Rice-growing Environments Research Articles

Genotypic variation for cold tolerance during reproductive development in rice: Screening with cold air and cold water

Rice ( Oryza sativa L.) plants are susceptible to low temperature during the young microspore stage, which occurs 10–12 days before heading. Low temperature at this time increases spikelet sterility which can cause massive yield loss. Increasing the cold tolerance of cultivars can reduce yield variability in temperate rice-growing environments. Two experiments were conducted in cold air screenings and two were conducted in cold water screenings to examine genotypic variation for cold tolerance, explore flowering traits related to spikelet sterility, and investigate whether the results reflect the level of cold tolerance determined previously in the field. Cold air screenings imposed day/night temperatures of 27 °C/13 °C, 25 °C/15 °C and 32 °C/25 °C following panicle initiation until 50% heading, while cold water screenings maintained a relatively constant 19 °C. The variation in the commencement of low air temperature treatment did not have an effect on the level of spikelet sterility, indicating that exposure to low temperature during the young microspore stage was more important than the duration of exposure. Spikelet sterility of common cultivars showed a significant correlation between cold air and cold water screenings ( r 2 = 0.63, p < 0.01), cold air and field screenings ( r 2 = 0.52, p < 0.01) and cold water and field screenings ( r 2 = 0.53, p < 0.01), indicating that cold air and cold water can be used for screening genotypes for low temperature tolerance. HSC55, M103 and Jyoudeki were identified as cold tolerant and Doongara, Sasanishiki and Nipponbare as susceptible cultivars. There was a significant negative relationship between spikelet sterility and both the number of engorged pollen grains per anther and anther area only after imposing cold air and cold water treatment hence, it was concluded that these flowering traits were facultative in nature. In addition, cultivars originating from Australia and California were inefficient at producing filled grain with similar sized anthers containing a similar number of engorged pollen grains as cultivars from other origins. One suggested reason for this poor conversion to filled grain of cultivars from Australia and California may be associated with their small stigma area, particularly when exposed to low temperature conditions.

Nitrogen fertiliser alleviates the disorder straighthead in Australian rice

Straighthead is a ‘physiological’ disorder of rice, the symptoms being floret sterility, deformed florets and panicles and reduced grain yield. Straighthead in rice is difficult to investigate because of its unpredictable occurrence under field conditions. An experiment was conducted in south-eastern Australia in 1996 to investigate the effect of rate and timing of N fertilisation on growth and yield of rice. The presence of straighthead at this location gave a unique opportunity to study the influence of crop N status. This paper reports the influence of N application on straighthead symptoms during this experiment. A significant reduction of straighthead occurred with higher rates of N application. Application of 250 kg N/ha pre-flood, improved plant growth and vigour with subsequent increased uptake and accumulation of S, P, K, Mg, Cu, Mn and Zn in the plant at panicle initiation. The reduction of straighthead at high nitrogen rates may be due to improved uptake of several essential nutrients, and Cu may be a critical nutrient. This study and earlier observations have shown the application of optimal levels of pre-flood nitrogen to achieve grain yields greater than 10 t/ha may reduce straighthead severity in the Australian rice-growing environment. The results in this paper are not presented as recommendations to growers but a contribution to the currently limited literature on straighthead in Australia.

Nutrient Distribution in the Profile of Valley Bottom Soils Cultivated to Rice in Ghana

