Field Water Balance Research Articles

Correlating the field water balance derived crop coefficient (Kc) and canopy reflectance-based NDVI for irrigated sugarcane

Studies of crop coefficients as a function of vegetation indices are reported less often for sugarcane than other crops because of the variation in crop evapotranspiration (ETc) and spectral response over the long growth period. In this study, the possibility of correlating crop coefficient (Kc) and ground based normalized difference vegetation index (NDVI) of a sugarcane crop was investigated based on 2 years field experiments conducted in 2015 and 2016 in semi-arid India. The Kc values for the full crop season were determined by the field water balance method and ground NDVI was estimated from spectral reflectance measurements using a field spectro-radiometer. The sugarcane Kc values for the tillering (development stage), grand growth (mid-season) and maturity stages (end season) were 0.70, 1.20 and 0.78, respectively. The results found that the Kc was 16.6% less than that suggested by FAO-56. The sugarcane NDVI ranged from 0.48 to 0.69 at the tillering stage and 0.69 to 0.93 in the grand growth stage. Unlike other crops, sugarcane NDVI at the maturity stage did not reduce from 0.85 even at harvest due to the continued production of fresh green leaves at the top of the plant. Regression equations were developed to estimate the seasonal distribution of Kc with NDVI as the dependent variables and ratio of days $$\left(\frac{t}{T}\right)$$ after planting (t) to the total crop period (T) as the independent variable. The relationship between crop Kc and NDVI was characterized with 2nd order polynomial regression but correlation was moderately strong (r = 0.75, n = 315). Stronger correlations between Kc and NDVI were obtained by splitting growth period into the growth phase (r = 0.98, n = 245) and decline phase (r = 0.99, n = 70). The estimated Kc will be helpful for correcting irrigation scheduling of sugarcane in semi-arid conditions. The Kc-NDVI relationships for sugarcane investigated in this study are important for potential real time irrigation water management in the future.

Field monitoring and model predicted water balance of monolithic cover

The use of the evapotranspiration cover for landfill is increasing because of its long-term enhanced performance. However, the performance of evapotranspiration cover primarily depends on the onsite geo-climatic conditions. Therefore, field verification of cover performance through constructed test plots is required before actual implementation. Additionally, numerical modeling and comparison with field results are necessary for future performance prediction. The objective of this study was to simulate the water balance hydrology of evapotranspiration cover using the code SEEP/W. Drainage lysimeter was constructed with fine-grained soil and native vegetation. Field water balance data from the lysimeter were obtained through instrumentation. Onsite climatological data, laboratory and field investigated soil parameters and actual field studied plant parameters were used as model input. Based on one year’s simulation, it was observed that the code nearly captured the seasonal variations in the water balance quantities measured in the field. Surface runoff was reasonably predicted in the model where precipitation intensity appeared to be responsible to some extent. Evapotranspiration was slightly overpredicted and the fluctuation in soil water storage was similar to the field results. The model predicted annual percolation was approximately 45 mm, which is under-predicted than the actual field measured annual percolation of 62 mm.

Crop Coefficient for Potato Crop Evapotranspiration Estimation by Field Water Balance Method in Semi-Arid Region, Maharashtra, India

Crop evapotranspiration (ETc) estimation is essential for many studies such as irrigation system design and management, crop yield simulation, and water resource planning and management. Field studies were conducted at MPKV Rahuri, Maharashtra from 2015 - 2016 and 2016 - 2017 (2 years) in clay soils to determine crop evapotranspiration and crop coefficients (Kc) of the potato crop. The experimental area was cultivated with irrigation applied at 7-days interval. The irrigation scheduling was based on the field water balance approach. The crop evapotranspiration was determined by the field water balance; reference evapotranspiration (ETo) by the Penman-Monteith method and crop coefficients were computed using the standard FAO-56 methodology. The total reference evapotranspiration (ETo) and crop evapotranspiration (ETc) were 226 and 240 mm for the year 2015–2016 and 248 and 250 mm for the year 2016–2017, respectively. The 2-year average reference evapotranspiration was 237 mm and the crop evapotranspiration was 245 mm. The average estimated Kc values for the semi-arid region during the vegetative, tuber development, and maturity stages for potato are 0.55, 1.11, and 1.01, respectively. The calculated values are slightly lower than those suggested by FAO-56 for the vegetative and tuber development stages and higher for the maturity stage of potato. The estimated values of crop coefficients for potato are 11.25% higher than those suggested by FAO-56. However, observed variation between values from the FAO-Kc and Kc calculated by the field water balance is not significant. So, these values can be used for irrigation scheduling of potato in the semi-arid region.

