Irrigated Rice Crop Research Articles

Relationship between tillering and leaf area index: quantifying critical leaf area index for tillering in rice

A field study was conducted at the International Rice Research Institute (IRRI), Philippines during the dry seasons of 1997 and 1998 under irrigated conditions. The objectives of this study were to quantify the critical leaf area index (LAIc) at which tillering stops based on the relationship between tillering rate and LAI, and to determine the effect of nitrogen (N) on LAIc in irrigated rice (Oryza sativa L.) crop. Results showed that the relative tillering rate (RTR) decreased exponentially as LAI increased at a given N input level. The coefficient of determination for the equation quantifying the RTR-LAI relationship ranged from 0·87 to 0·99. The relationship between RTR and LAI was affected by N input level, but not by planting density. The N input level had a significant effect on LAIc with a high N input level causing an increase in LAIc. Tillering stopped at LAI of 3·36 to 4·11 when N was not limiting. Under N limited conditions LAIc reduced to as low as 0·98. Transplanting spacing and number of seedlings per hill had little effect on LAIc. Results from this study suggest that LAI and plant N status are two major factors that influence tiller production in rice crops. The possibility that LAI influences tillering by changing light intensity and/or light quality at the base of the canopy where tiller buds and young tillers are located is discussed.

Salt balances of inland shrimp ponds in Thailand: implications for land and water salinization

Brackish water ponds for farming black tiger shrimp (Penaeus monodon) have recently proliferated in inland areas of Thailand's central plain, raising concerns about land and water salinization. The environmental impacts of inland shrimp farming were assessed by analysing the salt balance for an inland shrimp farm. Field data on water fluxes and pond salinity, collected from nine ponds in Chachoengsao Province from May–July 1999, were used to model the salt balance for a typical shrimp pond over one growout cycle. During growout, seepage represented 38% (11.5 tonnes crop−1) of salt losses, pond discharge 33% (9.7 tonnes crop−1), and accumulation of salt in pond sediment 6% (1.8 tonnes crop−1). About 23% of the initial salt content remained at harvest and could have been recycled. However, the majority (84% on average) was discharged to the irrigation canals. Much of the salt in pond sediment was also exported to the canal system through tidal flushing of the ponds. Field measurements of salinity were taken in adjacent canals and rice paddies to explore the impacts of salt exports from shrimp ponds. Pond discharge caused increases in canal salinity above levels that would impact on yields of irrigated rice and orchard crops, the main land uses in the region. Elevated soil and water salinity in adjacent rice fields was probably related to lateral seepage from the ponds. The salt budget was also modelled for a zero discharge farming system, promoted by proponents of inland shrimp farming as having few impacts. However, the results suggest that, even in zero discharge ponds, almost half of the initial pond salt content is exported through seepage (45%, 12.4 tonnes crop−1), with another 6% (1.8 tonnes crop−1) deposited in sediments. While techniques exist for mitigating much of the salt leakage, the likelihood of their uptake in Thailand is low. Further expansion of inland shrimp farming in the central plain is therefore likely to contribute substantial salt load to the area's land and water resources.

Melhoramento genético para tolerância ao frio em arroz irrigado

O melhoramento genético para tolerância ao frio é apresentado como estratégia para enfrentar o problema de temperatura baixa no Rio Grande do Sul durante o período de cultivo do arroz irrigado. A ocorrência de temperaturas baixas em outros países é comparada com a situação no sul do Brasil. Os estádios de desenvolvimento da planta mais afetados pela temperatura baixa, as estratégias de seleção disponíveis sob condições controladas e os problemas encontrados para o melhoramento dessa característica são discutidos. Finalmente, estratégias de seleção promissoras baseadas em estudos de Fisiologia e Biotecnologia são apresentadas.

