Rainfed Rice Production Research Articles

Delay of heading date as an index of water stress in rainfed rice in mini-watersheds in Northeast Thailand

Drought is recognized as a primary constraint for rainfed rice production. In this study, the spatial distribution of heading date of rainfed rice and its relation to field water conditions were investigated for 2 years in mini-watersheds called Nong in Northeast Thailand, in order to clarify the toposequential variation in the degree of water stress of rice. Although the difference in the relative field elevation in the mini-watersheds was only a few meters, the water availability in terms of standing water and soil moisture markedly decreased with ascending elevation. Rice cultivars, KDML 105 and RD 6, the two dominant genotypes in Northeast Thailand, reached the heading stage at nearly the same day in the absence of water stress, independent of transplanting or seeding date under customary management. As the water availability decreased with ascending field elevation, the heading date of rice was markedly delayed. The delay seemed to be related to the cumulative water stress before heading of rice. The rice harvest index and yield at farmers’ fields decreased linearly with the delay of heading. The observed toposequential distribution of heading date indicated that quite severe water stress was imposed in the uppermost fields of the mini-watersheds, while practically no water stress occurred in the lower fields, at least in the lower half of the mini-watersheds. These results suggest that the delay of heading is a good index for rice water stress in rice in Northeast Thailand and can be applicable to field classification with respect to drought risk.

Simulation model of rainfed rice production on sloping land in northeast Thailand

In northeast Thailand, the rapid expansion of rainfed paddy fields has decreased the stability of rice production. This paper describes a model that computes rice production on the basis of the hydrologic conditions of rainfed paddy fields on hill slopes. The model well expressed the hydrologic processes, rice yield, and production at the study site. We simulated rice production as uphill paddy plots are abandoned, increasing catchment area, under various rainfall conditions. The simulation showed that rice yield and stability increase as uphill plots are abandoned, although the total rice production decreases. Thus, the effect of catchment size on rice production in each plot was quantified. The model proved to be useful for analyzing rainfed rice production under various land and water conditions.

Toposequential Variation in Soil Fertility and Rice Productivity of Rainfed Lowland Paddy Fields in Mini-Watershed (Nong)in Northeast Thailand

Mini-watersheds called Nongin Thai are geographical components of rainfed lowland rice culture in Northeast Thailand, and constitute distinct units in understanding environmental constraints for low and unstable rainfed rice production there. The toposequential variation of soil fertility and its relation to rice productivity within mini-watersheds, was examined by phytometry of sampled soils and field measurements of rice growth and yield. The phytometry experiment with irrigated potted rice using soils sampled from various rice fields within each mini-watershed, revealed that soil fertility as evaluated by rice dry matter production showed a 5 times difference among the fields at most. The difference in the soil fertility was ascribed primarily to that in nitrogen (N) supply capacity, which itself had a strong correlation with soil organic carbon (SOC) content. Accordingly, the biomass production of pot-grown rice was proportional to SOC. content, which suggested the usefulness of SOC as an index for soil fertility evaluation. The effect of clay on the soil fertility was much less than that of SOC. The actual rice yield in each field also showed quite large field-to-field variation, most of which was explained by the SOC content, rice growth duration and fertilizer application rate even though water availability also affected the yield. The yield positively correlated with growth duration and hence with earlier transplanting. Both SOC and clay contents of fields showed steep gradients with ascending field elevation within mini-watersheds, resulting in a marked toposequential distribution of rice yield. The toposequential distributions of SOC and clay contents imply that rice culture after deforestation accelerated soil erosion from upper to lower fields. The large toposequential gradient in soil fertility requires different resource and crop management for each toposequential position, in order to improve rice productivity of the mini-watershed as a whole.

Risk Assessment of Herbicide-Resistant Crops: A Latin American Perspective Using Rice (Oryza sativa) as a Model1

Herbicide-resistant crops (HRCs), particularly glyphosate-resistant soybean, are increasingly important in Latin America. Prior to commercial release of these crops, their short- and long-term risks should be thoroughly assessed. A risk assessment should include the identification and characterization of potential hazards and an estimation of the likelihood of these hazards occurring. For HRCs the agro-ecological hazards are mostly related to the occurrence of herbicide-resistant (HR) weeds and crop volunteers and the adverse effects from the use of pesticides within the agricultural area. Herbicide-resistant rice is used as a case study to visualize the key components of such a risk assessment. For this purpose, a model that simulates a typical rain-fed rice production system in Central America was developed. The model was used to investigate the selection of HR weedy rice populations under various scenarios. Scenarios included contrasting weed management practices, hybridization levels between the comme...

