Integration of approaches to increasing water use efficiency in rice-based systems in southeast Australia

Field Crops Research 97 (2006) 19–33 www.elsevier.com/locate/fcr

Integration of approaches to increasing water use efficiency in rice-based systems in southeast Australia E. Humphreys b,*, L.G. Lewin a, S. Khan a,b, H.G. Beecher a,c, J.M. Lacy a,c, J.A. Thompson a,d, G.D. Batten a,e, A. Brown a,e, C.A. Russell a,e,1, E.W. Christen a,b, B.W. Dunn a,c a

The Cooperative Research Centre for Sustainable Rice Production, Australia b CSIRO Land and Water, PMB 3 Griffith, NSW 2680, Australia c NSW Department of Primary Industries, PMB Yanco, NSW 2703, Australia d NSW Department of Primary Industries, P.O. Box 736, Deniliquin, NSW 2710, Australia e Charles Sturt University, P.O. Box 588, Wagga Wagga, NSW 2678, Australia

Abstract Australian rice growers are under considerable pressure to increase water use efficiency to remain profitable and avoid soil salinisation. In particular, profitability is threatened by decreasing water availability and certainty of supply and by increasing water price, as a result of environmental and National Competition Policy agendas. Field irrigation water productivity has more than doubled in the past 20 years from an average of around 0.34 g paddy rice per kg water to around 0.77 g kg 1, largely due to increased yield from the development and adoption of improved varieties and management strategies, and to a lesser degree due to the introduction of rice water use and soil suitability policies. Future increases in rice field water productivity will come from greater yields through breeding for increased cold tolerance, precision agriculture and improved crop establishment, and from reduced water use due to reduced duration of ponding. A key challenge of the next decade will be to increase cold tolerance to the extent that deep water ponding for low temperature protection is no longer required, possibly allowing a complete shift away from ponded culture and reducing irrigation water requirement. While increasing the water productivity of rice is important, water productivity and profitability of the entire cropping system is of ultimate importance. Growing winter crops after rice and permanent bed systems offer potential benefits of increased productivity of crops traditionally grown in rotation with rice and increased cropping diversity and flexibility. Irrigation water productivity is also being improved through onfarm and regional technologies such as on-farm recycling systems and automatic data acquisition and control systems in irrigation supply systems. To increase water use efficiency and achieve sustainability of rice-based farming systems in Australia, irrigation communities are implementing a range of on-farm and regional technologies and policies. An integrated approach is required to evaluate options, prioritise investments, maximise economic returns, guide policy and balance the environmental demands of river ecosystems with the needs of irrigated agriculture and its dependent regional communities. Significant progress is being made, through the development and application of farm and irrigation area hydrologic models linked with production models and economics, combined with strong stakeholder participation. The progress in integrating science, people and policy makers was recognised in 2002 by the award of the first ‘‘Reference’’ catchment status to the lower Murrumbidgee catchment, a major Australian rice-growing region, under the UNESCO/WMO HELP (Hydrology for Environment, Life and Policy) program. # 2005 Elsevier B.V. All rights reserved. Keywords: Rice; Water use efficiency; Water productivity; Integrated water management; Policy; Models; SWAGMAN; Rice-based cropping systems

* Corresponding author. Tel.: +61 2 6960 1528; fax: +61 2 6960 1600. E-mail address: [email protected] (E. Humphreys). URL: www.clw.csiro.au/division/griffith 1 Present address: The Centre for Excellence in Natural Resource Management, 444 Albany Highway, Albany, WA 6330, Australia. 0378-4290/$ – see front matter # 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.fcr.2005.08.020

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1. Introduction Australian irrigation farmers, and rice growers in particular, are under considerable pressure to increase economic returns to water by increasing water productivity (g product per kg water) and/or producing higher value commodities. Major drivers are the increasing price and declining availability of irrigation water as a result of environmental and National Competition Policy agendas (Humphreys and Robinson, 2003) and the recent severe drought. The majority of the Australian rice crop is grown in the Murrumbidgee and Murray Valleys of southern New South Wales (NSW) at a latitude of around 348S. Here rice is the dominant broadacre crop, occupying 10–25% of the landscape in the major irrigation regions for about 7 months each year, and accounting for 50–70% of the total irrigation water use. Rice culture is entirely dependent on irrigation, with average rainfall of about 150 mm and evapotranspiration of about 1150 mm during the growing season. River water (0.1–0.2 dS/m) is the major source of irrigation water, although some groundwater is also used, normally mixed with river water to achieve a salinity of about 0.5 dS/m. The majority of the rice crop is sown into ponded water, and the fields remain ponded for about 5 months. Large areas of irrigated winter cereals and annual pastures are also grown in rotation with rice, together with smaller areas of a wide range of other summer and winter crops. Winter cereals can be sown after rice harvest, however, by the time that winter crops are harvested it is too late to sow rice in the same year. Therefore, production of winter crops immediately after rice is only practised on around one-third of all rice stubbles (Humphreys et al., 2001).

Average field water productivity of the total NSW rice crop roughly doubled over the period 1980–2000. For example, average field irrigation water productivity of the total rice area in the Murrumbidgee irrigation area (MIA) increased from 0.34 g kg 1 in 1980 to 0.77 g kg 1 in 1999 (input (irrigation + rain) water productivity 0.32– 0.70 g kg 1), largely due to increased yields, and partly due to reduced water use (Humphreys and Robinson, 2003). However, there is considerable variation in water productivity between fields, and input and irrigation water productivities of high yielding commercial rice crops in Australia often exceed 1 g kg 1. In comparison, typical irrigation water productivities for other summer crops range from 0.4 g kg 1 for soybeans to 1 g kg 1 for sorghum to 1.2 g kg 1 for maize (Table 1). Irrigation water productivities for crops grown in winter are much higher (1–2 g kg 1), largely due to much lower evaporative demand combined with slightly higher rainfall and therefore lower irrigation requirement. McCaffery (2002) reported irrigation water productivities for commercial wheat fields in the Coleambally irrigation area (CIA) ranging from 1.5 to 4.1 g kg 1, the higher values being for crops sown after rice due to high soil water content after rice, while total (irrigation + rain + soil water depletion) water productivity showed much less variation (1–1.5 g kg 1). For comparison with rice in southern Australia, typical field experiment input water productivities were 0.2–0.4 g kg 1 for rice in central and northern India, and 0.3–1.1 g kg 1 in the Philippines, with a maximum reported water productivity of 2.2 g kg 1 in a pot experiment in Japan (Bouman and Tuong, 2001). Hong et al. (2000) estimated that district irrigation water productivity of rice in the Zhanghe Irrigation District (122,000–173,000 ha) in Wuhan, China, increased from 0.82 to 2.32 g kg 1