Soil Water Content Below 33.7% Progressively Reduces the Latex Yield of Rubber PB 60, A Study in Sembawa, South Sumatra, Indonesia


 
 
 Rubber is one of the economically important tropical trees that produces natural rubber, an essential industrial raw material in Indonesia. In general, rubber can grow well in areas with 1,500 - 3,000 mm rainfall per year that evenly distributed round the year. During the dry season, water availability is reduced so that water becomes a limiting factor for the growth and production of the rubber tree. This paper aimed to determine minimum soil water content that must be maintained to prevent the reduction of PB 260 rubber production based on field water balance. This research was carried out at the Indonesian Rubber Research Institute Experimental Field, South Sumatra, Indonesia, between 2014 to 2019. This experiment used PB 260 clone which was planted in 2001 using a 6 x 3 m plant spacing. Soil analysis showed that the Sembawa had a clay loam soil texture. The measured parameters were latex production (kg per ha per year), rainfall, and evapotranspiration (mm). The results from our six years of study showed that rubber production always decreased when soil water content started to decline below field capacity (33.7 %, or equal to 337 mm with 1m depth of root zone).
 
 

The contribution of percolation to water balances in water-seeded rice systems

Rice (Oryza sativa) has one of highest applied water footprints of any crop, due in many cases to high percolation and lateral seepage rates in flooded rice fields. Better understanding the magnitude and variability of these subsurface water flows and their contribution to the rice field water balance is critical for efforts to reduce the water footprint of rice production and to limit the transport of pollutants to surface water and groundwater. Percolation was directly measured in eight direct-seeded California rice fields that ranged from 20 to 61% clay and a complete water balance was developed for three of these fields. For these latter fields, directly measured percolation rates were compared to percolation calculated with Darcy’s law, and combined percolation and lateral seepage calculated as the residual of a water balance was compared to directly measured values. Across eight fields, cumulative percolation over the growing season ranged from 0.04 to 6.95 cm season−1. The mean cumulative percolation for the three water balance fields was 2.1 cm based on direct measurements compared to 3.2 cm based on Darcy’s law calculations. Combined percolation and lateral seepage calculated as the residual term of a water balance for the three fields was 17.1 cm, compared to 4.4 cm based on direct measurements, corresponding to 13.2 % and 3.4 % of water inputs, respectively (inputs were 98–99 % from irrigation). Based on these results, water management strategies that remove floodwater (e.g. alternate wetting and drying) would have limited potential to reduce water inputs in California rice production (0.7–2.7 cm season-1). Furthermore, using the most conservative (largest) estimates for each component of the water balance, we conclude that the average water requirement for California rice fields is approximately 108 cm season-1.

Effect of Soil Type and Vegetation on the Performance of Evapotranspirative Landfill Biocovers: Field Investigations and Water Balance Modeling

Abstract The water balance performance of evapotranspirative landfill biocovers (ET-LBCs) under Canadian cold climate conditions is evaluated by constructing seven lysimeters at a field site in Alb...

What is the worth of drain discharge and surface runoff data in hydrological simulations?

