Season Rice Crop Research Articles

Dimension of Humidity in Various Rice Cropping Season at Rangpur District in Bangladesh

This research was intended to analyze the variation and trend of humidity pattern in the major cropping seasons like Aus, Aman and Boro season in Rangpur region of Bangladesh. Humidity data collected from the Bangladesh Meteorological Department (BMD) between 1990 and 2020 was utilized in this investigation. Analysis of linear trends was used to investigate the seasonal change in humidity. The investigation's findings demonstrated that there were numerous abnormalities in the daily, monthly, and seasonal variations of humidity where annual humidity rising in the Aman and Aus season and falling in the Boro season that main reasons are unusual monsoon pattern and abnormalities of temperature. According to the research's findings, there have been notable fluctuations in humidity during the Aus, Aman, and Boro seasons. Bangladesh's rice-based agriculture may suffer because of these adjustments. Bangladesh's climate-driven agricultural sector can benefit from the application of thresholding, regional and countrywide humidity analysis, and other environmental methodologies in combination with adaptation planning for sustainable agriculture.

Rice yield prediction through integration of biophysical parameters with SAR and optical remote sensing data using machine learning models

In an era marked by growing global population and climate variability, ensuring food security has become a paramount concern. Rice, being a staple crop for billions of people, requires accurate and timely yield prediction to ensure global food security. This study was undertaken across two rice crop seasons in the Udham Singh Nagar district of Uttarakhand state to predict rice yield at 45, 60 and 90 days after transplanting (DAT) through machine learning (ML) models, utilizing a combination of optical and Synthetic Aperture Radar (SAR) data in conjunction with crop biophysical parameters. Results revealed that the ML models were able to provide relatively accurate early yield estimates. For summer rice, eXtreme gradient boosting (XGB) was the best-performing model at all three stages (45, 60, and 90 DAT), while for kharif rice, the best-performing models at 45, 60, and 90 DAT were XGB, Neural network (NNET), and Cubist, respectively. The combined ranking of ML models showed that prediction accuracy improved as the prediction date approaches harvest, and the best prediction of yield was observed at 90 DAT for both summer and kharif rice. Overall rankings indicate that for summer rice, the top three models were XGB, NNET, and Support vector regression, while for kharif rice, these were Cubist, NNET, and Random Forest, respectively. The findings of this study offer valuable insights into the potential of the combined use of remote sensing and biophysical parameters using ML models, which enhances food security planning and resource management by enabling more informed decision-making by stakeholders such as farmers, policy planners as well as researchers.

Simultaneous improvement and genetic dissection of drought and submergence tolerances in rice (Oryza sativa L.) by selective introgression.

Drought and submergence are contrasting abiotic stresses that often occur in the same rice crop season and cause complete crop failure in many rain-fed lowland areas of Asia. To develop rice varieties with good tolerances to drought and submergence, 260 introgression lines (ILs) selected for drought tolerance (DT) from nine BC2 populations were screened for submergence tolerance (ST), resulting in 124 ILs with significantly improved ST. Genetic characterization of the 260 ILs with DNA markers identified 59 DT quantitative trait loci (QTLs) and 68 ST QTLs with an average 55% of the identified QTLs associated with both DT and ST. Approximately 50% of the DT QTLs showed 'epigenetic' segregation with very high donor introgression and/or loss of heterozygosity (LOH). Detailed comparison of the ST QTLs identified in ILs selected only for ST with ST QTLs detected in the DT-ST selected ILs of the same populations revealed three groups of QTLs underlying the relationship between DT and ST in rice: a) QTLs with pleiotropic effects on both DT and ST; b) QTLs with opposite effects on DT and ST; and c) QTLs with independent effects on DT and ST. Combined evidence identified most likely candidate genes for eight major QTLs affecting both DT and ST. Moreover, group b QTLs were involved in the Sub1regulated pathway that were negatively associated with most group aQTLs. These results were consistent with the current knowledge that DT and ST in rice are controlled by complex cross-talks between or among different phytohormone-mediated signaling pathways. Again, the results demonstrated that the strategy of selective introgression was powerful and efficient for simultaneous improvement and genetic dissection of multiple complex traits, including DT and ST.

Reduced tillage and crop diversification can improve productivity and profitability of rice-based rotations of the Eastern Gangetic Plains.