Variation in root penetration ability, osmotic adjustment and dehydration tolerance among accessions of rice adapted to rainfed lowland and upland ecosystems

AbstractDrought is the major constraint limiting rainfed rice production. The ability of rice roots to penetrate compacted soils and therefore to increase water extraction capacity, osmotic adjustment and dehydration tolerance of leaves enables the plant to tolerate drought. Experiments were conducted to determine the extent of genetic variation in root penetration index, osmotic adjustment and dehydration tolerance among indica accessions adapted to rainfed lowlands as well as traditional varieties from rainfed uplands. Root penetration index was evaluated in a system using wax–petrolatum layers to simulate soil compaction. Osmotic adjustment and dehydration tolerance were studied under slow development of water stress. Substantial genetic variation was found for root penetration index, osmotic adjustment and dehydration tolerance among indica ecotypes from lowlands, and the study of several traditional varieties from uplands showed variation in root penetration index and related root traits. An indica accession, IR58821‐23‐B‐1‐2‐1 had a high root penetration index of 0.38. The accessions, IR61079‐33‐1‐2‐2‐3, IR62266‐42‐6‐2 and IR63919‐38‐B‐1 had high osmotic adjustment capacities (1.91, 1.90 and 1.78 MPa, respectively); IR61079‐33‐1‐2‐2‐3 also had high dehydration tolerance. Good osmotic adjustment and dehydration tolerance were associated with poor root system. The traditional varieties ‘Kallurundaikar’ and ‘Norungan’ had higher root penetration indices (0.46 and 0.43, respectively), than even the japonica accessions. The study identified indica accessions and traditional varieties with superior root‐ and shoot‐related drought resistance traits that could be used in breeding for drought resistance in rice.

Rice responses to drought under carbon dioxide enrichment. 2. Photosynthesis and evapotranspiration

Future climate change is projected to include a strong likelihood of continued increases in atmospheric carbon dioxide concentration ([CO2]) and possible shifts in precipitation patterns. Due mainly to uncertainties in the timing and amounts of monsoonal rainfall, drought is common in rainfed rice production systems. The objectives of this study were to quantify the effects and possible interactions of [CO2] and drought stress on rice (Oryza sativa, L.) photosynthesis, evapotranspiration and water‐use efficiency. Rice (cv. IR‐72) was grown to maturity in eight naturally sunlit, plant growth chambers in atmospheric carbon dioxide concentrations [CO2] of 350 and 700 μmol CO2 mol–1 air. In both [CO2], water management treatments included continuously flooded controls, flood water removed and drought stress imposed at panicle initiation, anthesis, and both panicle initiation and anthesis. Potential acclimation of rice photosynthesis to long‐term [CO2] growth treatments of 350 and 700 μmol mol–1 was tested by comparing canopy photosynthesis rates across short‐term [CO2] ranging from 160 to 1000 μmol mol–1. These tests showed essentially no acclimation response with photosynthetic rate being a function of current short‐term [CO2] rather than long‐term [CO2] growth treatment. In both long‐term [CO2] treatments, photosynthetic rate saturated with respect to [CO2] near 510 μmol mol–1. Carbon dioxide enrichment significantly increased both canopy net photosynthetic rate (21–27%) and water‐use efficiency while reducing evapotranspiration by about 10%. This water saving under [CO2] enrichment allowed photosynthesis to continue for about one to two days longer during drought in the enriched compared with the ambient [CO2] control treatments.

