Living with less water: development of viable adaptation options for Riverina irrigators

In Australia, the best use of limited national water resources continues to be a major political and scientific issue. Average water allocations for rice-cereal irrigation farmers in the Riverina region have been drastically reduced since 1998 as a consequence of high rainfall variability and prolonged periods of drought, together with political changes. This has severely impacted regional crop production during the last decade, threatening the livelihoods of many farmers and is in stark contrast to much of this region’s 100 year agricultural history, where water resources were available to farmers in steady abundance. The water ‘landscape’ has changed - bringing with it considerable social, economic and environmental consequences and forcing a rethink of how valuable water resources are best used under such variable, changed and changing conditions. This thesis presents details of investigations into on-farm adaptation options for rice-cereal farmers, using field experimentation, participatory engagement, and farming systems modelling as the major tools of research. Additionally, a major component of this work has been the development and testing of new modelling tools and decision-support structures. Well-tested cropping systems models that capture interactions between soil water and nutrient dynamics, crop growth, climate and management can assist in the evaluation of new agricultural practices. At the beginning of this research project, all available models were lacking in at least some major element required for simulation of rice-based cropping systems. The capacity to simulate C and N dynamics during transitions between aerobic and anaerobic soil environments was added into the APSIM model, to facilitate our need to model farming system scenarios which involved flooded rice in rotation with other crops and pastures. Thorough testing against international datasets was subsequently conducted. Photosynthetic aquatic biomass (PAB – algae) is a significant source of organic carbon (C) in rice-based cropping systems. A portion of PAB is capable of fixing nitrogen (N), and is hence also a source of N for crops. To account for this phenomenon in long term simulation studies of rice-based cropping systems, the APSIM model was modified to include new descriptions of biological and chemical processes responsible for loss and gain of C and N in rice floodwater. Using this improved APSIM model as a tool, together with participatory involvement of Riverina case-study farmers, it was demonstrated that the best on-farm cropping and irrigation strategies in years of high water availability were substantially different to those when water supplies were low. The strategies leading to greatest farm returns vary on a season-by-season basis, depending primarily on the water availability level. Significant improvements in average farm profits are possible by modifying irrigation strategies on a season-by-season basis. The opportunities for Riverina farmers to exploit their irrigation water resources also extend beyond the farm gate. Currently there is considerable confusion amongst farmers on how to evaluate and compare on-farm and off-farm water options. Direct selling of water seasonally on the open market and even permanent sale of irrigation water entitlements are possibilities. In response to this confusion, a new conceptual framework was developed that enables quantitative comparisons between various options. The framework is based on a method regularly employed in the financial world for share portfolio analysis. Simulation modelling provided risk-return characteristics for on-farm options, and helped to elucidate circumstances under which off-farm options were viable. A modified version of alternate wet-and-dry water management for Australian rice-growing conditions (delayed continuous flooding, DCF) was investigated via a 2 year field experiment – aimed at reducing irrigation water requirement and increasing water productivity (WP). We demonstrated up to a 17% increase in WP, and field data was generated on system performance for a range of discrete irrigation strategies. The APSIM model was then parameterized, calibrated and validated before being used to extrapolate findings from the two year experimental period to a much broader climatic record (55 years), allowing detailed investigation of optimal management strategies and a more realistic estimation of likely long-term gains in water productivity, and associated risks, from this new rice irrigation practice. Best practice guidelines were developed, and the potential impact of a changing climate on both optimal practice and likely benefits was assessed. This thesis concludes by synthesising the approaches taken - addressing the question of whether improved rice irrigation practices, seasonally-flexible cropping and irrigation strategies and off-farm exploitation options, can in combination address the challenges of reduced irrigation water allocations in Australia’s Riverina region. Evidence is presented that the answer is yes under certain circumstances, but that limits to change exist beyond which the investigated on-farm adaptations are not enough. The thesis also proposes that the concepts and methods developed during this project are globally applicable and useful in the design of farming system adaptation options. Keywords: irrigation, limited water resources, farming systems modelling, participatory engagement.</p

Rice growth, yield and water productivity responses to irrigation scheduling prior to the delayed application of continuous flooding in south-east Australia

