Irrigation Water Input Research Articles

Measuring drought based on a CGE model with multi-regional irrigation water

There have been many droughts in China that have caused severe losses. Previous studies evaluating droughts were from meteorological and hydrological perspectives. We measure the Chinese drought of 2000 based on a static computable general equilibrium model of China's macroeconomy, which describes the relationships between drought, agricultural production, and rural households' welfare from an economic perspective. In the model, the irrigation water inputs of the 16 regions of China are estimated and combined with the same regions' cropland inputs. Thus, the drought is simulated as an external impact by reducing the productivity of different crops in different regions. The reductions in 10 crop outputs and the rural households' welfare, total consumption and food consumption from 16 regions are more severe than those from a perfect market reaction. The findings herein are also distinct in that the five rural households that suffer most as a result of drought are from southern areas. The results provide an available reference for the Chinese government's decision on what measures to take to prevent drought and its impacts. The model can be further improved by incorporating meteorological and hydrological models to identify droughts using more accurate indexes.

Bicarbonates in irrigation water contribute to carbonate formation and CO2 production in orchard soils under drip irrigation

Irrigated agriculture is conducted on approximately 257 million hectares worldwide and continues to expand, particularly in arid to semi-arid regions. Applications of water containing dissolved calcium and bicarbonate ions cause the precipitation of calcium carbonate in the soil and the release of carbon dioxide into the air. However, the contribution of inorganic C to CO2 emissions from the soil is rarely considered. Using a short-term incubation technique developed to examine changes in mineralizable organic C pools, we found that soils beneath drip emitters in an irrigated apple orchard released CO2 from both organic and inorganic C. Soils under drippers had higher concentrations of carbonates than soils that had not received direct inputs of irrigation water. The quantity of carbonates detected in the soil under the drippers at this site was small but may be greater on sites using irrigation water with higher concentrations of Ca2+ and HCO3−. Furthermore, site productivity may be reduced by unfavourable physical and chemical changes caused by carbonate deposition within the small soil volume occupied by tree roots in micro-irrigated orchards with dwarfing rootstocks. In order to better understand the implications for site productivity and for global C flux of carbonate precipitation in micro-irrigated systems, future work is required to quantify CO2 emissions during irrigation, and to characterize soil chemical and physical properties through the soil profile.

Grain yield, water productivity and CH4 emission of irrigated rice in response to water management in south China

Reducing water input and CH4 emission while maintaining grain yield is important for the sustainable rice production in south China. However, water-saving technology has not been widely adopted by farmers because of constrains in handling, effectiveness and reliableness. Recently a simplified and easy-to-use alternate wetting and drying technology, namely “safe” AWD, has been developed and recommended to farmers in Asian countries. However, the performance of the safe AWD technology has not yet been evaluated in south China. The objective of this study was to determine whether the safe AWD technology could maintain grain yield with reduced water input and CH4 emission as compared to the conventional farmer’s practice (FP) in south China. Two on-station field experiments were conducted in Guangzhou, Guangdong province during 2014 early and late seasons. In the early season, a hybrid rice variety, Tianyou 3618 (TY3618), was arranged in a randomized complete block design with three water treatments, i.e., AWD15, AWD30 and continuous flooding (CF). In the late season, a split-plot design was employed with four water management (AWD15, AWD30, CF and FP) as main plots and two varieties as subplots. The two varieties were TY3618 and Hefengzhan (HFZ, inbred). Field water level and soil water potential were recorded daily and the CH4 emission was monitored at 7-day intervals. Crop growth, grain yield and water productivities were measured. Results showed that grain yields under AWD15 and AWD30 were comparable with CF, while water input and total CH4 emissions were significantly reduced under the two AWD treatments for both seasons. In the late season, there were no significant differences in grain yield among the four irrigation treatments for HFZ. While for TY3618, grain yield in AWD30 was significantly lower than AWD15. Irrigation water input in AWD15 and AWD30 was 19.4% and 29.7% lower, and irrigation water productivity was 31.7–37.6% and 48.4–53.2% higher than FP, respectively. Over all, no significant differences were found in maximum tiller number, leaf area index, total aboveground dry weight, among the four irrigation treatments for HFZ. While for TY3618, the crop growth rate during grain-filling stage in AWD30 was significantly lower than CF and FP. The CH4 emission under AWD15 and AWD30 were 37.4–45.7% and 61.1–77.1% lower than FP, respectively. Multi-location on-farm comparisons were conducted in north, central, and southwest region of Guangdong province and the results confirmed that AWD15 could obtain comparable grain yield as FP with fewer irrigations. These findings suggested that the AWD15 could be used for water-saving and CH4 emission mitigation while maintaining grain yield in rice production in south China. This is the first report on the performance of safe AWD in south China.