Rice responses to drought under carbon dioxide enrichment. 1. Growth and yield

Projections of future climate change include a strong likelihood of a doubling of current atmospheric carbon dioxide concentration ([CO2]) and possible shifts in precipitation patterns. Drought stress is a major environmental limitation for crop growth and yield and is common in rainfed rice production systems. This study was conducted to determine the growth and grain yield responses of rice to drought stress under [CO2] enrichment. Rice (cv. IR‐72) was grown to maturity in eight naturally sunlit, plant growth chambers in atmospheric carbon dioxide concentrations [CO2] of 350 and 700 μmol CO2 mol–1 air. In both [CO2], water management treatments included continuously flooded (CF) controls, flood water removed and drought stress imposed at panicle initiation (PI), anthesis (ANT), and both panicle initiation and anthesis (PI & ANT). The [CO2] enrichment increased growth, panicles plant–1 and grain yield. Drought accelerated leaf senescence, reduced leaf area and above‐ground biomass and delayed crop ontogeny. The [CO2] enrichment allowed 1–2 days more growth during drought stress cycles. Grain yields of the PI and PI & ANT droughts were similar to the CF control treatments while the ANT drought treatment sharply reduced growth, grain yield and individual grain mass. We conclude that in the absence of air temperature increases, future global increases in [CO2] should promote rice growth and yield while providing a modest reduction of near 10% in water use and so increase drought avoidance.

On-farm rainwater and crop management for improving productivity of rainfed areas

Scarcity of water is a critical limitation to adoption of modern technology for increasing productivity of traditional rainfed rice growing areas of eastern Madhya Pradesh, India. The shortage of water results from uneven distribution of rains, significant gaps between rain events and field water losses rather than from low seasonal or annual rainfall totals. A feasible strategy to alleviate this limitation is to harvest excess rainwater in a farm pond during the wet season and use the conserved water for crop production in both wet (as insurance against drought) and dry seasons by adopting suitable crop and cropping systems. The results of water balance in a 1.05 ha field, on which a farm pond was built using 0.09 ha area, showed that 28–37% of seasonal rainfall was available as surface runoff from microcatchment (0.66 ha growing soybean, peanut and pigeonpea) for collection in the pond. This was sufficient for saving rice in a 0.30 ha area (in the lower side of the field) from drought stress, and for establishment of chickpea and mustard (in 0.90 ha) in the post-rainy season after harvest of rainy season crops. Soybean, peanut and pigeonpea, grown in the microcatchment during the rainy season, utilized respectively 371–726, 364–733 and 535–920 mm water in evapotranspiration (E,) and deep percolation (P). Rice grown below the pond required 28–317 mm water in different seasons to save the crop from in-season drought stress which commonly occurred during vegetative and reproductive stages. Water requirement (E, + P) of rice was 816–1342 mm in different seasons. Residual soil moisture after rainy season soybean, peanut and rice was sufficient (172–203 mm) to support post rainy season crops of chickpea and mustard. However, the losses of moisture from the soil surface layer after harvest of rainy season crops were rapid (7–23 mm), which necessitated a light irrigation (21–45 mm) for establishment of chickpea and mustard in the post-rainy season. The water balance results of soybean-mustard, peanut-mustard and peanut-chickpea were near identical to soybean-chickpea cropping. Similarly the water balance of rice-mustard was identical to Corresponding author. rice-chickpea in the vertisols. Soybean-mustard and rice-chickpea were the suitable and economical cropping systems for the microcatchment and service area of the farm pond.

Production Risk and Optimal Fertilizer Rates: A Random Coefficient Model

AbstractThis paper demonstrates that low levels of fertilizer use on rainfed rice in the Philippines cannot be attributed to production risk. A random coefficient model estimated the objective probability distribution of yield. This was incorporated into a utility‐maximization framework to predict that moderately risk‐averse farmers would apply only seven to ten kilograms less than the profit‐maximizing N‐rate. Previous studies have established that risk was not a major impediment to fertilizer use in irrigated areas. This paper extends this conclusion to rainfed rice production in the Philippines.

Potential Paddy Rice Yields for Rainfed and Irrigated Agriculture in China and Korea

Abstract YIELD, a water-balance and crop-yield model that calculates production and water consumption variables for a variety of major crops, was applied specifically for wetland rice to China and Korea in order to estimate the region's potential and actual yields for irrigated and rainfed rice production. A network of 241 stations provided the climatic data averaged over approximately a 25-year period. Highest potential yields under full irrigation for a single rice crop occurred in Kansu-Niangsia, the Yangtze River plain, Yunnan-Szechwan-Kweichow, coastal China and Korea, and the islands of Hainan and Taiwan. The yields ranged from 6,000 to 10,000 kg/ha. Smallest yields were found for the western interior and the northeast. In areas where multiple cropping was possible, total yields exceeded 16,000 kg/ha in the south. Under rainfed conditions, only the central and southern China region retained a viable production. In order to achieve optimum crop yields, about 1.000 mm of irrigation water was needed in...