Many experiments have been conducted to determine the amount of water used in the production of one pound of dry plant substance. Generally, the method of the experiments has been to grow plants in large pots containing weighed quantities of soil. As needed, weighed amounts of water were added to the pots. To determine the loss of water, the pots were weighed at regular intervals of three days to one week. At harvest time, the weight of dry matter was carefully determined for each pot. Since the water lost by the pots was also known, the pounds of water used for the production of every pound of dry matter were readily calculated. The first reliable experiments of the kind were undertaken under humid conditions in Germany and other European countries. From the mass of results, some have been selected and presented in the following table. The work was done by the famous German investigators, Wollny, Hellriegel, and Sorauer, in the early eighties of the last century. In every case, the numbers in the table represent the number of pounds of water used for the production of one pound of ripened dry substance: Pounds Of Water For One Pound Of Dry Matter Wollny Hellreigel Sorauer Wheat 338 459 Oats 665 376 569 Barley 310 431 Rye 774 353 236 Corn 233 Buckwheat 646 363 Peas 416 273 Horsebeans 282 Red clover 310 Sunflowers 490 Millet 447 It is clear from the above results, obtained in Germany, that the amount of water required to produce a pound of dry matter is not the same for all plants, nor is it the same under all conditions for the same plant. In fact, as will be shown in a later chapter, the water requirements of any crop depend upon numerous factors, more or less controllable. The range of the above German results is from 233 to 774 pounds, with an average of about 419 pounds of water for each pound of dry matter produced. During the late eighties and early nineties, King conducted experiments similar to the earlier German experiments, to determine the water requirements of crops under Wisconsin conditions. A summary of the results of these extensive and carefully conducted experiments is as follows:-- Oats 385 Barley 464 Corn 271 Peas 477 Clover 576 Potatoes 385 The figures in the above table, averaging about 446 pounds, indicate that very nearly the same quantity of water is required for the production of crops in Wisconsin as in Germany. The Wisconsin results tend to be somewhat higher than those obtained in Europe, but the difference is small.