Improving Irrigation Efficiency Research Articles

Spatial Analysis of Soil Moisture and Turfgrass Health to Determine Zones for Spatially Variable Irrigation Management

Irrigated turfgrass is a major crop in urban areas of the drought-stricken Western United States. A considerable proportion of irrigation water is wasted through the use of conventional sprinkler systems. While smart sprinkler systems have made progress in reducing temporal mis-applications, more research is needed to determine the most appropriate variables for accurately and cost-effectively determining spatial zones for irrigation application. This research uses data from ground and drone surveys of two large sports fields. Surveys were conducted pre-, within and towards the end of the irrigation season to determine spatial irrigation zones. Principal components analysis and k-means classification were used to develop zones using several variables individually and combined. The errors associated with uniform irrigation and different configurations of spatial zones are assessed to determine comparative improvements in irrigation efficiency afforded by spatial irrigation zones. A determination is also made as to whether the spatial zones can be temporally static or need to be re-determined periodically. Results suggest that zones based on spatial soil moisture surveys and simple observations of whether the grass felt wet or dry are better than those based on NDVI, other variables and several variables in combination. In addition, due to the temporal variations observed in spatial patterns, ideally zones should be re-evaluated periodically. However, a less labor-intensive solution is to determine temporally static zones based on patterns in soil moisture averaged from several surveys. Of particular importance are the spatial patterns observed prior to the start of the irrigation season as they reflect more temporally stable variation that relates to soil texture and topography rather than irrigation management.

Adaptation of a Scientific Decision Support System to the Productive Sector—A Case Study: MOPECO Irrigation Scheduling Model for Annual Crops

Despite the great number of models developed in research projects, only a small percentage have been successfully transferred to the productive sector. The PRIMA programme supported by Horizon 2020, the European Union Framework Programme for Research and Innovation, aims to reverse this situation. The SUPROMED project funded by PRIMA sought to develop an online platform composed of several models adapted to the requirements of end users for increasing the economic and environmental sustainability of Mediterranean agricultural systems. MOPECO, in its research version, was designed to maximize the profitability of irrigated farms in water-scarce regions. A simplified version of this model (MOPECO irrigation scheduling) was included in the SUPROMED platform for improving irrigation efficiency, providing farmers with a useful irrigation scheduling software. This paper shows the approach to adapt and transfer MOPECO to the productive sector. The tool was validated in three different demosite areas across the Mediterranean, involving local stakeholders in the design, validation, and dissemination of the software. The simplified tool reached similar or higher yields than farmers using less water. Thus, the average water saved was around 16%, while the average yield increased around 10% in the plots located in the three demosites of the project (Eastern Mancha in Spain, Bekaa valley in Lebanon, and Sidi Bouzid in Tunisia). This fact decreased the water footprint and increased the profitability of farms. The high applicability of the tool has generated interest among many technicians, farmers, and advisory enterprises. Furthermore, regional and national governmental extension services have shown interest in spreading the use of the tool across their territories, validating the methodology used for adapting and transferring a scientific model to the productive sector.

Identifying the main factors driving groundwater stress in a semi-arid region, southern Iran

ABSTRACT Groundwater resources are the most reliable freshwater supply in arid regions where many aquifers face dramatic depletion due to natural and anthropogenic causes. The annual average rate of decline of groundwater level is about 1.65 m. This research focuses on an aquifer that suffers from severe groundwater stress, and it aims to identify the main causes of the stress and to understand the effects of climate change and human activity. Monthly data on groundwater level, precipitation, temperature, river discharge, evapotranspiration, soil moisture, and vegetation cover were collected from 2000 to 2020. The results indicate that declining groundwater levels mainly resulted from the expansion of vegetation cover rather than changes in hydro-climatic variables. Finally, this work highlights how significant financial investment in improving irrigation efficiency in the absence of socio-economic plans, education, awareness, and monitoring programmes unproductively resulted in the expansion of agricultural activities rather than preserving groundwater storage.

