Newly planted rice shoots poking out of the Sudanese soil are as tiny as blades of grass, but they symbolise a big dream to turn around one of the world's largest irrigated farming schemes.

Bakri Elamin Awad Al-Karim farms a small plot in the vast Gezira region between the Blue and White Niles south of Khartoum.

Japanese aid has helped turn it into a showcase for a crop supporters say offers farmers better yields and bigger incomes in what is still an overwhelmingly agricultural economy.

In its 1920s heyday, when Sudan was under British and Egyptian colonial rule, the Gezira Scheme was touted as model for African development, with sheer gravity being used to tap water from the Blue Nile to irrigate hundreds of thousands of acres (hectares) of cotton.

But years of underinvestment and piecemeal privatisation have led to decay of the infrastructure, canals and dykes on which the region's farms depend, bringing the country's economy down with it, analysts say.

Unlike in other parts of Africa or in Asia, rice is still an uncommon crop in Sudan, where sorghum is the staple cereal, along with groundnut, millet and wheat. Cotton is also still grown.

"More farmers need to grow rice because it gives them a good yield," Karim says through a translator.

His fields are among several "demonstration farms" for rice, which Gezira state's agriculture minister, Abdullah Mohammed Osman, describes as a potential wonder-crop.

"The traditional cropping system in these big irrigation schemes is not economically feasible," says the minister, who himself studied fruit production in Egypt.

"The productivity is not so high," and neither are farm incomes, he says at his office in the state capital of Wad Medani.

Rice would boost crop yields and the earnings of farmers while providing Sudan a source of foreign currency and contributing to "national food security", he says.

Sudan cannot feed all of its roughly 31 million people, more than 12 percent of whom were expected to need food aid this year, according to the United Nations.

Osman says the yield from rice, an average of about 1.3 tonnes per acre (0.4 hectares), is about double that of wheat. It is also roughly 50 percent more than that of sorghum.

Net revenue to each rice farmer reached about 3,600 Sudanese pounds ($817) per acre last year, against 1,400 pounds for other crops, the minister said.

Having a sustainable supply of seed, herbicides, and the technology to de-husk, clean and package the grain are keys to expanding production, Osman said.

"Now we can produce rice. No problem.

"To process this to meet the international market requirements is a challenge ahead for us."

Even being able to replace the 50,000 tonnes of rice Sudan imports annually at a cost of $15 million would be a good start, Osman added.

But if rice is the crop of the future, and a source of potential export earnings, the future still seems far off.

The Japanese-backed Gezira rice programme began in 2010 and expanded to almost 480 feddans (about 500 acres, 190 hectares) last year.

Compared with the Gezira Scheme's total size of about two million feddans, that is like a single grain of rice in a large field.

"Of course, we cannot at one time tackle everything," says Osamu Nakagaki, chief adviser from the Japan International Cooperation Agency.

JICA has provided seeds, planting and milling equipment, and given overseas training to more than 70 Sudanese agricultural engineers.

The engineers have passed on their knowledge to more than 200 farmers - out of around 116,000 who Osman said are working in the Gezira Scheme and a nearby smaller irrigation area.

By the time it nears Karim's farm the main Gezira canal has already flowed for 99 kilometres (61 miles). It resembles an unusually straight river, with bushy green banks broken intermittently by small dams.

A secondary canal drains through a pipe under an unpaved road and into a dirt trough of glistening brown water which irrigates the young rice in Karim's fields.

Not all of the Gezira Scheme is working so well, experts say.

"It's in total disrepair," one agricultural expert told AFP, asking not to be identified. "You see channels filled in, banks are all eroded."

Much of the scheme's land is not producing, he said.

"Cotton, wheat and sorghum production dropped to very low levels, and many farmers migrated from Gezira to seek better work opportunities elsewhere," a report issued last year by the UN Children's Fund said, noting a lack of canal maintenance.

Veteran journalist Mahjoub Mohamed Salih wrote in a June column that privatisation led to "the complete collapse" of the scheme's other infrastructure.

Assets from the project's former railway, its cotton mills and other property have been "squandered", he wrote.

Osman said the government was moving away from a "paternal approach", in favour of privatisation and leaving the farmers free to choose what crops they wish to grow.

"The farmer should depend on himself," he said, adding that rice gives them a new option.

"It is a very promising crop."