Soil health and nutrient management

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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 SRDC Project CLW009 Improving yield and ccs in sugarcane through the application of silicon based amendments
(2003) Berthelsen, S; Noble, AD; Kingston, G; Hurney, A; Rudd, A; Garside, A
Under high leaching environments common to the wet tropics, soils undergo significant weathering, which, when combined with accelerated chemical and physical degradation due to soil perturbation and crop removal, results in increased soil acidification and dissolution of the alumino-silicate clay minerals (de-silication). The consequences are both a loss of plant available Si through leaching and a decline in cation exchange capacity and hence an inability to retain essential plant nutrients. The current project has highlighted that large areas of cane-growing soils in North Queensland have sub-optimal levels of plant-available Si. Based on the current soil test, some 85% of soils that were evaluated in the six mill areas on the wet tropical coast have sub-optimal to marginal levels of available Si. Hence the implications of silicon deficiency for substantial areas under sugarcane production, and therefore the benefit of prophylactic applications of silicate materials may have a significant impact of productivity. One of the primary objectives of this study was to quantify responses in cane yield and ccs to Si application. To address this objective, three field trials were established in Bundaberg, Innisfail and Mossman, using a range of application rates of calcium silicate slag. At Innisfail, over the 2 years of the trial, a rate of 9t/ha Ca-silicate gave a 32% increase in total cane yield (189 t/ha) when compared to the control treatment (128 t/ha). At Mossman, a rate of 12 t/ha gave a 35% total yield increase (161 t/ha) compared to the control (105 t/ha) over the same period. At Bundaberg, over a crop cycle of 3 years, the 12 t/ha rate of Ca-silicate resulted in a 23 % increase (278 t/ha) compared to the control (213 t/ha). The results clearly indicate that Si should be treated as an integral part of any fertilizer strategy associated with cane production on these soils.
Improving the management of acid and sodic soils with green trash retention using calcium-based ameliorants/products : SRDC final project report BSS199
(2003) Schroeder, BL; Noble, AD; Robertson, FA; Nelson, PN; Wood, AW
Although the advantages of leaving cane residues on the harvested land have been well documented, and nutrient cycling in relation to green-cane trash blanketing has been well examined within a Cooperative Research Centre for Sustainable Sugar Production (CRC Sugar) program activity, little work has been done to investigate the effects of trash management on soil chemical properties and the ameliorative advantages of applying Ca-containing amendments to crop residues. As lime, lime/gypsum applications are generally used to ameliorate acid soil conditions, a Ca-source followed by leaching is the principal strategy for managing sodic soils, and mill by-products (mill mud and mill ash) are often applied to plant cane, it was considered pertinent to investigate the effects of these and other amendments on the decomposition of trash on sugar industry soils.This project aimed at quantifying the effects of trash retention on soils acidity, examining the efficacy of Ca-containing amendments and trash for ameliorating sodic soils, assessing the effect of Ca-based amendments on trash decomposition and nutrient availability, and quantifying trash decomposition and C and N relationships. To do this, the project comprised four distinct but interlinked facets and included a series of laboratory investigations, glasshouse experiments and a field trial.

Soil health and nutrient management

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