Table 1 Measures of water use efficiency and productivity for irrigated crops in the Murrumbidgee Valley Crop

Irrigation water use (mm)

Rain (mm)

ETa (mm)

Yield (t ha 1)

WPi irrigation water productivity (g kg 1)b

WPi+r input water productivity (g kg 1)

WPET ET water productivity (g kg 1)

Rice (medium grain) Soybeans (crushing beds) Maize (feed beds) Sorghum (beds) Sunflower (monounsaturated-beds) Adzuki beans (beds) Wheat (ASW, contour) Wheat (APH, contour) Wheat (APH, beds) Canola (beds) Faba beans (beds)

1300 800 850 800 800

150 150 150 150 150

1180 900 850 850 650

9.4d 3 10 8 2.7

0.72 0.38 1.2 1.0 0.34

0.65 0.32 1.1 0.84 0.28

0.80 0.33 1.2 0.94 0.42

600 290 290 280 290 360

100 248 248 248 266 212

575 575 575 500 500

2 4 4 5.5 2.8 4.3

0.33 1.4 1.4 2.0 1.0 1.2

0.29 0.74 0.74 1.0 0.50 0.77

0.70 0.70 0.96 0.56 0.86

Gross margin ($ ha 1)c

Gross margin irrigation ($ ML 1)c

250 400 300 215 460

1202 564 1963 871 464

100 71 231 109 58

1200 200 251 251 375 280

1652 400 604 923 471 607

275 138 208 329 162 169

Price ($ t 1) c

Adapted and modified from O’Keeffe and Whitworth (2002, 2003). a ET values are best estimates from Humphreys et al. (2003a) and J. Thompson (unpublished data). b 1 g kg 1 = 1 kg m 3 = 1 g ha 1 cm 1 =1 t ML 1. c Prices vary greatly depending on supply and demand, affecting return to irrigation water and gross margins; summer crop prices are best estimates of prices at 3 September 2002; winter cereal prices are 10 year averages provided by the Australian Wheat Board, Griffith. $ = Australian dollar, AUD. d Average over 5 years to 2001/2002 for Amaroo in the CIA; average for Amaroo in the MIA was 9.8 t ha 1.

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between 1966/1978 and 1989/1998. These values are relatively high due to both the high annual rainfall of around 950 mm, most of which falls during the rice season, and capture and reuse of surface and sub-surface drainage water within the system. In the same region Loeve and Dong (personal communication) measured individual field irrigation and input rice water productivities of 1.62 and 0.81 g kg 1, respectively, compared with irrigation water productivities of 0.53 g kg 1 for a larger area including 117 ha of rice, and 1.75 to 2.98 g kg 1 in three main canal command areas of 5000–62,000 ha. Field irrigation water productivity was much lower in two other regions in China with much lower rainfall (0.56 and 0.45 g kg 1) and similar to total water productivity (Loeve and Dong, personal communication). The data demonstrate the importance of taking into account differences in rainfall by determining input water productivity as well as irrigation water productivity, and differences in scale e.g. individual field, group of farms, command area, total scheme, when comparing water productivities across locations or crop types. There is little scope for further significant increase in irrigation or input water productivity through reduction in water use in ponded rice culture in Australia, and future savings must come from changing to alternative, lower water use practices, which are currently under investigation. The need for deep water to provide low temperature protection during the early pollen microspore stage is a major constraint to completely moving away from ponded culture with current varieties. While average NSW rice yields are among the highest in the world, reaching 10.2 t ha 1 (paddy rice at 14% moisture) in 2003, yield and water productivity are currently constrained by high sterility in cold years (Section 3.1), poor establishment (Turner and Lewin, 1994), and in-field spatial variability (Section 3.2). While it is extremely important to increase the water productivity of rice per se, water productivity and profitability of the entire cropping system is of ultimate importance. However, yield of many crops grown in rotation with rice is often low, largely due to waterlogging and anaerobiosis as a result of the inherently low drainable porosity of the heavy clay soils used for rice culture, combined with poor surface drainage due to the very low (‘‘flat’’) grades required for ponded rice culture. The flat layouts used for rice also preclude the opportunity to diversify to many higher value waterlogging sensitive crops in rotation with rice. There is also considerable potential to increase returns to water through value adding for both rice and non-rice crops, for example, by growing varieties for specialist markets such as adzuki beans for export to Japan (Table 1) and by production of rice snack foods, instant meals and low glycaemic index foods (Humphreys et al., 2003b). Productivity in the rice growing areas is also threatened by rising watertables and secondary salinisation and waterlogging, with ponded rice a major contributor to

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watertable rise (GHD, 1985; Dwyer Leslie, 1992). Furthermore, shallow groundwaters (often saline) seep into surface drainage systems with the potential to impact adversely on downstream users and regional ecosystems. Therefore, watertable control is of paramount importance, not only to sustain soil fertility, but also to control the salinity of drainage waters leaving the irrigation areas. Since the 1940s, a range of evolving policies has been implemented to reduce deep percolation from rice (Humphreys et al., 1994a), and these measures inherently contribute to increasing water use efficiency. However, rice is not the only contributor to groundwater problems, and it is grown in a patchwork landscape with multiple landuses, complex hydrogeology and vibrant regional communities dependent on profitable irrigated agriculture and healthy river ecosystems. Over the past decade, it has been increasingly recognised that systems approaches are required at field, farm, irrigation area and catchment scales to identify optimal management of water and land resources that will achieve the desired economic, social and environmental objectives. It is also recognised that determination and adoption of solutions require participation of stakeholders at all stages of the process, from identification of values and vision to problem identification and prioritisation to development and implementation of recommendations and policies. While there are many challenges ahead, there has been considerable progress towards integrating people, science and policy. In 2002, the lower Murrumbidgee catchment, a major rice-growing area, was the first and only region to be awarded ‘‘Reference’’ catchment status in the UNESCO/WMO HELP (United Nations Education, Scientific and Cultural Organisation/World Meteorological Organisation Hydrology for Environment, Life and Policy) program, in recognition of the significant progress in integrated catchment management in this region (Khan, 2004). This paper reviews abiotic factors responsible for the recent increase in field level rice water use efficiency, and current and potential challenges and approaches for achieving further gains at field, farm and regional scales, from rice varietal improvement to integrated water resources management.

