Studying the effect of planting pattern and potassium fertilizer levels on some physiological characteristics and yield of potatoes (Solanum tubersum L.) under different irrigation levels

Introduction Considering the importance of potato in supplying the country's required food and its dependent industries and also the climatic situation of most regions of Iran as arid and semi-arid, studying the effect of water deficit stress on potatoes is very valuable. Since one of the suitable areas for cultivating potatoes in Iran is Khorasan province, comprehensive studies on this plant cultivation including planting arrangement and effects of water deficit on the plant, seems necessary. So, the purpose of this study was to evaluate the effects of different levels of moisture on potatoes in different planting patterns and also the possibility of potassium application for reducing the impacts of water deficit. Materials and methods In order to study the effects of different levels of moisture on potato under different cultivation systems, an experiment was conducted in the field on the plain of Rokh in Khorasan Razavi, Iran over 2016 cropping season. This research was set as split- spilt plot in randomized complete block design with three replications. Trial factors consisted of planting pattern at three levels (normal planting, usually dense planting and zigzag planting) in the main plot, irrigation with three levels [control (without stress), irrigation as 80% of required water (as deficit irrigation treatment), and irrigation as 60% of required water (as stress treatment)] in sub plots, and potassium fertilizer in three levels (0 (control), 75 and 150 kg potassium sulfate per hectare) as sub-subplots. Potato crop water requirement based on the amount of water needed which has been specified using OPTIWAT software under Rokh plain conditions, was determined. Drip irrigation methods using tapes was conducted. The data was analyzed using the SAS program, the FLSD method was used to compare the means. All graphs were drawn using Excel software. Results and discussion The results of the experiment showed that there was a significant difference between irrigation treatments for plant height, so that reducing water amount significantly reduced the plant height. The shortest and tallest plants were observed with stressed and control treatments, respectively. The number of stems produced in different treatments did not show significant differences. In this research, zigzag planting pattern under complete irrigation and consumption of 150 kg of potassium sulfate increased the maximum leaf area compared to common and dense common planting patterns. Moreover, the comparison of the mean for the interaction effect of cultivation pattern and potassium sulfate fertilizer on the dry weight of maximum leaf area showed that zigzag planting pattern and consumption of 150 kg ha-1 of potassium sulfate fertilizer, enhanced the dry weight of maximum leaf area compared to common and dense common planting patterns without potassium sulfate fertilizer. In this study, zigzag planting pattern under complete irrigation and consumption of 150 kg of potassium sulfate fertilizer resulted in the greatest relative water content of leaf. The Irrigation rate had a significant effect on the dry matter percentage, so that water stress caused a significant reduction in dry matter percentage. In fact, the dry matter percentage under water stress conditions was reduced by 12% compared to the control treatment. In this experiment, the number of tubers in common and dense common planting patterns with complete irrigation and consumption of 150 kg of potassium sulfate was 15% greater than that of zigzag planting pattern and 150 kg potassium sulfate consumption. Comparison of the mean for the interaction effect of planting pattern on irrigation rate and potassium sulfate fertilizer showed that the greatest number of non-marketable tubers was observed with the common planting pattern under water stress and no potassium sulfate fertilizer application and the lowest was obtained where the zigzag planting pattern was applied with full irrigation and consumption of potassium sulfate fertilizer. Yield measurement in this experiment showed that there was a significant difference between the levels of cropping pattern, irrigation and potassium sulfate rates. The tuber yield was enhanced by changing from usual to zigzag cultivation pattern and was reduced by lowering the irrigation rate, while application of potassium sulfate fertilizer increased this trait and this, reduced the effects of stress in all tested planting patterns. Conclusion It seems that the pattern of zigzag cultivation in potatoes can increase plant yield and on the other hand, due to the sensitivity of the potato plant to irrigation rate, providing enough water improved its performance. The remarkable thing was that application of potassium sulfate fertilizer increased and improved the quality and yield of the tubers under water stress conditions.