Weed species composition and diversity of 2-year-old oil palm tree/fruit vegetables intercrop in rainforest zone of Nigeria

The spacing pattern and growth habit of juvenile oil palm during the early stages of field establishment have often led to serious weed problem until canopy closure at subsequent years. This study was carried out during the rainy season of 2016 to evaluate the weed species composition and diversity of an intercrop between 2-year-old oil palm tree and two fruit vegetables at an oil palm plantation in Ala, Akure-North Local Government, Ondo state, Nigeria. Two accessions of tomato (NGB 01665 and NG/AA/SEP/09/053) and eggplant (NGB 01737) were intercropped within the alley of immature oil palm. Weed sampling was carried out using 0.25 m2 quadrat within each experimental plot. Quantitative analysis of weed species parameters and Simpson’s Diversity Index were evaluated. The result revealed that 28, 21 and 20 weed species were found across all the plots at 3, 6 weeks after intercropping (WAI), and after harvesting respectively. Members of Asteraceae produced the highest weed species at 3 WAI (17.857%); Poaceae recorded the highest weed species at 6 WAI and after harvesting (19.048% and 20%) respectively. A total of 23, 16 and 15 broadleaves were found at 3 and 6 WAI, and after harvesting. In all the juvenile oil palm/vegetable intercrops evaluated, the control plot recorded the highest weed species richness at 6 WAI, when compared to other intercropping regimes. The control and juvenile oil palm/tomato (NGB 01665) intercrop plot recorded the highest and lowest Simpson’s Indices of Diversity at 6 WAI (0.877 and 0.734) respectively.

Weed infestation during the transition phase from conventional to conservation agriculture

<p>Despite conservation agriculture and, overall, the reduction of soil disturbance are considered soil improving cropping systems, these practices could conflict with weed control. Indeed, reduced tillage is usually linked to increased weed species richness and abundance and, thus, it could increase the dependence on chemical treatments. Weed management is one of the reasons behind the distrust of European farmers in the conservation agriculture, that is still not widespread, despites European subsidies. In fact, conservation agriculture is implemented only in the 2.8% of European cropland.</p><p>The aim of this study is to evaluate the effect of different tillage intensities on spring-summer weeds richness and abundance in a maize monoculture, during the transition phase from conventional to conservation agriculture.</p><p>The weed survey was conducted in June 2019 on an experiment comparing three levels of tillage management: conventional agriculture (CT), which represents the most common choice in Veneto region, involving deep ploughing and harrowing in spring; minimum tillage (MT), consisting only in harrowing at 20 cm; and no tillage (NT), namely sod seeding. The experiment started in 2018, at Padova University experimental farm, in a sub-humid area, with a silty clay loam soil. The survey was conducted with a set of random throws of a 30×30 cm square frame in each plot (ca. 3300 m<sup>2</sup>).  Weed plants found within the frame were classified and counted. Subsequently, data analysis assessed which botanical families were promoted by each treatment.</p><p>The NT resulted the treatment with the highest weed density (915 plant/m<sup>2</sup>): 6% higher than MT (823 plant/m<sup>2</sup>) and four-fold more than CT (209 plant/m<sup>2</sup>). The latter showed to be the treatment with higher diversity, according to both Shannon and Simpson indices. The survey evidenced higher weed species richness in MT, where both annual and perennial species were identified, while the lowest number of species were detected in NT. Plantago major and Chenopodium album were the species with the highest density in CT (>32 plant/m<sup>2</sup>) while they are negligible in NT and MT (7 plant/m<sup>2</sup>, on average). Digitaria sanguinalis was instead the dominant species in MT and NT (>600 plant/m<sup>2</sup>) while a lower density was observed in CT (11 plant/m<sup>2</sup>). Low levels of Asteraceae weeds were measured in all treatments. These results shows that the actual flora rapidly changes depending on tillage intensity, with an increase of both dominance and number of species in MT. Differently, only a limited number of adapted species germinated in NT, despite higher infestations if compared with the other treatments.</p><p>It should be expected that other species more adapted to conservation agriculture (namely Asteraceae), still marginally present in the seed bank, will spread in the next years. This stresses the importance of a continuous monitoring and effective control of weeds to avoid uncontrolled evolutions of the weed flora and increase of seed bank in the transition phase from conventional to conservation agriculture.</p>

Weed community structure and soybean yields in a long-term organic cropping systems experiment

Weed management is a major challenge in organic crop production, and organic farms generally harbor larger weed populations and more diverse communities compared with conventional farms. However, little research has been conducted on the effects of different organic management practices on weed communities and crop yields. In 2014 and 2015, we measured weed community structure and soybean [Glycine max (L.) Merr.] yield in a long-term experiment that compared four organic cropping systems that differed in nutrient inputs, tillage, and weed management intensity: (1) high fertility (HF), (2) low fertility (LF), (3) enhanced weed management (EWM), and (4) reduced tillage (RT). In addition, we created weed-free subplots within each system to assess the impact of weeds on soybean yield. Weed density was greater in the LF and RT systems compared with the EWM system, but weed biomass did not differ among systems. Weed species richness was greater in the RT system compared with the EWM system, and weed community composition differed between RT and other systems. Our results show that differences in weed community structure were primarily related to differences in tillage intensity, rather than nutrient inputs. Soybean yield was lower in the EWM system compared with the HF and RT systems. When averaged across all four cropping systems and both years, soybean yield in weed-free subplots was 10% greater than soybean yield in the ambient weed subplots that received standard management practices for the systems in which they were located. Although weed competition limited soybean yield across all systems, the EWM system, which had the lowest weed density, also had the lowest soybean yield. Future research should aim to overcome such trade-offs between weed control and yield potential, while conserving weed species richness and the ecosystem services associated with increased weed diversity.