2. Extension and adoption of improved technology for increasing water use efficiency Australian rice growers are regarded as rapid adopters of improved technology (McDonald, 1994; Clampett et al., 2000). A recent review of extension services concluded that the rice industry is served by an exceptionally wellresourced and developed extension system, with 24 government agencies and types of businesses involved in extension to rice growers (Macadam et al., 2002). A characteristic of the extension system is the high quality of

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E. Humphreys et al. / Field Crops Research 97 (2006) 19–33

levelling, on-farm drainage recycling, net recharge management, conjunctive water use, and groundwater drainage and management. Adoption rates of such measures have been high (CICL, 2002; MI, 2001; MIL, 2001). For example, over half of the CIA was surveyed using electromagnetic induction (EM) (Section 4.2.1) between 1999 and 2002. Macadam et al. (2002) also found significant weaknesses in the extension system, which are slowing progress towards whole farm business management aimed at both economic and ecological sustainability. In particular, they identified considerable scope for improving the coordination and integration of programs with a production emphasis and programs with a sustainability emphasis. An emerging environmental champions program sponsored by the rice industry can be viewed as an appropriate response to the need for enhanced coordination and integration of activities, as the majority of agencies identified by Macadam et al. (2002) are active participants in formulating this scheme (Linnegar and Woodside, 2003).

personal relationships and networking between all stakeholders, providers and clients. Farmers consider that they have a direct role in determining the strategic direction of research and development through the Rice Research and Development Committee. A critical component of the rice extension system is the New South Wales (NSW) Department of Primary Industries Ricecheck approach to facilitating economic and environmental sustainability (Lacy et al., 2002a). Principles of the approach include experiential learning and collaborative exchange between researchers, extension agents and farmers, with the latter regarded as participants in the research and development process rather than mere end-users of information/technology generated solely by professional agricultural experts (Lacy, 1998). Farmers have been recording crop management practices since 1986, and records from 1994 to 2002 are held in a database of 6252 rice crops. The data allow evaluation of the rates of adoption of management practices. Recording of rice field water use was incorporated into Ricecheck in 1999. Ricecheck has had a key influence on raising rice yields and therefore water productivity (Lacy, 1994). Increasing rice water productivity has also been driven by an evolving range of restrictions designed to minimise deep percolation from rice (Humphreys et al., 1994a). Until recently, implementation of these restrictions was monitored and enforced by the state government water resource agency. With changes to irrigator management and subsequently ownership (privatisation) of the water distribution systems of the major rice growing regions in the mid 1990s, rice environmental policy and its monitoring and implementation were taken over by the new irrigation companies as part of their more comprehensive Land and Water Management Plans. The plans were developed and implemented by irrigation farmers and communities, and continue to evolve as new knowledge becomes available. Education is an important part of the plans, which also include incentives to encourage adoption of practices that lead to increased water use efficiency such as whole farm planning, soil surveying, laser Table 2 Comparison of commercial grain yield (t ha

1

3. Increasing rice yields 3.1. Rice varietal improvement New cultivars with greater yield potential have contributed significantly to improved water productivity over the last 20 years. This was particularly true after the release of improved semi-dwarf cultivars. Californian developed M7 (Carnahan et al., 1978) was the first semi-dwarf cultivar to be released for Australian rice growers in 1983. This was followed by a succession of releases of locally developed cultivars with a range of quality attributes and durations. Semi-dwarf cultivars accounted for 96.5% of the Australian rice area for the 2000/2001-rice crop. An indication of the contribution of these cultivars is provided by direct comparisons of average commercial yields for the major grain types (Table 2).

at 14% moisture) for major rice cultivars when grown in the same district and year Medium grain cultivars

Year released Produced commercially

Calrose (tall)

Amaroo (semi-dwarf)

Illabong (semi-dwarf)

1952 1952–1992

1987 1989

1993 1994

Yield (1989–1992) Yield (1994–2002)

7.9

9.3 8.8

10.1

Long grain cultivars

Year released Produced commercially Yield (1983–1985) Yield (1988–1997) Yield (1994–2002)

Inga (tall)

Pelde (tall)

Doongara (semi-dwarf)

Langi (semi-dwarf)

1973 1973–1985

1982 1983–1997

1989 1991

1994 1994

5.6

6.6 7.5

8.5 8.7

Medium grain cultivars were compared for the eastern Murray Valley and long grain cultivars for the Murrumbidgee Irrigation Area.

8.9

E. Humphreys et al. / Field Crops Research 97 (2006) 19–33 Table 3 Rate of uptake of major rice cultivars still in production in 2001/2002 in NSW Cultivar

Year released

Peak area % (year)

Steady uptake area % (year)

Amaroo Doongara Illabong Jarrah Kyeema Langi Millin Opus

1987 1989 1993 1993 1994 1994 1995 1999

59.8 3.1 5.9 12.3 5.8 22.7 17.6 4.4

51.0 3.0 2.0 12.3 2.6 19.0 17.6 2.6

(2002) (1995) (2002) (1994) (2001) (2000) (1997) (2002)

(1991) (1994) (1994) (1994) (1997) (1998) (1997) (2000)

Peak area is highest % area attained (and the year in which it was attained). Steady uptake area (%) (and the year in which it was attained) is when production is at the level set by the marketplace.

A feature of the release of new cultivars has been the rapid uptake by growers (Table 3). Most cultivars were taken up to the extent of seed availability for the first years following release. This has been facilitated by the close relationship between growers, plant breeders and extension services, and by industry self-regulation. The NSW rice industry operates a pure seed scheme and is the sole buyer of grain, and growers must buy new seed each year. Further increases in yield potential are possible. This is illustrated by the performance of Illabong, an ‘arborio’ type cultivar, which has consistently averaged 1 t ha 1 greater yield than Amaroo, the most widely grown cultivar (Table 2). Cultivars with the yield potential of Illabong but quality of the standard medium and long grain types will lift average production beyond 10 t ha 1. Water use efficiency can also be increased by reducing duration while maintaining yield. Reinke et al. (1994) argued that this could save up to 10% of the irrigation water, whereas Williams et al. (1999) concluded that reduced duration will always reduce yield potential and hence water use efficiency. While there is some evidence for the latter argument, Illabong has a higher yield potential than Amaroo with 10–14 days shorter duration. Short duration varieties also facilitate increased water use efficiency of the farming system. For example, earlier maturity allows earlier harvest, increasing the chance of establishing a winter crop after rice and making more efficient use of stored soil water and winter rainfall (Section 5.1). Yield increase to date has been made with little apparent improvement in cold tolerance. Cold weather during the reproductive stage is the main cause of yearly variation in grain yield in NSW (Section 3.3). The impact of low air temperature is currently moderated by deep water management during early pollen microspore formation. An improvement of 4 8C in tolerance combined with deep water management would eliminate the significant yield reduction caused by low temperature during the reproductive stage (Williams, personal communication). Cultivars with this level of tolerance have been identified (Farrell et al., 2001) and these are now contributing to the