Quantitative analyses of empirical data requirements for hydrological simulations are rare. This study aims to analyze how a multi-objective optimization framework and information content computations aid in quantifying field-scale data worth in drainage studies. The results showed how a 1D numerical model and a differential evolution algorithm performed in describing the field water balance. The choice of the optimization target (subsurface drain discharge and surface runoff) impacted the simulation results more than parameter deviations. While the information content of surface runoff data was higher than that of drain discharge, drain discharge data contained more information on most of the soil parameters. Uncertainties related to groundwater outflow data, which were not used in the optimization, were higher than those of drain discharge and surface runoff. A central weighing optimization scheme with two data types produced the best but still incomplete description of the field hydrology. Despite the modest model performance, the results demonstrated how the choice of empirical data and optimization strategy can lead to uncertainties in drainage simulations and how the uncertainties can be assessed. Practically, a low amount of information and a parameter sensitivity analysis can lead to a biased description of uncertainty related to such hydrological variables which are not used in the optimization. Benefits of the modeling framework were shown when assessing (1) model structure adequacy with the Pareto front analysis, (2) information content of different data types regarding different parameters, and (3) uncertainties related to simulating hydrological variables based on optimization against a given data type.

Determination of the water requirement and crop coefficient values of sugarcane by field water balance method in semiarid region

Sugarcane is a major agro-industrial crop in semiarid regions and generally has high evapotranspiration. Standardized reference evapotranspiration (ET) and location specific crop coefficients are used to estimate crop evapotranspiration. However, precise information on crop coefficient (Kc) is a major impediment in semiarid environments. Field studies were conducted during two seasons of 2015 and 2016 in clay soils to determine crop evapotranspiration and crop coefficients (Kc) of sugarcane for semiarid India.The experimental area was cultivated with irrigation applied at 7–10 days interval by a drip irrigation system in addition to rainfall and the irrigation scheduling was based on field water balance approach. The crop evapotranspiration was determined by field water balance, reference evapotranspiration (ETo) by the Penman-Monteith approach while crop coefficient were computed through the standard FAO-56 methodology.On an annual basis, the total reference evapotranspiration (ETo) and crop evapotranspiration (ETc) were 1318−1426 mm and 1291−1388 mm respectively. Two years average sugarcane crop evapotranspiration estimated by field water balance method was 1339 mm year−1. The irrigation water requirement andeffective rainfall was 991 mm year-1 and 424 mm year-1 respectively. Two years results showed that there was a notable symmetry between Kc obtained from field water balance measurements and FAO-56 reported Kc. The determined Kc values for tillering, grand growth and maturity stages of sugarcane were 0.70, 1.20 and 0.78, respectively. The Kc values were found 25.5 %, 4 % and 20.4 % less during the tillering, grand growth and maturity stage respectively over the FAO-56 Kc values. The 2nd order polynomial equation was fitted with crop coefficient as the dependent variables and ratio of days after transplanting to total crop period as the independent variable. The daily values of Kc from equation is very useful towards efficient management of irrigation water in terms of making a Decision Support System, Soil Moisture based Crop Yield Modeling, Crop Water Requirement based Computer programme or Mobile Application, Automation of irrigation system in the major sugarcane growing countries of semi arid regions.

Terrestrial laser scanning data combined with 3D hydrological modeling decipher the role of tillage in field water balance and runoff generation

Soil tillage is an anthropogenic factor affecting hydrological processes in agricultural fields. To demonstrate a novel method for increasing mechanistic understanding of the tillage impacts, we combined a process-based three-dimensional (3D) hydrological model with terrestrial laser scanning (TLS) data. This study aimed to (1) exploit high-resolution TLS data to estimate soil surface depression storage (SSDS) and roughness after different soil tillage operations (ploughing, harrowing vs direct drilling) on a heavy clay soil, (2) combine the estimates of SSDS and roughness with a 3D hydrological model to demonstrate the potential of the method in analyzing hydrological impacts of tillage, and (3) evaluate the value and uncertainties in coupling spatial microtopographical data and process-based modeling. The SSDS values showed low mean (0.3–2.9 mm) and rare high values (>5 mm) with clearly the highest variation of SSDS and roughness values in the ploughed conditions. These tillage impacts were reflected in the amounts of surface layer runoff (max. increase 23% due to the SSDS and roughness changes) and drain discharge (max. decrease 8%). The impact on other water balance components was negligible, and factors such as drainage methods and terrain slope were shown to have more control on the water balance. The tillage impacts had also a clear effect on peak surface runoff values. Most (99%) of the hydrological changes were caused by the SSDS variation whereas the roughness had a minor role. The simulations showed that tillage-induced long-term changes on soil hydraulic properties (such as conductivity and macroporosity), which were not detected by the TLS data, can have a high impact on surface layer runoff generation, as these tillage-impacts increased runoff by 25%. While the simulations showed how the various hydrological impacts of tillage can be discerned, a more comprehensive assessment would require more data derived from several sites and tillage conditions.

