Comparison of management strategies for controlling Nassella trichotoma in modified tussock grasslands in New Zealand: a spatial and economic analysis

The weedy grass Nassella trichotoma (nassella tussock), historically an economically damaging invader of modified tussock grasslands in New Zealand, currently causes little if any reduction in farm production. This is a result of successful historical regional management programmes in which plants have been removed manually (by grubbing) each year before they seed. To inform a debate about the need for ongoing regional management, we developed a stage‐structured spatially explicit integrodifference equation population model and linked this to a cost analysis. We used the model to compare the weed's future population trajectories and related regional control costs over 50 years under three alternative management scenarios. The total discounted (3% p.a.) costs of no management, three‐yearly grubbing and continued annual grubbing were NZ $417 million, $736 million and $131 million respectively. These analyses indicate that annual grubbing of N. trichotoma returns a net benefit of $286 million ($417 – $131 million) compared with doing nothing and a net benefit of $605 million ($736 – $131 million) compared with a 3‐yearly grubbing programme. These results support the continuation of annual grubbing as the long‐term economically optimal management strategy for N. trichotoma on pastoral farms infested by the weed in New Zealand.     

Using the age shift method to determine gains from weed management for Pinus radiata in New Zealand

Understanding the effects of interspecific competition on long‐term growth of plantation forestry crops is critical to forest management decisions around methods used for weed control. A series of permanent sample plots (31) incorporating trees maintained either weedy or weed‐free until canopy closure were established across New Zealand between 2000 and 2002. We used the age shift method to characterise growth responses of Pinus radiata, in New Zealand, to interspecific competition over the first third of a typical rotation. Eight years after planting, age shifts between treatments ranged between ?0.60 years and +3.07 years. On average, the age shift due to weed control increased from 0.62 to 0.96 years between 4 and 8 years of age. This was due to divergent tree growth between weedy and weed‐free plots at 55% of the sites, while at 32% and 13% of sites, respectively, differences between treatments remained constant or decreased beyond age 4 years. The magnitude of the age shift was found to be related to the type of weed dominating early interspecific competition, with woody weeds associated with significantly greater age shifts. Continued divergence in tree growth between weedy and weed‐free treatments up to 8 years after planting at the majority of sites was an unexpected result and contrasts with previous literature. In situations where growth divergence continues beyond 2 years, managers should consider continued treatment of weeds to mitigate the detrimental impacts of on‐going competition.     

Effects of weed harrowing and undersown clover on weed growth and spring cereal yield

Weed competition and nutrient scarcity often restrict organic cereal production, especially where the availability of livestock manure is limited. While harrowing of annual weeds and legume cover crops can be used, these methods are both executed in early spring and may hinder each other. Two cycles of a 2‐year crop rotation were carried out in south‐east Norway (60°42′N, 10°51′E, altitude 250 m) with weed harrowing and undersown cover crops (WHCC) at two fertiliser rates (40 and 100 kg nitrogen ha^?1). The effect of the WHCC treatments was measured by weed density and species, weed biomass, changes in weed seedbank and grain yield. The weed density depended on the interaction between WHCC, fertiliser and year. On average, pre‐emergence weed harrowing reduced weed density by 32% and weed biomass by 49%, while pre‐ and post‐emergence weed harrowing reduced weed density by 59% and weed biomass by 67% compared with the untreated control. Spergula arvensis became more abundant at low rather than at high fertiliser rates. On average, white clover cover crop sown after pre‐emergence weed harrowing resulted in the highest yields for both oat (+12.1%) and wheat (+16.4%) compared with the untreated control. Despite differences in weed population density and biomass among WHCC treatments within years, the weed biomass, weed density and seedbank increased for all WHCC treatments over the 4‐year period. More research is required into improving the efficacy of mechanical and cultural weed suppression methods that organic systems rely on.     