ABSTRACT The consumption of rice has increased in Ghana recently, but supply cannot meet demand; hence, there is a large annual importation to make up for the deficit. In Ghana, rice is cultivated under three main systems, namely rain-fed upland conditions, irrigated conditions, and rain-fed lowland conditions. Due to unpredictable rainfall, production under rain-fed conditions has been very unstable. Fortunately, inland valley systems (IVs), which have been cited by many authors as the environment best suited for efficient and sustainable rice production, abound in this country. This study was therefore undertaken to determine the soil nutrient status, and to document a plant species distribution that is useful for nutrient cycling in the IVs of the Ashanti region of Ghana. The goal is to develop a sustainable sawah-rice production system.** Valley bottom soil samples for laboratory analyses were collected from standard soil profiles in areas under use for rice cultivation or capable of supporting rice. Results showed these soils to be slightly acidic (topsoil mean pH = 5.7) with low exchangeable acidity [0.10 cmol(+)/kg]. Mean topsoil total carbon (C), nitrogen (N), and available phosphorus (P) (Bray 1) were 1.8%, 0.20%, and 4.4 mg/kg, respectively. Exchangeable cation [cmol (+)/kg] values of surface soils were 0.3 for potassium (K), 5.1 for calcium (Ca), 1.8 for magnesium (Mg), and 0.2 for sodium (Na), respectively. The concentrations of C, N, and most cations decreased down the profile. However, the overall fertility levels were well within the normal ranges for IVs of West Africa. The species dominating the valley bottoms were fairly similar in their carbon content. However, Manihot esculenta and Mallatus oppositifolium of the family Euphorbiaceae were higher than other species in N content. Species belonging to the family Euphorbiaceae were lower in P content (which ranged from 0.9 to 3.7 g/kg) while Physalis angulata and Manihot esculenta contained the highest (3.9 and 3.6 g/kg) P, respectively. The variable nutrient composition of these species has implications for nutrient cycling in the ecosystem. Knowledge of nutrient status of IVs will greatly assist in efforts at adopting the Asian type of sawah rice cultivation. If supported with appropriate farming practices that return crop residues to the soil and utilize inorganic fertilizer or organic manures, the inland valley ecology can contribute significantly to food security, especially of rice, and also conserve the environment. **The term sawah refers to bunded and leveled rice fields with both irrigation and drainage gates. It is of Malayo-Indonesia origin. The English term paddy originated from the Malayo-Indonesian word padi, meaning rice plant. It refers to unhusked rice in West Africa. Most of the paddy fields in the Asian countries fit the definition of sawah. However, the term paddy field refers only to a rice field, including upland rice fields in West Africa. To avoid any confusion between a rice plant paddy and the improved man made rice-growing environment, the authors use the term sawah.

The Cultural Diffusion of Rice Cropping in Cote d'Ivoire

Rice consumption and production have an ever-increasing impact on West African national economies and the changing local ecologies of the region. Cote d'Ivoire illustrates this point, with rising consumption, primarily in urban areas. Between 1984 and 1989 this rise cost an annual average of U.S.$93.7 million in imports, which increased to U.S.$107 million in 1993, making Cote d'Ivoire the largest importer in West Africa (FAO 1995). To meet this demand, large areas of moist lowlands and rain-fed uplands are being cleared for production. Rice is not a new crop to West Africa, and its cultivation has long been associated with a circumscribed rice zone. Today, as cultivation expands into new areas, farmers from various cultural backgrounds working in diverse ecologies adopt the crop to fit their particular needs and experiences. Its cultivation affects domestic and local economies and results in ecological change in ways that reflect the collective historical experience of the peoples who grow the rice. Many recent attempts to classify crop environments based on physical characteristics for the purpose of extending cultivation, such as Wim Andriesse and Louise Fresco's characterization of rice-growing environments in West Africa (1991), fail to consider the cultural and economic history of the crop and its diffusion. To do so examines a crop's potential only in a theoretical, laboratory-type physical setting devoid of cultural influence. Yet the human element in agriculture is anything but neutral: Crop distribution is not restricted to biogeographical patterns. In this article we combine the cultural history of cultivation in Cote d'Ivoire with the results of a field study of contemporary rice-cropping systems (Becker and Diallo 1992). based on data collected in interviews with farmers, local extension workers, and field observations in each of the fifty secondary administrative units, or departements, the country's cropping is divided into nine networks, or systems (Table I). Like Martin Lewis's regional agricultural geography in the Philippines (1992), these groupings are not territorially exclusive, although they mostly have a strong regional bond. Each takes into consideration the heterogeneous population of the country, where distinct systems of cropping are found side by side, often exploiting separate ecological niches and made up of sets of cropping technologies with their own histories. The approach is useful to development planners, especially when compared with the restricted biophysical focus so commonly used. An emphasis on networks addresses the production realities of farmers. No matter how many irrigation projects are built, farmers will only produce when it is in their best interest to do so. Beginning to recognize these self-interests is an essential step in efforts to improve agriculture. IVORIAN PHYSICAL AND HUMAN ENVIRONMENTS Cote d'Ivoire's physical landscape is underlain by Precambrian formations, dominated in the west by the granitic Mountains of Man, including 1,752-meter-high Mount Nimba at the point where Guinea, Liberia, and Cote d'Ivoire meet. Much of the landscape is undulating valley and upland, traversed by three major north - south-trending rivers - the Sassandra, the Bandama-Nzi, and the Comoe [ILLUSTRATION FOR FIGURE 1 OMITTED]. The climate is regulated by the relative positions of the tropical maritime air mass over the South Atlantic and the dry air associated with the North African anticyclone over the Sahara (Hayward and Oguntoyinbo 1987). The moist southwesterlies bring monsoon rains, with high rainfall totals (2,300 millimeters a year in Tabou). The longest rainy seasons are in the southwest, near the ocean, and in the mountains, along the border with Liberia and Guinea. But the dry Harmattan winds blow from the northeast, giving the Bouna Departement, bordering Burkina Faso (Upper Volta until 1984) and Ghana, low rainfall figures (less than 900 millimeters a year) (Atlas de Cote d'Ivoire 1979). …

