Effects of Farmyard Manure and Biochar Treatments on the Development and Water Use of Lettuce Under the Deficit Irrigation Regime

In this study, the effects of different organic matter additives [soil (control), 20 ton ha-1 farmyard manure, 20 ton ha-1 biochar, and 10 ton ha-1 farmyard manure+10 ton ha-1 biochar] to the soil of lettuce grown with different irrigation water levels [100% (full irrigation), 75% (25% deficit irrigation), 50% (50% deficit irrigation), and 25% (75% deficit irrigation)] on water and irrigation water productivity efficiencies and plant characteristics were investigated. Among the organic matter additives, the biochar reduced the amount of irrigation water and actual evapotranspiration of lettuce and increased its marketable yield, thus the highest water and irrigation water productivity efficiencies were obtained from biochar treatment. Despite the decreasing marketable yield in the 50% irrigation treatment, the proportionally decreasing amount of irrigation water and actual evapotranspiration caused the highest water and irrigation water productivity efficiencies to occur in the 50% irrigation treatment. While the root diameter, root fresh and dry weights, stem diameter and length, head fresh and dry weights, marketable leaf number and yield, chlorophyll, and leaf relative water content of lettuce decreased with decreasing irrigation water levels, root length and membrane damage increased. The effects of organic matter additives on all of these physical-physiological properties, except root diameter and membrane damage, were found to be significant, and the biochar provided the most effective development of these parameters under the deficit irrigation regime. Considering that the yield and yield characteristics in 75% irrigation treatment do not decrease at a very significant level compared to full irrigation (100%) and that these decreases can be compensated by biochar and that the farmyard manure+biochar as alternative treatment is also effective in improving the decrease in yield parameters, treatment of 10 ton ha-1 farmyard manure+10 ton ha-1 to the soil at 75% irrigation water level was found to be recommended in lettuce cultivation.