High Crop Density Research Articles

Effects of in situ habitat quality and landscape characteristics in the oil palm agricultural matrix on tropical understory birds, fruit bats and butterflies

The expansion of commercial oil palm crop has modified much of the natural landscape, subsequently leading to biodiversity loss in Southeast Asia. Aside from large-scale oil palm monoculture plantations, self-managed oil palm smallholdings are also becoming common in palm oil producing countries, but less is known about how management of the smallholdings affects faunal biodiversity. We argue that it is critically important to understand the role of habitat complexity at the local and landscape scales for maintaining faunal biodiversity in oil palm smallholdings. We used passive sampling methods to survey understory birds, fruit bats, and butterflies in oil palm smallholdings on the west coast of Peninsular Malaysia. We quantified the diversity in each taxon and measured in situ habitat quality and landscape metrics. We found that oil palm smallholdings located near rice fields supported fewer bird species. Proximity to roads can give rise to bird and fruit bat richness. Bird and fruit bat richness declined at sites with high crop density. Fruit bat richness declined, but butterfly richness increased, with the height of oil palm stands. Butterfly richness declined with distance from riparian habitats. Decreased coverage and height of ground vegetation also negatively affected butterfly species richness. We also found that the number of farm houses is positively related to bird, fruit bat, and butterfly species richness. Of the three taxa, only butterfly richness was positively influenced by crop diversity. We found that habitat complexity enables smallholdings to support a diverse community of birds and butterflies, but not fruit bats. These findings imply that oil palm smallholdings can be managed in a conservation agricultural matrix, as the smallholdings were able to maintain farmland biodiversity.

Olive genotypes cultivated in an adult high-density orchard respond differently to canopy restraining by mechanical and manual pruning

Three-year observations about the canopy restraining of 15 olive cultivars trained according to the high-density system were made in order to supply up-to-date information about the varietal behavior for adult orchards of this new cropping system. The mechanical pruning started at the end of the 6th year from planting and it was repeated for the following two years. Cultivar vigour affected pruning biomass and olive yield. Canonical discriminant analysis was performed to identify differences among cultivars. Medium-low vigour cultivars (Spanish and Greek) can be successfully controlled by mechanical and manual prunings without compromising their yield; instead, medium-high vigour cultivars (traditional and new Italian) require mechanical prunings to control canopy size, but this operation can hardly compromise their yield level and constancy. Further investigations are required to understand the right width of hedging to reach the correct equilibrium between vegetative and reproductive activity in adult orchards. At the moment, the correct varietal choice remains the only way to ensure the agronomical and economic sustainability of the high-density cropping systems, waiting for new results from breeding programs.

English

Plant-parasitic nematodes affect significantly the production of susceptible plants, including olive trees. In this context, nematode communities were determined in soil samples collected from 23 olive growing sites in the Haouz and Souss regions (southern Morocco). These sites corresponded to various modalities: wild (Olea europaea L. ssp. sylvestris) or cropped olive (Olea. europaea L. ssp. europaea), traditional or high-density cropping, rainfed or irrigated. Even free-living nematodes prevailed in most of the sites, high population levels of plant-parasitic nematodes were observed in rainfed cropping systems than in irrigated systems. Ten nematode families and 14 genera were identified. The most important plant-parasitic nematodes detected, in order decreasing frequency of infestation (percentage of samples), were spiral nematodes Helicotylenchus spp. (100%) and Rotylenchus spp. (87%), lesion nematodes Pratylenchus spp. (100%) and root-knot nematodes Meloidogyne spp. (40%). Most of the nematode species were assigned to more or less colonizer nematodes, whereas only one family (Longidoridae) was assigned to persistent nematodes. Considering the two producing areas, plant-parasitic nematodes were significantly more abundant in the Souss region than in the Haouz region, but nematode diversity was higher in the second one. The prevalence of Meloidogyne spp. in the Haouz region would be related to the predominance of irrigated cropping systems in this region. Hoplolaimidae nematodes (Helicotylenchus spp. and Rotylenchus spp.) are better adapted to rainfed conditions that prevail in the Souss region. Co-inertia analysis showed the importance of soil physic-chemical characteristics (e.g., pH, texture and nutrients) on the structure of the plant-parasitic nematode community patterns. The high occurrence of Helicotylenchus spp. in olive orchards may be induced by fertilization. Aphelenchoides spp., Gracilacus spp., Pratylenchus spp., Rotylenchidae and Tylenchidae were supported by coarse textures as it was observed in the Souss region. (C) 2015 Friends Science Publishers