The majority of rice grown in south-east Australia is continuously flooded for much of its growing season, but reduced irrigation water availability brought about by a combination of drought and environmental flow legislation has presented a need to maintain (or even increase) rice production with less irrigation water. Delaying the application of continuous flooding until prior to panicle initiation can increase input water productivity by reducing non-beneficial evaporation losses from free water and the soil. A field experiment was conducted over two growing seasons, 2008/9 and 2009/10, comparing a conventional dry seeded treatment (the control - continuous flooding from the 3 leaf stage) with delayed continuous flooding (10-20 days prior to panicle initiation) with several irrigation scheduling treatments prior to flooding commencement. In the first year, the delayed water treatments were irrigated at intervals of 40, 80 and 160 mm of cumulative reference evapotranspiration (ETo) prior to delayed continuous flooding, thereby imposing differing degrees of crop water stress. In year 2, the 80 and 160 mm treatments were modified by use of a crop factor (Kc) when the plants were small and the 40 mm treatment was replaced with a continuously flooded treatment throughout the crop duration. Decreases in net water input (irrigation + rain - surface drainage) and increases in input water productivity were achieved by reducing the flush irrigation frequency during the pre-flood period. Savings of 150 and 230 mm (10 and 15%) were achieved in Year 1 from the 80 and 160 mm cumulative ETo irrigation frequency treatments, respectively, in comparison to the control. In the second year, net water input savings of 230 and 330 mm (15 and 22%) were achieved with the 80/Kc and 160/Kc mm treatments, respectively. Input water productivity of the 160 mm treatment was 0.06 kg/m3 (8%) higher than the control in Year 1, while in Year 2 a 0.15 kg/m3 (17%) increase in input water productivity above the control was achieved by the 160/Kc mm treatment. Delaying the application of continuous flooding in the second year greatly extended the period of crop growth suggesting the need for earlier sowing (by 7-10 days) to ensure pollen microspore still occurs at the best time to minimise yield loss due to cold damage. Nitrogen fertiliser management is an important issue when delaying continuous flooding, and nitrogen losses appeared to increase with the frequency of irrigation prior to continuous flooding. This was likely due to increased denitrification from alternate wetting and drying of the soil. Further research is required to determine the most appropriate nitrogen management strategies, and to also better define the optimal pre-flood irrigation frequency.Rice Input water productivity Irrigation Delayed continuous flooding

Cropping system intensification for increasing crop productivity in salt-affected coastal zones of Bangladesh

In Global Climate Risk Index 2019, Bangladesh has been ranked seventh among the countries most affected by extreme weather events. The salinity intrusion has increased by 27% from 1973 to 2009 in coastal areas of Bangladesh due to impacts of climate change. The cropping intensities of the coastal zones are below than the country’s average intensity (195%), which causes severe food insecurity. In southern coastal zone, soil and water (river/canal) salinity remain the minimum (<4 dS/m) during in July/August but attain the maximum (upto 11 and 25 dS/m, respectively) in March/April. Farmers grow single T.aman rice a year. Therefore, five cropping patterns were tested under ACIAR funded project in Amtali (Barguna district) and Dacope (Khulna) upazilas during 2016–2017 and 2017–2018 irrigating with low salinity surface water (canal/pond) to increase crop productivity. In Amtali, T.aman-Potato-Mungbean-T.aus cropping pattern gave the highest (20.18 t/ha) rice equivalent yield (REY), which increased 360% REY over the farmers’ practice (T.aman-fallow-fallow). However, in Dacope, T.aman-spinach-fallow showed the highest REY (13.99 t/ha) that increased 211% REY compared to farmers’ practice. The improved cropping patterns can be practiced within the polder (embankment for water control) for increasing crop productivity and profitability in salt-affected coastal zones of Bangladesh

Model-based evaluation of rainfed lowland rice responses to N fertiliser in variable hydro-edaphic wetlands of East Africa

In East Africa, rainfed lowland rice is primarily produced by smallholders in alluvial floodplain and inland valley wetlands. These wetlands differ in their dominant soil types and water regimes that vary seasonally, inter-annually and between field positions. Yield responses to mineral nitrogen (N) fertiliser thus likely vary between and within wetlands and years, modulating the profitability of N fertiliser use. Therefore, the locally-validated APSIM model was used to study yield responses to N fertiliser rates (0, 30, 60, 90, 120, and 150 kg ha-1) and supplemental irrigation at different field positions in a floodplain in Tanzania (fringe and middle positions) and an inland valley in Uganda (valley-fringe, mid-valley and valley-bottom positions) over 30-years. Average rainfed yield gains with mineral N and N use efficiencies were high, ranging between 1.7 and 4.5 Mg ha-1 and 27–70 kg kg-1 in the floodplain and between 1.0 and 3.2 Mg ha-1 and 18–34 kg kg-1 in the inland valley, depending on field position, N rate and year. Consequently, N fertiliser use was generally profitable in both wetlands, with value/cost ratios ≥ 4 and marginal rates of returns > 150%. Profitable N rates in all years were 30–120 kg ha-1 in the fringe and 30–90 kg ha-1 in the middle positions of the floodplain, and 60–150 kg ha-1 in the mid-valley and 90–150 kg ha-1 in the valley-bottom positions of the inland valley. In the valley-fringe position, N fertiliser use was comparatively riskier and profitable only in 77–90% of years at N rates of 60–150 kg ha-1. Supplemental irrigation may help boost N fertiliser use efficiencies and use profitability with average yield gains of > 1.5 and > 0.4 Mg ha-1 in the floodplain and inland valley, respectively, while simulated spatial-temporal water stress pattern may help guide efficient irrigation scheduling

