Agriculture

The utilization data of RAINCATCHER that you will find in the different parts of this section are generic data: our specialists can direct you towards a use adapted to your horticultural or agricultural needs.

You will find in the chapter "AGRICULTURE AND IRRIGATION" a broad explanation of the possibilities of the use of the RAINCATCHER and its principle of operation.

The other chapters will show you how to use RAINCATCHER on a daily basis in the different fields of activity.

We will soon be giving access to the download of an automatic dosage , simulation tool from RAINCATCHER to apply.

Their draining characteristic does not allow a satisfactory retention of water from plant roots. In the same way, they are scarcely (if at all) capable of transporting water from the deep layers by capillarity, and to retain it.

Loamy soils (0 to 10% clay) 

These soils differ from sandy soils in their ability to form a crust, which is often very hard.

If they are too worked, they can become compact which reduces the infiltration capacity of the water during wet periods.

With a low rate of clay and organic matter, the formation of aggregates is often poor, which is a brake on the supply to roots of essential materials for their good development.

Clay soils (25 to 40% clay) 

These soils have a good ability to carry water by capillarity from the deep layers, but the diffusion is slow and does not cover the entire water requirements of plants.

The color of these soils is darker and their aggregations are more distinct. Aggregation decreases the risk of crust formation.

Clay soils (> 40% clay) 

Heavy clays have a high water-retention capacity, but most of this water is tightly bound and unavailable to plants.

The humus content is often higher than that of other mineral soils. They do not form a crust.

Soil texture

This is determined by the size of the soil particles and their respective proportions. Recall the dimensions of the three categories of soil constitutive particles:

• Coarse sand: 0.2 mm to 2 mm
• Fine sand: 0.05 to 0.2 mm
• Coarse silt: 0.02 to 0.05 mm
• Fine silt: 0.002 to 0.02 mm
• Clay: (commonly called clay) 0.002 mm and less

The structure of these particles can be compact or aggregated. In the latter case, the particles are bonded together while having spaces allowing the transport of oxygen and carbon dioxide to the roots.

The water content is a function of the porosity and permeability of the soil. The maximum volume of water that a soil can hold is the "field capacity" FC, or soil holding capacity that depends on its particle size.

Climates condition by the volumes of precipitation and by induction, the types of soils.  

The place and the type of soil of the location where RAINCATCHER will be used will be, of course, a determinant, but it will also be necessary to specify the type of climate according to the region and / or the latitude: in a country like France, one can find several types of climates that have a direct influence on the types of soils and geology they have carved for centuries.

Soil moisture

In the soil, water can be divided into 3 states:

1. The water of gravity or saturation contained in the gaps (between the aggregates) which flows by gravity towards the aquifer. The wetting point for saturated soil corresponds to the end of flow of water by gravity.
2. The Total Water Availability (TWA) or Soil Moisture Content (SMC) is the water used by the plant which is retained in the form of rather thick films around the earth particles or in the fine capillaries. When the TWA is exhausted, we are at the point of permanent wilting.
   The TWA can be divided into 2 parts: the RAW (Ready Available Water) or hydric comfort and the MAD (Management Allowable Depletion) which generates water stress.
3. Unusable water which is the water retained vigorously in the form of very thin films around the particles of earth and unusable by the plants. The retention capacity or Field Capacity corresponds to the TWA + unusable water. The TWA varies according to the soil types from 1/3 (in sandy soil) to 2/3 (in clay soil) of the retention capacity.

A plant that will leave the area of the TWA, either because of soil too waterlogged (or too much moisture in a greenhouse), or because of a drastic drying, will perish respectively by asphyxiation or wilting.
 

Total water available TWA – soil moisture content SMC

The volume of water available to plants, expressed in millimeters per centimeter of soil depth and called the Total Water Available TWA, therefore includes the “Ready Available Water” RWA and the “Management Allowable Depletion” MAD or "Survival Reserve".

The TWA is, as its name suggests, a reserve that must be regularly replenished to prevent the plant moving into water stress.

The TWA depends on 2 parameters: the soil depth colonized by the root system (about 1 m for an annual wheat or maize crop) and the soil texture.

For a depth of 1 m, useful reserve values are obtained ranging from 70 mm of water for coarse sandy soil, to 200 mm of water for loam-clay soil.

The root volume varies according to the plants. We can divide the vegetable plants in 3 groups according to their rooting:

• Low rooting: about 15 cm, radish, salad ...
• Average rooting: about 20 cm, onion, potato, cabbage ...
• Strong rooting: more than 30 cm, turnip, carrot, tomato, eggplant, zucchini, spinach ...

As an indication, the average value of the TWA is:

• 0.9 to 1.2 mm / cm of soil for sand,
• 1.3 to 1.6 mm / cm of soil for a clay loam,
• 1.8 to 2 mm / cm of soil for a clay soil, silty clay, sandy clay.

The texture of the soil has a direct influence on the UK:

• Sandy soils have low water retention capacity, which implies lower RUs.
• Soils with a high proportion of fine particles (silts and clays) store more water; in return, a large part of these water reserves remain unavailable for plants because of horizontal circulation or by difficult capillaries.

Other important points:

• The coarse elements (soil elements whose size is greater than 2 mm: pebbles, gravel ...) do not allow to store water. Soils with a high proportion of coarse elements therefore have a limited TWA.
• Organic materials have higher retention capacities than clays. By contrast, they make water restoration more difficult. However, the balance of organic inputs remains positive in the TWA.
• The TWA of a soil can be evaluated from the texture. This is determined by the granulometric analysis of the soil (distribution of particles of a soil according to their sizes). 

