the environmental impact of nutrient leaching becomes a greater concern options for better managing the moisture requirements of vegetable crops on sandy soils are needed. Drip irrigation systems coupled with soil moisture monitoring systems may represent the answer as they allow for application of small amounts of water (no nutrient leaching) whenever required by the crop. In a trial with onions in Oregon, Shock et al (2005) showed that a drip system calibrated to deliver ½” of water in a single irrigation event each day produced higher yields and better onion quality than systems calibrated to deliver water either more or less frequently. Munoz-Carpena et al (2005) showed that a drip system coupled to tensiometers could be used to begin irrigating a tomato crop whenever soil moisture levels dropped below a threshold amount (-15kPa). This system applied small amounts of water up to 5 times each day. The frequency of irrigation had no impact on yields but total water use with this system was substantially reduced relative to crops irrigated using other control systems.
Sources: Shock, Feibert and Saunders (2005). HortTech 15: 652-659
Munoz- Caprpena, Dukes, Li and Klassen (2005). HortTech 15: 584-590.