The effects of density and artificial substrate on intensive shrimp Litopenaeus vannamei nursery production

Recirculating aquaculture systems (RAS) can be installed indoors, allowing year-round production of tropical animals in nearly any climate. A nursery phase is commonly used in Litopenaeus vannamei production since it allows for enhanced biosecurity and better quantification of animals while reducing space requirements. However, it is unclear whether animal density and inclusion of artificial substrate may improve shrimp performance during the nursery phase. In this experiment, we compared shrimp production parameters in two stocking densities with or without the use of an artificial substrate by creating four treatments: low-density LD; 1500 PL/m⁻³, low-density with substrate LDS, high-density HD; 3000 PL/m⁻³), and high-density with substrate (HDS). The LDS and HDS treatments included 0.46-m² of high-density polyethylene 2.5-cm mesh as a substrate, which increased the tank surface area by 21 %. Each treatment was randomly assigned to four 160-l culture tanks, each with a biofilter. The shrimp had an initial weight of 4 mg and were grown for 50 days. The low-density treatments had significantly higher dissolved oxygen (DO) and pH than the high-density treatments (P ≤ 0.001). Specifically, LDS had the highest DO and pH followed by the LD, HD, and HDS treatments, respectively. High-density treatments had significantly higher NO₂-N levels than low-density treatments during week 2 of the experiment when an unusually high concentration of nitrite was observed. FCR was significantly lower in both low-density treatments than in high-density treatments. At harvest, the total biomass (kg m⁻³) was significantly higher in high-density treatments than in low-density treatments (P ≤ 0.001), and the HDS treatment had a significantly greater biomass output than HD. Producers should consider artificial substrate and higher densities during nursery production to maximize shrimp production; however, the effects on water quality should also be taken into account.     

扁穗牛鞭草人工草地中空心莲子草杂草防除效果研究

利用水花生净除莠剂可有效地防除扁穗牛鞭草人工草地中的杂草空心莲子草,平均株防效达26.7%～99.8%,并且在较高防效下药剂对扁穗牛鞭草较为安全。在空心莲子草杂草生长盛期,14%的水花生净乳油以浓度为675ml/hm2～900ml/hm2、各处理对水600ml的防除效果最佳,可达到100%。综合考虑,以525ml/hm2～675ml/hm2的浓度为宜。     

蒜地杂草的化学防除（上）

论述了我国蒜地除草剂应用概况，华东地区蒜地杂草有２０科５４种，组成５种不同杂草种群生态区。蒜草醚、旱草灵、乙草胺、恶草灵等对不同品种大蒜的安全性测定结果，蒜草醚、恶草灵、旱草灵安全系数４，乙划是胺，大惠利安全系数为２，嘧黄隆不可在大蒜地应用。     

萌前型除草剂对草坪草的影响和杂草防除研究

通过盆栽试验研究了4种萌前型除草剂(禾草净、农思它、施田补、乙草胺)对草坪草生长的影响和杂草防除效果。试验结果表明:除草剂对草坪草生长有不同程度的影响,其中乙草胺对草坪草影响最大,产生了伤害作用,不宜在草坪中使用;各种除草剂对杂草都有不同程度的防除效果,其中农思它和禾草净效果较好,乙草胺对杂草的防除效果最差。     

苏南丘陵区秋播苜蓿适用伴生作物筛选试验

为解决苏南丘陵区苜蓿苗期的杂草问题,从保护播种入手,在多年生黑麦草、一年生黑麦草、黑麦、小黑麦四种作物共五个品种中寻找适宜的伴生作物.通过对产量、株高、杂草率等多个指标测定分析,筛选出中新830小黑麦、赣选一号黑麦草适于用作苜蓿播种的伴生作物,同时获得两个苜蓿存活率最高的处理：苜蓿（15kg/hm^2）＋中新830小黑麦（150kg/hm^2）撒播及苜蓿（18 kg/hm^2）＋中新830小黑麦（250kg/hm^2）30cm条播.试验还表明撒播方式下,苜蓿播量与其竞争力不成正比。     

Reduced paraquat translocation in paraquat resistant Arctotheca calendula (L.) Levyns is a consequence of the primary resistance mechanism, not the cause

Resistance to paraquat has been studied in detail in many weed species for more than a decade, with the precise mechanism of resistance still unclear. Several studies have indicated that reduced movement of the herbicide to the site of action in the chloroplast is at least partly responsible for endowing resistance. Although paraquat translocation studies have been performed in the past it has been rare for these studies to have been conducted on whole plants in the light, despite early observations which clearly showed that paraquat translocation is minimal unless treated plants are exposed to light. This study has addressed this issue in Arctotheca calendula by tracing the movement of ¹⁴C-paraquat in resistant and susceptible plants in both the dark and light. Differences in paraquat translocation between the resistant and susceptible biotypes of A. calendula were only observed when treated plants were exposed to light. It was observed that paraquat translocation was significantly reduced in the resistant compared to the susceptible biotype when plants were exposed to light but not in the dark. It is postulated that paraquat translocation is dependent on light mediated damage. As paraquat-induced damage is less severe in paraquat resistant plants, overall paraquat translocation is reduced in the resistant biotype.     

