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Water-wise rice productionProceedings of a thematic workshop on water-wise rice production, 8-11 April 2002 at IRRI headquarters in Los Baños, Philippines. Book is
available The objective of this study was to compare
the effects of water-saving irrigation regimes on yield, irrigation water input,
water balance components, and water productivity of aerobic and conventional
rice varieties. The experiments were carried out in Tuanlin, Hubei Province, and
in Huibei, Henan Province, China. The main plots at each site were irrigation
water management regimes, ranging from rainfed to irrigated continuously
flooded. In the subplots, hybrid rice variety 2you725 was compared with aerobic
rice variety HD502 at Tuanlin and inbred variety 90247 with aerobic rice variety
HD502 at Huibei. The experiment in Tuanlin included two N-fertilizer treatments
(180 kg N ha–1 and
no N fertilizer) in the sub-subplots. The aerobic rice variety at Tuanlin was
heavily infested with stem borer, while that at Huibei yielded significantly
less than the inbred rice variety because of reduced tillering and duration in
all water regimes. Continuous flooding had the highest irrigation water inputs,
followed by alternate wetting and drying irrigation, saturated soil culture in
raised beds, flush irrigation in aerobic soil, and rainfed treatments. Rice
yields did not differ significantly among water treatments. Flush irrigation and
rainfed rice had the highest irrigation and total water productivity. The lack
of significant differences in rice yield between water treatments was probably
due to shallow groundwater tables at both sites. The shallow groundwater table
depth in these experiments has implications for extrapolating the effects of the
water-saving irrigation treatments to larger spatial scales. As the demand for industrial, municipal, and other water uses increases, less water will be available for Indonesian agriculture. To maintain food security, means must be developed to increase the productivity of water used in agriculture. This paper describes the results of three field experiments in a recently reclaimed lowland rice area of Riau Province assessing the effects of different water management practices (continuously flooded and intermittent wetting and drying), seedling age, and nutrient management. Regularly, the number of (effective) tillers, plant height, leaf area, and biomass distribution over plant parts were measured during growth. Because the experiments were severely damaged by rats from 90 to 110 d after transplanting (DAT), here results are reported of only plant characteristics measured before 90 DAT. Intermittent irrigation consistently performed better than continuously flooded irrigation, that is, it produced more (effective) tillers, leaf area, and biomass. Seedlings of 7 and 14 d had more vigorous vegetative plant growth than 21-d-old seedlings—they produced more (effective) tillers and biomass, taller plants, and longer roots. But the positive effect of younger seedlings on leaf area was not shown under flooded conditions. Organic manure applied at 3 t ha–1 showed positive effects on biomass production compared with 0 and 6 t ha–1. However, the effect of organic manure at 90 DAT was determined only in combination with a high fertilizer application. A crop receiving 1 t lime and 90 kg N-P2O5-K2O ha–1, of which 50% was given at 7 and 28 DAT, respectively, performed better than a crop receiving 1 t lime and 4 t manure ha–1. Biophysical
and economic implications of integrated crop and resource management for rice in
Indonesia
Rice production in Indonesia faces several problems simultaneously: water shortage, declining productivity, and environmental pollution. To cope with these problems, the Ministry of Agriculture promotes integrated crop and resource management (ICM) for rice. On-farm research and assessment are carried out in eight case-study areas throughout the country. One group of farmers applies ICM and another group conventional practices. Three ICM components are tested: improved nutrient management, planting of young single seedlings, and the application of intermittent irrigation. The biophysical and economic implications of the introduction of ICM for farm households are presented in this paper. Farmers applying all three ICM components obtained the highest average yield of 6.9 t ha–1, whereas conventional farmers attained on average 5.4 t ha–1. Variables that significantly affected yield were organic matter, irrigation method, and the interaction of P fertilization with irrigation method. Farmers using three ICM components need additional labor of 15 d ha–1, mainly for organic matter and split fertilizer application, weeding, and irrigation. Net returns of ICM farmers using three components are 37% higher than those of conventional farmers, despite 16% higher costs. The relatively low number of ICM farmers using intermittent irrigation is thought to have been caused by a lack of skill and cooperation among farmers and irrigation engineers and should get proper attention in the future on-farm development of ICM. Water
use of alternately submerged and nonsubmerged irrigated lowland rice
The
availability of freshwater for agriculture is declining in many parts of Asia,
thus affecting lowland rice production. One water-saving management option in
irrigated lowland rice systems is to reduce the amount of irrigation water per
rice cropping season. Although farmers traditionally aim at having continuously
flooded fields, water-saving techniques are receiving more and more attention.
