Water and solute dynamics in the soil are important for the design, operation, and management of the fertigation system by drip irrigation. Experiments were conducted to study the effects of emitter discharge rates on wetting patterns and Olsen-P distribution in the soil from a surface point source. Three widely used phosphate fertilizers of diammonium phosphate (DAP), potassium dihydrogen phosphate (KDP), and urea phosphate (UP) were tested. A 30° wedge-shaped plexiglass container was used to represent one twelfth of the complete cylinder. Monitoring of the wetting front movement in the tested sandy soil revealed that the increase in the surface wetted radius and in the vertical plane with water volume applied can be represented by a power function with power values of about 0.38 and 0.44, respectively. The dimensions of the wetted soil volume were clearly related to the emitter discharge rate. An increase in rate resulted in an increase in the wetted horizontal distance and a decrease in the wetted soil depth. The distribution of Olsen-P content in soil generally decreased with distance from the point source in the radial and vertical directions for all the three phosphate fertilizers. The absorption of phosphorus to soil increased with pH of the fertilizer solutions in an order of UP (2.78) -1 for the treatments with UP, KDP and DAP fertigated, respectively. Greater radial and smaller vertical distributed range of Olsen-P were observed in soil with higher discharge rates. The application strategy of phosphate fertilizer should be developed considering the absorption of fertilizers and emitter discharge rates. © ASABE 2021 Annual International Meeting

An appropriate irrigation schedule is of great importance for regional agricultural production. As a main grain production area of Shanxi Province, Fenxi Irrigation District (FID) was chosen to study the optimal irrigation amount based on the Agro-Hydrological & chemical and Crop systems simulator (AHC) model. The planting area ratio of maize, wheat and bean reached 93.3%. In this study, the AHC model was tested by the soil water content, crop yield data of maize, wheat and bean obtained from field experiments of 2008 and 2010, respectively. And the calibrated AHC model was used to predict the response of the maize, wheat and bean yield to irrigation amounts in different hydrological years. Results showed that the root mean square error (RMSE) of soil water content of winter wheat, maize and bean was 0.026 to 0.083 cm3 cm-3, the mean relative error (MRE) was -11.0 -7.5%, and the nRMSE was 9.1-33.3%. The determination coefficient R2 of simulated and measured yield of winter wheat, maize and bean reached 0.9818. Considering the yield and water use efficiency, the optimal irrigation amount of maize, wheat and bean were 354 mm, 327 mm, 228 mm for wet year, 369 mm, 380 mm, 247 mm for normal year, and 408 mm, 488 mm, 300 mm for dry year in the FID. © ASABE 2021 Annual International Meeting

Emitter clogging risk might be enhanced by the specific fertigation practice when applying saline water. Two stages of on-site drip irrigation experiments applying saline water were conducted to investigate the effects of the phosphorus (P) fertigation and combined P and nitrogen (N) fertigation and the water salinity on emitter clogging when using a plain channel emitter and a labyrinth emitter. During stage one, the water-soluble phosphate fertilizers monoammonium phosphate (MAP), diammonium phosphate (DAP), and urea phosphate (UP) were tested in comparison with a control treatment without fertigation (CK). During stage two, four combined P and N fertigation practices were tested by mixing one phosphate fertilizer (MAP or DAP) with one N fertilizer (urea (U) or ammonium sulphate (AS)). Four levels of water electrical conductivity measuring about 0.5 (groundwater, G), 2 (S2), 4 (S4), and 6 (S6) dS m−1 were tested at both experimental stages. The discharge rates of the emitters were measured following every other two fertigation events during stage one and following each fertigation event for stage two. At the end of the experiments, several representative emitters were sampled to measure the dry weight and the chemical constituents of the clogging substances in the emitters. The results demonstrated that the P fertigation with a weak or a slightly stronger acidic fertilizer such as MAP or UP reduced the emitter clogging effectively during groundwater application. For saline water application, the emitter clogging clearly increased with the water electrical conductivity. Phosphorus-coupled nitrogen fertigation accelerated the precipitation of phosphate sediments greatly when either groundwater or saline water was applied. In fact, the precipitation of phosphate sediments exceeded 80% of the dry weight in the emitters under saline water irrigation. Rapid development of emitter clogging occurred for both types of emitters when saline water with electrical conductivity higher than 4 dS m−1 was applied under phosphorus-coupled nitrogen fertigation. The phosphorus-coupled nitrogen drip fertigation should be applied with cautious when applying saline water with electrical conductivity higher than 4 dS m−1. Fertigating with nitrogen fertilizers along with acid phosphate fertilizers together is a promising way to alleviate the emitter clogging caused by the ion components in saline water. © 2020, Springer-Verlag GmbH Germany, part of Springer Nature.

