Fig. 2. Relative abundance of ureides (RAU) in petioles averaged across four sampling dates vs. the proportion of N derived from the atmosphere (^PNDA) between harvest dates, as determined by ¹⁵N-dilution for well-watered and drought treatments at Gainesville, FL. The dashed line is the relationship found by Herridge and Peoples (1990) between RAU and NDA for well-watered, vegetative soybean (y = 1.38 + 0.311x + 0.0057x²).