Soil health and nutrient management

Permanent URI for this collectionhttp://elibrary2.sugarresearch.com.au/handle/11079/13842

Research outcomes: Soil health is improved with a resulting positive impact on the environment and yield growth. Improved reputation and relationship between industry and environmental groups.

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Assessing clonal and nitrogen interaction on ccs in sugarcane in the wet tropis ; SRDC project BSS180 final report
(2003) Hurney, AP; Berding, N; Grace, D
There has been a negative trend in CCS in the Tully-Mossman region since the mid-1960s that has been linked to increased extraneous matter and suckers in the cane supply. The situation had become particularly bad during 1990-1996, with most mill districts within the region experiencing problems with low CCS. An increase in the frequency of lodging and incidence of suckers was possibly contributing to this problem and there was a perception that this was related to inappropriate use of nitrogen fertiliser for the locally grown cultivars. There were also concerns that current cultivars were not suited to the local environmental conditions. Growers choosing to grow inappropriate cultivars for particular locations were thought to be exacerbating the problem.Decisions on what cultivar to grow and how much fertiliser to apply are management options that could be modified if they were contributing to the low CCS problem. These issues were addressed in this project by studying the effects of four rates of nitrogen (0, 70, 140, 210 kg N/ha) on lodging, suckering, CCS and cane yield of the three cultivars Q117, Q120 and Q138. These experiments were conducted on three different soil types at three locations within the Tully mill district. The objectives of this project were to provide a better understanding of the role of nitrogen and cultivars in the low CCS issue to facilitate the development of improved management options.In the plant crops, which were planted after a fallow, nitrogen had no influence on cane yield, CCS, lodging or suckering under the environmental conditions in which these crops were grown. However, it did increase both cane yield and lodging in first- and second-ratoon crops. Responses were limited by adverse interactions with the wet conditions and nitrogen losses due to leaching and/or volatilisation. Nitrogen had no direct influence on CCS in the ratoon crops, but it did have an indirect negative effect, because it increased the incidence of lodging. Rates of N application could be reduced in both plant and ratoon crops, which would reduce production costs. It would also be beneficial environmentally.There was no evidence of nitrogen accumulation in the soil from high nitrogen fertiliser application even following a low-yielding crop. This is of concern from an environmental viewpoint if inappropriate nitrogen rates are applied, as any excess nitrogen will be lost from the soil due to leaching or denitrification. The data suggested that the critical leaf nitrogen concentration might vary between cultivars. This provides an opportunity to reduce nitrogen rates for cultivars with lower nitrogen requirements.Current cultivars do have high potential CCS, but this cannot be realised, partially because of their susceptibility to lodging and suckering. All three cultivars tested, Q117, Q120 and Q138, are susceptible to lodging in well-grown crops. It appears that the susceptibility of Q120 and Q138 is high in crops yielding more than 70-80 t/ha under the wet conditions of the wet tropics.The potential reduction in CCS from total lodging was estimated at about 10% across all cultivars in these trials. The actual loss in CCS is governed by the actual proportion of lodging in the crop and was estimated at 0.4 units in crops that had 25% lodging. This is a hidden cost of which growers are generally not aware. There are no management options that can be implemented to minimise this loss. Severe and multiple lodging events had a negative impact on CCS and cane yield in Q120 and Q138, reducing profitability. In these circumstances, the negative effects of lodging can be reduced if the time between harvesting and occurrence of lodging is reduced. Increased returns to the grower of $200 $300/ha are possible using this strategy.Lodging was less extensive in Q117 and lower-vigour cultivars, such as Q117, may offer a more appropriate ideotype for the wet tropics, because of their lower susceptibility to lodging. Economic impact was estimated at a loss of $7.5 million to growers within the region from a moderate lodging event affecting 25% of the crop. Adoption of agronomic practices to improve physical support of the crop is only partially successful in reducing the intensity of lodging. This can only be achieved by the implementation of a research program to select cultivars with a low incidence of lodging, while maintaining or improving productivity.The cultivars Q117, Q120 and Q138 are representative of those being grown in the wet tropics and demonstrated a high propensity to sucker. Lodging is not a pre-requisite for sucker initiation, as the emergence of suckers was generally first noted under a closed canopy. Suckers have a negative effect on CCS, because they dilute the cane juice through their high moisture and low