The Texture Triangle is used to estimate the TWA by soil type. The TWA is expressed in millimeters of water per centimeter of fine soil (particles less than 2 mm in size).

Ready available water (RAW)

Plants can never extract all the water from the soil because the root capacity differs according to the type of plant and the roo volume. The plants use only part of the TWA: The Ready Available Water.

The RAW of a soil is also expressed in millimeters of water per cm of fine soil. It is difficult to estimate, but can be estimated at 60% of the TWA in the absence of precise analysis and at least half of the hydrated RFU should be maintained to avoid water stress.

Example of estimating the TWA of a soil from the texture triangle 

For a low to medium stony soil over a horizon of 80 cm deep (= depth of colonizing roots) composed of:

• 0 to 30 cm: 90% of fine earth of which 15% of clays, 60% of silts and 15% of sands.
• 30 to 80 cm: 50% of fine earth of which 35% of clays, 40% of silts and 25% of sands.

Calculation of the TWA and the RAW on this horizon:

According to the Texture Triangle and the associated coefficients, this horizon corresponds to a fine silt soil in the first 30 cm and a clay loam soil in the 50 cm below.

• The fine silt TWA = 1.75 x 30 = 52.5 mm
  This soil consists of 90% fine earth (<2 mm), so the TWA is 52.5 x 0.9 = 47.25 mm.
• The TWA of clay loam = 1.95 x 50 = 97.50 mm
  This soil consists of 50% fine soil (<2 mm), so the TWA is 97.5 x 0.5 = 48.75 mm.

On 80 cm, the total TWA is therefore 47.25 + 48.75 = 96 mm.

The RAW of the horizon is therefore = 96 X 0.60 = 57.6 mm.
 

The coefficient of permeability 

The permeability (k) of a soil is defined by the rate of infiltration of water into the soil; k is measured by Darcy's law:

A layer is deemed impervious for values of k of the order of 9 - 10m / s. The water that falls on the soil surface begins to moisten the upper part of the soil (for a few centimeters): part of which is evaporated directly during and after the rain.

With the warming of the climate, natural irrigations have become increasingly outdated and are often applied to dry soils and the type of soil, that holds a coefficient of permeability limiting the penetration by gravity.

The plant receiving large amounts of water in a short time is not able to take advantage of this excess of abundance.

*mm/total crop period

Water requirements by plant cycle

Plants are living creatures that consume water for their growth and it is important to help them settle after planting. We must follow the watering the first 15 days to allow them to avoid later problems such as the "black ass" for tomatoes or peppers.

The quality of the plants has an influence on the resistance to drought: old plants will emit fewer roots and therefore have a lower resistance to drought (squash, salads in particular).

Throughout the growth of the plant, the water needs will be different and they can be quantified according to:

• ETo: Reference evapotranspiration in mm of evaporated water / day
• ETc: Crop evapotranspiration = K x ETo,
• K: crop coefficient varying according to the stage of the plants.

As an example, for a crop grown in a hot climate:

Vegetables do not have the same needs according to their stage of cultivation. For example, for the tomato, the ETc reaches a maximum at the 4th bouquet in flower or at the 1st fruit maturing ie turning to red.

Racinary values of the main crops

Effective Rooting Depth of Mature Crops for Irrigation System Design

Estimation of water requirements by difference between TWA and ET

Let's take an average plant with a depth of rooting of 20 cm in a soil of loams to the TWA of 1.8.

The TWA of the horizon will be (1.8 x 20) x 0.6 = 21.60 mm

With an ET= 4mm / day, the soil water reserve for the plant will then be 21.6 / 4 = 5.40 days.

We usually apply a correction of 80% in desirable water supply (excluding salad): 5.40 / 0.80 = 4.32

This results in about 4 to 5 days of reserve for a plant rooted at 20 cm.

Estimation of ET  

ET varies considerably depending on meteorological parameters such as wind, sunshine and heat. On average, we consider the values of the following table:

ET in mm according to climate:

Mean daily temperature

The values in the table above, which only take into account heat, are therefore only indicative and show that the ET can vary twice for an average ΔT of 20 °. Irrigation water evaporates very quickly on hot soil and at high temperatures, whether on the surface or in the soil. The heat increases in parallel the perspiration of the plant but in lesser proportions.

It is also necessary to increase the ET by 10 to 20% in windy regions.

By compiling all the theses that have been made on the ratio Perspiration / Evapotranspiration, we also find that the Latitude of the place of culture has an influence on the ET varying the perspiration of 30 to 70% by following the gradient of increase heat.

We estimate at -30% the influence of RAINCATCHER on the ET (and thus the ETc) under this type of climate.

We thus extrapolate this table which matches the new TWA of the ground vis-à-vis the ETc under the action of RAINCATCHER, by considering a complete TWA following a consequent watering after application of the RAINCATCHER:

Application 

The application of RAINCATCHER will be 15 to 100 kg per hectare depending on the terrain.

Our specialists will make a personalized study and advise you on the ideal dosage to apply according to your parameters. We will soon be providing our customers with an online simulation tool to tell you the earnings generated by using the RAINCATCHER.

Results observed with RAINCATCHER

• In Germany, in clay soils and in an ocean-continental climate, our customers have already given us feedback on the use of RAINCATCHER for carrot cultivation, which is consistent with our calculations:

• In South Africa, under a more arid climate, significant results were observed on the size of carrots with application of RAINCATCHER between 25 and 50 kg per Ha according to the time of the year:

• In France, an experiment on the cultivation of tomatoes with drip irrigation was conducted in the summer of 2019 in the region of Salon de Provence in hot weather: the weight of vegetables was more than doubled:

On the left, the biggest of the tomatoes pushed with RAINCATCHER, on the right the biggest of the tomatoes pushed without: