Radiation Balance Components of Maize Hybrids Grown at Various Plant Densities

Components of the energy and heat balances were examined in two maize hybrids grown at three different plant densities (40, 70 and 100 thousand plants per hectare). One of the hybrids was drought tolerant, while the other was bred for cultivation under irrigated conditions. An increase in plant density influenced not only the size of the leaf area, but also the distribution of the leaves at various plant heights. The extinction coefficient, which provides a quantification of radiation penetration, was higher in the irrigated treatments. By contrast to the other two treatments, the plant canopy in the thinly sown stands remained open throughout the vegetation period, and thus behaved quite differently to the closed stands, making it impossible to compare them. Smaller albedo values were recorded for the hybrid bred for irrigation and in thinly sown stands. The low plant density allowed more energy to reach the soil, from which it was reflected, making a considerable contribution to the final temperature in the stand. The latent heat, in keeping with the quantity of water transpired, was the greatest in the densely sown stands. There was little difference between the latent heat values of the normal and dense stands in either hybrid, indicating that they both had a similar sensitivity to increased stand density. If sufficient water is available it would appear that the stand density could be increased even for the drought-tolerant hybrid.     

Analysis of the Impact of Alfalfa Forage Production under Summer Water-Limiting Circumstances on Productivity, Agricultural and Growers Returns and Plant Stand

The trade-off between summer water conservation from alfalfa production and the effects on plant growth, agricultural crop value, and grower returns in the low desert area (Imperial, Palo Verde, Parker and Yuma Valleys of California and Arizona) was analysed using an experimental plot in the Palo Verde Valley. The purpose was to provide a basis for evaluating water conservation decisions and policies. Four summer dry-down periods (withdrawing water for a predetermined period) of 0 days (control), 35 days, 70 days, and 105 days were analysed. Our results show that whereas the various dry-down periods would provide water conservation ranging from 254 to 944 million m³, the region would experience agricultural income decline by US $16 to US $73 million. For growers, benefits of dry-down would be effective only if the water price exceeds US $0.045 m⁻³ in California and US $0.036 m⁻³ in Arizona. Also dry-down would have possible adverse effects in the following areas including declines in plant stand density, long-term productivity, service industry sales, employment and biological benefits of soil fertility and organic matter that is attributed by the alfalfa plant in which case agriculture's and growers monetary losses could increase.     

Infection pressure of potato virus YN

Potato virus Y^N (PVY^N) infection was determined by the tobacco test in Swifterbant (Eastern Flevoland). In plots with beet, wheat and seed potatoes the infection exhibited an identical course. No differences were found either between PVY^N infection in the border and that in the middle of a field planted with ware potatoes, although infection pressure was clearly higher here than in the plot with seed potatoes. A barrier crop of 10 rows of wheat did not decrease the infection pressure of the virus.From August onwards, the spread of PVY^N in Lienden (Betuwe) was followed. Here virus transmission was found continuously, even until mid-November.Potato volunteers outside as well as in potato fields are serious infection sources. In 1976 and in 1977 virus spread was detected before the flight ofMyzus persicae, as determined with yellow Moericke traps. Infection pressure can be measured more efficiently by the tobacco test than by aphid trapping. The effect of rogueing at the time of virus spread should be reconsidered.If infection pressures in different areas or successive years are to be compared, the tobacco test should be standardized. A proposal to this effect is made.Samenvatting In Swifterbant (Oostelijk Flevoland) werd de infectie met het aardappel-Y^N-virus (PVY^N) bepaald met behulp van de tabakstoests. In percelen met bieten, tarwe en pootaardappelen bleek de infectie hetzelfde verloop te hebben. Tussen het infectieverloop van PVY^N in de rand en in het midden van een veld consumptieaardappelen werd eveneens geen verschil gevonden. Wel was de infectiedruk hier duidelijk hoger dan in het pootgoedperceel. Een barrier crop van 10 rijen tarwe verminderde de infectiedruk niet.De volgende conclusies kunnen worden getrokken. Aardappelopslag buiten en in aardappelvelden vormt een zeer belangrijke infectiebron. Zowel in 1976 als in 1977 vond de virusverspreiding plaats vóór de vlucht vanMyzus persicae begon, zoals deze werd bepaald met behulp van de gele Moericke vangbakken. Het effect van opzuiveren ten tijde van de virusverspreiding dient aan een nader onderzoek te worden onderworpen. De infectiedruk kan met de tabakstoets op meer directe wijze worden vastgesteld dan met bladluisvangsten mogelijk is.Wil men overgaan tot het vergelijken van de infectiedruk in verschillende gebieden of in verschillende jaren, dan dient de tabakstoets te worden gestandaardiseerd. Een voorstel hiertoe wordt gedaan.     

Prepenetration stages in infection of clematis by Phoma clematidina

A detailed study of conidial germination, germ-tube growth and the formation of infection structures in Phoma clematidina , the causal agent of clematis wilt, is described for two clematis varieties differing in disease resistance. On both the resistant and susceptible varieties, the fungus entered leaves and stems by direct penetration of the cuticle, often, but not always, following the formation of infection structures. More germ tubes per conidium were formed on the susceptible host, but these germ tubes were on average shorter than on the resistant host. Although germ tubes regularly entered the plant via trichomes, stomata were not found to be sites of entry. Following penetration of the cuticle of resistant plants, germ-tube growth was sometimes restricted to the subcuticular region, and halo formation occurred at the sites where penetration was attempted. Subcuticular growth and halo formation were not observed on susceptible plants. These observations may partly explain the resistance of small-flowered clematis varieties to P. clematidina .     

