Influence of a non-copper algicide on the cyanobacterium, Nostoc spongiaeforme, and the green alga, Hydrodictyon reticulatum, in field and laboratory experiments

Cyanobacteria and algae grow in California rice fields where they form large mats that may smother seedlings or cause them to dislodge, resulting in reduced rice stand establishment and potential yield loss. The most troublesome species of cyanobacteria is Nostoc spongiaeforme. It is very difficult to control using currently accepted methods, i.e., aerial applications of copper sulfate. A non-copper algicide, the mono (N,N-dimethylalkylamine) salt of endothall has been suggested as an alternative method for controlling nuisance cyanobacterial and algal growths in California rice fields. The purpose of the experiments described here was to evaluate the effect of the mono (N,N-dimethylalkylamine) salt of endothall on growth of N. spongiaeforme and the green alga, Hydrodictyon reticulatum. In laboratory experiments, the mono (N,N-dimethylalkylamine) salt of endothall reduced N. spongiaeforme growth at 0.3 mg L^?1. This effect was removed when rice straw was added to the growth medium, indicating that the rice straw may have introduced bacteria capable of degrading the mono (N,N-dimethylalkylamine) salt of endothall. In outdoor experiments, which used rice field water containing decomposing rice straw, the mono (N,N-dimethylalkylamine) salt of endothall concentrations between 0 and 5 mg L^?1 had little effect on N. spongiaeforme. In contrast, H. reticulatum exhibited injury symptoms at 1 mg L^?1 or greater. However, H. reticulatum recovered by the end of the 7-day exposure. It is not clear how this algicide will be useful in the management of N. spongiaeforme or H. reticulatum in California rice fields.     

Soil fertility and establishment potential of inoculated cyanobacteria in rice crop grown under non-flooded conditions

An investigation was undertaken using a combination of microbiological and DNA-based approaches to evaluate combinations of two/three/four cyanobacterial strains (BF1 Anabaena torulosa; BF2, Nostoc carneum; BF3, Nostoc piscinale; BF4, Anabaena doliolum), using a novel vermicompost-based carrier, for their promise as inoculants in rice crop. The crop was maintained under 60% WHC through intermittent irrigation. Selected combinations (BF1 + 2 + 3; BF1 + 2 + 4; BF1 + 3 + 4) showed a consistent trend regarding their superiority over other treatments in terms of plant growth promotion and soil microbiological parameters. Microscopic examination of soil enrichment cultures raised from the treatments revealed their comparative abundance over native flora. A significant enhancement in terms of soil microbial biomass carbon and humus content was also recorded in these treatments. The soil enzymatic profile of the inoculated treatments involving FDA, dehydrogenase, acid phosphates, alkaline phosphatase, aryl esterase and β-glucosidase also revealed the promise of the inoculated strains. 16SrDNA sequencing, followed by BLAST analyses provided valuable information regarding the establishment of Anabaena strains. RFLP analyses of the 16SrDNA sequences of soil DNA and phylogenetic analyses vis a vis sequences of the inoculated cyanobacterial strains revealed the promise of treatments ?BF1 + 2 + 3, BF1 + 2 + 4 and BF1 + 3 + 4. Panicle weight (yield attribute) was statistically at par with the fertilizer controls 1/2N + PK and significantly higher than 1/3N + PK. To our knowledge, this represents a first report on evaluating the establishment of cyanobacterial inoculants in rice crop grown under non-flooded conditions (or intermittent irrigation) using a combination of agronomic, microbiological and soil DNA related attributes.     

Evaluation of Transplanting Date and Nitrogen Fertilizer Rate Adapted by Farmers to Toposequential Variation ofEnvironmental Resources in a Mini-Watershed (Nong) in Northeast Thailand