Investigation of hemp (Cannabis sativa L.) crop weediness

The investigation of hemp crop weediness was carried out at the Upytė Experimental Station of the Lithuanian Research Centre for Agriculture and Forestry in 2014. Bi-factorial trial was carried out: Factor A – variety (A1 – USO 31; A2 – Bialobrzeskie); Factor B – sowing rate (B1 – 45 kg ha<sup>-1</sup>; B2 – 70 kg ha<sup>-1</sup>). Data showed that seed rate had a significant influence on crop density at full hemp emergence as well as at harvesting time. Rainy vegetation period was favourable not only for hemp growing, but for weeds as well. Crop density (resulted by seed rate) had a significant influence on crop weediness – significantly more weeds (in average 166 plants m<sup>-2</sup>) were found in the plots with seed rate of 45 kg ha<sup>-1</sup>, consequently at lower crop density, and under 140 weed plants m<sup>-2</sup> were found in the plots with seed rate of 70 kg ha<sup>-1</sup>, consequently at higher crop density. Hemp crop weediness at harvesting time was much lower than that at the beginning of vegetation; reduction of weediness over the vegetation period was close to 87-90 percent.

Guidelines of Sustainable Soil Tillage System in Croatia (Contribution to Sustainable Land Management in 2015 - International Year of Soils)

Within soil degradation processes soil erosion is on the first place, as consequence of improper land man-agement, first of all soil tillage system and practices. Results of 10 years (1995-2004) of our investigation (investigation endure now 21st year) show guidelines in tillage practices. At first; traditional tillage practiced in this agricultural region up/down the slope on Stagnogley on slopes of 9 % and more is unsustainable in growing of row crops-maize and soybean, because of disastrous or extreme soil erosion. But, in growing of crops of high density, like wheat this practice is sustainable. On the other side, No-tillage and contour tillage resulted in much lower water erosion in comparison with up/down the slope tillage. At the beginning of experiment in the first two years No-tillage as system was not sustainable. Stabilization of yields of growing crops on the level which is statistically the same or higher than on other tillage treatments on notillage plot started after ten years of no-tillage practice. These investigations suggest the conclusion that high density crops like winter wheat, spring barley and oilseed rape are relatively suitable crops for growing under reduced tillage systems. Soybean tolerates no-till practices in climatically favourable years, but with higher risk in dry years. Maize was shown as a very risky crop without tillage even in climatically average years. We agree with assertion of Solbrig [1] that no tillage is a process, a new philosophy and way of thinking in arable farming of Europe, and not a technology.

A non-chemical system for online weed control.

Non-chemical weed control methods need to be directed towards a site-specific weeding approach, in order to be able to compete the conventional herbicide equivalents. A system for online weed control was developed. It automatically adjusts the tine angle of a harrow and creates different levels of intensity: from gentle to aggressive. Two experimental plots in a maize field were harrowed with two consecutive passes. The plots presented from low to high weed infestation levels. Discriminant capabilities of an ultrasonic sensor were used to determine the crop and weed variability of the field. A controlling unit used ultrasonic readings to adjust the tine angle, producing an appropriate harrowing intensity. Thus, areas with high crop and weed densities were more aggressively harrowed, while areas with lower densities were cultivated with a gentler treatment; areas with very low densities or without weeds were not treated. Although the weed development was relatively advanced and the soil surface was hard, the weed control achieved by the system reached an average of 51% (20%–91%), without causing significant crop damage as a result of harrowing. This system is proposed as a relatively low cost, online, and real-time automatic harrow that improves the weed control efficacy, reduces energy consumption, and avoids the usage of herbicide.