Analysis of phosphorus in two humic acid fractions of intensively cropped lowland rice soils by 31P‐NMR

SummaryThe organic forms of phosphorus in the soil appear to be changing as rice growing intensifies and the soil is flooded for longer in tropical Asia. To examine these changes, we extracted the labile mobile humic acid (MHA) and more recalcitrant calcium humate (CaHA) fractions from soils supporting long‐term field trials in the Philippines and analysed them by solution 31P‐nuclear magnetic resonance (NMR) spectroscopy. Diester P and sugar‐diester P accumulated moderately with increasing intensity of irrigated rice cropping, reaching a combined 42% of all MHA‐P for a triple‐cropped irrigated field compared with 28% for fully aerated fields growing dryland crops. The mono‐ to diester P ratio decreased by 43% for the MHA and CaHA from the aerated fields to the triple‐cropped field. Smaller effects on forms of P were noted for the rates and type of N, P and K fertilizer and site effects. The effects of treatment and site were more noticeable in the MHA than in the CaHA. The proportions in the NMR spectra were tightly correlated with visible light absorption, concentrations of organic free radicals and H, and 15N‐NMR spectral proportions, which indicate the degree of humification. The MHA and CaHA accounted for only 0.6–8.3% and 0.9–5.7%, respectively, of total P; most of the P is inorganic.

Decrease in Humification of Organic Matter with Intensified Lowland Rice Cropping A Wet Chemical and Spectroscopic Investigation

To address recent concerns of impaired nutrient cycling in intensively cropped lowland rice soils of tropical Asia, we have been investigating the effects of continuous rice cropping on the chemical nature of soil organic matter (SOM). In this study, the labile mobile humic acid (MHA) fraction and the more recalcitrant calcium humate (CaHA) fraction were extracted from soils of four long‐term field trials on the International Rice Research Institute (IRRI) farm, which varied in the number of annual irrigated rice crops and hence degree of soil submergence. The two humic acid (HA) fractions were analyzed by Fourier‐transform infrared, fluorescence, and electron spin resonance spectroscopies for elemental composition and acidic functional groups. With increasing soil submergence, the HA fractions became less oxidized or humified, with higher S and H and lower O concentrations, more amide or amino, hydroxyl, and methoxy groups, and fewer carboxyl groups and organic free radicals. The HA extracted from submerged soils appeared to have greater capacity for complexing Cu+2, Fe+3, and VO+2 than did HA from aerated soils. Fertilizer treatments had little effect on HA chemical structure. The MHA was less humified than the CaHA, having fewer acidic functional groups, smaller C:N and C:H ratios, richer concentrations of amides and carbohydrates, lower concentrations of COOH, higher fluorescence intensity, and shorter wavelength of fluorescence emission maximum, and lower concentration of organic free radicals. Free radical concentrations for both HA fractions were highly correlated with other indices of humification reported here and elsewhere.

A produção mais limpa como geradora de inovação e competitividade

Este artigo tem por origem uma dissertação de mestrado em administração. Seu objetivo é divulgar resultados referentes à adoção de estratégias de Produção Mais Limpa (PML), como forma de começar a adequar-se aos novos padrões de produtos saudáveis e limpos, exigidos pelo mercado consumidor, e que culminaram com a geração de inovações e de competitividade para a empresa. O método de pesquisa utilizado foi o estudo de caso. A empresa pesquisada foi a Fazenda Cerro do Tigre (FCT), de Alegrete, RS, Brasil, produtora de arroz irrigado. Os resultados indicam que a empresa, quando começa a preocupar-se com as questões ambientais e adota estratégias de Produção Mais Limpa, começa a usufruir de um processo de melhoria contínua, que propicia o surgimento de inovações em todos os sentidos (processo, produto e gerência). A principal conclusão é que a PML facilita o surgimento de inovações e que estas inovações facilitam o alcance da competitividade.

Changes in chemical properties of organic matter with intensified rice cropping in tropical lowland soil

SummaryRice systems in Asia have intensified rapidly in the past 30 years, and significant areas of irrigated lowland rice are now supporting two or three rice crops per year. Our objective was to compare the chemical composition of soil organic matter (SOM) from four fields with different histories of rice cropping intensity and soil submergence: (i) a single‐crop rainfed, dryland rice system without soil submergence, (ii) an irrigated rice and soybean rotation, and irrigated (iii) double‐ or (iv) triple‐crop rice systems in which soil remains submerged during much of the year. In all four soils, extracted mobile humic acid (MHA) and calcium humate (CaHA) fractions were of modern age by 14C‐dating, and represented about 20% of total N and organic C. The MHA was enriched in N and hydrolysable amino acids (AA) compared with CaHA in all soils. With increased frequency of irrigated rice cropping, however, there was a large increase in phenolic content of SOM. We speculate that slower lignin decomposition caused by deficiency of O2 in submerged soil leads to incorporation of phenolic moieties into young SOM fractions. The increased phenolic character of these fractions may influence N cycling and the N supplying capacity of lowland soils supporting two or three annual crops of irrigated rice.

