Effect of soil water stress and nickel application on micronutrient status of canola grown on two calcareous soils

Recently, application of sewage sludge/effluents to soils as an alternative source of organic matter in arid/semiarid regions and as a practical approach to remove its sanitary adverse effects in urban and industrial regions is gaining increased attention. This may lead to high levels of nickel (Ni) in soil and plants. On the other hand, in these regions water shortage is a major constraint of plant productivity. To determine the combined effects of Ni and water stress on the nutritional status of canola, we studied the effect of five Ni levels (0, 0.05, 0.1, 0.5 and 1 mg Ni /kg soil as Ni(NO3)sub(2)) and two levels of water status (field capacity, FC, and 0.6 FC) on the contents of iron (Fe), manganese (Mn), zinc (Zn) and copper (Cu) in canola (Brassica napus L.) on two loamy and sandy clay calcareous soils in greenhouse conditions. Shoot/root dry matter yield (SDMY/RDMY), their Fe, Zn and Mn content decreased under 0.6 FC conditions; whereas, their concentrations increased. Shoot/root Cu concentration/content decreased in water-stressed plants. Application of > 0.05 mg Ni /kg to loamy soil increased SDMY, however Ni did not affect SDMY positively or even decreased it in sandy clay soil. Application of 0.01-0.5 mg Ni increased RDMY in loamy soil under FC conditions; whereas, higher levels of Ni decreased it. Nickel decreased RDMY in sandy clay soil, whereas did not affect micronutrient concentrations in the root. The concentration and content of Mn in the shoot followed different patterns in response to applied Ni. Although the highest level of applied Ni increased shoot Zn content. Application of 0.05 and 1 mg Ni decreased the Cu concentration in the shoot on loamy and sandy clay soils, respectively. However, Ni did not affect the Cu content of shoot. Nickel had different impacts on the content of each micronutrient and was not effective in mitigating the adverse effects of drought stress.