Leaf Photosynthesis Response to Change of Soil Moisture Content in Sugarcane

It is necessary to practice efficient irrigation in any agricultural development strategy under the context of climate change and competition from other economic sectors. Irrigation based on the relationship between photosynthetic activity and change of soil moisture could be an effective practice. Herein, we investigated the response of sugarcane photosynthetic parameters on drought stress at yield formation stage. The experiment was carried out by withholding water for 3 weeks from 190 days after transplanting and then re-watering until the end of experimental period. Data were collected for photosynthetic parameters including potential photosynthetic rate, stomatal conductance, transpiration rate, internal CO2 concentration, SPAD, and soil physical parameters. The results showed that sugarcane photosynthetic parameters decreased with decreasing soil moisture content to certain extent and the stayed static before dropping off again. Internal CO2 concentration increased when soil moisture reached the most severe, and it caused a standstill in photosynthesis. However, photosynthesis also recovered with soil moisture recovery. Photosynthetic parameters could be used as indicators to evaluate drought stress’s effect as well as to determine the time to re-irrigate to maintain normal growth of the plants. Soil volume moisture content of 15% (recorded by the 5TE sensor) or at pF of 2.8 (recorded by the MPS-6 sensor) seems to be the initial time to start irrigation to keep standard growth. Soil moistures at 10% and 3.8 pF, respectively, could be the critical points beyond which irrigation was found to result in photosynthetic disorders.