An Assessment of Trends of Potential Evapotranspiration at Multiple Timescales and Locations in Sicily from 2002 to 2022

Climate change and the related temperature rise can cause an increase in evapotranspiration. Thus, the assessment of potential evapotranspiration (PET) trends is important to identify possible ongoing signals of climate change, in order to develop adaptation measures for water resource management and improve irrigation efficiency. In this study, we capitalize on the data available from a network of 46 complete meteorological stations in Sicily that cover a period of about 21 years (2002–2022) to estimate PET by the Food and Agriculture Organization (FAO) using the Penman–Monteith method at the daily time scale in Sicily (southern Italy). We then analyse the trends of PET and assess their significance by Sen’s Slope and the Mann–Kendall test at multiple temporal scales (monthly, seasonal, and annual). Most of the locations do not show significant trends. For instance, at the annual timescale, only five locations have a significantly increasing trend. However, there are many locations where the monthly trend is statistically significant. The number of locations where monthly trend is significant is maximum for August, where 18 out of these 46 stations have an increasing trend. In contrast, in March, there are no locations with a significant trend. The location with the highest increasing trend of PET indicates trend slopes of 1.73, 3.42, and 10.68 mm/year at monthly (August), seasonal (summer), and annual timescales, respectively. In contrast, decreasing PET trends are present only at the monthly and seasonal scales, with a maximum of, respectively, −1.82 (July) and −3.28 (summer) mm/year. Overall, the findings of this study are useful for climate change adaptation strategies to be pursued in the region.

Temporal and spatial diurnal dynamics of the hysteresis of weighed transpiration and water transport in tomatoes

In studies of terrestrial water cycles and farmland irrigation management, plant transpiration is an important reference data source. There is a hysteresis effect between plant transpiration and meteorological factors, which is important for predicting plant transpiration. However, the hysteresis effect in diurnal dynamics (time) and between the processes of water from soil to air in the soilplantatmosphere continuum (SPAC) system (space) remains unclear. In this study, the intensity of light radiation (high radiation, HR; low radiation, LR) and the amount of water used for irrigation (high irrigation, HW; low irrigation, LW) were used to form four treatments (HRHW, HRLW, LRHW, and LRLW) on tomato plants in a greenhouse. The diurnal dynamics of the transpiration of the whole plant by weighting (weighted transpiration, WT), sap flow (SF), and lag time in the process of water transport in tomato plants were analyzed by the data of every 10 min. The results showed that the WT exceeded the SF in the HRHW during 10:00–18:00 and in the HRLW during 10:00–16:00. In the HRHW, the proportion of SF in the upper part to the lower part of the plants was significantly lower than that in the other treatments during the daytime. The hysteresis effect was prevalent in the process of water transport from soil through plants to the atmosphere during the daytime. The lag time of WT to net radiation (Rn) and SF to WT changed more dramatically during the daytime under HR- conditions, and the maximum lag time was 60 min. Compared with the hysteresis of middle SF to low SF of plants, the lag time of top SF to middle SF had a greater fluctuation, with a maximum of 50 min (LRLW) and 60 min (HRHW and HRLW), respectively. The longest times at which of stem diameter (SD), fruit diameter (FD) and substrate water content (SWC) lagged behind SF were 60 min (LRHW), 70 min (HRHW and LRHW) and 50 min (HRHW and HRLW), respectively. After temporal and spatial dynamic hysteresis were added to the structural equation modeling (SEM), the path coefficients between most variables were improved, and the overall effect of the model was enhanced in all treatments. This provides a valuable direction for the future improvements in transpiration models, irrigation efficiency, and crop yield.

Research on the optimal allocation of agricultural water and soil resources in the Heihe River Basin based on SWAT and intelligent optimization

