Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

A cushion of air trapped under the rice fields of Senegal

30.04.2004


Irrigation by surge flooding, a technique used essentially in rice cropping, involves the input of large volumes of water. In some regions, this water does not infiltrate to any depth. Poor infiltration like this can cause severe loss in soil quality and harm crops. Recent investigations on such a situation in a rice field in the River Senegal valley, involving water budget monitoring for 100 days, the length of a cropping season, have confirmed a lack of water infiltration below 40 cm depth. Scientists from the IRD and Pernambuco Federal University of Brazil jointly conducted the project. Mathematical models revealed that air, trapped in dry soil owing to the clay content, is confined and compressed between the wetting front which progresses from the surface and the water table below. The resulting cushion of air creates a blockage, slowing down then stopping the water’s filtration deeper into the soil. This investigation offers new lines of approach that might explain intense salinization of the soil that occurs in some regions of the world.



Rice cultivation uses great volumes of water, especially where the submerged-field method involving surge flooding irrigation is practised. Maintenance of a layer of water on the soil surface throughout the cropping period usually favours its infiltration deeper down. However, it has been known for many years that in some regions water often does not reach deep into the soil. This unusual feature, poorly understood up to now, becomes a problem in rice fields in arid areas because it can have harmful effects. Although from one point of view it conserves a mass of water, in that flow does not penetrate too deeply and remains entirely available for the rice to grow, it can lead to soil quality loss. Absence of infiltration lets mineral salts accumulate in the root zone, and an intense salinization sets in. That process can generate hydraulic stress which acts on the plants, limiting their growth or even killing them.

How can such a low rate of drainage be explained? An IRD team from research unit 67-ARIANE Les sols cultivés à fortes contraintes physico-chimiques des régions chaudes, working jointly with a Brazilian researcher (1), determined the water budget in rice farmers’ plots in the River Senegal valley. They employed mathematical models to define the water-flow events in the soil.


The rice fields, located on clayey soils, were situated above a water table lying at between 1.50 and 2 m depth. The research team quantified water input and output throughout the cropping period, about 100 days. Most of the water input to the plot was consumed by the plant and the average infiltration rate was extremely low (below 0.1 mm/day). In order to obtain a more precise water budget, measurements were made of the soil water tension and capillary pressure, the water content profiles and the water table depth. These measurements showed that the water brought in by irrigation hardly filters down at all beyond 40 cm depth below the surface. A zone exists between 40 and 50 cm depth which does not become saturated during the cropping season. Moreover, calculations of the infiltration flux confirming the measured values at plot level indicated that the water table was essentially fed by leakage from the bed of the irrigation canal and not by infiltration of water from the s! urface layer.

These results prompted the research team to suggest the presence of an isolating body of air under the rice fields. This hypothesis was rapidly confirmed using digital models. Up to now, most soil water transfer models, such as Hydrus, considered that air escaped freely and did not affect the water infiltration. This theory, valid for many situations in the field, proved not to be so in the case under investigation. A model taking the presence of air into account showed the entrapment of air contained in the soil between two wet fronts: the wetting front of water infiltrating from above and the water table deeper down. This air under compression appears to inhibit downward penetration of water in that the air has to leave the soil pores if the water is to enter and take its place.

The great quantities of water pushed into the rice fields are therefore almost completely consumed by the crop plants. The lack of drainage at depth means that there no leaching occurs and salts are not diluted. Air entrapment is probably a feature common to all irrigated rice-growing areas on clayey soils throughout the world. This phenomenon could explain the extensive salinization affecting the North-East Thailand rice fields. Investigations are soon to be conducted there to quantify the influence of air entrapment on water budgets and salt levels. Eventually, cultivation practices that can overcome poor drainage and salt accumulation could be developed.