Modelling the role of algae in rice crop nutrition and soil organic carbon maintenance

Photosynthetic aquatic biomass (PAB – algae and other floodwater flora) is a significant source of organic carbon (C) in rice-based cropping systems. A portion of PAB is capable of fixing nitrogen (N), and is hence also a source of N for crop nutrition. To account for this phenomenon in long term simulation studies of rice-based cropping systems, the APSIM modelling framework was modified to include new descriptions of biological and chemical processes responsible for loss and gain of C and N in rice floodwater. We used well-tested algorithms from CERES-Rice, together with new conceptualizations for algal dynamics, in modelling the contribution of PAB to maintenance of soil organic C and soil N-supplying capacity in rice-based cropping systems. We demonstrate how our new conceptualization of PAB growth, turnover, and soil incorporation in flooded rice systems facilitates successful simulation of long-term soil fertility trials, such as the IRRI Long Term Continuous Cropping Experiment (35+ years), from the perspectives of both soil organic carbon levels and yield maintenance. Previous models have been unable to account for the observed maintenance of soil organic C in these systems, primarily due to ignoring inputs from PAB as a source of C. The performance of long-term rice cropping system simulations, with and without inclusion of these inputs, is shown to be radically different. Details of our modifications to APSIM are presented, together with evidence that the model is now a useful tool to investigate sustainability issues associated with management change in rice-based cropping systems

Opportunities and risks with early sowing of sunflower in a salt-affected coastal region of the Ganges Delta

On low-lying land in the Ganges Delta, waterlogging, salinity, and poor soil structure are constraints to intensifying cropping systems. Early sowing of dry season (rabi) crops in this area is hypothesized to increase yield potential because the current late sowing exposes the crop to less favourable temperature conditions, soil dryness, and salinity stresses. Field experiments were conducted over 2 years to identify the opportunities and challenges of early sowing between mid-November and mid-December for maximizing sunflower yield in Southern Bangladesh. Sunflower was dibbled into untilled wet soil on five occasions (23 and 30 November and 10, 20, and 30 December in 2016–2017 and 25 November, 14 and 25 December, and 10 and 25 January in 2017–2018), with two mulching treatments (rice straw at ~ 5 t ha−1 and 15–20% rice residue retention). Sowing before 15 December was associated with larger heads, more seeds per head, greater seed weight, and higher grain yield (3.5–4 t ha−1) in the first year, but early sowing was also risky since, in the second year, the sunflower sown on 25 November was hampered by heavy rainfall, which depressed yield compared to crops sown on 15 December. Increased yield from early sowing before 15 December was associated with higher soil water, lower soil salinity, and higher solute potential compared to sowing after 15 December. Lower yield in late sown crops was also associated with increased temperature at grain-filling stage. The rice straw mulch significantly improved soil water availability, reduced soil salinity, increased soil solute potential, and increased yield in the second year. In this paper, we show for the first time that sunflower sown before 15 December in the Ganges Delta has higher yield potential, but to gain the benefits of the earliest sowing, growers will need to manage the increased risk of yield loss due to waterlogging

Not Available

Not AvailabletResource shortages, driven by climatic, institutional and social changes in many regions of Asia,combined with growing imperatives to increase food production whilst ensuring environmental sus-tainability, are driving research into modified agricultural practices. Well-tested cropping systemsmodels that capture interactions between soil water and nutrient dynamics, crop growth, climateand farmer management can assist in the evaluation of such new agricultural practices. One suchcropping systems model is the Agricultural Production Systems Simulator (APSIM). We evaluatedAPSIM’s ability to simulate the performance of cropping systems in Asia from several perspec-tives: crop phenology, production, water use, soil dynamics (water and organic carbon) and cropCO2response, as well as its ability to simulate cropping sequences without reset of soil vari-ables. The evaluation was conducted over a diverse range of environments (12 countries, numeroussoils), crops and management practices throughout the region. APSIM’s performance was statistically.Not Availabl

Cropping system intensification under rice based system for increasing crop productivity in salt-affected coastal zones of Bangladesh