Environmental sustainability of different soil management techniques in a high-density olive orchard

Recent olive cultivation in Mediterranean Countries is characterised by the strong diffusion of high-density cropping systems and by the most environmentally conscious management regarding all the agronomic practices and the waste disposal as well. This research has investigated the possibility of the use of De-Oiled Pomace (DOP) as an eco-friendly tool for weed control in a high-density olive orchard providing an environmental comparison with other soil management techniques. Five methods of weed control have been compared in a two-year experimental orchard at the Bari University (Southern Italy): mulching with de-oiled olive pomace (DOP), nonwoven tissue (TNT) and polyethylene film (PEN), chemical (CHI) and mechanical (MEC) weeding, on the three most adapted to high-density orchards olive cultivars (Arbequina, Arbosana and Koroneiki). The data collected during the experimental test are submitted to an LCA (Life Cycle Assessment) analysis and five scenarios have been drafted based on DOP use and destinations.The results showed that the chemical wedding produced the greatest environmental burdens, and the higher environmental performances of DOP mulching scenarios for all environmental indexes, with burdens reductions and/or environmental credits. The presence in the following years of some biomarkers sensitive to macro and micro pollutants and heavy metals, in experimental plots mulched with DOP, confirmed the high environmental sustainability of this technique, excluding any kind of soil pollution in the medium-term period in the high-density olive orchard.

Response of the two rare arable weed species Lithospermum arvense and Scandix pecten-veneris to climate change conditions

Rare weeds are currently under pressure due to intensifying arable management practices, and as a consequence of climate change, these practices will likely become even more intensive, together with a greater uniformity of land use. As a result, ecological stresses will increase for most species of rare weeds, in some cases leading to their further decline or even extinction. Moreover, climate change will alter the suitability of the environment for many plants, since average temperatures are predicted to increase and precipitation extremes to become more common. For most arable weed species it is unclear, whether the anticipated changes in environmental conditions are disadvantageous or beneficial. Little is known about specific biological responses of rare weeds to climate changes, and this study attempts to close some of these knowledge gaps. Here, the rare arable weed Lithospermum arvense and the endangered arable species Scandix pecten-veneris were investigated with regard to the effects of higher temperature and different crop densities on flowering time, shoot development, plant height, dry mass and seed production. Semi-field experiments were conducted with winter wheat crop for 3 years, involving 48 climate cages, in which every second was a variant of warmer temperature and contrasting crop density. We observed that S. pecten-veneris flowered earlier under warmer conditions and had fewer seeds and less biomass in the dense wheat crop compared to control conditions, while L. arvense grew taller, it produced fewer seeds in the high density crop. We suggest that such data concerning the biological responses of weeds can improve the precision of bioclimatic distribution models. Finally, we discuss strategies, such as relocation or non-intrusive management practices, for preventing further disappearances of rare arable weeds. Our results should be of considerable interest for the fields of plant ecology, biodiversity research and conservation.

Does irrigation with reclaimed water significantly pollute shallow aquifer with nitrate and salinity? An assay in a perurban area in North Tunisia

In Tunisia, reclaimed water is increasingly used for irrigation in order to mitigate water shortage. However, few studies have addressed the effect of such practice on the environment. Thus, we attempted in this paper to assess the impact of irrigation with reclaimed water on the nitrate content and salinity in the Nabeul shallow aquifer on the basis of satellite images and data from 53 sampled wells. Ordinary and indicator kriging were used to map the spatial variability of these groundwater chemical parameters and to locate the areas where water is suitable for drinking and irrigation. The results of this study have shown that reclaimed water is not an influential factor on groundwater contamination by nitrate and salinity. Cropping density is the main factor contributing to nitrate groundwater pollution, whereas salinity pollution is affected by a conjunction of factors such as seawater interaction and lithology. The predictive maps show that nitrate content in the groundwater ranges from 9.2 to 206mg/L while the electric conductivity ranges from 2.2 to 8.5dS/m. The high-nitrate concentration areas underlie sites with high annual crop density, whereas salinity decreases gradually moving away from the coastline. The probability maps reveal that almost the entire study area is unsuitable for drinking with regard to nitrate and salinity levels. Appropriate measures, such as the elaboration of codes of good agricultural practices and action programs, should be undertaken in order to prevent and/or remediate the contamination of the Nabeul shallow aquifer.