除杂灌和松土抚育措施对柚木及其林下植被的影响

为了解除杂灌、松土抚育措施对柚木、林下植被的影响及柚木与林下植被的相互作用,笔者于造林后第2年在柚木幼林中布设了除杂灌（全砍与全铲）和松土（松土与不松土）抚育试验。结果表明：不同除杂灌、松土处理措施对柚木生长和林下植被生长影响显著：（1）全砍与全铲除杂灌处理相比,柚木树高、胸径分别减少39.2%和39.5%;林下灌木高度、盖度和干重分别增加32.6%、76.2%和184.0%,草本则分别增加36.8%、5.8%和39.3%;灌木和草本种类分别减少16.7%和50.0%。（2）松土与不松土措施相比,柚木树高、胸径分别提高13.5%和11.0%;对林下灌木及草本的生长也有显著影响,但较除杂灌措施程度小。（3）柚木树高和胸径生长与林下草本盖度存在显著负相关关系。     

甘蔗除草地膜全膜覆盖栽培技术应用效果研究

介绍了甘蔗除草地膜全膜覆盖栽培技术应用效果,认为甘蔗全膜覆盖栽培技术配合甘蔗除草地膜技术对甘蔗栽培节本增效显著;同时,阐述了该栽培技术推广过程中存在问题,如除草、残留地膜污染、整地质量等问题,并提出了解决措施,建议使用甘蔗除草光降解地膜替代不可降解的除草地膜。     

Weed suppression by cover crops: comparative on‐farm experiments under integrated and organic conservation tillage

Cover crops are increasingly being used for weed suppression and to enhance the sustainability of agro‐ecosystems. However, the suitability of cover crops for weed suppression in integrated and organic conservation tillage systems is still poorly investigated. Therefore, a 2‐year field study at eight sites was conducted to test the weed suppressive potential of six legume‐based cover crops, with the aim to reduce herbicide input or mechanical weed management interventions. In all experiments, cover crops were directly sown after cereals before next year's main crop (grain maize or sunflower). The presence of cover crops caused a 96% to 100% reduction of weed dry matter at the four sites managed under integrated production, while effects were lower at the four sited managed under organic production, ranging from 19% to 87%. Cover crops that covered soil quickly and which produced much dry matter had the best weed suppressive potential. However, their weed suppressing effect was difficult to predict, as it depended on the year of the investigation, experimental site, cover crop species, the speed of soil cover in autumn and the density of the resulting mulch layer in spring. The study demonstrated that cover crops are a useful tool to suppress weeds under integrated and organic conservation tillage practices. Our recommendation for supporting weed management in conservation tillage systems is to use locally adapted cover crops that have rapid establishment, good soil coverage and high dry matter production. However, additional weed management measures are required for reliable weed control under on‐farm conditions.     

水稻秸秆还田结合炔草酯对禾本科杂草和小麦生长发育的影响

为改进水稻秸秆还田条件下小麦田杂草治理技术,通过田间小区试验研究了不同还田量单独或结合炔草酯施用对后茬小麦田禾本科杂草的控制效果和小麦生长发育及产量的影响。结果表明,随着水稻秸秆单独还田量从1 125 kg/hm2增至4 500 kg/hm2,小麦田杂草发生密度显著下降,4 500 kg/hm2秸秆还田量下小麦分蘖期前杂草发生密度下降60%左右;结合炔草酯施用时,杂草发生密度随秸秆还田量的增加而下降,但不同还田量之间无显著差异,且炔草酯除草活性未受到影响。秸秆还田或炔草酯单独或结合施用均对小麦生长发育无明显的胁迫影响,4500 kg/hm2秸秆单独还田量下,小麦苗期功能叶SPAD值较对照增加7.0%,净光合速率和蒸腾速率分别增加14.9%和12.2%;抽穗期净光合速率、气孔导度、蒸腾速率分别增加28.3%、85.2%和100.0%;千粒重、有效穗数和产量分别增加3.9%、6.7%和16.1%。4 500 kg/hm2秸秆单独还田量对杂草控制效果、小麦生长及产量的影响均与炔草酯推荐剂量单独施用无显著差异,表明该秸秆还田量具有良好的农田生态效应。     

