SAO PAULO, Oct 27 (Reuters) -

Scarce rainfall due to the El Nino climate phenomenon has caused disparities in the speed of soy planting in Brazil's top grain state Mato Grosso and could impact sowing of second corn, farmers and experts said on Friday.

The risk for the second corn, which is planted after soy is harvested, is greater in areas where the oilseed may have to be replanted.

"We are already seeing a tightening of the calendar, and El Nino could cut rains in advance," said meteorologist Desiree Brandt.

Soybean farmers in Mato Grosso are worried that unusual heat and dryness will lead to replanting of some areas while lowering yields in others.

Cayron Giacomelli, a producer in mid-north Mato Grosso, said he had already sown his entire soybean area, despite the possibility of having to redo the work.

"It's very dry in our region. I know farmers who planted very little, and replanting is present in most areas here," he said.

According to Brandt, even though the maps are showing a significant accumulation of rain in recent days, it is necessary to pay attention to the "quality of this rain".

"Last year, at this time, we already had much more widespread rain. Last year we had a La Nina and this year we have an El Nino," Brandt said.

Better rain conditions are expected next week in states such as Goias and Mato Grosso, two major producers suffering from scarce rainfall.

However, soybean sowing could be 15 days late on average in relation to the previous cycle, she added.

Marcos da Rosa, a grower in eastern Mato Grosso, said that many farmers planted soy "without the prospect of rain". He himself had to stop sowing for around eight days and resumed work this week.

"From yesterday to today it rained well," he said. "I thought it would rain all around but 130 km from here it didn't rain... Things are still uneven."

Rosa said there are growers in his area who had planted nothing and others with 100% of the area sown.

In Nova Xavantina, also in the east of Mato Grosso, grower Endrigo Dalcin said he also had to stop planting for ten days.

Due to delays in soybean sowing, growers are likely to plant sesame instead of corn, which has a much lower risk, Dalcin said.

"Now it's raining a little more... but it hasn't regularized yet. People are quite worried." (Reporting by Ana Mano Editing by Marguerita Choy)