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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.

Tuesday, January 3, 2017

What is the optimal irrigation depth?

Root growth and exploration of the soil volume is dependent on available

water and nutrients therefore irrigation depth strongly affects rooting depth.

The choice of irrigation depth is based on several factors. Woody plants have

as a rule deeper rooting system (0-100 cm) than annuals (0-60 cm). Plant

species differ in rooting pattern, some tend to be shallow rooting (i.e. pepper,

lawn) and others deeper (i.e. maize). Soil texture, aeration and the existence of

a hard pen have to be taken into account when choosing an optimal irrigation

depth. The top soil layer contains organic matter and it is rich in nutrients

compared to the deeper soil layers. Wherever water is readily available,

adopting a strategy of minimal soil depth irrigation is a good practice from the

standpoints of increasing irrigation efficiency and exploiting the top soil layer

rich in nutrients and aeration.

How much water can be saved by the Tevatronic controller?

In an olive irrigation experiment an extreme case of 75% water was saved. In a

lemon orchard 58% water was saved, as compared to the extension service

recommendations. In a tomato irrigation experiment we saved 24% water,

compared to the best irrigation practiced today, based on previous

experiments. A 30% saving of water, without loss of yield, and sometimes an

increase in yield, is a conservative estimate of the water that can be saved.

Does the Tevatronic system improves yield and how much?

With the Tevatronic irrigation system it is possible to achieve the optimal

balance between vegetative and reproductive growth for top yields. An

increase of 4%-8% yield was achieved in many cases as a result of the precise

irrigation that prevented stress or water-logging. Furthermore, the ability to

impose precise stress for any length of time at any stage of the plant growing

cycle is a powerful tool that can be exploited to increase yield beyond what we

have achieved so far.

What consequences have precise and reduced irrigation on fruit quality?

Precise irrigation is essential to achieve maximum fresh fruit size when there

are no other limiting factors (i.e. light, photosynthesis, nutrient availability).

Reduced irrigation to a level when water becomes a limiting factor, reduce

yield and affects fruit composition. Changes have been found in dry weight,

oil content, soluble solids, titratable acidity, pH, juice viscosity and vitamin C

of fruits grown under stress. Using precise tension control it is possible to

maximize water saving without yield loss and alternately compensate yield

reduction by enhanced quality to avoid financial loss.

Can we incorporate the Tevatronic controller in existing irrigation controllers of other companies?

The Tevatronic irrigation system use solenoid valves, water and fertilizer

counters and fertilizer pumps available on the market and may exist in

controllers of other companies. All other components are unique and specific

for the Tevatronic irrigation system.

What is the unique aspect of the tension controlled irrigation of Tevatronic compared to conventional and other tensiometer in use?

Tevatronic tension controlled irrigation is autonomous, due to the integration of hardware and software developed by the company and the adoption of an appropriate method of operation.
Traditional tensiometers are analogs. The incorporation of pressure transducers into tensiometers enabled digital output,
continuous readings, processing the data and taking advantage of up to date communication for viewing the data.
The technology to couple tension readings to solenoid valves to initiate irrigation is already known for several decades.
More recently the ability to terminate the irrigation when a pre-set tension is reached, at the position where the tensiometer is located, was also introduced.
The next step of development was missing until Tevatronic developed a propriety algorithm that control precisely irrigation depth, independent of the tensiometer location.
The control of irrigation depth enabled a revolutionary change in the method of operation that finally transformed the system to fully autonomous:
initiating and terminating the irrigation without human intervention using shallow monitoring of tension combined with irrigation to any desired depth.
The Tevatronic system does not rely on statistical averaging of root density and soil variability, as common in other tension controlled irrigation systems,
but actively eliminate the root density variability (shallow monitoring) and bypass the existing soil variability (irrigation depth control). 

Do we need to fit threshold tension to soil type (sand, light soil, heavy soil, soil-less media)?

- Yes we do. The question is why. Soil water tension is a measure of suction, it

is the force by which the soil particles bind water and quantitavely is

expressed in units of Paskal (i.e. kPa – kilo Paskal). The force is negative and

absolute and therefore it is independent of the soil type. A -30 kPa is the same

potential energy in sand, light or heavy soil types. It can be argued therefore

that the plant need to invest the same amount of energy to extract water from

all soil types and threshold tension does not have to be adjusted. However,

Soil texture varies in different soil types and volumetric water holding

capacity varies according to soil type. A 20% available volumetric water

content in sand has a much lower water tension (ca. -10 kPa) than a heavy soil

water tension (ca. -80 kPa). To supply the same amount of water needed for a

plant in sand as in heavy soil we need to maintain a lower water tension in