Intensive rice (Oryza sativa)-based cropping systems in south Asia provide much of the calorie and protein requirements of low to middle-income rural and urban populations. Intensive tillage practices demand more resources, damage soil quality, and reduce crop yields and profit margins. Crop diversification along with conservation agriculture (CA)-based management practices may reduce external input use, improve resource-use efficiency, and increase the productivity and profitability of intensive cropping systems. A field study was conducted on loamy soil in a sub-tropical climate in northern Bangladesh to evaluate the effects of three tillage options and six rice-based cropping sequences on grain, calorie, and protein yields and gross margins (GM) for different crops and cropping sequences. The three tillage options were: (1) conservation agriculture (CA) with all crops in sequences untilled, (2) alternating tillage (AT) with the monsoon season rice crop tilled but winter season crops untilled, and (3) conventional tillage (CT) with all crops in sequences tilled. The six cropping sequences were: rice-rice (R-R), rice-mung bean (Vigna radiata) (R-MB), rice-wheat (Triticum aestivum) (R-W), rice-maize (Zea mays) (R-M), rice-wheat-mung bean (R-W-MB), and rice-maize-mung bean (R-M-MB). Over three years of experimentation, the average monsoon rice yield was 8% lower for CA than CT, but the average winter crops yield was 13% higher for CA than CT. Systems rice equivalent yield (SREY) and systems calorie and protein yields were about 5%, 3% and 6%, respectively, higher under CA than CT; additionally, AT added approximately 1% more to these benefits. The systems productivity gain under CA and AT resulted in higher GM by 16% while reducing the labor and total production cost under CA than CT. The R-M rotation had higher SREY, calorie, protein yields, and GM by 24%, 26%, 66%, and 148%, respectively, than the predominantly practiced R-R rotation. The R-W-MB rotation had the highest SREY (30%) and second highest (118%) GM. Considering the combined effect of tillage and cropping system, CA with R-M rotation showed superior performance in terms of SREY, protein yield, and GM. The distribution of labor use and GM across rotations was grouped into four categories: R-W in low-low (low labor use and low GM), R-M in low-high (low labor use and high GM), R-W-MB and R-M-MB in high-high (high labor use and high GM) and R-R and R-MB in high-low (high labor use and low GM). In conclusion, CA performed better than CT in different winter crops and cropping systems but not in monsoon rice. Our results demonstrate the multiple benefits of partial and full CA-based tillage practices employed with appropriate crop diversification to achieve sustainable food security with greater calorie and protein intake while maximizing farm profitability of intensive rice-based rotational systems.

Rice-based Cropping System Intensification in the Coastal Saline area of Bangladesh: Problems and Prospects

The coastal zone environment of Bangladesh is characterised geographically by river deltas and estuaries, where tidal and riverine flooding and varying salinity levels affect agriculture and livelihoods. In this area, the land and agricultural productivity is very low because of several constraints, particularly waterlogging, high salinity of soil and water, freshwater scarcity for crop irrigation and natural disaster. In this review, the objectives are to focus on the limiting factors for crop intensifying and highlighting the opportunities to increase coastal agriculture while enhancing farmer’s livelihoods. Some recent studies demonstrated many opportunities for increasing cropping systems that have not yet been exploited extensively. Rainwater or low saline river water storing in the internal canal can fulfil the water requirement for dry season rice and non-rice crops, thereby increasing growth and yield. Early establishment of “Rabi” crops (non-rice) can utilize maximum low-saline soil water and escape high salinity/drought or heat/storms at later period of the growing stages, but this early sown Rabi crops needs early harvest of Aman rice around 15-30 days earlier than farmer practices. Moreover, early sowing by zero tilled dibbling (such as sunflower, maize, wheat, and potato) in wet soils results in higher yield potential. Using rice straw mulch ~5 t ha-1 has been shown to be highly beneficial for ameliorating soil constraints. A recent study revealed that straw mulch application on soil surface increased soil water and soil solute potential in the upper root zone, reduced soil salinity, soil strength, and cracking which attributed to higher yield. Considering the successful dry season crop establishment and yield potential requires early drainage to remove excess soil water and a drainage system that mitigates waterlogging from heavy rainfall events during the growing season. We expect this review will facilitate the future research planning and execution in this vulnerable coastal environment. Bangladesh Rice J. 25 (2) : 31-43, 2021

Adapted Conservation Agriculture Practices Can Increase Energy Productivity and Lower Yield-Scaled Greenhouse Gas Emissions in Coastal Bangladesh

