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Monday, March 6, 2017

How does the Tevatronic system handles fertilizer application?

Fertilizer is applied by the Tevatronic system as in other systems, by continuous fertigation, injecting diluted liquid fertilizer using fertilizer pumps

Traditionally tensiometer use requires usually averaging of several locations. How can the use of a single tensiometer overcome the variability in the field?

Traditionally tensiometers are positioned in 2-3 depths at several locations to obtain a statistically average value of tension because of soil and root density variability.
Tevetronic eliminate these variability, therefore it can use a single controllers. How the variability is eliminated?

a. By positioning the tension control at a shallow soil layer close to the dripper (15 cm deep, up to 15 cm from a dripper) where a dense root system exist.
We exploit the existing dense root layer and actively developing and maintaining it.

b. By controlling precisely irrigation depth.
The Tevatronic company developed the mathematical algorithm to irrigate precisely any soil depth while monitoring the tension at a shallow soil position.
When we aim to develop the root system at certain depth by precise irrigation and water percolate somewhat bellow (because of soil variability), it is not lost because the root system adjust and grow after the water. Soil variability is not eliminated but adjusting the soil layer to be explored by the root system and precisely irrigating that layer accommodate it.

Can precise irrigation without leaching cause salinity?

It is customary to maintain a leaching fraction to avoid salinity. In the Tevatronic system increasing irrigation depth is equivalent to a leaching fraction.

An alternate approach is to irrigate precisely and apply periodically an extra volume of water for leaching, when needed. Precise irrigation reduces salt and fertilizer input and periodical leaching can be as efficient as continuous leaching while wasting less water. Pepper was successfully irrigated with 2.8-3.5 dSm water

What is the maximal area that can be irrigated with a single controller?

A single controller normally irrigates a size of a field covered by a single valve.

In practice there are various consideration that dictates what actually is the

size of a plot that is controlled by a single valve: technical consideration can

limit the size of a plot (i.e. rate of water delivery), topography limitation and

uniformity of soil and plant size. Where there are no limitations on plot size, a

single controller/valve can irrigate as much as 20 ha.

How does the Tevatronic controller handles sequential irrigation?

The valve switch controller is programed to open a single valve at any time.

The first sensor to reach the threshold tension starts the sequence. Other

sensors will wait their turn. The sequential order is not fixed, it depends on the

soil water tension of the various sensors at any moment.

Why tension controlled irrigation is preferable to other soil sensor controllers?

Soil sensor probes are relatively cheap, require minimum maintenance and can

be automated for feedback irrigation but they have to be calibrated for water

content. Calibration is specific for the substrate (soil type, soil-less media) and

some of them are affected by temperature and salinity. In contrast, soil water

tension does not require calibration and it is not affected by salinity and

temperature. Furthermore, the water movement in the soil-plant- atmosphere

continuum is governed by tension difference. Soil water tension, plant water

tension and plant photosynthesis are directly related. Soil water tension is

therefore a direct measurement of plant performance, contrary to indirect

measurements by other soil sensor.

Do we need to fit threshold tension to plant and cultivar (vegetable, fruit trees, flowers, turf)?

Very likely yes because of the hydraulic resistance to water flow in

transpiration. More research is needed to evaluate the quantitative aspects of

the relation between hydraulic resistance and water potential in various plant

species. Water flows trough the plant in xylem vessels. The hydraulic

resistance is dependent on the anatomy of xylem vessels and the length for

water transport that are different in various plants. The higher the hydraulic

resistance a lower water tension is required to enable sufficient transpiration

and stomatal opening for photosynthesis.

Do we need to fit threshold tension to stage of growth (vegetative, flowering, fruit set, fruit development stages)?

Low threshold tension promotes vegetative growth. Leafy plant species (i.e.

lettuce, etc.) can benefit from low tension threshold that will promote rapid

growth. A low tension threshold is also beneficial in early stage of plant

development after seeding or planting when the root system is sparse and

during the development of a vegetative framework that flowers and bears fruit

at a later stage. A relatively low tension is required to achieve maximum fresh

fruit size.

Excess vegetative growth reduces fruitfulness. An appropriate tension,

specific for each species, is required to achieve the right balance between

vegetation and fruitfulness.

Stress, induced by low tension, affects fruit composition (i.e. increase dry

weight accumulation, oil concentration). The right stress can save water

without reduced yield or fruit size or alternately improve fruit quality, when

yield or fruit size is reduced, without financial loss.

How does the Tevatronic system knows and decides how much water to apply?

In the Tevatronic system the user adjust two parameters: threshold tension of

irrigation and irrigation depth. The plant dictates the frequency by the rate of

the drying soil and the mathematical algorithm calculates the required volume

to vet the chosen depth in each cycle of irrigation. It is that simple, no need to

calculate Penman for estimating evapotranspiration and plant coefficients.

Why monitor irrigation at a shallow soil layer and ignore deeper soil layers?

Monitoring a shallow soil layer has two main advantages: high root density

and response in real time. It is well known that there is a high density of fine

roots developing at a close proximity to the dripper. Positioning the

tensiometer at this position further enhance active root development for

monitoring, rather than relying on a sparse root system in deeper soil layers

that require measuring several locations for averaging.

The response time in a shallow position is shorter, enabling response in real

time. It takes longer for the water to reach the tensiometer in deeper soil

layers, extending the response time and making it difficult to maintain the

desired threshold tension.

How can Tevatronic irrigation controller control the irrigation depth?

A propriety mathematical algorithm was developed to determine the depth of

water percolation, based on parameters measured by the system in situ, taking

into account the soil texture.