Influence of deficit irrigation on accumulation and partitioning of sugarcane biomass under drip irrigation in commercial varieties

Studies of sugarcane varieties grown under water-restrictive conditions are necessary because climate changes may result in insufficient rain for agriculture and selecting or breeding drought-tolerant cultivars will become more and more important. This study aimed to quantify the accumulation and partitioning of biomass, as well as water use efficiency of commercial sugarcane varieties under different soil water availability conditions throughout the growing season. The study was conducted during two cropping cycles in Southeast Brazil (22.7 degrees S, 47.6 degrees W). Four soil moisture availability regimens were set up to provide 100, 75, 75* and 50% of the water demand of eight commercial varieties of sugarcane (CTC15, CTC17, RB867515, RB92579, RB931011, RB966928, IAC5000, and NCo376). The total aboveground biomass was measured in both crop cycles. Our results indicate that two Brazilian varieties (CTC15 and CTC17) and one South African variety (NCo376 - Canegrow DSSAT reference), increased their water use efficiency when grown under an irrigation deficit of 75% of normal, without yielding less biomass. We did not observe any change in sucrose content under controlled water deficits; however, the studied varieties showed different biomass partitioning: RB966928 had the largest biomass fraction allocated in the stalks (0.59), while IAC5000 showed the lowest fraction (0.51). We verified that the harvest index for sucrose was not altered by reduced irrigation, but that its variability was attributed to the genotype inherited from traditional breeding programs. Thus, we conclude from these results that increased sugar yield per unit area is only possible nowadays by increasing sugarcane biomass productivity under highly efficient irrigation conditions to minimize the loss of yield from water stress.