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15 How did prairie soils develop? Will prairie plants grow equally well in rich and poor soils? Prairie soils, which support today’s agriculture so successfully, developed over a period of thousands of years. Research by David Montgomery, cited in the July 2008 issue of Scientific American, indicates that topsoil formation is a very slow process; it can take from 700 to 1,500 years to form an inch of soil. Before cultivation, the growth and subsequent death of the roots and crowns of prairie plants form humus in the upper soil layers, giving them a dark brown to almost black appearance. Humus mixed with fine clays and sand gives soils the ability to hold water and nutrients and keeps them site selection c h a p t e r f o u r  Open, gently rolling landscapes devoid of trees work best to give your site more opportunities for diversity. 16 friable (somewhat loose and crumbly). When soil is moist, you can press it between your thumb and forefinger, and it will break apart easily. Virgin prairie soils may have a topsoil layer that extends eighteen inches below the surface. Plowing of prairies and subsequent agricultural use oxidize the humus, leaving the soils less able to hold water and nutrients. The erosive action of moving water on an unprotected soil surface also removes organic material in the form of silt. Silt floats in a watery suspension and is carried by heavy rains to rivers and streams, where it is deposited in lakes, reservoirs, and quiet river backwaters. Some prairies started the soil-building process on glacial till, a mixture of rock ground by glacial ice into a flourlike consistency. Other prairies began on loess deposits , which consist of fine wind-blown particles lifted from major river and stream valleys, formed during a period when glaciers were receding. Prairie vegetation effectively started on very poor soil, which had no topsoil and few nutrients. Prairie plants can become established on very poor soil and survive; however, they do far better where at least some topsoil remains to hold nutrients and water. Prairie plants, like other crops, require nutrients and an adequate water supply to reach maximum height and maturity; thus, their size reflects the quality of the soil. In 1975, I planted two small areas of prairie flowers and grasses in a borrow ditch along a county road where the topsoil had been completely removed and used for fill. The borrow had been seeded to smooth brome grass by the county road department during the mid 1960s, but the grass was short, thin, and unproductive with bare soil between the plants. After a light disking, I seeded about thirty species, which included three or four grasses and twenty-five forbs. The area remained bare most of the summer, but by the following season many small prairie seedlings began to appear , and gradually over a period of years the plants became well established. Today, more than thirty-five years later, most plants are generally short when compared with similar species on better soil, but only a few small open spaces remain. The plants are also adversely affected by wetter or drier than normal weather conditions. There is still very little or no appreciable topsoil; however, the prairie appears to be well established, and it has virtually halted the erosion that still persists where brome dominates other sections of the road grade. 17 One of the advantages of planting on poor versus rich soil is a reduction in weedy competition. Very poor soil does not support weeds well and, over the long term, prairie plants are the survivors. In comparison, prairie plantings on rich soil tend to be tall and lush unless the weather conditions are extremely wet or dry; however, initial establishment is more difficult because of weed competition. Tallgrass prairie plants grow best in full sunlight. Even partial shade may adversely affect a prairie planting. Savanna, a transition zone between open prairie and forest , contains scattered trees. The relatively open yet partially shaded savanna areas often contain cool-season grasses and a number of sedges not common in tallgrass prairie, but some tallgrass species such as Culver’s root and rough blazing star also thrive there. The open shade requires many different species to fill this niche. Savanna mixes are available from some seed suppliers. When you select a site, you should also consider its potential for future management . Will burning be permitted? Will there be future development, which can lead...

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