Technical Note:<br>Practical considerations on the use of down-sized time-domain reflectometry (TDR) probes

International audienceNine time-domain reflectometry (TDR) probes, 2 to 10 cm long, were evaluated by comparing their measurement accuracy of TDR-pulse travel time in a sand and sandy loam soil, and electrical conductivity in NaCl solutions. TDR probes tTDR varied erratically with the predicted pulse travel time tg (from volumetric soil-water content) for the probes tTDR varied linearly with tg and followed the 1:1 line. TDR could not measure tTDR Lmin and the lowest allowable soil-water content qmin that the probe can accurately measure govern this lowest pulse travel time tmin. The mean absolute deviation between tTDR and tg was 77 ps for the 2.3 cm long probe and 1.39 ps for all probes ?2.5 cm in length. All probes ?2.5 cm in length measured electrical conductivity of salt solutions sTDR that compared well with the electrical conductivity measured by a conductivity meter sm. The length of the probes did not exert any noticeable influence on the accuracy of electrical conductivity measurement. Keywords: TDR probe, pulse travel time, dielectric constant, electrical conductivity</p

Performance of Wheat in Five Soils of Different Textures under Freshwater and Wastewater Irrigation

This study investigated the effects of five soils of different textures on wheat cultivation under irrigation with freshwater (FW) and municipal wastewater (WW). The experimental design was a split-plot with irrigation water quality as main factor and soil texture as sub-factor in three replications. These factors respectively comprised 2 and 5 treatments. Soil texture significantly (p£0.05) influenced plant height, leaf area index (LAI), spike length, number of grains per spike, above ground dry matter (ADM), grain yield, straw yield and biomass yield of wheat in most cases both under FW and WW irrigation. The harvest index (HI) of wheat responded significantly under FW irrigation only. Under FW, treatment T5 (silt loam) produced the highest grain yield (4.2 t ha–1) followed by T3 (loam-1) (3.1 t ha–1); the lowest yield (2.0 t ha–1) was in the control treatment, T1 (loamy sand). Under WW, treatment T2 (sandy loam) produced the highest grain yield (5.0 t ha–1) followed by T4 (loam-2) (4.5 t ha–1) both of which are statistically similar; the lowest yield (3.4 t ha–1) was in the control treatment. Treatments T2 and T4 provided the highest straw yield (5.6 t ha–1) and treatment T2 provided the highest biomass yield (10.6 t ha–1), both under WW; both T2 and T4 produced invariant biomass yields. Compared to other treatments, T2 and T4 gave statistically similar but significantly higher water productivity with respect to straw and grain yields. The lowest water productivity was in treatment T1 under both water qualities. The results of this study provided sound criteria in selecting suitable lands for wheat cultivation based on irrigation water quality, specifically in alluvial plains where soil texture is prone to high variations. Also, the observed facts of improved productivity of lower quality coarse-textured soils due to addition of easily available and inexpensive clay would provide guidance to bring unproductive sandy soils under production by clay amendments

Coupled Irrigation–Drainage Management Practice for HYV Rice Cultivation with Saline-Irrigation Water: Evidence from Lysimeter Experiment

Irrigation with saline water adversely affects rice production and degrades land productivity in the coastal zones of many countries in the world. This study aimed at developing a suitable irrigation management practice to reduce the harmful effects of salinity on rice production under saline water irrigation. An experiment in raise-bed lysimeters was set in a split-split-plot design with irrigation–drainage practice as the main factor, irrigation water salinity as the sub-factor and rice variety as sub-sub factor; main factor and sub-factor comprised four treatments and the sub-sub factor comprised three treatments, each with three replications. The treatments of the main factor were – T1: 2-5 cm continuous ponding, T2: continuous saturation, T3: changing irrigation water after 3 days of application by maintaining 2-5 cm ponding depth, and T4: changing irrigation water after 5 days of application by maintaining 2-5 cm ponding depth. The sub-factor comprised – SL1: fresh water as control, SL2: saline water of 6 dS m-1, SL3: saline water of 9 dS m-1, and SL4: saline water of 12 dS m-1. The sub-sub factor comprised three salt-tolerant rice varieties V1: Binadhan-8, V2: Binadhan-10, and V3: BRRI dhan-47. The irrigation–drainage practices T2 and T3 provided significantly (p£0.05) improved growth and yield attributes of the rice varieties under salinity water level SL3 and SL4 compared to T1 and T4 treatments. The treatment T3 maintained least exposure of the crop to high degree of salinity and produced satisfactory plant attributes by inhibiting the detrimental effects of salinity. Therefore, T3 is suggested for adoption in practical fields when provision for removing high saline water from the rice fields can be arranged

Trends of Water Requirements of Major Crops and Cropping Patterns in Bogura and Rajshahi Districts of Bangladesh

