Avoid uncomposted manure. It contains large numbers of weed seeds. Another method of improving poor soils is to plant a green manure crop , such as buckwheat or winter wheat. These crops improve the soil by bringing up nutrients from the lower soil and converting them into organic plant matter. The crop is plowed under while actively growing to incorporate the roots and leaves into the soil.
Clay soils with low levels of organic matter can be difficult to work.
The fine soil particles pack together tightly, impeding drainage and air exchange. In the heat of summer, clay soils harden and prevent downward root growth. Clay soils warm up slower in spring and compact if worked when wet. Each of these problems will retard root development and plant growth. There are many prairie plants that can grow in clay soils.