The annual decline is good news for rival exporters such as Brazil and the United States, which are hoping to expand sales to India's traditional customers in Southeast Asia including Malaysia, Indonesia and Vietnam.
"We've had a sudden spurt in export deals in the past few months, but the jump in shipments is not enough to help this year's exports cross last year's levels," said Raju Choksi, vice-president at India's top corn exporter Anil Nutrients.
Corn shipments are likely to fall to 3.5-3.7 million tonnes in the year to September 2014 from 4.7 million tonnes last year, Choksi said by telephone from the western city of Ahmedabad.
Exports between October and April totalled 2.1 million tonnes, about a million tonnes less than the same period in 2012/13, he added.
Indian corn prices were $20-$25 a tonne higher than South American grain on a free on board basis (FOB) at the start of the marketing year, said a trader from Nizamabad, a trading hub in the newly formed southern state of Telangana.
But recent export deals have been struck at $240 a tonne FOB, while supplies from South American would cost about $265 a tonne FOB in most Southeast Asian countries, Choksi said.
Indian prices have become more competitive as domestic supplies have swollen in the wake of the winter crop that was harvested in March, traders said.
They also said that appetite in Southeast Asia had been picking up, buoyed by demand for animal feed as a growing middle class in the region starts to consume more meat.
India's share of the 90 million tonnes of annual world corn trade is small, but it has become a key supplier to Southeast Asia due to its proximity and as it is willing to supply in small containers or vessels of 15,000-20,000 tonnes, rather than the 50,000-tonne panamax ships that ply the waters from South America.
But exports could also take a hit in 2014/15 if an expected El Nino weather pattern leads to patchy monsoon rains, cutting output and pushing up local prices.
"Forecasts of poor monsoon rains are worrying and we could be heading for a bit of trouble. Any drop in our exports would encourage Malaysia, Indonesia and Vietnam to (turn to) leading American producers," Choksi said. India's weather office has already forecast a high chance of El Nino, a weather warming event associated with droughts in some regions.
The country's rapidly rising local consumption could also curb exports.
India consumes about 17 million tonnes of corn each year, with poultry and cattle feed accounting for annual demand of about 10.5 million tonnes.
The demand has largely been driven as Indian diets change due to living standards.