A remote sensing and GIS-based methodology for the delineation and characterization of rainfed rice environments

Abstract Accurate information on the extent and characteristics of rainfed rice-growing environments is lacking because of the high degree of temporal variability and spatial heterogeneity of the ecosystem/subecosystem-differentiating parameters. Although the repeated classification and mapping capture the temporal variability, the information generated reflects post facto conditions and the same geographical area gets classified under different ecozones over years; hence, the delineated ecosystems/subecosystems seem to be transitional. This limits the utility of such an enormous effort. To overcome these problems, this study developed a remote sensing and GIS-based methodology which captures the temporal variability as well as spatial heterogeneity of the ecozone-differentiating parameters and their effect on vegetation (crop) conditions, and prepared criteria for accurate delineation and characterization of rainfed rice ecosystems/subecosystems. The results showed vegetation condition to be a comprehensive reflection of the crop-growing situations and the vegetation index as an excellent criterion for ecosystem/subecosystem classification when combined with the existing classification criteria. These methods have been successfully applied in pilot areas and show greater promise for applicability in similar situations, as well as in other environments with some modifications.

Combined use of watershed, aquifer and crop simulation models to evaluate groundwater recharge through percolation ponds

Percolation ponds are constructed in many parts of the tropics to augment fast-depleting groundwater resources. Increased agricultural productivity due to additional well irrigation water is the direct benefit from the pond schemes. Usually, location-specific empirical relationships are adopted for hydrologic and economic design of ponds. In this paper, an approach is presented to evaluate hydrologic pond design, by combining watershed, aquifer and crop simulation models of the pond system. A watershed model (CAPSIM) was developed based on the ‘state variable approach’ describing the dynamic catchment-pond hydrologic processes such as runoff, runoff due to interflow, evapotranspiration, direct percolation, pumping and irrigation. CAPSIM operates on a daily basis, using rainfall and pan evaporation data. Based on the Alternating Direction Implicit Algorithm (ADIA), a finite difference Aquifer Simulation model (ASIM) was developed to simulate two-dimensional recharge mounds beneath the pond. Predictability of CAPSIM and ASIM was verified with observed field data from one pond site, from which the models were improved. The models were further validated separately for three pond locations and for different years of weather data, by comparing observed pond and well water levels. The crop model, SAHEL, was adapted to the rice-growing environments of pond command areas, by representing water stress, runoff and well irrigation. Total Additional well Irrigation made possible Due to recharge (AID-recharge) in two space dimensions during a crop season was predicted by linking CAPSIM and ASIM. AID-recharge thus computed was input to the crop model for predicting the spatial distribution of crop response to different well irrigation scenarios. A series of ‘distance-capacity-yield’ curves were developed, which quantify the benefits associated with a modification in the pond structure. The batch of models thus linked could serve as a decision support tool for pond designers for evaluating desired hydrologic economic strategy.

A characterization of rice-growing environments in West Africa

Building on past classifications, this article proposes a comprehensive characterization of rice-growing environments in West Africa on the basis of ecological and agronomic parameters. Using climate, soils, toposequence, land types and rice cropping system as classificatory principles, 18 different environments are distinguished and their characteristics are summarized in three sets of tables. Current constraints to rice production in each of the environments and the implications for rice research are briefly highlighted, as well as the need for field-level verification of the characterization.