What Science Says About Wood Colony Soil

One of Vance Kennedy’s first jobs for the U.S. Geological Survey (USGS) was a study of “sediment transport” in streams throughout the state of Georgia. He probably got the job because of his degree in Chemical Engineering from the University of Pennsylvania and because he was the first student ever in the first course ever in the subject of Applied Geochemistry.

When you study the streams and sediments of an entire state you acquire a lot of first-hand knowledge about soil and water. Kennedy’s study took two years and provided a nice pragmatic base for his later college courses in geology and hydrology. Kennedy has a PhD in hydrology from the University of Colorado.

He also has an award from the Department of Interior for “Distinguished Service.” It’s the highest possible award for an employee of the USGS. Among the things Kennedy did to earn the award was his research into the causes of acid rain. He also developed methods for tracing the origins of sediments and minerals in streams and rivers.

Though he’s been retired for years, Kennedy stays current with USGS research in soil and water. At ninety years old, he still farms eight acres north of Modesto. He’s just a short jaunt from Wood Colony. Wood Colony has been in the news because the City of Modesto wants to designate the land there for industrial uses.

Kennedy will tell you the soil at Wood Colony, like the soil on his farm, is world class sandy loam.

“The only other places I know with soil like this are in Chile and New Jersey—but New Jersey really doesn’t have the ideal climate we have here,” he says.

Vance Kennedy rates soil on the basis of several criteria. One is permeability. There has to be a precise mixture of sandy grains:

“It’s a combination of grain size distribution and the minerals involved. As far as grain size distribution is concerned, a sandy loam, which is what many our best soils here are, has enough fine grains to hold moisture and enough larger grains to allow permeability. So you have the ideal situation where, from a physical aspect, oxygen can easily get to the roots, and yet there’s enough moisture held on the clay that the moisture stays there.”

The right proportion of large grains to fine also allows the water to infiltrate the soil and recharge the aquifer.

Kennedy also rates soil fertility. The fertile soil in the northern San Joaquin Valley has exactly the right amount of illite. Illite plays an important role in crop production because it enables plants to better benefit from the potassium in fertilizer. Illite adsorbs potassium (as opposed to absorbs), which means it holds the potassium for a while but later releases it for the plants to take it in via their root systems.

The fertile soil is just one reason the northern San Joaquin Valley can grow over 400 different crops. The other key factors are climate and water.

The long hot summers provide plenty of sunlight and the pure Sierra snowmelt delivers enough water to grow everything from almonds to zucchini. When people talk about agriculture, they almost never acknowledge that only a tiny few places on earth can grow such a wide variety of crops.

According to Kennedy, the soil is a prime component not only in fertility and recharge, but sustainability of farming. If the soil is too compact, not only is there no recharge of the aquifer, there’s also a deadly accumulation of salts. If a hard clay or rocky layer is too close to the surface, the result is “perched water,” which also results in rapid accumulation of salt and nitrates.

Ask Vance Kennedy to sum up the differences between soil in the northern San Joaquin Valley and elsewhere, and he’s got a short answer: “This soil is a national treasure,” he says.