Performance evaluation of venturi aeration system

The venturi aeration is an effective practice to increase the dissolved oxygen accessibility in the water bodies. This study aims to optimize the various geometrical parameters of the venturi aeration system. A non-dimensional technique was applied to find the optimum performance of various geometric parameters i.e. throat lengths (t_l), number of air holes (N), and converging and diverging angles (α and β). These experiments have been carried out using 1124 L capacity of tank having dimensions of 105 cm long, 105 cm wide and 102 cm deep. The experiments were conducted at a constant flow velocity of water (1.096 m/s) with varying throat length (t_l = 20–100 mm keeping 20 mm as interval between two consecutive length), number of air holes (N = 1–17 at an equal hole to hole distance of 5 mm between them), and converging and diverging angles (α and β = 10°, 15°, 20° and 25°). Multiple non-linear regression equations were also developed from the linear relation with the dependent variable (Non-dimensional form of standard aeration efficiency, NDSAE) and independent variables (t_l and N). With the geometrically optimized venturi aerator the optimum performance was found for t_l =100 mm, N = 17, and α and β = 15°. The maximum value of standard oxygen transfer rate (SOTR) and standard aeration efficiency (SAE) obtained was 0.0216 kgO₂/h and 0.611 kgO₂/kWh respectively. From the non-dimensional study, it was found that the NDSAE is the function Reynolds number (Re) and Froude number (Fr). The simulation equations were developed on the basis of Re and Fr for NDSAE, and subjected to 7.378 × 10⁻⁶ < Re < 3.689 × 10^-5 and 0.163 < Fr < 0.817, respectively.     

水肥调控对滴灌马铃薯生长、品质及水肥利用的影响

研究生育期土壤水分下限调控和施肥对陕北榆林地区滴灌马铃薯生长、品质和水肥利用的影响,以期探寻马铃薯优质高产的水肥调控模式。以马铃薯紫花白为材料,分别在苗期、块茎形成期、块茎膨大期、淀粉积累期、成熟期设置3个土壤水分调控下限水平:W1(55%、60%、65%、55%、55%)、W2(65%、70%、75%、65%、65%)、W3(75%、80%、85%、75%、75%),4个施肥水平N-P_2O_5-K_2O (kg·hm~(-2))分别为F1(100-40-150 kg·hm~(-2))、F2(150-60-225 kg·hm~(-2))、F3(200-80-300 kg·hm~(-2))、F4(250-100-375 kg·hm~(-2)),共12个处理,在生育期内对马铃薯生长、产量及品质等指标进行观测,分析马铃薯各指标对水肥的响应机制。结果表明:(1)在同一施肥水平下,W2灌水处理的马铃薯生长、产量、品质、水肥利用效率(WUE)均显著高于W1和W3处理。W2处理的平均产量为43 187.15 kg·hm~(-2),比W1和W3分别增加了24.59%和5.26%,淀粉和维生素C含量分别增加了15.32%和6.37%,8.04%和4.66%,WUE分别增加了15.53%和7.54%,肥料偏生产力(PFP)分别增加了21.65%和4.41%。(2)在同一灌水水平下,F3施肥处理的马铃薯生长、产量、WUE均显著高于F1、F2和F4处理,淀粉含量和维生素C含量在F2处理最高。F3处理的平均产量为44 691.32 kg·hm~(-2),比F1、F2和F4处理分别增加了41.79%、10.98%和6.34%。WUE随施肥量的增加均呈抛物线变化趋势,PFP随施肥量增加呈减小趋势,F1处理的PFP平均为108.69 kg·kg~(-1),比F2、F3和F4处理分别显著增加了17.41%、41.06%和87.50%。(3)运用主成分分析法评价马铃薯品质表明,F3W2处理排名第一,是榆林地区马铃薯优质高产的最优水肥组合。     

