More than 25 percent of the soils of the central prairie subregion are of level to nearly level topography and usually require artificial drainage. The Webster and Clyde soils of Iowa and Minnesota and the Drummer-Sable soils of Illinois are typical examples of naturally poorly drained soils that have been extensively drained with tile.
The Muscatine silt loam soil, in eastern Iowa and central Illinois where the loess blankets the glacial till, is considered by some agronomists to be the best soil type in the region. In a sense it has become a benchmark soil, against which other soils are compared for productivity, yield, and suitability for crops. It has a thick, dark surface layer, occurs on nearly level slopes, and seldom requires artificial drainage.
Associated with the level soils in many places are soils of moderate slope and good natural drainage but apt to erode because of their topography when they are cropped intensively.
Because of the pronounced suitability of the soils of the central prairie subregion for corn and because of the marked economic advantage of corn over other feed crops, about 50 percent of the harvested cropland in the subregion is in corn, according to the 1950 Census, compared to about 38 percent in the whole region and to about 25 percent in the northern forest subregion. The central prairie subregion also has the highest percentage of harvested cropland in soybeans, the other leading intertilled crop of the region. The total intertilled acreage, expressed as a percentage of the harvested cropland, is nearly 60 percent, compared to 28 percent in the northern forest subregion.
The most intensive grain production in the subregion is in east-central Illinois and parts of north-central Iowa, where the type of farming is cash grain (corn, oats, and soybeans). In all other parts, the feed usually is fed on the farms where it is grown, and raising hogs is a major enterprise. In northeastern Iowa and south-central Minnesota, where the acreages of hay and pasture are somewhat higher, dairying predominates. Livestock feeding and hogs are both important in east-central Iowa and west-central Illinois.
A system based on lime, legumes, and phosphates has been advocated and followed to some extent for several decades. Because of the intensive grain cropping, however, many soils have lost one-fourth to more than one-third of their original content of nitrogen and organic matter. With less than 10 percent of the harvested cropland in legume hay and approximately 50 percent in corn (1950 Census), the legumes cannot supply the nitrogen needs of the grain crops in the rotation.
Nitrogen fertilizers have come to have an important place. Experimental work has shown that the use of 80 to 100 pounds of fertilizer nitrogen on even the best of these prairie soils can sometimes double the yield of corn. If favorable relationships exist between the price of commercial nitrogen and the price of farm products, nitrogen fertilizers undoubtedly will become even more important in supplementing nitrogen from legumes and manure.
More phosphorus and potassium also are needed on these prairie soils, even though the total use of fertilizer tripled in the three States of the subregion between 1945 and 1956.
Another important problem is tillage, particularly as it relates to economy of operation and the maintaining of satisfactory tilth. Excessive tillage, especially for corn, has been partly responsible for a decline in soil organic matter, a deterioration of tilth, and (on sloping soils) an increase in soil erosion.
Experiments have proved that tillage operations can be cut considerably. Some farmers have adopted new methods, which are aimed at minimum tillage for corn in order to save time and money and to maintain better tilth, reduce soil compaction, and enhance water absorption. Among them are the substitution of chemicals for at least one cultivation in the control of weeds; the use of subsurface tillage instead of plowing, with residues left on the surface; and the so-called plow-plant method, in which the corn is planted in the wheel tracks immediately after plowing and the seedbed between the rows is kept loose with minimum tillage.
These new methods, combined with contour tillage, may become especially important on soils subject to erosion. Subsurface tillage with a mulch of crop residues can reduce erosion loss by at least one-half of the loss that comes with plowing and conventional tillage.
The central prairie subregion is also well adapted to alfalfa and other forages. These crops produce high yields and supply some nitrogen to the other crops in the rotation. Cheap nitrogen fertilizers and improved tillage methods, however, have made it possible to vary considerably the amount of legumes and grasses in the rotation without loss of productivity. In fact, it seems probable that on permeable, nonerosive soils high yields can be maintained with continuous corn under a system of heavy fertilization, green manuring, and proper management.
A wide range of choices in soil-management systems and in type of farming are therefore possible in the central prairie subregion. Likewise, because of its favorable soils and topography, this subregion is well adapted to mechanization and to other advances in technology.
THE EASTERN FOREST SUBREGION Comprises an area of about 30 million acres in northwestern Ohio, northern Indiana, and southwestern Michigan. It gets 35 to 40 inches of well-distributed rainfall. It has a growing season of 160 to 180 days.