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development of improved cultivars for Australian growing and market conditions. While improved cold tolerance will directly increase yield and water productivity, it will also allow growers to raise yields and water productivity by using higher rates of N fertiliser. Many growers tend to be conservative in the use of N due to the interaction between N and cold (Section 3.3). 3.2. Improved nitrogen management With increasing use of yield monitors on combine harvesters, it is now widely recognised that there is large yield variation across commercial rice fields (Russell and Dunn, 2001; Rawlinson and Brown, 2002). A field which produces an average yield of 10 t ha 1 may be comprised of areas ranging in yield from zero to in excess of 14 t ha 1. Yields of 0 t ha 1 are likely to be due sterility due to cold damage and excessive N, however they can also be caused by heavy weed infestation or poor establishment (e.g. duck damage). There is potential to substantially increase average yield and water productivity by identifying and selectively managing lower yielding areas within fields to raise their yields to those of the best parts of the field. Understanding the extent and source of the soil and crop variability can be greatly assisted using remote sensing technology such as electromagnetic survey (Beecher et al., 2002), near infra-red reflectance soil analysis (Russell and Dunn, 2001; Dunn et al., 2002; Russell et al., 2002) and canopy spectral properties (Spackman et al., 2000; Ciavarella et al., 2003). The spatial variation is greatest in heavily landformed fields, and is attributed to the altered pattern of soil organic matter concentration and mineralisable N (Russell, unpublished data). Such fields with areas of low mineralisable N have subsequently been shown to benefit from spatially variable rates of N application (Russell and Dunn, 2001; Rawlinson and Brown, 2002). Nitrogen is the nutrient, which has the greatest influence on yield and therefore water productivity of rice. The average application rate is approximately 120 kg N ha 1, mostly as urea (Batten et al., 2001a). The amount of fertiliser N required to optimise yield varies considerably (0–300 kg N ha 1) depending on field history (Williams et al., 1997; Beecher et al., 1994; Dunn and Beecher, 1998), and N applied prior to permanent flood is used more efficiently than N applied during the growing season (Batten et al., 1998; Dunn et al., 1998). However, too much N early in the season can lead to large yield losses due to lodging and sterility, which are exacerbated in cold seasons (Williams and Angus, 1994). Nitrogen application decisions are further complicated by the fact that the N supplying capacity of the soil is influenced by seasonal temperatures (Angus et al., 1994). At present there is no reliable soil N test, and presowing fertiliser N rate is determined from knowledge of the pasture and cropping history of the field and experience based on the amount of N in the shoots of previous crops. However, recent research indicated that mineralisable N in the 0–10 cm layer

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E. Humphreys et al. / Field Crops Research 97 (2006) 19–33

gave predictions that were correlated (R2 = 0.64) with rice biomass across a wide range of soils (Russell et al., unpublished data). Furthermore, an evaluation of rice productivity at two rates of preflood N across 21 trial sites showed the proposed new soil N test to be reasonably comparable (r = 0.72 versus r = 0.88) to the current tactical mid season tissue test in its correlation with above-ground biomass and N uptake at maturity (Russell et al., unpublished data). Rice growers know that crops which have access to insufficient N from soil reserves or fertiliser applications will produce sub-optimal yields. Depending on the rice cultivar and occurrence of low temperature during early pollen microspore, crops which accumulate more than 62– 132 kg N ha 1 in shoots by the PI stage require no additional N fertiliser to achieve the optimum yield (Lacy et al., 2002a). Since 1987, rice producers have been able to assess the N requirements of their crops at the PI stage based on the amount of N accumulated in shoots. A crop analysis service based on near infrared (NIR) technology is provided by the Ricegrowers’ Cooperative Ltd., and is used by about 40% of growers (Batten et al., 1991, 2001b). Around 5000 samples collected at panicle initiation are tested in a 4–5 week period each season. Farmers collect shoot samples from nine 0.1 m2 areas of crop, weigh them on kitchen scales, dry sub-samples in microwave ovens and take the samples and data sheets to a local collection point for delivery to a central laboratory. The amount of N in the shoots is calculated (kg N ha 1) and used to determine the N fertiliser recommendation (Lacy et al., 2002a). The results and recommendations are phoned or faxed back to the growers within 2 days of sampling. Rice growers are now able to purchase digital images, at 4 m2 resolution or better, showing the spatial variability of dry matter across rice fields (Rice CRC, 2003). These images enable rice growers to identify representative areas of their crops to sample and apply the appropriate N rate to each area across the field using aircraft fitted with GPS and variable fertiliser rate technology. In conjunction with the NIR Tissue Testing Service, an increasing number of rice growers are using the MANAGE RICE decision support software to assist determination of N application rates (Williams et al., 1996; Angus et al., 2002). The software is based on TRYM (temperate rice yield model), a simplified process model developed for the NSW rice industry (Williams, 2002). MANAGE RICE can be run for the current crop by downloading weather data from the internet, and is used to evaluate the risk of N management strategies as they are affected by sowing date, seasonal conditions, variety and water depth. It also includes economic analysis of options. Until recently, updates of the software were sent to about 30% of rice farm businesses. Now it is sent to all rice farm businesses on a CD together with a range of other information packages. The NIR Tissue Testing Service and MANAGE RICE raise the understanding of crop N fertiliser requirements and have

led to yield increases of the order of 0.6 t ha 1 (Batten, 2004), reduced waste of fertiliser and reduced environmental impacts. An evaluation of the benefits and costs showed that the research projects in NIR and MANAGE RICE rice clusters jointly produce significant economic and environmental benefits (CIE, 2003). The net present value of benefits generated by these projects are $166 million, $150 million and $147 million at 0, 5 and 10% discount rates, respectively, over the period 1990–2015. The challenge now is to identify and fertilise the responsive areas within crops using remote sensing and variable rate technologies. 3.3. Deep water during early pollen microspore Low temperatures during early pollen microspore development can dramatically reduce rice yields in individual fields by increasing pollen sterility (Williams and Angus, 1994). Highly significant linear or quadratic relationships can be demonstrated between industry average yields and mean minimum temperature during the early pollen microspore stage, however the nature and strength of the relationships vary across varieties and are not well understood. Pollen sterility is exacerbated by high soil N fertility and high rates of N application, more so for earlier N applications than for N applied at panicle initiation. Strategies to reduce the risk of damage include genetic improvement in low-temperature tolerance (Section 3.1), conservative N fertiliser management (Section 3.2) and deep water management to protect the developing pollen cells from low air temperatures. Williams and Angus (1994) showed that grain yield response to N fertiliser varied with sowing date, water depth and variety. For early sown crops with deep (20 cm) water during the period of microspore development, yields of an early maturing and a mid-season medium grain variety increased from 7 to 13 t ha 1 with increasing N application rate. However, with shallow (5 cm) water, yields decreased from 7 to 3 t ha 1 with increasing N rate. The minimum temperature of the deep water ranged from 17.3 to 19.1 8C for the 20 days around early pollen microspore, while minimum air temperatures ranged from 9.5 to 24.4 8C. The panicles were largely below the surface of the deep water during the microspore development period, and thus protected from the low night temperatures. Deep water management (20–25 cm) during early pollen microspore has been one of the key ‘‘Ricecheck’’ recommendations (Lacy et al., 2002a) since the early 1990s. Farmer adoption of deep water for early pollen microspore protection increased from about 20% in 1986 and 1987 (Moore and Lacy, 1991) to about 65% in the 1990s (Lacy et al., 2002b). Adoption has remained at about 65% over the last 8 years as there are many factors, which can prevent the application of deep water. Some of these, such as the inability of system channel flow capacity to meet crop demand, are sometimes out of farmer control.

