Brian: I'm a bit confused with your question. The total N fixation amounts that you give are quite normal for a good soybean crop (40-50 bu/ac) on a soil that is fairly low in N-supplying capacity. I think the "old book" maximum of 200 kg/ha is low, conditioned on lower, historical yields. The only other option, is that the modeled N uptake is low. Actually, this is something I have complained about for a year or two. The problem is using the Ritchie-CERES maize approach for N uptake as a function of root length density. That is fine for maize which has 3 to 4 fold greater root length, but gives an underestimate of soil N uptake for soybean's lower root length. We need soil N uptake to be driven partly by mass flow of water to the root. This would reduce the simulated leaching a bit. Any way, you are discussing two problems that you have not separated well. Is the problem excess simulated N leaching from insufficient root N uptake? Or is it excess simulated N leaching a year later because of N coming from the soybean crop (that you think fixes too much N). For a Millhopper fine sand with good water supply, Bragg soybean accumulated a total of 320 kg N/ha (210 in harvested seed, 35 kg N in standing stem and podwall, and 75 kg in abscised leaf and petiole). The total N accumulation came from 292 kg N-fixed and 28 kg N uptake. The model says 110 kg of N is left in the field in the residue. Some of this would decompose rapidly, providing an N credit of about 50 kg N. Is that the problem, too much left-over N for the next crop? As I see it, we do not want to make the model fix less N. That is not the problem (high yielding soybean crops require a lot of total N). We could have too much leaching: 1) during the season if root N uptake is too low, 2) after harvest if the residue left is too high in N conc. (which is a possible problem with the modeled N mobilization) and thus decomposes too fast. I need more information on what the problem is? Regards, Ken Boote