Modeling soil water dynamics in a drip-irrigated intercropping field under plastic mulch

Intercropping, drip irrigation, and the use of plastic mulch are important management practices, which can, when utilized simultaneously, increase crop production and save irrigation water. Investigating soil water dynamics in the root zone of the intercropping field under such conditions is essential in order to understand the combined effects of these practices and to promote their wider use. However, not much work has been done to investigate soil water dynamics in the root zone of drip-irrigated, strip intercropping fields under plastic mulch. Three field experiments with different irrigation treatments (high T1, moderate T2, and low T3) were conducted to evaluate soil water contents (SWC) at different locations, for different irrigation treatments, and with respect to dripper lines and plants (corn and tomatoes). Experimental data were then used to calibrate the HYDRUS (2D/3D) model. Comparison between experimental data and model simulations showed that HYDRUS (2D/3D) described different irrigation events and SWC in the root zone well, with average relative errors of 10.8, 9.5, and 11.6 % for irrigation treatments T1, T2, and T3, respectively, and with corresponding root mean square errors of 0.043, 0.035, and 0.040 cm³ cm^?3, respectively. The results showed that the SWC in the shallow root zone (0–40 cm) was lower under non-mulched locations than under mulched locations, irrespective of the irrigation treatment, while no significant differences in the SWC were observed in the deeper root zone (40–100 cm). The SWC in the shallow root zone was significantly higher for the high irrigation treatment (T1) than for the low irrigation treatment, while, again, no differences were observed in the deeper root zone. Simulations of two-dimensional SWC distributions revealed that the low irrigation treatment (T3) produced serious severe water stress (with SWCs near the wilting point) in the 30–40 cm part of the root zone, and that using separate drip emitter lines for each crop is well suited for producing the optimal soil water distribution pattern in the root zone of the intercropping field. The results of this study can be very useful in designing an optimal irrigation plan for intercropped fields.     

Measuring versus estimating net radiation and soil heat flux: Impact on Penman–Monteith reference ET estimates in semiarid regions

The standardized ASCE Penman–Monteith and FAO-56 equations were used to estimate reference evapotranspiration (ET₀) using estimated and measured net radiation (R_n) and soil heat flux (G), based on hourly and daily meteorological data. The estimates were evaluated against lysimeter measurements. The results indicate that using measured or estimated values of R_n and G can have significant effect on the accuracy of the ET₀ estimations, especially when calculations were made on an hourly basis. The FAO-56 version performed very well during the irrigation season on a daily basis. The use of measured R_n and G did not improve ET₀ estimation on a daily basis, therefore, the use of estimated R_n and G appears to be dependable when calculations are based on 24-h weather data. When daily ET₀ was calculated from hourly estimations, the results were different depending on the version used. The ASCE version was more accurate, especially when R_n and G were measured. Therefore, measurement of R_n and G may have potential to improve estimation only when daily ET₀ is calculated from hourly estimations. The PM FAO-56 version was always a little less accurate than the ASCE version. For hourly calculations, using a constant surface resistance (as in FAO-56 version), the PM method underpredicted for high evaporative demand and vice versa. The ASCE version performed better than PM FAO-56 version when R_n and G were measured and estimated. Therefore, ASCE version tended to provide quite accurate values of hourly ET₀, even using estimated values of R_n and G. As conclusion, the methods proposed by FAO-56 for estimating R_n and G tended to produce accurate estimates for daily and hourly ET₀ under semiarid conditions and can be used with some degree of confidence for estimating ET₀. In addition, results suggest that the ASCE standardized equation on an hourly basis improved the accuracy of ET₀ estimation with respect to the FAO-56 version.     

Controlled water table management as a strategy for reducing salt loads from subsurface drainage under perennial agriculture in semi-arid Australia

