In spite of the increasing use of synthetic fertilizers in agricultural practice and subsequent raise of crop yields, it is found generally that to maintain a high level of inherent fertility, their use must be accompanied by periodic applications of bulky organic manure, either in the form of farm manure, compost, or other organic by-product, rather of the farm or of certain industries. The maintenance of high productivity depends on a number of factors; the soil must be in the optimum condition for crop growth and must be in a position to furnish both food and water; it must have a suitable reaction in the chemical sense and it must contain no substances toxic to growth. It must be physically amenable to cultivation, resistant to forces of erosion and the micro-flora and micro- fauna must be of a character to meliorate the general chemical and physical properties of the soil and the soil- plant relationship. Any substance which when added to the soil brings about an improvement in any one of those directions could be considered as a fertilizer or manure using the terms in their widest sense, and it is in connection with these indirect benefits that organic manures are of such great importance in fertilizer practice. Задайте 5 вопросов к тексту ?

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