Application and evaluation of Stanghellini model in the determination of crop evapotranspiration in a naturally ventilated greenhouse

Stanghellini model is one of the few models primarily developed to predict the evapotranspiration of crops(ET_(c))in naturally ventilated greenhouses.However,there are insufficient data on the model regarding its use,particularly in China where solar greenhouses without heating systems are fast spreading for vegetable growth and production.The application of Stanghellini model and the evaluation of its performance using meteorological and tomato plant data generated inside an unheated and naturally ventilated multi-span Venlo-type greenhouse is exploited in this study.Model capability was evaluated by utilizing data from sap flow measurements,meteorological and crop data.Measured meteorological data included solar radiation(R_(s)),air temperature(T_(a)),relative humidity(RH)and net radiation(Rn).Average leaf area index(LAI)values measured during the experimental period were 1.00,3.30,4.05 and 2.93;while determined crop coefficients(K_(c))changed from 0.40,0.62,1.12 to 0.83 for the initial stage,development stage,mid-season stage and late-season stage,respectively.Results from the study indicated that the average hourly ET_(c) values of tomato plants using sap flow measurements were 0.165 mm/h,0.148 mm/h,0.192 mm/h and 0.154 mm/h for the initial stage,development stage,mid-season stage and late-season stage,respectively.Meanwhile,the ET_(c) values obtained from calculation using Stanghellini model were 0.158 mm/h,0.152 mm/h,0.202 mm/h and 0.162 mm/h for the initial stage,development stage,mid-season stage and late-season stage,respectively.These ET_(c) values calculated by the Stanghellini model were close to the measured values within the same period.The coefficients of correlation(R^(2))based on hourly ET_(c) for the calibration data was 0.94 and that of the validation dataset was 0.90.Scatter plots of the estimated and measured hourly ET_(c) revealed that the R^(2) and the slope of the regression line for May,June and July were 0.94,0.90,0.96 and 1.15,0.97,1.10 respectively.These data were well represented around the 1:1 regression line.A model sensitivity analysis carried out illustrates how the changes in R_(s) and T_(a) affect greenhouse ET_(c).Stanghellini model was therefore proven to be suitable for ET_(c) estimation with acceptable accuracy in unheated and naturally ventilated greenhouses in the Northeast region of China.

Performance experiment and numerical prediction on the optimization design of the micro-sized water turbine for the hose reel irrigator

In order to significantly improve the efficiency of driving water turbine used in hose reel irrigator,a new water turbine structure was proposed by the method of performance test and numerical calculation.The internal flow characteristics of original water turbine were analyzed,and it was found that unreasonable design of main flow passage components such as inlet,outlet and runner could not effectively translated pressure energy of upper stream into impact kinetic energy of blade,and gave rise to low energy conversion efficiency of water turbine.The inadequate internal flow and uneven pressure distribution were also not conducive to energy conversion efficiency.Then a new structure of water turbine structure was presented,in which the inlet has a tangential nozzle jet and the outlet is in axial direction.The computational analysis showed that the nozzle jet at the inlet of the new water turbine runner,which makes jet flow mainly concentrate in the impacted blade passage,can reduce the loss of flow kinetic energy.The axial outflow increases the distance of inflow in the runner,which is more conducive to the runner blades work.Performance experiments on both original and new water turbines showed that the highest efficiency of the new turbine is almost 20 percentages higher than that of the original turbine,and the new turbine is nearly triple output power over the original turbine.The internal flow characteristic analysis and the performance experiment were conducted to assess the feasibility of the replacement of the original water turbine by the new water turbine.

Irrigated agriculture for food self-sufficiency in the sub-Saharan African region

Increasing agricultural productivity in Africa will have important impacts not only on the agricultural sector but also can be a catalyst for industrialization through agro-processing.Irrigation,therefore,has a crucial role in enhancing food security and reducing hunger in the region.Numerous countries in Africa consider water and irrigation management as a key factor in improving their food security and ensuring access to drinking-water for their populations.Fortunately,there is evidence from a number of places on the continent where the adoption of efficient irrigation systems has led to higher productivity among smallholder farmers.While the appropriate interventions for the diverse agro-ecological zones of sub-Saharan Africa are known,adoption among smallholder farmers still remains a challenge.Digital technology opens the vast untapped potential for farmers,investors,and entrepreneurs to improve the efficiency of food production and consumption in Africa.From precision farming to an efficient food supply chain,technology could bring major economic,social,and environmental benefits.Increasing investment and involvement of the private sector is crucial for the up-scaling of irrigation technologies.Indeed,the sheer optimism across the startup ecosystem is that extreme hunger can be cured in Africa,in this generation,by significantly transforming the industry that employs most of its citizens.This paper draws on lessons from past trends in the irrigation industry and emphasizes on novel directions to ensure that farmers,as well as other stakeholders reap the benefits associated with improved technologies.