不同氮效率型苜蓿氮素吸收差异与根系形态的关系及其对氮的响应

以高效型苜蓿（‘龙牧806’‘肇东苜蓿’）和低效型苜蓿（‘公农1号’‘陇东苜蓿’）为试验材料，采用营养液砂培法，在4个供氮量下（2.1，21，210和420 mg·L^-1），研究紫花苜蓿苗期氮素吸收、分配的氮效率型差异及其与根系形态之间的关系。结果表明高效型苜蓿品种的株高、地上生物量、根重、总根长和根体积均显著高于低效型品种（P<0.05）；供氮量较低时（2.1和21 mg·L^-1），高效型向根系分配了较大比例的氮素，而低效型则向地上部分配了较大比例的氮素，根系形态参数与总氮量呈显著正相关（P<0.05），且根重对氮素吸收的直接作用较大，直接通径系数是1.230和1.102。因此，在氮胁迫下，根系形态对氮吸收效率起重要作用，尤其是根系形态中的根重对其影响较大。     

Screening and identification of soybean varieties with high phosphorus efficiency at seedling stage

In order to simplify the workload and find a reliable method for screening soybeans with different phosphorus(P)efficiencies,47 soybean varieties were screened from 90 varieties according to yield under normal phosphorus,and 10 indicators including root phenotype,phosphorus utilization efficiency at the seedling stage and yield were measured.Through single-index cluster analysis,the performance value and relative value of the abovementioned indexes under low-phosphorus conditions were analyzed,and then,the combined indexes were analyzed by principal components method.The membership function method and the cluster analysis method was used to calculate and analyze the comprehensive score value.Three indexes of root P utilization efficiency(X₁),relative value of root P utilization efficiency(X₂),and root volume(X₃)under low P at the seedling stage were selected as the most consistent with the yield screening results under low P condition,and the mathematical model of the comprehensive score value was obtained:D=1.218X₁t 0.320X₂t 0.007X₃-0.664(P=0.000,R²=1.000).The comprehensive score can screen and identify the P efficiency of soybeans with fewer indexes in the early growth stages,which provides a more rapid and reliable mathematical model for screening and identifying a larger number of germplasm resources for P efficiency.     

京西稻的百年传承与发展

京西稻是清康熙、雍正、乾隆等亲自选育的优良品种,在与紫禁城并重的“三山五园”政治中心内外种植,具有多重价值属性,属于皇家御稻。从2000年起,基于北京水资源匮乏等原因,京西稻种植面积大幅度降至134 hm²左右,处于濒危状态。在保护传承过程中,京西稻入选中国重要农业文化遗产目录。在新修订的《北京历史文化名城保护条例》中,又将京西稻列入遗产保护目录。在海淀区,京西稻已经深入公园、学校、社区、酒店等地,在教育文化中发挥着农业以外的作用。     

不同氮效率油菜种质苗期氮吸收转运与利用差异研究

氮效率研究是油菜营养性状遗传改良的前提,为探究不同氮效率油菜种质苗期氮吸收、转运和利用的异同,以2个氮效率差异油菜种质H6（氮高效）和L18（氮低效）为供试材料,利用水培营养液设置正常氮（CK）和低氮（LN）2个氮浓度处理,培养14d后检测植株氮含量,计算氮累积量、氮转运系数和氮利用效率。结果显示,不同氮浓度处理对油菜苗期氮的吸收、转运和利用效率影响的差异达到极显著水平（P＜0.01）。与CK相比,LN处理的油菜生物量、氮含量和氮累积量均显著降低,而氮利用效率和根冠比显著提高;氮高效油菜种质H6的生物量、氮累积量、氮转运系数和氮生理利用效率均显著大于氮低效种质L18,分别为L18的2.07、1.42、3.23和1.56倍。从氮的吸收、转运和利用3个方面探讨了低氮胁迫处理下油菜种质苗期氮效率差异的原因,对深入开展油菜氮高效机理研究及油菜品种氮效率改良具有一定的指导意义。     

Preliminary assessment of large‐scale co‐culture of sandfish (Holothuria scabra) with the Babylon snail (Babylonia areolata) in earthen ponds and in raceways

