World Environment Day 2015: Aiming for high yields with a thirsty crop in drought conditions

Call it virtual water, or indirect water use, the "unseen" water consumed by crops and products is slowly being seen and it is not just mere drops.

Plant scientists are sitting up to take note of the colossal amounts of water guzzled by crops, and take action to reduce the same.

Among the cereals that form the mainstay of a population's diet, rice is top on the global water consumption table, needing up to 5000 litres for just one kilogram of rice, adding up to several hundred trillion litres of water for the annual crop.

MS Sheshashayee, professor of crop physiology at the University of Agricultural Science (UAS) in Bangalore and team are addressing the combined requirements for improving yield and using water efficiently.

The molecular breeding technique adopted at the lab managed to reduce water consumption of rice by 50%.

Talking to IBTimes UK, Sheshashayee minced no words in deploring the prevalent wasteful practices. "We have taken Indian agriculture for granted!"

Two-thirds of the water used in agriculture today in India is taken up by rice alone, he says. "But knowing that is not going to make anyone give up eating rice! So we decided to look for a way to grow a variety that gives more out of less."

The professor goes on to explain how plants need much more water than animals. "Believe it or not, plants use 98% of the water intake just for cooling, with less than 2% going for nutrient absorption or photolysis."

This water is lost when exchanged with carbon dioxide in the transpiration process.

One rice plant alone loses 1.5 litres of water per day in this process.

With a square metre plot housing 50 plants, and considering that a rice crop grows for 100 days, one hectare of area (10,000 metre square) with an upper yield of 10 tonnes of rice would need more than 50 million litres of water for the cooling process.

On a conservative basis of the FAO recommended daily intake of 400g rice, by a little less than half the population for 300 days in a year, Sheshashayee calculates it would require around 450 trillion litres of indirect water just to cool the crop.

The total available freshwater available for irrigation from rainfall is around 380 trillion litres and "this is not going to increase".

Water stressed

In fact, with other sectors catching up and drawing more water, there is going to be a major water problem in the country, he warns. It would look almost impossible to double the foodgrain output by 2030 under reduced water availability.

For the latest figures of 200 million tonnes of rice produced in India, more than 1000 trillion litres of water would have been used. The rough calculations are just to give an idea of the stupendous amounts of water that go to keep a population fed, he says.

Excellent yields of rice fetch 10 tonnes per hectare while the national average is around 3 tonnes per hectare. This is mostly due to low water intake.

Projecting the population growth to 2030 the crop production will have to go up to 400 million tones. "You can imagine how difficult that will be when water available is only getting lesser and soil nutrition getting poorer. If in 1900, most of water withdrawal was for agriculture, the trend has changed in the last few years. Industry and domestic use is now more than agriculture use," the professor notes.

While more water means more growth of the plant, scientists are beginning to take note of the amount of water consumed. Especially, when available water is shrinking fast.

The agriculture university team is focusing on changing the agronomy of rice by using a semi irrigated aerobic cultivation method.

Here the soil which is more aerated takes in less water by as much as 60%. But there is a problem. The growth of the crop is reduced too.

"We decided to look at how to improve the yield. For that we need deep root systems that suck water from deeper soils. This means first there must be water, and second, the plant will use up water soon and by end of the season suffer.

"So in addition to a good root architecture, we have to address making the plant more water efficient so that yield also increases," he added.

Molecular breeding

Shifting the focus to the cellular level, the team looked to increase tolerance to drought-like conditions and water use efficiency. They then identified desired traits in some progeny and crossed them with a mega variety of rice called IR64.

This strategy was developed working with the Genetic and Plant Breeding division led by Dr Rajanna at the zonal research station in Mandya, in the southern Indian state of Karnataka.

A series of crossing and double-crossing plants with the traits followed with a back-crossing resulted in 1500 lines that were chosen from 10,000 that were screened by doctoral student Pratibha MD in the crop physiology department at UAS.

These are now being grown for yield trials.

"Even if we get ten good lines that would be great. It would mean we have a crop which uses less water, and even that, efficiently, to produce maximum yield under drought conditions. That would be great, and I don't see any reason why we won't have such a variety of rice very soon," says a confident Sheshashayee.

His team calculates that improved water efficiency by the rice crop could result in 30-50% water saved.

The UN declared theme for Environment Day this year is "Seven Billion Dreams. One Planet. Consume with Care".

Water comes on top of the list of essentials for survival. Any opportunity to optimize use of water must not be ignored. The effort at Bangalore does that and more in aiming at more food grains from less water, crucial at a time when monsoon predictions are hinting at deficits.