sucrose composition. In these experiments, 10% by weight of suckers in the cane supply reduced CCS by a little over 1 unit. The increased cane yield from suckers is inflating productivity estimates but not improving profitability; the level of suckering experienced in these experiments would reduce regional grower-income by approximately $6 million. It is possible to select against suckering propensity and this has already been introduced into the crop improvement program. However, research into the relationship between suckers and longevity of ratoons is required because of the potential impact on productivity.An appropriate extension program needs to be developed to disseminate the findings of this research to growers. The results from this project have been extended to the industry. There have also been extension programs for BMP of cultivars. However, there is still a large gap between extension and adoption, which is why additional extension programs are recommended. Adoption of findings on nitrogen will reduce production costs, as well as have a positive environmental impact. Management strategies are available to partially alleviate the negative impacts of lodging and suckering. However, further research is required to fully overcome the effects of these phenomena.
Evaluating the potential for improved sugar yields by assessing the climatic and soil constraints to production in southern cane-growing districts
(1999) Muchow, RC; Hughes, RM; Horan, HL
This project conducted strategic research to better understand the processes of yield accumulation in low temperature NSW environments and to identify limits to yield. The fundamental knowledge gained in this project can be used to assess yield limitations and the scope for yield improvement. In addition, the findings are a pre-requisite to the design of management and genetic improvement strategies to boost production in southern sugarcane growing environments. An additional spin-off of this project is a better functional basis of the processes of yield accumulation encapsulated in the APSIM Sugarcane systems model to allow extrapolation of the findings more broadly across the sugar industry. An analysis framework was used to express sucrose yield in terms of biomass accumulation and the proportion on biomass present as sucrose. Crop biomass was analysed in terms of radiation capture and utilisation. Partitioning was examined in terms of the proportion of crop biomass present as stalk and the stalk sucrose concentration on a dry matter basis. Crops growing under "potential yield" conditions were analysed and compared to those growing under "commercial yield conditions".
Evaluating the leaf chlorophyll meter as a tool for nitrogen management in sugarcane
(1995) Keating, BA; Smith, K
Nitrogen is an important constituent of chlorophyll, the compound that gives plants their green colour and the compound that absorbs radiation energy as the basis of plant growth. When nitrogen is in short supply, the chlorophyll content of leaves is reduced and in extreme cases, the leaves take on a yellow (or chlorotic) colour. There is an upper limit to leaf "greenness" and leaf nitrogen can continue to rise even when chlorophyll has reached a "plateau". These simple concepts are illustrated in the figure below. This project was aimed at evaluating a portable leaf chlorophyll meter as a tool in nitrogen management of sugarcane. As chlorophyll is a critical component of the photosynthetic system, reductions in leaf chlorophyll may result in lower sugarcane growth rates and this may impact on final sugar yields. In addition, leaf nitrogen is expensive and time consuming to determine on an extensive basis. The notion was that the chlorophyll meter could provide a far simpler alternative to leaf analysis for the monitoring of nitrogen status of sugarcane crops. The project consisted of measurements of leaf nitrogen and chlorophyll on sugarcane crops grown under a range of nitrogen regimes at locations in the Herbert, Bundaberg and northern NSW regions. Leaves at various levels in the canopy were measured and in the majority of instances samples of the bulk canopy were taken. Samples of the sap from the leaf mid-ribs were collected at the same time and analysed for nitrate using a rapid field test. In all 450 leaf N - chlorophyll meter comparisons were collected at various occasions over the November 1993 to June 1994 period.
Overcoming on-farm constraints to productivity and profitability in a wet tropical area
(2003) Goodson, M; Thorburn, P
