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.     

The effects of artificial substrate and stocking density on Pacific white shrimp (Litopenaeus vannamei) performance and water quality dynamics in high tunnel-based biofloc systems

The use of artificial substrates in shrimp aquaculture may allow for production of shrimp at increased densities while providing a growth medium for microbes that assist with water quality processes and provide supplemental nutrition for shrimp. Greenhouse-based shrimp production systems can extend the shrimp production season in temperate climates while conserving water and energy. For this study, we evaluated the effects of providing extra substrate and shrimp density on water quality and shrimp production in greenhouse-based biofloc systems. Four 11-m³, wood framed, and rubber-lined tanks were constructed in each of four high tunnel greenhouses (for a total of 16 tanks). Four treatments were evaluated: high-density stocking with substrate (HDS), high-density stocking with no substrate (HDNS), low-density stocking with substrate (LDS), and low-density stocking with no substrate (LDNS). Each treatment was randomly assigned to one tank in each tunnel to block for location. No artificial heat was used, and shrimp were grown for 120 days. High-density systems were stocked at 200 shrimp/m³ while low-density tanks had 100 shrimp/m³. Adding substrate increased total in-tank surface area by 13.4%. The addition of substrate had no significant effect on any shrimp production or standard water quality parameters. Shrimp had significantly greater final weight, faster growth rate, and lower feed conversion rate in low-density treatments (P ≤ 0.02 for all). Total shrimp biomass production was significantly higher in high-density treatments (HD: 4.0 kg/m³; LD: 2.3 kg/m³; P < 0.05). There were no significant differences in survival between densities (HD: 91.3%; LD: 94.5%; P = 0.43). Peak and overall mean nitrite levels were significantly higher in high-density treatments compared to low-density treatments. Dissolved oxygen levels and pH over the course of the study were significantly lower in high-density treatments, likely due to increased respiration rates in the water column. This project shows the feasibility of shrimp production in temperate climates with no artificial heat using high tunnel greenhouses, few impacts of added substrate on shrimp production, and increased shrimp density can result in much larger harvests with few negative impacts on production metrics.     

内蒙古地区不同生育期组大豆品种的应用分析与评价

为明确内蒙古2 500℃以上有效积温区不同播期适宜种植的大豆品种及种植密度,本文以MG000、MG00、MG0、MGⅠ生育期组大豆品种为试验材料,开展不同播期、密度试验,通过产量特征分析,确定各生育期组品种的适宜播种期及种植密度。结果表明:MG000组品种适宜作救灾播种品种,适宜生育日数为85~90 d,最佳种植密度在24万~30万株·hm~(-2),叶面积指数范围为2.0~2.2;MG00和MG0组品种适宜晚播,适宜生育日数为90~100 d,最佳种植密度24万~30万株·hm~(-2),叶面积指数范围分别为2.3~2.7、2.8~3.1;MGⅠ组品种种植应适时晚播,适宜生育日数为100~110 d,最佳种植密度21万~24万株·hm~(-2),叶面积指数范围为3.0~3.3。     

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。     

播期和密度对马铃薯原种扩繁生长发育及产量的影响

在马铃薯原种生产中,播种密度和播种期对原种繁育的产量、种薯大小等有着明显的影响。选用当地主栽品种大西洋,于2017-2018年在山丹县冷凉区域,同一地点开展不同播期和密度试验。播种选择4月25日、5月5日、5月15日、5月25日和6月5日,种植密度设置60 000、90 000、120 000、150 000和180 000粒/hm ² 5个水平。结果表明,在当地的栽培模式大垄双行覆膜种植下,4月25日-5月15日播种,播种密度为120 000、150 000粒/hm ²,产量在45 285~46 770kg/hm ²,中种薯率在75.3%~79.6%,合格种薯多,均为最高,且此范围产量差异不显著。考虑到节约原原种投入降低成本,生产中优选120 000粒/hm ²的播种密度,在4月25日-5月15日种植,是大西洋原种繁育的最佳选择方案。     

Urban land-use impacts on composition and spatiotemporal variations in abundance and biomass of earthworm community

Soil fauna can sensitively respond to alterations in soil environment induced by land-use changes.However,little is known about the impact of urban land-use changes on earthworm communities.In this study,three land-use types(i.e.,forest,nursery and abandoned lands)were chosen to identify differences in diversity,abundance and biomass of earthworm community in Kunming City.Urban land-use had a pronounced difference in species composition,evenness and diversity of earthworm communities.Forest land had the highest density,biomass and diversity of the earthworm communities.Total abundance was dominated by endogeic species in nursery land(70%)and abandoned land(80%),whereas in the forest land,the earthworm community comprised epigeic,endogeic and anecic species.Temporal changes in earthworm density and biomass were also significantly affected by land-use change.Total density and biomass of earthworms in the forest and nursery lands were highest in September,but highest in the abandoned land in October.The influence of soil physicochemical properties on the earthworm density and biomass also varied with land-use types.Soil temperature significantly affected earthworm density and biomass in the three land-use types.Soil pH was positively correlated with earthworm biomass in the forest land,but negatively associated with earthworm density in the abandoned land.Soil organic matter was positively correlated only with density and biomass of earthworms in the nursery and abandoned lands.Our results suggest that the species composition,abundance and biomass of earthworm communities can be determined by the modification of soil properties associated with urban land-use type.     

