The Effect of Grapevine Wood Biochar on Maize Response to Water Deficit Stress in Greenhouse Condition

A greenhouse study was conducted to investigate the effect of biochar on vegetative and reproductive stages of maize (Zea mays L.) under water deficit stress. A biochar produced from the pyrolysis of grapevine wood chips (at 350℃), was mixed with a sandy loam soil (from Alborz province) at the rates of 0, 0.5, 1, 2, 3, 4 and 5 % w/w, which were used for planting maize. The experiment consisted of two deficit irrigation treatments in vegetative (I1) and reproductive (I2) stages and one sufficient daily irrigation treatment throughout the growing season (I3). Plants in the period of deficit irrigation were subjected to successive wetting (via watering up to FC) and drying (via plant transpiration) soil cycles with water content varying between 0.30 and 0.18 cm3cm-3, respectively. Some plant physiological characteristics including transpiration rate, stomatal conductance and photosynthesis rate were determined during the drying cycles and biomass at the end of experiment. Soil water retention curve and unsaturated hydraulic conductivity (Kh) were measured by a combination of the Sandbox, Pressure plate, and Hyprop apparatus. The results showed that the addition of four percent biochar to the soil increased transpiration rate by 81, 100 and 49% in I1 and 228, 198 and 61% in I2 at soil water contents of 0.18, 0.20 and 0.23 cm3 cm-3, respectively. The effect of biochar on improving the physiological parameters of plants under drought stress in the reproductive stage was greater than the ones in the vegetative stage. Due to this improvement, the harvest index of plants in soils containing biochar increased by 35 and 50% in I1 and I2, respectively. Under the biochar impacts, grain water use efficiency also increased by 42% and 49% in I1 and I2, respectively. Given the small effect of biochar on increasing soil water retention especially in the dry range, it seems that the performance of biochar to keep higher Kh and matric flux potential were the most important factors to improve transpiration rate in the soil drying cycles.