Levels and Potential Sources of Heavy Metals in Major Irrigated Rice Areas of the Philippines

Industrialization, urbanization and intensive use of farm inputs can pollute agricultural areas. The study was then conducted to assess the levels of chromium (Cr), nickel (Ni), copper (Cu), cobalt (Co), zinc (Zn), arsenic (As), molybdenum (Mo), cadmium (Cd), mercury (Hg), and lead (Pb) in the country’s major rice areas. The study also determined the contributions of soil properties, land uses, irrigation water, and farm inputs to the metal levels. Strategic collections of soil, plant and water samples in the country’s major soil series planted to rice, analyses of samples using x-ray fluorescence or atomic absorption spectroscopy, and farmer interviews were done. Metal levels were very high in Zambales and Negros Occidental soils due to deposition or use of metal-enriched mine tailings and irrigation water. Soil metal concentrations in Zambales far exceeded the intervention values of 180 mg/kg for Cr and 100 mg/kg for Ni. Soil metal levels in Negros Occidental exceeded the intervention value of 190 mg/kg for Cu and Mo. Rice plants in Negros Occidental exceeded the toxic levels of 30 mg/kg for Cu and 10-50 mg/kg for Mo due to the very high soil Cu and Mo concentrations in the area. Molybdenum concentrations of rice plants in Sultan Kudarat and Camarines Sur exceeded the toxic level due to the high amounts of foliar chemicals applied at >66 sprayer loads per year. The study implies that rice areas deposited with mine wastes have high heavy metal levels, and foliar chemicals can increase metal levels in rice. Keywords - Environmental toxicology, heavy metals, heavy metal sources, rice soils, Philippines

Modelling to increase the eco-efficiency of a wheat–maize double cropping system

The winter wheat- summer maize rotation is the main cropping system in the North China Plain (NCP). While its productivity has been constantly increased, the sustainability of the double cropping system has been increasingly questioned due to the high resource use and negative environmental impact. This paper combined field data with scenario modelling to investigate the productivity, resource (water and nitrogen) use efficiency and environmental impact of the wheat–maize rotation in response to management changes at a representative site Wuqiao in NCP. In addition the potential options to increase the system’s eco-efficiency, i.e., producing more with less input and less negative impact on the environment were explored. The results show that 180kg/ha/year of nitrogen could be considered as the optimal N rate for summer maize. For the wheat–maize double cropping rotation, 225mm of irrigation water for wheat and 330kg N/ha (150 for wheat and 180 for maize) are required to maintain the potential grain yield at 18t/ha and to have minimum impact on environment in terms of N leaching to the groundwater and N loss due to denitrification. These derived rates are 175mm/year less and 120kg N/ha less than the highest irrigation and N rates currently practiced. The reduced water and N inputs could reduce the annual totals of drainage, N leaching and denitrification N loss to a minimum of 117mm, 12kg N/ha and 28kg N/ha, respectively. Our simulation results also enabled derivation of yield response curves to water and nitrogen inputs, which can be used to optimise N applications under various levels of irrigation water inputs.

More rice with less water – evaluation of yield and resource use efficiency in ground cover rice production system with transplanting

