Volume 2 covers nitrogen fertilizer efficiency, acid tolerance of the legume symbiosis, fruit tree nutrition, rhizosphere pH change, iron deficiency in crop production, the effects of nutrient deficiences on seed production, the elemental composition of plants, and the role of potassium. The articles in this volume join together both the fundamental and the applied parts of this discipline. The editors' aim to make the reviews comprehensible to scientists in relevant disciplines, rather than purely to the specialist. The format of each volume is a small number of full-length reviews of important topics, plus an editorial which briefly mentions other rapidly developing topics that may therefore be reviewed in future volumes.