Gypsum’s Role in Worldwide Rice Production
Brent Rouppet, Ph.D., Agronomist
Rice (Oryza sativa L.) is the most important human food crop in the world, directly feeding more people than any other crop. In 2012 (latest data) nearly half of world’s population, more than 3 billion people, relied on rice every day. It is the staple food across Asia where approximately half of the world’s poorest people live, and is becoming increasingly more important in Africa and Latin America. Ninety percent of the world crop is grown and consumed in Asia. Rice is the only major cereal crop that is primarily consumed by humans directly as harvested, and only wheat (Triticum aestivum) and corn (Zea Mays L.) are produced in comparable quantity (source: Infoplease.com).
Rice has fed more people over a longer time than has any other crop. It is especially diverse both in the way it is grown and how it is used by humans. Rice is unique because it can grow in wet environments that other crops cannot survive in. Such wet environments are abundant across Asia. The domestication of rice ranks as one of the most important developments in history and now thousands of rice varieties are cultivated on every continent except Antarctica. (source: ricepedia.org)
Though rice is a staple food for half of the world’s population, farmers need to produce more food in less area since agricultural land use is diminishing day by day. The world population is
expected to be exceeded 9 billion by 2040 with an increase of about 50% in less than 40 years (U.S census Bureau, Population Division, 2009). Therefore, production of enough food to feed the growing world population is a continuous challenge for farmers.
While the current world population is over 7.5 billion, it is projected to be 9.8 billion by the year 2050. Already of the 7.5 billion, 2 billion people suffer from malnutrition and hunger is soaring to levels without modern precedent. Now farmers, agronomists and soil scientists are being called upon to do an additional job of producing the extra food.
Among the yield limiting factors of rice, several soil conditions play an important role that affect the quality and quantity of all agricultural crops. In irrigated agriculture worldwide, the number one issue that growers are facing is soil structure related problems, and these problems are escalating. There are specific problems for plant growth and production in saline and sodic soils; especially poor soil structure which limits water and air infiltration, and root penetration into the soil. Reclamation of these soils requires the leaching of exchangeable sodium and other harmful salts from the root zone.
How Gypsum (CaSO4.2H20) Can Help Worldwide Rice Production: The only way improved soil structure has been accomplished worldwide is with the application of calcium sulfate products, mainly gypsum. The calcium removes the sodium and magnesium from the cation exchange sites, and now these ions can be leached down through the soil profile. Other calcium products simply cannot supply enough calcium to get the job done. High levels of sodium and magnesium are especially detrimental to overall soil health.
Climatic changes, especially water shortage, have also driven agronomists and soil scientists to develop production technologies for cultivation of rice under limited water conditions. Developing technologies to save water such as cultivation of direct seeded rice by drum seeder, maintain of alternate wetting and drying condition in rice field, plus the use of gypsum have proved to make rice production much more productive under limited water conditions.
A field experiment was conducted on a zinc deficient highly deteriorated sodic soil of the Ghabdan soil series in Asia to determine the effect of different rates of gypsum and different rates of zinc on rice production. Gypsum application significantly increased yield and zinc uptake in rice due to a significant decrease in soil pH and increase in calcium and zinc supply. Zinc application alone significantly increased soil and plant Zn but yields were poorer than with gypsum application alone because of calcium deficiency and/or sodium toxicity. Zinc applied together with gypsum markedly increased yield and zinc uptake. (source: researchgate.net).
Also, investigations on the nutritional aspects of calcium in improving rice growth and yield were conducted in solution and soil cultures in naturally salt-affected fields. In the case of solution culture, gypsum was applied in the presence of sodium chloride salinity. Three rice cultivars of differential salinity tolerance were used. Application of gypsum proved to increase panicle length, number of tillers, paddy and straw yield under both saline and saline sodic soils as well as in naturally salt affected field. Also, seed setting was improved in all the three cultivars (Source: Soil Science Society of America Journal).
Gypsum has been proven to help soils and plants for myriad reasons since in nature it is unique and incomparably versatile and multifunctional. This naturally mined product serves without equal as a fertilizer, a soil conditioner and a soil amendment.
Major benefits of high-quality gypsum:
- An excellent fertilizer source for calcium and sulfur. With calcium and sulfur deficiencies appearing more and more frequently worldwide, gypsum is a practical and economical source of these essential nutrients.
- Improves soil structure and compacted soils. Water penetration problems cause ponding and runoff, depriving root systems of needed moisture and oxygen, and wastes irrigation water.
- Amends and reclaims soils high in destructive sodium and magnesium. Sodium and magnesium (to a lesser extent) act the opposite as calcium in soils by destroying structure and reducing water, air movement and root growth.
- Replaces harmful salts. Sodium, chlorine and many other salts in higher levels in irrigation water and soil are detrimental to plant growth.
- Helps with high bicarbonate irrigation water. Bicarbonates form free lime when water evaporates resulting in reduced available calcium and increased soil pH.
- Enhances water use efficiency. Twenty-five to 100 percent more water is available in gypsum treated soils vs. untreated soils; less irrigation water is required to achieve the same results.
- Reduces runoff, erosion and soil crusting. Aggregates stabilized by gypsum are less prone to crusting and erosion since there is limited runoff due to larger, more stable aggregates.
- Along with humic acid, composts, manures and other plant materials, use of gypsum helps rebuild the supply of soil organic matter.
It has been stated that gypsum’s routine and frequent application is actually necessary for the sustainability of all irrigated soils.