The CCS in the wet tropics has been declining steadily for over three decades, a period in which green cane harvesting-trash blanketing (GCTB) has become standard practice among growers throughout the wet tropics. In the Babinda Mill region, where this situation is most acute, it has been hypothesised that a part of the low CCS problem is due to the effect of GCTB in increasing soil moisture and soil fertility, which aggravates lodging and suckering in the crop and restricts the opportunity for drying crops out. During the 1990’s Babinda growers were assessing alternative management systems to overcome some of these perceived problems associated with trash blanketing. This project aimed to implement best-bet initiatives to overcome problems associated with trash blanketing, and so improve productivity and profitability in a wet tropics environment. The project was directed by stakeholders and conducted using a participative approach. There were four interrelated ‘strands’ of activity undertaken in this project: 1. Liaison and interaction with Babinda growers and the wider industry, achieved through establishment of a Grower Management Group, conducting all trials on farms (as opposed to research stations), distributing regular newsletters and holding regular bus tours and shed meetings to view demonstration sites and discuss trial results. 2. Demonstration of ‘best-bet’ trash management practices (for improved profitability). Trials were established on four farms comparing the impact of raking trash from the stool and/or incorporating it into the soil. 3. Exploration of improved nitrogen fertiliser placement (for improved profitability). Trials were established on two farms comparing different placement of N fertiliser (in the ground or on the trash blanket) and different N carriers (urea and Nitram). 4. Determination of soil and plant nitrogen status in response to different soils and/or management practices. Soil and crop N status were determined in all trials and a survey of amino-N in juice from sugarcane (a good indicator deficiency and over-supply of N to the crop) from all blocks on eight farms in the region. The trash management trial sites consistently failed to demonstrate any advantage of either raking trash from the stool, incorporating trash into the soil, or doing both. Thus the extra cost of purchasing and operating a trash rake is not justified. At one site, in a flood prone area where trash blanketing is impractical, trash burning consistently gave higher yields than trash raking and incorporation. This result suggests that raking and incorporation of trash is economically disadvantageous, in the short term, in these areas. However, damage to the stool during raking caused the lower yields in the raked incorporated treatments at this site and improved methods of raking trash may overcome this problem.
A stocktake of the levels and sources of nitrate in groundwaters associated with sugarcane areas
(2000) Thorburn, PJ; Weier, KL; Biggs, JS
Water containing high concentrations of nitrate is unfit for human consumption and, if discharging to freshwater or marine habitats, can contribute to algal blooms and eutrophication. Previous studies have found elevated nitrate concentrations in groundwaters underlying sugar-growing areas, particularly the Bundaberg and Burdekin areas, and that in Bundaberg the problem was escalating. Nitrate pollution of groundwaters of the sugar industry is of particular concern because of the proximity of the industry to environmentally sensitive areas and the large number of people (in cities and rural areas) relying on groundwaters for drinking water. However, apart from recent studies in Bundaberg, data on nitrate in groundwater has generally come from inconsistent studies. These studies examining either a limited number of groundwater bores, or large databases of groundwater chemistry where sampling and analytical methods have been variable and, in some cases, inappropriate. So a reliable, consistent, industry-wide definition of the problem does not exist. This project determined the extent of nitrate contamination in groundwater underneath sugargrowing regions of eastern Australia, and examined the likely source of the nitrate. In bores where nitrate concentrations were elevated, and therefore likely to be a result of human activities, concentrations were monitored to provide an assessment of trends in nitrate concentrations. This information was used to promote “best management practices” through relevant extension, industry and regulatory groups, to restrict leaching of nitrate to groundwater.
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.
Project No 2025: Final report bench testing of new nitrogen products for potential ammonia volatilisation: when boradcast onto soil or sugarcane trash (N-gold "A", N-gold "B")
(1996) Chapman, LS; Haysom, MBC; Makepeace, P
N-Gold "A" and N-Gold "B" are granulated products containing urea and calcium oxide with 42.4 and 43.2 % N and 1.5 and 1.3 % Ca respectively. When broadcast onto soil or a green cane trash blanket, ammonia volatilisation losses were not different to those from prilled or granulated urea when tested in the maboratory. These products produced a more alkaline solution than urea and, in theory, this would slightly increase the ammonia volatilisation losses, but this did not happen in this experiment.N-Gold "A" and N-Gold "B", when analysed for N content in 0.5g samples, showed more variation than for the prilled or granulated urea. This variation is unlikely to cause any deleterious effects when used as a fertiliser but could have implications for quality control
Comparison of 'into' and 'beside' stool nitrogen placement
(1992) Smith, MA
There are now two alternative methods of subsurface nitrogen placement available: beside the stool or into the stool. The second, into the stool treatment, is easier to accomplish. Comparison of cane yields from strips fertilised by the two methods revealed no significant differences.

Soil health and nutrient management

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