Savings in irrigation water in the ASNS treatments were 53–87 mm (13–16%) compared with the CS regime. Rice grain yields ranged from 7.2 to 8.7 t ha–1 and were not significantly affected by the water regimes. Water productivity was 0.91–1.48 kg grain m–3 water applied. In two out of three experiments, water productivity was significantly higher in the ASNS regime than in the CS regime. The depth of the (perched) groundwater level was 0–30 cm below the soil surface in all experiments, thus minimizing the effect of aboveground water status on water availability for the rice plant. The soil moisture potential at PhilRice was never below –20 kPa. The experiments were conducted in extremely poorly drained, heavy-textured soils with a low seepage and percolation rate (max. 3.9 mm d–1 in the CS regime). The evaluation of ASNS regimes was based on soil texture, the formation of cracks that can cause bypass flow, and groundwater depth. These criteria were identified as the most relevant for recommendations on water management of water-saving regimes for lowland rice production. Water
management of rice in southern New South Wales, Australia
The Australian rice crop is grown on the Riverine Plain with surface water supplied from the Murray and Murrumbidgee rivers and their associated creek systems. A few crops are irrigated with groundwater. The majority of the crop is grown in ponded water from sowing or the 3-leaf stage. Average growing-season evapotranspiration is 1,100–1,200 mm, with only 160 mm (range 30–350 mm) being contributed from rainfall. Daily evapotranspiration averages 9–10 mm d–1 from late tillering to flowering and can be as high as 15 mm d–1. More than 50% of the water delivered to the irrigation areas is used for the rice crop; thus, the crop’s water requirement is constantly under scrutiny. The industry has developed a policy that limits the area of rice that can be grown on an individual farm. Rice production is also restricted to soils considered suitable for rice, that is, those where drainage below the root zone is less than 200 mm ha–1. Investigations into irrigation strategies to reduce the length of ponding have shown that there is some scope to reduce water use before panicle initiation, although weed control, particularly of barnyardgrass, is less effective. There is increasing pressure to provide more water for “environmental flows” in the river systems, thus reducing farmers’ water entitlement. Mechanisms are in place to allow the transfer of water from farm to farm and to carry over unused water to the following season. Reducing
water use in irrigated rice production with the Madagascar System of Rice
Intensification (SRI)
The System of Rice Intensification (SRI) developed in Madagascar increases yields substantially, 50% to 100% or more, while requiring only about half as much water as conventional rice. There is no need for different varieties or to purchase external inputs. Most water-saving methods to date show little decline in yield or, at most, small gains in output. The large increase in the productivity of irrigation water use with SRI could make water savings more attractive, compensating farmers well for the extra labor or expenditure involved. The returns to land, labor, capital, and water are all increased by the use of SRI practices. This paper discusses the SRI and its increasing acceptance outside of Madagascar. It reviews the common thinking that rice is an aquatic or at least hydrophilic plant, which is contradicted by SRI experience. Continuously flooded soils constrain root growth and contribute to root degeneration. They also limit soil microbial life to anaerobic populations. This excludes contributions to plant performance from mycorrhizal fungal associations that are of benefit to most plant species. Keeping paddy fields flooded also restricts biological nitrogen fixation to anaerobic processes, forgoing possibilities for aerobic contributions. Evidence is presented that the SRI produces different phenotypic expressions of existing genetic materials. SRI methods have been able to raise yields of any rice variety, but the highest yields have come from improved high-yielding varieties. Factorial trials in Madagascar explain synergistic dynamics among the SRI practices that account for 100–200% increases in yield. The main constraints to SRI use (requirements for more labor, skill, and water control) can be reduced with more experience or investment. Farmer
implementation of alternate wet-dry and nonflooded irrigation practices in the
System of Rice Intensification (SRI)