Modelling the effects of permafrost loss on discharge from a wetland‐dominated, discontinuous permafrost basin

AbstractPermafrost degradation in the peat‐rich southern fringe of the discontinuous permafrost zone is catalysing substantial changes to land cover with expansion of permafrost‐free wetlands (bogs and fens) and shrinkage of forest‐dominated permafrost peat plateaux. Predicting discharge from headwater basins in this region depends upon understanding and numerically representing the interactions between storage and discharge within and between the major land cover types and how these interactions are changing. To better understand the implications of advanced permafrost thaw‐induced land cover change on wetland discharge, with all landscape features capable of contributing to drainage networks, the hydrological behaviour of a channel fen sub‐basin in the headwaters of Scotty Creek, Northwest Territories, Canada, dominated by peat plateau–bog complexes, was modelled using the Cold Regions Hydrological Modelling platform for the period of 2009 to 2015. The model construction was based on field water balance observations, and performance was deemed adequate when evaluated against measured water balance components. A sensitivity analysis was conducted to assess the impact of progressive permafrost loss on discharge from the sub‐basin, in which all units of the sub‐basin have the potential to contribute to the drainage network, by incrementally reducing the ratio of wetland to plateau in the modelled sub‐basin. Simulated reductions in permafrost extent decreased total annual discharge from the channel fen by 2.5% for every 10% decrease in permafrost area due to increased surface storage capacity, reduced run‐off efficiency, and increased landscape evapotranspiration. Runoff ratios for the fen hydrological response unit dropped from 0.54 to 0.48 after the simulated 50% permafrost area loss with a substantial reduction of 0.47 to 0.31 during the snowmelt season. The reduction in peat plateau area resulted in decreased seasonal variability in discharge due to changes in the flow path routing, with amplified low flows associated with small increases in subsurface discharge, and decreased peak discharge with large reductions in surface run‐off.

Simulation and analysis of return flow at the field scale in the northern rice irrigation area of China

To study variations in the field return flow, a field water balance model was established according to the water balance principle, and the field return flow was simulated using system dynamics and tested with field-measured data collected in a trial district in the Hu Lanhe irrigation area in 2016. The main conclusions are as follows: trends of the simulated and measured field water storage and field runoff were consistent. The daily error range between the simulated and measured field water storage values was (−0.1996, 0.2034) mm, and the daily error range between the simulated and measured field runoff values was (−0.2183, 0.1853) mm. Comparison of the trends among the water inflow, the surface return flow, the underground return flow and the total return flow revealed that the greater the water inflow was, the more similar the trends of the surface return flow and total return flow were, with no obvious change in the underground return flow. The total return flow increased with increasing field ridge length and decreased with increasing field ridge height and width. The range of the return flow coefficient of irrigation in 2011˜2016 was (0.5825, 0.6395), and the range of the return flow coefficient of irrigation and precipitation was (0.2734, 0.3386); the impact of irrigation water on the return flow was greater than that of precipitation. The research results are significant to the evaluation and analysis of field return flow and the management of agricultural irrigation water and provide a comparative reference for the study of return water in other areas.

