Effects of Zinc and Phosphorus on Nutrients, Starch and Reducing Sugar Concentrations of Potato Tubers under with or without Water Deficit Stress

In natural environments, plants are subjected to biotic (insects, bacteria, fungi, and viruses) and abiotic (light, temperature, water availability, nutrients, and soil structure) stresses that can have negative effect on growth, metabolism, and yield. Among these, drought is a major abiotic factor that limits agricultural crop production. Potato production has fourth rank in the world after rice, wheat, and maize with the production of 321 million tons from 19.6 million hectares. By about 3 percent of cultivation area, potato had 7.2 percent of total agricultural production (5.57 million tons) in our country (Iran). Limited studies have been conducted on the interactive effects of Zn and P on potato tubers quality under water deficit conditions.
This study was conducted for evaluating the effects of soil moisture, phosphorus (P) and zinc (Zn) levels on the chemical composition and nutrients content of potato (Solanum tuberosum L. cv. Agria) as a factorial experiment based on randomized complete blocks design with three factors under greenhouse conditions. The study was performed with factors of Zn at three levels (0, 10 and 20 mg Zn per kg dry soil as ZnSO4.7H2O), P at three levels (0, 30 and 60 mg P per kg dry soil as Ca(H2PO4)2.H2O (monocalcium phosphate)) and soil moisture at three levels (0.5FC-0.6FC, 0.7FC-0.8FC and 0.9FC-FC) using three replications and 81 pots. The soil moisture levels were imposed three weeks from the flowering (64th day) until harvest (85th day after planting). After imposing of soil moisture levels and at the harvest, the yield and yield components, reducing sugars concentration in fresh weight by di- nitro phenol method (Mostofi and Najafi, 2005) and starch by Antron method (Mostofi and Najafi, 2005), N, P, K, Mg, Na, Fe and Zn concentrations in dried potato tubers were measured. Data were subjected to analysis of variance as factorial 3×3×3 with n=3 by using MSTATC software. Duncan's multiple range tests at p≤0.05 probability level was applied to compare the mean values of measured attributes. The Excel software was used to draw Figures.
The results showed that water deficit significantly affected most of qualitative attributes and nutrients concentration of potato Tuber N, P and reducing sugar concentrations were significantly increased (p The results showed that water deficit imposing had adverse effects on tubers quality and P and perhaps Zn requirement enhanced by increasing of water deficit. In general, to achieve the optimum potato tuber yield in similar soils, application of 10 mg Zn and 30 mg P per kg dry soil would be recommended under normal irrigation conditions while at water deficit conditions application of 10 mg Zn and 60 mg P per kg dry soil could be recommended.