In the context of global climate change, changes in precipitation and temperature conditions, especially the increasing frequency of extreme climate events, have a severe impact on agricultural production. Predicting climate change and adjusting planting structures over time are critical to sustainable agricultural development. In this study, the Coupled Model Intercomparison Project Phase 6 (CMIP6) and Soil and Water Assessment Tool (SWAT) models were used to simulate the future climate and runoff in the middle reaches of the Heihe River Basin (MHR). Then, the MOPSO and NSGA-II were used to plan future planting structures. The results showed that the temperature and precipitation in the MHR showed an increasing trend. By the 2070 s, the temperature was projected to increase by more than 2 °C under SSP245, while that under SSP585 was more than 4 °C. The annual mean precipitation was projected to increase, but the distribution was uneven, and the increased precipitation was mainly concentrated in spring and autumn. Under the interaction of temperature and precipitation, the runoff of the Heihe River will increase in the future, especially under SSP585, and the runoff of the Heihe River is projected to reach 2.48 billion m³/a in the 2070 s. Crop water demand was projected to increase with temperature, and crop irrigation water demand would increase by 14.4 % in the 2070 s under SSP245. Planting vegetables helps to improve agricultural economic benefits and carbon sinks, but to control soil erosion, the area of vegetables is best kept at approximately 16 %. Fertilizers and agricultural films are the primary carbon sources in agricultural production activities in MHR, accounting for more than 60 % of the total carbon. This study suggests promoting sustainable agricultural development by improving irrigation efficiency, using low-carbon fertilizers, controlling soil erosion, and gradually expanding the vegetable planting area with a considered ecological environment.

Has Property Rights Reform of China’s Farmland Water Facilities Improved Farmers’ Irrigation Efficiency?—Evidence from a Typical Reform Pilot in China’s Yunnan Province

China is implementing a pilot project to reform the property rights of farmland water facilities to solve the serious problems of chaotic end-of-pipe governance and inefficient irrigation from farmers. Based on microscopic research data of farm households in a typical pilot in Lu Liang County, Yunnan Province, in China, this study uses the Tobit model, and SEM was used to explore the impact of property rights reform on the irrigation efficiency of farmers and the potential mechanism paths. We further analyzed the differences in governance logic and irrigation efficiency between the two property rights models of “multiple cooperative governance” and “private contract governance” formed after the reform. The findings are as follows: (1) Compared with nonreformed areas, reformed areas have a higher promotion of adoption of water-saving technologies and a better quality of facility maintenance, which significantly contributes to irrigation efficiency, but farmers’ perception of water scarcity negatively affects irrigation efficiency; (2) there are differences between the “multiple cooperative governance model” and “private contract governance model” in terms of the mechanism paths to improve irrigation efficiency, resulting in different focuses between the two models, in which the former one has better irrigation efficiency while cutting off some of the farmers’ benefits and the latter benefits more farmers while losing some of the irrigation efficiency. Finally, this study recommends that China should continue to promote the reform of farmland water property rights while focusing on promoting water conservation technologies, improving the quality of facility maintenance and facility water supply capacity, enhancing farmers’ awareness of water scarcity, and implementing a more water-efficient “multiple cooperative governance model”. The results of this study provide a model with Chinese characteristics for developing property rights policies and governance models for farmland water facilities in developing countries.

Development and Implementation of an Automatic Plant Watering System

The aim of this paper is to Automatic watering or irrigation control system has been designed and constructed. The prototype of the system worked according to specification and quite satisfactorily. The system components are readily available, relatively affordable and they operate quite reliably. The system helps to eliminate the stress of manual irrigation and irrigation control while at the same time conserving the available water supply. Improving Irrigation efficiency can contribute greatly to reducing production costs of agricultural products, thereby making the industry to be more competitive and sustainable .It can be seen from the results obtained that the system responded linearly with respect to the degree of dryness for the three soil types. There is a linear relationship between the degree of soil dryness and the time taken to irrigate the soil. At 50% dryness, irrigation duration was 2.0, 2.0 and 2.5 seconds for sandy, loamy and clayey soils respectively. While at 70% dryness, irrigation duration increased to 3.0, 7.5 and 8.0 seconds for sandy, loamy and clayey soils respectively. It is seen that irrigation in loamy soil generally took longer in loamy soil than in sandy soil, and clayey soil irrigation took longest.