Reliable past trends of water requirements of individual crops and cropping patterns at local level, although crucially important for irrigation forecast and agricultural planning, are yet inadequate for the water-scarce Barind region of Bangladesh. This study, therefore, determined water requirements and their trends of eight major crops (aus, aman, boro, vegetables, mustard, sugarcane, wheat and potato) and six cropping patterns (aus–aman–boro, aus–aman–potato, aman–potato–fallow, vegetables–aman, aman–mustard–fallow and aus–fallow–wheat) of Bogura and Rajshahi districts of the Barind region. Water requirements were determined from crop, soil and weather data for the period 1985–2013 by using Soil-Water Balance via CropWat (SWBcropwat) model. Trends of rainfall, crop evapotranspiration (ETc) and irrigation requirement (IR) were determined with MAKESENS statistical tool. Monthly total rainfall revealed increasing trend in January, August and October but decreasing trend in the other months, with significant (p£0.05) trend in July in Bogura. Monthly total ETc decreased except in July and September, with significant trend in October–April/May. Seasonal ETc for the crops decreased significantly except for aman rice and sugarcane in Bogura and for aman rice in Rajshahi. ETc also decreased for the cropping patterns except for aman–mustard–fallow in Rajshahi. While effective rainfall (ER) for the crops and cropping patterns decreased only minimally, IR decreased significantly for boro, potato and vegetables in Bogura and for mustard and vegetables in Rajshahi. IR decreased for all cropping patterns, with significant trend for aus–aman–potato, aman–potato–fallow and vegetables–aman patterns. In response to changing cropping area, total volume of ETc increased gradually from 1985 to 2005 in Bogura and from 1985 to 2010 in Rajshahi for boro rice, but it decreased until 2005 before increasing for aus rice in both districts. After the year 2000, total volume of ETc decreased for wheat but increased for potato, indicating a shift from wheat to potato cultivation. Due to contrasting trends of ER and ETc and self-motivated shift in crop-choice, continuous adjustment of irrigation-based crop planning is necessary. The results of this study can guide future investigation for all other crops and cropping patterns to help planning agriculture of the study areas by choosing appropriate crops and cropping patterns based on available water resources

Soil amendments in suppressing salinity effects on HYV rice cultivars

Suppressing the harmful effects of salinity is a critical issue for expanding rice acreage in saline areas under demographic pressure and climate change contexts. In need of comprehensive information, this study evaluated the effectiveness of cowdung and gypsum (CaSO4.2H2O) for their individual and combined usages in ameliorating salinity stress for cultivation of Binadhan-8 (V1), Binadhan-10 (V2), and BRRI dhan47 (V3) rice cultivars with standard fertilizer doses under irrigation with four salinity levels: fresh water (SL1, control), 6 dS m-1 (SL2), 9 dS m-1 (SL3), and 12 dS m-1 (SL4). A pot experiment was laid in a Split-Split arrangement in a completely randomized design (CRD) with three factors (soil amendments, salinity levels, and rice cultivars) and three replications. The amendment treatments included: no amendment (T1, control), cowdung @ 6 t ha–1 (T2), gypsum @ 150 kg ha–1 (T3), and combination of cowdung @ 6 t ha–1 and gypsum @ 150 kg ha–1 (T4). SL4 significantly (p£0.05) suppressed all attributes of the rice cultivars. Treatments T3 and T4 most effectively reduced salinity stress on the rice cultivars, which could tolerate up to 12 dS m–1 irrigation-water salinity without significant yield loss, with T3 performed the best. The generated information would help rice cultivation under irrigation with saline water, specifically in the coastal region having limited fresh water for irrigation

Design, Construction and Performance Study of a Solar Assisted Tri-cycle

Solar energy is one of the important sources of renewable energy which can be a feasible alternative to fossil fuels. There are many works has been done in order to incorporate solar energy to everyday transportation including tricycle. However, most of the tricycle develops are expensive and not feasible for developing countries. In this study, a cheaper solar tricycle with more capability of utilizing the solar energy is designed for developing countries. The main content of the tricycle is Solar PV panel, Brushless PMDC motor, controller, and battery. The power transmission of the solar tricycle is also simple. It is found that tricycle serves 24% back up for running, by the solar panel. Also, the total construction cost of the tricycle is only 240$ with near about zero impact on the environment. This paper highlights the advantages of the dual mode of charging, including the economic and environmental feasibility of the tricycle

Improving irrigation water delivery performance of a large-scale rice irrigation scheme

The availability of irrigation water and its equitable allocation in a large-scale rice irrigation scheme of Malaysia have been modeled. The model reliably estimates available water for irrigation at the intake of the main canal and simulates the recommended irrigation deliveries for 120 tertiary canals. Different water allocation and management scenarios were evaluated based on the sensitivity of the growth stages of rice to water, varying field-water demand, and perceived water shortages. The model provides a quantitative assessment not only of water allocation for irrigation but also of day-to-day or periodic irrigation delivery performances for a large-scale rice irrigation system. It provides 86% adequacy and 87% equity of irrigation delivery in the main season (August-December). The corresponding performance indicators provided by the model are 74 and 89% in the off-season (February-June). The dependability of water supply is higher in the off-season than in the main season, while the relative water supply (RWS) is the converse. RWS often becomes >1.0 in the main season, while such a RWS is rarely obtained in the off-season. The model augments the water delivery performance of the scheme and hence would serve as a useful tool for irrigation managers in decision making

