Effect of different levels of biochar on physiological traits of pumpkin under water shortage stress

Biochar has recently attracted lots of attention as a viable strategy for increasing crop productivity. Water shortage limits the productivity of agriculture, and one possible solution to this problem is the application of biochar. The objective of this study was to investigate the effects of biochar on physiology and yield of pumpkin (Cucurbita pepo L.) under different irrigation regimes. For this purpose, a factorial experiment in randomized complete block design with four replicates was conducted in Gorgan, in two successive years (2014-2015) and consisting of a factorial combination of four irrigation regimes including 45%, 60%, 75%, and 90% (I1-I4) of maximum allowable depletion (MAD) of available soil water (ASW) and biochar was applied at rates 0, 5, 10, and 20 tons per ha(B0–B20). Drought increased the activity of antioxidant enzymes, and the content of reactive oxygen species in leaf compared to control. In contrast, all of the antioxidant activities, reactive oxygen species and proline contents of leaves in soil treated with biochar, particularly at B20 biochar, declined. With the addition of biochar, the contents of MDA, O2•− and H2O2displayed remarkable decrease, however, maximum and minimum of these substances belonged to I4B0 and I1B20, respectively. Interestingly, biochar application alleviated the negative impact of reduced irrigation on the leaf gas exchange parameters, crop yields, water use efficiency, chlorophyll content, uptake of nutrients, and plant water status. Measured and simulated results revealed a special biochar application threshold for each irrigation regime with respect to seed yield. Response rate to biochar was ceased at lower biochar rates by prolonging irrigation. But the response of I2 treatment to biochar ceased at higher biochar rate as Bcritical (14 t ha-1). This implies that I2 improved response of pumpkin to biochar, which was accompanied by its higher WUE. These results indicate that biochar amendment could be considered as a successful strategy for improving the water productivity and increased crop production in study region (Gorgan).