河套地区种植方式与密度对'张杂谷19号'产量的影响

为明确河套地区不同栽培模式对'张杂谷19号'产量的影响,以新抗旱谷子杂交种'张杂谷19号'为试验材料,研究3种种植方式（干旱无膜、干旱覆膜及灌溉无膜）和5种密度（4.5万、9万、13.5万、22.5万、45万株/hm²）对'张杂谷19号'稳产和丰产性的影响。结果表明,正常灌溉条件下,'张杂谷9号'的产量随着种植密度的增加而增加。当密度为45万株/hm²时产量最高,达到8724.36 kg/hm²。而干旱条件下,适宜种植密度可以同样获得较高产量,与正常灌溉条件下最高产量差异不显著。当种植密度为9万~ 45万株/hm²时,产量普遍提高到7700 kg/hm²以上,最高可达8654.33 kg/hm²。河套地区'张杂谷19号'播前灌溉1次足水、地膜覆盖及种植密度9万~45万株/hm²,可以实现水分高效利用和产量达到较高水平。     

棉花离体不定根系的发生对色素腺体密度和棉酚含量的影响

为探明根系对色素腺体密度和棉酚含量的影响，以离体条件下的无根幼苗、不同生根状态幼苗以及无菌种子苗作为研究对象，对其茎叶色素腺体密度、棉酚含量以及棉酚生物合成关键基因表达量进行分析。结果表明，不同生根状态幼苗中，色素腺体密度和棉酚含量与一定范围内生根数呈显著正相关，随后趋于平稳。荧光定量PCR显示，棉酚生物合成关键基因GhCDN1和GhWRKY1表达量在生根数多的无菌苗中显著增高，而对棉酚合成具有反馈调节作用的 GhCYP706B1表达量呈现相反趋势；无根幼苗茎叶腺体密度和棉酚含量均显著低于有根幼苗，棉酚生物合成关键基因GhCDN1、GhWRKY1和 GhCYP706B1表达量反而高于有根幼苗。有根幼苗中根的棉酚含量显著高于茎和叶，无菌种子苗根系中棉酚生物合成关键基因表达量显著高于茎和叶。说明棉花根系能对棉酚含量产生直接影响，同时影响腺体密度。本研究进一步验证了根系是棉酚主要合成部位，地上部分也存在少量的棉酚合成，只是不能引起棉酚发生显著变化。     

Soil aggregation and the stabilization of organic carbon as affected by erosion and deposition

The importance of soil aggregation in determining the dynamics of soil organic carbon (SOC) during erosion, transportation and deposition is poorly understood. Particularly, we do not know how aggregation contributes to the often-observed accumulation of SOC at depositional sites. Our objective was to assess how aggregation affects SOC stabilization in comparison to interactions of SOC with minerals. We determined and compared aggregate size distributions, SOC distribution in density fractions, and lignin-derived phenols from aggregated soil samples at both eroding and depositional sites. The stabilization effect of aggregation was quantified by comparing mineralization from intact and crushed macro-aggregates. Deposition of eroded soil material resulted in carbon (C) enrichment throughout the soil profile. Both macro-aggregate associated SOC and C associated with minerals (heavy fraction) increased in their importance from the eroding to the depositional site. In the uppermost topsoil (0–5 cm), SOC mineralization from intact aggregates was larger at the depositional site than at the eroding site, reflecting the large input of labile organic matter (plant residues) promoting aggregation. Contrastingly, in the subsoil, mineralization rates were lower at the depositional site because of effective stabilization by interactions with soil minerals. Aggregate crushing increased SOC mineralization by 10–80% at the eroding site, but not at the depositional site. The content of lignin-derived phenols did not differ between eroding and depositional sites in the topsoil (24.6–30.9 mg per g C) but was larger in the subsoil of the eroding site, which was accompanied by higher lignin oxidation. Lignin data indicated minor effects of soil erosion and deposition on the composition of SOC. We conclude that SOC is better protected in aggregates at the eroding than at the depositional site. During transport disaggregation and consequently SOC mineralization took place, while at the depositional site re-aggregation occurred mainly in the form of macro-aggregates. However, this macro-aggregation did not result in a direct stabilization of SOC. We propose that the occlusion of C inside aggregates serves as a pathway for the eroded C to be later stabilized by organo-mineral interaction.     

不同肥力水平下种植密度对浚单29产量性状及产量的影响

[目的]探寻浚单29不同肥力水平地区的适宜种植密度。[方法]研究在高产田与一般田2种肥力水平下浚单29种植密度与产量及其相关产量性状的关系。[结果]2种肥力水平下通过种植密度变化影响穗部性状来影响产量,相同密度,一般田肥力水平下,密度对穗部性状影响大于高产田对穗部性状影响。[结论]在一般田肥力水平下,浚单29最适宜密度为6.75万株/hm2,高产田肥力水平下,浚单29最适宜密度为7.50万株/hm2。