研究自2016年开始执行以来，在城郊再生水安全高效灌溉标准化技术模式方面，着重考虑再生水灌溉条件下的病原体污染风险、滴灌系统堵塞机制及其控制方法和再生水灌溉养分有效性，开展了再生水灌溉草坪试验、滴灌系统堵塞及其控制试验和再生水灌溉大田试验，主要进展情况如下:(1)揭示了喷灌和地下滴灌等不同灌溉形式下大肠杆菌(E.coli)在作物和土壤中的分布特性及其衰减规律，提出了采取加氯等措施以降低再生水灌溉条件下的病原体污染风险的技术模式;(2)对比了不同类型滴灌灌水器的化学堵塞特性，分析了水质和加氯处理对堵塞的影响机制，提出了针对不同水质的灌水器加氯加酸处理方案;(3)研究了再生水滴灌和加氯处理对土壤酶活性、作物吸氮量和产量的影响，提出在田间降雨作用下对于中等耐氯作物(如玉米),生育期内采取加氯措施不会对土壤环境及作物生长造成明显负面影响;(4)构建了基于EPANET 2.0软件构建了再生水滴灌管网氯衰减模型，模拟分析了初始投加氯浓度及管网规模对再生水滴灌管网氯衰减的影响，提出了基于余氯分布均匀特征为约束条件下的滴灌系统设计方法;(5)研究了再生水灌溉条件下土壤氮磷养分时空动态变化规律，评价了再生水滴灌技术参数及水肥管理措施对水肥利用效率的影响，提出了高效的再生水滴灌技术模式。 Since 2016,there years of experiments have been conducted to evaluated the effects of technical parameters of drip irrigation on the risk of pathogen pollution,emitter clogging,and the effectiveness of nutrients under reclaimed water irrigation.The main results are as follows:(1)the distribution and attenuation of Escherichia coli(E.coli)in crops and soil under different irrigation methods such as sprinkler irrigation and drip irrigation were revealed.Adding chlorine to irrigation water was recommended to reduce the risk of pathogen pollution under the condition of reclaimed water irrigation.(2)The effects of water quality,emitter types,and chlorination methods on emitter clogging were evaluated while different scheme of chlorine application methods were put forward corresponding to different water quality of reclaimed water.(3)The effects of chlorine treatment on soil enzyme activity,crop nitrogen absorption and yield were studied.It is proposed that the chlorination did not cause a substantial chlorine accumulation in the root zone.The enzyme activities for sewage application with chlorination was slightly lower than those for the reclaimed water application without chlorination.(4)A model simulating the hydraulic performance and residual chlorine transport,attenuation and distribution in a drip irrigation system was constructed using the EPANET software package.A design method of the drip irrigation system based on the uniform distribution of residual chlorine was put forward.(5)The temporal and spatial dynamic changes of soil nitrogen and phosphorus contents were studied under reclaimed water and groundwater irrigation.An technology mode was put forward for efficient use of reclaimed water.

