Field calibration of an impedance soil water probe for the shallow seedbed across field topography

Impedance soil water probes enable frequent and non‐destructive determination of soil water status in situations where gravimetric soil sampling is too demanding of time and sampling space. The ThetaProbe is an impedance soil water probe requiring calibration for local soil conditions, because measurement accuracy can be affected by properties of the soil. Often, only a single calibration is performed for an experimental site. An experiment investigating the seedbed to 75‐mm depth across a field topography with variable soil properties was examined to determine which soil properties affected the calibration of the ThetaProbe, and if soil‐specific calibration was required to derive suitable estimates of the water status in the experiment. Experimental factors examined included hillslope aspect, hillslope position, crop residue and soil depth. Soil properties, other than volumetric water content, significantly affecting the probe measurements were bulk density, electrical conductivity and temperature. The probe underestimated soil water at very low water contents, and overestimated soil water at contents greater than 11 m³ m^?3, compared with gravimetric measurements. A single calibration, not corrected for hillslope position at a water content of 20 m³ m^?3, overestimated water content by 0.02 m³ m^?3 in the summit hillslope position and underestimated water content by 0.04 m³ m^?3 in the toeslope position. A single calibration, not corrected for soil depth at a water content of 20 m³ m^?3, overestimated water content by 0.02 m³ m^?3 in the 0‐ to 25‐mm soil layer and underestimated water content by 0.03 m³ m^?3 in the 50‐ to 75‐mm layer. The complexity of microsites in a shallow seedbed requires soil‐specific calibration in field experiments containing heterogeneous soil properties.     

肥床旱育水稻恶苗病的发生原因初探

检测了昆山，常热，吴县等地的自然稻种，其恶苗病菌带菌率为１００％．播前采集田间水妥病残体，共分离了５２个镰刀菌株，恶苗病菌占３．８５％，是其次是病源，振荡培养试验表明，供氧条件好有于恶苗病菌的生长繁殖，温室模拟肥床肥旱育和常规育种结果表明，无论接菌与否，前者秧苗恶苗病均重于后者，田间调查表明，药剂浸后后不经催芽或催至露白播种能有效控制苗期恶苗病。     

烤烟托盘水床育苗大田示范效应研究

对烤烟托盘水床育苗和常规（营养袋）育苗的烟苗素质及其大田生长发育情况和产量、质量进行了对比分析，结果表明：托盘水床育苗烟苗素质优于常规育苗；托盘水床苗移栽大田后生长迅速，植物学性状优于常规苗，并对烟株上部叶开秸开片作用明显，收获叶片平均增加2片左右；托盘水床苗抗花叶病效果明显，且大田生育期延长，对叶片干物质的形成和积累有利；其产量、产值、均价和上等烟比例等各项指标均优于常规苗，特别是产值和上等烟比例提高幅度较大，分别达到25.52%和24.15%。     

免耕直播下秸秆还田方式对夏玉米苗期生长的影响

为了研究小麦秸秆还田后玉米免耕播种方式下种床秸秆处理对玉米苗期形态特征、群体整齐度的影响,于2018年6月在安徽宿州市皖北综合试验站进行了田间试验,共设置条带浅耕防堵(ST-X)、侧抛覆秸防堵(SMT-Y)、条带立式浅耕防堵(ST-Z)和条带深松破茬(SST) 4种不同免耕播种方式,测定分析了种床土壤平整度S_(MN)、横向最大垂直高度差Δh、苗期形态特征(叶龄、株高、茎粗、单株根系长)以及苗期群体整齐度Q。结果表明,相较于条带深松对照组SST,ST-X、SMT-Y、ST-Z的土壤平整度平均值分别降低7. 67、16. 33、11. 00 mm,种床土壤平整效果排序为:SMT-Y、ST-Z、ST-X、SST;在相同田间管理条件下,相较于SST,ST-X、SMT-Y、ST-Z的苗期群体整齐度分别提高4. 34、11. 10、10. 18个百分点;随着种床土壤平整效果变差,玉米苗期株高稳定性变异系数呈现递增趋势,其群体整齐度从大到小顺序为:SMT-Y、ST-Z、ST-X、SST;侧抛覆秸防堵(SMT-Y)方式种床秸秆覆盖量大,玉米种子发芽后难以突破秸秆层,苗期的平均株高、茎粗、根系长度均最低。相关性分析结果表明,S_(MN)、Δh与Q之间均呈线性显著负相关关系(P 0. 01),决定系数分别为0. 963和0. 914。综上所述,种床土壤平整效果有助于提高玉米苗期群体整齐度; 4种免耕播种方式中,条带立式浅耕防堵(ST-Z)的免耕播种方式,能够有效改善耕层土壤结构,提供清洁平整的种床,抑制种沟积水涝渍,且促进苗期生长,是淮北平原砂姜黑土区夏玉米免耕直播最适宜的种床秸秆处理方式。     

