Silveira, J., R. Costa, R. Viegas, J. Oliveira, and M. Figueiredo. “N-Compound Accumulation and Carbohydrate Shortage on N2 Fixation in Drought-Stressed and Rewatered Cowpea Plants”. Spanish Journal of Agricultural Research, Vol. 1, no. 3, Sept. 2003, pp. 65-75, doi:10.5424/sjar/2003013-36.