Crop water requirements of date palm based on actual applied water and Penman\u2013Monteith calculations in Saudi Arabia

This study was conducted in eight different regions of Saudi Arabia to estimate monthly and annual crop water requirements (CWR). Fields that have been selected are located in regions of the Medina (Al Ula), Tabuk (Teimaa), Makkah (Al Jumum), Al Jouf (Sakakah), Riyadh (Sodos), Qassim (Riyad Al Khabra), Hail (AL Kaedh), and East Region (Al Ahsa). The determination of CWRs was based on Penman Monteith method, field water balance, actual water applied in each field, and actual water applied by farmers in adjacent fields. The results based on Penman–Monteith method showed that the crop evapotranspiration, ETc (mm/year) of the sites in, Medina, Tabuk, Makkah, Al Jouf, Riyadh, Qassim, Hail, and East Region were 2418.75, 1940.51, 1837.76, 2259.03, 2139.23, 2207.41, 2008.23, and 2144.87 mm/year, respectively. The CWRs (m3/ha) after taking into account the proportion of cultivated area for each tree were: 9495.24, 7340.18, 7298.93, 8913.59, 8614.96, 8568.68, 7996.99, and 8510.72 m3/ha, respectively. The average date palm numbers were 100 trees/ha. The total annual CWRs (m3/tree) in these sites were 95, 73.4, 73, 89, 86, 85.7, 80, and 85 m3, respectively, as the radius of shaded area per tree is 3.5 m with an effective diameter of 90%, and the rate of leaching was 12, 8, 13, 12, 14, 11, 13, and 13%, respectively. The average overall irrigation water requirements was 8342.41 m3/ha/year (1 ha. = 100 trees). The results of water balance method showed that the water consumed for Qassim and Al Jouf was 3604.31 and 3515.25 m3/ha/year, respectively. The actual irrigation water added by a flow meter for all study sites was 11,305.0, 9463.9, 9692.0, 11,252.75, 1007.40, 10,035.0, 10,272.5, and 10,082.8 m3/ha/year, respectively, while these amounts added by the farmers in adjacent fields were 13,717, 12,277, 12,220, 13,340, 12,050, 12,880, 12,620, and 12,610 m3/ha/year, respectively.

Field Water Balance Closure with Actively Heated Fiber-Optics and Point-Based Soil Water Sensors

While traditional soil water sensors measure soil water content (SWC) at point scale, the actively heated fiber-optics (AHFO) sensor measures the SWC at field scale. This study compared the performance of a distributed (e.g., AHFO) and a point-based sensor on closing the field water balance and estimating the evapotranspiration (ET). Both sensors failed to close the water balance and produced larger errors in estimated ET (ETε), particularly for longer time periods with >60 mm change in soil water storage (ΔSWS), and this was attributed to a lack of SWC measurements from deeper layers (>0.24 m). Performance of the two sensors was different when only the periods of ˂60 mm ΔSWS were considered; significantly lower residual of the water balance (Re) and ETε of the distributed sensor showed that it could capture the small-scale spatial variability of SWC that the point-based sensor missed during wet (70–104 mm SWS) periods of ˂60 mm ΔSWS. Overall, this study showed the potential of the distributed sensor to provide a more accurate value of SWS at field scale and to reduce the errors in water balance for shorter wet periods. It is suggested to include SWC measurements from deeper layers to better evaluate the performance of the distributed sensor, especially for longer time periods of >60 mm ΔSWS, in future studies.

Modeling rice development and field water balance using AquaCrop model under drying-wetting cycle condition in eastern China

Various crop growth models have been developed to simulate the crop development and were used to assess the effects of climate, cultivation and irrigation methods. To evaluate the feasibility of water driven model-AquaCrop in simulating crop development, production and field water balance in paddy soil under drying – wetting cycle condition, the model was calibrated and validated based on data during 2012–2013 rice season in Eastern China. Results showed that the accuracy of this model in simulating canopy cover (CC), evapotranspiration (ET), biomass, yield were generally acceptable, with the root mean square of error (RMSE) less than 10% for CC, 1.0 mm for ET, 0.61t ha−1 for biomass and with relative deviation of 3.6% for yield. Meanwhile, AquaCrop tended to overestimate CC, biomass and yield slightly during the midseason. Yet, its performance in simulating soil moisture content was not as good as expected. It tended to underestimate soil moisture with a RMSE of 14.81%, but overestimated the water deficit coefficient (Ks). The method for Ks calculation incorporated in AquaCrop should be revised for rice under drying-wetting cycle condition.

