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Updated: Feb 13, 2026

Microplot Design and Plant and Soil Sample Preparation for 15Nitrogen Analysis
Published on: May 10, 2020
Crops, Nitrogen, Water: Are Legumes Friend, Foe, or Misunderstood Ally?
Mark A Adams1, Nina Buchmann2, Janet Sprent3
1Swinburne University, PO Box 218, Hawthorn, VIC 3122, Australia; Centre for Carbon Water and Food, The University of Sydney, 380 Werombi Road, Camden, NSW 2480, Australia.
Abstract:
Biological nitrogen fixation (BNF) by crop legumes reduces demand for industrial nitrogen fixation (INF). Nonetheless, rates of BNF in agriculture remain low, with strong negative feedback to BNF from reactive soil nitrogen (N) and drought. We show that breeding for yield has resulted in strong relationships between photosynthesis and leaf N in non-leguminous crops, whereas grain legumes show strong relations between leaf N and water use efficiency (WUE). We contrast these understandings with other studies that draw attention to the water costs of grain legume crops, and their potential for polluting the biosphere with N. We propose that breeding grain legumes for reduced stomatal conductance can increase WUE without compromising production or BNF. Legume crops remain a better bet than relying on INF.
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