Showing papers in "Paddy and Water Environment in 2017"

Climate variability and yield risk in South Asia's rice-wheat systems: emerging evidence from Pakistan

Abstract: Rice and wheat are the principal calorie sources for over a billion people in South Asia, although each crop is particularly sensitive to the climatic and agronomic management conditions under which they are grown. Season-long heat stress can reduce photosynthesis and accelerate senescence; if extreme heat stress is experienced during flowering, both rice and wheat may also experience decreased pollen viability and stigma deposition, leading to increased grain sterility. Where farmers are unable to implement within-season management adaptations, significant deviations from expected climatic conditions would affect crop growth, yield, and therefore have important implications for food security. The influence of climatic conditions on crop growth have been widely studied in growth chamber, greenhouse, and research station trials, although empirical evidence of the link between climatic variability and yield risk in farmers’ fields is comparatively scarce. Using data from 240 farm households, this paper responds to this gap and isolates the effects of agronomic management from climatic variability on rice and wheat yield risks in eight of Pakistan’s twelve agroecological zones. Using Just and Pope production functions, we tested for the effects of crop management practices and climatic conditions on yield and yield variability for each crop. Our results highlight important risks to farmers’ ability to obtain reliable yield levels for both crops. Despite variability in input use and crop management, we found evidence for the negative effect of both season-long and terminal heat stress, measured as the cumulative number of days during which crop growth occurred above critical thresholds, though wheat was considerably more sensitive than rice. Comparing variation in observed climatic parameters in the year of study to medium-term patterns, rice, and wheat yields were both negatively affected, indicative of production risk and of farmers’ limited capacity for within-season adaptation. Our findings suggest the importance of reviewing existing climate change adaptation policies that aim to increase cereal farmers’ resilience in Pakistan, and more broadly in South Asia. Potential agronomic and extension strategies are proposed for further investigation.

Performance of drip-irrigated dry-seeded rice (Oryza sativa L.) in South Asia

Abstract: Drip irrigation in dry-seeded rice (DSR) is a new water-saving cultivation technology; however, very little is known of its productivity and water-saving capacities. The study was conducted for 2 years (2013 and 2014) in a split-plot design in three replicates with treatment combinations of four irrigation regimes [drip irrigation at 1.5, 2.25, and 3.0× pan evaporation (Epan) and flood irrigation at 3.0× Epan] and three nitrogen (N) levels (120, 150, and 180 kg ha−1). Drip irrigation in DSR resulted in higher grain yield (7.34–8.01 t ha−1) than flood irrigation (6.63–7.60 t ha−1) , with water savings of more than 40 %. Water-use efficiency with drip irrigation was higher (0.81–0.88 kg m−3) than flood irrigation (0.42–0.52 kg m−3) , being highest with drip irrigation at 1.5× Epan. Root density at soil depths of 15–30 cm was also higher in drip (0.86–1.05 mg cm−3) as compared to the flood (0.76–0.80 kg m−3)-irrigated crop. This study implicated that under water-scarce scenario, drip-irrigated DSR is a profitable, and water- and energy-saving technology. This study also suggested that policy focus in future must be tilted towards the promotion of solar-operated drip irrigation in those regions, where DSR is being promoted in the face of water and energy crisis.

Estimating time of concentration in large watersheds

Abstract: For hydrologists, time of concentration (TC) is one of the most important parameters to be able to predict the response of a watershed to a given rain event and plays a key role in rainfall-runoff simulation. There are several methods to calculate the TC. The time of concentration is defined as the time from the hydraulically furthermost point to watershed outlet. In this study, we integrated 22 formulas from various references for calculating time of concentration and selected seven formulas by considering the specific conditions and limitations that are suitable for Shafaroud watershed with an area of 345.4 km2, located in the western Guilan province of northern Iran. They included Ventura, Passini, Bransby-Williams, Carter, Johnstone-Cross, Izzard and Papadakis-Kazan. The TC values obtained from the mentioned methods were applied in HEC-HMS software for the four rainfall events of June 5, 2003; October 20, 2005; December 2, 2007; and June 19, 2008. The results indicated that peak flow values obtained by the Bransby-Williams method are most consistent with the observed peak data values and better presents the hydrologic condition of the watershed.

Effect of organic, inorganic and slow-release urea fertilisers on CH4 and N2O emissions from rice paddy fields

