“…Nitrogen, an essential macronutrient for plants (Covelo et al, 2008;Zhang et al, 2008), is a constituent of numerous important compounds including amino acids, proteins (enzymes), nucleic acids, chlorophyll, and several plant hormones (Britto and Kronzucker, 2004;Guo et al, 2008). Because of the important influence of nitrogen on plant growth, a number of studies have examined the basis of nitrogen use efficiency in cotton (Li et al, 2007), rice (Koutroubas and Ntanos, 2003) and maize (Presterl et al, 2002).…”