David Dawe

How extensive are yield declines in long-term rice–wheat experiments in Asia?

The rice–wheat cropping system, occupying 24 million hectares of the productive area in South Asia and China, is important for food security. Monitoring long-term changes in crop yields and identifying the factors associated with such changes are essential to maintain and/or improve crop productivity. Long-term experiments (LTE) provide these opportunities. We analyzed 33 rice–wheat LTE in the Indo-Gangetic Plains (IGP) of South Asia, non-IGP in India, and China to investigate the extent of yield stagnation or decline and identify possible causes of yield decline. In treatments where recommended rates of N, P and K were applied, yields of rice and wheat stagnated in 72 and 85% of the LTE, respectively, while 22 and 6% of the LTE showed a significant (P<0.05) declining trend for rice and wheat yields, respectively. In the rice–wheat system, particularly in the IGP, rice yields are declining more rapidly than wheat. The causes of yield decline are mostly location-specific but depletion of soil K seems to be a general cause. In over 90% of the LTE, the fertilizer K rates used were not sufficient to sustain a neutral K input–output balance. Depletion of soil C, N and Zn and reduced availability of P, delays in planting, decreases in solar radiation and increases in minimum temperatures are the other potential causes of yield decline. A more efficient, integrated strategy with detailed data collection is required to identify the specific causes of yield decline. Constant monitoring of LTEs and analysis of the data using improved statistical and simulation tools should be done to unravel the cause–effect relationships of productivity and sustainability of rice–wheat systems.

Rice yields in tropical/subtropical Asia exhibit large but opposing sensitivities to minimum and maximum temperatures

Data from farmer-managed fields have not been used previously to disentangle the impacts of daily minimum and maximum temperatures and solar radiation on rice yields in tropical/subtropical Asia. We used a multiple regression model to analyze data from 227 intensively managed irrigated rice farms in six important rice-producing countries. The farm-level detail, observed over multiple growing seasons, enabled us to construct farm-specific weather variables, control for unobserved factors that either were unique to each farm but did not vary over time or were common to all farms at a given site but varied by season and year, and obtain more precise estimates by including farm- and site-specific economic variables. Temperature and radiation had statistically significant impacts during both the vegetative and ripening phases of the rice plant. Higher minimum temperature reduced yield, whereas higher maximum temperature raised it; radiation impact varied by growth phase. Combined, these effects imply that yield at most sites would have grown more rapidly during the high-yielding season but less rapidly during the low-yielding season if observed temperature and radiation trends at the end of the 20th century had not occurred, with temperature trends being more influential. Looking ahead, they imply a net negative impact on yield from moderate warming in coming decades. Beyond that, the impact would likely become more negative, because prior research indicates that the impact of maximum temperature becomes negative at higher levels. Diurnal temperature variation must be considered when investigating the impacts of climate change on irrigated rice in Asia.

Do organic amendments improve yield trends and profitability in intensive rice systems

Opinions differ as to the importance of organic amendments (OA) for sustaining crop productivity in the intensive, irrigated rice systems of Asia. Our objectives were to (1) quantify the effects of farmyard manure (FYM) and straw incorporation on yield trends in long-term experiments (LTEs) with rice–rice (R–R) (Oryza sativa L.) and rice–wheat (R–W) (Triticum aestivum L.) systems and (2) assess the potential effects of OA on profitability, taking into account long-term effects on yield. We analyzed yield trends in 25 LTE (seven R–R, 18 R–W systems) across a wide geographical range in Asia. Three main conclusions emerged from this analysis. First, application of either manure or straw did not improve grain yield trends in R–R and R–W cropping systems. Second, depending on socio-economic conditions, use of manure or straw in these cropping systems may be profitable, provided these OA are used as a complement to a recommended dose of inorganic NPK (i.e. organic materials should not be used as the primary nutrient source). Third, current experimental designs to assess the suitability of OA need to be improved in order to allow a better comparison of the relative advantages of inorganic and organic fertilizers. The major shortcoming of current designs is that they do not properly adjust mineral fertilizer rates in the inorganic treatments to account for the macronutrient input from OA. Thus, our tentative estimates of the profitability of OA may be overstated.

Golden rice: what role could it play in alleviation of vitamin A deficiency?

Abstract Golden rice (GR) is a new rice variety that has been genetically modified to contain beta-carotene, a source of vA. This modification was undertaken as a strategy to address VAD, which is widespread in less developed countries of Asia. Children’s food intake data from a poor rural region of the Philippines are used to simulate the potential impact of GR on vA intake. The potential impact, coverage of deficient subpopulations, and costs of GR are compared to two other interventions, food fortification and supplementation. While investments in future development of GR compare favorably with other interventions in terms of costs and coverage, GR would deliver amounts of vA that are modest, and unlikely to fulfill requirements. Thus, it should be viewed as a complement to existing interventions. To have greatest impact at a cost comparable with wheat fortification, GR varieties should be suited for widespread adoption in Asia and should deliver as much beta-carotene as possible.

The changing structure of the world rice market, 1950–2000

Abstract The world rice market has been unstable for much of its post-world war II history, with prices volatile and the availability of supplies uncertain. These characteristics, exemplified by the world food crisis of the mid-1970s, influenced domestic price and production policies in a number of Asian countries. However, the structure of the world rice market has evolved and changed during the past 50 years. This paper identifies three distinct phases in the history of the market based on trends in the level and stability of production and the trade orientation of major exporters. The level and stability of production increased steadily over the entire period. Exporters have generally been active in the world market, with the period 1965–1981 being an important exception. Since the mid-1980s, prices have been low and quite stable, and the patterns identified in the paper suggest that prices will remain so in the future. The policy implication is that Asian rice importers can afford to rely more on the world market than was warranted in the past.

