An Analysis of Electrical Impedance Measurements Applied for Plant N Status Estimation in Lettuce (Lactuca sativa) oleh Rafael F. Muñoz-Huerta, Antonio de J. Ortiz-Melendez, Ramon G. Guevara-Gonzalez, Irineo Torres-Pacheco, Gilberto Herrera-Ruiz, Luis M. Contreras-Medina, Juan Prado-Olivarez, Rosalia V. Ocampo-Velazquez