Competition for limited water resources and low rice yields in developing countries have renewed interest in finding better ways to grow more rice with less water. In recent years, alternate wet-dry (AWD) and nonflooded (NF) irrigation have shown promise for reducing water consumption without a significant effect on rice grain yield. In 2001, a survey of 109 farmers was conducted in four rice-producing areas in Madagascar to investigate farmer implementation of AWD and NF irrigation as part of the recently introduced System of Rice Intensification (SRI). SRI recommends aerating the soil during the vegetative development period and transplanting young seedlings (8–12 days old) at low plant hill density (25 hills m–2 or fewer) and with one plant per hill. The survey showed that farmers have adapted their AWD irrigation practices to fit the soil type and their availability of water and labor. The primary drawbacks reported by farmers with implementing AWD and NF irrigation were the lack of a reliable water source, little water control, and water-use conflicts. SRI was associated with a significantly higher grain yield of 6.4 t ha–1 compared with 3.4 t ha–1 from conventional practices. On SRI plots, grain yields were 6.7 t ha–1 for AWD irrigation, 5.9 t ha–1 with NF irrigation, and 5.9 t ha–1 for continuously flooded. The results of the study suggest that, by combining AWD irrigation with SRI cultivation practices, farmers can increase grain yields while reducing irrigation water demand. The System of Rice
Intensification in practice: explaining low farmer adoption and high disadoption
in Madagascar1 The System of Rice Intensification (SRI) has received a fair amount of attention in recent years both in and outside of Madagascar, where incredible yield increases have been achieved using few external inputs and less water and seed than conventional rice production systems. SRI initially seemed well suited to Madagascar because of the unavailability or high cost of fertilizer and the inability of most farmers to grow enough rice to feed their families. Despite the promise of this technology, farmer adoption of SRI in the areas where it was promoted has been low, “disadoption” (abandonment) of the method has been high, and those who continue to practice the method rarely do so on more than half of their land. To help explain this phenomenon from an economic perspective, a study was conducted in five communities in Madagascar in 2000, using both participatory research methods and a household survey of more than 300 farmers. Based on the study, we find that SRI is difficult for most farmers to practice because it requires significant additional labor inputs at a time of the year when liquidity to hire labor is low and family labor effort is already high. Thus, the poorer the farmers and the more their income depends on rainy-season crops, the less able they are to take advantage of the technology. The results point to the challenge facing researchers and policymakers concerned with the promotion of water-saving rice technologies: even when yields can be increased while saving water, adoption by farmers is still far from assured. Effects
of SRI practices on hybrid rice performance in Tamil Nadu, India
This paper describes a field experiment conducted in the wetlands of Tamil Nadu Agricultural University, Coimbatore, India, to test components of the System of Rice Intensification (SRI) using hybrid rice variety CORH2. The following four factors were studied: seedling age (14-d-old seedlings vs 23-d-old seedlings), irrigation (limited vs conventional), weeding (weeds incorporated with a conoweeder vs manual removal of weeds), and nutrient management (recommended amount of fertilizer with and without green manure). The experiment was a strip-plot design in four replicates. The results show savings in irrigation water of 56% and 50% using conventional and young seedlings, respectively, without a significant effect on grain yield. The average grain yield for the limited irrigation treatment (6,352 kg ha–1) was not significantly different from that of the conventional irrigation practice (6,461 kg ha–1). No significant main effect of seedling age and nutrient management was found. In situ incorporation of weeds increased yield significantly to 6,737 kg ha–1 compared with that of conventional weeding of 6,076 kg ha–1. A significant interaction was found among weeding, seedling age, and nutrient management. The highest yields for both conventional and limited irrigation conditions were obtained with a combination of young seedlings, green manure application, and incorporation of weeds using a conoweeder. This implies that our attempts to reduce water use in rice cultivation will have to be accompanied with a set of appropriate agronomic measures. System
of Rice Intensification (SRI): evaluation of seedling age and selected
components in Indonesia
Aerobic
rice in northern China: opportunities and challenges
Aerobic rice is a new way of cultivating rice that requires less water than lowland rice. It entails the growing of rice in aerobic soil, with the use of external inputs such as supplementary irrigation and fertilizers, and aiming at high yields. The main driving force behind aerobic rice is the increasing water scarcity, especially in northern China, which threatens the sustainability of lowland rice production. A group of first-generation elite aerobic rice varieties such as Han Dao 297, Han Dao 277, Han Dao 502, Han 58, Danjing 5, and Danjing 8 have been developed and released since the early 1990s. It is estimated that these varieties are currently grown on 140,000 ha in northern China, replacing traditional lowland rice in water-short irrigated areas and traditional upland crops (such as maize, soybean, cotton) in low-lying flood-prone areas. The adoption of aerobic rice is facilitated by the availability of efficient herbicides and seed-coating technologies. Case studies showed yields to vary from 4.5 to 6.5 t ha–1, which is about double that of traditional upland varieties and about 20–30% lower than that of lowland varieties grown under flooded conditions. However, the water use was about 60% less than that of lowland rice, total water productivity 1.6 to 1.9 times higher, and net returns to water use 2 times higher. Aerobic rice requires less labor than lowland rice and can be highly mechanized. Further developments of aerobic rice need to concentrate on continued breeding and the development of sustainable and farmer-acceptable crop management strategies. Yield