Environmental resources for rainfed rice production show large variability even within a small area in Northeast Thailand, and it is said that farmer’s management is well adapted to the variability. This study evaluated transplanting date and nitrogen (N) fertilizer rate in the management to improve rice productivity. The effect of transplanting date and N fertilizer rate on rice productivity was analyzed by investigating rice growth, and also by dividing rainfed rice fields located in a mini-watershed into 4 subecosystems: (1) medium deep water, waterlogged (MDW), (2) shallow water, favorable (SWf), (3) shallow water, drought- and submergence-prone (SWds), and (4) shallow water, drought-prone (SWd). Rice grew at almost a constant rate until maturity and the growth rate was higher at a lower field. The difference in productivity was derived from not only a water condition but also soil fertility, and was associated with the rate of N uptake. Small leaf area index was found to be one of the causes for low productivity in rice. Statistic analysis showed that earlier transplanting increased biomass production in all subecosystems. The biomass-increase resulted in a higher yield in SWds and SWd fields while it resulted in a reduced harvest index (HI) and did not increase yield in MDW and SWf fields. The effect of N fertilizer was apparent in the field where rice biomass was small due to later transplanting or unfertile soil, but the effect was generally small. Earlier transplanting in upper fields and later transplanting in lower fields in mini-watersheds were suggested to improve rice production, and proper distribution of N fertilizer use is considered necessary.     

Evaluation of potential biocides for control of the earthworm Eukerria saltensis (Oligochaeta: Ocnerodrilidae), a pest of rice in southern Australia

The earthworm Eukerria saltensis can cause severe crop establishment problems in aerially sown rice grown on heavy clay soils in southern Australia. Damage occurs indirectly through destabilization of the topsoil, increased water turbidity, and mobilization of soil nutrients into the water column which leads to increased algal growth. We investigated the possibilities for chemical control of E. saltensis using laboratory bioassays and a series of field trials involving either the use of enclosures in flooded crops or soil incorporation of pesticides into rice fields during fallow periods or shortly before flooding. The four most toxic compounds in 7 day soil/water laboratory bioassays were carbofuran, acetamiprid, bendiocarb and lambda-cyhalothrin which provided corrected mortalities of 86–100% at 2 mg a.i. L⁻¹. Other compounds that showed some level of efficacy (corrected mortality >20% at one or more rates) were imidacloprid, esfenvalerate, thiacloprid, niclosamide and alpha-cypermethrin. Twenty-six of the 38 pesticides evaluated failed to produce mean corrected mortalities >6% at application rates of up to 2 mg a.i. L⁻¹. Eight trials were conducted in flooded rice crops using small stainless steel enclosures and carbofuran, thiodicarb, niclosamide and bendiocarb at rates of 1 and 2 kg a.i. ha⁻¹. Trials were assessed 8–14 days after chemical application. None of these treatments produced a statistically significant decrease in Eukerria biomass, although consistent downward trends in response to higher treatment rates were evident in 2 trials (one with carbofuran and one with bendiocarb). Three trials with liquid pesticides watered into fallow rice fields were conducted with carbofuran (0.5, 1.0 and 5.0 kg a.i. ha⁻¹) and thiodicarb (0.94 and 1.87 kg a.i. ha⁻¹) however only the 5.0 kg a.i. ha⁻¹ carbofuran treatment provided significant (P < 0.05) levels of control. Preflood soil applications of liquid carbofuran, thiodicarb and niclosamide (2 kg a.i. ha⁻¹), granular carbofuran and granular ethoprophos (0.5–2 kg a.i. ha⁻¹) also did not provide statistically significant levels of control, although the 2 kg a.i. ha⁻¹ liquid and granular carbofuran treatments did provide moderate levels of suppression (49–84%). Although further field trials with compounds such as acetamiprid and lambda-cyhalothrin may prove valuable, our results suggest chemical control of E. saltensis may be difficult to achieve with environmentally acceptable pesticides applied at economically viable rates. Cultural approaches such as appropriate crop rotations and landforming to ensure uniformly shallow water should continue to form the basis of Eukerria management programs.     

Effect of N-fertilizer application on return flow water quality from a terraced paddy field in Northern Taiwan

Intensive use of chemical fertilizer for crops may be responsible for nitrogen and phosphate accumulation in both groundwater and surface waters. The return flow polluted by nutrients not only results in the limitation of water reuse goals but also creates many environmental problems, including algal blooms and eutrophication in neighboring water bodies, posing potential hazards to human health. This study is to evaluate the N-fertilizer application of terraced paddy fields impacting return flow water quality. Water quality monitoring continued for two crop-periods around subject to different water bodies, including the irrigation water, drainage water at the outlet of experimental terraced paddy field, and shallow groundwater were conducted in an experimental paddy field located at Hsin-chu County, Northern Taiwan. The analyzed results indicate that obviously increasing of ammonium-N (NH₄ ⁺-N) and nitrate-N (NO₃ ^?-N) concentrations in the surface drainage water and ground water just occurred during the stage of basal fertilizer application, and then reduced to relatively low concentrations (<0.1 mg/l and <3 mg/l, respectively) in the remaining period of cultivation. The experimental results demonstrate the potential pollution load of nitrogen can be reduced by proper drainage water control and fertilizer application practices.     

