Evaluation of the effect of chemical nutrition systems on yield, phosphorus and potassium content and proline content of rice under different irrigation conditions

Introduction Due to the continuous water shortages in rice cultivation areas, unbalanced use of nitrogen chemical fertilizers, the need to pay less attention to the use of water in rice cultivation and balance in the use of chemical fertilizers in saving and preventing water loss is important. Periodic irrigation has been introduced as an important research finding to reduce water consumption and increase water use efficiency in paddy lands. As water stress increases, the uptake of nitrogen, phosphorus and potassium decreases. Materials and methods Therefore, this study conducted for evaluation the effects of different irrigation regimes and N fertilizer on yield, and the content of micronutrients in brown and white rice was conducted in Rashat during cropping season of 2016-2017 and 2017-2018 in Rasht. Experiment was arranged in split split plot based on completely randomized block design with 3 replications in which water regimes were main factor included continuous submergence, 7  and 15 day interval irrigation and nitrogen fertilizer levels were sub factor included 50 , 75 , and 100 kg ha-1 and cultivars were sub sub factor included Gilanh and Hashemi. Before conducting the composite data analysis, Bartlett's test was used to ensure the homogeneity of experimental error variance. Analysis of variance and statistical calculations were performed using SAS software version 9.1 and the mean of the studied traits were compared using Duncan test at 5% probability level. In order to check the normality of the data, the normality test in SAS program was used. Results and discussion The results showed that by increasing the irrigation interval, paddy yield decreased, while application of 75 and 100 kg ha-1 nitrogen fertilizer increased paddy yield in all three irrigation levels compared to the level of 50 kg ha-1 nitrogen fertilizer. There was a significant effect (at the level of one percent probability) between the treatment of irrigation regimes, nitrogen fertilizer and cultivar on brown and white rice and macro elements. The highest yield of rice for the Gilaneh variety was achieved under flooded irrigation treatment combined with the application of 100 kg ha-1 of nitrogen fertilizer, resulting in 12.4 T ha-1  in 2017 and 4.05 T ha-1  in 2018. Increasing the irrigation interval also increased the content of macro elements in brown and white rice. The highest protein content in brown rice was recorded at an average of 9.45% from the flooded irrigation treatment, with the application of 100 kg ha-1 of nitrogen fertilizer, specifically in the native Hashemi variety. The highest phosphorus in brown rice in the treatment of 7 days of irrigation, 75 kg of nitrogen per hectare in Gilaneh cultivar with a rate of 0.303% and the lowest amount in the treatment of 7 days of irrigation with 50 kg of nitrogen and in Gilaneh cultivar with 0.056 percent and the highest percentage of potassium in white rice in the treatment of 14 days of irrigation, 50 kg of nitrogen per hectare and in Hashemi cultivar with the amount of 0.246 percent and the lowest amount in the flooded treatment with Consumption of 50 kg of nitrogen in Hashemi cultivar was 0.143%. Conclusion The results of this study showed that the application of nitrogen fertilizer has the ability to increase yield and yield components at all three irrigation levels and in both Hashemi and Gilaneh cultivars. In all three levels of irrigation in this study with increasing nitrogen fertilizer application with increasing vegetative growth, increasing the number of spikes per square meter, number of seeds per spike and paddy yield was observed. Consumption of 100 kg ha-1 of nitrogen fertilizer resulted in the highest yield of paddy in both cultivars and all three irrigation levels.