of aerobic rice (Han Dao) under different water regimes in North China
Lowland rice in Asia has relatively high water inputs. Because of increasing water scarcity, there is a need to develop alternative systems that require less water, especially in northern China, where water shortages are acute. “Aerobic rice” is high-yielding rice grown in nonpuddled aerobic soils under supplementary irrigation. Special aerobic rice varieties, called Han Dao, have been developed by the China Agricultural University. Field experiments began in 2001 to determine the yield potential of these varieties under different irrigation regimes. In one experiment, aerobic varieties Han Dao 297 (HD297) and Han Dao 502 (HD502) and lowland variety Jin Dao 305 (JD305) were grown in aerobic soil under five irrigation regimes. In a second experiment, the same varieties were grown under flooded lowland conditions. Under flooded lowland conditions, the total water input (irrigation plus rainfall) was about 1,400 mm. Lowland variety JD305 recorded the highest yield (8.8 t ha–1) and the yields of HD502 and HD297 were 6.8 and 5.4 t ha–1, respectively. Under aerobic conditions, the total water input varied from 470 to 644 mm. The aerobic varieties outyielded the lowland variety. With 470 mm water, HD297 yielded 2.5 t ha–1, HD502 3.0 t ha–1, and JD305 1.2 t ha–1; with 644 mm water, HD502 and HD297 yielded 5.3 and 4.7 t ha–1, respectively, while JD305 yielded 4.2 t ha–1. The water-use efficiencies of the aerobic varieties under aerobic conditions were 164–188% higher than that of the lowland variety under lowland conditions. Aerobic rice maximizes water use in terms of yield and is a suitable crop for water-limiting conditions. The
potential of aerobic rice to reduce water use in water-scarce irrigated lowlands
in the tropics
Water scarcity in Asia threatens the sustainability of traditional flooded lowland rice systems and ways must be sought to grow rice using less water. A promising new cropping system is “aerobic rice,” which is rice grown in nonflooded and nonpuddled soil using supplementary irrigation. In 2001, a field experiment was undertaken at the International Rice Research Institute to characterize the hydrology and compare the yield and water use of rice grown under aerobic and under flooded conditions, using different upland varieties and one hybrid rice variety. The aerobic plots were irrigated up to field capacity when soil water tension at 15-cm depth reached 30 kPa. Yields under aerobic conditions were 2.4–4.4 t ha–1, which were 14–40% lower than under flooded conditions. The total water input from transplanting to harvest was 650–830 mm under aerobic conditions and about 1,350 mm under flooded conditions. Because water use decreased relatively more than yield, water productivity under aerobic cultivation increased by 20–40% (in one case even 80%) over that under flooded conditions. The groundwater table was very shallow, being above the soil surface under flooded conditions and on average 53 cm deep in the dry season and 28 cm in the wet season under aerobic conditions. Because of this shallow water table and frequent rainfall, the soil water content in the aerobic plots in the wet season was mostly between saturation and field capacity. A successful change from flooded to aerobic rice production requires the breeding of special aerobic rice varieties and the development of appropriate water and crop management practices. Crop-water
responses of aerobically grown rice: preliminary results of pot experiments
Aerobic rice is a new technology to reduce water input in rice production. Two pot experiments were carried out at IRRI in 2001 to study the physiological water use (transpiration), growth, and yield formation of high-yielding upland rice grown under irrigated aerobic conditions. The treatments consisted of different combinations of flooded and aerobic conditions in the vegetative, reproductive, and grain-filling stages using two varieties and two soil types. Three levels of aerobic conditions were used: minimum allowed soil water potentials of –10, –30, and –70 kPa. In general, the highest yields were obtained under continuously flooded conditions. The introduction of aerobic phases reduced physiological water use, biomass, and yield. Under continuously aerobic conditions, yield reductions were 34–74%. There was no relationship between the magnitude of yield reduction and soil water potential reached in the aerobic phase. The reduction in yield can be minimized, and water productivity maximized, by “smart” water management. Yield reductions in clay soil were only 2–6% under aerobic conditions with flooding in the reproductive phase and 8–12% under continuous flooding with aerobic conditions in the reproductive phase. In the clay-loam soil, the yields under such aerobic-flooded combinations were even higher than under continuous flooding. Water productivity was highest under aerobic conditions with flooding during the reproductive phase (values up to 0.96–1.24 g L–1, with no demonstrated effect of level of soil water potential). The second highest water productivities were obtained under continuous flooding with aerobic conditions during the reproductive stage, with values of 0.81–0.95 g L–1. The