Rhamphicarpa fistulosa, a parasitic weed threatening rain-fed lowland rice production in sub-Saharan Africa - A case study from Benin

Expansion of the facultative parasitic plant Rhamphicarpa fistulosa as a weed of rain-fed lowland rice was studied in 2007 on a national level (Benin) by repeating a survey from 1998. Wider species’ distribution was investigated in 2008. Current and potential impact and management strategies were investigated through farmer surveys and pot experiments. Out of 36 cultivated inland valleys visited across Benin, eight were found to be infested with Rhamphicarpa. Out of nine inland valleys inspected in 1998, Rhamphicarpa was found in five in 2007, compared with only three in 1998. Farmers estimated Rhamphicarpa-inflicted yield losses could exceed 60% and indicated that heavily infested fields are abandoned. In a pot experiment with a wide infestation range, the popular cultivar Gambiaka, combining resistance with sensitivity, showed a mean relative yield loss (RYL) of 63%. Parasitic Rhamphicarpa biomass (PRB), the difference between the above-ground biomass produced with and without a host, was suggested as indicator for infection level of this facultative parasite and hence as a practical measure for host resistance. Genetic variation in resistance and tolerance levels was observed among rice cultivars, but fertilizer applications significantly reduced parasite numbers, biomass and effects, cancelling out such genotypic differences. Depending on the tolerance level of the cultivars, the PRB only accounted for 3.7-38.8% of the average parasite-inflicted host biomass reductions, indicating phytotoxic effects of Rhamphicarpa infection.R. fistulosa is an apparently increasing constraint to rain-fed lowland rice in Benin, threatening rice production in the wider region. The use of resistant and tolerant cultivars, combined with fertilizer applications could reduce Rhamphicarpa infections and mitigate negative effects on rice yields.     

Effects of straw retention and phosphorous fertilizer application on available phosphorus content in the soil solution during rice growth

Phosphorus (P) is an essential nutrient for proper rice growth, and available P in the soil solution is a direct source of P for rice uptake. In this study, a field experiment (experiment A: straw retention (SRT) treatment versus straw removal (SRM) treatment) exposed to 3 years of continuous SRT and a pot experiment (experiment B: five P levels; SRT and SRM treatments) with different concentrations of applied P fertilizer were conducted to study the effects of SRT and P fertilizer application on the available P concentration in the soil solution during rice growth and on rice yield. SRT decreased the available P concentration in the soil solution, although it did not alter the trend of available P concentration in the soil solution during plant growth. In addition, in the 10–20-day period after transplantation, the available P concentration in the soil solution was high, although it decreased thereafter. The available P concentration in the soil solution increased with the amount of applied P fertilizer, and the rice yield also increased with increasing applications of P fertilizer. The results of experiments A and B showed that SRT had no significant impact on the rice yield; however, continuous observations over a number of years are required to verify the results.     

Tracing the fate of nitrogen with <Superscript>15</Superscript>N isotope considering suitable fertilizer rate related to yield and environment impacts in paddy field

While the application rate of nitrogen fertilizer is believed to dramatically influence rice fields and improve the soil conditions in paddy fields, fertilization with low use efficiency and nitrogen loss may cause environmental pollution. In this paper, ¹⁵N-labeled urea was used to trace the fate of nitrogen at four rates (0, 75, 225 and 375 kg N/ha) of urea fertilizer over three split applications in Hangzhou, Zhejiang, in 2014. Plant biomass, the soil nitrogen content of different layers, NH₃ volatilization and N₂O emissions were determined using the ¹⁵N abundance to calculate the portion from nitrogen fertilizer. The results indicated that rice yields increased with the application rate of nitrogen fertilizer. NH₃ volatilization is the main nitrogen loss pathway, and N₂O emissions were significantly associated with nitrogen application rates in the paddy. The percent of nitrogen loss by NH₃ volatilization and N₂O emissions increased with the nitrogen application rate. This study showed that the suitable N fertilizer in a loam clay paddy, considering the yield requirements and environmental issues, is approximately 225 kg N/ha in Hangzhou, with a distribution of 50.06% of the residual in the rice and soil and 48.77% loss as NH₃ volatilization and N₂O emissions. The nitrate from fertilization mainly remained in the 0–20 cm level of the topsoil.     