While numerous studies have documented the benefits of conservation agriculture (CA) in South Asia, most focus on favorable environments where farmers have reliable access to energy supporting irrigation and inputs. The performance of CA in South Asia’s under-developed coastal environments is comparatively understudied. In these environments, farmers are increasingly interested in growing a second crop to meet food security and income generation objectives in rotation following the predominant monsoon season rice crop, though labor, energy costs, and investment constraints limit their ability to do so. We hypothesized that rotating rice (Oryza sativa) with maize (Zea mays) using conservation agriculture, or CA (i.e., strip-tilled maize followed by unpuddled transplanted rice), or seasonally alternating tillage (SAT, i.e., strip-tilled maize followed by fully-tilled, puddled rice with residues retained across rotations) would reduce costs and energy use, increase energy-use efficiency, and reduce yield-scaled CO2-eq emissions (YSE) and total global warming potential (GWP), compared to farmers’ own practices (FP) and conventional full-tillage (CT) under the same rotation in Bangladesh’s coastal region. Starting with winter maize followed by summer rice, we evaluated four tillage and crop establishment treatments in farmer-managed experiments in partially irrigated and rainfed environments over three years in 35 farmer’s fields across Bangladesh’s coastal districts. Treatments included FP, CT, complete CA, and SAT under a rice-maize rotation. Across years, the full suite of CA practices and SAT were significantly more energy-efficient and energy-productive than FP or CT. The order of YSE in rice was CA< CT or FP < SAT while in maize, it was CA or SAT < FP < CT. Across environments, CA and SAT resulted in 15-18% higher yield at the cropping systems level (maize and rice yields combined) and 26-40% less manual labor than CT or FP. CA and SAT also reduced by 1-12% and 33-35% total production costs respective to CT and FP. This was associated with 13-17% greater grain energy output in CA and SAT, and 2-18% lower YSE, compared to CT or FP. While our data suggest that both CA and SAT can result in a range of positive agronomic, economic, and environmental outcomes compared to FP or CT, post-trial surveys and discussions with farmers revealed a strong practical aversion to use of the full suite of CA practices and preference for adapted practices due to logistical constraints in negotiating the hire of laborers for unpuddled manual transplanting.

Season and No-Till Rice Crop Intensification Affect Soil Microbial Populations Involved in CH4 and N2O Emissions

Rice is an important source of methane (CH4) and other crops may be sources of nitrous oxide (N2O), both of which are powerful greenhouse gases. In Uruguay, irrigated rice rotates with perennial pastures and allows high productivity and low environmental impact. A long-term experiment with contrasting rice rotation intensification alternatives, including rice–soybean and continuous rice, was recently carried out in an Argialboll located in a temperate region of South America. To know if rotation systems influence soil microbial activity involved in CH4 and N2O emissions, the abundance and potential rate for gas production or consumption of microbial populations were measured during the rice crop season. CH4 was only emitted when rice was flooded and N2O emission was not detected. All rotational soils showed the highest rate for methanogenesis at tillering (30 days after rice emergence), while for methanotrophy, the maximum rate was reached at flowering. The abundance of related genes also followed a seasonal pattern with highest densities of mcrA genes being observed at rice flowering whereas pmoA genes were more abundant in dry soils after rice harvest, regardless of the rotation system. Differences were found mainly at tillering when soils with two consecutive summers under rice showed higher amounts of mcrA and pmoA gene copies. The potential denitrification rate was highest at the tillering stage, but the abundance of nirK and nirS genes was highest in winter. Regarding ammonium oxidation, bacterial amoA abundance was higher in winter while the archaeal amoA gene was similar throughout the year. A strong influence of the rice growth stage was registered for most of the parameters measured in rice paddy soils in this no-till rice intensification experiment. However, differences among rotations begin to be observed mainly at tillering when the abundance of populations of the methane and nitrous oxide cycles seemed to respond to the rice intensification.