Abstract: Vietnam is one of the world’s top two rice exporting countries. However, rice cultivation is the primary source of agriculture’s greenhouse gas (GHG) emissions in Vietnam. In particular, strategies are required to reduce GHG emissions associated with the application of organic and inorganic fertilisers. The objective of this study was to assess the effects of various combinations of biochar (BIOC), compost (COMP) and slow-release urea (SRU) on methane (CH4) and nitrous oxide (N2O) emissions. In total, 1170 gas samples were collected from closed gas chambers in rice paddies at Thinh Long commune and Rang Dong farm in northern Vietnam between June and October 2014. The gas samples were analysed for CH4-C and N2O-N fluxes using gas chromatography. The application of BIOC alone resulted in the lowest CH4 emissions (4.8–59 mg C m−2 h−1) and lowest N2O emissions (0.15–0.26 µg N m−2 h−1). The combined application of nitrogen–phosphorus–potassium (NPK) + COMP emitted the highest CH4 (14–72 mg C m−2 h−1), while ½NPK + BIOC emitted the highest N2O (1.03 µg N m−2 h−1 in the TL commune), but it was the second lowest (0.495 µg N m−2 h−1) in the RD farm. Green urea and orange urea reduced N2O emissions significantly (p < 0.05) compared to white urea, but no significant differences were observed with respect to CH4 emissions. SRU fertilisers and BIOC alone measured the lowest greenhouse gas intensity, i.e. <2.5 and 3 kg CO2 eq. kg−1 rice grain, respectively. Based on these results, application of fertilisers in the form of BIOC and/or orange or green urea could be a viable option to reduce both CH4 and N2O emissions from rice paddy soils.

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

Abstract: 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.

Drought forecasting using ANFIS- a case study in drought prone area of Vietnam

Abstract: Drought occurs throughout the world, affecting people more than any other major natural hazards. An important requirement for mitigating the impact of drought is an effective method of forecasting future drought events. This study investigated the applicability of Adaptive neuro-fuzzy inference system (ANFIS) for drought forecasting and quantitative value of drought indices, the Standardized Precipitation Index (SPI) and Standardized Precipitation Evapotranspiration Index (SPEI). Khanhhoa Province Vietnam with three meteorological stations was selected as the study area. The sea surface temperature anomalies (SSTA) events at NinoW and Nino4 zones were selected as input variables to forecast drought. Fifteen ANFIS forecasting models for SPI/SPEI (1, 3, 6, and 12 months) were trained and tested. The results show the performance of the ANFIS forecasting models for SPI/SPEI of all stations is equivalent and most ANFIS forecasting models for SPEI are better than SPI; the performance of the ANFIS forecasting models for SPI/SPEI-12 is better than other ANFIS models for SPI/SPEI-1 to SPI/SPEI-6; the models with high performance are M10–M13; model with the highest performance is M12 model. The results of this research showed that ANFIS forecasting models with SSTAs events as input variables can forecast longer term than SPI and precipitation as input variables. The ANFIS forecasting model with SSTA events as input variables can be successfully applied and provide high accuracy and reliability for drought forecasting.

Distribution, fractionation, and contamination assessment of heavy metals in paddy soil related to acid mine drainage

Abstract: Soil heavy metal contamination is a major environmental concern, especially soil affected by acid mine drainage (AMD), and attention about potential ecological risk associated with heavy metals is increasing. Heavy metal contents of soil samples collected from 6 sites alongside Hengshi River were analyzed to investigate the contamination degree of heavy metal in paddy soil irrigated with AMD. Fractional distribution of heavy metal and the potential ecological risks (E r) of the polluted soil were discussed as well. The results showed that Cu, Zn, and Cd in topsoil were 2.5–7.5, 1–2.1, and 2.2–5.5 times, respectively, exceeding the maximum allowable concentrations for Chinese agricultural soil. The single (P) and the comprehensive (P N ) factor pollution index revealed that the contamination degree followed the sequence of Cd > Cu > Zn > Pb. Furthermore, Pb, Cu, and Zn in vertical soil profiles reduced as soil depth increased, while Ni and Cd increased with the depth increasing slightly. Results of European Community Bureau of Reference (BCR) sequential extraction procedure indicated that the non-residual form of Pb, Cu, and Cd were pretty high in spatial variation, suggesting they were potentially mobilizable and bioavailable. Results implied that the order of the Er of heavy metals was Cd > Pb > Cu > Ni > Zn > Cr; the Er in Wengcheng (S9) and Xuwu (S10) were 353.30 and 327.60, which were considered as very high ecological risk. Thus, some effective measures should be taken to prevent heavy metal from polluting paddy soil and to reduce metal translocation from soil to edible crops.

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

Abstract: 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 < 005) 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

Salinity intrusion and rice production in Red River Delta under changing climate conditions

Abstract: This study was carried out to identify the vulnerability of rice production to salinity intrusion arising from climate change in Giao Thuy, a coastal district of Nam Dinh Province, located in Red River Delta in Vietnam. From the analysis of historical climate data at Nam Dinh city, both mean maximum and minimum temperatures increased by about 0.3 and 0.1 °C per decade, respectively, during the period of 1961–2010. Salt concentration of the river water was higher at the irrigation gate closer to river mouth (Con Nhat) than at the upstream gate (Ha Mieu), which generally increased from 2003 to 2012, with the average maximum concentration up to 2.13 % at Con Nhat gate in 2010. The salt water concentration in the riverside field outside the dyke reached 3.6 %, while among the fields within dyke the salinity was only 0.7 % at maximum in January 2013, and the values were higher in paddy fields close to the dyke than far from the dyke. Average yield among the selected 27 fields from 2011 summer to 2013 spring rice was higher in spring rice (748 g m−2) but lower in summer rice (417 g m−2) mainly due to unfavorable weather such as cold spell at flowering and flood at harvesting time. Rice yield was lowest in general in the most downstream commune Giao Thien, and was significantly lower in field located close to the dyke than those far from the dyke. This spatial variability of rice yield may not be directly attributable to salinity, but to the other factors such as shift of irrigation intake gate to further upstream and/or different management such as less input of N fertilizer and use of traditional local variety.