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4.2. Reducing deep percolation

Fig. 1. Average yields of Amaroo with different early pollen microspore water depths 1994–2001 (Lacy et al., 2002b); * less than five crops.

Yield increases due to the adoption of deeper water at early pollen microspore are suggested by the Ricecheck database results of farmer crops for 1994–2001. Average yield increased with water depth to 26–31 cm in 6 out of 8 years, which were average to cold years (Fig. 1). The yield response to increasing water depth was most notable in the coldest, lower yielding years of 1996 and 2000.

4. Reducing rice water use 4.1. Rice water use limit A rice water use limit of 1600 mm was phased in commencing in 1985, based on the fact that approximately 1200 mm are evaporated from rice fields during the season, and allowing for 400 mm of surface and deep drainage (Humphreys et al., 1994a). Of the water evaporated, about 40% is evaporated direct from the water surface, and 60% is transpired by the crop (Simpson et al., 1992). Each season the water use of each rice field is determined from its area and the volume of water used. The area is determined from aerial photography or satellite imagery, and the volume of water is most commonly measured using a Dethridge meter at the farm offtake. In many situations one meter records the supply of water to more than one crop, simultaneously and/ or at separate times, and the assignment of the amount delivered to each crop is estimated and provided to the irrigation company by the farmer. Since 1993/1994 the limit has been adjusted up or down to allow for seasonal variation in potential evaporation and rainfall, which can be substantial (Humphreys et al., 1994b). In the mid 1990s the limit was lowered to 1400 mm in most of the rice growing regions. The rice water use limit is implemented by the irrigation companies under their Land and Water Management Plans. However, it is becoming increasingly difficult to establish reliable rice field water use data due to inability to monitor water use of individual fields combined with the increase in on-farm recycling of drainage waters and groundwater pumping.

4.2.1. Soil survey A major focus of rice environmental policy has been the identification and exclusion of excessively permeable soils from rice culture. The clay soils of the rice growing areas often have low permeability, however, these soils are part of a variable riverine and aeolian deposition system whose stratigraphy has a complex pattern of fine to coarse textured layers. The prior stream systems that cross the landscape are characterised by sinuous, sand-filled discontinuous stream channels that can occur at depth or at the surface, providing points at which significant percolation losses can occur. van der Lelij and Talsma (1978) found that cumulative infiltration during rice growing varied significantly between the four broad soil categories of the rice growing areas. They also found large differences in long-term infiltration within these soil categories. Thus sites with high infiltration rates may exist within rice fields, and their delineation and exclusion are important as percolation below the root zone from small highly permeable areas can be significant (Humphreys et al., 1998b). Hand texturing of the profile to a depth of 3.6 m has been used to assess soil suitability for rice since the 1970s (Humphreys et al., 1994a). One soil profile per 4 ha (i.e. a 200 m grid) was generally assessed, with at least 2 m of continuous medium to heavy clay required for approval for rice growing. The limitations of this method are the low intensity of sampling in a variable landscape and the poor relationship between texture and permeability for some soils, such as sodic soils and self-mulching clays. Electromagnetic induction (EM31) measures bulk soil electrical conductivity, and is a powerful tool for identifying soil variability within rice fields. There is often a trend for infiltration rate to be related to EM31 value (Beecher et al., 2002). Beecher and Hume (1996) showed the potential for using EM31 instruments combined with global positioning systems to provide spatial detail on variation in soil properties across rice fields (Fig. 2), and to locate representative sampling sites to provide better assessment of soil suitability for rice, while reducing the number of sites requiring investigation. The technique allows rapid, low cost assessment and identification of permeable areas, which can be isolated by redesign of the rice field layout, or treated to reduce permeability. EM31survey has been adopted as part of the whole farm planning and rice land classification process in all rice growing areas of southern Australia. Within these areas, individual growers have reported significant decreases in rice water use of up to 25–30% as a result of exclusion of areas with low EM31 values from rice growing. Large areas have been investigated in major rice growing areas (MIL, 2001; CICL, 2002). Between 1999 and 2003 approximately one-third of the Murray Districts irrigated land, two-thirds of the CIA and less than 25% of the MIA were surveyed.

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Fig. 2. Apparent electrical conductivity (ECa) contour map of a rice field, with a history of high water use, determined using EM31.

included the slowness of the puddling operation at a busy time of year, turbidity problems where water management was not optimal, reluctance to operate machinery in the mud and water, and mixed results at the whole field scale. This led to some farmer-driven research to evaluate impact compaction for its use in rice culture (Clark and Humphreys, 1997; Humphreys et al., 1998a). Impact compaction has the advantage of being able to be applied well in advance of preparation for rice sowing, whereas puddling is a ‘‘last minute’’ operation. Impact compaction was very effective in reducing infiltration on both high and low water use sites, with no effect on crop performance. For impact compaction to be economic, the effect needs to last for 2–3 seasons; some farmers have recently reported that the effect only lasted for two seasons. The effects of impact compaction on soil structure were transmitted to depths of at least 0.4–0.5 m below the soil surface at some sites. The depth, nature, extent and reversibility of changes in soil structure as a result of impact compaction and its implication for crops grown in rotation with rice have not been investigated. Therefore, widespread application is not recommended, although it may be useful in sealing small highly permeable areas. 4.3. Water management