May the Inclusion of a Legume Crop Change Weed Composition in Cereal Fields? Example of Sainfoin in Aragon (Spain)

Onobrychis viciifolia (Scop.) (sainfoin) is promoted in the Spanish Aragón region through the Agro-Environmental Schemes (AES) since 2007 with the aim of enhancing biodiversity. Also, in other countries, the interest in this legume crop is growing due to its rusticity and beneficial effects on the soil and livestock. However, the effect of the crop on weed flora in the subsequent cereal crops has hardly been investigated yet. With this aim, weed flora has been characterised in 2011–2014 in sainfoin fields in the second and third year of establishment (S2 and S3), in cereal monocrop (CM), in cereal after sainfoin (CS) and in organic cereal fields (OC). Additionally, the soil seedbank was determined in two years in CM and S3 fields. Weed species richness of emerged flora and of the soil seedbank was highest for sainfoin and lowest for CM, being intermediate for OC and CS regardless of the sampling year. The most feared weed species in winter cereal did not increase by growing sainfoin or in CS compared to CM. Curiously, summer annuals dominated in the soil seedbank. Sainfoin fields cause thus a shift in the weed flora, which does not seem to damage subsequent cereal crops provided fields are mouldboard ploughed after sainfoin.

Extractable and Germinable Seedbank Methods Provide Different Quantifications of Weed Communities

Seedbank sampling and quantification methods vary in their ability to describe weed diversity and density, so proper method selection is critical for studying weed communities. The germinable seedbank (GSB) method is commonly preferred over extractable seedbank method (ESB), because the latter is more time-consuming. However, these two methods have only been compared using a few weed species and a relatively small number of samples. A total of 204 weed seedbank samples were used to compare both methods for weed density, richness, evenness, and Shannon-Weiner diversity using a split-sample approach. The two methods yielded dramatically different results. The ESB had 418% higher density and 35% more species per sample but 11% less evenness than the GSB. Diversity was estimated to be only 9% higher using the extractable compared with the germinable method. While the extractable method had higher density and richness overall, this was not true for every species, with only 7 of 14 common species detected in higher amounts by the extractable method. The results indicate the two methods are not strongly correlated, limiting the possibility of generating a conversion factor between methods. Nevertheless, evenness and Shannon-Weiner diversity might allow comparisons between both methods when the emphasis is on characterizing predominant weed species. The GSB is a practical approach to compare treatments or conditions; however, the ESB is more useful to accurately quantify weed species richness, diversity, and density.

Organic fields sustain weed metacommunity dynamics in farmland landscapes

Agro-ecosystems constitute essential habitat for many organisms. Agricultural intensification, however, has caused a strong decline of farmland biodiversity. Organic farming (OF) is often presented as a more biodiversity-friendly practice, but the generality of the beneficial effects of OF is debated as the effects appear often species- and context-dependent, and current research has highlighted the need to quantify the relative effects of local- and landscape-scale management on farmland biodiversity. Yet very few studies have investigated the landscape-level effects of OF; that is to say, how the biodiversity of a field is affected by the presence or density of organically farmed fields in the surrounding landscape. We addressed this issue using the metacommunity framework, with weed species richness in winter wheat within an intensively farmed landscape in France as model system. Controlling for the effects of local and landscape structure, we showed that OF leads to higher local weed diversity and that the presence of OF in the landscape is associated with higher local weed biodiversity also for conventionally farmed fields, and may reach a similar biodiversity level to organic fields in field margins. Based on these results, we derive indications for improving the sustainable management of farming systems.

Influence of field margin type on weed species richness and abundance in conventional crop fields

Natural vegetation occurring on farms in field margins, fallow fields, ditch systems and neighboring forests, provides increased biodiversity, structural diversity, habitat for wildlife and beneficial insects, and can act as a protective buffer against agrochemical drift. Nevertheless, farmers frequently view these areas as non-productive and as potential sources of weeds, insect pests and diseases. Weed species richness and abundance were examined in crop fields in 2002–2003 at the Center for Environmental Farming Systems near Goldsboro, NC to determine if crop field weed infestation was associated with field margin management (managed versus unmanaged). Weed species abundance and richness were measured over two growing seasons on four occasions in crop fields along permanent transects that extended from the field edge toward the center of the field. The presence/absence of data for all plant species in the field margin was also recorded. For both margin types, managed and unmanaged, more weeds were found near the field edge than in the center of the field. Weed species richness was slightly higher in cropland bordering managed margins than in cropland along unmanaged margins. Several significant interactions led to an examination of nine dominant weed species in each field margin type and their distribution in crop fields. When all sampling dates were pooled, only 42 (40%) of 105 species identified in the field margins were observed in the crop field. Managed margins had lower species richness than unmanaged field margins—less than half the mean number of species (15 versus 6 species, respectively). Contingency table analysis did not reveal any association between plant species occurring in the margin and those found in the crop field. Furthermore, margin type and weed presence in the field margin were not effective predictors of weed occurrence in the crop field as determined by logistic regression.