Surface drainage nitrate loading estimate from agriculture fields and its relationship with landscape metrics in Tajan watershed

Abstract: Pasture, forest, and farmland are the dominant land covers in the Tajan River watershed and this landscape status has a direct connection with nitrate pollution. Understanding the correlations between landscape variables and nitrate pollutant is a priority in order to assess pollutants loading and predicting the impact on surface water quality. The soil and water assessment tool was used to simulate nitrate loads in different land cover types in different years. The landscape pattern was calculated by FRAGSTATS. The contributing share of each land use/land cover shows nitrate pollutant produced by grassland (5.7%) and forest (29%) are less than those produced by agricultural land (64.2%). Agricultural land was identified as the main source of nitrate pollution. Paddy fields and orchards had the most intensive soluble nitrate loss especially in spring and summer. Statistical analysis indicated that nitrate was positively associated with patch density, edge density, patch number, total edge, effective mesh size, largest patch index, and landscape shape index (p ≤ 0.01). We then analyzed how nitrate was related to landscape attributes in six different sites. Also the regression analysis results suggested that landscape metrics could account for more than 94% of the variance of nitrate in the whole catchment. The regression models confirmed the great importance of the agriculture metrics and forest metric in predicting nitrate in watershed. Defining the generation and extent of pollution in this particular watershed which discharges into the Caspian Sea can constitute an important step toward protecting this ecosystem.

Agronomic fortification of rice grains with secondary and micronutrients under differing crop management and soil moisture regimes in the north Indian Plains

Abstract: Although the System of Rice Intensification (SRI) has been reported to produce higher paddy (Oryza sativa L.) yields with better-quality grains, little research has addressed the latter claim. This study investigated the interactive effects of rice cultivation methods with different irrigation schedules and plant density on the uptake and concentration of sulfur (S), zinc (Zn), iron (Fe), manganese (Mn) and copper (Cu) in the grain and straw of two rice cultivars during two rainy seasons in the northern plains of India. As the two seasons differed in amounts of rainfall, there were impacts of soil moisture differences on nutrient uptake. Plots with SRI cultivation methods enhanced the grain uptake and concentrations of S, Zn, Fe, Mn and Cu by 36, 32, 28, 32 and 63%, respectively, compared to conventional transplanting (CT). Under SRI management, the highest concentrations of S, Zn and Cu in the grain and straw occurred with irrigation intervals scheduled at 3 days after disappearance of ponded water (DADPW; 3D), whereas Fe and Mn concentrations in the grain and straw were higher with irrigation at 1 DADPW (1 D ) compared with plots under 3 D or 5 DADPW (5 D ). The higher nutrient uptakes were also manifested in higher grain yield in 1 D and 3 D plots (by 9 and 6%, respectively) compared with 5 D . Wider spacing (25 × 25 cm) compared with closer spacing (20 × 20 cm) significantly increased yield and the uptake and concentrations of all the said nutrients in the grains. When comparing the performance of two cultivars, the total uptakes of Zn, Fe, Mn and Cu in both grain and straw were significantly more in Hybrid 6444 than the improved variety Pant Dhan 4. Overall, SRI crop management compared to CT practices led to more biological fortification of rice grains with respect to S and the four micronutrients studied, giving a concomitant yield advantage of about 17% on average in this region.

Evapotranspiration, irrigation water requirement, and water productivity of rice (Oryza sativa L.) in the Sahelian environment

Abstract: 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.

Comparative energy and economic analyses of conventional and System of Rice Intensification (SRI) methods of rice production in Thai Nguyen Province, Vietnam

Abstract: The consumption of energy inputs in agricultural production has been increasing rapidly during the past decades. However, given the limitations and costs of non-renewable energy, increasing production while using the least energy possible has become a major concern of most nations. Prompted by this concern, we conducted a face-to-face survey of 90 farming households in Thai Nguyen Province, Vietnam, to find out how energy is being used in agriculture and, specifically, in their rice production. Through analysis of energy input–output balances, combined with economic efficiency analysis, a comparison was made of conventional and SRI methods of rice production. The study found that applying the SRI method can save around 23% of energy inputs, while increasing energy outputs by 11%. Economic benefits per hectare also rise by more than 8 million dong (USD 364) compared to those under the conventional cultivation system. The study also showed conflicts between the energy and economic balances for manual compared with machine ploughing operations. This study contributes to providing an overview of energy consumption in rice cultivation at the household level. Its findings can help stakeholders to assess current policies and make better decisions on the uses of energy in agricultural production. In addition, the comprehensive approach taken here to analysing energy use and efficiency could expand the analysis and comparison of energy uses at sectoral or activity level—still a new field in Vietnam and many other countries.