However, the poor relationship between permeability and texture for some soils is a weakness. The work of Beecher et al. (2002) highlights the importance of soil sodicity in controlling the rate of deep drainage. They proposed a three-stage classification scheme of rice land suitability involving EM31 soil mapping and measurement of soil sodicity as follows: (1) the soil is suitable if EM31v  150 mS/m; if EM31v < 150 mS/m, the soil is suitable if (2) the exchangeable sodium percentage (ESP) of the top 60 cm of the soil profile >6, or if (3) ESP of the 60–150 cm layer >12. This scheme was recently adopted in the Murray Districts, and is being trialled in the CIA. 4.2.2. Puddling and compaction In the 1990s puddling and compaction were evaluated for their effects on infiltration, rice crop performance, soil properties, the performance of crops sown after rice and the economics of these techniques (Humphreys et al., 1994c, 1996; Ringrose-Voase et al., 1996). The results showed that puddling reduced infiltration, although in some situations the reduction was not large enough to meet the rice field water use limit. Rice yields with puddling were generally comparable to those without puddling, and puddling appeared to be economic as the value of the water saved exceeded the additional cost of puddling. Yields of wheat and canola direct drilled after rice harvest were not impaired, and there was no evidence of medium term soil structural decline, consistent with the observation that there was no carryover effect on infiltration in subsequent rice crops. However, very few farmers adopted puddling in the rice growing areas of southern NSW. Major constraints probably

The requirement for deep water protection during early pollen microspore currently limits the scope for water saving strategies for rice without increasing the risk of a substantial yield penalty. For non-ponded rice culture to be viable, cold tolerance would need to be improved to cope with night temperatures as low as 10 8C during microspore development. Furthermore, during the period from panicle initiation to flowering, crop growth rates are as high as 250– 300 kg ha 1 d 1 with potential evapotranspiration frequently in excess of 10 mm d 1, thus the risk of water deficit stress during this period is likely to be high with nonponded culture. The degree of soil water depletion that the rice crop can experience without losing yield in the southeast Australian rice-growing environment is currently unknown. In the heavy clay soils used for rice growing most roots are in the top 100 mm (Heenan and Thompson, 1984), therefore, available soil water is limited and the crop could quickly experience water deficit during the reproductive stage. Bouman and Tuong (2001) concluded that there is variation in water deficit sensitivity among rice cultivars in a review of 31 water management studies in Asia, suggesting that there is scope for breeding and selecting cultivars that are more suitable to non-ponded culture. Incorporation of sufficient cold tolerance into Australian rice cultivars to obviate the need for deep water protection would also need to be accompanied by incorporation of deeper rooting characteristics to reduce the possibility of water deficit in a nonponded system. Intermittent ponding also presents challenges for other aspects of rice culture including fertiliser and weed management.

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4.3.1. Intermittent irrigation Numerous studies around the world have shown that continuously flooded rice out-yields rice grown under intermittent flooding. Bouman and Tuong (2001) reported that yields were reduced by 10–40% when soil water potential at 10–20 cm was allowed to reach 10 to 30 kPa, and that the reduction in yield was more related to the duration of water stress than to the growth stage at which it occurred. Considerable research on intermittent flood and sprinkler irrigation for rice was carried out in Australia in the 1980s. Heenan and Thompson (1984, 1985) found that ponding water for 2–3 h (sufficient time to saturate the rootzone) every 7 days throughout the season reduced water use by 60%, but yields were very low (1–2 t ha 1) compared with 9 t ha 1 for conventional management) and grain quality was unacceptable. Sprinkler irrigation to replace evaporative loss reduced water use by 30–70% (Humphreys et al., 1989), however, even at frequencies of up to three times per week, yield declines of 35–70% occurred (Muirhead et al., 1989). There are also several reports of reduced irrigation water use with sprinkler irrigation to replace evaporative demand in the USA, with associated yield losses of 14–28% (e.g. Westcott and Vines, 1986; McCauley, 1990). With intermittent flooding during the vegetative phase, and continuous flood commencing about 2 weeks prior to panicle initiation, both yield and quality compared favourably with conventional management (Heenan and Thompson, 1984, 1985). Savings in total water use of around 25% were achieved, with deep percolation reduced considerably. It therefore seemed that considerable water savings could be achieved, without yield penalty, by delaying permanent flood until just before panicle initiation. However, this work was carried out on a relatively freedraining soil, therefore the reported water savings may overestimate what can be achieved on more typical rice soils. Intermittent flooding is currently being re-evaluated using modern semi-dwarf varieties on less permeable soils, and indications are that water savings of about 20% can be achieved with no effect on yield (Thompson, unpublished data). Rice has been grown successfully under intermittent irrigation in the USA, although additional fertiliser N was sometimes required (Wells and Shockley, 1978; Bucks et al., 1982). However, Vories et al. (2002) found a consistent yield decline of about 16% for rice on raised beds furrow-irrigated twice weekly or when the soil water deficit reached 19 mm. 4.3.2. Saturated soil culture on raised beds In raised bed saturated soil culture, irrigation water is maintained in the furrows rather than ponded over the entire soil surface. Research in semi-tropical southern Queensland (208S) found that water use of rice grown on beds was 32% less than when grown using conventional permanent flood, while yields were maintained, resulting in a large increase in water use efficiency (Borrell et al., 1997). At this site drainage below the rootzone was considerable. Investiga-

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tions in southern NSW, conducted over four growing seasons on rice-suitable soils, showed irrigation water savings of around 10%, with a similar reduction in grain yield, resulting in no improvement in water use efficiency (Thompson et al., 2003).

5. Systems approaches to increasing water use efficiency at field, farm and irrigation area scales To increase water use efficiency and achieve sustainability of rice based farming systems in Australia, irrigation communities are implementing a range of on-farm and regional management actions, policies and technologies. These include monitoring irrigation water use (at field, farm and irrigation area scales), soil surveying (Section 4.2.1), whole farm planning, laser levelling, shallow and deep groundwater pumping, lining of earthen channels and installation of on-farm drainage recycling systems, and installation of automatic data acquisition and channel control systems. The impacts of these technologies and policies need to be investigated in an integrated manner. Therefore, a range of systems approaches, with the potential to facilitate significant increases in water productivity and returns to water ($ ML 1) and land ($ ha 1), and to achieve sustainability, is currently being developed or implemented. 5.1. Cropping systems Rice fields commonly lie fallow for 5–6 months after harvest, until the next rice crop is planted, or for much longer periods depending on the crop rotation. Rice is ponded until shortly before the crop matures, therefore, the soil profile has a high water content after harvest. Growing winter crops immediately after rice harvest increases the water use efficiency of rice-based cropping systems by using the stored soil water and creating capacity in the profile to capture winter rainfall instead of losing it as runoff or deep percolation (Humphreys et al., 2001). Crop water use from capillary upflow from the watertable can also be significant, and varied from 10 to 36% of total evapotranspiration for well-irrigated wheat with a shallow (1–1.3 m), fresh watertable (Meyer et al., 1990; Meyer et al., 1987). Permanent raised bed rice-based cropping systems are currently under investigation for their potential to increase cropping system water use productivity and profitability (Beecher et al., 2003). Thompson and North (1994) found that yields of wheat or barley on raised beds were greater than yields on a border check layout by an average of 26% (range 18–43% over 4 years). In their review of ridge (bed) tillage, Tisdall and Hodgson (1990) also found higher yields of crops grown on ridges compared with flats due to better soil aeration. Permanent beds in a rice-based system are also likely to increase the chance of sowing and establishing winter crops after rice due to improved surface drainage, allowing more timely access by headers and reduced wheel

