1. Automatic water emitting-sensing system, based on integral tensiometers placed in homogenous environment
Department of Soil and Water Science, Faculty of Agricultural Food and Environmental Sciences, Hebrew University of Jerusalem, Rehovot, Israel1
Sharon Dabach1, Naftali Lazarovitch2 and Uri Shani1
Introduction
Figure 1: System discharge (dots) and total radiation (line) during the 5th and 8th weeks after planting
Figure 2: Matric head as measured by Geo-Tensiometer and ceramic tensiometer during the 33rd and 52nd DAP
2 cm 1 3 2
A new tensiometer, Geo-Tensiometer, was developed. The Geo-tensiometer is inexpensive, reliable and easy to maintain.
Integrating the Geo-Tensiometer into the wrapped dripper created a homogenous media in which the matric head reading took place. The Geo-Tensiometer was indifferent to soil mechanical changes.
The IOD system with the irrigation regime responded to daily and seasonal changes of the plant water uptake.
The IOD system maintained high and constant matric head in the soil while keeping the drainage minimal.
Objectives
Results
Irrigated agriculture is using increasing quantities of water and fertilizers to supply the growing food demand. However, the uptake by various plants is only 30 to 50% of the water applied. The remaining water flows to surface water and groundwater.
Irrigation water should be applied according to the plant demand to improve water use efficiency. In order to achieve this, an inexpensive and reliable matric head sensing system and an irrigation system that can adjust its discharge, are required. The location of the sensors in the soil and the irrigation algorithm are of great importance in this kind of systems.
To develop a dripper-sensor instrument (Tensiodripper) which emits water, enhances root growth and is part of the sensing system.
To design and test an irrigation regime which adjusts the irrigation system discharge rate according to the change in the plant water uptake during a single day and a whole season (IOD, Irrigation On Demand).
Geo-Tensiometer - Consists of 3 parts:
Filter holder
Filter
Geo-textile wick
Irrigation regime experiment
Ten lysimeters were filled with ‘Havazelet’ sand and subsurface drippers were installed. Each dripper was covered with a double layer of Geo-textile. A Geo-Tensiometer was inserted between those layers to form the Tensiodripper. A ceramic tensiometer was installed in each of the lysimeters at a distance of 3 cm from the Geo-Tensiometer. The plants used were sunflowers (Helianthus annuus L., cv. Yellow Dwarf)
Every night the system automatically determined the irrigation threshold, for that day. Each time the matric head dropped below the irrigation threshold an irrigation pulse was applied.
Figure 1 shows the system discharge rate and the net radiation. The system discharge rates changed during each day in accordance to the net radiation measured at the growth site. In the 8th week, even though the radiation was lower, the water demand of the plants was higher and therefore the system increased its discharge rate to supply the water uptake.
The matric head measured by the Geo-Tensiometer and a ceramic tensiometer is depicted in Figure 2. The changes in pulse density cause the system discharge rate to change. The increase in total irrigation pulses between day 33 and 52 explain the increase in the total system discharge rates as seen in Figure 1. There was no change in the Geo-Tensiometer response to irrigation during the entire experiment as opposed to the ceramic tensiometer.
Figure 3 shows the average root weight in the lysimeters at 3 different locations. The root weight in the dripper area was higher than in the other locations even though plant density was uniform in the lysimeter surface area. The Geo-textile provides an ideal media for root growth since it is a part of the water source in the soil and it has low mechanical strength.
Blaustein Institutes for Desert Research, Ben-Gurion University of the Negev, Israel2
5th week
8th week
Figure 3: Average root weight between laterals, between drippers along the drip line and near the dripper in the lysimeters
Conclusions
Materials & Methods