Increasing Water Productivity in Rice-Based Systems in Asia–Past Trends, Current Problems, and Future Prospects

Abstract Rice is the largest user of water in Asia, probably accounting for more than half of irrigation water withdrawals. Two key trends in the Asian rice economy that may be affecting water productivity are the rapid spread of pump irrigation and direct seeding. The number of pumps has grown exponentially in Bangladesh and Vietnam, and pump irrigation now dominates gravity irrigation in many countries. Direct seeding accounts for about one-fifth of the rice area in Asia, but this share is increasing. Comparing water productivity values is difficult across space and time; in general, it is more relevant across time. Water productivity has increased over time in several selected systems, primarily due to increased yields of modern varieties and improved management of large-scale water flows. There is less evidence that improved field-level water management has led to increased water productivity, although this may have also contributed. The extent to which agricultural water scarcity will affect poverty in Asia depends crucially on how well societies will be able to create incentives for users to save scarce water, thus facilitating the adoption of new technologies. Because of the rapid spread of pumps, incentives to save water in rice cultivation are growing. Even for gravity-flow surface water, new institutions are developing in China that promise to improve incentives. International trade in agricultural products, or trade in“virtual water,” may also have a role to play and should be encouraged.

How far down the path to free trade? The importance of rice price stabilization in developing Asia

Abstract International trade agreements are pushing the world in the direction of free trade. But price stabilization, which is inconsistent with completely free trade, remains important in developing Asia because of the large share of rice in economic output. A policy of pure price stabilization for rice, without consistent protection (either subsidization or taxation), can help to create the macroeconomic stability that is essential for sustained rapid economic growth by increasing the quantity and efficiency of investment throughout the economy. Pure price stabilization can also generate significant equity gains by protecting poor consumers and farmers from sharp fluctuations in prices. While domestic commodity price stabilization schemes have a checkered history around the world, the experience of Asian countries in stabilizing rice prices offers more scope for optimism. Asian governments have been generally successful in stabilizing rice prices, and there are several instances where this has been accomplished without sustained protection of either consumers or farmers. However, there is room for improved stabilization mechanisms that would lower the costs of intervention.

Economics of water productivity in managing water for agriculture

In Kijne, J. W.; Barker, R.; Molden. D. (Eds.). Water productivity in agriculture: limits and opportunities for improvement. Wallingford, UK: CABI; Colombo, Sri Lanka: International Water Management Institute (IWMI)Comprehensive Assessment of Water Management in Agriculture Series 1

Iron supplementation compliance among pregnant women in Bicol, Philippines

OBJECTIVE To quantify factors influencing iron supplementation compliance and haemoglobin (Hb) concentrations among pregnant women participating in an iron supplementation programme under routine field conditions. DESIGN Cross-sectional interviews and Hb measurements. SETTINGS Albay and Sorsogon provinces, Bicol, Philippines. SUBJECTS Three hundred and forty-six pregnant women receiving iron supplements via the Philippine iron supplementation programme. RESULTS Women had a mean Hb concentration of 10.75 +/- 1.43 g dl-1, and 56.4% were anaemic (Hb < 11.0 g dl-1). On average, the first prenatal visit occurred at nearly 4 months (3.80 +/- 1.56). The ratio of visits to number of months pregnant was 0.51 +/- 0.24. Self-reported consumption of pills received was 85% (0.85 +/- 0.23), although pill counts suggested that consumption was 70% (0.70 +/- 0.35). Using multiple regression, an earlier first prenatal visit and greater self-reported compliance were positively associated with Hb concentrations. Additionally, perceived health benefits from taking the supplements and higher health programme knowledge were positively associated with pill consumption, while experiencing side-effects and disliking the taste of the supplements were associated with lower pill consumption. A greater number of living children was negatively associated with the frequency of prenatal visits. The number of children was also directly negatively associated with Hb concentrations. CONCLUSIONS Compliance was positively related to Hb concentrations. Several factors associated with greater compliance were identified, including marital status, number of children, health programme knowledge, side-effects, perceived health benefits, and dislike of taste. Some of these factors may serve as avenues for interventions to increase compliance, and ultimately Hb concentrations.

The impact of on-farm water saving irrigation techniques on rice productivity and profitability in Zhanghe Irrigation System, Hubei, China

To optimize the use of limited water resources, surface irrigation systems in parts of China have introduced a new water saving irrigation method for rice termed alternate wetting and drying (AWD). The basic feature of this method is to irrigate so that the soil alternates between periods of standing water and damp or dry soil conditions from 30 days after crop establishment up to harvesting. However, many Chinese rice farmers still practice the continuous irrigation method with late- season drying of the soil.A comparative assessment of these two methods of on-farm water management for rice was conducted at two sites within the Zhanghe Irrigation System (ZIS) in Hubei province of China for the 1999 and 2000 rice crops. The objective was to evaluate the impact of AWD on crop management practices and the profitability of rice production. In conjunction with irrigation district officials, two sites within ZIS were selected for study, one where AWD was supposed to be widely practiced (Tuanlin, TL) and one where it had not been introduced (Lengshui, LS). It was found that farmers at both sites do not practice a pure form of either AWD or continuous flooding. However, farmers in TL did tend to let the soil dry more frequently than their counterparts in LS.Because most farmers practice neither pure AWD nor pure continuous flooding, an AWD score was developed that measures the frequency with which farmers allow their soil to dry. This AWD score was not significantly correlated with yield after controlling for site and year effects and input use. AWD scores were also not correlated with input use. We conclude that AWD saves water at the farm level without adversely affecting yields or farm profitability.