Does green cane harvesting conserve soil water?

A benefit claimed for the practice of green cane harvesting is conservation of water through suppression of soil evaporation by the trash mulch. A combination of gravimetric and micro meteorological techniques was used to measure evaporation from soil, trash and plants in ratoon crops of sugar cane with leaf area indices ranging from 0.7 to 2.5. Those measurements were compared with the predictions of models of canopy evaporation from row crops with bare soil surfaces. Micrometeorological measurements of vapour transfer in the cane canopy confirmed the reliability of the gravimetric measurements of evaporation from the soil and trash, which together comprise the surface evaporation Es. Es amounted to 39% of the total water loss in one crop and 21 % in another. However, only when the trash was wet after rain was Es as large as the model predictions. Usually, it was up to half that rate. The conclusion is that the trash mulch is effective in suppressing surface evaporation in the first weeks of regrowth of ratoon crops, and estimate that over the study period, it reduced Es by 0.4 to 0.8 mm d-1.