Except for wood ash, there was no readily accessible source of potash prior to the mid-1800s. There were attempts to develop greensand (glauconite) marl in New Jersey during the 1860s, but this material (4 to 5% K) was bulky to transport and not sufficiently soluble to provide significant value as a K source. Discovery of extensive K deposits in Germany in the 1860s marked the beginning of the modern potash industry. German imports were the most important source of potash in North America until the outbreak of World War One, when the sudden embargo on German potash led to severe shortages. Widespread K deficiencies were reported during the time of the embargo for a variety of crops. This sudden loss of the sole potash supply spurred the search for alternative domestic sources, such as by-products from blast furnaces and cement mills, as well as seaweed. It was also during the embargo that the development of domestic potash deposits in California, Utah, and Nebraska occurred. The discovery of large potash reserves in New Mexico during the late 1920's marked the beginning of large-scale potash production in North America. Vast potash reserves from Canada now serve as the major source of this nutrient for most of North America. A number of different approaches have been developed to extract potash from different deposits, including continuous room-and-pillar mining, drill and blast mining, solution mining, and surface brine evaporation to meet the increasing world demand for this essential plant nutrient.