ground-cover rice production system (GCRPS): a successful new approach to save
water and increase nitrogen fertilizer efficiency
To evaluate a new production technique for rice, the so-called ground-cover rice production system (GCRPS), three field experiments were started in 2001 at three locations (Beijing, Nanjing, and Guangzhou) representing a wide range of environmental and agricultural conditions. Within these experiments, water balance (precipitation/irrigation, surface runoff, leaching, evaporation, and evapotranspiration), nitrogen balance (plant uptake, leaching, N2O and NH3 emissions), and greenhouse gas emissions (N2O and CH4) were determined. Preliminary data demonstrate that the GCRPS reduced water demand by up to 60% and increased water-use efficiency by 54% in Beijing. Yields under the GCRPS were 11–31% lower than in paddy rice. Lower soil water content during the tillering period and deficiency of nitrogen and microelements might be responsible for these lower yields (particularly in Beijing). Nitrogen fertilizer-use efficiency (isotope 15N method and difference method) was lower in the GCRPS treatments than in the paddy rice system. However, pot experiments indicate a substantial improvement of 10–20% in the very low nitrogen-use efficiency of 20–40%, which is frequently reported for paddy rice. Saving
water with ground-cover rice production systems (GCRPS) at the price of
increased greenhouse gas emissions
Greenhouse gas emissions of two water-saving ground-cover rice production systems (GCRPS) and a conventional flooded rice (Oryza sativa L.) production system were compared in three field experiments in China. In combination with reduced irrigation, plastic film (0.014 mm) and straw soil covers were evaluated in three major water-scarce lowland rice production regions in northern (Beijing), eastern (Nanjing), and southern China (Guangzhou, late rice). In all three regions, first results showed a pronounced effect of altered water management on greenhouse gas emissions. CH4 emissions from GCRPS were low at all locations. The exception was Guangzhou, where heavy rainfall raised soil water contents during early growth and induced high initial CH4 emissions. N2O emissions were adversely affected by GCRPS. With both cover materials, increased N2O emissions were measured and these emissions were closely linked to N fertilization events. With respect to the different global-warming potentials of CH4 and N2O, the importance of CH4 declined and N2O became the most important greenhouse gas in this first experiment. Overall, a small increase in the contribution to global-warming can be expected. Within the ongoing project, management of nitrogen fertilizer will be optimized for good rice yield and to mitigate N2O emissions. Adopting
conservation agriculture in the rice-wheat system of the Indo-Gangetic Plains:
new opportunities for saving water
Agricultural policy in the 1960-70s focused on achieving food security through increased coverage of high-yielding varieties, expansion of irrigation, and increased use of external inputs. This enabled rice-wheat to emerge as a major cropping system in the Indo-Gangetic Plains (IGP), ushering in the "Green Revolution" (GR). GR technologies have remained the cornerstone of the South Asian strategy for food security, rural development, conservation of natural resources, and poverty alleviation. Evidence is now appearing that the rice-wheat system has weakened the natural resource base. The growing realization that agriculture of the post-Green Revolution era will be guided by the need to produce more better-quality food from more marginal-quality land and water resources, besides sustaining environmental quality, only adds to the challenge. Thus, the major challenge for the Rice-Wheat Consortium countries is to develop a rice-wheat system that produces more at less cost and improves profitability and sustainability. This suggests that agriculture in consortium countries needs an infusion of new technologies that are able to tap new sources of productivity growth and are more sustainable. On the basis of driving variables for agricultural development, the IGP have been delineated into five relatively homogeneous transects to address location-specific rice-wheat system ecology problems. Thematic issues of crop improvement, water management, nutrient management, weed and pest management, and policy research are integrated with crop establishment and tillage, which are at the center of all agronomic and crop management practices developed for the RW system ecology within each transect for sustained production, diversification, and enhanced system productivity. This paper will describe in a matrix the relative potential of improved technologies, particularly in relation to water savings and water-use efficiency. Crop-water