Tall oil fatty acid inclusion in the diet improves performance and increases ileal density of lactobacilli in broiler chickens

1. Studies were conducted with tall oil fatty acids (TOFA) to determine their effect on broiler chicken performance and ileal microbiota. TOFA, a product originating from coniferous trees and recovered by fractional distillation of side-streams from pulp production, mainly comprises free long-chain fatty acids (~90%) and resin acids (~8%). Conjugated linolenic acids and pinolenic acid are characteristic fatty acid components of TOFA.

2. TOFA products at 750 mg/kg feed were tested in two 35-day broiler chicken trials, each using a wheat soya-based diet and with 12 replicate pens per treatment. In both trials, TOFA improved body weight gain at all time points (P < 0.001) and feed conversion efficiency during the first 21 days (P < 0.01). Two different dry TOFA formulations (silica carrier and palm oil coating) were tested and showed performance effects similar to liquid TOFA.

3. Ileal digesta of the broiler chickens was analysed for total eubacteria, Lactobacillus spp., Enterococcus spp., Escherichia coli and Clostridium perfringens on days 14 and 35. TOFA significantly increased total eubacteria and lactobacilli density on day 14 (P < 0.05). There was a significant positive correlation between these bacterial groups and broiler body weight on day 14 (P < 0.01).

4. A numerical reduction in C. perfringens was observed. In vitro growth inhibition studies showed that C. perfringens was strongly inhibited by 10 mg/l TOFA (P < 0.001), while common lactobacilli were resistant to >250 mg/l. The in vitro results were thus in line with in vivo observations.

5. The mechanisms behind the bacterial shifts and their role in performance improvement are unknown. Further purification of TOFA components is needed to identify the effective agents.     

土壤微塑料影响植物生长的因素与机制研究进展

土壤中的微塑料可通过多种方式影响植物生长,并且其在植物体内积累会最终通过食物链进入人体,厘清微塑料对植物生长的影响及机制,有助于系统掌握其在土壤-植物体系中的环境行为。微塑料的赋存状态和理化特征均可影响其对植物的作用效果,本文从粒径、形状、浓度、种类、塑料添加剂和老化程度等方面,梳理了土壤微塑料影响植物生长的主要因素及作用机制,并对未来研究的重点内容提出展望,以期为进一步明晰微塑料对土壤生态系统的影响提供参考。     

不同植物精油对草莓灰霉病菌的体外抑菌效果研究

为筛选出对草莓灰霉病菌具有显著抑菌作用的植物精油,采用熏蒸法,研究茶树精油、牛至精油等6 种植物单方精油及其复配精油对草莓灰霉病菌的体外抑菌效果。结果表明：牛至精油的抑菌效果最佳,其次为1-辛烯-3-醇和茶树精油,其抑菌效果明显优于肉桂精油、桉叶精油和茉莉酸甲酯;茶树精油、1-辛烯-3-醇和牛至精油的最低抑菌浓度（MIC）分别为200、100、100 mg/L;茶树精油与牛至精油复配具有协同增效作用,且二者以质量比1∶4 进行熏蒸时,对草莓灰霉病菌的抑制作用最强。综上,牛至精油、1-辛烯-3-醇、茶树精油及茶树精油与牛至精油复配（质量比1∶4）对草莓灰霉病菌的抑菌效果较优。该研究结果可为新型草莓保鲜剂的开发利用提供新的研究思路。     

东江水源涵养林不同混交组合林下植物多样性研究

为揭示东江水源涵养林5 年生8种不同混交组合林下植物多样性的差异及其规律。对8种 不同混交组合林分样地开展植物多样性调查,对每种混交组合林下的灌木、藤本、草本层进行植物 多样性评价。结果表明,林下植物丰富度指数均不高,Simpson指数与种间相遇机率(PIE) 在数值 上相等,但其与Shannon-Wiener指数间则相差较大;从林下植物多样性指标的聚类分析看,混交组 合楠木×锥栗、红苞木×枫香、火力楠×红锥、椆木×红锥、格木×海南红豆的植物多样性指数较高,而 混交组合红锥×枫香的植物多样性指数较低。     

赏食兼用型辣椒品种选择与工厂化盆栽管理技术

为了满足人们对美好生活的向往和需求,顺应蔬菜多功能利用开发的新业态发展趋势,佛山市近年来在观赏、食用型辣椒盆栽生产方面进行了大胆尝试,在观赏型辣椒品种的特征特性、盆栽管理技术特点及延长果实观赏期方面进行了深入探索,总结出一套适合当地观赏、食用型辣椒种植的栽培技术,主要包括育苗基质配比、适宜播种时期、定植营养土调配、肥水...     

高效液相色谱法测定4.5%氯氰菊酯乳油中两种异构体的含量

采用高效液相色谱法对4.5%氯氰菊酯乳油中高效cisB及transB的含量进行测定,该方法测定结果稳定,线性良好,重复性较高。