Competition between Imperata cylindrica and maize in the forest savannah transition zone of Nigeria

SummaryImperata cylindrica is a noxious weed that infests annual and perennial crops in most tropical regions. High crop densities may offer opportunities to reduce I. cylindrica competition in small‐scale farming systems. The competitive ability of maize relative to I. cylindrica was evaluated in an addition series experiment in the forest savannah transition zone in 2006 and 2007 at Ibadan, Nigeria. Maize and I. cylindrica were planted in eight monoculture densities (4, 8, 12, 16, 20, 32, 48 and 64 plants m−2) and in a 1:1 mixture at eight total densities (2:2, 4:4, 6:6, 8:8, 10:10, 16:16, 24:24 and 32:32 maize: I. cylindrica plants m−2) as in monoculture. Non‐linear regression models were used to relate crop and weed shoot biomass to their densities and total grain yield to maize density. In maize, intraspecific competition was more than interspecific competition; in I. cylindrica, interspecific competition was higher than intraspecific. As expected, total grain yield was lower in the mixture than in maize monoculture at all total densities. Average maize grain yield in maize monoculture differed from that in mixtures by 0.77 t ha−1 in 2006 and 0.57 t ha−1 in 2007. Niche differentiation indices were <1 in 2006 and >1 in 2007, indicating that both species competed for similar resources in 2006, but not in 2007. The greater competitive ability of maize over I. cylindrica may be associated with rapid growth and canopy development observed in the field.

The Effects of Some Technological Sequences and Environmental Factors on Plant Development and Yield of Kale (Brassica oleracea var. acephala L.)

Normal 0 21 false false false RO X-NONE X-NONE MicrosoftInternetExplorer4 Abstract. Kale or Brassica oleracea L. var. acephala is not well known and cultivated in our country, so it could be considered a new vegetable or a very rare one. From the Brassicaceae group, kale is the most valuable in terms of nutrition. The therapeutic qualities of kale are recognized since antiquity by Hippocrates, Pliny the Elder, Cato the Elder, Galen. Kale was considered a panacea by the romans. (P A‚RVU C., 2005). Kale can be sown between 15 to 30 April or 1 to 15 June, depending on the time when they are to be harvested (C EAUșESCU I. et al., 1984; B UTNARIU H. et al., 1992; P A‚RVU C., 2005). Seedling planting is done in June until the first decade of July (I NDREA D. et al., 2009). A high density crop can be made by direct sowing using calibrated seeds in the amount of 12-15 kg / ha and small distances between rows (21-30 cm). The culture is established later (July-August) and is harvested in autumn, the product is intended for industry (V OGEL , 1996, quoted by I NDREA D. et al., 2009). The main purpose of this paper was to establish an optimal sowing date that ensures the highest yield, adapted to the specific environmental factors of Transylvania.The organized experience was tri-factorial, with factor A - planting period, factor B - hybrid and factor C - seedling type. All factors had two graduations, thus resulted 8 experimental variants. The first planting period was the second decade of May and the second period was the third decade of June. The hybrids used were F1 Winterbor and F1 Redbor and the seedlings, one part were transplanted and the other part were not transplanted.The crops from the first planting period achieved the best results. The conducted study concluded that kale is sensitive in the immediate period after planting in terms of environmental conditions, especially regarding the humidity and temperature. Thus, in regards to the environmental conditions of the Transylvanian Plateau, optimal planting period for kale is the third decade of April.

Integrating Cultural and Mechanical Methods for Additive Weed Control in Organic Systems

Effective weed management strategies are limited in organic cropping systems because herbicide use is prohibited. Enhancing crop competitive ability by integrating both cultural and mechanical weed control methods is a key strategy in such instances, but the relative efficacy of different cultural and mechanical strategies and their interactions and additive effects when combined is not well known. The objective of this study was to determine the individual and additive effects of cultural and mechanical methods on weed suppression and crop yield under organic conditions. A study was performed in two organically managed oat (Avena sativa L.) cropping systems in Saskatoon, SK, Canada, in 2008 and 2009. Three cultural practices, two crop genotypes (competitive and less competitive), high and standard crop densities (500 and 250 plants m–2), narrow and standard row spacings (11.5 and 23 cm), and two post‐emergence tillage levels (harrowing and nonharrowed control) were factorially applied in a randomized block design. Increasing crop density and harrowing increased grain yield by 11 and 13%, respectively. Competitive genotype and high crop density reduced weed biomass by 22 and 52%, respectively. Combining high crop density with post‐emergence harrowing increased the grain yield by 25%. The combined treatment effects on weed biomass were more profound, as the competitive genotype, increased seeding rate, and post‐emergence harrowing decreased weed biomass by 71% compared with standard practices. Integrating cultural and mechanical weed management practices was superior to the use of individual practices because they additively control weeds in an organic cropping system.