RICA: A rice crop calendar for Asia based on MODIS multi year data

Information on when and where rice is planted and harvested is important for crop management under a changing climate and for monitoring crop production for early warning and market information systems. The diversity of plant genetic, crop management, and environmental conditions leads to a wide variation in the number of rice crops per year and the dates of crop establishment and harvesting across Asia. Asia-wide rice crop calendars exist (e.g., RiceAtlas) but are based on heterogeneous data sources with varying levels of detail and are challenging to update. Earth observations can contribute to consistent and replicable crop calendars. Here we demonstrate and validate a method for generating a rice crop calendar across Asia. Our analysis at administrative unit-level is based on pixel-level analysis with the PhenoRice algorithm using MODIS imagery (2003–16) to estimate start of season (SoS) and end of season (EoS) dates. PhenoRice outputs were post-processed to generate representative statistics on the number of rice crop seasons per year and their SoS/EoS dates per administrative unit across Asia, called RICA (a RIce crop Calendar for Asia). RICA SoS and EoS dates across all seasons correlated strongly with RiceAtlas crop establishment and harvesting dates (R2 of 0.88 and 0.82 respectively, n = 1,186). The mean absolute errors were around 26 and 33 days for SoS and EoS, respectively. A detailed assessment in the Philippines where data in RiceAtlas are particularly accurate had even better results (R2 of 0.93 and 0.85 respectively, n = 131). Comparisons to other published rice calendars also suggested that RICA captured rice cropping season dates well. Our study results in a unique and validated method to estimate rice crop calendar information on continental scale from remote sensing data.

The potential of crop residue recycling for sustainable phosphorus management in non-flooded rice-lentil system in alkaline soil

Aerobic rice is gaining global recognition for its role in the conservation of water. However, its productivity is often constrained by several deficiencies in the soil-plant system. Particularly, in absence of flood-induced phosphorus (P) desorption, it is likely that P availability in aerobic soils would be reduced thus affecting the productivity. Presently, our understanding of soil P dynamics and its bioavailability in aerobic rice-based system(s) is limited, particularly in alkaline soils. In this study, the impact of sole fertilizer and integrated P management on soil P dynamics, biochemical and biophysical properties and crop yields in direct-seeded rice (DSR)-lentil rotation in alkaline soil was assessed to devise sustainable management option(s). Seven different P treatments in aerobic direct seeded rice-lentil system [subscript value (kg P ha−1)] i.e., P control (P[0−0]), three sole fertilizer-P treatments with variable rate application to component crops (P[22−22], P[33−11], P[11−33]), and three integrated treatments ([P11−11+ phosphate solubilizing bacteria (B)], [P16.5−5.5+ rice residue recycling (RR)+B], [P5.5−16.5+lentil residue recycling (LR)+B]) in aerobic direct seeded rice-lentil system along with a conventional flooded rice-lentil system with the recommended fertilizer-P rate (P[22−22]FR) were studied. Given the recommended sole fertilizer-P rate, the aerobic rice soil (P[22−22]) had lower available-P (8–10 %) compared to the flooded rice soil (P[22−22]FR). The rice residue recycling integrated treatment (P16.5−5.5+RR + B) increased soil available-P in both the rice (5–6 %) and lentil (12–13 %) crop season over the recommended sole fertilizer-P treatment (P[22−22]), and also increased the system productivity by 6–7 %. The higher NaHCO3-Pi (13 %) and dissolved non-reactive P (DNRP) (7%) in the treatment P16.5−5.5+RR + B over the treatment P[22−22] suggested a higher soil P mobilization potential of rice residue recycling integrated treatment. The effect of lentil residue recycling integrated treatment (P5.5−16.5+LR + B) and recommended sole fertilizer-P treatment P[22−22] was similar on soil P and crop yields, and would thus be an option when considering the reduction of P fertilizer use in aerobic rice. Soil aggregation, very-labile carbon, microbial biomass carbon, DNRP exhibited positive correlations with P bioavailability in the aerobic rice soil. Our results suggested that C-stabilization in aerobic rice soil is altered with P input, the lowest rate being recorded in the control treatment. Hence, the study concluded that reduced soil P availability could limit the productivity potential of aerobic rice-lentil system in alkaline soils, and integrated treatments involving in-situ crop residue recycling (rice in particular) and suboptimal fertilizer rate could improve soil P bioavailability, soil quality parameters, and crop yields, thus, recommended for sustainable management.