Adoption of the innovative water-saving ground cover rice production system (GCRPS) based on transplanting of rice seedlings under high soil moisture conditions, resulted in an overall increase in grain yield compared to previous reports on GCRPS employing direct seeding. However, there is a lack of quantitative information on water and nitrogen use efficiency as affected by water and nitrogen management in GCRPS-transplanting. To close this knowledge gap, we conducted a two-year field experiment with traditional paddy rice (Paddy) and GCRPS-transplanting under two soil moisture conditions (GCRPSsat and GCRPS80%), combined with 3 nitrogen fertilizer management regimes (0, 150kg urea-N/ha as basal fertilizer for Paddy and GCRPS, 150kg urea-N/ha in 3 splits for Paddy or 75kg urea-N/ha plus 75kg N/ha as chicken manure for GCRPS). Grain yield, water and nitrogen use efficiency, stable isotope 13C of plant shoots and yield components were evaluated.The study showed: (1) compared to Paddy, both GCRPSsat and GCRPS80% produced significantly more grain yield, while no significant difference in grain yield was found between both GCRPS treatments. (2) Irrigation water use efficiency was increased by 140% in GCRPSsat and >500% in GCRPS80%, while total water use efficiency was improved by 52–96% as compared to Paddy. (3) δ13C of plant shoots was significantly higher in GCRPS than in Paddy, and showed significant positive correlations with total and irrigation water use efficiencies. (4) Compared to Paddy, agronomic N use efficiency was significantly higher in both forms of GCRPS. However, N recovery rates were only significantly higher in GCRPS than in Paddy when all urea nitrogen was applied as basal fertilizer before transplanting. With improved fertilizer N management, i.e., split N application in Paddy or combined application of urea and chicken manure in GCRPS, there were no significant differences. Overall, this quantitative evaluation of water use efficiency highlights that the use of GCRPS involving transplanting of seedlings has a great potential to reduce irrigation water input, increase grain yield and resource use efficiency.

Puddles – A trigger for heterogeneous chemical influx into the unsaturated zone

Spatial heterogeneity in the chemical concentration of interstitial water in the vadose zone was previously observed under apparently homogeneous surface conditions on two leveled fields sprinkler irrigated with treated sewage effluents on the phreatic Coastal Plain aquifer of Israel. This phenomenon greatly hampers the monitoring of groundwater quality. In this study we report on the presence of puddles of different size and shape that were sporadically observed in these fields. Temporal variability noted in the concentration of treated sewage effluents components in the puddles were considered to be related to evapotranspiration and degradation. For example: increases in the electrical conductivity (up to 1.32mS/cm), and in the concentrations of chloride (up to 521mg/L), dissolved organic carbon (up to 28.4mg/L), and carbamazepine (up to 780ng/L) and decreases in the concentrations of nitrate (up to 20.1mg/L) and caffeine (3396ng/L). Variable trends in concentration were observed for sulfamethoxazole, venlafaxine, 10-hydroxy-10,11-dihydrocarbamazepine and o-desmethylvenlafaxine. The presence of puddles was not necessarily related to areas with high irrigation water input. It is postulated that the continuous chemical variability in the puddles, whose location and size are also variable, determine a heterogeneous influx of solutes into the soil and subsequently into the vadose zone.

Light interception, leaf nitrogen and yield prediction in almonds: A case study

Crop yield prediction is important for the optimization of irrigation water, fertilizers, and other inputs and resources on the farm. In perennial crops, yield prediction is influenced by multiple factors regulated within the tree such as carry over effects from previous years, source-sink interactions and resource allocation and remobilization, but the bases for those regulation mechanisms are not well understood. This study reports the analysis of intensive sampling of light interception, leaf and nut nutrient concentration and yield of 768 almond trees subjected to fertilization and irrigation treatments within a mid-age commercial orchard. Nitrogen fertilization had a significant effect on individual tree fPAR, LAI, leaf nitrogen content and nut yield. While light interception and leaf area index (LAI) were poor predictors of kernel yield (R2=0.16–0.36 for light interception and 0.21–0.40 for LAI), leaf nitrogen pool (LNP) was able to predict 71–76% of the tree yield variability observed in two and three years. Near harvest, the LNP was highly correlated with fruit nitrogen pool (FNP) (R2=0.87). The results indicate that tree yield and nitrogen demand can be predicted based on leaf nitrogen content.

Evaluation of groundwater-based irrigation systems using a water–energy–food nexus approach: a case study from Southeast Nepal

This study aims to evaluate the performance of groundwater-based tube well irrigation systems of Sarlahi District in Nepal considering a water–energy–food nexus approach. The deep tube well (DTW) irrigation systems showed better performance over shallow tube well (STW) irrigation systems in terms of water supply and agricultural output per unit of irrigated area. On the other hand, the STW-based irrigation systems showed better performance in terms of energy use, management operation and maintenance (MOM) cost and benefit–cost ratio compared to DTW-irrigated systems. The productivity of irrigation water and energy input to major crops showed the best performance for maize followed by rice and wheat. The simulated yields of cereal crops through the AquaCrop model showed significant scope for enhancing crop yields and associated benefits through judicious use of water and fertilizer.

