Effect of fertilizer management systems and water stress conditions on nutritional status of grapes (a greenhouse study)

Grapes are one of the most important garden products in the world as well as in Iran. The management of plant nutrition under water stress conditions is one of the important issues in the production of the plant. When the plant has adequate nutrition, it will result in higher resistance to environmental conditions. The use of organic and chemical fertilizers as amendments of the physical, chemical and biological properties of soil can be one of the strategies to reduce the adverse effects of drought stress.

In order to evaluate the effect of potassium sulfate, compost and biochar on some soil properties and grapes nutritional status under water stress conditions, a greenhouse experiment were carried out as a factorial experiment based on a block of randomized completely design with two factors and four replications. Water stress had two levels (40, 80 % FC) and fertilizers’ treatments included potassium sulfate (10 g pot-1), compost (5 % w/w) and biochar (10% w/w). The macro- and micro-elements’ contents of grapes’ leaf and soil properties included the macro and micro-elements, pH, EC, OC. were also measured.

The results showed that the interaction effect of water stress and fertilizers’ treatments was significant for nitrogen(N), magnesium (Mg), ferrous (Fe), zinc (Zn) and copper (Cu) concentrations of grapes’ leaves (P<0.01). ANOVA indicated that the simple effects of water stress and fertilizers’ application had a significant effect (P<0.01) on macro- and micro-elements’ concentrations of grapes’ leaf. The results also showed that under water stress conditions, the highest N concentration was observed for compost and potassium sulfate applications. Without water stress conditions, there was no significant difference between treatments. Under the water stress conditions, the highest concentration of Mg of grapes’ leaves was achieved with biochar application. While without water stress conditions, the lowest concentration of Mg was observed for biochar treatment. With and without water stress conditions, the concentration of Fe and Cu was higher for organic treatments compared to potassium sulfate application. With and without water stress conditions, the highest concentration of Zn was achieved for potassium sulfate application. The ANOVA results showed that the interaction effect of water stress and fertilizers’ treatments was not significant for soil properties except soil calcium. The water stress caused a significant decrease in soil phosphorus (P) and Mg (P<0.05) as well as calcium (Ca) (P<0.001). The effect of fertilizers’ treatments was significant on electrical conductivity, organic carbon, N, P, potassium (K), and sodium (Na) (P<0.01), Ca and Mg (P<0.001) concentrations of soil. The application of potassium sulfate and compost increased the Na concentration of soil as 8.53 and 60.52 percent, respectively. While the Na concentration of soil decreased as 3.73 percent with the biochar application.

Under water stress conditions, the application of compost and biochar in comparison with potassium sulfate enhanced the nutritional status of grapes because of the improvement of soil fertility status. The highest K concentration and uptake of grapes’ leaves and soil were observed with biochar application. Under water stress conditions, in comparison with no fertilizer application, K uptake increased as 69.85, 36.21 and 178.97 percent by potassium sulfate, compost and biochar applications, respectively. Since K is a critical element to regulate the water content of plant tissue and reduces the hazards of water stress, the application of compost and biochar is recommended for the improvement of plant resistance under water stress conditions. However, biochar is suggested due to properties such as highly porous structure, high specific surface area, higher water holding capacity of the soil, the long-term stability in the soil and the reduction of Na hazards in soil.