relations in rice-wheat cropping under different tillage systems and
water-management practices in a marginally sodic, medium-textured soil
Management of resources and sustainability of the rice-wheat cropping system have become a matter of concern in South Asia, especially where water is increasingly scarce. New soil and water management technologies, such as aerobic cultivation of rice on raised beds or on flat nonpuddled land, and zero-tillage in wheat, are rapidly emerging. This paper reports on a field experiment carried out at Modipuram, Uttar Pradesh, India, to study some of these new technologies. Rice (Pro-agro 6111) was direct-seeded on raised beds and on flat land and grown under two aerobic water regimes: (1) irrigation was applied when the soil water tension at 15-cm depth reached 10 kPa or (2) when it reached 20 kPa. The control was continuously flooded transplanted rice. Wheat (BPW 343) was sown after rice using five tillage practices: conventional tillage, zero-tillage with or without controlled traffic, zero-tillage with paired-row planting, and bed-planting (same beds as used for rice). Flooded transplanted rice and conventionally tilled wheat gave the highest yields. With irrigation at 10 or 20 kPa soil water tension, bed-planted rice reduced water input by 45–51% but lowered yield by 52–53% compared with transplanted rice, whereas dry-seeded rice on flat land reduced water input by 51–57% and lowered yield by 36–46%. Zero-tilled wheat with controlled traffic gave yields similar to those of conventional wheat and had the same water use. More study is needed to understand the effect of aerobic rice on flat land or on raised beds, and of wheat under zero-tillage, on soil properties, crop productivity, and water use. Effects
of rice establishment methods on crop performance, water use, and mineral
nitrogen
To mitigate the increasing water scarcity in Asia, new ways of growing rice need to be developed that use less water than conventional lowland rice. An experiment was conducted in New Delhi, India, to evaluate the yield and water use of rice established by different methods: transplanting, wet seeding, and dry seeding with subsequent aerobic soil conditions on flat land and on raised beds. Transplanted rice yielded 5.5 t ha–1 and used 360 mm of water for wet-land preparation and 1,608 mm during crop growth. Compared with transplanted rice, dry-seeded rice on flat land and on raised beds reduced total water input during crop growth by 35–42% when the soil was kept near saturation, and by 47% and 51% when the soil dried out to 20 and 40 kPa moisture tension in the root zone, respectively. Most of the water savings were caused by reduced percolation losses. Moreover, no irrigation water was used during land preparation. However, the dry seeding of rice reduced yield by 23–41% on flat land and by 41–54% on raised beds compared with transplanted rice. There were no large differences in water productivity among treatments. In the topsoil, nitrogen occurred relatively more as ammonium under flooded transplanted and flooded wet-seeded conditions and as nitrate under dry-seeded aerobic conditions. The dry seeding and subsequent aerobic growing of rice face several potential yield-reducing factors that need to be studied further: micronutrient deficiency (iron), nematode and weed infestation, and proper cultivar development. When grown on raised beds, the variety needs to be able to compensate for the loss in cropped area (caused by the relatively large row spacing between the beds) by producing more productive tillers. Physiological
characterization of rice grown under different water management systems
In a cement-box experiment in Nanjing (China), production characteristics, water-use efficiency, nitrogen-use efficiency, and the major physiological characteristics of three alternative water management practices—the System of Rice Intensification (SRI), plastic ground-cover system (PGS), and intermittent irrigation system (IIS)—were compared with a conventional flooded rice system (CK). In addition, the effect of two nitrogen levels (150 and 300 kg ha–1) was studied. Water supply in SRI and IIS was 46% and 36% lower than in CK, respectively, whereas their yields were similar or significantly higher, 5% (SRI at 150 kg N ha–1) and 8% (IIS at 300 kg N ha–1), resulting in greater water-use efficiency and nitrogen-use efficiency. The higher yields of SRI and IIS compared with CK were associated with higher harvest indices but not with differences in total biomass production. Water supply and yield in PGS were 65% and 62% lower than in CK, respectively. At jointing stage, leaf photosynthesis, transpiration rate, and stomatal conductance decreased with reduced water input. High nitrogen levels increased leaf photosynthesis and transpiration rate in IIS, SRI, and PGS more than in CK. At heading, leaf-soluble sugar, nonprotein nitrogen content, and nitrate reductase activity were higher in IIS, SRI, and PGS than in CK. Nitrogen uptake in SRI and IIS was similar to that in CK, but nitrogen redistribution from the vegetative organs to grain was larger than that in CK. High nitrogen levels increased water-use efficiency and decreased nitrogen-use efficiency in all water treatments. Requirements