Alternate wetting and drying irrigation-mediated changes in the growth, photosynthesis and yield of the medicinal plant Tulipa edulis

Tulipa edulis is an important medicinal plant with a variety of anti-cancer properties. There is an urgent need to reduce water consumption in T. edulis under greenhouse cultivation. A greenhouse experiment was performed to study the effect of well-watered (80% of field capacity, Control), persistent drought (50% of field capacity, D) and alternate wetting and drying (50% and 80% of field capacity, AWD) regimes on the growth traits, photosynthetic pigment contents, chlorophyll fluorescence parameters, photosynthetic characteristics and yield of T. edulis. The results showed that compared with the well-watered control, persistent drought inhibited plant growth and yields dramatically, presumably due to the significantly lower photosynthetic rate caused by a decrease in photosynthetic pigments and a reduced chlorophyll fluorescence efficiency (Fv/Fm, Fv/F0). In contrast, the AWD plants showed a capacity for photosynthesis comparable to the well-watered control, which could be associated with similar photosynthetic pigment levels and chlorophyll fluorescence parameters (Fv/Fm, Fv/F0). AWD reduced the irrigation water input by 25.09% while leading to comparable yields and increased water productivity by 21.21% compared with the well-watered control. The results suggested that an alternate wetting and drying (50% and 80% of field capacity) regime can be an effective means of saving water, promoting bulb production, and improving water production for T. edulis.

Application of mulch under reduced water input to increase yield and water productivity of sweet corn in a lowland rice system

While straw mulch usually reduces soil evaporation and stabilizes soil temperature, hence increasing yield, this effect may depend on the irrigation water input conditions. Two experiments in lowland rice paddies in Lao PDR tested the effect of rice straw mulch under various water input—standard farmer condition to reduced input condition by using either drip irrigation or lower furrow irrigation water input (WI) by increasing the furrow irrigation interval before flowering—on growth and yield of sweet corn. The time course of water balance components was determined to elucidate the mechanisms of mulch and water input interaction for row planted maize after rice harvesting.The experiments found that adding straw mulch reduced estimated soil evaporation by 114–163mm, but only some of this was partitioned into extra transpiration, so the non-transpiration flux (the difference between water input and transpiration) changed little. Only when mulch was added and water input also reduced did it maintain or increase transpiration, reduce the non-transpiration flux and hence substantially increase water productivity (WP). Most if not all of the non-transpiration flux occurred in the first 60 days; the opportunity to apply treatments to increase water productivity arose mostly in the first 60 days.Mulch had a greater effect with extended furrow irrigation intervals before flowering than with standard intervals, but there was no effect under drip irrigation. In Experiment 1, mulch increased fresh ear yield and water productivity to water input (irrigation plus rainfall) (WP) by 42% with Low WI, but had no effect with High WI or with drip irrigation. The combination of mulch and reducing water input from High WI to Low WI increased gross margin (GM) per hectare by 20% and GM per m3 water input by 66% due to increased yield and reduced water and labour costs. In Experiment 2, mulch increased fresh ear yield, WP by 93% and consequent GM with low WI, but also increased fresh ear yield and WP by 60% and GM with High WI.In these Southeast Asian experiments, mulching and reducing water input—by increasing irrigation interval before flowering—maintained or increased yield, and increased gross margin per hectare and per m3 water input. Particularly in areas with restricted water supply, and hence the need to reduce water input and increase water productivity, mulch allows a reduction in water input while also maintaining or increasing farm income from sweet corn.

Comparison of adaptative strategies to climate variability in rural areas of Argentine Chaco and US Southern Plains during the last century