不同饲养密度对鳝苗的生长性能研究

本试验以水蚯蚓作为饵料,研究了60日龄鳝苗不同密度下的增重、存活率及饵料转化率。试验分3个密度组,其对应的密度分别为2000尾/m2、3000尾/m2、4000尾/m2,每个密度组设4个平行;试验时间为30d。结果表明:在本试验条件下,3个密度组鳝苗的增重率、存活率随着密度的增大呈下降趋势,而其饵料系数随着密度增大而增大;其中在4000尾/m2的密度下,鳝苗的增重率最低,仅为1.12±0.13;饵料系数最高,为5.71±1.37。     

除虫菊地上部分水浸液对杂草种苗生长的影响

采用室内培养皿法,测试除虫菊地上部分水浸液对田间常见6种杂草种苗生长的影响。结果表明:不同质量浓度水浸液对杂草种苗生长的抑制作用依质量浓度梯度存在差异,除播娘蒿外其他5种总体均表现"低促高抑"趋势,在最高质量浓度0.03g·mL-1处理下,抑制作用最强;杂草种苗所受抑制作用大小依受体杂草种类存在差异,总体抑制作用由大到小依次为播娘蒿泽漆雀麦婆婆纳反枝苋野燕麦;除虫菊地上部分水浸液对试验杂草生理代谢影响测试表明,高质量浓度水浸液处理下,杂草幼苗受氧化胁迫严重。双子叶杂草较单子叶杂草对水浸液更敏感。     

Four years validation of decision support optimising herbicide dose in cereals under Spanish conditions

The Danish decision support system Crop Protection Online (CPO) optimises herbicide weed control. CPO recommends specific herbicide solutions to achieve a required level of control. The aim is to apply herbicides as little as possible but as much as necessary. CPOWeeds is a version of CPO adjusted to conditions in North-eastern Spain. The predicted efficacies and the yield obtained with CPOWeeds were validated in winter cereal field trials from 2010 to 2013. All CPOWeeds treatments were related to the efficacies obtained with standard herbicide treatments decided upon by local advisors. The predictions from CPOWeeds were compared to the actually achieved efficacies in the field trials for the nine weed species at different developmental stages and for 84.2% of the comparisons the obtained efficacies were equal to or higher than predicted. The average difference between predicted and observed efficacies was 2.35 percentage points. Yield was measured in three trials and the recommendations from CPOWeeds were maintaining yield. There were two situations where CPOWeeds were performing suboptimal. One is in the early weed growth stages, as the model is not yet prepared to account for water stress on root action herbicides applied at 10-11 BBCH. The second situation was in fields with a prior unidentified population of resistant Alopecurus myosuroides. For key species in winter cereals in Spain, such as Avena sterilis, Lolium rigidum and Papaver rhoeas, CPOWeeds achieved a satisfactory control level. It was concluded that the use of CPOWeeds allowed optimisation of the herbicide application with a very high robustness. The recommendations were satisfactorily for the conditions of the Northeast of Spain and have the potential to decrease the amount of applied herbicides by at least 30%. Therefore, it can be an important tool in Integrated Weed Management.     

Biology,impact, and management of Echinochloa colona (L.) Link

Echinochloa colona (L.) Link. is one of the most problematic weeds across the world. It is an annual C₄ summer grass, native to tropical and subtropical Asia, emerged as a serious and persistent threat in 35 cropping systems in more than 60 countries. E. colona is reported as an important associated weed species in transplanted and direct-seeded rice. Diverse ecotypes, high seed production, short seed dormancy, rapid growth, competitive potential, allelopathic interaction, and resistance against several herbicides makes it a more adaptable and persistent challenge in various agro-ecosystems. Development of resistance to recommended or higher doses of numerous herbicides, including ametryn, atrazine, bispyribac-sodium, clefoxidym, cyhalofop-butyl, fenoxaprop-p-ethyl, glyphosate, metribuzin, propanil, and triazine, is a serious concern for the farming and scientific community. Crop infestation with resistant E. colona biotypes may ultimately increase the weed control cost. Unfortunately, investigations on seed dormancy release, genetic diversity, allelopathic interference, and competitive ability of this weed are inadequate in accomplishing its appropriate control in different environments. Therefore, a comprehensive review is presented here to gather the existing information, to pin point key findings, and to highlight the research gaps in the biology, interference, and management of E. colona. Different management options have been discussed in relation with eco-biology of this noxious weed. The potential research endeavours have also been highlighted in order to provide an insight of its existing scenario and to facilitate the future management strategies.