Quantifying farmers' preferences for cropping systems intensification: A choice experiment approach applied in coastal Bangladesh's risk prone farming systems

CONTEXTSustainable intensification (SI) is envisioned as an effective strategy for developing countries to increase farm productivity while reducing negative environmental and social externalities. The development of regionally appropriate SI options however requires accounting for the knowledge and preferences of key stakeholders. In Bangladesh, the Government has requested international donors to support the development of dry season rice expansion in the coastal region. Policies however tend to be made without adequate study of farmers' preferences and ambitions; this can render crop intensification efforts ineffective. Understanding farmers' preferences for alternative crops and crop management practices are therefore crucial for success where agricultural development investments aim at incorporating the principles of SI. OBJECTIVE(S)Using coastal Bangladesh as a case study– we aim to (1) quantify farmers' preferences for alternative irrigated crop and crop management options in comparison to the status quo (land fallowing), (2) analyze whether farmers' preferences are conditioned by concerns regarding the cost and availability of irrigation and fertilizer inputs in comparison to expected net revenues, (3) understand how the heterogeneity in preferences can be attributed to farmer and/or farm characteristics, institutional, and biophysical factors, (4) determine how much farmers' are willing to invest in different crops and crop management options – including those reliant and not reliant on irrigation. METHODSTaking 300 farmers in two diverse coastal environments, a choice experiment (CE) was employed to explore the heterogeneity in farmers' preferences for different dry “rabi” season intensification options (‘boro’ rice, maize, wheat and mungbean) against the status quo (dry season land fallowing after harvest of the monsoon season rice crop). Analyses included random parameter logit modeling followed by willingness-to-invest and profit simulations. RESULTS AND CONCLUSIONSAnalyses revealed strong farmer preferences against rice and in favor of irrigated maize, and also in favor of rainfed or partially irrigated mungbean as an alternative to land fallowing. Irrespective of their location and environmental conditions, respondents had largely a negative preference for irrigation and fertilizer use due to high investment costs and associated production risks in the dry season. Nonetheless, a significant positive effect on their willingness-to-intensify cropping was observed where farmers felt it feasible to provide in-field drainage to limit waterlogging risks. SIGNIFICANCEThe study signifies the importance of accounting for farmers' preferences while developing context-specific SI policies. Improving agronomic investments, tenure security, market, credit and extension support are likely prerequisites, alongside targeted diffusion of stress-tolerant mungbean and maize varieties for SI in coastal Bangladesh.

Greenhouse gas emissions during rice crop year affected by management of rice straw and ryegrass

ABSTRACT One of the challenges in rice areas is the sustainable post-harvest system, which involves using rice straw management and cover crop species. In this context, this study aimed to evaluate the emission of methane (CH4) and nitrous oxide (N2O) with the use of different post-harvest management of rice straw as well as with the combined use of ryegrass. A field experiment was conducted during the 2016 off-season and 2016/17 rice crop season with different post-harvest rice straw management: maintaining [...]

Preceding (Rice-Okra) Crops Herbicide Residual Effects on Weed, Growth, Yield and Economics of Succeeding Blackgram Under Different Ecosystem

Field experiments were carried out during summer seasons of 2017 and 2018 to study the effect of preceding (Rice-Okra) crops herbicide residue on weed, growth, yield and economics of succeeding blackgram. Residual effect of butachlor at 1.25 kg/ha on 3 days after transplanting (DAT) fb hand weeding (HW) on 40 DAT imposed in the first season rice crop and followed by hand weeding (HW) twice at 20 and 40 days after sowing (DAS) (T6) in okra and blackgram significantly influenced the reduction of weed dry weight accumulation by 8.75 and 7.44 times in mainland and island ecosystem, respectively at 20 DAS. The same treatment recorded the highest weed control efficiency (WCE) of 88.6, 86.5 and 86.2, 80.7 % observed at 20 and 40 DAS under mainland and island ecosystem, respectively. Among, the weed control treatments, residual effect of butachlor at 1.25 kg/ha on 3 DAT fb HW on 40 DAT to rice and HW twice at 20 and 40 DAS (T6) to okra and blackgram has recorded 64.8 and 65.0% higher seed yield of blackgram under main and island ecosystem, respectively.

Methane and Nitrous Oxide Flux after Biochar Application in Subtropical Acidic Paddy Soils under Tobacco-Rice Rotation