Considering uncertainties regarding climate variability, the objective of this study was to make a long-term (1901–2011) comparative assessment of the impact of land-use decision (changes in the cultivated area) and technology adoption as adaptative mechanisms of the rural sector in the Argentine Chaco and the US Southern Plains. Different sources of data on climate (precipitation, minimum, mean and maximum temperature and evapotranspiration), land-use change (proportion of cultivated area) and technology adoption were used. This work involved three main analytical steps: i) Principal Components Analysis (PCA) was applied to identified the dominant components of data variance, ii) the relationship between the residuals of precipitation and land-use change was assessed by means of a simple regression analysis and iii) technology adoption was evaluated through a proxy based on historical changes in the yield of maize (Zea mays L.). The results showed that farmers in both countries relied on two common adaptative strategies to face climate perturbations during the study period: i) land-use change (a simple binary decision of planting or not planting in response to climate conditions) during a first stage, and ii) the introduction of adaptative technologies to smooth the impact of climate during the second one. That substitution of adaptative strategies begun during the 1940 decade in the US Southern Plains, and around 30 years later in the Argentine Chaco. The adoption of technologies and agronomic practices explained the sensitivity decay of the cultivated area to the climatic variability during the second stage. The incorporation of improved hybrids with higher drought resistance plus the adoption of tilling practices like minimum tillage or no-till, the input of fertilizers, pesticides and irrigation water (the last one in US, only) became a successful strategy to mitigate the risk of climate perturbation.

Biomass accumulation and partitioning of newly developed Green Super Rice (GSR) cultivars under drought stress during the reproductive stage

Drought is a major abiotic threat in rice production; thus, there is a need to develop adaptable rice varieties that can withstand drought stress and still produce high yield in non-stressed environments. Green Super Rice (GSR) cultivars address this issue. These cultivars are bred through an innovative introgression breeding strategy that requires less irrigation water and chemical inputs without compromising grain quality and yield. This study verified the physiological efficiency and performance of newly developed GSR cultivars that previously showed favorable response to drought during advanced yield trials. Five drought-tolerant GSR cultivars and two checks were subjected to continuously flooded (CF) and drought-stressed environments during the dry seasons of 2011 and 2012 at the International Rice Research Institute (IRRI) experimental farms in Los Baños, Philippines. The cultivars’ ability to allocate assimilates and accumulate biomass under drought stress during the reproductive stage was verified. Leaf area index (LAI), biomass dry weight, and panicle yield were measured at the panicle initiation (PI), flowering (FL), and physiological maturity (PM) of the sample cultivars. All the cultivars performed satisfactorily in the CF environment with grain yield ranging from 5 to 11.5tonsha−1. Water stress during the reproductive stage significantly reduced grain yield by 75–88% in the moderate drought (soil water tension between 100 and 300kPa in upper 15cm soil layer) and 77–96% in the severe drought (soil water tension >300kPa in upper 15cm soil layer) experiments. The shortened reproductive duration mainly contributed to the significant reduction in yield under drought stress. Two GSR cultivars, GSR IR1-5-S10-D1-D1 and IR83142-B-19-B, responded well in severe drought environments, with grain yield almost similar to the drought check (1.79tonsha−1). Under moderate drought stress, there was a relative yield advantage of 25% and 40% for the two GSR cultivars over the drought check, respectively. Yield advantage across environments, varying from fully irrigated to drought-stressed, was 31–36%. These two GSR cultivars were effective in mobilizing stored carbohydrates from the vegetative organs to the panicles and not shortening the duration from flowering to maturity, to allow all reserved carbohydrates be allocated to storage organs as a mechanism to cope with drought stress. Lower leaf area index (LAI), which allowed balanced biomass accumulation and lower transpiration, without a significant decrease in grain filling duration, was another drought-coping strategy. These physiological responses and characteristics apparently enabled the GSR cultivars to withstand drought stress; these are key indicators for varietal selection in drought-prone environments, particularly in severe drought stress in the reproductive stage. Despite the poor ability of some cultivars to cope with severe drought, three out of five selected GSR cultivars produced grain yield (2.0–2.9tonsha−1) that was the same or higher than the drought check in moderate drought stress. The introgression breeding technique applied in the newly developed drought-tolerant cultivars through the GSR breeding strategy was found to be effective. It could produce high yields in both CF and water-limited environments, and thus, it could serve as a model for other breeding programs to adopt.