Spatial scale effect of irrigation efficiency paradox based on water accounting framework in Heihe River Basin, Northwest China

Improving irrigation efficiency (IE) to alleviate water shortage has been deemed viable. However, the so-called irrigation efficiency paradox (IEP) can complicate this process, where agricultural water consumption remains high despite the enhanced irrigation efficiency, particularly in arid regions. This study developed a judgment method of IEP based on a water accounting framework and the IEP definition to detect the IEP occurring across spatial scales in the middle Heihe River Basin, the second-largest inland river basin in Northwest China. Furthermore, the scale effects of the IEP were analyzed. The results showed that evaluated by evapotranspiration (ET) and transpiration (T), the scale effect occurred because IEP does not necessarily occur at the field scale but at the irrigation district scale and basin scale. Evaluated by Inflows (I) and surface water diversion and groundwater extraction (Isg), the scale effect occurred because IEP may occur at the field and the irrigation district scales but not at the basin scale. Further, the IEP was also influenced by time scales and regional agricultural characteristics. The results can be referenced for water-saving measures, avoiding the potential IEP for actual water savings in arid regions worldwide.

Sodium Alginate-g-acrylamide/acrylic Acid Hydrogels Obtained by Electron Beam Irradiation for Soil Conditioning

Being both a cause and a victim of water scarcity and nutrient deficiency, agriculture as a sustainable livelihood is dependent now on finding new suport solutions. Biodegradable hydrogels usage as soil conditioners may be one of the most effective solutions for irrigation efficiency improvement, reducing the quantity of soluble fertilizers per crop cycle and combating pathogens, due to their versatility assured by both obtaining method and properties. The first goal of the work was the obtaining by electron beam irradiation and characterization of some Sodium Alginate-g-acrylamide/acrylic Acid hydrogels, the second one being the investigation of their potential use as a soil conditioner by successive experiments of absorption and release of two different aqueous nutrient solutions. Alginate-g-acrylamide/acrylic Acid hydrogels were obtained by electron beam irradiation using the linear accelerator ALID 7 at 5.5 MeV at the irradiation doses of 5 and 6 kGy. For this were prepared monomeric solutions that contained 1 and 2% sodium alginate, acrylamide and acrylic acid in ratios of 1:1 and 1.5:1, respectively, for the obtaining of materials with hybrid properties derived from natural and synthetic components. Physical, chemical, structural and morphological characteristics of the obtained hydrogels were investigated by specific analysis using swelling, diffusion and network studies and Fourier Transform Infrared Spectroscopy and Scanning Electron Microscopy. Four successive absorption and release experiments of some synthetic and natural aqueous solutions with nutrients were performed.

Impacts of precipitation variations on agricultural water scarcity under historical and future climate change

Both blue water and green water contribute to agricultural water scarcity, which is subjected to impacts of precipitation variations in the context of climate change. However, an explicit quantification of the possible effects of precipitation variations on agricultural water scarcity index (AWSI) under historical and future climate is absent. In this study, we applied an integrated AWSI, which incorporates blue water and green water, to estimate agricultural water scarcity in China and to determine the association of AWSI with precipitation variations over the historical (1971–2010) and future (2031–2070) periods. Precipitation variations have substantial effects on changes in AWSI. Especially during extremely dry years with precipitation anomaly lower than −2 standard deviation, changes of AWSI from the multi-year average could be as high as 31%. Future climate change would further intensify AWSI and amplify the effects of precipitation variations, particularly in Inner Mongolia with changes of AWSI over 200%. Southwestern China could also experience expanding agricultural water scarcity under future climate scenarios. Improving irrigation efficiency has potential to alleviate water scarcity by up to 30%. This study provides valuable information for scientists and policy decision makers to cope with the impacts of precipitation variations on AWSI.

Global Assessment of Groundwater Stress Vis-à-Vis Sustainability of Irrigated Food Production

