because it offers the advantage of precisely applying both water and fertilizer at a high efficiency, thus creating a potential for larger yields and reduced water and fertilizer applications.
The desired frequency of drip irrigation depends on factors such as soil texture, rooting pattern about the drip line, wetting around the drip line, evapotranspiration (ET) rate, rainfall, and crop type.
Frequent irrigations maintain relatively constant soil moisture content with time, an objective of drip irrigation. However, very frequent irrigations, such as multiple irrigations per day, can result in much time spent filling pipelines and laterals; and, the frequent drainage of pipelines after cutoff of irrigation water can create nonuniform water applications and increase the potential for phytophthora (Phytophthora parasitica) caused by excessive soil moisture content along the lower end of the field, a problem experienced by some growers.
Infrequent drip irrigations may cause water stress between irrigations in some crops and soil textures because of a limited amount of stored soil moisture, due to both the wetting and root patterns around the drip line.
Infrequent irrigations on coarse-textured soils also could result in substantial percolation below the root zone during irrigation because of their limited soil-moisture storage capacity, which reflects the wetting pattern around the drip line.
From a grower’ perspective, however, less frequent irrigations reduce labor and management requirements, although automation could reduce labor needs even under very high-frequency irrigation.
A number of projects on drip irrigation frequency have been conducted.
Drip irrigation frequencies of 7 to 8 times per day and about every 3 d during periods of maximum ET had no statistically significant effect on tomato yield in clay loam.
On loam soil, greater cantaloupe (Cucumis melo) yields occurred for weekly irrigations compared to daily irrigations and higher onion yield for daily irrigations compared with weekly irrigations; irrigation frequency had little effect on carrot (Caucus carota) yield.
A trend of increasing tomato yield with decreasing irrigation interval was found on a loam for irrigation intervals of 1, 2, and 5 d.
Little irrigation-frequency effect was found on cabbage (Brassica oleracea Capitata Group) yield for intervals of 3, 6, and 12 d on clay loam.
The effect of drip irrigation frequencies of 1, 3, 5, and 7 d on corn (Zea mays) yield grown in a silt loam was not critical in this study.
The effect on crop yield of drip-irrigation frequencies of two irrigations per day (2/d), one irrigation per day (1/d), two irrigations per week (2/week), and one irrigation per week (1/week) was investigated for lettuce (Lactuna sativa), pepper (Capsicum annuum), and onion (Allium cepa) grown on sandy loam, and processing tomato (Lycopersicon esculentum) grown on silt loam during experiments conducted during 1994 to 1997.
All treatments of a particular crop received the same amount of irrigation water per week.
Results showed that the 1/week frequency should be avoided for the shallow-rooted crops in sandy soil.
Irrigation frequency had little effect on yield of tomato, a relatively deep-rooted crop.
These results suggest that drip irrigation frequencies of 1/d and 2/week are appropriate in medium to fine texture soils for the soil and climate of the project site.
There was no yield benefit of multiple irrigations per day.
Other soil types and environmental conditions may produce similar results.