An Assessment of the Vertical Movement of Water in a Flooded Paddy Rice Field Experiment Using Hydrus-1D

A quantitative estimation of the major components of the field water balance provides management decisions on how the scheme ought to be operated to ensure better distribution of irrigation water and increased delivery performance. Therefore, in this study, the water balance component in transplanted and broadcasted rice fields with conventional irrigation (flooding irrigation) in the Tanjung Karang Rice Irrigation Scheme (TAKRIS), Sawah Sempadan were observed and then modeled using Hydrus-1D numerical model during two consecutive rice growing seasons. During the off-season, irrigation water accounted for 59.6% of the total water input (irrigation + rainfall), but about 76.2% of total water input during the main season. During the main season, rainfall water only contributed to 23.8% of total water input and 40.4% during the off-season. Drainage water accounted for 37.3% of the total water input during the off-season and 43.7% during the main season, respectively, which was the main path of water losses from conventional rice fields, which indicates that maintaining a high water level and huge rainfall events during both seasons increased drainage water. Simulated ET during the off-season and the main season accounted for 38.1% and 49.5% of the total water input, respectively. Observed and simulated water percolation revealed about 17.1% to 19.2% of total water input during both seasons, respectively. Additionally, the water productivities analyzed from total water input and irrigation water were 0.43 and 0.72 kg m−3 during the off-season and 0.60 and 0.78 kg m−3 during the main season, respectively. The water productivity index evaluated from observed and modeled evapotranspiration was 1.03 and 1.13 kg m−3 during the off-season and 0.98 and 0.94 kg m−3 during the main season, respectively. The overall results revealed that Hydrus-1D simulations were a reasonable and effective tool for simulating vertical water flow in both broadcasted and transplanted rice experimental fields.

Vapor Condensation in Rice Fields and Its Contribution to Crop Evapotranspiration in the Subtropical Monsoon Climate of China

Abstract While vapor condensation in arid and semiarid areas has garnered much attention, such information is scarce for humid crop production areas such as rice fields. In a water-saving irrigation (WSI) rice field, high-precision weighed microlysimeters allowed the direct and independent quantification of condensation over plants (Cc) and soil (Cs) through mass balance calculations. The occurrence frequency and rate of Cc generally exceeded that of Cs. Predominantly occurring between sunset and sunrise, particularly between 0400 and 0500 local time, Cc showed an overall maximum rate of 0.096 mm h−1. In contrast, Cs was highest between 0100 and 1100 local time and showed an overall maximum rate of 0.044 mm h−1. The occurrence of Cc, unlike that of Cs, required a surface temperature lower than the ambient temperature or dewpoint. Of 65 rain-free days, Cc and Cs occurred on 60 and 33 days, respectively. Seasonal Cc, Cs, and Cc + Cs were estimated as 32.3, 3.1, and 35.4 mm, respectively, and their contributions to seasonal rice transpiration T, evaporation E, and evapotranspiration (ET) were 9.5%, 1.6%, and 6.7%, respectively. The seasonal Cc + Cs was similar in magnitude to a routine irrigation quota and accounted for 10.8% of rainfall and 14.4% of irrigation in the WSI rice field. Therefore, vapor condensation in rice fields in a subtropical monsoon climate is an important component of the hydrological cycle and cannot be ignored when tabulating the field water balance, calculating field water consumption, or in irrigation scheduling.

Making sense of cosmic-ray soil moisture measurements and eddy covariance data with regard to crop water use and field water balance

Changes in soil moisture influence the water availability to crop plants and soil ecological processes like carbon and nutrient cycling, impacting on crop productivity and environmental performance (greenhouse gas emissions, leaching) of agricultural systems. While traditional soil moisture measurements are done using point-based methods, the recent development of the cosmic-ray soil moisture neutron sensor (CRNS) offers the opportunity to measure soil water at the field scale. However, due to its shallow (<300 mm) and variable measurement depth, the relevance of the measurements to crop water use has been questioned. In this paper, we combine point-based soil moisture measurements (soil cores, TDR), areal-based soil moisture and evapotranspiration measurements (CRNS, eddy covariance), and soil-plant systems modelling together to investigate the consistency in measured soil moisture and crop water use with these different methods We also quantify how relevant the CRNS soil moisture measurements are in understanding the water use of cereal crops (wheat and barley). Our results show that crop water uptake from CRNS layers accounted for 50–90% of the total water uptake in dry environments (location, year) with annual rainfall <300 mm, but only 30–50% of the total crop water uptake in wetter environments (locations, years). This demonstrates a higher relevance of CRNS measurements in semi-arid and arid regions where water is a limiting factor for crop growth and other ecological processes. The high temporal resolution of soil moisture data from CRNS can be assimilated with eddy covariance measurements and point measurements in field to better calibrate soil-plant models and to more accurately simulate field water balance.