Biochar amendment is a good means of mitigating methane (CH4) and nitrous oxide (N2O) emissions. However, the effects of biochar amendment on N2O and CH4 reduction in soil under rotation with different soil moisture contents is not well understood. To understand CH4 and N2O flux from soil with biochar amendment under water-unsaturated and water-saturated conditions, a field experiment was conducted in a tobacco-rice rotation field in subtropical China to investigate N2O and CH4 emissions following soil amendment with tobacco straw biochar at rates of 0, 10, 40 and 80 t·ha−1 (B0, B10, B40 and B80, respectively). N2O and CH4 emissions were monitored by a closed-chamber method in the water-unsaturated tobacco (UT) and water-saturated rice (SR) seasons during the 2015 planting season. The soil pH increased from 5.4 in the control to 6.1 in the soil amended with biochar at 80 t·ha−1 in the UT season. During both the UT and SR seasons, with biochar amendment at 40 and 80 t·ha−1, the soil bulk density (BD) decreased, while the soil organic matter (SOM) and available potassium (Av. K) contents increased. N2O flux was significantly greater in UT than in SR in the controls but decreased with the application of biochar during both the UT and SR seasons. The cumulative CH4 emission decreased with the rate of biochar application and the methanotroph pmoA gene copy number in soils and increased with the methanogenic archaea 16Sr DNA gene copy number in soils during the rice-cropping season. These results indicated that biochar amendment could decrease methanogenic archaea and increase of methanotroph pmoA gene, which are the mechanistic origin for CH4 reduction.

Ambient air quality changes after stubble burning in rice-wheat system in an agricultural state of India.

Ground-based ambient air monitoring was conducted to assess the contribution of crop residue burning of wheat (Triticum aestivum) and rice (Oriza sativa) at different locations in three districts (Kaithal, Kurukshetra, and Karnal) of the agricultural state of Haryana in India for two successive years (2016 and 2017). The Air Quality Index (AQI) and concentration of primary pollutants (SOx, NOx, and PM2.5) were determined in rice and wheat crop season, for burning and non-burning periods. During crop residue burning periods, concentrations of SOx, NOx, and PM2.5 were exceeded the NAAQS values by 78%, 71%, and 53%, respectively. A significant increase in SOx (4.5 times), NOx (3.8 times), and PM2.5 concentration (3.5 times) was observed in stubble burning periods as compared to pre-burning (p < 0.05). A positive and significant correlation among the three pollutant concentrations was observed (p < 0.01). The AQI of KA site in Karnal district fell in severely polluted category during 2016 for rice as well as wheat residue burning period, and of KK site in Kaithal during wheat residue burning in year 2017. Results of present study indicate a remarkable increase in pollutant concentration (SOx, NOx, and PM2.5) during the crop residue burning periods. To the best of our knowledge, the outcomes of present study in this region have not been reported in earlier reports. Hence, there is an urgent need to curb air pollution by adopting sustainable harvesting technologies and management of residues.

Enhanced Ozone Production in Ambient Air at Patiala Semi-Urban Site During Crop Residue Burning Events

The continuous in situ measurements of criteria pollutants (O3, CO and NOx) and meteorological variables were done at a semi-urban site (Patiala) of North-West Indo-Gangetic Plains (NW-IGP) for the years 2014 and 2015. The influence of meteorology on the levels of criteria pollutants was investigated on daily, monthly, seasonal and diurnal basis. The average rate of increase in O3, calculated to be 1.1 ppb h−1 and pollution index (daily O3 max/O3 min ratio), values (10.2) indicates remarkable ozone pollution. Ozone is negatively correlated (represented as r value) with its precursor gases CO (− 0.28) and NOx (− 0.32), as they get consumed in the photochemical production of ozone. The impact of meteorology on ozone production was positively correlated with SR (0.63), AT (0.49), MT (0.59) and WS (0.23) and negatively correlated with RH (− 0.83). Pre-, during and post-biomass burning periods were determined using Terra-MODIS images over the study area. Enhanced levels of ozone were recorded as 20 ppb and 15 ppb during daytime, respectively, for rice and wheat crop seasons, and 12 ppb during nighttime for both seasons. Ozone exceedance of 24 h national standard occurred on 50% and 8% of the sampling periods during wheat and rice crop residue burning, respectively. Ozone generation with its precursor gases was analyzed quantitatively.

The feasibility of high yielding aus-aman-rabi cropping systems in the polders of the low salinity coastal zone of Bangladesh