Drip irrigation with saline water has been recognized as one effective method to alleviate the current worldwide water shortage. However, emitter clogging risk could be increased substantially by the complex of ions in saline water. Drip fertigation might aggravate the risk when applying saline water. On-site drip irrigation experiments with a daily operation of 8 h applying saline water were conducted using a plain channel emitter and a labyrinth emitter to investigate the effect of the phosphate fertilizers and the water salinity on emitter clogging. Eight fertigation events were conducted with intervals of 2 operation days. Three typical water-soluble phosphate fertilizer of Monoammonium Phosphate (MAP), Diammonium Phosphate (DAP), and Urea Phosphate (UP) and four levels of water salinity of 0.5 (groundwater, G), 2 (S2), 4 (S4), and 6 (S6) dS m-1 were tested. The treatments without fertigation (NP) for each water salinity level were considered as control. The discharge rates of emitters were measured followed by every 2 fertigation events. Several representative emitters were sampled to measure the dry weight of clogging substances (DW) at the end of the experiments. The plain emitters demonstrated significantly better anti-clogging performance than the labyrinth emitters. For the G treatments, emitter clogging occurred gradually with increasing number of fertigation events. Moreover, the decline rates of the discharge ratio (Dra) were in the order of G-DAP > G-NP > G-MAP > G-UP. The average Dra over the two types of emitters at the end of experiments were 0.56, 0.79, 0.86, and 0.97 for the G-DAP, G-NP, G-MAP, and G-UP treatments, respectively. The better anti-clogging performance of the MAP and UP fertigation could be attributed to the relatively lower pH (6.5 for G-MAP and 2.7 for G-UP, respectively) of the fertilizer solution. Emitter clogging increased greatly with increasing water salinity. For the S2 and S4, the Dra of the treatments with MAP or DAP applied generally decreased to less than 0.6 after 4 fertigation events. However, much slighter emitter clogging was observed for the treatments with UP applied while the average Dra over the two types of emitters at the end of experiments were 0.96, 0.90, and 0.79 for the S2-UP, S4-UP, and S6-UP, respectively. The ANOVA results indicated that the phosphate fertilizer type and water salinity imposed significant effect on the Dra at a significance level of 0.05. In addition, the DW were generally negatively correlated with the Dra for all treatments. Therefore, the strategies for protecting emitter clogging should be developed through comprehensively considering water quality and phosphate fertilizer type used. Using acid phosphate fertilizer is a promising way to alleviate the emitter clogging caused by iron components in saline water. © 2019 ASABE Annual International Meeting. All rights reserved.

The trend of secondary soil salinization when shifting traditional surface irrigation to advanced drip irrigation in the arid region has been increasingly concerned in recent decade in China. It remains unclear whether a lower system uniformity due to increasing lateral length leads to salt harmfulness and reduced crop yield. Field experiment was conducted during the growing season of cotton in Xinjiang to evaluate the effects of drip system uniformity and irrigation amount on the dynamics of water and salt in soil and yield under mulched drip irrigation. Three Christiansen uniformity coefficients of 0.95 (C1), 0.89 (C2), and 0.63 (C3) were obtained by using different lateral lengths of 40 m, 80 m, and 120 m, respectively. Three irrigation upper limits of 90% (I1), 100% (I2), 110% (I3) of field water capacity along with a trigger point of 60% - 70% of field water capacity were used to determine irrigation amount. The dynamics of water and salt in soil and cotton yield were observed for all treatments. The results indicated that soil water content in the 100 cm profile tended to decrease with an increasing distance from the lateral inlet for the C2 and C3 treatments while approximately similar soil water contents along the lateral for the C1 treatments were observed during the irrigation season. Similarly, the soil salt content for the C1 treatments demonstrated little change along the lateral, but obvious variation in soil salt content along the lateral was observed for the C2 and C3 treatments. In general, the mean soil salt content values in the 100 cm profile decreased slightly with time for all treatments during the irrigation season. A slight increase in soil salt content, however, was observed from the late flowering stage to the boll opening stage during which no irrigation was applied. The soil salt content in 100 cm profile was slightly greater for the C1 treatments than the C2 and C3 treatments during the irrigation season, being 7.69 g kg-1, 6.22 g kg-1, and 6.02 g kg-1 for the C1, C2, and C3 treatments, respectively. For a given irrigation uniformity, the soil salt content in 100 cm profile for the I3 treatments was lower than that for I1 and I2 treatments. The ANOVA results indicated that drip system uniformity imposed significant effect on cotton yield although no obvious difference in cotton lint yield was observed between C1 and C2 treatments. Moreover, cotton yield showed an increasing trend with irrigation amount for a given system uniformity. Our results recommended that a medium uniformity along with adequate leaching is a promising practice to maintain sustainable production in the arid region. © 2019 ASABE Annual International Meeting. All rights reserved.

