SUCKERING IN THE WET TROPICS: CONSEQUENCES, ENVIRONMENTAL STIMULI AND POTENTIAL SOLUTIONS

摘要

SEVERAL studies in the late 1990s attributed a major problem of low CCS in the wet tropics to an increase of suckers as a component of the harvested material reaching the mill. The low CCS of suckers was diluting the CCS of mature stalks, and significantly affecting profitability. The problem was hypothesised as becoming worse due to a run of wet years and to changes in the sugarcane production system including a shift to near complete green cane trash blanketing. Analysis of the situation led to identifying soil moisture, nitrogen and light as potential candidates for environmental stimuli promoting suckering. Experiments were designed to investigate the effects of increased soil moisture, nitrogen and penetration of light into the canopy on the stimulation of suckering. These experiments unambiguously demonstrated the stimulatory effects of nitrogen and moisture on suckering. In all three experiments performed to date, nitrogen applied late in the crop cycle stimulated suckering. Different ratesof nitrogen applied at the beginning of the growing season showed more varied responses. The stimulatory effect of soil moisture was dramatic and, when combined with higher levels of nitrogen either applied early or late, had a major effect on promotingsuckering. These results provide good evidence that the observed higher rates of suckering observed in the years with wet harvest seasons of the 1990s could be due to the stimulatory effect of soil moisture on suckering. The role of light in promoting suckering remains more elusive and will need further experimentation to clarify. This aspect of suckering deserves more attention in the future. Results of a factorial experiment also have demonstrated that suckering may have a larger impact in some cropson reducing CCS realised at the mill than previously reported. Suckers caused a CCS depression in the harvested material of up to 1.6 units of CCS for every 10% of the mass of the crop that was suckers. The results to date, though not providing a complete explanation of environmental factors affecting the suckering process, can be used to reduce the effects of suckering. More closely matching N fertilisation to crop demand and the ability of the soil and trash blanket to supply N, is one possibility. Additionally the conditions for a potential managed environment screen of cultivars and parents in breeding programs can now be defined. Incorporating low suckering propensity, where appropriate, would reduce suckering in commercial crops.