It’s said that the soil along Spring Creek, in the Mississippi River valley near Millville, Minn., is unusually rich. While that makes it prized by farmers, it’s also become known for producing something other than bumper crops.

The Martin brothers, Alex and Jeremy, grew up riding dirt bikes over a course cut from that land. Saturday, they return to Spring Creek MX Park — owned by their parents — as two of the favorites in the Spring Creek National, part of the Lucas Oil AMA Pro Motocross Championship series. Jeremy Martin sits atop the standings in the 250cc class, while elder sibling Alex has risen to fifth place during the most successful season of his career.

The races also are a homecoming of sorts for Ryan Dungey of Belle Plaine, a frequent winner at Spring Creek who leads the 450 class with five events left in the season. The Martins, though, are coming back to the place where a sibling rivalry was born, one that has played a vital part in driving both to the highest levels of motocross.

“There is definitely a brotherly competition there,’’ said Jeremy, 22, the defending series champion in the 250 class. “Every day, we’re talking smack, and we’re always trying to outdo each other, whether it be on the dirt bike or on a mountain bike or a road bike.

“We push each other. We always have. And that just makes it easier on race day for us to hopefully beat the competition.’’

Through the first seven events of the 12-event series, Jeremy Martin has 298 points, giving him a seven-point edge over Marvin Musquin for the lead in the 250 class. Alex Martin is fifth with 188 points.

Dungey, who won the Spring Creek National three consecutive times from 2010-2012, tops the 450 class with 303 points and holds a 44-point lead over defending champ Ken Roczen.

Like so many younger brothers, Jeremy Martin idolized his sibling and wanted to do everything Alex did. That included buzzing around the family property on a dirt bike — emulating their father, John, a former pro racer.

John and Greta Martin bought the Spring Creek complex in 1987, two decades after it had been carved out of that soft, loamy soil. Though his boys loved to race, John discouraged them from making a career of it, hoping to spare them from the danger of the sport and the constant travel required to compete and train at the highest level. It didn’t work; by the time Alex was 15, the family began spending winters in Texas and Florida to train for major amateur races, and his parents began home-schooling two boys intent on turning pro.

While John and Greta didn’t forbid it, they did insist that their sons shoulder full responsibility for building themselves into pro athletes.

“They weren’t kicking us out of bed in the morning to make us go running,’’ said Alex, 25. “It was on us to make it happen. And I think the drive and self-discipline that instilled is what’s keeping us going today.’’

In previous seasons, Alex has trained on the East Coast. This year, he is living and training in California with his brother, which has benefited both of them. Their ability to motivate and support each other has helped put Alex on pace for his highest career finish in the final point standings — ahead of the eighth-place finish he earned in 2011 — and helped Jeremy regain the lead in a tight race for first place.

Jeremy is the defending 250 champion at the Spring Creek National, and Alex also has turned in some of his best performances on their home track. While their knowledge of its hills, jumps and much-acclaimed soil has played a part, Alex said the biggest assist comes from the same place it always has: the strength of their family ties.

“Jeremy and I both believe that family comes first, and everything else comes next,’’ he said. “The real advantage is from having our friends and family there. When you have people there that you care about, sometimes there’s a little extra push you can squeeze out of yourself.’’