Lodging resistance locus prl5 improves physical strength of the lower plant part under different conditions of fertilization in rice (Oryza sativa L.)

High fertilizer application rates increase grain yield and biomass in rice, but reduces lodging resistance. Lodging resistance locus prl5 enhances pushing resistance through delaying leaf senescence and increasing carbohydrate reaccumulation in stems. This study demonstrates the effects of prl5 under different levels of Nitrogen·Phosphorus·Potassium basal fertilizer application using a chromosome segment substitution line based on the genetic background of Koshihikari, which contains prl5. High fertilizer application rates enhanced pushing resistance of the lower part, but did not consistently affect the pushing resistance of the whole plant. Independent of fertilizer application rates, prl5 enhanced pushing resistances of both the lower part and the whole plants. Plant height, biomass and grain yield were increased by high fertilizer application rates, but stem diameter and the dry weight of basal culms did not show consistent increases as determined over a period of 2 years. In leaves just after heading, chlorophyll (Chl) contents, rather than Rubisco contents, were correlated with fertilizer application rates. At the fully ripe stage, fertilizer application did not affect Chl and Rubisco contents in leaves, while prl5 increased the contents in the second leaf. High fertilizer application rates did not affect the concentration of non-structural carbohydrates (NSCs) in basal culms, but prl5 increased them at the fully ripe stage. These results suggest that fertilizer application reduces lodging resistance by highly elevating the center of gravity, but that prl5 can counteract this effect by enhancing the physical strength of the lower part through delaying leaf senescence and increasing NSC reaccumulation in culms without any effects of different fertilizer application rates.     

A model driven by crop water use and nitrogen supply for simulating changes in the regional yield of rain-fed lowland rice in Northeast Thailand

Climate change will have significant impacts on the rain-fed rice production ecosystem, and particularly on the ecosystem’s hydrology and water resources. Under rain-fed lowland conditions, substantial variations among fields in grain yield are commonly observed, but a method that can account for field-scale yield variability to produce regional-scale yield estimates is lacking, thereby limiting our ability to predict future rice production under changing climate and variable water resources. In this study, we developed a model for estimating regional yields of rain-fed lowland rice in Northeast Thailand, by combining a simple crop model with a crop calendar model. The crop model incorporates the effects of two important resources (water and nitrogen) on crop growth. The biomass accumulation is driven by water use, whereas the nitrogen supply determines canopy development and thereby constrains crop water use. Accounting for the wide range of planting dates and the strong photoperiod-sensitive characteristics of rice varieties through the calendar model is an essential component in determining regional yield estimates. The present model does not account for the effects of mid-season drought or flooding, but was nonetheless able to explain the spatial and temporal yield variations at the province level for the past 25 years. Thus, it can be used as a prototype for simulating regional yields of rain-fed lowland rice.     

Effects of Applying Potassium,Zeolite and Vermiculite on the Radiocesium Uptake by Rice Plants Grown in Paddy FieldSoils Collected from Fukushima Prefecture

Abstract

Radionuclides were released into the environment as a consequence of the Fukushima Daiichi Nuclear Power Plant accident that occurred on 11 March 2011. Radiocesium at an abnormal concentration was detected in brown rice produced in paddy fields located in northern part of Fukushima Prefecture. We examined several hypotheses that could potentially explain the excessive radiocesium level in brown rice in some of the paddy fields, including (i) low exchangeable potassium content of the soil, (ii) low sorption sites for cesium (Cs) in the soil, and (iii) radiocesium enrichment of water that is flowing into the paddy fields from surrounding forests. The results of experiments using pots with contaminated soil indicated that the concentration of radiocesium in rice plants was decreased by applying potassium or clay minerals such as zeolite and vermiculite. The obtained results indicated that high concentrations of radiocesium in rice are potentially a result of the low exchangeable potassium and sorption sites for Cs in the soils. Application of potassium fertilizer and clay minerals should provide an effective countermeasure for reducing radiocesium uptake by plants. Radiocesium-enriched water produced by leaching contaminated leaf litter was used to irrigate rice plants in the cultivation experiments. The results indicated that the radiocesium concentrations in rice plants increased when the radiocesium-enriched water was applied to the potted rice plants. This indicated the possibility that the radiocesium levels in brown rice will increase if the nuclide is transported with water into the rice paddy fields from surrounding forests.     

