In order to quantify the relationships between dry matter (DM) yield, resources use efficiency and changes in response to different levels of nitrogen (N), phosphorous (P) and water, field experiments were performed in research farm of Ferdowsi University of Mashhad, Iran, in 2014 and 2015. Three levels of irrigation water including 80 (ETc80), 100 (ETc100) and 120% (ETc120) of crop evapotranspiration (ETc) were considered as the main plots, and the factorial combination of three levels of zero (N0), 200 (N200) and 400 (N400) kg N ha-1 with three levels of zero (P0), 100 (P100) and 200 (P200) kg P ha-1 was considered as the sub plots. The results showed that increasing the consumption of water and P was led to the reduction of N and P utilization efficiency (NUtE and PUtE), while radiation use efficiency (RUE) increased. Water use efficiency (WUE) was also increased in response to application of N and P, but decreased when ETC increased. DM yield under ETc80 treatment reduced by 11 and 12%, respectively, compared to ETc100 and ETc120 which was due to reduction of cumulative absorbed radiation (Rabs(cum)) (p<0.01) and RUE (p<0.05). Under these conditions, changes of stomatal conductance (gs) had little effect on DM yield. It was also found that N limitation caused 11 and 20% reduction in DM yield compared to N200 and N400, respectively. This yield reduction was mainly the result of decrease in RUE (p<0.01), whereas changes of maximum leaf area index (LAImax) and Rabs(cum) were of lower importance. By decreasing Rabs(cum) (p<0.01), P deficiency also reduced DM yield by 5 and 9%, respectively, relative to P100 and P200 treatments.

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