Due to poor water resources management, groundwater-dependent agriculture induces substantial stress on several aquifer systems worldwide, which poses a serious threat to water and food security. However, only a few studies have addressed this vital issue. This study aimed to evaluate stress on aquifers due to the overuse of groundwater for food production and explore pathways for stress reduction via improved irrigation efficiency and productivity. Groundwater stress was characterized using the ratio of water use to availability, with consideration for environmental flows. The results indicated that out of 107 countries—dependent on groundwater irrigation, about half are overexploiting groundwater, while one-fifth of these countries are extracting moderately-to heavily. Over 90% of the non-renewable groundwater abstraction occurs in 7 countries. Further, about 450 million tonnes (Mt) of global annual food production is from non-renewable groundwater exploitation. If the existing irrigation efficiency is increased to 90%, current groundwater stress would be reduced by 40%. Additionally, in unstressed regions, it would be possible to produce additional 300 Mt of food by using saved water while maintaining groundwater stress at acceptable levels. Moreover, improved water productivity in conjunction with increased irrigation efficiency could reduce the current level of unsustainable food production by 47%. These results provide important insights into the dynamics of irrigation stress on groundwater systems, and the role of managerial interventions.

Water resources of Kazakhstan as a factor in the growth of agro-industrial production in the context of transition to "green" economy

The purpose – is to show the state of water resources, their use as a factor in the growth of AIC and development of water strategy of Kazakhstan. Statistical indicators that have direct impact and significantly affect the effectiveness of management of water sources in the republic are systematized. Methods – economic-mathematical, predictive calculations in order to solve the problems of water supply for national economic needs of the country with high-quality drinking water. Results – the degree of development of this topic in scientific works of domestic and foreign environmental scientists and economists was studied. Particular factors are determined on the basis of econometric model in the form of joint equations, their significance for the future is proved and justified. It is proposed to analyze the situation that has developed in the system of water objects of agricultural sector of the Republic of Kazakhstan in the context of implementation of "green" economy projects with the help of multifactorial probabilistic-statistical models that characterize the mechanism of functioning of socio-econometric system. Statistical series of initial data were compiled, presented by the Bureau of National Statistics of the Agency for Strategic Planning and Reforms of the Republic of Kazakhstan. Conclusions – it is noted that agriculture is the most water-intensive sector, characterized by the greatest losses of water during its transportation and use. The authors recommend that farmers implement innovative methods to improve irrigation efficiency with more sustainable water harvesting. It was revealed that primary reasons for the growing shortage of used water objects are worn-out infrastructure, the use of outdated technologies in construction of water supply networks. The results of calculations of management of structural economic-mathematical model for the analysis and forecasting of ec onomic processes of different levels for the period 2022-2025 are obtained.

Assessing the economic effects of drought using Positive Mathematical Planning model under climate change scenarios

In recent decades, regions all around the world have experienced severe droughts adversely affecting their agricultural production. Climate change, along with limited access to water will alter future production and agricultural development. The purpose of this study is to provide a perspective for the future cultivation regime in the Divandarre region in the Sepidrood catchment in Iran, using historical climatic, agricultural, and economic information. Future precipitation values are determined for three climate scenarios, then downscaled and converted to pixel-based precipitation maps using the Moving Least Squares method. Future droughts are identified using the Standardized Precipitation Index at 3, 6, and 9-month intervals based on precipitation values and the relationship between different types of droughts (meteorological, agricultural and hydrological). We introduce a new coefficient, the water cost coefficient, derived from drought characteristics that captures the added irrigation cost in drought years because of increased water price. Using the Positive Mathematical Planning method and considering limited land and water, predicted future prices and costs based on a linear regression of supply-demand, and the annual water cost coefficient values, an agroeconomic model is built. After prediction of future price and cost based on historical data from 2005 to 2018, we run future scenarios based on various price and cost values to determine the optimal annual cultivation area for each crop from 2020 to 2040. All scenarios indicate a decline in cultivation area for all crops making agriculture less beneficial in the future. The cultivation regime moves away from more water-consuming products with less economic value (e.g. watermelon) toward less water-consuming, more expensive products (e.g. lentils). The findings of this model along with expert economic judgments help determine the economic effects of climate change on irrigation, farmers' decisions, and water policies, including water markets, and improving irrigation efficiency. Authorities and farmers could adapt to drought shocks and changes in the market while experiencing less revenue loss.

