JACKSON (AP) — Mississippi farmers who saw vital planting time washed away by persistent spring showers are now in desperate need of rain as heat and abnormally dry conditions threaten to reduce grain crop yields significantly.

The wet weather that kept farmers out of the field had already dimmed the prospects of a stellar planting season, experts say. Since that time, the rain has been replaced with heat and dry conditions as grain crops, especially corn, have hit a critical period.

In May, Ernie Flint, an agronomist for the Mississippi State University Extension Service, was worried about heavy showers with the planting of summer crops crawling at a slow pace.

‘‘Did we ever do a roundabout there,’’ said Flint, a farm extension agent for Carroll County, which is located in the Mississippi Delta and Attala County, which just on the edge of the Delta. ‘‘There are people in my area that haven’t had a measurable rain in almost two months. When it quit, it quit entirely.’’

With most corn already through the germination and seedling and reproductive stages, farmers need rain for the crop to complete its kernel development.

‘‘This is a real critical time for corn right now,’’ John Coccaro, a farm extension agent in Warren County, said. ‘‘And the heat, golly, not only is it dry and no rainfall, but these temperatures are considerably above average for this time of year … and that’s pretty stressful for a grain crop that’s trying to fill out its grain.’’

Corn grown on sandy soils need even more water and Flint said ‘‘we’ve got sandy fields that are already burned up past redemption.’’

Soybeans are withstanding the dry condition better than corn, Flint said, but will probably be reduced this year if dry conditions continue. Corn yields in some areas of the state could fall to 50 or 60 bushels if there’s no rain in the next two weeks, he said.

Corn yields are usually on average 180 to 220 bushels in irrigated fields and 140 to 150 bushels in non-irrigated fields, Flint said.

‘‘If people who have not had rain for almost two months go another two weeks without rain, we’re going to be looking at yields under a 100 bushels,’’ he said. I’m still hoping that nothing like that happens, but the potential is there.’’

The potential for low grain crop yields also extends to Louisiana.

The U.S. Department of Agriculture, in its weekly crop report, said 46 percent of Louisiana’s corn crop was rated in poor or fair condition. In Mississippi, 50 percent of corn crop fell under those ratings.

‘‘Crops are near burning up,’’ Allen McReynolds, a farm extension agent in Wayne County in southeast Mississippi, said in the weekly crop report. ‘‘It may be too late for corn. Beans and peanuts need a rain now.’’

Coccaro said he’s hoping the weather follows the same pattern as last year. It was the second consecutive year that Mississippi River flooding delayed planting in Warren County.

‘‘Last year, when that floodwater receded and farmers finally got a chance to plant, I think we had about a 9-week stretch … with no rain and it had an impact on the crops and how they performed in the fall,’’ Coccaro said.

‘‘Even though when we broke out of the drought, I think that we recorded 21 inches of rainfall in August, which was very rare. It probably did help some recover.’’