Many areas of the sugarcane in Queensland are irrigated by furrow or flood irrigation. Previous research with small plot trials for sugarcane and other crops has demonstrated the benefits of drip and subsurface drip irrigation for yield and also the opportunity to save irrigation water. As part of the Reef Rescue Research and Development Program, this project (RRRD004) compared the efficiency of furrow and subsurface drip irrigation at the paddock level for sugarcane (Ayr) and bananas (Bundaberg) in the Great Barrier Reef (GBR) catchments. Comparative assessments were carried out to evaluate crop performance and soil water movement, and water quality leaving the farm.
Farmers’ participatory on-farm trials were conducted in 2011-2014, evaluating irrigation options for sugarcane and bananas that are consistent with enhancement of on-farm water use efficiency (WUE), nitrogen use efficiency (NUE), and that limit the dispersal of herbicides from the paddock in two soil types (vertisol and ferrosol). These aims are also consistent with developing resilience in the farming systems in the face of climate change. The project provided a tool to measure the extent of nutrients, suspended solids, and herbicides removed from the paddock, evaluated the response of crops to different irrigation methods for yield, quality, WUE, NUE and contributed data for modeling impacts of irrigation on hydrological aspects at the paddock and farm scales. It also allowed for socio-economic benchmarking, and probed policy implications of these interventions at the catchment scale by the way of systematic survey of all relevant stakeholders in the sugarcane industry.
Sugar cane trials
The project trialled furrow and subsurface drip irrigation methods for sugarcane at Ayr in the Burdekin region. For sugarcane on a clay loam soil, the deep drainage load was significantly larger for the furrow irrigation compared to the drip irrigation; in the first year it was up to 16%, while in the second year it was as high as 23% of the total irrigation water inputs. Deep drainage under drip irrigation was as much as 15% of the total irrigation during the first season. While in the third year after optimisation of drip irrigation, the deep drainage was reduced to 10%.
Sugarcane surface run-off accounted for 15% and 2.5% of the total irrigation water inputs in the first year for furrow and drip irrigation respectively. While in the third year, 11% and 2.1% of the total irrigation water inputs was lost as run-off for the furrow and drip irrigation, respectively. A lower soil infiltration rate was recorded under the furrow irrigation (12.56 mm/hr) on sugarcane compared to drip irrigated treatment (25.19 mm/hr) when the crop was in full canopy cover at 165 days of crop age. Greater infiltration in the drip irrigation plot compared to the furrow irrigation plot allowed for more rainfall water storage in the root zone, hence, for the given rainfall amount, the run-off from the drip irrigated plot was smaller.
The first year of drip irrigation trial was on a five year old planting hence a ratoon crop, in the following year it was a plant cane, and in the third year a first ratoon crop. Likewise, for the furrow irrigation block a ratoon cane was harvested in the 2011-12 season, a plant cane harvested in the 2012-13 season, and a first ratoon crop was harvested for the third year. In the first year (2011-2012 season) both irrigation treatments produced yield over 100 t/ha (101 vs 121 ton/ha for drip and furrow, respectively). In the second year (2012-2013 season), the harvested cane yield for the drip and furrow irrigation was 82 t/ha and 112 t/ha respectively. Consistently, in the third year (2013-2014 season) also the yield of cane in the drip irrigation block was lower compared to that for the furrow irrigation (72 vs 114 t/ha), indicating continuously declining yield of drip irrigation (caused by root intrusion, mice damage, and emitters blockage. Therefore, immediate major maintenance of the drip irrigation infrastructures has been recommended for this site. Drip irrigation maintenance through hydrogen peroxide treatment has commenced on this site following the completion of the Reef Rescue R&D research activities in this site. The drip irrigation installation in sugarcane has been able to demonstrate positive water quality outcomes leaving the farm, however, in the current site, drip irrigation is poorly competing with furrow for harvestable yield of sugarcane. Drip irrigated sugarcane yield needs to be improved above that of the furrow in order to attract growers’ interest for further adoption of environmentally benign and water saving irrigation methods, such as subsurface drip irrigation for sugarcane.
Traces of herbicides were detected in the deep drainage samples in both irrigation methods. Traces of 2,4-D, MCPA (2-methyl-4-chlorophenoxyacetic acid), Glyphosate and Diuron were noted in the deep drainage samples under both irrigation management systems, however, to a greater quantity in deep drainage of furrow compared to subsurface drip irrigated crops particularly for 2,4-D. Substantial quantities of 2, 4-D and Glyphosate and small amounts of MCPA and traces of Diuron were also noted in the run-off samples under both irrigation management. Volume of run-off and loads of herbicides were greater for furrow irrigation compared to the subsurface drip irrigated sugarcane crop in Home Hill.
Nitrogen (N) distribution in the soil, soil water, and plant was assessed throughout the trial period. There were no great differences among treatments for leaf N concentrations across different growth periods in either crop. Tissue N concentrations were within the optimal range. Hence N fertiliser deficiency was not a cause of poor crop growth. Higher concentrations of nitrate-N loads were recorded in deep drainage and run-off samples collected during the early stage of both sugarcane crops in the field. N applied in sugarcane ranged from 77 to 120 kg/ha per crop; the crop did not have luxuriant growth across this range.
The amount of NH4-N, urea N, and Filterable reactive phosphorus (FRP) loads were greater in deep drainage of furrow irrigation compared to the deep drainage samples of the drip irrigation. Estimates of NUE of sugarcane ranged from 0.6-1.32 ton/kg of N, with higher NUE recorded for drip irrigation compared to furrow in the first year (1.32 vs 0.72 ton/kg), but the difference between the two treatments was reversed in year 3 of the trial (0.60 vs 0.69 ton/kg) due to poor cane yield in subsurface drip irrigation.