Simulation-optimization based real-time irrigation scheduling: A human-machine interactive method enhanced by data assimilation

Efficient irrigation scheduling is crucial for both improving crop production and saving irrigation water use in arid/semi-arid agricultural regions threatened by water shortage and soil salinity. However, irrigation scheduling optimization is hindered by the uncertainties of data and optimization model, and adopting the optimal irrigation scheduling is subject to farmers' acceptance. To effectively tackle these challenges, this paper presents a novel human-machine interactive framework for real-time irrigation scheduling (RIS). The developed modeling framework couples a simulation-optimization model, irrigation farmers, and a data assimilation procedure within the human-machine interactive framework for RIS. The proposed approach is capable of: 1) searching optimal irrigation scheduling through the simulation-optimization model; 2) making actual irrigation decisions based on farmers' experiences, knowledge, behaviors, or optimal solutions; and 3) updating soil water content based on the model simulations and real-time observations at each time period. The RIS is applied to a real-world case in a typical arid agricultural region of China. Based on the comparisons with historical irrigation records and a tradition simulation-optimization model, the proposed RIS can not only achieve higher economic benefit with less irrigation water allocation quotas, but also improve irrigation efficiency. This study contributes to the methodology by integrating computer model, real-time observations and farmers' experiences to optimization modeling framework for supporting sustainable irrigation water management.

Irrigation water use efficiency: A water balance approach

AbstractIrrigated agriculture plays a major role in the livelihoods of nations all over the world and with the agricultural water use sector being the largest of all water use sectors, there have been increased expectations that the sector should increase efficiency. Irrigation efficiency should be assessed by applying a water balance and the purpose of an irrigation system is to apply the desired amount of water, at the correct application rate and uniformly to the whole field, at the right time, with the least amount of nonbeneficial water consumption (losses), and as economically as possible. The fraction of the water abstracted from the source that can be utilized by the plant, can be called the beneficial water use component, and optimized irrigation water supply is therefore aimed at maximizing this component. A water use framework that covers four levels of water management infrastructure: the water source, bulk conveyance system, the irrigation scheme, and the irrigation farm can be used to improve irrigation efficiency. The water balance approach can be applied at any level, within defined boundaries, or across all levels to assess performance within the whole Water Management Area.

Managing irrigation under increasing water scarcity

AbstractWith rising physical and economic scarcity of water, increasing or sustaining agricultural production while limiting or reducing consumptive water use is an urgent challenge. This article examines the case of four countries—India, China, western United States, and Israel—where there is a long history of irrigated agriculture with significant public and private investments, to identify key themes for managing irrigation under increasing physical and economic water scarcity. The focus of irrigation management has expanded from investing in irrigation infrastructure to reforming institutions; strengthening policies pertaining to irrigation prices and rights; using incentives to reward reductions in irrigation application; and improving irrigation efficiency. However, this may not be sufficient to reduce consumptive use of water in agriculture. Reducing freshwater use in agriculture will require cost‐effective harnessing of other water sources through processes such as desalination and wastewater reuse, which may be difficult to implement in most geographies. Changes to policies in other sectors will likely be needed, especially in food procurement and land‐use, which require balancing water security with food security, and supporting potential losses in livelihoods and incomes from such changes. Finally, reductions in agricultural water use in a country will likely have implications for water use in other countries, through imports.

Proper irrigation amount for eggplant cultivation in a solar greenhouse improved plant growth, fruit quality and yield by influencing the soil microbial community and rhizosphere environment.

Water scarcity is a worldwide problem, and in order to obtain plenty of production, agricultural irrigation water accounts for a large portion. Many studies have shown that the interaction of root microorganisms and soil can promote crop growth. Developing ways to reduce irrigation to maintain soil fertility and ensure crop yield by regulating the root microenvironment is an important research goal. Here, we developed a reasonable irrigation plan for eggplant cultivation in a solar greenhouse. The maximum theoretical amount of water demand during eggplant planting obtained from a previous study was used as the control (CK), and the irrigation in the treatments was reduced by 10, 20 and 30% relative to this amount. The 10% irrigation reduction treatment (T1) significantly improved soil nutrients and increased soil catalase, urease and alkaline phosphatase activities (p < 0.05). Further analysis of rhizosphere microorganisms revealed the highest richness and diversity of the microbial community under the T1 treatment, with Bacilli as the most abundant bacteria and Aspergillaceae as the most abundant fungi and lower relative abundances of Chloroflexi and Acidobacteria (p < 0.05). Changes in microbial community structure under the influence of different irrigation treatments resulted in improvements in rhizosphere N cycling and nutrient catabolism. The plant–microbe interactions led to significant increases in eggplant plant height, root vigour, root surface area, leaf chlorophyll a, leaf net photosynthetic rate, water use efficiency, transpiration rate, and stomatal conductance under the T1 treatment compared to the CK treatment; soluble sugar, soluble protein and free amino acid contents in eggplant fruit increased by 10.8, 12.3 and 6.7%, respectively; and yield increased by 3.9%. Our research proved that the 10% irrigation reduction treatment (T1) could improve microbial community richness and fruit yield, which would improve irrigation efficiency and cost reduction in agriculture.