油菜基质块移栽机苗床带整备装置设计与试验

针对现有油菜基质块苗移栽机开沟装置作业存在沟宽稳定性差、沟底面平整度低、土壤扰动大等现象,导致立苗率低、覆土作业难度大等问题,基于船式开沟器腔体大以及芯铧式开沟器作业构建宽苗床、平沟底特点,结合类铧式曲面衔接过度,设计了一种适用于油菜基质块苗移栽机苗床构建的苗床带整备装置。建立了土壤与整备装置互作力学模型,确定了苗床带整备装置构建稳定苗床的主要结构参数。以整备装置作业速度、作业深度、类铧式曲面前端宽度、刃口角为因素,以土壤扰动量、沟宽变异系数为评价指标,利用EDEM开展四因素三水平二次正交组合仿真试验,试验结果显示：作业深度为41 mm、作业速度为0.52 m/s、类铧式曲面前端宽度为40 mm、刃口角为61o时土壤扰动量较小且沟宽变异系数较小;较优参数组合下台架试验得出土壤扰动量为13.01 cm²,沟宽变异系数8.52%。田间试验结果显示：安装在移栽单元上的苗床带整备装置相较船式开沟器的载苗基质块立苗率增加2.09百分点,沟宽变异系数减少13.3%,土壤扰动量减少20.9%,沟底面紧实度增加28.7%,满足油菜基质块苗机械移栽苗床构建要求。     

油菜机械直播铲锹式种床整备机振动特性分析与结构改进

针对油菜机械直播铲锹式种床整备机作业时机组振动大,易导致关键零部件磨损、降低整机可靠性的问题,该研究利用Coco-80动态信号测试分析系统对机组在怠速和田间作业工况下的振动加速度进行测试,采用时域和频域分析相结合的方法,确定了两种工况下不同位置测点的振动加速度大小及机组主要激振源,并以此为依据提出了通过优化曲柄相位角排列方式降低整机所受合惯性力、合惯性力矩,减小铲锹式种床整备机振动的方案。进一步地,基于质量代换法建立了整机共10组曲柄摇杆机构的惯性力、惯性力矩受力模型,运用MATLAB软件分析得出整机受到合惯性力、合惯性力矩最小的曲柄相位角排列方式,在此排列方式下,整机合惯性力基本平衡,绕x、y轴的合惯性力矩绝对值均值分别降低了37.40%、30.09%。对改进后的机组在振动较大处采集加速度时域信号,与改进前相比,测点振动总量在怠速和田间作业工况下分别降低了36.42%、31.97%。该研究可为基于平面连杆机构群的农业机械减振研究提供参考。     

Impact of clod (aggregate) size on evaporation rate and soil moisture profile during the drying process

