Effect of slope and plant cover on run‐off,soil loss and water use efficiency of natural veld

Abstract

Run‐off and soil loss were monitored from a climax, subclimax and pioneer veld, each on a 5,9%, 4,1% and 2,1% slope, by means of a rainfall simulator on a Valsrivier soil form. With rainfall intensity, soil moisture content at the beginning of each rain storm, and soil texture the same for each treatment, plant cover and composition had a significant (positive) (P≤0,05) influence on the amount of soil loss and run‐off that occurred, as against the insignificant influence of the slope.

An average of 6,2 t/ha soil loss and 80,6% run‐off of the amount of water applied occurred from the pioneer veld (0,7% basal cover) on the steepest slope. In all the successional stages more run‐off and less soil loss occurred from wet soil than from dry soil. Significant (P≤0,01) relationships between basal and canopy cover were obtained with run‐off and soil loss.

The climax, subclimax and pioneer veld produced on average 0,57 g, 0,23 g and 0,07 g aboveground phytomass for each litre of water evapotranspirated.     

基于效益背反理论对商业连锁企业的物流配送 效率的研究文献综述

效益背反一直是物流需要攻克的重点难题。企业在降低物流成本的过程中,总会陷入 “效益背反”的窘境。本研究论述了效益背反理论的深层含义,分析了商业连锁企业的物流配送 效率的本质,并梳理了国内外连锁商业企业配送效率的研究现状,进一步提出了连锁企业提高 物流配送效率的几项措施。     

Sowing date effects on dry matter remobilization and yield of triticale (Triticosecale wittmack) under late season drought stress

A 2-year field experiment using a randomized complete block design with the treatments arranged as split-split-plot with three replicates was conducted to investigate the effects of different sowing dates. Different irrigation regimes and different triticale cultivars were tested during 2014 and 2015 growing seasons. Under cutting off irrigation at the milk development stage, Sanabad with 46.2% had higher relative water content on December 3 sowing date. Assimilate remobilization in cutting off irrigation at dough development was more than that at milk development and Sanabad had the highest assimilate remobilization on 3 December sowing date in both years. In both years, Sanabad had the highest remobilization efficiency. The highest contribution of pre-anthesis assimilates to grain was obtained on 3 December sowing date in both years in Sanabad. Lower grain yield in Juanillo cultivar under cutting off irrigation, appeared to be due to reduction in remobilization efficiency, especially by cutting off irrigation at milk development stage in late sowing date. Overall, Sanabad was more tolerant to cutting off irrigation than Juanillo.     

泄洪闸胸墙压坡段的数值模拟

采用RNG k-ε紊流数值模型对具有不同坡度的胸墙压坡段的泄洪闸出口水流进行了三维数值模拟.通过数值模拟计算得到了具有4种不同坡度的泄洪闸胸墙压坡段的流线、流速和压力,并对比分析了胸墙压坡段坡度变化对泄洪闸泄流能力、水流脱壁情况、负压分布区域的影响情况.研究结果表明:随着胸墙压坡段坡度的增大,虽然闸口的泄流能力减弱,但是出口水流的脱空长度和脱空高度变小,也即增大胸墙压坡段的坡度使得出口水流的脱壁现象减弱直至消失;胸墙压坡段内的负压最值及负压的分布区域均随着坡度的增大而变小.在泄洪闸胸墙底缘压坡段的设计过程中要避免平坡式链接,可通过合理的方式比选出适用于自身工程的压坡坡度,有利于提高消力池的消能效率,避免压坡段的空化空蚀,从而增强了工程的安全性.研究方法和结果对类似工程的优化设计及安全运行具有一定的指导意义.     

The quality of baby spinach as affected by developmental stage as well as postharvest storage conditions

Baby spinach is rich in phytochemicals that provide great benefits to consumers’ health. The study aim was to investigate the effect of the growth harvest stage, postharvest storage duration and temperature on quality of baby spinach leaves. A 3?×?5?×?3 factorial experiment was laid out in a randomised complete block design with four replicates per treatment. The treatments were arranged as follows namely: stage I [28 days after sowing (DAS)], stage II (35 DAS)and stage III (42 DAS), and leaves were kept up to 12 d at three different temperatures – 4, 10 and 20°C. The study demonstrated that the overall appearance and odour were both well maintained in the leaves of baby spinach harvested at stage II. The baby spinach harvested 28 DAS led to higher content of iron [1.13?mg?g^?1 dry weight (DW)], magnesium (14.4?mg?g^?1 DW), and zinc (0.17?mg?g^?1 DW). The highest level of total antioxidant activity (0.43?mg?g^?1 DW) and flavonoids (12?mg?g^?1 DW) after 12 d of storage was observed in baby spinach leaves at stage I when stored at 4°C. Therefore, baby spinach leaves harvested 28 DAS and store at 4°C for 6 d improved shelf life and nutraceutical quality. Thus, early harvest of fresh produced baby spinach harvested in order to attain high phytochemical and mineral content when stored at low temperature (4°C) without exceeding 6 days is recommended.     