Quantifying streamflow sources to improve water allocation management in a catchment undergoing agricultural intensification

Changes in streamflow contributing sources in semi-arid catchments undergoing agricultural intensification are often poorly understood. As a result, pathways to increase resilience to environmental change are not well established. Mixing model analysis using stable water isotopes and hydro-chemical tracers was applied to evaluate streamflow sources in the Kaleya Catchment, Zambia. Results showed that strong agricultural intensification signal influenced streamflow sources in time and space. In the rainy season, streamflow mainly originated from stormwater runoff from non-irrigated areas (43 ± 13%), the perennial spring (39 ± 21%) and stormwater runoff from irrigated areas (18 ± 17%). But in the dry season, the spring (65 ± 15%) and irrigation return flows (35 ± 15%) became the important upstream sources, while downstream sources were irrigation return flows (73 ± 15%) and wastewater containing vinasse (27 ± 15%), both associated with water originally transferred from the adjacent Kafue River. Given the current importance of irrigation return flows to downstream users including ecosystems, social cooperate responsibility and/or water markets must help to improve irrigation efficiency while simultaneously ensuring downstream flows are maintained.

Tomato Evapotranspiration, Crop Coefficient and Irrigation Water Use Efficiency in the Winter Period in a Sunken Chinese Solar Greenhouse

In the Northern China Plain (NCP), sunken solar greenhouses (SSG) are now increasingly being used for vegetable cultivation in winter due to low winter temperatures. Investigating plant transpiration and determining crop coefficients are helpful when developing irrigation scheduling and improving crop growth. In this study, a three-season experiment was conducted in a commercial tomato SSG to investigate changes in microclimate, sap flow (SF), photosynthesis traits and plant physiological parameters, and to calculate the crop coefficient and evaluate the irrigation efficiency using current irrigation management practices. Results show that the average transmissivity from top plastic covers was 0.69, and the inside temperature increased by approximately 10 °C in November and 15–18 °C in December, which guaranteed the growth of tomatoes in winter. The leaf photosynthesis rate (Pn) is linearly related to radiation, however, a concave quadratic function is a better fit for Pn and VPD, with the highest Pn at approximately 1.0 kPa VPD; leaf transpiration is positively and linearly related to both radiation and VPD. Therefore, increasing greenhouse transmissivity and maintaining an internal VPD of approximately 1 kPa could produce a high leaf Pn and low transpiration concurrently. Daily total SF was linearly correlated with solar radiation, VPD and temperature with determination coefficients of 0.87–0.96, 0.89–0.91 and 0.62–0.84, respectively. Correcting the slope of SF to radiation with VPD (SF = (0.12 + 0.14VPD)Rs), R2 increased by 0.08, and the root mean square error and relative error decreased by 0.047 mm day−1 and 6.53%, respectively. Therefore, this integrated equation is recommended to estimate daily tomato transpiration when plant height is approximately 1.5 m, and the leaf area index (LAI) is between 2 and 2.5. During the fruit expansion and ripening period, the average basal crop coefficients (Kcb) for greenhouse tomatoes in winter was between 0.99 and 1.11. The irrigation efficiency increased from 0.3 in the first season to 0.6–0.69 in the second and third seasons when the tensiometer method was used. Therefore, using the tensiometer method to guide tomato irrigation could markedly improve irrigation efficiency in greenhouses.