Grain yield responses of lowland rice varieties to increased amount of nitrogen fertilizer under tropical highland conditions in central Kenya

Tropical highland conditions in Mwea Kenya, ensure the high radiation and the large day–night temperature differences. Such conditions are generally believed to promote rice growth and yield, but the current grain yield is lower than the expectation. In the current standard N fertilizer practice in Mwea, 75 kg nitrogen (N) ha^?1 is applied in three splits at fixed timing. The effects of increases in N fertilizer amount (125, 175, and 225 kg N ha^?1) on rice growth and yield were evaluated to test the hypothesis that unachieved high rice grain yield in Mwea is due to insufficient amount of N fertilizer. Two popular lowland varieties in Mwea (Basmati 370 and BW196) and two varieties reported as high yielding in other countries (Takanari and IR72) were used. Shoot dry weight (DW) increased with increases in the amount of N fertilizer applied in three splits at fixed timing, irrespective of variety. It reached approximately 20 t ha^?1 under increased N conditions (>75 kg N ha^?1) in several cases, indicating that high biomass production could be achieved by increasing N application rate. However, the increased biomass did not increase grain yield, due to decreased grain filling under high N conditions in all varieties. Thus, N amounts above 75 kg ha^?1 were ineffective for increasing grain yields in Mwea, where N fertilizer was applied in three splits at fixed timing. Increasing influence of low temperature under high N conditions may be one of the reasons for the decreased grain filling in Mwea.     

Prediction of the environmental concentration of pesticide in paddy field and surrounding surface water bodies

Pesticides are very important in European rice production. For appropriate environmental protection, it is useful to predict the potential impact of pesticides after application, in paddy fields, in paddy runoff, and in the surrounding water, by calculating predicted environmental concentrations (PECs). In this paper, a joint simulation is described, coupling a field-scale pesticide fate model (RICEWQ) and a transportation model (RIVWQ) to evaluate the potential for predicting environmental concentrations of pesticides in the paddy field and adjacent surface water bodies and comparing the predicted values with the monitoring data. The results demonstrate that the application of the calibrated field-scale RICEWQ model is a conservative method to predict the PEC at the watershed level, overestimating the observed data; the coupled RICEWQ and RIVWQ models could be adequately used to predict PECs in the surrounding water at watershed level and in the higher tier risk assessment procedure.     

Modeling the water and nitrogen transports in a soil–paddy–atmosphere system using HYDRUS-1D and lysimeter experiment

Efficient water and fertilizer use is of paramount importance both in rain-fed and irrigated rice cultivation systems to tread off between the crop water demand during the dry spell and the fertilizer leaching. This lysimeter study on paddy in a lateritic sandy loam soil of the eastern India, to simulate the water and solute transports using the HYDRUS-1D model, reveals that this model could very well simulate the soil depth-specific variations of water pressure heads and nitrogen (N) concentrations with the efficiency of >86 and 89%, respectively. The change in the level of water ponding depth did not have a significant effect on the time to peak and the temporal variability of N concentration in the bottom soil layer. The lysimeter-scale water balance analysis indicated that the average deep percolation loss and crop water use were 35.01 ± 2.03 and 39.74 ± 1.49% of the total water applied during the crop growth period, respectively. Similarly, the amount of N stored in the plant and lost through soil storage, deep percolation, and other losses (mineralization, denitrification, and gaseous N loss to the atmosphere through plant leaves) were 1.60 ± 0.16, 0.17 ± 0.04, 12.00 ± 0.48, and 86.23 ± 0.41% of the total applied nitrogen, respectively. The simulation results reveal that a constant ponding depth of 3 cm could be maintained in paddy fields to reduce the N leaching loss to 7.5 kgN/ha.     