Effects of land use change on hydrological cycle from forest to upland field in a catchment,Japan

Understanding the effects of land use change on the hydrological cycle is very important for development of sustainable water resource in an upland field catchment.In this study,soil and hydrological properties in an upland field catchment,which was reclaimed partially from a forest catchment,were compared with another forest catchment.The soil properties of surface and subsurface layers were investigated in the two catchments.The soil was compacted and waterholding capacity of soil in the upland field catchment became smaller after the reclamation from forest to upland field,which decreased infiltration rate and water storage in the soil layers.We found that peak discharge and direct runoff in the upland field catchment increased compared with the forest catchment.Annual evapotranspiration from the upland field catchment tended to be lower due to the change in vegetation type and soil properties.Furthermore,a semi-distributed hydrological model was applied in the upland field catchment to understand the integrated effects of reclamation on the hydrological cycle.The model parameters,which were determined using a nonlinear optimization technique—the Shuffled Complex Evolution method(SCE),were compared between the two catchments.The Nash and Sutcliffe coefficient was used to evaluate the model performance.The simulated results indicated that evapotranspiration was decreased and change in discharge was more obvious in the surface layer.We considered that declined infiltration and water storage and increased peak discharge and direct runoff have a negative impact on water resources in the upland field catchment.This study will provide information for forest managers in planning and making decisions for land and water resource management.

Response of tomato growth to continuous elevated CO_(2)concentration 2 under controlled environment

CO_(2)fumigation has been extensively used in greenhouses cultivation to enhance crop yield.The effects under the precise level of elevated CO_(2)(e[CO_(2)])on crop morphology,yield,and fruit quality remain largely elusive yet.To explore the response of plant growth to the continuous RCPs(Representative Concentration Pathways)projected CO_(2)concentration[CO_(2)],tomato(Hezuo 908)plants were grown under ambient CO_(2)(a[CO_(2)],462μmol/mol)and e[CO_(2)](550,700,850 and 1000μmol/mol):named as EC550,EC_(700),EC_(850),and EC_(1000),respectively,under uniform environmental condition for two planting seasons.Collective growth of tomato plants(plant height,stem diameter,and leaf area index)was significantly enhanced under EC_(700)and showed a slightly negative response under EC_(850).The optimum yield was stimulated under EC_(700)by 74.05%and 55.91%,while maximum total dry weight(DW_(t))was enhanced under EC_(1000)by 58.23%and 39.78%during autumn-winter and spring-summer planting seasons,respectively,as compared to a[CO_(2)].The greatest yield and least DWt stimulated under EC_(700)for both seasons indicated that EC_(700)improved the ability of the tomato plants to translocate carbohydrates to fruits.Optimum water use efficiency related to yield(WUE_(y))was enhanced by 55.91-210.87%under EC_(700)compared to a[CO_(2)].The titratable acid(TA)was improved by 19.94%(EC_(700)),29.17%(EC_(850)),and 97.92%(EC_(1000)),and the lycopene(Lp)was increased by 2.22%(EC_(700))and reduced by 2.28%(EC_(1000)).Thus,the overall optimum impact on tomato growth was explored under EC_(700).Super e[CO_(2)]did not positively influence the tomato growth process and yield under adequate water and fertilizer conditions.The present study results are beneficial for greenhouse crop production and might be used as a reference to validate the climate change influence modeling.

Overview of modelling techniques for greenhouse microclimate environment and evapotranspiration

Domestication of plants by man through greenhouse crop production has revolutionized agricultural farming systems worldwide.Selecting the appropriate greenhouse technology together with the user-friendly evapotranspiration(ETc)model can optimize crop water use.The greenhouse microclimate environment has nearly zero wind speed and low radiation,hence low transpiration due to high temperature and humidity.Therefore,matching the greenhouse microclimate with the appropriate ETc model will certainly optimize crop water use efficiency since water is becoming a scarce resource globally,more so in the greenhouse environment.This is one of the main reasons why the gap between the dissemination of various advanced ETc models and the application by the greenhouse crop producers’community needs to be bridged.The likelihood or chances of rapidly disseminating and adopting advances in ETc estimating technology by a larger greenhouse crop producers community will increase if greenhouse ETc models become more user-friendly and available.The contribution of the greenhouse system to increased and sustainable food production must come through improved disseminating,adopting and use of existing greenhouse ETc models.FAO recommends a standard approach for the determination of crop water requirements utilizing the product of reference evapotranspiration(ET0)and crop coefficient(Kc)values.The FAO approach can also be used in greenhouse cultivation systems.However,studies connecting greenhouse technologies and methodologies for measuring ET0 or ETc in greenhouses are not available.There are also few studies undertaken that compared the performance of ET0 or ETc models under different categories of greenhouse conditions.In this review,a link between greenhouse technology and ET0 model or ETc model,and how existing knowledge and methodologies in ET0 or ETc measurements can actually enhance the sustainability of greenhouse farming have been highlighted.The categories of greenhouses,equipment commonly used,and the data collected for ET0 and ETc measurements have been established in the article.This review aimed to evaluate and summarize ET0 and ETc models currently available and being used in the various greenhouse categories.The accuracy assessment levels of the ET0 models about the category of the greenhouse microclimate environment were carried out.