Effects of Combined Application of Nitrogen and Phosphorus on the Growth Characteristics of Rice Plants under Flooded and Periodic Saturation Conditions

Nitrogen is one of the most important macronutrients for plants that accompanied with phosphorus plays an important role in rice production. On the other hand، soil moisture conditions affect availability of these two elements، markedly. In order to study the effects of nitrogen and phosphorus on the growth characteristics of rice (Oryza Sativa L.) plant، a factorial experiment was done in a randomized complete blocks design with three replicates. The treatments included two rice cultivars (Hashemi and Alikazemi)، two moisture regimes (submerged and periodic saturation)، three nitrogen levels (0، 75،150 mg­/kg) as urea and three phosphorus levels (0، 25، 50 mg/­kg) as mono calcium phosphate. The results showed that dry weight of shoot in Alikazemi cultivar was greater than that in Hashemi cultivar. Shoot and root dry weight، root length and volume، number of leaves and tillers and stem diameter under submerged conditions were greater than those under periodic condition. By increasing N levels، shoot and root weight and root volume increased. Also، by increasing P levels، root volume and weight increased. Interaction between the nitrogen and phosphorus levels showed a significant effect on wet and dry weight of shoot and root، root length and volumes، leave chlorophyll index and shoot nitrogen concentration (p<0. 05). Moreover، interaction between nitrogen and water regime left marked effect on leave chlorophyll index. The interaction between phosphorus and moisture regime also changed the dry weight of shoots، significantly. The interaction between nitrogen and soil moisture regime showed significant effects on the leave chlorophyll index of shoots. Maximum shoot dry weight was observed under submerged conditions in Alikazemi cultivar for 75 mg ­kg-1 nitrogen at control level of phosphorus