This volume looks at the impact that different cropping systems and tillage have on soil¿s biologically active substances. It considers how phytotoxins accumulate and can inhibit the development of cultivated plants. Coverage explores the continuous cropping of rye, crop rotation, no tillage, and conventional tillage. It offers a comprehensive, comparative approach to allelopathic plant-soil interactions. The authors focus on free and bounded biologically active substances such as amino acids, auxins, humic and fulvic acids, transient radicals, and enzymes in light sand soils fertilized with different mineral and organic fertilizers. The chapters address fundamental questions relevant to the environmental challenges we face today and will deal with