云杉幼苗猝倒病化学防治药剂筛选

通过试验,对云杉猝倒病（Ｒｈｉｚｏｃｔｏｎｉａｓｏｌａｎｉ,Ｆｕｓａｒｉｕｍｓｐｐ）化学防治中使用的杀菌剂进行了筛选,结果表明,杀菌剂的混合使用可以明显提高防治效果。混合使用防治效果较好的为福美砷＋代森锌、退菌特＋代森锌、甲基托布律＋代森锌、甲基托布津＋退菌特、多菌灵＋福美砷等。如果单用,防治效果优劣依次为退菌特,甲基托布津,多菌灵、福美砷,代森锌。     

祁连山东端封山育林效果初步分析

通过对祁连山东端17块具有代表性的封育地与封育前及对照区的天然更新、幼树高生长、灌木高度、盖度进行对比分析,得出了封山育林效果显著的结论,并运用森林群落演替理论对试验结果进行了论证,从而说明封山育林是发展祁连山水源涵养林的一项重要而有效的措施.     

Appraisal and standardization of curvilinear velocity (VCL) cut‐off values for CASA analysis of Japanese quail (Coturnix japonica) sperm

One of the basic steps in objective analysis of sperm motility is the subdivision of a motile sperm population into slow, medium and rapid categories based on their velocity. However, for CASA analysis of quail sperm, the velocity values for categorization of slow, medium and rapid sperm have not yet been standardized. To identify the cut‐off values of “velocity curvilinear” (VCL) for quail sperm categorization, we captured and analysed 22,300 tracks of quail sperm using SCA^®‐CASA. The median and mean VCL values were 85 and 97 μm/s. To define the VCL cut‐off values, we used two methods. In the first, we identified the upper (rapid sperm) and lower (slow sperm) cut‐off values using: (i) median VCL ± 25% or ± 50% or ± 75% of median VCL value; (ii) first and third quartile values of VCL data (i.e. 25% cut‐off setting); and (iii) 33% and 66% of VCL data. Among these settings, sperm categories and their corresponding motility characteristics recorded using the “25%” setting (i.e. slow ≤36 ≤ medium ≤154 ≤ rapid) were found the most realistic and coherent with male ranking by fertility. In the second method, we calculated heteroscedasticity in the total VCL data using PCA and the two‐step clustering method. With this approach, the mean of the high and low clusters was 165 and 51 μm/s, respectively. Together, the mean from two methods suggested that, for SCA^®‐CASA categorization of quail sperm, sperm should be classed as “rapid” at VCL ≥160 μm/s and “slow” at VCL ≤45 μm/s.     

On‐site and off‐site effects of wind erosion on European light soils

In intensively cultivated areas with light soils in Europe, wind erosion can have important on‐site and off‐site effects. In the framework of the EU research project Wind Erosion and European Light Soils (WEELS), an assessment has been made of these effects and of the order of magnitude of the damage and costs caused by these effects. An analysis is made of the land use and cropping in four selected sites, and farmers have provided information about the damage of wind erosion. This damage consists mainly of crop losses and additional inputs in the case of resowing. Detailed information from one of these sites shows that depending on the crop the average annual on‐site costs in high‐risk areas amount to about €60 per hectare. However, for sugar beet and oilseed rape the costs can be once in five years as much as €500 per hectare. Farmers are generally well aware of the erosion risk and do apply a variety of control measures. With these measures the average annual costs of wind erosion can be reduced significantly. Copyright © 2001 John Wiley & Sons, Ltd.     

Geosmin causes off‐flavour in arctic charr in recirculating aquaculture systems

The ‘earthy’ and ‘muddy’ off‐flavours in pond‐reared fish are due to the presence of geosmin or 2‐methylisoborneol in the flesh of the fish. Similar off‐flavours have been reported in fish raised in recirculating aquaculture systems (RAS); however, little information is available regarding the cause of these off‐flavours. Our hypothesis was that earthy and muddy off‐flavour compounds, found previously in pond‐raised fish, are also responsible for off‐flavours in fish raised in RAS. In this preliminary study, we examined water, biofilms in RAS and fillets from cultured arctic charr known to have off‐flavours and requiring depuration using instrumental [solid‐phase microextraction procedure and gas chromatograph‐mass spectrometry (GC‐MS)] and human sensory analyses. Geosmin was present in the samples taken from the biofilter and on the side walls of the tanks. Two‐methylisoborneol was only found in low levels in the samples. The GC‐MS results indicated the presence of geosmin in the fillets (705 ng kg^?1), but lower levels were found in the water (30.5 ng L^?1). Sensory analyses also detected an earthy flavour (i.e., geosmin presence) in the fillets, and, therefore, it appears that geosmin is the main compound responsible for the off‐flavour in RAS. Further studies are being performed to identify the microorganisms responsible for geosmin production in RAS.