Effects of plastic-hole mulching on effective rainfall and readily available soil moisture under soybean (Glycine max) cultivation

Abstract: Plasticulture is becoming popular to control soil temperature and increase water-use efficiency in rain-fed agriculture. Non-perforated plastic mulching reduces effective rainfall by preventing infiltration, while perforated plastic mulching (plastic-hole mulching) increases effective rainfall by enhancing infiltration; both mulching control soil temperature. The comparative performance of these mulching is not, however, well investigated yet. So, a field experiment was conducted by cultivating soybean (Glycine max) under non-perforated plastic mulching (hereafter denoted by P), plastic-hole mulching (hereafter denoted by PH) and bare soil to investigate soil temperature, effective rainfall, total readily available soil moisture (TRAM), soil-moisture extraction pattern (SMEP) and yield of soybean. The mulching treatments reduced soil temperature by 2 °C at 5 cm depth compared to the bare treatment and created a favorable environment for soybean growth under high air temperature during summer in Japan. The PH treatment increased effective rainfall by as much as 9% of total rainfall compared to the P treatment. The SMEP in the 0- to 30-cm soil profile revealed that soil moisture was consumed, mostly, from the upper soil layer in the bare treatment, while in the P and PH treatments, soil-moisture consumption occurred both from the upper and from the lower soil layers. Consequently, the P and PH treatments provided greater TRAM (57.3 and 54.0 mm) than the bare treatment (48.0 mm), indicating that mulching contributed increasing soil-moisture availability in the root zone. The mulching treatments augmented plant height, number of nodulations per plant, and seed and biomass yields; the PH treatment produced the maximum seed yield.

Production efficiency of rice farms in Thailand and Cambodia: a comparative analysis of Ubon Ratchathani and Stung Treng provinces

Abstract: Rice farmers in developing countries need to increase production efficiency in order to meet a growing rice demand. To identify and compare the determinants of rice production efficiency at different stages of economic development, a one-stage stochastic frontier model is applied to a cross-sectional dataset collected in 2013 of 623 households in Ubon Ratchathani (Thailand) and 407 households in Stung Treng (Cambodia). The results indicate that the average level of rice production efficiency is 72 % in Thailand and 64 % in Cambodia. There are a number of factors that commonly affect the production efficiency in both countries. These factors are the farm size, per capita income, amount of agricultural credit, degree of commercialization, and share of nonfarm income. However, there are also a number of country-specific factors that are unique to the respective environments. These factors are the distance to fields, mechanization, agricultural assets, share of remittances, education of household heads, and distance to town in Thailand, and household size in Cambodia. These findings suggest that promoting the development of household capital, access to rural infrastructure as well as the specialization and commercialization of rice production would contribute to increasing production efficiency of rice farms in developing countries.

Effect of nitrogen root zone fertilization on rice yield, uptake and utilization of macronutrient in lower reaches of Yangtze River, China

Abstract: Improper application of nitrogen (N) has led to high N losses and low N use efficiency in the lower reaches of Yangtze River in China. An effective method to solve such problems is the deep fertilized N in root zone (RZF). Limited information is available on the effect of RZF on the uptake of macronutrients (N, P and K) and rice yield. Field experiments, conducted from 2014 to 2015, compared the farmer fertilizer practice (FFP, with 225 kg ha−1 of N, split into three doses) and RZF using the same rate but placing N 5 cm away from rice roots in holes 10 cm deep (RZF10) or 5 cm deep (RZF5) as a single application. The highest mean yield (10.0 t ha−1) was obtained in RZF10, which was 19.5% more than that in FFP. Root zone fertilization of urea (whether 10 cm deep or 5 cm deep) resulted in greater accumulation of N, P and K in stem, leaf sheaths, leaf blades and grains compared to that in FFP in sandy and in loam soils. The uptake of N, P and K was the highest in RZF10 (average at 176.7, 66.2 and 179.1 kg ha−1, respectively), higher than that in FFP by 45.0, 17.0 and 22.6%, respectively. N apparent recovery efficiency was markedly higher in RZF10 (53.1%) than in FFP (27.5%). RZF10 significantly increased the N, P, K uptake compared with FFP under different N rates in both sandy and loam soils. These results suggest that the N, P and K input amount should be re-determined under RZF.

Evaluation of HYDRUS-2D model to simulate the loss of nitrate in subsurface controlled drainage in a physical model scale of paddy fields

Abstract: Agriculture is a major source of nitrogen usage and release to environment. Due to the effect of water movement on solute transport, investigating the effect of different management scenarios of irrigation and drainage could be useful for reducing nitrate loss and environmental pollution. This study is a scientific attempt to assess the ability of HYDRUS-2D model to simulate the effect of subsurface controlled drainage on nitrate loss of paddy fields. So, two physical models with difference in depth of subsurface controlled drainage (40 and 60 cm) were constructed. The tanks were filled with loam silty soil texture and then transplanted rice. 90 kg/ha potassium nitrate fertilizer was added in two stages of rice growth. Mid-season drainage was applied 26 days after transplantation. After 17 days, drains were closed again and applied flooded irrigation with 5-cm water stagnant layer above soil surface. During experiment, nitrate concentration of drain water was measured. HYDRUS-2D was calibrated with measured data in 60 cm drain depth and validated with 40 cm drain depth. HYDRUS-2D could simulate nitrate concentration with the coefficient of determination 0.95 and 0.89 in calibration and validation stages, respectively. The comparison between the volume of drain water and nitrate concentration from the drains in the depths of 40 and 60 cm indicated lower nitrate load in depth of 40 cm. The results obtained proved that the presence of hardpan layer in depth of 25 cm rather than the absence of it causes increase in 3 % of average nitrate concentration and reduce in 17 % of water discharge.