Cropping intensity and agricultural productivity in the polders of the coastal zone of Bangladesh are much lower than that of most of the country. The main reasons for this are waterlogging, the late harvest (December/January) of the rainy season rice crop (known as ‘aman’), and the lack of readily accessible fresh water during the dry season in the polders. Waterlogging prevents the production of high yielding and earlier maturing rainy season rice varieties (HYV aman), and of high yielding/value rabi (dry season) crops such as maize and sunflower. However, gravity drainage of excess water from the polders is physically feasible. Furthermore, the rivers surrounding the polders in the central coastal zone (Barisal Division) contain large volumes of fresh river water throughout the year. Research was therefore undertaken to evaluate, under good water management, the feasibility of intensifying to high yielding rice-rice-rabi cropping systems in the low salinity central coastal zone. A replicated cropping system experiment was conducted for two years at Patuakhali using a short duration modern ‘aus’ variety (aus is the name of the rice crop grown during the early rainy season) (BRRI dhan65), a medium duration modern aman variety (BRRI dhan44), and high yielding/value rabi crops. The cropping systems included four aus sowing dates (20 March, 5 and 20 April, 5 May) which resulted in four aman and four rabi sowing dates. Two rabi crops were compared within each sowing date (maize – Pacific 984, sunflower – Hysun 33). Annual cropping system rice equivalent yield (REY) ranged from 13.7 to 20.0 t/ha. All systems were profitable with 100% of labour purchased, although benefit cost ratios (BCR) were not always >3, suggesting low attractiveness to farmers. However, most polder farms are small, with 30–60% of labour provided by the family. With 75% or less of labour purchased (the rest provided by family), all cropping systems were financially attractive, even with a 10% decline in grain price. Rabi crop yield was the main determinant of total system REY and profitability, both of which declined as sowing date of the rabi crops was delayed beyond 15 December. Optimisation of sowing date of the rabi crops should therefore be the first consideration in cropping system intensification for the low salinity coastal zone. The optimum sowing date of both the maize and sunflower was mid-December. For adequate "turn around" time between all crops, for the varieties used in this study, the aus crop should be sown in mid-April and the aman crop in mid-August. This research shows that, with good water management, it is possible to implement highly productive and profitable aus-aman-rabi cropping systems in the low salinity coastal zone of Bangladesh.

Unexpected higher decomposition of soil organic matter during cold fallow season in temperate rice paddy

In temperate paddy fields, rice is generally cultivated under flooding for 100–140 days during summer season, and thereafter, the soil is left without management under dried soil condition during cold fallow season. In this area rice straw is mostly removed for cattle feeding. Therefore, soil organic carbon (SOC) stock could be decreased with conventional practices, but the seasonal changes of SOC stock have not been evaluated well. To investigate SOC stock changes in temperate rice paddy, two seasonal C balances during rice cropping and fallow season were compared by the net ecosystem C budget (NECB) in the chemical fertilizer (control) and two different green manure treatments for three years. In the control treatment only chemical fertilizer was conventionally fertilized for rice cropping, but maintained without human control during the fallow season. In two green manure treatments, barley and hairy vetch (hereafter, vetch) were cultivated during the fallow season, and their whole biomasses were incorporated before rice transplanting. The conventional soil management with only chemical fertilization decreased small level of SOC stock (minus 0.70–0.84 Mg C ha−1 y−1 of NECB), which was attributed by high harvest removal (approximately 70% of total C input) and mineralized C loss (30%). Cover cropping and its biomass recycling as green manure was effective to increase SOC stock. High C/N ratio of non-leguminous barley produced high biomass yield, and its biomass incorporation significantly increased SOC stock with 1.21–3.43 Mg C ha−1 y−1 of annual NECB. In comparison low C/N ratio of leguminous vetch application increased slightly SOC stock (0.17–1.34 Mg C ha−1 y−1 of NECB), due to low biomass productivity and high mineralized C loss. However, irrespective with fertilization background, approximately 70% of mineralized C loss were occurred during the cold fallow season. Rice grain yields were similar between the control and hairy vetch treatment, but around 10% lower in barley treatment. Conclusively, high C/N ratio of cover crop cultivation during the fallow season could be better to increase SOC stock in mono-rice paddy, but additional nutrient management to increase rice productivity should be developed for barley utilization as green manure.

Intensification of rice-based farming systems in Central Luzon, Philippines: Constraints at field, farm and regional levels

