Flood Simulation and Flood Risk Reduction Strategy in Irrigated Areas

The potential risk of flood or waterlogging in irrigation districts has increased due to global climate change and intensive human activities. This paper employed a waterlogging process simulation model for flat irrigation districts in the paddy fields to simulate floods under different scenarios. The scenarios of the rainfall conditions, initial storage depths, and work scales are designed, respectively. The risk of flood damage increases as rainfall increases, with a maximum increase of 62.8%, comparing the extreme scenario with the current scenario. A moderate rise in pumping station flow and using pre-rain drainage measures in the paddy fields can effectively reduce waterlogging loss. The total regional flood damage was reduced by up to 10.9%, 15.8%, and 35.9% when the pump station flow in the study area was increased by 10%, 20%, and 30%. The insights from this study of the possible future extreme flood events may help flood control planning

Evaluation of Improved Model to Accurately Monitor Soil Water Content

The accurate monitoring of soil water content during the growth of crops is of great importance to improve agricultural water use efficiency. The Campbell model is one of the most widely used models for monitoring soil moisture content from soil thermal conductivities in farmland, which always needs to be calibrated due to the lack of adequate original data and the limitation of measurement methods. To precisely predict the water content of complex soils using the Campbell model, this model was evaluated by investigating several factors, including soil texture, bulk density and organic matter. The comparison of the R2 and the reduced Chi-Sqr values, which were calculated by Origin, was conducted to calibrate the Campbell model calculated. In addition, combining factors of parameters, a new parameter named m related to soil texture and the organic matter was firstly introduced and the original fitting parameter, E, was improved to an expression related to clay fraction and the organic matter content in the improved model. The soil data collected from both the laboratory and the previous literature were used to assess the revised model. The results show that most of the R2 values of the improved model are >0.95, and the reduced Chi-Sqr values are <0.01, which presents a better matching performance compared to the original. It is concluded that the improved model provides more accurate monitoring of soil water content for water irrigation management

Surface Energy Partitioning and Evaporative Fraction in a Water-Saving Irrigated Rice Field

Surface energy distribution in paddy fields and the ratio of latent heat flux (LE) to available energy, termed as the evaporative fraction (EF), are essential for an understanding of water and energy processes. They are expected to vary in different ways in response to changes in the soil moisture condition under water-saving irrigation practice. In this study, the diurnal and seasonal variations in energy distribution were examined based on the data measured by the eddy covariance system and corrected with enforcing energy balance closure by the EF method in water-saving irrigated rice paddies in 2015 and 2016. Soil heat flux (G) values were similar in magnitude to sensible heat flux (Hs) values, with both accounting for approximately 5% of the energy input. Both magnitudes of G and Hs were significantly lower than that of LE. Generally, EF in water-saving irrigated rice paddies was larger than that of other ecosystems, and varied within a narrow range from 0.7 to 1.0. Diurnally, EF decreased till noon and then increased slowly in the afternoon till sunset. It was found be less varied between 10:00 and 14:00. Seasonally, the alternative drying-wetting soil water conditions in water-saving irrigated rice paddies resulted in a change in the variation of the EF. The LE flux is the largest component of available energy, with EF being mostly higher than 0.9. EF, increasing consistently till the tillering stage, remaining high from the late tillering to milk stage, and then following a declining trend. The maximum EF (approaching 1.0) was found in the milk stage. The results of EF in water-saving irrigated rice paddies will be helpful for estimating daily or long temporal scale evapotranspiration (ET) by the EF method based on satellite-derived ET

Effect of straw return on soil respiration and NEE of paddy fields under water-saving irrigation.

Straw return (SR) and rice water-saving irrigation (WSI) affect the greenhouse gas emission of paddy fields. However, studies on CO2 exchange between paddy fields and the atmosphere with joint regulation of SR and WSI are few. We conducted a two-year field experiment to investigate the effects of SR on soil respiration and net ecosystem exchange of CO2 (NEE) in paddy fields under controlled irrigation (CI), which is a typical WSI technique. The rice yields, irrigation water use efficiency, seasonal variations in soil respiration, NEE, and soil organic carbon content were measured. Compared with the control (flooding irrigation and traditional chemical fertilizer), a significant increase in rice yield and irrigation water use efficiency in the paddy fields under CI and SR joint management (CS) was observed. CS increased the soil respiration rate during most of the rice growth stage and increased the net CO2 absorption rate before approximately 80 days after transplanting; afterward, the pattern reversed. Total CO2 emissions through soil respiration in CS paddy fields increased by 43.7% and 182% compared with the control in 2014 and 2015, respectively. However, CS also caused an increase in the total net CO2 absorption by 18.1% and 30.1% in these two years, respectively. The acceleration in the consumption and decomposition of soil organic carbon induced by frequent alternate wet-dry cycles of the CI paddy fields increased the soil respiration and decreased the net CO2 absorption. SR promoted soil respiration but also improved rice growth, increasing the net CO2 absorption. The soil organic carbon content of the CS paddy fields after harvesting increased by 23.2% compared with that before transplanting. The present study concluded that joint regulation of WSI and SR is an effective measure for maintaining yield, increasing irrigation water use efficiency, mitigating CO2 emission, and promoting paddy soil fertility