Daily pan evaporation modeling in climatically contrasting zones with hybridization of wavelet transform and support vector machines

Abstract: The estimation of evaporation has been under surveillance, which is being carried out by many researchers toward applications in the fields related to hydrology and water resources management. Due to complexities associated with its estimation, research has employed several modes via direct and indirect methods to estimate. Accurate estimations are still the thrust area of research in these fields. The pan evaporation estimations with the help of data modeling techniques have provided better results in the recent past. The advancement in the field of data modeling has introduced several techniques which can best fit the data type and provide accurate estimations. The novel gamma test (GT) was used to decide the best input–output combination. Parameter optimization was carried out by grid search. The developed models gave better estimations of pan evaporation, but exhibited some limitations with nonlinearity, and sparse and noisy data. These limitations paved way for data pre-processing techniques such as wavelet transform. This study made an attempt to explore hybrid modeling using discrete wavelet transform (DWT) and support vector machines (SVR) for pan evaporation estimation. Two stations representing contrasting climatic zones namely ‘Bajpe’ and ‘Bangalore’ located in the state of Karnataka, India, are selected in this study. The meteorological datasets recorded at these stations are analyzed using gamma test and grid search to use the best input–output combinations for the models. The modeled pan evaporation estimations are very promising toward ever demanding accuracy expected in the associated fields.

Woody habitats promote pollinators and complexity of plant–pollinator interactions in homegardens located in rice terraces of the Philippine Cordilleras

Abstract: Bees are important pollinators of wild plants and crops, but little is known about bee habitat requirements and pollinator management in tropical mountainous agricultural regions. Here, smallholder farmers produce fruits and vegetables in homegardens that depend upon or benefit from bee pollination. We hypothesized that abundance and richness of wild and domesticated bees and the complexity of plant–pollinator interactions are higher in homegardens surrounded by woody habitats than in homegardens found farther from woodlands. Bees were sampled in 20 homegardens in the rice terraces of the Philippine Cordilleras. We used linear mixed effect models to analyse effects of woody habitats around homegardens on bee richness and abundance. Based on pooled observations for each garden category, we built pollinator–plant interactions networks to illustrate shifts in interaction frequencies. We recorded 354 bee individuals of 13 wild and one domesticated bee species (Apis cerana). Wild bee richness was significantly higher in homegardens surrounded by woody habitats. Bee abundance increased significantly with increasing flower cover. Wild bees visited cultivated plants significantly more often than domesticated bees. Six vegetable species and 76% of all flower visits on cultivated plants in total were performed by wild bees and three plant species and 24% by domesticated bees. Pollinator–plant networks were more complex in homegardens surrounded by woody habitats. We conclude that woody habitats increase abundance and richness of wild and domesticated bees. Increasing availability of floral resources also promotes bee abundance. In order to promote pollination services in the landscape mosaic of smallholder rice farms, woody habitats and forest fragments together with numerous floral resources should be protected and restored.

Nitrogen loss and its health risk in paddy fields under different drainage managements

Abstract: Subsurface drainage is a prerequisite for year-round crop production in a large area of northern Iran, s paddy fields. Minimizing environmental and health issues related to nitrogen (N) losses through subsurface drainage systems provides suitable condition for sustainable agriculture in these fields. A field study was conducted to evaluate nitrogen loss and its health risk in the conventional and subsurface-drained paddy fields. Ammonium, nitrate, and total N concentrations of subsurface drainage effluents, surface runoff, and leachates were monitored during three successive rice-canola-rice growing seasons from July 2011 to August 2012. Different components of N balance and health risk of nitrate leaching to groundwater were also investigated. Ammonium in drainage effluents collected during the experimental period ranged from approximately zero to 1.72 mg L−1, while nitrate fluctuated from 0.5 to 28.6 mg L−1. Average nitrate concentration in leachates of subsurface-drained area was 7.7–81.4 % higher than that in subsurface drainage effluents, while it was 126.8 % higher than that in surface runoff for the conventional field. Subsurface drainage provided a better utilization of soil N through providing winter cropping and reduced the potential for non-carcinogenic risks of nitrate leaching to groundwater. The results are encouraging for producers engaged in rice-canola production in the study area with respect to the environment and human health quality.

The effect of waterlogging on electrochemical properties and soluble nutrients in paddy soils.

