Search Results (6)

At present, a sustainable and wise management of water resources requires more insight into drainage/irrigation practices in river valleys. Since efficient sub-irrigation, based on reliable hydrometeorological forecasts, has been extensively considered with respect to water saving, the proper modeling tools were subsequently developed. An original, conceptual model for the management of drainage/irrigation systems was presented, taking into account the water inflow and storage in the soil profile. The aim was to propose a relatively simple procedure with parameters that relate to easily obtainable variables, e.g., groundwater table depth in the form of uncomplicated equations. The results of this tool were compared with the groundwater heads simulated using the recognized, common Modflow model. The comparisons proved a close match of the modeled variables and point at possibilities to calibrate it on polder areas. Full article

Dissolved arsenic (As) may appear at the tile line level through preferential flow (PF), leading to contamination of shallow water bodies. Limited work on the movement of As forms in field soils urged the need for more research. The PF of arsenate (As(V)) and arsenite (As(III)) compared to chloride (Cl) at constant flow under saturated (10 mm), slightly unsaturated (−10 mm), and unsaturated (−40 mm) pressure heads was evaluated in replicated large field columns varying in subsoil structure. A solute containing As(V), As(III), and Cl was pulsed until the Cl concentration ratio in the drainage samples reached maxima and flushed with solute-free irrigation. HYDRUS-1D software version 4.15 was utilized to fit the breakthroughs of As(V) and As(III) in the dual-porosity physical non-equilibrium model (DP-PNE). The Langmuir equation was used to fit the As(V) and As(III) sorption isotherms, and blue dye staining was used for the marking of flow paths. Dye leaching was observed up to 50 cm or deeper in the soils. Under saturated conditions (+10 mm), Kotli, Guliana, and Mansehra soils showed chemical non-equilibrium (CNE) for As(V) and As(III); however, the extent of CNE was less under unsaturated conditions (−40 mm). These results implied that these well-structured soils had enough large macropores, which cause PF, but at the same time, they were also small enough to retain water and leach solutes under unsaturated conditions (−40 mm). It is concluded that irrigation of contaminated water or dumping solid waste on well-aggregated soil may exhibit PF of dissolved As during and after rains, and additionally As(III), which is more toxic and mobile under reduced conditions, has equal or greater potential for movement. Full article

Energy is required in all agricultural activities. Diagramming material flows needed by crop production systems supports the proper analysis of energy flows interactions within a system’s boundaries. The latter complemented with an economic analysis gives a clear view of how beneficial a new practice within a crop cycle is—in this case, the variable slope (VS) land leveling (LL) operation. VS is a global navigation satellite system (GNSS, with real time kinematics—RTK—accuracy) LL technique used to create a smooth continuous surface with a constant slope, by cutting and filling topsoil layers only in those points presenting “anomalies” of micro-relief which make the movement of water difficult. This operation is important for paddy production since: (i) it enables to crop during dry seasons by harnessing the water of rivers and wells, and (ii) improves the production during rainy seasons, by allowing the farmer to manage the drainage timely and homogeneously. The present study aims to analyze, from the energy perspective, the effects of the VS leveling implementation in a paddy field (located in the Costa Rican Pacific), throughout input (labor, gas oil, etc.) and output (yield and price) data of five consecutive years (2011–2015). A material flow diagram was created representing two scenarios: before and after leveling the land. The materials were converted into energy (MJ ha⁻¹) data, used for the estimation of EROI (energy return on investment), EP (energy productivity) and EB (energy balance) indices, while looking for a clearer understanding of the LL impact on the use of energy within the agroecosystem. Moreover, in order to complement the energy perspective, an economic point of view was considered as well through a profitability analysis where the total gain obtained over the years with LL was compared with that obtained without LL. Results showed that the increase in energy consumed by incorporating VS leveling is compensated by the gradual increase of energy embodied in yield, increasing energy balance (EB) from 26,192 MJ ha⁻¹ up to 91,166 MJ ha⁻¹. Similarly, EROI and EP were duplicated with LL. Economic total gain after incorporating the VS increased from less than 500 USD ha⁻¹ up to 1800 USD ha⁻¹ in the third year after leveling. Yield is more affected under adverse weather conditions with irregular water supply, either limited or excessive; and effects are less pronounced when the yield limiting factor is associated with biotic stress unrelated to irrigation and drainage facts. An environmental positive impact should also be noted, since VS allowed the production benefits of having highly-efficient irrigation and drainage systems, while avoiding major damage to topsoil layers. Full article