Tomato and cowpea crop evapotranspiration in an unheated greenhouse

With the development of protected cultivation of vegetables in China, it is necessary to study the water requirements of crops in greenhouses. Lysimeter experiments were carried out to investigate tomato (2001) and cowpea (2004) crop evapotranspiration (ETc) in an unheated greenhouse in Eastern China. Results showed remarkably reduced crop evapotranspiration inside the greenhouse as compared with that outside. ETc increased with the growth of the crops, and varied in accordance with the temperature inside the greenhouse and 20-cm pan evaporation outside, reaching its maximum value at the stage when plants' growth was most active. Differences between the variation of crop evapotranspiration and pan evaporation inside the greenhouse were caused by shading of the pan in the later period when the crops were taller than the location where the pan was installed, 70 cm above ground. The ratio of crop evapotranspiration to pan evaporation was not constant as reported in previous studies, and the variation of the inside ratio αin lagged behind that of the outside ratio αout. Simulation of crop evapotranspiration based on 20-cm pan evaporation inside the greenhouse is more reasonable than that based on 20-cm pan evaporation outside, although pan evaporation outside is more consistent with ETc than that inside. The value of αin, calculated based on air temperature, relative humidity, and ground temperature inside, plays a dominant role in the calculation of ETc. As the crop height increases, altering the location of the inside pan and placing it above the canopy, out of the shade, would help to achieve more reasonable values of crop evapotranspiration

Effects of Biochar Amendment on CO₂ Emissions from Paddy Fields under Water-Saving Irrigation

The role of carbon pool of biochar as a method of long-term C sequestration in global warming mitigation is unclear. A two-year field study was conducted to investigate the seasonal variations of CO2 emissions from water-saving irrigation paddy fields in response to biochar amendment and irrigation patterns. Three biochar treatments under water-saving irrigation and one biochar treatment under flooding irrigation were studied, and the application rates were 0, 20, 40, and 40 t ha−1 and labeled as CI + NB (controlled irrigation and none biochar added), CI + MB (controlled irrigation and medium biochar added), CI + HB (controlled irrigation and high biochar added), and FI + HB (flood irrigation and high biochar added), respectively. Results showed that biochar application at medium rates (20 t ha−1) decreased CO2 emissions by 1.64⁻8.83% in rice paddy fields under water-saving irrigation, compared with the non-amendment treatment. However, the CO2 emissions from paddy fields increased by 4.39⁻5.43% in the CI + HB treatment, compared with CI + NB. Furthermore, the mean CO2 emissions from paddy fields under water-saving irrigation decreased by 2.22% compared with flood irrigation under the same amount of biochar application (40 t ha−1). Biochar amendment increased rice yield and water use efficiency by 9.35⁻36.30% and 15.1⁻42.5%, respectively, when combined with water-saving irrigation. The CO2 emissions were reduced in the CI + MB treatment, which then increased rice yield. The CO2 emissions from paddy fields were positively correlated with temperature. The highest value of the temperature sensitivity coefficient (Q10) was derived for the CI + MB treatment. The Q10 was higher under water-saving irrigation compared with flooding irrigation