Recent community based actions to ensure the sustainability of irrigation and protection of associated ecosystems in the Murrumbidgee Irrigation Area (MIA) of Australia has seen the implementation of a regional Land and Water Management Plan. This aims to improve land and water management within the irrigation area and minimise downstream impacts associated with irrigation. One of the plan objectives is to decrease current salt loads generated from subsurface drainage in perennial horticulture within the area from 20 000 tonnes/year to 17 000 tonnes/year. In order to meet such objectives Controlled Water table Management (CWM) is being investigated as a possible ‘Best Management Practice’, to reduce drainage volumes and salt loads.During 2000–2002 a trial was conducted on a 15 ha subsurface drained vineyard. This compared a traditional unmanaged subsurface drainage system with a controlled drainage system utilizing weirs to maintain water tables and changes in irrigation scheduling to maximize the potential crop use of a shallow water table. Drainage volumes, salt loads and water table elevations throughout the field were monitored to investigate the effects of controlled drainage on drain flows and salt loads.Results from the experiment showed that controlled drainage significantly reduced drainage volumes and salt loads compared to unmanaged systems. However, there were marked increases in soil salinity which will need to be carefully monitored and managed.     

Sensitivity analysis of optimal operation of irrigation supply systems with water quality considerations

A model for optimal operation of water supply/irrigation systems of various water quality sources, with treatment plants, multiple water quality conservative factors, and dilution junctions is presented. The objective function includes water cost at the sources, water conveyance costs which account for the hydraulics of the network indirectly, water treatment cost, and yield reduction costs of irrigated crops due to irrigation with poor quality water. The model can be used for systems with supply by canals as well as pipes, which serve both drinking water demands of urban/rural consumers and field irrigation requirements. The general nonlinear optimization problem has been simplified by decomposing it to a problem with linear constraints and nonlinear objective function. This problem is solved using the projected gradient method. The method is demonstrated for a regional water supply system in southern Israel that contains 39 pipes, 37 nodes, 11 sources, 10 agricultural consumers, and 4 domestic consumers. The optimal operation solution is described by discharge and salinity values for all pipes of the network. Sensitivity of the optimal solution to changes in the parameters is examined. The solution was found to be sensitive to the upper limit on drinking water quality, with total cost being reduced by 5% as the upper limit increases from 260 to 600 mg Cl l^–1. The effect of income from unit crop yield is more pronounced. An increase of income by a factor of 20 results in an increase of the total cost by a factor of 3, thus encouraging more use of fresh water as long as the marginal cost of water supply is smaller than the marginal decrease in yield loss. The effect of conveyance cost becomes more pronounced as its cost increases. An increase by a factor of 100 results in an increase of the total cost by about 14%. The network studied has a long pipe that connects two distinct parts of the network and permits the supply of fresh water from one part to the other. Increasing the maximum permitted discharge in this pipe from 0 to 200 m³ h^–1 reduces the total cost by 11%. Increasing the maximum discharge at one of the sources from 90 to 300 m³ h^–1 reduces the total cost by about 8%.     

“WaterMan”: an on-farm water management game with heuristic capabilities

A modern computer-based simulation tool (WaterMan) in the form of a game for on-farm water management was developed for application in training events for farmers, students, and irrigators. The WaterMan game utilizes an interactive framework, thereby allowing the user to develop scenarios and test alternatives in a convenient, risk-free environment. It includes a comprehensive soil water and salt balance calculation algorithm. It also employs heuristic capabilities for modeling all of the important aspects of on-farm water management, and to provide quantitative performance evaluations and practical water management advice to the trainees. Random events (both favorable and unfavorable) and different strategic decisions are included in the game for more realism and to provide an appropriate level of challenge according to player performance. Thus, the ability to anticipate the player skill level, and to reply with random events appropriate to the anticipated level, is provided by the heuristic capabilities used in the software. These heuristic features were developed based on a combination of two artificial intelligence approaches: (1) a pattern recognition approach and (2) reinforcement learning based on a Markov decision processes approach, specifically the Q-learning method. These two approaches were combined in a new way to account for the difference in the effect of actions taken by the player and action taken by the system in the game world. The reward function for the Q-learning method was modified to reflect the suggested classification of the WaterMan game as what is referred to as a partially competitive and partially cooperative game.     

Consequences of ignoring variable and spatially autocorrelated detection probability in spatial capture-recapture

Landscape Ecology - Spatial capture-recapture (SCR) models are increasingly popular for analyzing wildlife monitoring data. SCR can account for spatial heterogeneity in detection that arises from...     

