How to produce rice with low water consumption

Study finds that irrigation by aspersion, coupled with rain, raised the productivity of dryland crops to levels similar to those of flooded plants.

By José Tadeu Arantes

Agência FAPESP – A Brazilian study on rice growing in non-flooded conditions, with water supplied through rainfall and complemented by a system of aspersion irrigation in drought periods, has been drawing significant international attention.

The study, coordinated by Carlos Alexandre Costa Crusciol, full professor at Universidade Estadual Paulista’s School of Agronomic Sciences (Unesp) in Botucatu, and conducted with FAPESP funding, was recently published in the Agronomy Journal. The study has broad implications, particularly in Asia.

The reason for the significance of the study findings is easy to understand: rice growing under the traditional system of irrigation by flooding (in which crops are submerged in between 7 to 10 centimeters of floodwater for up to 120 days) consumes 24% to 30% of all fresh water in the world.

Fresh water has become one of the planet’s most precious resources, disputed not only among different countries but also in the interior of every country, between urban and rural areas, among productive activities and among individual consumption, farming and industry. “Our research has shown that it is possible to reach an elevated productivity level, with major water savings,” explained Crusciol, in an interview with Agência FAPESP.

Rice-growing in aerobic soil conditions, that is, on firm ground (the technical terms for this type of crop are “dryland rice” and “upland rice”) is nothing new in Brazil. Dryland rice has been grown in Brazil for many years, principally in the Cerrado (savanna) region. The new development, as a result of the study, was reaching a higher level of productivity achieved by complementation with irrigation by aspersion. “Without the complementation, the average productivity is approximately 2,700 kilos per hectare, while in inundated growing, the average is 7,000 kilograms/hectare. With hydric complementation, we have obtained productivities of up to 6,000 kg/ha, using much less water,” affirmed the researcher.

To have an idea of the impact that this technological innovation could have on farming, consider that 65% of Brazilian rice plantations utilize the two other systems. Plantations that depend solely on rain for water account for only 35% of rice produced.

“The explanation for this low productivity is that rice domesticated in inundated environments presents low tolerance to lack of water, particularly in the pre-flowering and flowering periods. If there is a warm period in this critical stage, the result for the harvest is disastrous. However, by complementing the rainwater supply with aspersion irrigation, it is possible to eliminate the risks associated with climatic instability and practically double the average productivity,” sums up Crusciol.

In the experiment conducted by the scientist, aspersion irrigation accounted for 8.7% of the water supplied to crops during the first year, with the remainder provided by rainfall. The increase in productivity was 54.4%. In the following year, aspersion irrigation provided 14.5% of the water and the increase in productivity was 48.1%. “As can be noted by the numbers, the technique affords an impressive increase in productivity, reaching levels compatible to those of the flooded irrigation system (rice in submerged environments); however, this increase is not proportional to the quantity of water provided by irrigation,” commented the researcher.

In addition to complementary irrigation, one additional factor that contributed to the success of the experiment was the quality of Brazilian rice, the result of several decades of genetic selection, initially promoted by the Campinas Agronomic Institute (IAC) and later by the Brazilian Agricultural Research Corporation (Embrapa). “We have the best materials on the planet, crops that have good tolerance to short periods of hydric stress (water deficiency),” explained Crusciol. “For many years, rice growing was the first practice in areas of agricultural expansion, paving the way for other productive activities.”

“Aspersion irrigation clearly implies costs for acquisition of equipment (central pivot and aspersers) and electrical energy consumption (to pump the water). Rice is a very cheap product whose price deserves special government attention because it impacts the price of the basic basket of goods, which is controlled by regulatory mechanisms.

This paradox—a high production cost and low final product cost—tends to intimidate farmers. The solution, according to Crusciol, is to alternate rice with other agricultural crops, such as grains (beans, soybean and corn), fiber (cotton) and vegetables (potatoes, tomatoes, bell peppers, etc.) with higher aggregate value, optimizing the use of equipment and obtaining additional advantages from crop rotation, which interrupts the cycle of pests and disease that affect these other crops, particularly in the rainy season (when rice is grown).

Small farmers in the world’s poorest regions—in Asia, Africa and Latin America—have grown both flooded rice crops and dryland rice crops, with water exclusively from rainfall, extensively. The major growth in the production of rice with rainfall only, compared to the more productive inundation method, is not due to farmers making free choices based on ecological considerations related to the use of water but rather to the brutal consequences of economic development in these regions. In China and India, which rank first and second among countries in rice production, rice growing has been pushed to aerated environments (dry land), due to intense disputes over hydric resources, which are increasingly absorbed by accelerated urban and industrial growth.

In this context, the technological innovation that aspersion irrigation represents could have not only important economic repercussions but social repercussions as well. It is no surprise that the Chinese are interested in this Brazilian research.