Understanding the opportunities for sustainable intensification requires an integrated assessment at field, farm and regional levels of past developments. Two hypotheses regarding current rice production in Central Luzon (Philippines) were developed for this purpose. First, we hypothesize that there are trade-offs between rice yields, labour productivity, gross margin and N use efficiency and, second, that farm(er) characteristics and socio-economic conditions at farm and regional level affect the management practices used by farmers. These hypotheses were tested using two household surveys characterizing rice-based farming systems in Central Luzon in terms of changes over time (1966–2012) and spatial variability. Over the past half-century there was an increase in the proportion of irrigated fields and adoption of improved varieties, which allowed the cultivation of a dry season rice crop in Central Luzon. Moreover, transplanting has been replaced by direct-seeding and herbicides substituted hand-weeding. These resulted in greater rice yields and labour productivity, and contributed to gradual transition from subsistence to commercial farming systems, as observed in the increasing proportion of hired labour and rice sold. Our results indicate the existence of a trade-off between rice yields, labour productivity and N use efficiency as yield levels maximising labour productivity and N use efficiency were ca. 25% and 35% lower than climatic potential yield in the wet and dry season, respectively. At field level, this can be explained by 1) the use of transplanting as crop establishment method, which resulted into higher yields but lower labour productivity as compared to direct-seeding, and 2) the high N application levels, which led to higher yields but lower N use efficiency. In contrast, yield levels which maximised gross margin were ca. 80% of the climatic potential in both wet and dry seasons, so there was little trade-off between rice yields and economic performance. Regarding the second hypothesis results were not always conclusive. As an example, N application per ha was negatively associated with farm size and the timing of the first fertiliser application positively associated with household size and with the number of parcels. More intensive practices, and better farm performance, were recorded in the province at the heart of the irrigation system. We thus conclude that closing rice yield gaps in the production systems of Central Luzon incurs trade-offs with environmental and social objectives at field and farm levels but less with economic objectives. However, we could not clearly show whether, and to what extent, management practices used by farmers are influenced by farm or regional level constraints.

Epidemiological Study on Respiratory Health of School Children of Rural Sites of Malwa Region (India) During Post-harvest Stubble Burning Events

A study on effects of particulate matter fractions (PM10, PM2.5 and PM1) on health of school children was done from September 2014 to December 2015 covering one wheat and two rice crop seasons. The study was undertaken at 3 rural sites in the districts of Patiala, Fatehgarh Sahib and Sangrur (Malwa region of Punjab). The monthly average values of PM10, PM2.5 and PM1 were about 3–4 times higher than the National Ambient Air Quality Standards (NAAQS) given by Central Pollution Control Board during the crop residue burning periods. The MODIS data images of crop residue burning events confirmed the active fire operations over the region. The lung function parameters (Forced Vital Capacity, Forced Expiratory Volume in one second) of children (10–16 years) decreased with increase in particulate matter concentration while no significant effect was observed on Oxygen saturation level of children. The decrease in Forced Vital Capacity was slightly more in male subjects as compared to the female population. The sharp decrease in Pulmonary Function Test parameters during the crop residue burning period indicated the severity of the episodic burning events on the health of the children.

Soil N transformation mechanisms can effectively conserve N in soil under saturated conditions compared to unsaturated conditions in subtropical China

The connection between moisture and nitrogen (N) transformation in soils is key to understanding N losses, particularly nitrate (NO3−) losses, and also provides a theoretical framework for appropriate water management in agricultural systems. Thus, we designed this study to provide a process-based background for management decision. We collected soil samples from the long-term field experiment in subtropical China, which was designed to examine tobacco and rice rotations under a subtropical monsoon climate. The field experiment was established in 2008 with four treatments: (1) no fertilization as control; (2) N, phosphorus (P), and potassium (K) fertilizers applied at recommended rates; (3) N fertilizers applied at rates 50% higher than the recommended amounts and P and K fertilizers applied at recommended rates; and (4) N, P, and K fertilizers applied at recommended rates with straw incorporated (NPKS). Soil samples were collected during the unsaturated tobacco-cropping season and saturated rice-cropping season and were incubated at 60% water holding capacity and under saturated conditions, respectively. Two 15N tracing treatments (15NH4NO3 and NH415NO3) and a numerical modeling method were used to quantify N transformations and gross N dynamics. Autotrophic nitrification was stimulated by N fertilizer both under unsaturated and saturated conditions. The rate of NO3− consumption (via immobilization and denitrification) increased under the NPKS treatment under saturated conditions. Secondly, the rates of processes associated with ammonium (NH4+) cycling, including mineralization of organic N, NH4+ immobilization, and dissimilatory NO3− reduction to NH4+, were all increased under saturated conditions relative to unsaturated conditions, except for autotrophic nitrification. Consequently, NO3−-N and NH4+-N concentrations were significantly lower under saturated conditions relative to unsaturated conditions, which resulted in reduced risks of N losses via runoff or leaching. Our results suggest that under saturated conditions, there is a soil N conservation mechanism which alleviates the potential risk of N losses by runoff or leaching.