Evaluation of low-head drip systems for vegetable farming in Bangladesh

Bangladesh is in the phase of introducing drip irrigation (DI) system in the country. Several types of drip emitters are now becoming available in the market although their performance indices are yet to be matched for local farming practices. This study reports the results of a series of experiments carried out to quantify the hydraulic performances indices of two different types of emitters available in Bangladeshi marketplace. One of the emitters, E1 was designed and manufactured locally, while the other, E2 was imported and highly priced. Followed by the hydraulic experiment, these emitters were also employed in comparative field experiments for tomato and brinjal production at two separate locations in the country. Irrigation schedules were designed based on the local evapotranspiration regime. During the study, both the emitter types exhibited non pressure compensating features as their flow rate increased with pressure. Interestingly, both types of emitters gave a persistent trend of flow rate along the laterals. Standard uniformity indices for DI systems were also calculated, and the DI systems were categorized (good to excellent) based on the established guidelines for microirrigation. Very good performance indices were obtained at 3 m head for emitter E1, and at 2.5 m head for emitter E2. The results of the field experiments also showed that yield, water saving and water productivity of drip irrigated tomato was increased by 12%, 49.48% and 49% respectively when compared with furrow irrigation that is considered as a farmer practice. Similar results were also obtained for brinjal fields irrigated under DI systems. These experiments showed promising comparative benefits of drip technology for vegetable cultivation in water scarce coastal areas of Bangladesh.

Extension of the measurement range of electrical conductivity by time-domain reflectometry (TDR)

International audienceThe electrical conductivity (EC) of a medium invaded by TDR sensors can be estimated from the impedance of a TDR reflectogram. Four categories of sensor were tested in salt solutions and the impedances of the TDR pulse wave were correlated to the EC of the solution. The relation between the impedance and EC over a wide range of conductivities is non-linear but stable. Second- to fourth-degree polynomials can extend the measurement range to 44 dS m-1 (equivalent to a NaCl concentration of 28 g l-1 or 0.48 N) and result in better prediction of the conductivities than linear relations. For automatic measurement of EC with a datalogger, the method of Giese and Tiemann (1975, Adv. Mol. Rel. Processes, 7: 45-59) gives accurate measurement of conductivities lower than 10 dS m-1. Polynomial relations between EC and the datalogger's record provide an accurate estimate of the conductivity over a wide range. However, for both manual and automatic measurements, the sensors need to be calibrated individually. In particular, in the non-linear region, the differences between sensors are larger. Fortunately, the relation is sufficiently stable to eliminate significant error

Projected streamflow in the Kurau River Basin of Western Malaysia under future climate scenarios

Climate change-induced spatial and temporal variability of stremflow has significant implications for hydrological processes and water supplies at basin scale. This study investigated the impacts of climate change on streamflow of the Kurau River Basin in Malaysia using a Climate-Smart Decision Support System (CSDSS) to predict future climate sequences. For this, we used 25 reliazations consisting from 10 Global Climate Models (GCMs) and three IPCC Representative Concentration Pathways (RCP4.5, RCP6.0 and RCP8.5). The generated climate sequences were used as input to Soil and Water Assessment Tool (SWAT) to simulate projected changes in hydrological processes in the basin over the period 2021–2080. The model performed fairly well for the Kurau River Basin, with coefficient of determination (R2), Nash-Sutcliffe Efficiency (NSE) and Percent Bias (PBIAS) of 0.65, 0.65 and –3.0, respectively for calibration period (1981–1998) and 0.60, 0.59 and −4.6, respectively for validation period (1996–2005). Future projections over 2021–2080 period show an increase in rainfall during August to January (relatively wet season, called the main irrigation season) but a decrease in rainfall during February to July (relatively dry season, called the off season). Temperature projections show increase in both the maximum and minimum temperatures under the three RCP scenarios, with a maximum increase of 2.5 °C by 2021–2080 relative to baseline period of 1976–2005 under RCP8.5 scenario. The model predicted reduced streamflow under all RCP scenarios compared to the baseline period. Compared to 2021–2050 period, the projected streamflow will be higher during 2051–2080 period by 1.5 m3/s except in February for RCP8.5. The highest streamflow is predicted during August to December for both future periods under RCP8.5. The seasonal changes in streamflow range between –2.8% and –4.3% during the off season, and between 0% (nil) and –3.8% during the main season. The assessment of the impacts of climatic variabilities on the available water resources is necessary to identify adaptation strategies. It is supposed that such assessment on the Kurau River Basin under changing climate would improve operation policy for the Bukit Merah reservoir located at downstream of the basin. Thus, the predicted streamflow of the basin would be of importance to quantify potential impacts of climate change on the Bukit Merah reservoir and to determine the best possible operational strategies for irrigation release. MD ROWSHON KAMAL// HABIBU ISMAIL, MUHAMMAD ADIB BIN MOHD NASIR/ Md Abdul Moji