(1) The partners involved in this research work carried out in Senegal belong to the Federal University of Pernambuco in Brazil (A.C.D. Antonino of the Department of Nuclear Energy), and to IRD (P. Boivin, C. Hammecker and J.L. Maeght from research unit UR 67)


FOR FURTHER INFORMATION

Contact: Claude Hammecker – IRD UR 067 " Les sols cultivés à fortes contraintes physico-chimiques des régions chaudes " - 300 avenue Emile Jeanbreau, 34095 Montpellier cedex ? France. Tel.: +33 (0) 4 67 14 90 28. Fax.: +33 (0) 4 67 14 90 68. Email: Claude.Hammecker@msem.univ-montp2.fr

Contact IRD Communication: Bénédicte Robert (press officer), Tel.: +33 (0)1 48 03 75 19, Email:presse@paris.ird.fr

Reference:
C. Hammecker, A.C.D. Antonino, J.L. Maeght, P. Boivin, 2003 - Experimental and numerical study of water flow in soil under irrigation in northern Senegal: evidence of entrapment, European journal of soil science, vol. 54, n°3, pages 491-503 (13).

To obtain illustrations concerning this research
Contact Indigo Base, IRD picture library, Claire Lissalde or Danièle Cavanna, Tel.: +33 (0)1 48 03 78 99, Email: indigo@paris.ird.fr

Bénédicte Robert | IRD
Further information:
http://www.ird.fr/us/actualites/fiches/2004/199.htm

More articles from Agricultural and Forestry Science:

nachricht Combination of Resistance Genes Offers Better Protection for Wheat against Powdery Mildew
22.01.2018 | Universität Zürich

nachricht New study shows producers where and how to grow cellulosic biofuel crops
17.01.2018 | University of Illinois College of Agricultural, Consumer and Environmental Sciences

All articles from Agricultural and Forestry Science >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Artificial agent designs quantum experiments

On the way to an intelligent laboratory, physicists from Innsbruck and Vienna present an artificial agent that autonomously designs quantum experiments. In initial experiments, the system has independently (re)discovered experimental techniques that are nowadays standard in modern quantum optical laboratories. This shows how machines could play a more creative role in research in the future.

We carry smartphones in our pockets, the streets are dotted with semi-autonomous cars, but in the research laboratory experiments are still being designed by...

Im Focus: Scientists decipher key principle behind reaction of metalloenzymes

So-called pre-distorted states accelerate photochemical reactions too

What enables electrons to be transferred swiftly, for example during photosynthesis? An interdisciplinary team of researchers has worked out the details of how...

Im Focus: The first precise measurement of a single molecule's effective charge

For the first time, scientists have precisely measured the effective electrical charge of a single molecule in solution. This fundamental insight of an SNSF Professor could also pave the way for future medical diagnostics.

Electrical charge is one of the key properties that allows molecules to interact. Life itself depends on this phenomenon: many biological processes involve...

Im Focus: Paradigm shift in Paris: Encouraging an holistic view of laser machining

At the JEC World Composite Show in Paris in March 2018, the Fraunhofer Institute for Laser Technology ILT will be focusing on the latest trends and innovations in laser machining of composites. Among other things, researchers at the booth shared with the Aachen Center for Integrative Lightweight Production (AZL) will demonstrate how lasers can be used for joining, structuring, cutting and drilling composite materials.

No other industry has attracted as much public attention to composite materials as the automotive industry, which along with the aerospace industry is a driver...

Im Focus: Room-temperature multiferroic thin films and their properties

Scientists at Tokyo Institute of Technology (Tokyo Tech) and Tohoku University have developed high-quality GFO epitaxial films and systematically investigated their ferroelectric and ferromagnetic properties. They also demonstrated the room-temperature magnetocapacitance effects of these GFO thin films.

Multiferroic materials show magnetically driven ferroelectricity. They are attracting increasing attention because of their fascinating properties such as...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

10th International Symposium: “Advanced Battery Power – Kraftwerk Batterie” Münster, 10-11 April 2018

08.01.2018 | Event News

See, understand and experience the work of the future

11.12.2017 | Event News

Innovative strategies to tackle parasitic worms

08.12.2017 | Event News

 
Latest News

Thanks for the memory: NIST takes a deep look at memristors

22.01.2018 | Materials Sciences

Radioactivity from oil and gas wastewater persists in Pennsylvania stream sediments

22.01.2018 | Earth Sciences

Saarland University bioinformaticians compute gene sequences inherited from each parent

22.01.2018 | Life Sciences

VideoLinks Wissenschaft & Forschung
Overview of more VideoLinks >>>