for aerobic rice: physiological and molecular considerations
Developing
and testing rice varieties for water-saving systems in the tropics
The principal breeding target environments for water-saving systems are likely to be (1) near-saturated (NS) systems, in which rice is grown in nonflooded fields where soils are usually kept saturated, but occasionally dry to field capacity or below; (2) aerobic systems where rice is direct-seeded in nonpuddled, nonflooded fields in which soil moisture status is usually at or below field capacity. There is evidence that selection can be effective in both regimes, and that the requirement for a separate screening program for any irrigation regime is closely related to the difference in mean yield between the new target regime and standard management. NS systems are likely to exhibit only slight yield reductions relative to conventionally irrigated management and are therefore unlikely to require cultivars that are radically different from current elite irrigated varieties. The most efficient strategy for identifying cultivars for NS systems is therefore to screen short-duration, elite irrigated varieties under NS management to eliminate cultivars that are particularly susceptible to episodes of soil drying. Aerobic systems, which produce mean yields intermediate to those of irrigated and conventional upland management, are likely to require cultivars that have been selected from early generations under high-input aerobic management to produce genotypes that combine moderate tolerance of moisture stress with high harvest index and lodging resistance. Cultivars that perform well under aerobic management usually contain germplasm from both traditional upland and elite irrigated parents, but some cultivars without elite irrigated high-yielding variety parentage and some developed for irrigated systems also produce high yields in aerobic systems. Field-level
water savings in the Zhanghe Irrigation System and the impact at the system
level
The demand for freshwater from cities, industries, and environmental uses is growing rapidly throughout Asia. Less water will be available for agriculture and for rice in most places, yet more rice will be needed to feed a growing population. The per capita freshwater availability in China is among the lowest in Asia and it is becoming increasingly difficult to develop new freshwater sources. Much of the water will have to come from water savings—and rice, a water-intensive crop, is a major target for such savings. On-farm water-saving practices, such as alternate wet and dry irrigation (AWDI), have been developed to reduce irrigation application requirements and to improve growing conditions, thereby increasing yield. However, the question is, If these practices have led to “real” water savings, which can be transferred to other agricultural and nonagricultural uses? This paper explores water savings and water productivity on different scales to see if and how field-scale interventions scale up to subbasin-scale water savings in the Zhanghe Irrigation District (ZID) in Hubei Province, Central China. To study water savings and effects on different scales, the water-accounting procedure developed by IWMI was considered at four different spatial scales ranging from field to ZID. Results show that at the field level, the water productivity per unit of irrigation water was much higher under AWDI than under the traditional methods because of lower irrigation water input. Farmers put much effort into making full use of irrigation water and rainfall. Moving up the scales, other land uses gain more importance. Apparently, a certain size of scale is needed to have an impact from reuse of water, which becomes evident only at the main canal command scale, where the water productivity per unit of irrigation increased dramatically and almost all water is used within the domain. It becomes clear that the ZID, with its possibilities of capturing rainfall and runoff in all the reservoirs with the system, is very effective in capturing and using water for productive use. The scope for additional real water savings in the Zhanghe Irrigation District is limited. Only 12% of the combined rainfall and irrigation water releases flow out of the basin. A further reduction in drainage outflow from the ZID may have negative downstream effects. The results clearly indicate that scale effects are important for understanding and planning for water savings and water productivity. Modeling
approaches to quantify the water balance in groundwater-dominant irrigation
systems: an example of Rechna Doab, Pakistan
