Completed projects and reports

Now showing 1 - 2 of 2

Final report SRDC Project CSR024 Improving the environment for sugarcane growth through the amelioration of soil acidity
(2002) Wood, AW; Noble, AD; Bramley, RGV
Most soils used for growing sugarcane in wet tropical northern Queensland are highly acidic. Comparisons between new cane land and land that has been growing sugarcane for many years have demonstrated that our soils have become degraded under continuous sugarcane monoculture and that many of the changes in soil chemical properties are associated with soil acidification. Continued acidification, due to heavy applications of nitrogen fertilizer and the removal of base cations in the cane sent to the mill, will not only further acidify surface soils but will also progressively acidify the lower parts of the soil profile, making amelioration difficult and costly. Low soil pH not only reduces the availability of some nutrients to plants but also reduces soil surface charge resulting in a permanent reduction in the capacity of the soil to hold nutrients. Since many soils in the wet tropics already have a low cation exchange capacity, further reductions in cation exchange capacity (CEC) due to accelerated acidification may lead to sub-optimal levels of exchangeable calcium, magnesium and potassium, which will have a direct impact on sugarcane yields. Current industry recommendations for applying lime are based on perceived economic crop responses to calcium and are based only on the level of soil exchangeable calcium in the surface layer. Whilst this philosophy may be appropriate for soils with very low cation exchange capacities and suboptimal levels of exchangeable calcium, where frequent lime applications would be required to maintain soil calcium levels, it does not offer a sustainable management solution for highly acidic soils with adequate exchangeable calcium levels. Over 85% of cane growing soils in the Herbert River District fall into this category, having exchangeable calcium levels above the critical level and yet having an average soil pH of less than 5. This project aims to enhance the sustainability of the sugar industry by investigating and developing strategies for ameliorating soil acidity and thus making soils more amenable not only for sugarcane production but also for leguminous fallow crops which are now considered to be an important part of a sustainable sugarcane production system. Replicated experimental trials involving five rates of lime and three rates of gypsum were established on farms in the Herbert River District with contrasting soils that were highly acidic but had exchangeable calcium above the critical level. A fourth trial site was included later in the project with very low exchangeable calcium levels. Cane yields and ccs were monitored and soil samples taken from different depths in selected treatments in each trial were analysed in order to monitor changes in soil chemical properties.
Final report Improving the cation retention capacity of cane-growing soils using high activity clays
(2009) Sacchi, A
The Australian sugar industry largely relies on tropical soils that have low cation exchange capacities (CEC) and are prone to becoming deficient in Ca, Mg and K without appropriate management. Adding bentonite is an option for increasing the CEC, water holding capacity and fertility of these soils. This research project investigated if bentonite treatments could indeed be used to improve the fertility of low CEC sugar producing soils and enhance commercial cane yield. Two field trials conducted on old sugarcane producing soils in the Innisfail region in the Wet Tropics of far north Queensland over the 2006, 2007 and 2008 growing seasons showed that at rates of 10 - 30 t/ha banded additions of natural sodium bentonite improved soil properties and significantly raised sugarcane yields at final harvest. The best results were achieved with 20 and 30 t/ha rates of bentonite addition, in which cane yield was increased by up to 39.6 % in comparison to an untreated control. The main mechanisms responsible for the yield increase were found to be higher plant available water content (PAWC) and increased nutrient cation availability, which led to improved canopy development, greater radiation interception and overall enhanced growth and increased biomass accumulation within stalks. The results of the field trials were supported by five individual glasshouse trials that showed that various bentonite treatments could effectively be used to enhance soil CEC, nutrient cation levels and PAWC to bring about significant yield increases on a variety of low CEC soil types. Additional important information yielded by the glasshouse trials included the discovery that rates of above 80 t/ha bentonite had a detrimental impact on soil structure leading to reduced yields. Furthermore, the effect of increased PAWC as a result of bentonite treatment on yield was found to be much stronger than initially anticipated. An economic analysis assessing the feasibility of using bentonite treatments to improve soil fertility and increase cane yields has not yet been finalized. Preliminary results of this analysis suggest that bentonite treatment can indeed be an economically feasible option for increasing production and profitability in the long term in a permanent bed system under precision agriculture. Using an example from the Wangan trial where the cane yield in the 30 t/ha treatment was 97 t/ha compared to 75 t/ha in the control: assuming a sugar price of $480/t and a CCS of 12.5, the return per hectare for the 30 t/ha treatment is $772 higher than that of the control. At a bentonite cost of $336 per tonne, the cost of a banded application at a rate of 30 t/ha is $3360. Based on the increased return of $772 per hectare, the investment in the bentonite product would be paid off after five seasons. However, caution must be applied, as due to the high product cost of bentonite, the technique is economically unfeasible both in the short term and in a conventional farm system were the ground is reworked after three to four seasons.

Completed projects and reports

Browse

Filters

Advanced Search

Filter by

Settings

Sort By

Results per page

Search Results