Land drainage in relation to soils and crops

This chapter discusses the demands of plants for air, the water requirements of crops, examples of the calculation of a drainage operation, and the additional effects of a physical nature caused by drainage. Since little is known, quantitatively, about the physiology of plant roots with respect to consumption of oxygen and the mechanism by which oxygen and carbon dioxide respectively influence growth, the chapter first presents a review of the pertinent literature. It then discusses the calculation of evapotranspiration, since evapotranspiration is by far the main cause of water requirement. In addition, the chapter presents methods used to calculate the water content of a soil and the rate of water supply from subsoil. It briefly indicates the interrelations among the presence of high groundwater levels and the development and reclamation, or amelioration, of saline and alkali soil conditions