Research project summary: Field experiments at ACRI Narrabri were devised to evaluate summer and winter growing legumes with respect to the amounts of atmospheric N2 fixed using the I SN natural abundance technique. Commercial legume crops were also be assessed in this way. The benefit of these legume crops was assessed in the following year, by detennining the N response of cotton to N fertilizer. Associated experiments were used to study the decomposition of I SN-labelled legume crop residues and the uptake by the following cotton crop of legume N mineralised from the legume residues. In addition, the CRC farming systems experiments are being used to evaluate the benefits of legume rotation crops. This project is continuing to evaluate the benefits of those treatments with respect to N, through assessing N2 fixation and regular monitoring of the soil and crop N status