Wetland Rice Fields Research Articles

Effects of pesticides on soil and water microflora and mesofauna in wetland ricefields: a summary of current knowledge and extrapolation to temperate environments

This review summarises information on the behaviour of pesticides and their impacts on microorganisms and non-target invertebrates that was collected in, or is applicable to, temperate wetland ricefields. An extensive bibliographic survey shows that current knowledge is fragmentary and partly outdated. Pesticides applied on soil at recommended levels rarely had a detrimental effect on microbial populations or their activities. They had more effect on invertebrate populations, inducing the blooming of individual species of floodwater zooplankton and reducing populations of aquatic oligochaetes in soil. Available information raises concerns regarding the long-term effects of pesticides on (i) microorganisms, primary producers, and invertebrates of importance to soil fertility, (ii) predators of rice pests and vectors, and (iii) microbial metabolism of pesticides.

Methane Emission from Rice Fields

Journal Article Methane Emission from Rice Fields: Wetland rice fields may make a major contribution to global warming Get access Heinz-Ulrich Neue Heinz-Ulrich Neue Search for other works by this author on: Oxford Academic Google Scholar BioScience, Volume 43, Issue 7, July/August 1993, Pages 466–474, https://doi.org/10.2307/1311906 Published: 01 August 1993

Network Analysis of Nitrogen Cycling in Temperate, Wetland Ricefields

Nitrogen is considered an important limiting element in ricefields. The importance of fertilizer as a source of nitrogen for rice and denitrification as a pathway of nitrogen varies among ricefields depending on agricultural practices. Ecological network analysis was applied to ricefields of the Ebro Delta (N. E. Spain) in order to establish the fate of nitrogen sources to the fields the importance of and interaction between aquatic and benthic processing of nitrogen cycling and the importance of internal recycling and the role of straw buried in sediment at the end of the cultivation period. Fertilizer is the major source of nitrogen during the first month of the cultivation period (...)

Agronomic aspects of wetland rice cultivation and associated methane emissions

Wetland rice cultivation is one of the major sources of atmospheric methane (CH4). Global rice production may increase by 65% between 1990 and 2025, causing an increase of methane emissions from a 92 Tg CH4 y−1 now to 131 Tg in 2025. Methane production depends strongly on the ratio oxidizing: reducing capacity of the soil. It can be influenced by e.g. addition of sulphate, which inhibits methanogenesis. The type and application mode of mineral fertilizers may also affect methane emissions. Addition of organic matter in the form of compost or straw causes an increase of methane emissions, but methane production is lower for materials with a low C/N ratio. High percolation rates in wetland rice soils and occasional drying up of the soil during the cultivation period depresses methane release. Water management practices aimed at reducing emissions are only feasible during specific periods in the rice growing season in flat lowland irrigated areas with high security of water availability and good control of the water supply. Intermittent drying of soils may not be possible on terraced rice lands. Assuming a 10 to 30% reduction in emission rates per unit harvested area, the global emission may amount to 93 Tg CH4 y− in 2025. A reduction of global emissions seems very difficult. To develop techniques for reducing CH4 emissions from wetland rice fields, research is required concerning interactions between soil chemical and physical properties, and soil, water and crop management and methanogenesis. Such techniques should not adversely affect rice yields.

Chemical properties of subsurface peats and their decomposition kinetics under field conditions

Abstract Samples of high moor peat consisting of Sphagnum moss, high moor peat consisting of Sphagnum moss and Carex middendorffii, and low moor peat consisting of Carex spp. taken from the subsurface layers of a non-cultivated site or cultivated fields were analyzed for the content in inorganic and organic constituents, and their decomposability in soil was examined under field conditions in upland and wetland rice fields. For comparison with the peat samples, rice and wheat straw and compost were also examined. Decomposition rate constants (k) of peats mixed with soil for a single compartment exponential decay model, Y t = C 0exp(− kt), ranged from 0.0032 to 0.0096 (month−1), equivalent to 3.7-11% carbon loss after 1 year, and the decomposition was enhanced by mixing with soil. Changes in the amounts of nitrogen of the peat materials were also fitted to the model and gave rate constants (k) of 0.0015-0.0078, equivalent to 1.8-9.0% loss after 1 year, for samples mixed with soil. The decomposition of rice...

