Supplementary irrigation in Sudan grass: Leaf area index, dry matter production and water use efficiency

The study was carried out in the municipality of Santiago, Rio Grande do Sul, Brazil, with the objective of evaluating the effect of the application of increasing supplementary irrigation depths on the leaf area index , dry matter  accumulation and water use efficiency of Sudan grass ( Sorghum sudanense (Piper) Stapf) submitted to four standardization cuts of the aerial part, at 50, 80, 110 and 140 days after sowing (DAS) with irrigation depths of 60%, 80%, 100%, 120% and 140% of the difference between reference evapotranspiration (ETo) and effective precipitation-(EP), plus the control treatment (without irrigation: only EP). Between cuts, leaf area index and shoot dry mass were evaluated every fortnightly. The experimental design was in randomized blocks, with six treatments and four blocks, totaling 24 experimental units. Both the leaf area index and the dry mass production showed an increasing behavior until the treatment with 100% of ETo-EP; after this treatment the production was stable, with some of the highest averages in the treatment with 140% ETo-EP, and the lowest averages were observed in the treatment without irrigation. There was a decrease in dry mass production throughout the experiment due to the natural loss of the yield potential of the crop. At second cut (80 DAS), the leaf area index showed the highest values. The highest water use efficiency in the sum of the four cuts was in the treatment with 100% of ETo-EP and the lowest in the treatment with 60% of ETo-EP.