Leaching loss of dissolved organic nitrogen from cropland ecosystems

Although widely studied in grassland and forest ecosystems, dissolved organic nitrogen (DON), an important form of nitrogen (N) lost through leaching, has received little attention in cropland ecosystem research. A global literature review and partial least squares path modeling (PLS–PM) were adopted to assess the quantity and composition of N leaching loss under different cropping systems, soil types, and management practices, as well as to identify the major factors controlling DON leaching. Annual total dissolved nitrogen (TDN, organic + inorganic N) leaching under different cropping systems ranged from 4.0 to 383.2 kg N ha−1. Vegetable and rice production systems showed the greatest and least TDN leaching, respectively. Across different cropping systems, DON accounted for 4.7%–34.9% of TDN in leachate. The NH4+–N form of N leaching is negligible in most upland cropping systems (<2.3%), but not so in lowland rice systems. The largest ratio of DON leaching to TDN leaching was found in a rice–wheat rotation (34.9%). Catch crop slightly increased DON leaching; however, it greatly decreased TDN leaching. Cropping systems in which animal manure or plant compost was applied or lowland rice was included showed a relatively high DON leaching ratio. Accordingly, in investigating DON leaching, more attention should be focused on cropping systems with manure application or lowland rice systems. Compared with climatic conditions and soil properties, field management practices (irrigation, chemical N input, and manure amendments) proved to be the factors most strongly influencing DON leaching. This suggests that optimizing water and N management practices is the most effective way of reducing the risk of DON leaching and increasing N use efficiency, particularly for vegetable and rice production systems.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Evaluating the Neural Network Ensemble Method in Predicting Soil Moisture in Agricultural Fields

Soil is an important element in the agricultural domain because it serves as the media that bridges the water consumption and supply processes. In this study, a neural network ensemble (NNE) method was employed to predict the soil moisture to eliminate the effects of random initial parameters of neural network (NN) on model accuracy. The constructed NNE model predicts daily root zone soil moisture continuously for the whole crop growing season and the water consumption and supply processes were separately modeled. The soil profile was divided into multiple layers and modeled separately. Weather data (including air temperature, humidity, wind speed, net radiation, and precipitation), rooting depth, and the hesternal soil moisture of each layer were used as the input. A calibrated root zone water quality model for maize (Zea mays L.) was used to generate training and evaluation data. The result showed that with 100 randomly initialized NN models, the NNE model achieved an average R2 of 0.96 and nRMSE of 5.93%, suggesting that the NNE model learned the soil moisture dynamics well and sufficiently improved the robustness of soil moisture prediction with high accuracy

Ammonia Volatilization Losses from Paddy Fields under Controlled Irrigation with Different Drainage Treatments

The effect of controlled drainage (CD) on ammonia volatilization (AV) losses from paddy fields under controlled irrigation (CI) was investigated by managing water table control levels using a lysimeter. Three drainage treatments were implemented, namely, controlled water table depth 1 (CWT1), controlled water table depth 2 (CWT2), and controlled water table depth 3 (CWT3). As the water table control levels increased, irrigation water volumes in the CI paddy fields decreased. AV losses from paddy fields reduced due to the increases in water table control levels. Seasonal AV losses from CWT1, CWT2, and CWT3 were 59.8, 56.7, and 53.0 kg N ha−1, respectively. AV losses from CWT3 were 13.1% and 8.4% lower than those from CWT1 and CWT2, respectively. A significant difference in the seasonal AV losses was confirmed between CWT1 and CWT3. Less weekly AV losses followed by TF and PF were also observed as the water table control levels increased. The application of CD by increasing water table control levels to a suitable level could effectively reduce irrigation water volumes and AV losses from CI paddy fields. The combination of CI and CD may be a feasible water management method of reducing AV losses from paddy fields

Controlled Irrigation and Drainage Reduce Rainfall Runoff and Nitrogen Loss in Paddy Fields

In southern China, the growing period of rice is synchronized with the rainy period, and the loss of nutrients (such as nitrogen) due to unreasonable irrigation and drainage, along with rainfall and runoff, has become the main source of agricultural nonpoint source pollution. The laws of runoff and nitrogen loss in paddy fields under different irrigation and drainage modes are not clear. In this study, field experiments were adopted to observe the runoff and nitrogen loss under typical rainfall and throughout the whole growth period. The results showed that, compared with the traditional irrigation and drainage mode, the controlled irrigation and drainage mode reduced the drainage of two typical rainfall processes by 47.5% and 31.3% and the peak drainage by 38.9% and 14.4%. Compared with those under the traditional irrigation and drainage mode, the average concentrations of total nitrogen, nitrate nitrogen, and ammonium nitrogen under the controlled irrigation and drainage mode were reduced by 22.2%, 22.7%, and 27.8%, respectively, during the whole rainfall process on July 21 and were decreased by 27.1%, 11.4%, and 25.6%, respectively, on August 25. In irrigated rice areas, under the controlled irrigation and drainage mode, drainage was reduced after two intercepts through paddy fields and drainage ditches. The nitrogen concentration in the drainage ditch decreased due to the increase in retention time and the effect of the ditch and field wetland. Compared with the traditional irrigation and drainage mode, the total nitrogen, nitrate nitrogen, and ammonium nitrogen loads of the controlled irrigation and drainage mode were reduced by 69.8%, 65.3%, and 69.7%, respectively