ABSTRACT
Water moves in the plant as a continuous stream from the root hairs to the leaf surfaces in response to the cell diffusion pressure-deficit gradient. One of the important functions of plant water is that the moist leaf surfaces absorb atmospheric carbon dioxide, but this maintenance of moisture implies a continuous water supply to the leaf surface to replenish that which is inevitably evaporated. The purpose of irrigation is the control of soil moisture between a lower limit that will not restrict plant growth and an upper limit that avoids the disadvantages of water-logging. Soil drainage has other generally beneficial effects on crops by increasing the nitrogen supply which can be obtained from the soil and by changing the thermal properties of the soil. Quality of soil water is as important as quantity in achieving optimum plant growth, for certain amounts of dissolved salts derived from mineral and organic soil constituents are vital for plants.
