Effects of certain soil amendments on the autochthonous Ercis grape (Vitis vinifera L.) cultivated under different water deficit conditions at high alttudes

In recent years, global climate change and the threat of drought have increased the significance of scientific research aimed at developing alternatives for water scarcity in agriculture. This study evaluated the effects of full irrigation, 25% deficit irrigation, and 50% deficit irrigation, along with biochar (2.5 tons/ha) and pumice (5 tons/ha) applications, on yield, morphological characteristics, grape juice biochemical composition, and nutrient elements of the autochthonous Erciş (Vitis vinifera L.) grape variety over a two-year period. Irrigation amounts were determined based on evaporation rates obtained from an A-class evaporation pan. Under full irrigation conditions, pumice provided the highest increase in yield, while biochar was more effective under deficit irrigation levels. Biochar enhanced shoot length and internode diameter under full irrigation, whereas pumice positively affected cluster weight and size under full irrigation and both biochar and pumice showed favorable effects under deficit irrigation. Similar results were obtained for berry weight, berry size, and berry diameter. In terms of grape juice characteristics, the control group provided the highest values under full irrigation, while biochar and pumice increased grape juice yield and total soluble solids under deficit irrigation, with biochar showing higher values for maturity index. For acidity and pH, the control group had the highest values under full irrigation, whereas biochar increased these values under deficit irrigation. In biochemical properties, biochar provided the highest levels of phenolic compounds, antioxidant capacity, proanthocyanidins, and flavonoids under full irrigation, while biochar and pumice showed variable effects under deficit irrigation. Biochar exhibited high values for antioxidant enzyme activities (CAT, SOD, APX) under both irrigation levels. Biochar and pumice had positive effects on leaf chlorophyll content and leaf relative water content under deficit irrigation. An increase in membrane damage index was observed under deficit irrigation, with biochar and pumice partially mitigating this increase. Biochar and pumice also showed stabilizing effects on leaf and soil temperatures under deficit irrigation. Deficit irrigation levels resulted in reduced P, Mg, and Na contents, with increased K content; a trend towards decreased Fe content, adequate Mn levels, and deficiencies in Zn and Cu were detected. Biochar was found to be more effective in enhancing nutrient uptake. In conclusion, biochar and pumice showed positive effects under deficit irrigation conditions, with biochar demonstrating a more favorable impact on plant water balance, nutrient uptake, and plant health. Despite its higher initial cost, biochar stands out under limited irrigation conditions due to its long-term agronomic benefits, while pumice is also suggested as a suitable alternative under varying irrigation levels.