Knowing the effects of various environmental stresses on plant's physiology is necessary to get information about the plant's resistance and survival mechanisms. Drought stress is one of the most common stresses that always threatening agricultural products in widespread parts of the world. Therefore, considering the shortage of water resources, improving water use efficiency in agricultural fields and paying more attention to usage and development of water saving strategies are necessary. As freshwater resources have declined, irrigating crops to meet their full demands are difficult. To reduce the irrigation volume, irrigation techniques such as Deficit irrigation (DI) have been developed meeting the minimum crop water requirement without any significant reduction in crop yield and quality. During the last decade, a novel deficit irrigation strategy named Partial rootzone drying (PRD) has been developed. In PRD one half of the root zone is irrigated while the other half falls dry out. Irrigated and dry sides are periodically switched. PRD irrigation has been tested for different field crops, fruit trees and vegetables. In most cases, PRD irrigation has shown a great potential to increase water use efficiency and to maintain yield. It has been shown that PRD can greatly induce the initiation and growth of secondary roots, which improved the ability of the plant to absorb both water and nutrients from the soil matrix. It seems the combination of irrigation techniques and mechanized irrigation systems such as drip irrigation can significantly improve agricultural water use efficiency.
For this purpose, the effects of deficit irrigation and partial rootzone drying techniques on potato (Solanumtuberosum L. cv. Agria) yield and some components of yield has been studied. This research was done in a field at Shahrekord University in spring, 2012.
The soil texture's field was clay and soil moisture contents at field capacity (FC) and wilting point (PWP) were 37.33% and 15.49%, respectively. A completely randomized block design with seven treatments and three replications was used. Each block (23m × 2.5m) was divided into seven plots. Each plot consisted of three rows of 2.5 m in length. Blocks were bordered by a 1.5m wide protection area.
The tubers were planted on June in rows (75cm between rows and 25cm between tubers). Potatoes were subjected to water treatments Full Irrigation (FI), Deficit irrigation (DI) and Partial rootzone drying (PRD) in three level of soil matric potential (-60, -80, -120 kPa) after tuber initiation. Drip irrigation was used in field and time domain reflectometry (TDR) sensors were used to monitor soil moisture. In FI and DI treatments, one drip line was placed in the center of each ridge. The distance between emitters was 25cm and they were placed near plants. Their discharge rate was 2 (L h-1). In PRD treatment, two drip lines were placed in the center of the ridge. The two drip lines were placed in parallel and emitters distance were 50cm. Some of the physiological and morphological characteristics of the plant were measured in final crop harvest and analyzed by SAS v.9 software. Analysis of variance showed that the difference between irrigation treatments was significant in 1% probability level in most of plants characteristics. Also, with increasing the stress severity, the difference between PRD and DI irrigation was increased. PRD was able to maintain higher biomass production plant under water stress. The results showed that highest and lowest dry biomass was observed in FI (226.49 gr/plant) and DI-120 (187.45 gr/plant), respectively. The maximum and minimum dry weight of root were observed in PRD-120 (8.98 gr/plant) and FI (7.69 gr/plant), respectively. Tubers from each treatment were graded into various size classes and weighed. Among the tuber sizes, the categories of 40-60mm diameter were considered as marketable. Results showed PRD technique increased the marketable yield more than DI.
The maximum and minimum dry matter tuber were seen in PRD-120 (113.03 gr/plant) and DI-120 (98.169 gr/plant), respectively. The maximum and minimum fresh weight of tubers were observed in FI treatment (0.570 kg/plant) and DI-120 (0.430 kg/plant) .the maximum and minimum water use efficiency (WUE) was observed in PRD-120 (5.11 kg/m3) and DI-60 (4.268 kg/m3), respectively. This treatment increased WUE by 14.33%. Also, the obtained results showed that water stress induced in level of soil matric potential (-60, -80 and -120 kPa), reduced water used by 9.85, 16 and 22.45% in field, respectively.
These results showed in comparison to the traditional deficit irrigation strategy (DI) in which the crop is subjected to some degree of water stress, PRD is a successful alternative to FI for saving irrigation water.