A geochemical study of the impact of irrigation and aquifer lithology on groundwater in the Upper Yakima River Basin, Washington, USA

The Yakima River, a major tributary of the Columbia River, is currently overallocated in its surface water usage in part because of large agricultural water use. As a result, groundwater availability and surface water/groundwater interactions have become an important issue in this area. In several sub-basins, the Yakima River water is diverted and applied liberally to fields in the summer creating artificial recharge of shallow groundwater. Major ion, trace element, and stable isotope geochemistry of samples from 26 groundwater wells from a transect across the Yakima River and 24 surface waters in the Kittitas sub-basin were used to delineate waters with similar geochemical signatures and to identify surface water influence on groundwater. Major ion chemistry and stable isotope signatures combined with principal component analysis revealed four major hydrochemical groups. One of these groups, collected from shallow wells within the sedimentary basin fill, displays temporal variations in NO3 and SO4 along with high δ18O and δD values, indicating significant contribution from Yakima River and/or irrigation water. Two other major hydrochemical groups reflect interaction with the main aquifer lithologies in the basin: the Columbia River basalts (high-Na groundwaters), and the volcaniclastic rocks of the Ellensburg Formation (Ca–Mg–HCO3 type waters). The fourth major group has interacted with the volcaniclastic rocks and is influenced to a lesser degree by surface waters. The geochemical groupings constrain a conceptual model for groundwater flow that includes movement of water between underlying Columbia River basalt and deeper sedimentary basin fill and seasonal input of irrigation water.

Actual evapotranspiration and dual crop coefficients for dry-seeded rice and hybrid maize grown with overhead sprinkler irrigation

In lieu of the decreasing availability of water for irrigated rice, we examined two alternatives to traditional rice cultivation on puddled and saturated soil–maize and dry-seeded rice production grown with an overhead sprinkler irrigation system. We characterized the inter-seasonal daily variations of actual crop evapotranspiration (ET), transpiration (T), and evaporation (E) using the eddy covariance (EC) technique during 2011 and 2012 dry seasons. The average growing season ET rate of maize was 3.90mmd−1 in 2011 and 3.74mmd−1 in 2012. For the dry-seeded rice, the average growing season ET rate was 4.36mmd−1 in 2011 and 4.13mmd−1 in 2012. Growing season ET of maize (484mm) and dry-seeded rice (523mm) in 2011 were higher than during 2012 (453mm for maize and 475mm for dry-seeded rice) because of higher net radiation (Rn) in 2011. Partitioning ET showed that T accounted for 66–74% of seasonal ET for maize and 53–60% for dry-seeded rice. On average, dry-seeded rice had 6.5% more ET than maize due to higher irrigation water inputs. The average total water input (irrigation+precipitation) for maize was 618mm while that of the dry-seeded rice was 908mm. The large difference between crop coefficient (Kc) and basal crop coefficient (Kcb) values during the initial and crop development stages of both maize and dry-seeded rice provides a good opportunity to optimize irrigation water input by designing a more efficient irrigation schedule that is appropriate to the water needs of the crops.

Emergy evaluation of the contribution of irrigation water, and its utilization, in three agricultural systems in China

Emergy theory and method are used to evaluate the contribution of irrigation water, and the process of its utilization, in three agricultural systems. The agricultural systems evaluated in this study were rice, wheat, and oilseed rape productions in an irrigation pumping district of China. A corresponding framework for emergy evaluation and sensitivity analysis methods was proposed. Two new indices, the fraction of irrigation water (FIW), and the irrigation intensity of agriculture (IIA), were developed to depict the contribution of irrigation water. The calculated FIW indicated that irrigation water used for the rice production system (34.7%) contributed more than irrigation water used for wheat (5.3%) and oilseed rape (11.2%) production systems in a typical dry year. The wheat production with an IIA of 19.0 had the highest net benefit from irrigation compared to the rice (2.9) and oilseed rape (8.9) productions. The transformities of the systems’ products represented different energy efficiencies for rice (2.50E + 05 sej·J−1), wheat (1.66E + 05 sej·J−1) and oilseed rape (2.14E + 05 sej·J−1) production systems. According to several emergy indices, of the three systems evaluated, the rice system had the greatest level of sustainability. However, all of them were less sustainable than the ecological agricultural systems. A sensitivity analysis showed that the emergy inputs of irrigation water and nitrogenous fertilizer were the highest sensitivity factors influencing the emergy ratios. Best Management Practices, and other agroecological strategies, could be implemented to make further improvements in the sustainability of the three systems.