Irrigated agriculture in alluvial basins is characterized by high seepage losses from rivers, channels, and irrigated fields to the aquifer systems. Water accounting at the farm or management unit level tends to underestimate the productive use of water since losses from the supply system can be reused for irrigation through downstream groundwater pumping. However, pumping can mobilize poor-quality groundwater and can cause an overall loss of good-quality water supplies. Increased groundwater pumping also increases seepage losses from irrigation channels and watercourses. This situation requires an understanding of spatial and temporal variation of surface-water and groundwater interactions and salt movements under variable scenarios of surface-water availability. This paper describes details of hydrological studies in the Rechna Doab basin, Punjab, Pakistan. The basin has 3 million ha, of which 2.3 million ha are cultivated land with rice, cotton, and fodder crops dominating in the summer and wheat and fodder in the winter. A top-down nodal network was developed to determine the irrigation water balance for individual administrative units. The spatial groundwater recharge estimates obtained from the nodal network were used to check the water balance estimates from a more distributed bottom-up approach. The bottom-up approach used a distributed dynamic model that simulated surface-water and groundwater interactions at the desired level of interest. The distributed nature of the surface-groundwater interaction model enabled a performance assessment of individual administrative units by taking into account downstream beneficial use and quality variation of lost surface water. This water and salt balance approach highlighted the need for integrated management of surface water and groundwater from the administration unit to the basin level. Options
for regional water savings and reallocation
Water savings at the micro level, constituting a reduction in evaporation and percolation losses and/or an improved matching of water supply and demand, are only effective if the savings at one place and time can be reallocated at a different time and/or different place to a different user. The regional configuration of the water resources system and the way it is managed strongly determine the possibilities for reallocation and thus the overall effectiveness of water savings. An overview is presented of different water supply systems and the role of operational management in the potential to save and effectively reallocate water. The concepts are further illustrated with simulations for the complex Citarum River basin (Indonesia). The tests for this basin demonstrate that savings in irrigation water supply through demand management and operational management are very promising for systems with a large irrigation component. Such measures can strongly contribute to an effective use of scarce water resources. The
effects of pumping on water use and profitability in dry-season rice: a case
study in UPRIIS, Philippines
| Farmers in many parts of Asia are increasingly using pumps to irrigate their rice crops. This has occurred because pumps have become less expensive and because of an increased scarcity of gravity-flow surface water. One such system is the Upper Pampanga River Integrated Irrigation System in Nueva Ecija, Philippines, where this study was conducted. In spite of the high cost of pumping water, pump users in our survey still received a substantial amount of farm profits from rice production, although less than those with good access to a surface gravity system. There are no significant differences in yields or input use between farms irrigated by pumps and the surface gravity system, with the exception of water use. Farms that rely on pumping irrigate fewer times and have a lower degree of flooding. Land rents are higher for farms with good access to gravity-flow water compared with farms that rely heavily on pumping. It is important to note that the findings of this study are applicable only to this specific site, especially since rice prices are substantially higher in the Philippines than in neighboring countries. Additional studies on the economic and water management effects of pumping in different parts of Asia would provide useful information. Estimation
of spatially distributed evapotranspiration through remote sensing: a case study
for irrigated rice in the Philippines
Water for agriculture in Asia is
increasingly scarce and ways must be sought to optimize the use and efficiency
of irrigation systems, especially in water-consuming irrigated rice systems.
This requires an understanding of the water balance at different spatial scales
of the irrigation system. An important component of the water balance is actual
evapotranspiration (ETa).
This paper reports on the use of remote sensing to estimate spatially
distributed ETa from
irrigated rice in the Upper Pampanga River Integrated Irrigation System (UPRIIS)
in Central Luzon, Philippines. The surface energy balance algorithm for land (SEBAL)
was used to compute ETa from three Landsat 7 ETM+ images acquired during the second
part of the crop growth period in the dry season of 2001. Ground-truth data for
the calibration of SEBAL were obtained during satellite overpass.
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Effects of different water management practices on rice growth |
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