And even today those ancient loess deposits profoundly continue to affect the ecology wherever the winds dropped them.
LOESS AS FERTILIZER
When ancient glaciers advanced over northern North America, they scrapped atop many kinds of rock, grinding them into tiny, silt-size particles. When the glaciers melted, the particles washed downstream in meltwater. Since the particles had been derived from rocks of many mineral compositions, the mud deposited downstream consisted of a rainbow of different minerals. When the mud dried, crumbled into dust, was blown eastward, and deposited as loess atop our hills, it fertilized the soil with all those mineral elements, many of which were necessary for the growth of living organisms.
spreading lime; image courtesy of Mark Robinson & Wikimedia CommonsAt the right, you see something that farmers and gardeners often are advised to do when they have their soil tested. The farmer is spreading lime across his field, because lime makes soil less acidic and, in general, neutral or slightly basic soils are more productive than acidic ones. Well, lime is Calcium oxide, and our loess is full of it. In fact, Mississippi Valley loess contains markedly more lime than loess types in China, central Alaska and the Great Plans, as charted by D.R. Muhs in the freely downloadable "The geochemistry of loess: Asian and North American deposits compared."
During the 1960s, a team from Millsaps College in Jackson, Mississippi conducted a battery of tests on Mississippi loess. Their findings were published in 1968 as Mississippi Geological, Economic & Topographical Survey Bulletin 111, Loess Investigations in Mississippi. Below is one of several charts produced in the book:
| THICK LOESS pH = ±6.85 |
THIN LOESS pH = ±5.08 |
UPLAND NON-LOESS pH = ±4.75 |
Soil acidity is measured in terms of pH; The more acid the soil, the lower the pH, and the more basic, the higher the pH. Neutral soil has a pH of 7. Therefore, the team clearly showed that where the loess was thickest, the soil was close to neutral in pH. Where the loess thinned, it grew acidic. Where no loess was present, the soil was quite acidic.
In short, the thicker the loess, the higher the soil pH (the more basic the soil), and the more congenial that soil was for most (but not all) crop plants.
LOESS HELPS ORGANIC MATTER
Loess is a nearly pure form of silt. There's little or no sand (particles larger than those of silt), and very little clay (particles smaller than those of silt). Generally speaking, living things do better in soil that's neither too sandy nor too clayey, but rather silty. Adding loess to soil that's "too sandy" or "too clayey" produces a variety of good effects.
One important effect is that added loess may considerably improve a soil's capacity to hold and retain organic matter. To a certain point, the more organic matter a soil contains, the easier it is to farm and garden. Organic matter makes the soil at the left dark, crumbly, moist and "earthy smelling"; It's great soil for growing things.
One reason organic matter in soil is so wonderful is that it consists of the remains of once-living organisms. The dead bodies still contain nutrients needed by other living things, and as the dead bodies continue to decompose, those nutrients are released for the use of living organisms.
Moreover, organic matter acts like a sponge holding water in the soil. Organisms during severe droughts do much better in organic-matter-rich soils than in those with little or no organic matter.
The above-mentioned Millsaps College team also measured available water (water available to plant roots and soil organisms) in well drained soil from various locations with "thick loess," "thin loess," and "upland non-loess." Below, you see that well drained soil derived from thick loess contained significantly more available water per unit of well drained soil than soil from areas of thin loess, or no loess at all.
| % AVAILABLE WATER IN WELL DRAINED SOIL | ||
| THICK LOESS 19.8% |
THIN LOESS 12.5% |
UPLAND NON-LOESS 9.0% |