Limited Si-nutrient status of rice plants in relation to plant-available Si of soils, nitrogen fertilizer application, and rice-growing environments across Sub-Saharan Africa

Rice is a specific silica-accumulator among higher plants. The Si in rice enhances resistance to biotic and abiotic stresses. The booming demand for rice in Sub-Saharan Africa (SSA) requires rapid increases in rice production, and hence more Si supply will be needed from soils, irrigation water, and external inputs. However, the current Si-nutrient status of rice plants and relevant factors has been so far paid little attention in the region. Therefore, an extensive survey was conducted for evaluating variability of Si concentration in rice straw in relation to soil properties, fertilizer management practices, and rice-growing environments across a wide range of local farmers’ fields in SSA. Plant and soil samples were collected at harvesting time from 99 fields in Benin, Ghana, Guinea, Kenya, Madagascar, Mozambique, and Nigeria, and then chemically analyzed. The Si concentration in straw ranged 1.7–8.4%, and the values in 68% of the fields were below the critical deficiency level of 5%. The Si concentration in straw was most significantly correlated with the amounts of water-soluble Si in soils after 1-week anaerobic incubation at 40°C (hereafter, plant-available Si). The plant-available Si was particularly low in the acidic soils of Highland and Humid Agro-ecological zones, mainly consisting of weathered Oxisols and Ultisols. The mean Si values were greatest in the order of irrigated lowland (5.3%)>rainfed lowland (4.3%)>upland (3.4%) among different rice-growing environments. Multiple regression analysis revealed that 59% of the variation in Si concentration in straw was explained by the plant-available Si in soils, rice-growing environments, N application rates, and mineralizable N in soils. The regression model indicated that improvement of plant-available Si in soils could increase the Si concentration in straw at a rate of 0.043% permgkg−1, while external N application lowered the Si concentration in straw at a rate of 0.0068% per kgNha−1 input. This extensive survey revealed that low Si nutrient status was widely observed for rice as associated with limited plant-available Si in the SSA soils. The probability of Si deficiency can be increased with abundant N application and non-submerged field conditions. By focusing on these Si-deficient field conditions, further studies should quantify the relationship between Si-nutrient status and occurrence of environmental stresses such as blast infection so as to develop appropriate Si-management practices for rice production in SSA.

Nitrogen Loss from Paddy Field with Different Water and Nitrogen Managements in Taihu Lake Region of China

High rates of nitrogen (N) fertilizer were applied to a paddy field in the Taihu Lake region of China to maximize crop production. Excessive N input has resulted in serious agricultural nonpoint pollution. Water and N management are two important approaches to regulating N loss from paddy fields. This study aimed to determine N losses through ammonia volatilization, runoff, and leaching from a paddy field during the rice-growing season in Taihu Lake region. Field experiments with two water and two N managements were conducted. The N exported to the environment through ammonia volatilization, runoff, and leaching from the paddy field was 37.2 kg N ha−1 to 102 kg N ha−1, with ammonia volatilization accounting for 69.6% to 83.5% of N loss. Ammonium and dissolved organic N significantly contributed to N loss through runoff and leaching. Controlled irrigation and site-specific N management (CS) significantly decreased N losses through ammonia volatilization, runoff, and leaching. Compared with the N and irrigation water inputs in traditional water and N management, those generated by controlled irrigation and site-specific N management were reduced by 34.6% to 43.0% and 59.2% to 63.3%, respectively. Moreover, the reduction in N and water input in the CS paddy field enabled the maintenance of high rice yield; it significantly increased N use efficiency by 15.1% to 34.9% and decreased the N exported to the environment by ammonia volatilization, runoff, and leaching by 53.1% to 56.1%. Therefore, the joint application of controlled irrigation and site-specific N management efficiently reduces agricultural nonpoint pollution through N loss from paddy fields.

Effects of hardpan disruption on irrigated dry-season maize and on subsequent wet-season lowland rice in Lao PDR