Coating of cage wheel lugs to reduce soil adhesion

Cage wheel blocking with mud is a serious impediment to vehicle mobility in wetland rice fields in Asia, most of which have heavy clay soils. In order to find a suitable coating material on a lug surface to reduce soil sticking to the lugs, experiments were conducted in a laboratory soil bin in wet Bangkok clay soil. The lug surface was coated with various materials, all readily available in the region, viz. lead oxide paint, silicone lubricant oil, gloss paint, gloss apint and varnish, ceramic tile, Teflon tape and sheet, chromium plating and enamel plating to find a practical method of reducing clay soil adhesion to the lugs. Results showed that the coating of a lug surface significantly affected the soil adhesion. The most promising coating seems to be enamel plating and further experiments are being carried out to determine the practicality of this method.

A semi-empirical model for calculating evaporation and transpiration from wetland rice

A model for evapotranspiration ( ET) from wetland rice fields was formulated, using the combination method and the wind functions of Penman (1956) and Stigter (1980) to calculate evaporation and transpiration, respectively. The partitioning of the total evaporation among the two surfaces, water and crop, was accomplished by assuming an exponential extinction of net radiation with leaf area index, and by introducing into the aerodynamic terms empirical aerodynamic efficiency functions, representing the ratio of the aerodynamic conductance in the presence of the other surface to the conductance when the surface is present alone. These two functions were calibrated and the model tested based on a dry season lysimeter field investigation on Bangkok Plain, including measurement of evaporation, transpiration and evapotranspiration. Although the model was not tested on a truly independent dataset, it was concluded that when accumulating daily estimates over 5-day periods, the model performed well with an ET estimation error of 2.3 mm per 5-days or 6%. There was a tendency for daily values to be underestimated on days of high ET, probably due to the prevailing intermediate advective condition ( λET/ R n = 1.31). The aerodynamic efficiency functions remained constant in the period 25–84 days after transplanting, at values of 0.58 (water) and 0.75 (crop), and it was concluded that aerodynamically, the rice crop reached full cover at a leaf area index of ∼ 1.5, but energetically at a leaf area index of 3. During the same period, evaporation was 1.4 mm day −1 and transpiration 6.1 mm day −1, with a peak during flowering of 9.0 mm day −1. For the entire crop season, it was estimated that evaporation contributed ∼ 1 3 of ET . The importance of surface-water evaporation, when analysing water stress situations and for formulating a soil-plant-atmosphere concept applicable to wetland rice, is pointed out.

The effects on N2 fixation (C2H2 reduction), bacterial population and rice plant growth of two modes of straw application to a wetland rice field

The effects of incorporation and surface application of straw to a wetland rice field on nitrogen fixation (C2H2 reduction), bacterial population and rice plant growth were studied. Rice straw (5 t ha−1) was chopped (10- to 15-cm pieces) and applied to the field 2 weeks before transplanting IR42, a long-duration variety, and IR50, a short-duration variety. The acetylene-reducing activity (ARA) of IR42 and IR50 measured at heading stage for 3 consecutive days showed significantly higher ARA in IR42 as a result of the 2 straw application methods. Mostly up to 20 days after straw surface application and incorporation, the dark ARA in the soil, total and N2-fixing heterotrophs, and photoorganotrophic purple nonsulphur bacteria (POPNS) in the soil and in association with degrading straw were stimulated. Higher bacterial populations were associated with straw on the surface than with straw incorporated. The POPNS counts, in particular, were increased hundreds fold in the surface-applied straw treatment. Straw applications also increased the root, shoot and total plant biomass at heading stage and the total dry matter yield at harvest in both varieties. The data show the potentials of straw as a source of substrate for the production of microbial biomass and for the non-symbiotic N2 fixation to improve soil fertility and plant nutrition.

Composition ofAzospirillum species associated with wetland rice plant grown in different soils

Total aerobic heterotrophs and N2-fixing putative azospirilla associated with rice plant grown in long-term unfertilized wetland rice field at 5 sites in the Philippines were enumerated. Several azospirilla isolates were identified based on cellular morphology, biochemical tests and reaction to immunodiffusion. Azospirilla constitute about one percent of the total aerobic heterotrophs. Most (85%) of the Azospirillum isolates belong toA. lipoferum indicating its preferential colonization to the rice plant.

