Soil health and nutrient management

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Final report SRDC project BSS197 : Products and mechanisms for the amelioration of sodic soils
(2005) Ham, GJ
This project set out to examine a number of issues associated with sodic soils. These included: 1) the impact of soil sodicity on crop production; 2) the reduction of adverse impacts of soil sodicity through irrigation management and/or the use of soil ameliorants; 3) the properties and potential efficacy of a range of products being marketed as 'soil ameliorants' throughout the northern part of Queensland; 4) the means by which a selection of these ameliorants effected beneficial changes to sodic soils; and 5) to establish a close linkage between these investigations and a method for the field identification and measurement of sodicity being developed in a closely associated Sugar CRC project.
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.
Review of sodic soils research in the Queensland sugar industry
(1995) Cox, AZ; Ham, GJ; McMahon, GG
Increasing levels of sodium on the clay, in the absence of high levels of soluble salts, are not believed to be toxic to the cane plant. Any adverse effect on crop production is through deterioration of the soil structure (Crema, 1994). Under wet conditions, increased clay dispersion accompanies increasing exchangeable sodium percentage (ESP). This is associated with sealing and crusting in surface soils and dense subsurface clays which resist penetration of roots. Even if water does penetrate the surface, it is held very strongly in the very small pores formed in the dispersed soil. It is difficult for roots to withdraw this moisture. The end result of sodicity is similar to that of salinity, water stress. Both infiltration and water storage are adversely affected. Reclamation of sodic soils can be achieved by application of gypsum or lime to promote replacement of sodium on the clay particles by calcium, and hence improve soil structure. Research work indicates that sugarcane yields on sodic soils with ESP less than 25 can be improved by up to 20% with the application of gypsum 10t/ha (Ham etal., 1995). Improvements in yield can also be achieved by improving surface and subsurface drainage to promote leaching of displaced sodium salts from the soil profile. Reduction of natural slope from 0.49% to 0.07% has also improved sugarcane yield by 24% over the crop cycle (Ham etal.,1995). Research has developed ways of increasing production on sodic soils. With the expansion of the cane industry into marginal areas there has been associated extension campaign, concentrating on farm planning and demonstrating the benefits of applied gypsum (Ham etal., 1995). A good example of this is the Burdekin where the BSES program on sodic soils is estimated to have resulted in an extra 26,000 tonnes of cane to the Burdekin district in 1994 alone with a gross value to the industry of $1.02m.

Soil health and nutrient management

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