The hardpan in a lowland rice soil, produced by the puddling process, can both restrict percolation to preserve wet-season rice yield and restrict the root growth and yield of subsequent non-rice crops. Disrupting the hardpan could benefit a post-rice crop grown in the dry season, but may increase wet-season percolation and hence can decrease wet-season rice yield.The effect of hardpan disruption on dry-season maize was assessed in three experiments under different irrigation water input conditions (high input under furrow irrigation, low input by increasing irrigation interval, and, in one experiment, with drip irrigation as well); two on a sandy-loam soil and one on a loamy-clay soil. The effect of disruption on subsequent wet-season percolation was measured in two of these experiments.On a loamy-clay soil, the hardpan had a soil mechanical resistance (SMR) of 3.1MPa and hardpan disruption had no effect on maize grain yield. On a sandy-loam soil with a hardpan of average peak SMR of 4.5MPa, in one year, disruption increased yield by 14% and there was no interaction between hardpan disruption and water input. In the previous year with an average peak hardpan SMR of 5.2MPa, however, there was interaction between hardpan disruption and water input: hardpan disruption increased grain yield and water productivity (grain yield per unit water input) by 29% with drip irrigation and by 24% with high water input, but had no significant effect with low water input.Hardpan disruption had no effect on percolation in the following wet season, although it increased percolation by 56–70% in two of the four fields in the first 30 days after transplanting. Consequently, hardpan disruption gave gross benefits 2.7–9.8 times the costs of disruption, with a maize price of US$ 180t−1, in those situations where it increased maize grain yield.

시설오이 지중관비시 자동관수센서의 적정 매설깊이

시설오이 지중관비에서 지중 점적호스를 30 cm에 매설 시에 텐시오미터를 이용한 자동관수센서의 적정 깊이를 제시하고자 2010-2011년까지 2년간에 걸쳐서 조사하였다. 오이의 생육은 텐시오미터 30 cm 깊이에서 낮았으나 텐시오미터 10 및 20 cm에서는 유의성 있는 차이는 없었다. 1년 및 2년차 수량에서도 텐시오미터 30 cm에서 각각 40.9 및 41.2 <TEX>$Mg\;ha^{-1}$</TEX>로 가장 적은 생산량을 나타내었나, 텐시오미터 10 cm에서는 57.0 및 56.9 <TEX>$Mg\;ha^{-1}$</TEX>, 텐시오미터 20 cm에서는 56.0 및 60.5 <TEX>$Mg\;ha^{-1}$</TEX>로 처리간의 차이가 없이 동일한 수량을 나타내었다. 오이재배에서 한 작기 당 질소 및 일일 물 공급량은 63 <TEX>$kg\;N\;ha^{-1}$</TEX>의 질소와 1.3 <TEX>$mm\;day^{-1}$</TEX>로 물이 공급된 텐시오미터 20 cm 처리에서 질소 및 수분 이용효율이 높았다. 또한 토양깊이 0-30 cm에 대한 뿌리길이에서도 텐시오미터 20 cm에서 0.87 <TEX>$cm\;cm^{-3}$</TEX>으로 유의성은 없었지만 가장 높은 값을 나타내었다. 이러한 결과로부터 시설오이에서 지중 점적호스를 30 cm 깊이에 매설 시에 텐시오미터를 활용한 자동관수센서의 적정 깊이는 20 cm인 것으로 판단되었다. Vegetables production in greenhouse are typically intensely managed with high inputs of fertilizers and irrigation water, which increases the risk of ground-water nitrate contamination. In 2010 and 2011, a study was conducted to determine the appropriate depth of soil moisture sensor for automatic irrigation control to use water and nitrogen efficiently under subsurface drip irrigation (SDI) systems. The irrigation line for SDI placed 30 cm below soil surface and tensiometer was used as soil moisture sensor. Three tensiometer treatments placed at 10 (SDI-T10), 20 (SDI-T20) and 30 cm (SDI-T30) depths below soil surface under SDI. These are also compared to SUR-T20 treatment where tensiometer placed at 20 cm below soil surface under surface drip irrigation (SUR) systems. The growth of cucumber was not statistically different between SUR and SDI without SDI-T30 treatment. Fruit yields (Mg/ha) were 57.0 and 56.9 (SDI-T10), 56.0 and 60.5 (SDI-T20), 40.9 and 41.2 (SDI-T30) and 56.6 and 54.3 (SUR-T20) for 2010 and 2011, respectively. Slightly higher total yield was observed in tensiometer placed 20 cm below the soil surface, although no significant differences were found between SDI-T10 and SDI-T20 under SDI treatments. In addition, nitrogen application rates and daily irrigation rates were lowest in SDI-T20 compared with other SDIs and SUR treatments. Nitrogen and daily irrigation application under SDI-T20 was lower than that under SUR-T20 by 6.0%. These findings suggested tensiometer 20 cm depth under SDI systems was best for cucumber production in greenhouse.