Growth, nitrogen fixation, and mass culture of isolatedAnabaena azollae

An independent strain ofAnabaenaazollae was evaluated for its potential as a biofertilizer in wetland rice fields. Sustained rapid growth (doubling time=10.5 h) and nitrogenase activity (32 nmol C2H4 h−1 μg−1 chl) was recorded. Mass cultivation (up to 300 litres) for the first time with this species was also achieved.

Contribution of ammonia volatilization to total nitrogen loss after applications of urea to wetland rice fields

The contribution of NH3 volatilization to the total N loss after the application of urea to flooded rice fields was evaluated in a series of experiments at two locations in the Philippines. Urea was applied in three ways: A. Broadcast and surface incorporated before transplanting (BI treatments), or B. Broadcast into the floodwater 14–21 days after transplanting (AT treatments), or C. Broadcast into the floodwater 5–7 days before panicle initiation (PI treatments).

Effect of phenyl phosphorodiamidate on the fate of urea applied to wetland rice fields

The effect of phenyl phosphorodiamidate (PPD) on floodwater properties, N uptake,15N recovery, and grain yield of wetland rice (Oryza sativa L.) was evaluated in a series of field studies conducted at Munoz and Los Banos, Philippines. Prilled urea and PPD-amended urea were applied to soil and incorporated immediately prior to transplanting or applied to floodwater after transplanting. Urea was also deep-placed or added in a coated form in two studies.

Effect of grazer regulation and algal inoculation on photodependent nitrogen fixation in a wetland rice field

A dry season field experiment conducted for two consecutive years highlighted problems of achieving increased populations of N2-fixing blue-green algae (BGA) in wetland rice fields. Inoculation of non-indigenous BGA strains, either dried or as fresh viable inocula even at high levels of application, was unsuccessful. A limiting effect of grazing invertebrate populations on BGA establishment was evident, but other factors were involved. Reducing grazer pressure did not permit establishment of inoculated BGA; interspecific competition and environmental factors may explain the inoculation failure. Grazer regulation permitted the establishment of a fast-growing indigenous N2-fixing Anabaena and the doubling of N2-fixing activity over a control. Neither inoculation nor grazer control affected grain yields significantly.

Effect of urea on the N2-fixing algal flora in wetland rice fields at ripening stage

Effect of urea on the N2-fixing algal flora in wetland rice fields at ripening stage

In situ water transmission characteristics of a tropical soil under rice-based cropping systems

In soils under rice-based cropping systems in Asia water movement and distribution in the root zone of rice and dryland crops are important for efficient water management. Saturated hydraulic conductivities in the wetland soil profile were evaluated from measurements of hydraulic gradients and percolation rates in the field. The subsoil layer (15–60 cm) restricted percolation rate to a greater degree than the puddled top soil. Unsaturated hydraulic conductivities and soil water diffusivities in the soil profile under dryland conditions were obtained from simultaneous measurements of soil water content using the neutron moderation technique and the soil matric potential by tensiometers over time and soil depth. Soil matric potential versus hydraulic conductivity and soil water content versus soil water diffusivity relations of various soil depths were established. At equivalent soil matric potentials, the hydraulic conductivity of surface soil was greater than that of the subsoil layers. Soil water diffusivity at different depths responded similarly. The study describes a simple in situ technique to measure percolation rates in wetland rice fields and evaluation of water transmission properties of field soil profiles.

Nitrogen‐15 Balance and Residual Effects of Urea‐N in Wetland Rice Fields as Affected by Deep Placement Techniques