The field trial was conducted at farmers’ field at Bandra village in Amtali upazila of Barguna district and Pankhali village in Dacope upazila of Khulna district in Bangladesh during two consecutive years (2016-17 and 2017-18) starting from monsoon (aman) season of 2016. The experiment areas face slight to moderately drought and saline prone and salinity exists at later part of winter season and beginning of summer. Farmers generally cultivate only single transplanted aman (T. aman) rice during monsoon season a year in south and south-western coastal saline areas. However, the lands remain fallow in other seasons of the year. In this respect, the experiment was designed to increase the cropping intensity as well as crop productivity through crop intensification under rice based cropping systems. In Amtali (Barguna), treatments of the experiment were five cropping patterns viz., CP1 = T. aman - Potato - Mungbean - T. aus, CP2 = T. aman - Mustard - Mungbean - T. aus, CP3 = T. aman - Gardenpea – Mungbean - T. aus, CP4 = T. aman - Spinach - Mungbean - T. aus, and CP5 = T. aman - Fallow - Fallow (Farmers’ practice). Whereas in Dacope (Khulna) six cropping patterns were: CP1 = T. aman - Wheat - Fallow, CP2 = T. aman - Mustard - Fallow, CP3 = T. aman - Gardenpea - Fallow, CP4 = T. aman - Spinach - Fallow, CP5 = T. aman - Potato - Fallow, CP6 = T. aman - Fallow - Fallow (Farmers’ practice). Research findings showed that the cropping patterns can be established by judicious application of irrigation with comparatively low salinity content surface water (canal/pond). In Amtali, Barguna, T. aman - Potato - Mungbean - T. aus cropping pattern gave the highest (20.18 t ha-1) rice equivalent yield (REY) (360% higher REY over the farmers’ practice). However, in Dacope, Khulna, T. aman - Spinach - Fallow registerd the highest REY (13.99 t ha-1) that increased REY by 211% compared to farmers’ practice. The improved cropping patterns can be practiced within the polder (embankment for water control) with suitable irrigation water for increasing crop productivity and profitability in salt-affected coastal zones of Bangladesh

Rice in cropping systems - Modelling transitions between flooded and non-flooded soil environments

Water shortages in many rice-growing regions, combined with growing global imperatives to increase food production, are driving research into increased water use efficiency and modified agricultural practices in rice-based cropping systems. Well-tested cropping systems models that capture interactions between soil water and nutrient dynamics, crop growth, climate and management can assist in the evaluation of new agricultural practices. The APSIM model was designed to simulate diverse crop sequences, residue/tillage practices and specification of field management options. It was previously unable to simulate processes associated with the long-term flooded or saturated soil conditions encountered in rice-based systems, due to its heritage in dryland cropping applications. To address this shortcoming, the rice crop components of the ORYZA2000 rice model were incorporated and modifications were made to the APSIM soil water and nutrient modules to include descriptions of soil carbon and nitrogen dynamics under anaerobic conditions. We established a process for simulating the two-way transition between anaerobic and aerobic soil conditions occurring in crop sequences of flooded rice and other nonflooded crops, pastures and fallows. These transitions are dynamically simulated and driven by modelled hydraulic variables (soil water and floodwater depth). Descriptions of floodwater biological and chemical processes were also added. Our assumptions included a simplified approach to modelling O-2 transport processes in saturated soils. The improved APSIM model was tested against diverse, replicated experimental datasets for rice-based cropping systems, representing a spectrum of geographical locations (Australia, Indonesia and Philippines), soil types, management practices, crop species, varieties and sequences. The model performed equally well in simulating rice grain yield during multi-season crop sequences as the original validation testing reported for the stand-alone ORYZA2000 model simulating single crops (n = 121, R-2 = 0.81 with low bias (slope, alpha = 1.02, intercept, beta = -323 kg ha(-1)), RMSE = 1061 kg ha(-1) (cf. SD of measured data = 2160 kg ha(-1))). This suggests robustness in APSIM's simulation of the rice-growing environment and provides evidence on the usefulness of our modifications and practicality of our assumptions. Aspects of particular strength were identified (crop rotations; response to applied fertilizers; the performance of bare fallows), together with areas for further development work (simulation of retained crop stubble during fallows, greenhouse gas emissions). APSIM is now suitable to investigate production responses of potential agronomic and management changes in rice-based cropping systems, particularly in response to future imperatives linked to resource availability, climate change, and food security. Further testing is required to evaluate the impact of our simplified assumptions on the model's simulation of greenhouse gas emissions in rice-based cropping systems. Crown Copyright (C) 2012 Published by Elsevier B.V. All rights reserved