High concentration of insecticides may appear in waters surrounding paddy fields shortly after application. Capturing the dynamic feature of this insecticide pulse may help control insecticide load to receiving waters. Based on continuous monitoring of the drainage process and two monitoring campaigns of three insecticides—chlorpyrifos, abamectin and thiamethoxam—in a paddy, this study examined the pattern of insecticide concentrations at different locations of paddy waters during the period of insecticide application accompanied with pest-control irrigation, and analyzed the factors affecting the environmental behavior of these insecticides. The results showed that the pulse-type drainage exhibited the following features: short duration (normally less than 1 d), large flow rate (as large as 4 L s⁻¹), frequent occurrence (20 times during a 40-d period) and long time interval (as long as 5 d). Concentrations of the insecticides with higher Henry’s constant and vapor pressure peaked quickly (within several hours) post application in the field ditch; more than half of chlorpyrifos and abamectin loads were detected within merely 1 h after application. The high insecticide concentrations in the ditch were partly attributed to the primary and secondary drift. Moreover, a new kinetic model was proposed to describe the behavior of chlorpyrifos at the field edge. It is recommended that controlled drainage be implemented for at least 1 d post application to prevent the loss of insecticides. Findings from this study may provide new insights into insecticide behavior in the paddy environment for preventing adverse environmental impacts. Full article

Nitrogen (N) accounts for more than 80% of the total mineral nutrients absorbed by plants and it is the most widely limiting element for crop production, particularly under water deficit conditions. For a comprehensive understanding of sunflower Helianthus annuus N uptake under deficit irrigation conditions, experimental and numerical simulation studies were conducted for full (100% ET_C) and deficit (65% ET_C) irrigation practices under the semi-arid conditions of the Imperial Valley, California, USA. Plants were established with overhead sprinkler irrigation before transitioning to subsurface drip irrigation (SDI). Based on pre-plant soil N testing, 39 kg ha⁻¹ of N and 78 kg ha⁻¹ of P were applied as a pre-plant dry fertilizer in the form of monoammonium phosphate (MAP) and an additional application of 33 kg ha⁻¹ of N from urea ammonium nitrate (UAN-32) liquid fertilizer was made during the growing season. Soil samples at 15-cm depth increments to 1.2 m (8 layers, 15 cm each) were collected prior to planting and at three additional time points from two locations each in the full and deficit irrigation treatments. We used HYDRUS/2D for the simulation in this study and the model was calibrated for the soil moisture parameters (θ_s and θ_r), the rate constant factors of nitrification (the sensitive parameter) in the liquid and solid states (μ_w,3, and μ_s,3). The HYDRUS model predicted cumulative root water uptake fluxes of 533 mm and 337 mm for the 100% ET_C and 65% ET_C, respectively. The simulated cumulative drainage depths were 23.7 mm and 20.4 mm for the 100% ET_C and 65% ET_C which represented only 4% and 5% of the applied irrigation water, respectively. The soil wetting profile after SDI irrigation was mostly around emitters for the last four SDI irrigation events, while the maximum values of soil moisture in the top 30 cm of the soil profile were 0.262 cm³ cm⁻³ and 0.129 cm³ cm⁻³ for 100% ET_C and 65% ET_C, respectively. The 16.5 kg ha⁻¹ (NH₂)₂CO (50% of the total N) that was applied during the growing season was completely hydrolyzed to NH₄⁺ within 7 days of application, while 4.36 mg cm⁻¹ cumulative decay was achieved by the end of the 98-day growing season. We found that 86% of NH₄⁺ (74.25 mg cm⁻¹) was nitrified to NO₃⁻ while 14% remained in the top 50 cm of the soil profile. The denitrification and free drainage of NO₃⁻ were similar for 100% ET_C and 65% ET_C, and the maximum nitrate was drained during the sprinkler irrigation period. By the end of the growing season, 30.8 mg cm⁻¹ of nitrate was denitrified to N₂ and the reduction of nitrate plant uptake was 17.1% for the deficit irrigation section as compared to the fully irrigated side (19.44 mg cm⁻¹ vs. 16.12 mg cm⁻¹). This reduction in N uptake due to deficit irrigation on sunflower could help farmers conserve resources by reducing the amount of fertilizer required if deficit irrigation practices are implemented due to the limited availability of irrigation water. Full article

Constructed wetlands (CW) have gained recognition as a management option for the treatment of various agricultural wastewaters. This study involved the design, construction, and initial evaluation of a wetland-reservoir-irrigation (WRI) system. The system was established in Truro, Nova Scotia, Canada, with the goal to capture, treat, and re-use agricultural sub-surface drainage water. It consisted of a 1.8-ha area of a cropped field that was systematically tile drained. Drainage water was directed through a 2-cell CW and then into a reservoir-irrigation pond. Flow rate hydraulics, residence time distributions, and treatment efficiencies for nitrate-nitrogen (NO₃⁻-N) and Escherichia coli (E. coli) were monitored for 14 months. Mass reductions of NO₃⁻-N and E. coli from the CW were 67.6% and 63.3%, respectively. However, average E. coli concentrations increased to 178 CFU 100 mL⁻¹ in the reservoir during the warm season. It may therefore be best to use reservoir water for irrigation of crops that are not consumed raw. To aid in the future design of similar systems, mean first-order rate constants (k_s) for NO₃⁻-N and E. coli were calculated to be 8.0 and 6.4 m y⁻¹, respectively. The volume of water collected in the reservoir exceeded typical irrigation requirements of the drained land and could therefore provide irrigation to additional land beyond the drainage area. Full article