AbstractThe 15N balance at harvest, the residual effects of applied N fertilizer, and the distribution of N by depth in a wetland rice (Oryza sativa L.) soil (Alfisol) were determined in field experiments using 15N‐labeled urea. Nitrogen‐15 balance data show that with point, deep placement of urea supergranules (USG), only 4 to 5% of the applied N was unaccounted for after harvest of both the dry‐season and wet‐season crops. In contrast, when prilled urea was basally broadcast and incorporated and topdressed at panicle initiation (PI), 11 to 35% of the applied N was not recovered at harvest, indicating substantial loss of fertilizer N, especially when poor incorporation resulted in high floodwater mineral‐N levels. Uniform deep placement also resulted in high recovery of 15N (92–107%), confirming that the high total 15N recovery obtained with point deep‐placement of USG was largely a function of depth of placement. Band application of urea gave complete 15N recovery (102%) in the dry season and low recovery (61%) in the wet. Nitrogen‐15 balance data showed that 22 to 56% of the applied urea‐N still remained in the soil after the final harvest. The uptake by the wet season crop of the residual labeled soil N from the dry season experiment was about 5% of the initial applied N (87 kg N/ha) for all treatments. Placement method appeared to influence the actual recovery of residual soil 15N; the percentage recovery from the USG treatment was highest and that from the split urea treatment lowest. In neither the dry season nor the wet season was 15N enrichment significant in soil below 30 cm. Generally, the distribution of the residual 15N in soil reflected the placement pattern of urea.

Regulation of Invertebrate Grazers as a Means to Enhance Biomass and Nitrogen Fixation of Cyanophyceae in Wetland Rice Fields

AbstractThe effect of invertebrate grazing on the growth and N fixation of blue‐green algae (Cyanophyceae) in flooded rice soils was investigated by depressing grazer populations. Grazers were controlled with commercial pesticides and seeds of neem (Azadirachta indica). Algal N fixation and standing biomass were estimated by acetylene‐reduction activity and chlorophyll a measurements. Suppression of ostracod (Ostracoda) grazing by Pertbane or neem seeds tripled blue‐green algal biomass and increased N fixation rates 10‐fold. In the absence of ostracods, free living blue‐green algae multiplied rapidly early in the rice cultivation cycle to be succeeded by chlorophytes. Carbofuran was not an effective control measure. Suppression of molluscan grazing had little effect. The population of tubificids (Tubificidae) was higher in the plots where algal growth was stimulated than in other plots. Total rice grain N was increased up to 37% when grazing was arrested.

Water use in lowland rice cultivation in Asia: A review of evapotranspiration

The literature on and basic principles affecting transpiration, evapotranspiration and the ratio of actual evapotranspiration to open pan evaporation (ET/EP) in wetland rice culture of South and Southeast Asia are reviewed. Based on existing information a simple model is suggested to predict evapotranspiration from wetland rice. Large differences in daily as well as seasonal total transpiration and evapotranspiration values exist for various locations. Crop transpiration rate is low at the early stage of growth and increases almost linearly, reaching 3–4 mm/day at maximum tiller number stage and 5–7 mm/day at heading time. Evapotranspiration also follows a similar trend for the maximum rate and varies with crop growth stage. The seasonal average evapotranspiration in wetland rice fields is in the range of 4–7 mm/day. The value of crop growth coefficient factor (ET/EP) is 1 at transplanting, reaching about 1.15 at maximum tiller number stage and around 1.3 at flowering stage. For a crop season this ratio is about 1.2 This information will aid significantly in developing better water management practices for rice.

Design and Testing of a Microlysimeter for Wetland Rice1

AbstractAssessment of water loss as transpiration and evapotranspiration for each hour or for each day in the field is difficult because the available methods are either very expensive or inaccurate. This paper introduces a simple, sensitive, and accurate microlysimeter for wetland rice (Oryza sativa L.) fields.The microlysimeter was designed and tested to measure transpiration and evapotranspiration in wetland rice fields. It consists of a poly‐vinyl‐chloride cylinder, sealed at the lower end and connected to a water reservoir/manometer through flexible tubing. A constant water level is maintained in the microlysimeter with a Mariotte system and water loss from the reservoir/manometer is measured. Total water loss as evaporation from free water surface in the cylinder and transpiration from canopy was measured as evapotranspiration. To measure transpiration, the cylinder was covered to stop evaporation from free water surface in the cylinder.The microlysimeters were laboratory‐calibrated and compared in the field with large square tanks. Water use pattern as evapotranspiration per unit land area was essentially the same with both the units. The microlysimeter is accurate even for time intervals as short as 1 hour and can be fabricated locally.

A Simple Microlysimeter to Measure Transpiration and Evapotranspiration in Wetland Rice Fields

A Simple Microlysimeter to Measure Transpiration and Evapotranspiration in Wetland Rice Fields