OVERCOMING ON-FARM CONSTRAINTS TO PRODUCTIVITY AND PROFITABILITY IN A WET TROPICAL AREA

GREEN cane harvesting and trash blanketing has been widely adopted by growers in the wet tropics. However, it is possible that this practice has contributed to a decline in CCS due to increased nitrogen (N) supply from the soil and trash blankets hindering the ‘drying out’ process and therefore hindering development of high CCS. In 1999, four participative on-farm experiments were established to assess the effects of trash, trash raking, and trash incorporation on sugar production, soil N and soil moisture in the Babinda region. In addition, a survey of sugarcane N status was undertaken via measurements of amino-N in the sugarcane juice on eight farms in the region. After two crops, there was no consistent effect of raking on yields or CCS. There was also no difference in soil or leaf N between the treatments and little difference between the sites. A consistent result was that there were substantial amounts of soil mineral N at all sites during the two crops and much of the mineral N was in the form of ammonium. The results of the survey of amino-N in sugarcane juice showed that the majority of farms surveyed had an adequate supply of N, with some exhibiting luxury uptake of N. It was unlikely that N was limiting yields of these crops, but also there was no evidence of N suppressing CCS. This study suggests that it is unlikely that growers would recoup any money spent on trash raking and/or incorporation through increased productivity. It also suggests that crop N status is not contributing to low CCS. If the amounts of mineral N and the dominance of the ammonium form of N found in this study prove to be more widespread in wet tropical soils, it will have substantial implications for how we should think about N dynamics in that region.