Rouchaud, J., Moons, C., Meyer, JA., Benoit, F., Ceustermans, N., & Vanlinden, F. (1984). Effects of Soil Fertilization and of Covering of the Culture With Plastic Film On the Provitamin-a Content of Early Lettuces. Plant and Soil : international journal on plant-soil relationships, 80(1), 139-141. https://doi.org/10.1007/BF02232948 (Original work published 1984)