Author: Mr. Guy Sela, CEO of SMART! Fertilizer Management software and an international expert in plant nutrition and irrigation.
When properly designed and managed, drip irrigation has many advantages over other irrigation methods, including: elimination of surface runoff, high uniformity of water distribution, high water usage efficiency, flexibility in fertilization, prevention of weed growth and plant disease. Drip systems are also easily integrated in fertigation systems and automation.
Traditionally, irrigation water is applied to the entire field, whether by sprinklers or by flood irrigation, resulting in a significant loss of water. Drip irrigation (or trickle irrigation) is a modern irrigation method in which water is delivered directly into the root zone of the plant.
This kind of system uses low pressure and low flow rates and water is applied only to specific zones in the field, where plants are grown. Typical drip emitter flow rates are 0.6 - 16 L/hr (0.16-4.0 gal/hr), and the most commonly used emitters are of 1-4 L/hr.
The main challenge in designing a drip irrigation system is selecting the right combination of dripper spacing, their total number and their required discharge for a given soil and crop.
The two major factors that affect the selection of the proper combination are the physical characteristics of the soil and the water requirements of the crop.
Drip emitters create different sub-soil wetting patterns in different soil types.
The texture of the soil determines the vertical and horizontal distribution of water in it.
In coarse textured soils (sandy soils) water will tend to spread more vertically, while in fine textured soils (clay soils) there will be a considerable lateral movement, resulting in a larger radius of the wetted zone.
Effect of soil type and drip emitter discharge
on water distribution
Q = Drip emitter discharge Q (1) > Q (2)
(Click image to enlarge)
Therefore, spacing between drip emitters in sandy soils should be smaller than in fine textured soils. To get a uniform irrigation in row crops, spacing between drip emitters should result in an overlap between the wetted zones of each two drip emitters.
Another factor affecting the radius of the wetted zone is the emitter discharge.
The water requirement of the crop and the time available for irrigation are used to determine the number of emitters needed.
A 1.2 l/hr drip emitters were selected, the water requirement of the crop is 3 l/day, irrigation frequency is once in 4 days and time available for irrigation is 2 hours.
Water amount needed per irrigation : 3 l/day/plant X 4 days = 12 liter/plant.
Irrigation rate required: 12 liter / 2 hours = 6 l/hr.
Number of drip emitters required: (6 l/hr) / (1.2 l/hr/emitter) =
5 drip emitters per plant.
Drip irrigation allows for flexibility in the application of fertilizers, since fertilizers can be easily applied through the irrigation water (fertigation). This way nutrients are delivered with the irrigation water, directly to the active root zone of the plants.
Nutrients are supplied frequently at low concentrations, to meet the plants' needs. It was found that roots in the wetted area increase their efficiency of water and nutrient uptake.
Therefore, selective wetting of the soil, as achieved by drip irrigation, allows for savings both in water and fertilizers. Drip irrigation can also reduce nitrate losses due to leaching.
Traditional irrigation methods are characterized by high fluctuations in soil-moisture content, as high quantities of water are applied at long intervals.
These fluctuations affect plant growth and crop yields. Drip irrigation systems are able to supply small amounts of water at high frequency intervals. As a result, a relatively constant moisture level of the soil can be maintained.
The optimal range of moisture in the soil can be maintained at all times and managed more easily, because water is applied in precise quantities on a precise schedule, according to the crop requirements. This promotes water saving, as well as enhances growth and production.
In addition, the selective wetting prevents evaporation of water from areas outside the wetted zone.
If properly designed and managed, drip irrigation allows for better salinity management, and a lower salt content of the soil can be achieved, compared with other irrigation methods.
Because water is applied at high frequencies and the moisture content of the soil is relatively high, the salt content of the soil is approximately similar to that of the irrigation water.
In addition, fertilizers applied through the irrigation water are much more diluted. The high frequency of fertilizer applications, given at precise rates, can prevent salt stress to the crop.
However, in drip irrigation salts tend to accumulate close to the margins of the wetted zone, midway between the drip emitters. The accumulated salts may be washed by rain into the root zone of the plants and cause salinity shock.
Salt accumulation at the top soil
Another problem that might occur is that during the change of crops, the high concentration of salts at the top soil may prevent the germination of new seeds and damage young plants planted in the regions of high salt concentrations.
Possible solutions to these problems are to design the drip system with closely spaced emitters or alternatively, leach the salts periodically, using a sprinkler system.
Effect of emitter spacing on wetting pattern
Because pores in the drip emitters are very small, emitters tend to clog frequently. Read more about emitters clogging potential.