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track damage during harvest. Furthermore, with raised beds, a wide range of high value waterlogging sensitive crops unsuited to flat layouts on clay soils could be grown in rotation with rice, enhancing the opportunity for diversification in response to market opportunities and increasing economic returns to irrigation water (Table 1). 5.2. Whole farm net recharge management To achieve environmental sustainability, farmers need to manage cropping systems to avoid the development of shallow watertables and salinisation of the rootzone. Watertable fluctuations are determined by complex interactions between regional groundwater dynamics, climate and on-farm biophysical factors and management. SWAGMAN1 (Salt Water And Groundwater MANagement) Farm is a farm scale hydrologic economic model that integrates the effect of these factors on watertables and root zone salinity (Khan et al., 2000). On-farm factors that influence watertables include recharge from all land uses (irrigated and non-irrigated fields, fallow and non-farmed areas), discharge from bare soil evaporation and crop water use from capillary upflow, and groundwater pumping (Fig. 3). Net recharge is the difference between recharge and discharge, and where recharge exceeds discharge watertables will rise. SWAGMAN1 Farm can be used to simulate the effects of the chosen mix of landuses across soil types on the farm on gross margin, net recharge, depth to the watertable and rootzone salinity for individual fields and the whole farm. It can also compute the optimum mix of landuses that maximises gross margin subject to chosen constraints on watertable change and rootzone salinity. Analyses using SWAGMAN1 Farm show that initial soil water content, weather, irrigation water availability and the interaction between shallow and deeper aquifers are very

important factors in the overall environmental sustainability and economic viability of farms, and that these factors need to be taken into account in determining rice environmental policy such as water use limits (Khan et al., 2001c). The development, testing and adoption of SWAGMAN1 Farm has involved the development of close working relationships between farmers and their irrigation company environmental staff and researchers. Education has also been important, involving the development and delivery of customised training material and hands-on training sessions. An education program has been in operation in the CIA for the past 5 years, attended by members of about half the farm businesses in the area to date. SWAGMAN1 Farm has also been run with about 40 farmers to evaluate options for controlling net recharge on their own farms, and is about to be implemented in four pilot catchments in the CIA. Implementation of net recharge management agreements and trading of net recharge credits are also being explored. The major objectives are to reduce saline flows into the regional surface drainage system by controlling watertables and to manage environmental assets in the irrigation areas. Current research is helping to develop policy options for the rice growing areas through the application of SWAGMAN1 Farm in combination with regional groundwater studies. A new GIS-based SWAGMAN1 Farm has been developed which will allow ready application of the model across large numbers of farms by linking with irrigation company databases (Khan et al., 2001b). Development of policy options in terms of allowable crops, irrigation intensity (ML ha 1) and sub-regional net recharge targets is a very sensitive task which requires much input from irrigation companies and the community for wider acceptance. A web-based version of SWAGMAN1 Farm has also been developed which will enable wider access to the model through irrigation company websites. Each user will be able to access to their own farm information held on the irrigation company databases and run the model, view results and make landuse decisions. The web-based SWAGMAN1 Farm is also being used for teaching undergraduate university students. 5.3. Integrated water management for irrigation areas

Fig. 3. Schematic diagram showing biophysical processes under shallow watertable conditions for the farm level model, SWAGMAN1 Farm (Khan et al., 2000).

To assist the implementation of Land and Water Management Plans, it is important to assemble GIS databases of infrastructure and natural resources, which can be linked with hydrologic models to simulate the spatiotemporal impacts of management and climate. These models can be used to evaluate options, prioritise investment and guide policy (Khan et al., 2001b,c). GIS based representations of modelling results can be used as educational tools to create community awareness and to enable transparency of policy development and implementation and wider acceptance of Land and Water Management Plans. The components of a decision support system (DSS) being developed for the lower Murrumbidgee catchment for

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Fig. 4. Schematic diagram of distributed hydrologic decision support system for evaluating Land and Water Management Plan options in irrigation areas (Khan et al., 2001d).

evaluating environmental management options in the rice growing areas are shown in Fig. 4 and include: a. a GIS database to help integrate various types of spatial information, b. a crop production model to assess groundwater recharge, salinity, soil, climate and irrigation dynamics for individual crops, c. a farm scale hydrologic economic model to assess watertable, salinity and economic management options for individual farms (SWAGMAN1 Farm), d. a hydrologic model (MODFLOW) of the irrigation and surrounding area to evaluate regional impacts of on-farm and regional management options, e. scenario setting and display of results in a GIS environment. A range of hydrogeological features, compiled in collaboration with the irrigation companies, is represented in the GIS databases. These include aquifer lithology and hydraulic characteristics, vertical interactions between aquifers, interactions between channels, drains and rivers and adjoining aquifers, and groundwater abstractions. The hydrogeological features provide input to a three-dimensional surface-groundwater interaction model, which simulates aquifer dynamics on a detailed grid (e.g. 750 m  750 m) to identify climate and management impacts on groundwater levels and salinity. The surface-groundwater interaction model is based on MODFLOW (McDonald and Harbaugh, 1988; Christensen et al., 1998) and MT3D codes, with user interfaces that make it easy to operate, maintain and visualise system scale hydrology using GIS databases. However, a major limitation of a stand-alone MODFLOW-MT3D approach is its inability to explicitly consider crop interactions under shallow watertable conditions, hence the need for inclusion of crop and farm models in the DSS. These models have been calibrated according to the statistical measures defined in the Australian Groundwater

