Soil health and nutrient management

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Nitrate retention at depth under sugarcane in Far North Queensland Wet Tropics
(2002) Rasiah, V; Armour, JD; Menzies, NW; Heiner, DH; Don, MJ
Nitrogen mass-balance studies for sugarcane grown on Ferrosols (Krasnozem) in the Far North Queensland (FNQ) wet tropics have shown 30 to 50 kg N/ha/yr of the applied fertiliser+N leached below the root-zone (<0.75 m) as nitrate-N compared to <10 kg/ha/yr transported in surface runoff. Because, large quantities of N (guesstimate of ≈ 3,000 tonnes per annum for the catchment) was leaching below the root-zone, major emphasis has been placed on its fate, particularly in relation to off-site land and water resources and ecosystem health issues and more specifically that related to the Great Barrier Reef (GBR). The leached nitrate could be adsorbed at anion exchange sites, denitrify, enter streams/rivers through lateral-flow and/or aquifers by deep drainage. Because the ferrosols in general possess the capacity to absorb and retain nitrate-N at anion exchange (AE) sites, there exists the potential reduced risk of contamination of off-site water bodies, including GBR. The issues address in the project include (i) the assessment of sub-surface nitrate loading in Ferrosols of north Queensland wet tropical coast (ii) measurement of those physical and chemical properties, which influence nitrate mobility and retention (iii) provide from inferred processes, estimates of future nitrate movement to ground and surface waters (iv) propose management strategy(s) with regional industry group(s) to address the nitrate problem (v) improve industry and community understanding of water and nutrient dynamics and the potential environmental impacts. Soil cores to 12.5 m depth were taken from 28 sites distributed across the catchment, representing 9 Ferrosol soil types under sugarcane cultivation for at least 50 yr and from rainforest. Depth incremented (0.5-1m) sub-samples from the cores were analysed for nitrate- N, cation- (CEC) and anion- (AEC) exchange capacities, pH, exchangeable cations (Ca, Mg, K., Na), soil organic C (SOC), electrical conductivity (EC), sulphate (SO4 2-) and chloride (CI-), Nitrate-N concentration under sugarcane ranged from 0 to 72.5 mg/kg compared with 0 to 0.31 mg/kg under rainforest. The average N-load, in 12 m depth, across the 19 Pin Gin soil type was 1550 kg/ha compared with 185 kg/ha unde4r 8 non-Pin Gin and 11 kg/ha in rainforest and most of the retention in the catchment and the source of this nitrate was that leached below the rootzone. Compared to the current average N-load, the average maximum potential nitrate retention capacity (MPNRC) of 10.8 t/ha for the Pin Gin and 4.7 t/ha for the non-Pin Gin indicates these soils still possess large capacity to adsorb and retain nitrate in profiles.
Sugar Research and Development Corporation final report Increasing sugar cane yields by improvements in soil structure
(1998) Hughes, M; Nielsen, P; Grabski, A
A project to increase sugar cane yields by improvements in soil structure was conducted at Broadwater, NSW. It was instigated in response to the poor physical structure of many cane soils and poor root development in many sugar cane crops resulting in low cane yields. A number of alternative management practices were tested and cane and sugar yield as well as appropriate soil parameters were measured. The main findings were that ridging had the biggest effects on cane and sugar yields and on soil bulk density, soil moisture (drier in the top 30 cm and wetter at depth), and a leaching of Cl, Na and S when in excess amounts. Ridging also resulted in a stable inter-row and hence far less damage during wet harvests. Intensity of tillage had some small effect on yields and soil structure; it is not clear if these would have increased over a longer period of time. The main effect of soybean production during the fallow period was due to nitrogen input. There were some small but positive effects on subsequent cane root growth soil organic carbon and soil bulk density. Mole drains and deep ripping provided no clear advantage over laser levelling alone.
Sugar Research & Development Corporation final report Pesticide transport in sugar production systems
(2000) Simpson, BW; Hargreaves, PA
The fate and persistence of a number of the key pesticides used in Australian sugar production have now been quantified for a range of soil types and conditions, In general there is no evidence of season-to-season build up in the soil from annual pesticide applications, However the herbicide diuron was shown to be highly persistent on the red ferrosol (krasnozem) site, Calculated dissipation rates (DT50) were used to establish risk windows for potential off-site losses, Sampling of the soil profile showed that most of the applied pesticide remained (and dissipated) in the upper 15 cm, Rainfall and surface runoff were measured throughout the project with samples of runoff collected throughout runoff events, Pesticide concentrations measured in runoff from the end of furrows were relatively high at times, particularly when runoff events followed shortly after application, This fouryear study highlights the need for careful management of application timing and chemical selection, particularly in areas close to waterways and sensitive habitats, Limited studies on the effect of pesticide application on trash, suggest that trash retention reduces the pesticide concentrations entering the soil and provides conditions for reduced off-farm losses, Information obtained will be incorporated into improved management guidelines,

Soil health and nutrient management

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