Climatic and Soil Water Balances for the Melon Crop

The correct estimate of the water requirements of a crop, besides favoring its full development, also allows the rational use of water. In this context, this study aimed to evaluate water balance in the soil and estimated through climatic methods for the melon crop. Field water balance was daily determined along a period of 70 days. Climatic water balance was determined based on the reference evapotranspiration estimated by the methods of Penman-Monteith, Thornthwaite and Hargreaves-Samani. It was concluded that climatic methods do not estimate correctly water storage in the soil and, consequently, also the balance. Therefore, they should not substitute the soil water balance method to determine these variables. The water management for the melon crop based on evapotranspiration estimated through climatic methods results in overestimation of the water depth to be applied in the soil, in the initial growth stage, and underestimation in the periods of highest water demand.

Optimization of equitable irrigation water delivery for a large-scale rice irrigation scheme

Equitable water allocation is essential in an irrigation scheme for obtaining potential crop yields from the entire scheme, especially when water supply is inadequate. An optimization model achieved this goal by coupling an optimal water allocation model with available water supply and irrigation water demand for a river-fed rice irrigation system in Malaysia. This model consists of a paddy field water balance module and an optimization module. The outputs from the module are daily irrigation demand and surface runoff, if there is any. The optimization module consists of an objective function, which minimizes water shortage across the scheme area while maintaining equity in water allocation. This model performs optimization subject to several system constraints, and the decision variable of the model is daily releases or supply to the tertiary canals. Performance of this model remained unaffected under different water supply conditions, and the optimization model reliably examined the effects of alternate water allocation and management rules with field information. It improves efficiency and equity in water allocation with respect to crop growth stages and water shortages rather than simply cutting irrigation supply on a proportional basis to overcome water shortages. Keywords: irrigation, optimization, simulation, equitable deliveries, rice DOI: 10.25165/j.ijabe.20181105.3536 Citation: Rowshon M K, Iqbal M, Mojid M A, Amin M S M, Lai S H. Optimization of equitable irrigation water delivery for a large-scale rice irrigation scheme. Int J Agric & Biol Eng, 2018; 11(5): 160–166.

Portable canopy chamber measurements of evapotranspiration in corn, soybean, and reconstructed prairie

Evapotranspiration (ET) is a vital component of a field water balance. Canopy chambers are a promising method for determining crop ET because they are portable and applicable at a relatively small plot (m2) scale. Although a variety of canopy chamber designs have been proposed, field tests are still necessary to evaluate chamber performance for measuring crop ET. The objectives of this study are (1) to construct and use an improved canopy chamber to measure ET of three crops [corn (Zea mays, L.), soybean (Glycine max), and reconstructed mixed prairie] and (2) to compare the canopy chamber measurements with flux tower results and field water balance measurements (i.e., rainfall, soil water storage, ET and drainage). Three cropping systems including corn/soybean in a corn-soybean rotation, and reconstructed mixed prairie were studied in central Iowa. Canopy chamber daytime measurements were performed on 18days in 2013 (a relatively dry growing season) and on 15days in 2014 (a relatively wet growing season). Based on the results, the differences in daily ET and seasonal cumulative ET between canopy chambers and an eddy covariance flux tower over the measurement periods were within 5%, providing evidence that the portable canopy chamber can accurately measured ET. The chamber ET values and field water balance ET values had similar patterns over the 2013 and 2014 measurement periods, and the differences of cumulative results were less than 10%. In conclusion, the canopy chamber was proven to be an effective method for measuring small plot ET.