Rice yield and productivity gaps in irrigated systems of the forest zone of Côte d'Ivoire

Much of the rapidly growing demand for rice in West Africa will be met from increased production in irrigated lowlands, which cover about 12% of the regional rice-growing area. A large potential for expansion of irrigated areas exists particularly in the inland valleys of the humid forest zone. Current production is characterized by large variability in productivity, management practices and production constraints. Quantifying the variability in rice yield and identifying the determining factors are prerequisites to the development of site-specific recommendations and to improved targeting of technologies. Diagnostic on-farm trials were conducted on 64 irrigated lowland fields in the humid forest zone of southern Côte d'Ivoire, in 1995–1996. This was a part of the regional gradient study of irrigated systems from the desert margin to the humid forest zone. Cropping calendars, field operations and input use were monitored. Weed biomass, rice N uptake, and grain yield were determined in farmers' fields as well as in super-imposed, researcher-managed subplots (clean weeding, no N control, and mineral fertilizer N application). Rice yield potential was simulated by using the Oryza-S crop growth model. Yield losses were attributed to management factors based on performance of rice in researcher-managed subplots (management-related yield gap) and by multiple regression with management options. Grain yields varied between 0.2 and 7.3 Mg ha⁻¹ with mean yields of 3.2 in partially and 4.2 Mg ha⁻¹ in fully irrigated systems, 44% and 57% of the potential yield of 7.3 Mg ha⁻¹, respectively. Age of seedlings at transplanting, timeliness of operations and application of P fertilizer were correlated to yield and explained 60% of the observed variability. Grain yield was correlated with N uptake (r² = 0.93^***) but not with N application rate. Split application of mineral fertilizer N was associated with a 0.48 Mg ha⁻¹ yield increase (p = 0.002), regardless of the quantity applied. Additional weeding increased yield only in systems with imperfect irrigation. Weed biomass was reduced with improved water control and it increased with age of seedlings at transplanting, and was higher in direct-seeded than in transplanted rice. Echinochloa spp. were the most common weeds in fully irrigated systems and Panicum laxum was more common in the imperfectly irrigated fields. While improved water management was associated with substantial rice yield increases (1.16 Mg ha⁻¹), the timeliness of transplanting, weeding and N fertilization appears to be the key to increased rice yields in the forest zone of West Africa.     

豫南“籼改粳”理论与技术研究进展

简要介绍了豫南稻区"籼改粳"的基本情况和在理论技术方面的研究进展。高温、稻瘟病和纹枯病、三代三化螟危害是豫南粳稻产量低、品质差的三大障碍因子,而播期早是产生障碍的根源,推迟粳稻播期是"籼改粳"的关键技术;豫南"籼稻-小麦"轮作存在制度缺陷,推迟粳稻播期可以得到修复,因秧龄过长而减产、机插秧以及抛秧难以利用等问题得到解决;增产提质、机械化、轻简化、规模化生产是"籼改粳"的必然选择;"东粳西移"是解决豫南粳稻品种利用的有效途径;机插秧、抛秧有利于实现粳稻推迟播种,而"泥质法"育秧解决了高温条件下育秧的问题,提高了机插秧、抛秧的秧苗素质;粳稻晚播稻瘟病、纹枯病和三化螟已不再是豫南"籼改粳"的毁灭性病虫害,恶苗病、干尖线虫病、稻蓟马、稻曲病上升为主要病虫害;水稻两段栽培技术是根据水稻高产稳产生长发育规律,分别从群体、形态和机能构建三个方面进行栽培设计,按照营养生长和生殖生长两个阶段进行定向培育的一种栽培方法,不仅高产稳产,而且减肥减药。     

Evapotranspiration,irrigation water requirement,and water productivity of rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.) in the Sahelian environment

Rice is the main crop produced in the Senegal River Valley under the semiarid Sahelian climate where water resource management is critical for the resource use sustainability. However, very limited data exit on rice water use and irrigation water requirement in this water scarcity environment under climate change conditions. Understanding crop water requirements is essential for better irrigation practices, scheduling and efficient use of water. The objectives of this study were to estimate crop water use and irrigation water requirement of rice in the Senegal River Valley at Fanaye. Field experiments were conducted during the 2013 hot and dry season and wet season, and 2014 hot and dry season and wet seasons. Three nitrogen fertilizer treatments were applied to rice variety Sahel 108: 60, 120, and 180 kg N ha^?1. Rice water use was estimated by the two-step approach. Results indicated that crop actual evapotranspiration (ETa) varied from 632 to 929 mm with the highest ETa obtained during the hot and dry seasons. Irrigation water requirement varied from 863 to 1198 mm per season. Rice grain yield was function of the growing season and varied from 4.1 to 10.7 tons ha^?1 and increased with nitrogen fertilizer rate. Rice water use efficiency relative to ETa and irrigation requirements increased with nitrogen fertilizer rate while rice nitrogen use efficiency decreased with the nitrogen fertilizer rates. The results of this study can be used as a guideline for rice water use and irrigation water requirement for the irrigation design projects, consultants, universities, producers, and other operators within rice value chain in the Senegal River Valley.     