Population dynamics of an outbreak population of house mice (Mus domesticus) in the irrigated rice-growing area of Australia

Conditions appear ideal for annual plagues of house mice in irrigated rice-growing areas of Australia, yet plagues in these areas usually coincide with those in the dry farms. In an irrigated rice crop near Jerilderie, New South Wales, we examined in detail the demography of an incipient plague population of Mus domesticus. Breeding occurred from winter 1983 to autumn 1984 and the population increased from low levels to plague levels (2500 ha-1) by May. We found no evidence for a rigid territorial social organisation. Dispersal of tagged animals was low throughout the breeding season, yet between 60% and 76% of the trappable population was new each trapping session. Testosterone levels increased when the average male body weight was low, suggesting that social suppression of reproduction was not occurring. We conclude that plagues in these areas can develop within approximately 12 months from the onset of drought-breaking rains.

Floods and agricultural change. Some observations from Bangladesh 1986–1990

Over the last decade Bangladesh has witnessed several devastating floods. Despite this, cereal production has grown steadily, mainly as a result of the spread of irrigation and modern rice varieties. On the basis of data from, Madaripur Upazila, a small flood-prone community in southwest Bangladesh, the article discusses the relationship between floods and the spread of new agricultural technology. The floods in 1987 and 1988 led to excessive damage to traditional rain-fed rice crops and in order to avoid future damage of this kind the farmers shifted to a modern, irrigated rice crop. A basic argument of the article, therefore, is that natural disasters, here in the form of excessive flooding, can act as a triggering force behind a process of agricultural modernization. At the same time it is clear that the 1987 and 1988 floods alone cannot fully explain the changes observed in Madaripur. Public reforms concerning distribution of vital inputs such as irrigation equipment and fertilizers, as well as broader changes in rural-urban relationships have been important.

Seasonal Abundance of Rice Stem Borer Species in Upland and Irrigated Rice in Nigeria

Studies were carried out in 1983 to determine the relative abundance and species composition of three lepidopterous stem borers in upland and irrigated rice at Ibadan, southwestern Nigeria. The relationship between irrigated rice crop phenology and the population of the borers and stalk-eyed fly was also studied. White stem borer, Maliarpha separatella was the predominant species in upland and irrigated rice, followed in upland rice by pink stem borer, Sesamia calamistis, and striped stem borer, Chilo zacconius and in irrigated rice by C. zacconius and S. calamistis. The proportion of M. separatella was higher in irrigated rice than upland. Three population peaks were observed annually in both upland and irrigated rice. Studies on the relationship between irrigated rice phenology and field population of lepidopterous borers and a dipteran borer showed that the stalk-eyed fly, Diopsis spp., occurred before 20 days after transplanting (DAT) in ITA 212 and continued up to 90 DAT: the peak was observed at 40 DAT. The lepidopterous borers did not appear until 40 DAT and populations peaked at 80 DAT.

Evapotranspiration from Irrigated Rice in the Tropical Dry Season

Few studies are available on evapotranspiration and crop-water relationships of rice in the tropical dry season. We measured evapotranspiration, leaf water potential, stomatal resistance and attendant micrometeorological parameters in an irrigated rice crop during the 1979 dry season. A wind barrier of 50% porosity was used to vary primary meteorological parameters. Diurnal changes in crop water status provided a characterization of the dynamic nature of evapotranspiration, water potential in the crop and stomatal behavior. Modification of vapor pressure deficit (saturation deficit) and wind speed over the canopy by the wind barrier resulted in a 20% decrease in daily evapotranspiration.Estimations of actual evapotranspiration (Ec) rates based on micrometeorological measurements and a generalized combination formula agreed well with measured evapotranspiration (ET). The concurrence of Ec with ET values and their relation to potential evapotranspiration (E0) indicate a significant crop resistance in these tropical dry season conditions, i.e., Ec (ET)=0.82E0. A significant downward heat flux illustrated the importance of sensible heat in this season. Measurements on five dates throughout the crop season showed that ET is approximately 1.5 times equivalent net radiation.