The soils, formed mostly under forest vegetation, generally are light in color and low in organic matter, although areas of dark-colored, poorly drained soils are extensive. Developed from various types of glacial material, they differ considerably in texture. Fine-textured soils, such as the Brookston and Paulding clays, are extensive in the lacustrine lake plain area of northwestern Ohio. Sands and sandy loam soils occur in northwestern Indiana. Most of the soils in other areas, however, have a friable loam to silt loam surface.
The land is mostly level to gently rolling, except on moraines and near the main streams. where the soils may be rolling to steep. Much of the land was originally poorly drained; most of it is now in drainage enterprises, but inadequate drainage still is a problem on many farms. Peat and muck soils are rather extensive in northwestern Indiana, and are drained by ditching and tiling.
The types of farming are many. Livestock farms predominate in the southern part; hog raising is the important enterprise, but there are also many cash-grain and dairy farms. Cash-grain production and dairying are relatively more important in the northern part. There are also many livestock and general farms.
The acreages in corn and soybeans are high, making up about 50 percent of the harvested crop, which is only about 10 percent less than in the central prairie subregion. Instead of oats, however, wheat is the most important small grain, especially in the southern part, where the acreage is about 50 percent greater than that of oats.
Small grain and hay are grown on 34 and 14 percent, respectively, of the harvested acreage. The amount of cropland pasture amounts to about 17 percent of the total cropland, which in 1949 was about 50 percent higher than in the central prairie subregion.
Because of the relatively small amounts of legumes in the rotations, nitrogen is a limiting element in crop production despite the large increase in the use of nitrogen fertilizer since 1945.
Sod crops (legumes and grasses) have been found to be especially beneficial to sugar beets and other crops in the rotation on the fine-textured soils of northwestern Ohio, partly because of their effect in improving soil structure. In experiments at the Ohio Agricultural Experiment Station, however, good results were had even on these fine-textured soils from the addition of large amounts of nitrogen with carbonaceous residues as a means of maintaining good tilth and yields.
Because, in general, the soils of this subregion have been farmed longer than those of any other subregion and because forest soils have a naturally lower fertility than prairie soils, fertilizers have been used for a longer time and in larger amounts than in other parts of the Midland feed region. Even greater amounts are needed, however, for most efficient production of pastures and harvested crops. Pastures on the more rolling, eroded soils are particularly in need of improvement through fertilization, liming, and legumes.
Liming has been practiced for many years, but most soils still are acid and in need of moderate amounts of lime particularly for the good growth of alfalfa, which is exceeded in acreage by red clover, a less productive crop on most soils.
Some of the black sandy soils in northern Indiana and the fine-textured soils in northeastern Indiana have too little manganese for soybeans, oats, and wheat. Alfalfa in northern Indiana has responded to applications of boron.
The high acreage of intertilled crops and the usual type of tillage methods mean that the control of erosion has become an important problem on rolling lands. Contour tillage and strip-cropping need to be used much more extensively in supplementing rotations. Minimum tillage methods also offer opportunities for reducing soil compaction, increasing water absorption, and reducing erosion. Mulch-residue tillage can be used effectively for erosion control on the coarser textured and the better aerated soils. Manure mulches also are effective.
Winter cover crops need to be used wherever feasible, especially because, of the relatively heavy precipitation in winter. On the sandy and muck soils in the northwestern part where wind erosion is a problem, cover crops of rye and other small grains are valuable. High amounts of fertilizers, especially potassium, are also necessary there.
Although the soils of the subregion are of lower natural fertility than the soils of the central prairie subregion, yields of corn are nearly as high an average of 52 bushels in 1946-1955.
THE NORTHERN FOREST SUBREGION covers about 52 million acres in southern Wisconsin, southern Michigan, and east-central Minnesota.
Because the climate of most of the subregion is cooler and the growing season is shorter than in other parts of the Midland feed region, corn loses its dominance, and hay and pasture crops are more important. The total acreage of hay and cropland pasture is about double the acreage of corn (including corn for silage), whereas in the central prairie subregion it is about half. Dairy farming therefore predominates in most parts of the subregion, especially in eastern and southern Wisconsin. In southeastern Wisconsin and in the Mississippi Valley hill area, the corn yields compare favorably with those in the central prairie subregion, but in the other sections the yields averaged only about 40 to 45 bushels an acre in 1946-1955 no doubt because of the shorter growing season and the relatively poorer soils.