Field experiments on maize (Zea mays L.) under surface drip irrigation were carried out during two consecutive growing seasons to examine the influence of water quality (groundwater and secondary sewage effluent) and nitrogen (N) application rate on growth and yield, N agronomic efficiency, and N availability of effluent. Pot experiments were conducted using the N-15 isotope tracer method and the fertilizer equivalence (FE) approach to provide direct evidence of the effluent N availability derived from the field experiments. Four N application rates ranging from 0 to 180 kg ha(-1) for field experiments and from 0 to 2.64 g pot(-1) (0 to 210 kg ha(-1) equivalent) for pot experiments were investigated with secondary sewage effluent (SW) and groundwater (GW). Results showed that either irrigation with sewage effluent or increasing N application rates from 0 to 120 kg ha(-1) were conducive to increasing maize productivity. Nonetheless, SW irrigation reduced the agronomic efficiency of applied N compared to GW irrigation supplemented with fertilizers, suggesting greater potential N losses under SW irrigation. Effluent N that was absorbed by maize was negatively correlated to increasing N application rates. On average, the N contained in effluent was only 51% to 69% as available as an equivalent application rate of urea N in improving maize production. The organic N fraction of effluent (20%) and higher potential N losses from SW irrigation primarily explained the lower effluent N availability in comparison to fertilizer urea. Overall results recommended an economic and ecological N application rate of 107 kg ha(-1) for maize under drip irrigation when applying SW, with an approximate 14% urea N reduction to attain a satisfactory yield in comparison to GW irrigation.

The risk and inducing mechanism of emitter clogging vary with the types of ions in the irrigation water. The effectiveness of chlorination and acidification treatments in reducing emitter clogging has seldom been comparatively studied. The objective of this study was to quantify the influence of chlorination and acidification in reducing clogging in emitters applying secondary sewage effluent with different types of ions. Two types of emitters with plain channels and one type of emitter with a labyrinth structure were selected to investigate the clogging control strategy by measuring the dry weight of biofilm substance (DW) and the organic matter fraction in the biofilm and analyzing the mineral constituents of the clogging solids and the exfracellular polymeric substance (EPS) of the attached biofilm. In general, chemical injection decreased the DW and EPS, resulting in less clogging than in emitters without chlorine and acid injection. For the emitter structures tested, chemical injection was more effective in controlling clogging in plain channel emitters than in labyrinth emitters. Different chemical injections produced similar mineral constituents of the clogging solids: quartz, calcium + magnesium carbonate, silicate, and iron oxide. Chlorine injection interval and targeted acidification pH are both important parameters in determining chemical injection schemes. Under the experimental conditions, weekly chlorination of sewage effluent acidified to pH 6.5 was more effective in reducing the growth and reproduction of microorganisms and the precipitation of solid particles in the drip emitters when applying sewage effluent containing high iron + calcium. However, when sewage effluent containing high calcium was used, acidification was more effective in removing the chemical precipitates. We conclude that the selection of chemical treatment strategies should consider the constituent ions in the sewage effluent.

Chlorination is an effective method to prevent and reduce emitter clogging caused by algae and bacteria in drip irrigation system. The optimal chlorination schemes should be developed to alleviate the potential negative effect of chlorination on soil properties and crop growth. A 2-year experiment was conducted to evaluate the effects of chlorine injection concentrations and duration on soil urease and alkaline phosphatase activities and production of maize for drip irrigation while applying secondary sewage effluent. The experiments were designed with injection concentrations of free chlorine residual at the end of laterals ranging from 0 to 8mgL(-1) and injection duration ranging from 0.5 to 3h for each irrigation event. The control experiments with groundwater were applied in both seasons. Sewage application increased the residual Cl in soil while chlorination did not cause a substantial chlorine accumulation in the root zone. Compared to enzyme activities measured prior to sowing, soil enzyme activities were generally enhanced by sewage application with or without chlorination. The effects of chlorine concentration and injection duration on plant biomass, nitrogen uptake, enzyme activities, and yield of maize were insignificant although chlorination weakened the increment of soil enzyme activities to some extent. The yield of maize ranged from 12.1 to 13.3Mgha(-1) and from 10.1 to 10.7Mgha(-1) in the 2015 and 2016 seasons, respectively. For the treatments with chlorine injected, the yield of maize peaked at 0mgL(-1) in 2015, while the yield of maize peaked at 1.3mgL(-1) of free chlorine residual at the end of laterals and the 3h chlorine duration in 2016. The results suggested that chlorination is safe for field crops with precipitation leaching.