Water use efficiency (WUE), expressed as harvestable yield (t/ML) ranged from 12.89 to 22.04 t/ML, with greater WUE recorded for drip compared to the furrow in the first year (22.04 vs 14.17). However, the gain in WUE for drip was not prominent during third year due to poor sugarcane performance in the drip irrigation block.
The project trialled drip and micro sprinkler (MS) irrigation for bananas in the Bundaberg region. For bananas grown on the ferrosol (red loam soil), the deep drainage under drip irrigation was only 2.6% of the total irrigation water inputs during the crop period. The deep drainage load was slightly larger for the micro sprinkler compared to the drip irrigation system, i.e. 3.1% of the total irrigation water inputs to the crop. Similarly, the run-off load was 9 and 12.7% of the total irrigation for the drip and micro-sprinkler treatment, respectively.
In the banana site, a set of piezometers (supplied by Hydroterra Australia) was installed for ground water monitoring, drainage lysimeters (Decagon USA) for deep drainage, Parshall flumes with water height sensor (Odyssey data flow) for run-off measurement and ISCO 3700 samplers for run-off sampling. Low soil infiltration rate (2.60 mm/hr), accompanied with greater run-off (5.99 ML/ha) was noted for the micro sprinkler block compared to drip irrigated bananas (infiltration 2.34 mm/hour and run-off 3.88 ML/ha) in the red loam (ferrosol) soil. Traces of herbicides including Atrazine and Metolachlor were recorded in the irrigation water source; Imidaclorpid was recorded in the ground water under the drip irrigation plot, whereas Diuron, Imidaclorpid and Metolachlor were recorded in the ground water samples under the micro-sprinkler irrigation plot.
For bananas, the experimental crop was at two different maturity stages, the drip irrigated block was a mature stand, whereas the MS plot was a new plantation. Yearly average yield of bananas was calculated as 33.67 t/ha for drip and 15.85 t/ha/year for micro-sprinkler. The micro-sprinkler crop was still not at full bearing stage at the end of this trial period, hence the reported yield for MS in this trial does not represent the potential yield of micro-sprinkler for banana. Yield of banana was presented as the total weight of fruit bunches. The current industry practice in Bundaberg selectively harvest mature bunches and incorporate the biomass (pseudo stem, part of the fruit stem) of the harvested plants back into the soil in the same paddock.
N applied to banana was largely as a basal dose, and small amount side dressed twice a year (total 584 kg N/ha). Based on the N input applied to the soil and using data on the crop performance, the NUE has been calculated (yield ton/kg N input) as 0.173 and 0.0271 ton fruit/kg N for drip and micro-sprinkler irrigation, respectively. Therefore, the NUE was significantly higher (0.173 ton/ML) for drip irrigation compared to poor performance of micro-sprinkler irrigation (0.026 ton/kg). Likewise, the WUE was significantly greater for drip irrigation compared to that of the micro-sprinkler (2.34 t/ML vs 0.0336 t/ML).
In these experiments, a sizable reduction in deep drainage and surface run-off volumes, and therefore a reduction in the loss of N, were evident for subsurface and drip irrigation compared to either furrow or microsprinkler irrigation in sugarcane and bananas respectively. Reduced deep drainage also led to reduced contamination of ground water by applied agrochemicals. The optimised subsurface dripper irrigation kept the soil surface drier, hence allowed for a greater interception of rainfall that potentially lower the run-off from subsurface dripper irrigation compared to furrow irrigation.
A multidisciplinary team of collaborating organisations provided significant contributions to the project outputs, through their active involvement in their components of research activities and their respective roles in the team activities of the project. This collaboration provided a unique forum of expertise ensuring the translation of research output into practical adoption of irrigation innovation by the growers and industry. The project has made a positive change in perception about run-off and deep drainage impacts on water quality of sugarcane and banana farming areas in the catchments of the GBR.
The 4 year project period enabled presentation of results from a single full crop season of banana. The results for the second season banana crop and the combined results from the three years of sugarcane trials are being presented for separate publication as journal manuscripts. These results show occurrence of rainfall and irrigated induced run-off and deep drainage for furrow irrigation while for subsurface drip irrigation, run-off are only noted with repeated and heavier rainfall events, in excess of 50 mm and more. Although drip irrigation resulted in reduced deep drainage compared to furrow, opportunities exist for further reduction of deep drainage in subsurface drip irrigated sugarcane crops. Optimisation of the subsurface drip irrigation to match soil, crop, growth stage and weather conditions will lead to further improvements in the irrigation efficiency. Current levels of deep drainage noted in subsurface drip irrigation can be reduced through soil and crop specific pulsing and matching in season water balance more specifically by accurate timing the irrigation with crop water demand. In spite of higher cane yields in the furrow compared to the subsurface drip irrigation in all three harvest seasons, water use efficiency and nitrogen use efficiency were consistently greater for subsurface drip irrigation compared to furrow. However, in the banana crop, these early observations need to be confirmed and substantiated by at least two seasons’ data from the comparable irrigation treatments, crops and irrigation water quality. Hence, multi-season data collection from these trial sites is suggested as is the continuation of optimisation of subsurface drip irrigation for water and nutrient management of sugarcane and bananas so that the effects of different irrigation methods on soil water movements and hydrological processes for wet and dry years can also be evaluated.