Soils under old pastures generally have good characteristics, and the use of cover and green manure crops can improve the texture even more. Any good loam soil will be suitable for blueberry growth after some amendments, though very sandy or very clayey loams should be avoided. Sandy soils are usually too low in organic matter, drain too quickly, and heat too excessively in the summer for good growth. Clay soils are poorly drained and compacted. These have pom aeration and restrict root growth. Loams with an organic matter content of 3%-15% are excellent. In a recent German study, researchers reported that blueberries generally made poor growth when planted on arable land but good growth when planted on virgin forest soil (Biasing 1989a,b). These differences could not be explained by soil characteristics or nutrient supply. Plants on die forest soil produced sparse, spreading root systems, while those on arable land produced dense root systems with small volume. Mycorrhizal infection was greater in the forest soil.