Nutrients efficiency index of maize in response to interactions of water use and nitrogen and phosphorus fertilizers

Water and nutrient deficiency often limit the growth and productivity of crop in agricultural systems (Cao et al., 2007). It has been reported that the effects of nutrient supply and water regimes may interact significantly on plant growth (Hu and Schmidhalter, 2005). A simple assessment of the effect of each input may not show a complex interaction with the other inputs. Therefore, it is necessary to understand the interactive effects of soil water and nutrients on plant growth in the arid environments. Hence, the objectives of this study were to: (1) determine the interactive effects of ETc, nitrogen and phosphorus on yield and N-P efficiency indicators in maize crop and (2) evaluate the importance of uptake efficiency versus utilization efficiency of nitrogen and phosphorus on NUE and PUE.
This study was carried out at the research farm of Ferdowsi University of Mashhad, Iran, located 10 km east of Mashhad at 36.16° North latitude, 59.36° East longitude, and height of 985 m above sea level, in two growing years of 2014 and 2015. The experiment was conducted as split plot based on a randomized complete block design with three replications. The main plot consisted three levels of 80 (ETc80), 100 (ETc100) and 120 (ETc120) of plant evapotranspiration, and sub plot included a factorial combination of three N levels (0, 200 and 400 kg ha-1) and three P levels (0, 100 and 200 kg ha-1). Combined analysis of variance was performed by SAS 9.4 software, and means of different treatments were compared by Tukey test at the probability level of 5%.
Maize grain yield increased significantly as a result of increase in all inputs. However, effect of nitrogen on grain yield was more than others. Application of 200 and 400 kg ha-1 N caused 24% and 38% increases in maize yield, respectively. The interaction effect of ETc and N for grain yield was significant, and the highest and the lowest yield of maize with the values of 9486.8 and 5836.4 kg ha-1 was obtained with ETc100N400 and ETc80N0, respectively. When applied water increased up to ETc100, all levels of nitrogen increased yield but water use higher than this level decreased grain yield in N400. It appears that under these conditions, leaching increases, which ultimately led to the reduction of yield. According to these findings, irrigation more than ETc100 decreased N uptake in this treatment.
The trends of NUE and PUE in response to treatments were similar to that of grain yield. It has been reported that changes in each of the P use efficiency components are significantly dependent on plant yield (Fageria et al., 2014). The interaction of nitrogen and phosphorus showed that in N0, the effect of different levels of phosphorous on grain yield was not significant, while phosphorus application at levels N200 and N400 significantly increased maize grain yield. These findings suggest that the interaction of nitrogen and phosphorus on grain yield and nutrient uptake is synergistic. The results of path analysis indicated that in most of the treatments, the role of N and P uptake efficiency was superior to that of their utilization efficiency on the NUE and PUE.
The results showed that maize grain yield improved with increasing the inputs. The magnitude of the effects of all inputs on yield was in the order of N > ETc > P. The interaction effect of ETc and N showed that ETc100N200 was the optimum treatment to improve the yield and nitrogen efficiency simultaneously. The interaction of N and P on the yield and nutrient uptake was positive and synergistic. Overall, this study emphasized the importance of the interactive relationships between water and nutrients for achieving both the highest grain yield and nutrient use efficiency.