Holothuria scabra (sandfish) and Babylonia areolata were trialed in two large‐scale co‐culture experiments. Experiment 1 assessed co‐culture in 4 × 400 m² earthen ponds where Babylonia were cultured in a central pen at a density of 400 individuals/m² with sandfish occupying the remaining pond space at 1.1 individuals/m². Sandfish grew from 18.20 ± 6.67 g to 119.03 ± 17.74 g in 92 days and Babylonia (fed trash fish in both experiments) grew from 0.90 ± 0.38 g to 4.93 ± 1.44 g, but Babylonia growth was not increased in co‐culture compared to monoculture. Water and sediment quality varied between co‐culture and monoculture ponds. Neither showed clear improvement due to sandfish culture. Experiment 2 compared non‐segregated sandfish‐Babylonia co‐culture with Babylonia monoculture in 20 m² concrete raceways. Sandfish were cultured at 2 individuals/m² and Babylonia at 300 individuals/m². Sandfish grew up to 1.91 g.day^?1 with 100% survival. Babylonia weight gain was significantly greater in co‐culture raceways (3.35 ± 0.64 g over 61 days), which was double that of Babylonia in monoculture. Substrate total N was reduced by 20% in co‐culture compared with monoculture (p = .032). This provisional study of commercial scale sandfish‐Babylonia co‐culture demonstrates culture compatibility, providing a basis for further system development.     

Maize harvest index and water use efficiency can be improved by inhibition of gibberellin biosynthesis

Possibilities to improve maize harvest index and nutrient utilization efficiency by application of plant growth regulators were investigated. In container experiments, the effects of different growth regulators on the development of the maize (Zea mays L.) cultivars Pioneer 3906 and Fabregas were tested. Paclobutrazol (PAC) and chlorocholine chloride (CCC), two inhibitors of gibberellin biosynthesis, as well as gibberellic acid (GA₃) were applied at growth stage V5. Three weeks after application of PAC, shoot growth of both maize cultivars was strongly affected with a significant decrease in plant height in the PAC treatment by 44% and 36% for Pioneer 3906 and Fabregas, respectively. The growth‐retarded plants had higher leaf areas and reduced transpiration rates. The higher shoot growth after GA₃ application was accompanied by a reduction in leaf area and an increase in transpiration rate during 1 week before anthesis. CCC treatment showed no significant effects on plant height, leaf area and transpiration rate. The PAC‐treated cultivar Pioneer 3906 produced several cobs per plant, which were mainly barren at maturity. However, PAC application to Fabregas resulted in just one cob per plant with good kernel development and a grain yield, which was not significantly reduced in comparison with the control. With this similar grain yield in combination with a straw yield decrease of 32%, the harvest index was significantly improved by 12%. In addition, with PAC‐treated Fabregas plants, a 19% increased water use efficiency of the grain (WUE_grain) during the critical period of kernel setting was achieved. In this maize cultivar, CCC application also improved harvest index by 5%, but no effect on WUE_grain occurred. GA₃ treatment decreased harvest index of both maize cultivars, and it either reduced WUE_grain (Pioneer 3906) or showed no effect (Fabregas). Utilization efficiencies of N, P and K were not increased with growth regulator application, even in the PAC‐treated Fabregas plants with a significantly improved allocation of assimilates to the grain, mirrored by the higher harvest index. The results indicate that fertilizer applications must be adjusted to the reduced demand of growth‐retarded plants, most likely leading to higher nutrient utilization efficiencies.     

Straw mulching with fertilizer nitrogen: An approach for improving crop yield,soil nutrients and enzyme activities

Field experiments were conducted to study soil properties, soil enzymes activities, water use efficiency (WUE) and crop productivity after six years of soya bean straw mulching in the semi‐arid conditions of China. The experiment included four treatments: CK (Control), N (240 kg N ha^‐1), H (soya bean straw mulching at half rate 700 kg ha^‐1 with 240 kg N ha^‐1) and F (soya bean straw mulching at full rate 1,400 kg ha^‐1 with 240 kg N ha^‐1). Soil organic carbon (SOC), soil labile organic carbon (LOC), soil available N (AN), available P (AP) and enzyme activities were analysed after wheat harvesting in 2016 and 2017. Results show that straw amounts had positive effects on the soil fertility indices being higher for treatment F. The SOC, LOC, AN, AP and enzyme activities (i.e. saccharase, urease and alkaline phosphatase) were in the order of F > H > N > CK. High wheat grain yield and WUE were observed for F treatment. A total of six years mulching along with 240 kg ha^‐1 nitrogen fertilizer application is sufficient for wheat yield stability and improving soil properties except urease activities in the semi‐arid condition of China. However, the straw mulching amount should be further studied with minimum nitrogen fertilizer for an environment‐friendly and effective approach for improving the soil biological properties with adequate crop production on a sustainable basis in the semi‐arid region of China.