Large clods (centimetres in size) can be formed by tillage in clayey paddy fields where upland crops are planted. These clods cause early water depletion near the soil surface, which decreases crop germination and emergence rates. Because of the difficulty in reducing clod size, desiccation damage to seeds can be avoided by adjusting the seeding depth based on the clod size-dependent soil moisture profile. This study aimed to clarify the effect of clod size on (1) the evaporation rate (E) and soil moisture profile and (2) the mobility of soil water during the drying process. Evaporation experiments were conducted in an air-conditioned greenhouse with natural light using cylindrical columns filled with artificially made clods 3 (L columns) and 1 cm (S columns) in diameter. We measured E, potential evaporation rate (PE), and total soil moisture content (w_tot) throughout the experiment and the soil moisture profiles at the end of the experiment. The water diffusivity (D_w) and apparent vapour diffusion coefficient (d_vap) were calculated as the mobility of soil water and water vapour, respectively. We found that w_tot was lower in the L column than in the S column, although not at the onset of the experiment. At the end of the experiment, the soil moisture content was lower in the L column than in the S column throughout the soil layer. In contrast, E/PE was higher in the L column than in the S column throughout the experiment and even at the same w_tot. Regarding mobility, D_w was slightly greater in the L column than in the S column in the soil moisture content range, where vapour movement could be greater than liquid water movement. In addition, the ratio of d_vap to the diffusion coefficient of water vapour in soil was higher than unity in both columns and was 2.4–3.2 times higher in the L column than in the S column. In summary, larger clods caused a higher evaporation rate and lower soil moisture content, owing to the increased enhancement of water vapour movement probably induced by wind.     

小白菜复式播种机犁旋辊压驳岸型种床起垄装置研究

针对长江中下游地区小白菜直播作业时,因土壤含水率波动大导致播种机后托板起垄种床厢面不平整的问题,提出了适应小白菜生长的犁耕开沟、旋耕碎土和主动辊压式起垄与平整结合的联合耕整作业方案,结合小白菜种床合理构建技术及大田旱作耕整作业要求,设计了一种小白菜复式播种机犁旋辊压驳岸型种床成型装置。根据土壤挤压和垄体曲面成型原理,分析了种床辊压成型的动力学原理,确定了起垄辊的主要结构和工作参数。田间起垄试验表明,整机作业速度为2.0~5.0km/h,作业后垄体的垄高合格率、垄顶宽合格率和垄间距合格率分别为90.00%、93.33%和96.67%;双垄垄顶处的土壤坚实度稳定性系数均不低于92.36%,双垄垄壁处的土壤坚实度稳定性系数均不低于92.53%;垄顶厢面地表粗糙度的最大差值为2.19mm。采用驳岸型种床装置垄播的小白菜单行苗数变异系数及各行苗数一致性变异系数均低于10%,满足小白菜直播农艺要求。     

An investigation to enhance understanding of the stimulation of weed seedling emergence by soil disturbance

Enhanced understanding of soil disturbance effects on weed seedling recruitment will help guide improved management approaches. Field experiments were conducted at 16 site‐years at 10 research farms across Europe and North America to (i) quantify superficial soil disturbance (SSD) effects on Chenopodium album emergence and (ii) clarify adaptive emergence behaviour in frequently disturbed environments. Each site‐year contained factorial combinations of two seed populations (local and common, with the common population studied at all site‐years) and six SSD timings [0, 50, 100, 150, 200 day‐degrees (d°C, base temperature 3°C) after first emergence from undisturbed soil]. Analytical units in this study were emergence flushes. Flush magnitudes (maximum weekly emergence per count flush) and flush frequencies (flushes year^?1) were compared between disturbed and undisturbed seedbanks. One year after burial, SSD promoted seedling emergence relative to undisturbed seedbanks by increasing flush magnitude rather than increasing flush frequency. Two years after burial, SSD promoted emergence through increased flush magnitude and flush frequency. The promotional effects of SSD on emergence were strongest within 500 d°C following SSD; however, low levels of SSD‐induced emergence were detected as late as 3000 d°C following SSD. Accordingly, stale seedbed practices that eliminate weed seedlings should occur within 500 d°C of disturbance, because few seedlings emerge after this time. However, implementation of stale seedbed practices will probably cause slight increases in weed population densities throughout the year. Compared with the common population, local populations exhibited reduced variance in total emergence measured within sites and across SSD treatments, suggesting that C. album adaptation to local pedo‐climatic conditions involves increased consistency in SSD‐induced emergence.