Modelling Guidelines. The calibrated models enable integration of biophysical processes with crop production and economic components for different management scenarios. Scenario design and evaluation need to involve local farmers and irrigation company staff to enable ready identification and adoption of preferred actions. The integrated DSS allows identification of suitable and unsuitable (high recharge) rice areas, leaky channel and drain sections and river reaches. Overlaying the surfacegroundwater interaction model results with the GIS model grid and channel network layers can help identify groundwater hotspots in the irrigation areas. Groundwater model simulations give predictions of watertable heights under different scenarios, and these heights can be combined with aquifer hydraulic properties to derive groundwater flow vectors. The groundwater flow vectors can be used to identify groundwater recharge and discharge zones, providing an understanding of how management actions at the farm level affect watertables in other areas (Khan et al., 2004a). On the basis of knowledge of groundwater dynamics derived from complex aquifer models, the CIA has been divided into groundwater management zones which are independent of each other—any changes in rice water use in one zone will have no impact on the other zones. This has helped to change the mindset of farmers and irrigation companies to link rice growing with the sub-surface aquifer capacity of the irrigation areas. Conjunctive use of surface and groundwater can be an option to manage shallow watertables and salinity in rice growing areas while increasing the availability of water for irrigation (Christen and Khan, 2002). In the CIA, water quality in the shallow (12–30 m) aquifers is generally poor and extremely variable, ranging from 1 to 30 dS/m. These shallow aquifers are generally considered to be too saline with hydraulic conductivities too low to be used as an irrigation resource. The deep (100–150 m) groundwaters, however, are generally of good quality (0.5–0.7 dS/m) and in highly transmissive aquifers. Deep groundwater pumping

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may also serve to promote downward leakage from the upper aquifers and hence assist in shallow groundwater and soil salinity control. The pumped groundwater can be used conjunctively with low salinity surface water, however, this requires that in the long term the deeper aquifer salinity is not increased significantly due to the enhanced vertical gradients as a result of pumping. This tradeoff between aquifer salinity and soil salinity control is a critical consideration when evaluating the usefulness of deep groundwater pumping. A feasibility study of deep groundwater pumping in the CIAwas conducted using a regional groundwater flow and salt transport model based on MODFLOW and MT3D (Prasad et al., 2001). The results showed that a widespread drawdown could be created in the deeper aquifers but this did not translate into equivalent drawdowns in the shallow formations either spatially or temporally. The resulting small increase in vertical leakage is unlikely to have a significant impact on existing salinity problems. However, maintaining and enhancing the current leakage to deep aquifers should assist with salinity control in combination with other measures. 5.4. Achieving sustainability and maximising net revenue for irrigation areas Understanding the possibilities for maximising water use efficiency ($ ML 1) for regions with shallow saline watertables requires integration of spatial hydrologic dynamics with economics. However, the inputs and outputs of economic significance need to be defined over much larger scales than those appropriate for modelling hydrologic responses as described in Section 5.3. Stubbs (2000) and Khan et al. (2001a) describe a new approach for integrating hydrogeological variability with the unsaturated zone, crop production and economic optimisation. A key aspect is the reduction of the number of possible states of the groundwater using ‘state reduction’ techniques, which are commonly used in control engineering. Khan et al. (2001a) used this approach to investigate the impact of rice area restrictions and water trading on watertables, economics and changes in landuse over space and time in the CIA. They compared the results for two different objectives—maximisation of annual net revenue for the entire area (‘‘the social optimum’’), or for each of the smaller economic units (‘‘the common pool’’) over 30 years. With no rice restriction and water trading, maximisation of net revenue was associated with a shift in rice from deeper to shallow watertable areas since less irrigation water is required to grow rice under shallow watertable conditions. The intensity of rice production in some units increased to 50% of the rice-suitable area and decreased to less than 10% in other units. 5.5. Reducing risk and spreading irrigation demand Due to the wide variability in seasonal rainfall, there is considerable risk in making cropping decisions under the

present system of announcement of irrigation water allocations. The allocations at the start of the irrigation season depend on the amount of water in storage and the minimum expected inflows during the season. Allocations generally increase during the season, but this can be extremely variable from year to year. In years of initially low allocations, farmers have the choice of over-planting in the hope that allocations will increase, or planting low areas and losing the opportunity of higher production when allocations increase. For example, in 2001/2002, a year in which the allocations remained low, the price of water available for temporary transfer in the CIA increased from AUD 20– 30 ML 1 to AUD 210 ML 1, and significant areas of rice ran out of water, due to the fact that farmers had planted more area than could be irrigated. Uncertainty in water allocations, supply system limitations and intensive cropping patterns require spreading of irrigation water demand to optimise productivity of irrigation areas and management of river flows for healthy river ecosystems. Water availability risk and demand management models are currently under development (Khan et al., 2004b) to assist farmers to quantify the risks involved when deciding crop types and areas at the start of the irrigation season, and to spread irrigation demand over time within and across seasons.

6. Conclusions Water productivity of rice in Australia has approximately doubled in the past 20 years, largely a result of improved varieties and crop management. At the same time, rice culture has been increasingly restricted to less permeable soils through the introduction of policies, which include field water use limits and soil suitability criteria. There is considerable potential for increasing the economic returns to water and land of rice-based systems by increasing yield and water productivity of rice and other crops grown in rotation with rice, and by crop diversification and value adding (Humphreys et al., 2003b). The biggest potential for future gains in rice water productivity lies in increasing yields by breeding for improved cold tolerance, precision agriculture, and improved establishment, and by moving away from continuously ponded rice cultural systems to intermittently irrigated systems. There is no yield loss with intermittent irrigation for the first 10–11 weeks, offering the opportunity to save irrigation water and increase water productivity now. A key challenge of the next decade is to increase cold tolerance to the level where deep water low temperature protection is no longer required, allowing a complete shift away from ponded culture, and reducing the irrigation water requirement. While increasing the water productivity of rice is important, water productivity and profitability of the entire cropping system is of ultimate importance, and growing crops after rice and permanent bed systems offer potential

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benefits of increased yields of crops traditionally grown in rotation with rice and increased cropping diversity and flexibility. This will be increasingly important as water availability continues to decline. To increase water use efficiency and achieve sustainability in rice based farming systems in Australia, irrigation communities are implementing a range of on-farm and regional management actions including whole farm planning, recycling systems, groundwater pumping, channel lining and automatic channel control systems. An integrated approach is required to evaluate options, maximise economic returns, prioritise investments and guide policy, and this is being assisted by the development and application of farm and irrigation area hydrologic models linked with production models and economics. Balancing the environmental demands of river ecosystems with the needs of irrigated agriculture and the regional communities it supports will require farm and irrigation area management systems with altered water demand patterns and quantities. It will also require better assessment of the likelihood of water availability for irrigation. Integration of social, economic and biophysical considerations is critical to achieving the multiple goals of higher water use efficiency, sustainable rice-based production systems and healthy river ecosystems.

Acknowledgments Many organisations provided financial support to the work reported here, especially the CRC for Sustainable Rice Production, RIRDC – Rice Research and Development Committee, Coleambally Irrigation Cooperative Ltd., Murray Irrigation Ltd., Murrumbidgee Irrigation Ltd., Land and Water Australia and the Australian Centre for International Agricultural Research. We are also grateful to many farmers for their cooperation and input into this work.

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