Abstract: This study was conducted to investigate the influence of waterlogging on availability of nutrients in paddy soils. The five soils were incubated under a waterlogged condition at 30 °C for 12 weeks. The EC, Eh, pH, NH4, K, Na, Ca, Mg, Cl, P, Fe, and Mn of soil solutions were monitored over the waterlogged period. The Eh values generally dropped to the lowest point within 14 days of waterlogging, then increased, and reached equilibrium after 8 weeks of waterlogging. The soil pH decreased in the first 2–4 weeks of waterlogging. The EC values increased partly due to dissolution of soluble salts in the first 2 weeks. The concentrations of soluble NH4 were significantly increased with waterlogging, reached maximum values at week 4–6, and then declined to the initial level. Waterlogging increased the concentration of soluble K, Ca, Mg, Fe, and Mn ions, the magnitudes of changes were greatly affected by soil properties. Increases in soluble Na, K, Ca, and Mg were attributed to the increase in solubility of insoluble salts and increase in competition for the exchange sites. Increases in soluble Fe and Mn induced by waterlogging were attributed to the dissolution of Fe and Mn oxides under reduced conditions.

Modelling of groundwater recharge potential from irrigated paddy field under changing climate

Abstract: Groundwater recharge from irrigated paddy field under various projected climate change scenarios was assessed using HYDRUS-1D model Recharge flux, root water uptake, evaporation and surface runoff were simulated on daily time step for the growing period of paddy Crop evapotranspiration and effective rainfall during the simulation period were estimated to be 3019 and 2694 mm, respectively Cumulative bottom flux, root water uptake, evaporation and surface runoff were 692, 232, 308 and 00 cm for sandy loam and 372, 230, 308 and 07 cm for clay loam soils, respectively Simulation results showed that the groundwater recharge potentials in sandy loam and clay loam soils with paddy crop are 692 and 372 cm, respectively Cumulative recharge under various climate change scenarios from paddy field varied from 639 to 744 cm, 337 to 398 cm, 293 to 354 cm and 271 to 343 cm from land units A1 (sandy loam), B1 (clay loam with slight salinity), C1 (clay loam with moderate saline and slight sodic) and D1 (clay loam with strong saline and sodic), respectively Cumulative recharge flux under the scenarios in which increase in relative humidity along with decrease in duration of sunshine hours was associated with rise in average temperature and wind speed, groundwater recharge would increase by 74 % Cumulative recharge flux under the scenarios which were based on rise in temperature along with the increase in rainfall, groundwater recharge would increase by 02–39 % Simulation results also showed that cumulative recharge would decrease under all those scenarios, which were based on rise in temperature only

Performance of direct-seeded rice under various dates of sowing and irrigation regimes in semi-arid region of India

Abstract: Rice (Oryza sativa L) is the most important staple food crop in the southern region of Asia, and Indian subcontinent being one of the major producers Production of conventional transplanted rice requires a large amount of irrigation water, labor, and energy The scarcity of irrigation water has encouraged farmers to adopt an alternative rice production system, ie the direct-seeded rice (DSR), which is proposed to be farmers’ friendly with a potential to save water Our study reports the performance of DSR with respect to yield and water expense efficiency based on different irrigation regimes and dates of sowing A field experiment was conducted in the semi-arid region of northern India during the rainy season of 2011 with two treatment combinations (dates of sowing: 15th May and 5th June and three irrigation regimes: irrigation scheduled at irrigation water-to-cumulative potential evapotranspiration; IW/CPE ratio of 10, 15 and 20) in a completely randomized design We found statistically higher water expense efficiency of DSR sown on 5th June as compared to DSR sown on 15th May without any significant differences in growth and yield A significant yield difference between DSR grown with irrigation regimes of IW/CPE 10 and 15 and DSR grown with irrigation regimes of IW/CPE ratio 20 were observed The DSR grown with irrigation regimes of IW/CPE ratio of 15 resulted in significantly higher water expense efficiency than the one with IW/CPE ratio of 20 Obtaining a higher yield of DSR under scarce irrigation water might be a trade-off between optimum water use and maximum yield avoiding excess ground water exploitation in sub-tropical semi-arid regions of India Our study suggests that sowing time and irrigation regimes are two important aspects of “rice production” to attain “win–win” solution Thus, strategic and judicial use of irrigation water with management of sowing time could potentially escalate the rice production in water scarce regions of India

Adoption of conservation farming practices for sustainable rice production among small-scale paddy farmers in northern Iran

Abstract: The availability of natural resources often becomes a limiting factor for increasing per capita food production, particularly among small-scale farmers in developing countries. The adoption of conservation farming practices, as a way to tackle this challenge, has become a major issue in the development policy agenda, but data on the sustainable production of lowland rice are limited. A survey of small-scale paddy farmers was conducted to analyze factors determining adoption of conservation farming practices in Fumanat plain in northern Iran. The majority of the farmers showed high levels of adoption, corresponding to 8–10 conservation practices. Removing weeds from irrigation canals, dredging irrigation canals (i.e., cleaning bottom sediments), using a plastic cover on field borders, draining land, using organic fertilization, leveling land, and practicing conservation tillage were popular farming practices. Well-educated farmers, who were using canals as the main source of irrigation, and farmers with a large land area under cultivation, high income, access to machinery and farming inputs, and high social participation were more likely to adopt conservation practices. On the contrary, farmers’ age (farmers of advanced age), household distance from the main road (remote areas), and number of family members available for farming (large families) limited the possibility of adoption. Up to 42.6 % of the variance regarding the adoption of conservation practices could be predicted by a stepwise multiple regression model. Access to machinery, access to farming inputs, the use of canals as the main source of irrigation, and farm income had the greatest share in predicting adoption. Tailored extension programs can be highly effective instruments, not only for increasing conservation of natural resources but also for reducing poverty, especially in small farms in remote and isolated areas.