Incidence,risk factors,and outcomes for early postoperative seizures in dogs with rostrotentorial brain tumors after intracranial surgery

BackgroundSeizures in the early postoperative period after intracranial surgery may affect outcome in dogs.ObjectivesTo determine the incidence of early postoperative seizures (EPS) in dogs with brain tumors, identify specific risk factors for EPS, and determine if EPS affects outcome.AnimalsEighty‐eight dogs that underwent 125 intracranial surgeries for diagnosis and treatment of rostrotentorial brain tumors.MethodsRetrospective cohort study. All patients with a diagnosis of rostrotentorial brain tumor from 2006 to 2020 were included. Early postoperative seizures were diagnosed by observation of seizure activity within 14 days of neurosurgery. Previously diagnosed structural epilepsy, perioperative anticonvulsant drug (ACD) use, magnetic resonance imaging (MRI), and tumor characteristics were evaluated. Outcome measures included neurologic and nonneurologic complications, duration of hospitalization, and survival to discharge.ResultsDogs with rostrotentorial brain tumors had EPS after 16/125 (12.8%) neurosurgical procedures (95% confidence interval [CI], 7%‐19%). Presence of previous structural epilepsy was not associated with EPS risk (P = 1). Perioperative ACD use also was not associated with EPS (P = .06). Dogs with EPS had longer hospitalization (P < .001), were more likely to have neurologic complications postsurgery (P = .01), and were less likely to survive to discharge (P = .01).Conclusions and Clinical ImportanceIt is difficult to predict which dogs are at risk of EPS because the presence of previous structural epilepsy and the use of perioperative ACDs was not associated with EPS. However, seizures in the early postoperative period are clinically important because affected dogs had prolonged hospitalization, more neurologic complications, and decreased short‐term survival.     

接种沙门氏菌苗可使新生雏鸡和强制换羽母鸡得到免疫保护

过去人们常认为,由于刚出壳雏鸡的免疫系统尚未发育成熟,同时肠道内缺乏有益的微生物,因而处于高度的敏感期,此时接种沙门氏菌苗产生的保护作用很有限。然而,最新的研究表明,在这些敏感期接种疫苗,可诱发产生保护作用。     

PCB removal,soil enzyme activities,and microbial community structures during the phytoremediation by alfalfa in field soils

Purpose  

An in situ phytoremediation trial was developed in order to investigate the function of alfalfa during a 2-year bioremediation of an agricultural soil contaminated with polychlorinated biphenyls (PCBs). The study was conducted with the aim to better understand the application potential of PCB phytoremediation at field scale.     

Carbon isotopic ratios of wetland and terrace soil sequences in the Maya Lowlands of Belize and Guatemala

This article provides new data and synthesizes earlier findings on the carbon isotope ratios of the humin part of soil organic matter from a range of sites in the central Maya Lowlands. Changes down the soil profile in carbon isotope ratios can provide an important line of evidence for vegetation change and erosion over time, especially in well dated aggrading profiles. Research thus far has provided substantial evidence for significant inputs from C₄ vegetation in buried layers from the Ancient Maya periods in depositional soils but equivocal evidence from sloping soils. We present new findings from soil profiles through ancient Maya wetland fields, upland karst wetlands, ancient Maya aguadas (reservoirs), and ancient Maya terraces. Most of the profiles exhibited δ¹³C enrichment greater than the 2.5–3‰ typical from bacterial fractionation. Seven of nine ancient Maya wetland profiles showed δ¹³C enrichment ranging from 4.25 to 8.56‰ in ancient Maya-dated sediments that also contained phytolith and pollen evidence of grass (C₄ species) dominance. Upland karst sinks and ancient reservoirs produced more modest results for δ¹³C enrichment. These seasonal wetland profiles exhibited δ¹³C enrichment ranging from 1 to 7.3‰ from the surface to ancient Maya-period sediments. Agricultural terraces produced mixed results, with two terraces having substantial δ¹³C enrichment of 5.34 and 5.66‰ and two producing only equivocal results of 1.88 and 3.03‰ from modern topsoils to Maya Classic-period buried soils. Altogether, these findings indicate that C₄ plants made up c. 25% of the vegetation at our sites in the Maya Classic period and only a few percent today. These findings advance the small corpus of studies from ancient terraces, karst sinks, and ancient wetland fields by demonstrating substantial δ¹³C and thus C₄ plant enrichment in soil profile sections dated to ancient Maya times. These studies are also providing a new line of evidence about local and regional soil and ecological change in this region of widespread environmental change in the Late Holocene.