Effect of water management on soil respiration and <Emphasis Type="Italic">NEE</Emphasis> of paddy fields in Southeast China

Water management is an important factor in regulating soil respiration and the net ecosystem exchange of CO₂ (NEE) between croplands and atmosphere. However, how water management affects soil respiration and the NEE of paddy fields remains unexplored. Thus, a 2-year field experiment was carried out to study the effects of controlled irrigation (CI) during the rice season on the variation of soil respiration and NEE, with flooding irrigation (FI) as the control. A decrease of irrigation water input by 46.39% did not significantly affect rice yield but significantly increased irrigation water use efficiency by 0.99 kg m^?3. The soil respiration rate of CI paddy fields was larger than that of FI paddy fields except during the ripening stage. Natural drying management during the ripening stage resulted in a significant increase of the soil respiration rate of the FI paddy fields. Variations of NEE with different water managements were opposite to soil respiration rates during the whole rice growth stages. Total CO₂ emission of CI paddy fields through soil respiration (total R _soil) increased by 11.66% compared with FI paddy fields. The increase of total R _soil resulted in the significant decrease of total net CO₂ absorption of CI paddy fields by 11.57% compared with FI paddy fields (p < 0.05). There were inter-annual differences of soil respiration and the NEE of paddy fields. Frequent alternate wetting and drying processes in the CI paddy fields were the main factors influencing soil respiration and NEE. CI management slightly enhanced the rice dry matter amount but accelerated the consumption and decomposition of soil organic carbon and significantly increased soil respiration, which led to the decrease of net CO₂ absorption. CI management and organic carbon input technologies should be combined in applications to achieve sustainable use of water and soil resources in paddy fields.     

Intermittent drainage in paddy soil: ecosystem carbon budget and global warming potential

Intermittent drainage of rice fields alters soil redox potential and contributes to the reduction of CH₄ emission and thus may reduce net global warming potential (GWP) during rice cultivation. Incorporation of green biomass helps maintaining soil organic matter, but may increase CH₄ emission. We investigated net ecosystem carbon budget (NECB) and net GWP under two water management regimes—continuous flooding and intermittent drainage—having four biomass incorporation levels (0, 3, 6 and 12 Mg ha^?1). Water management and biomass incorporation level demonstrated significant (P < 0.05) interaction effect on the NECB and GWP. Intermittent drainage decreased the NECB by ca. 6–46 % than continuous flooding under same rates of cover crop biomass (CCB) incorporation. Moreover, intermittent drainage reduced seasonal CH₄–C fluxes by ca. 54–58 % and net GWP by 35–58 % compared to continuous flooding. There was also no significant reduction in rice yield because of intermittent drainage under similar CCB. This implies that incorporation of 3 Mg ha^?1 CCB and intermittent drainage could be a good option for reducing net GWP and higher grain yield.     

The effects of water management,timing and the rate of several herbicides on the growth of Murdannia keisak (Hassk.) Handel-Mazz

Murdannia keisak is a competitive rice weed found throughout the world. The aims of this study were to investigate the influence of different water managements on the growth of M. keisak under greenhouse conditions, and to assess the efficacy of common rice herbicides against it under field conditions.Three water management techniques were tested under greenhouse conditions: saturation, intermittent irrigation, and continuous flooding. The efficacy against M. keisak was evaluated in paddy fields during 2003–2005. In 2003, bispyribac-sodium was applied alone or in combination with triclopyr or metosulam at 20, 27, and 32 days after seeding (DAS). In 2004 and 2005, bispyribac-sodium was applied once (30 DAS), but at two application rates.Results for the three water treatments showed continuous flooding reduced M. keisak biomass most as confirmed by aboveground fresh weights. In the paddy field experiments, bispyribac-sodium also proved highly effective against M. keisak and was selective to rice with more than 90% efficacy. The addition of tryclopyr or metosulam to bispyribac-sodium failed to improve its herbicidal efficacy. Finally, the best M. keisak control at field condition was obtained with continuous flooding combined with bispyribac-sodium.