Distribution patterns and traits of weed communities along an urban–rural gradient under rapid urbanization in Shanghai,China

In order to better understand the effects of urbanization on weed communities, the distribution of weed communities in Shanghai, China, was systematically investigated. The diversity of weed communities and four environmental factors, including the relative light intensity, soil moisture, soil compaction and soil pH, were measured in 1375 plots along an urban–rural gradient. The species diversity indices in each area along the urban–rural gradient were compared by using a one‐way ANOVA. The weed communities were identified by using clustering methods that were based on relative dominance information. A canonical correspondence analysis was used to reveal the relationships between the species composition and the environmental factors at the community level and the Spearman's rank correlation test was used to test the relationship between the number of weed communities and each environmental factor. A total of 183 species, belonging to 41 families and 123 genera, was recorded. It was found that the species richness, Shannon–Wiener diversity index and Pielou evenness index followed a unimodal curve along the urban–rural gradient. The 1375 plots were divided into 133 weed community types. All four environmental factors significantly affected the species composition of the weed communities, but only soil compaction had significant effects on the number of weed communities. It was concluded that the diversification of habitat type and environmental change along the urban–rural gradient led to more weed communities in rural areas and fewer weed communities in urban areas. Based on the species' habitats and distribution patterns, the weeds were divided into “widespread”, “urban” and “rural”.     

Field evaluation of allelopathic plant extracts alongside herbicides on weed management indices and weed–crop regression analysis in maize

Synthetic herbicides are posing problems owing to the development of weed resistance and emerging debate on their associated health hazards and ecological threats. Allelopathic manipulations are evolving as applicable substitutes for weed management in agroecosystems. In order to assess the efficacy of potential allelopathic water extracts from different plant species, field experiments were conducted during 2010 and 2011. Sorghum bicolor L., Helianthus annuus L., Brassica napus L., Oryza sativa L., Zea mays L. and Morus alba L. aqueous extracts in different combinations alone or along with a reduced dose of herbicide were evaluated for weed suppression in a maize crop. A weedy check and two herbicidal treatments, S‐metolachlor + atrazine (pre‐emergence) and atrazine alone (early postemergence), were included for comparison. Sorghum, brassica or sunflower tank‐mixed with 25% of the recommended dose of atrazine significantly suppressed the total weed density and dry biomass, along with a concomitant decrease in the crop resistance indices and treatment efficacy indices over the control. The weed density and dry biomass that were recorded at 60 days after sowing showed a strong negative correlation, while the leaf area index, crop growth rate, dry matter accumulation and net assimilation rate predicted a strong positive correlation, with the stover and grain yield of maize.     

Effect of the burial depth and environmental factors on the seasonal germination of bearded sprangletop (Leptochloa fusca [L.] Kunth ssp. fascicularis [Lam.] N. Snow)

Bearded sprangletop recently was introduced to Turkey, where it has adapted to rice cultivation and become an important weed in many regions of the country. Experiments were conducted to determine the effects of light, temperature, osmotic stress, salt stress, pH and flooding on bearded sprangletop germination and emergence. Mature bearded sprangletop seeds were collected from rice fields in August 2008. Approximately 1250 seeds were wrapped in plastic fabric and buried at 2 or 10 cm in pots in flooded or non‐flooded conditions. In this experiment, seed germination in the light from the flooded and non‐flooded treatments began in the spring, peaked in summer and decreased in the fall. This pattern was repeated the following year after exposing the seeds to natural seasonal temperature changes. As either the level of water stress or NaCl concentration increased, cumulative seed germination decreased. No seed germinated when the NaCl concentration exceeded 400 mole. The level of seedling emergence decreased with an increasing burial depth. Under the flooded conditions, emergence began in late April and continued until early July, with peak emergence in the first week of June. Under the non‐flooded conditions, bearded sprangletop emerged later than under the flooded conditions and the overall level of emergence was lower. The depth of burial and water stress appear to be the most important factors that limit seed germination. Germination was stimulated by light, suggesting that the seeds are positively photoblastic.