Application of machine-learning models for diagnosing health hazard of nitrate toxicity in shallow aquifers

Abstract: There is a growing concern about health hazards linked to nitrate (NO3) toxicity in groundwater due to overuse of nitrogen fertilizers in rice production systems of northern Iran. Simple-cost-effective methods for quick and reliable prediction of NO3 contamination in groundwater of such agricultural systems can ensure sustainable rural development. Using 10-year time series data, the capability of adaptive neuro-fuzzy inference system (ANFIS) and support vector machine (SVM) models as well as six geostatistical models was assessed for predicting NO3 concentration in groundwater and its noncarcinogenic health risk. The dataset comprised 9360 water samples representing 26 different wells monitored for 10 years. The best predictions were found by SVM models which decreased prediction errors by 42–73 % compared with other models. However, using well locations and sampling date as input parameters led to the best performance of SVM model for predicting NO3 with RMSE = 4.75–8.19 mg l−1 and MBE = 3.3–5.2 mg l−1. ANFIS models ranked next with RMSE = 8.19–25.1 mg l−1 and MBE = 5.2–13.2 mg l−1 while geostatistical models led to the worst results. The created raster maps with SVM models showed that NO3 concentration in 38–97 % of the study area usually exceeded the human-affected limit of 13 mg l−1 during different seasons. Generally, risk probability went beyond 90 % except for winter when groundwater quality was safe from nitrate viewpoint. Noncarcinogenic risk exceeded the unity in about 1.13 and 6.82 % of the study area in spring and summer, respectively, indicating that long-term use of groundwater poses a significant health risk to local resident. Based on the results, SVM models were suitable tools to identify nitrate-polluted regions in the study area. Also, paddy fields were the principal source of nitrate contamination of groundwater mainly due to unmanaged agricultural activities emphasizing the importance of proper management of paddy fields since a considerable land in the world is devoted to rice cultivation.

Manganese nutrition improves the productivity and grain biofortification of fine grain aromatic rice in conventional and conservation production systems

Abstract: Manganese (Mn) deficiency is prevalent in rice-growing regions resulting in poor paddy yield and human health. In this study, role of Mn, applied through various methods, in improving the productivity and grain biofortification of fine grain aromatic rice was evaluated. Manganese was delivered as soil application (SA) (0.5 kg ha−1), foliar spray (FA) (0.02 M Mn), seed priming (SP) (0.1 M Mn) and seed coating (SC) (2 g Mn kg−1 seed) in conventional (puddled transplanted flooded rice) and conservation (direct seeded aerobic rice) production systems at two different sites (Faisalabad, Sheikhupura) in Punjab, Pakistan. Manganese application, through either method, improved the grain yield and grain Mn contents of fine grain aromatic rice grown in both production systems at both sites. However, Mn application as SC and FA was the most beneficial and cost effective in improving the productivity and grain biofortification in this regard. Overall, order of improvement in grain yield was SC (3.85 t ha−1) > FA (3.72 t ha−1) > SP (3.61 t ha−1) > SA (3.36 t ha−1). Maximum net benefits and benefit–cost ratio were obtained through Mn SC in flooded field at Faisalabad, which was followed by Mn SP in direct seeded aerobic rice at the same site. However, maximum marginal rate of return was noted with Mn SC in direct seeded aerobic rice at both sites. In crux, Mn nutrition improved the productivity and grain biofortification of fine grain aromatic rice grown in both conventional and conservation production systems. However, Mn application as seed treatment (SC or SP) was the most cost effective and economical.

Influence of crop establishment methods on yield, economics and water productivity of rice cultivars under upland and lowland production ecologies of Eastern Indo-Gangetic Plains

