Optimum Irrigation Levels for Cane under Burnt and Trashed Conditions

Increasing irrigation levels from 37% to 84% of Class "A" Pan evaporation produced a linear increase in cane yield from 65 to 146 tonslha. The response with burnt cane was greater due to more severe moisture stress, and there was also an increase in cane yield between 84% and 100% Pan which was absent in trashed cane. Maximum sucrose content, as well as brix, purity and recoverable sugar % cane were obtained with a level of 68% Pan; both higher and lower irrigation levels were significantly poorer in cane quality. Burnt cane produced higher sucrose content than trashed cane except at 37% Pan. Maximum yields of sucrose per hectare were obtained at 84 % Pan with trashing and 100 % Pan with burning. At 37% Pan, trashing produced 4 tons sucrose/ha more than burning; this difference declined with increasing irrigation IeveIs up to 80 % Pan when there was no difference between burning and trashing. At 100% Pan, burning yielded 2 tons sucrose/ha more than trashing. Maximum efficiency of water use (expressed as kg sucrose/m3 water) was obtained generally at 68 % Pan, with drier levels of irrigation giving far poorer efficiencies, especially with burnt cane. Increasing irrigation levels also increased stalk numbers, stalk height, lodging and flower counts. Burning produced more stalks than trashing at all levels of irrigation except 37 % Pan; it also resulted in less lodging than did trashing.