Abstract: A field study on assessment of crop establishment methods on yield, economics and water productivity of rice cultivars under upland and lowland production ecologies was conducted during wet seasons (June–November) of 2012 and 2013 in Eastern Indo-Gangetic Plains of India. The experiment was laid-out in a split-plot design (SPD) and replicated four times. The main-plot treatments included three crop establishment methods, viz. dry direct-seeded rice (DSR), system of rice intensification (SRI) and puddled transplanted rice (PTR). In sub-plots, five rice cultivars of different groups like aromatic (Improved Pusa Basmati 1 and Pusa Sugandh 5), inbreds (PNR 381 and Pusa 834) and hybrid (Arize 6444) were taken for their evaluations. These two sets of treatments were laid-out simultaneously in two production ecologies, upland and lowland during both years. In general, lowland ecology was found favourable for rice growth and yield and resulted in 13.2% higher grain yield as compared to upland ecology. Rice grown with SRI method produced 19.4 and 7.0% higher grain yield in 2012 and 20.6 and 7.1% higher in 2013, over DSR and PTR. However, PTR yielded 13.1 and 14.5% higher grain over DSR during 2012 and 2013, respectively. On an average, Arize 6444 produced 26.4, 26.9, 28.9 and 54.7% higher grain yield as compared to PS 5, P 834, PNR 381 and IPB1, respectively. Further, the interaction of production ecologies × crop establishment methods revealed that, in upland ecology, SRI recorded significantly higher grain yield as compared to PTR and DSR, but in lowland, grain yield resulting from SRI was similar to the yield obtained with PTR and significantly higher than DSR. The latter two methods (PTR and DSR) yielded alike in lowland ecology in both study years. The production ecologies × crop establishment methods × cultivars interaction on grain yield showed that the growing of Arize 6444 cultivar using SRI method in upland ecology resulted in the higher grain yield (8.87 t/ha). But the cost of production was also highest in SRI followed by PTR and DSR across production ecologies and cultivars. Cultivation of hybrid (Arize 6444) involved higher cost of production than all other cultivars. Irrespective of crop establishment methods and cultivars, gross returns, net returns and B:C ratio were significantly higher in lowland compared to upland ecology. Owing to higher grain yield, SRI method fetched significantly higher gross returns and net returns over PTR and DSR. Average increase in net return with Arize 6444 was 68.8, 41.0, 37.7 and 33.1% over IPB 1, PNR 381, P 834 and PS 5, respectively. There was a saving of 30.7% water in SRI and 19.9% in DSR over PTR under upland ecology. Similarly in lowland ecology, water saving of 30.2% was observed in SRI and 21.2% in DSR over PTR. Due to higher yield and saving on water, SRI returned significantly higher total water productivity (TWP) (5.9 kg/ha-mm) as compared to DSR (3.5 kg/ha-mm) and PTR (3.6 kg/ha-mm) under upland ecology. In lowland ecology, also SRI (6.2 kg/ha-mm) resulted in higher TWP as compared to other two methods. However, DSR gave significantly higher TWP as compared to PTR. Among cultivars, hybrid Arize 6444 recorded the highest TWP in both upland and lowland production ecologies across crop establishment methods. Hence, growing of hybrid Arize 6444 with SRI method can enhance rice productivity and water-use efficiency in lowland and upland production ecologies of Eastern Indo-Gangetic Plains and in other similar regions.

Research on the joint probability distribution of rainfall and reference crop evapotranspiration

Abstract: The relationship between rainfall and reference crop evapotranspiration (ET0) can be complex in an irrigation district. To reveal such complex and possibly a nonlinear relationship, rainfall and ET0 data were collected at the Xinxiang irrigation experiment station from the years 1961 to 2010. Marginal distributions of the two variables derived from fitting the Pearson Type III distribution were incorporated for the development of the joint probability distribution using a copula model. Subsequently, the joint probability as well as the return period of given specific rainfall and ET0 values can be computed. For the analysis of the variations in drought conditions over the 50 years, the copula-based joint probability is further decomposed into several subcomponents using the empirical mode decomposition method. The variations under distinct frequencies and over different time periods were observed. Our results showed that the joint probability distribution of rainfall and ET0 can facilitate the planning for drought resistance in an irrigation district.

Hydro-geochemical classification and spatial distribution of groundwater to examine the suitability for irrigation purposes (Golestan Province, north of Iran)

Abstract: One of the most important agricultural areas in Iran is Golestan Province. In this study, the suitability of groundwater for irrigation purposes was assessed. To determine hydro-geochemical classification of the station and assessment of spatial modeling of the study area, 12 groundwater stations were selected and an average of the last 5 years of sampling (2011–2015) has been considered. Suitability of groundwater for irrigation was assessed based on Sodium Adsorption Ratio (SAR), Residual Sodium Carbonate (RSC), Na%, Permeability Index (PI), Magnesium Adsorption Ratio (MAR), Kelley’s Ratio (KR), Corrosion Ratio (CR), Residual Sodium Carbonate (RSC), Potential Soil Salinity (PSS), Chloro-Alkaline Indices (CAI), Meteoric genesis (Met. gen) and Wilcox classification. The abundance of major ions followed a HCO3 > SO4 > Na > Ca > Mg > Cl > K trend. CAI results indicate reverse cation exchange for this area, and Wilcox classification indicates that only Kalou, Kafshgari, and Kia stations are appropriate for irrigation. The spatial distribution of groundwater quality demonstrates a decreasing trend from SE to NW based on CAI, Cl, CR, EC, TSS, and TDS and shows reverse trends for KR, MAR, Met. gen, Mg/Ca, Na%, pH, PI, and RSC. In addition, the results of hydro-geochemical classification of irrigation parameters have categorized the irrigation water of this area into three different classes. Based on EC, MAR, Mg/Ca, Cl and CR, this area is suitable, but based on PSS, KR, and TH, all stations are unsuitable and according to SAR, TDS, Na% and PI, this area’s groundwater is moderate.

Effect of water management on soil respiration and NEE of paddy fields in Southeast China

Abstract: 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.