Assessing the impact of within crop heterogeneity (‘patchiness’) in young Miscanthus × giganteus fields on economic feasibility and soil carbon sequestration

AbstractIn Ireland, Miscanthus × giganteus has the potential to become a major feedstock for bioenergy production. However, under current climatic conditions, Ireland is situated on the margin of the geographical range where Miscanthus production is economically feasible. It is therefore important to optimize the yield and other ecosystem services such as carbon sequestration delivered by the crop. A survey of commercial Miscanthus fields showed a large number of areas with no Miscanthus crop cover. These patches can potentially lead to reduced crop yields and soil carbon sequestration and have a significant negative impact on the economic viability of the crop. The aim of this research is to assess patchiness on a field scale and to analyse the impacts on crop yield and soil carbon sequestration. Analysis of aerial photography images was carried out on six commercial Miscanthus plantations in south east Ireland. The analysis showed an average of 372.5 patches per hectare, covering an average of 13.7% of the field area. Using net present value models and a financial balance approach it was shown that patchiness has a significant impact on payback time for initial investments and might reduce gross margins by more than 50%. Total and Miscanthus‐derived soil organic carbon was measured in open patches and adjacent plots of high crop density showing significantly lower Miscanthus‐derived carbon stocks in open patches compared to high crop‐density patches (0.47Mg C ha−1 ± 0.42 SD and 0.91Mg C ha−1 ± 0.55 SD). Using geographic information system (GIS) it was shown that on a field scale Miscanthus‐derived carbon stocks were reduced by 7.38% ± 7.25 SD. However, total soil organic carbon stocks were not significantly different between open patches and high crop density plots indicating no impact on the overall carbon sequestration on a field scale over 3–4 years since establishment for these Miscanthus sites.

The relationship between root biomass and productivity of spring oilseed rape (Brassica napus L.) as influenced by crop density and fertilization

A field experiment was conducted from 2008 to 2010 at the Experimental Station of the Lithuanian University of Agriculture (currently – Aleksandras Stulginskis University) on a Calc(ar)i-Endohypogleyic Luvisol (LVg-n-wcc). The objective of this study was to establish the relationship between root biomass and productivity of spring oilseed rape (Brassica napus L.) as influenced by crop density and fertilization level. Treatments of the experiment: factor A – fertilization: 1) without fertilizers, 2) with fertilizers (N 134 P 64 K 94 ); factor B – crop density: 1) 2 kg ha -1 (50.1–100 plants m -2 ), 2) 4 kg ha -1 (100.1–150 plants m -2 ), 3) 6 kg ha -1 (150.1–200 plants m -2 ), 4) 8 kg ha -1 (200.1– 250 plants m -2 ), 5) 10 kg ha -1 (250.1–300 plants m -2 ), 6) 12 kg ha -1 (300.1–350 plants m -2 ), 7) 14 kg ha -1 (350.1–400 plants m -2 ), 8) 16 kg ha -1 (400.1–450 plants m -2 ). It was established that without fertilizers, the highest root dry biomass (2.48 t ha -1 ) of spring oilseed rape at the 0–10 cm soil layer was formed at a plant density of 150.1–200 plants m -2 , while in the crop with fertilizers at a plant density of 100.1–150 plants m -2 (2.64 t ha -1 ). Plant root biomass in the 0–10 cm soil layer at a very high crop density (400–450 plants m -2 ) with and without fertilizers was significantly (P < 0.05) lower (by 35.0% to 37.9% and by 32.2% to 40.9%, respectively) as compared with those densities, where root biomass was the highest. In the treatment without fertilizers parabolic statistically significant (P < 0.05) relationships were established between rape crop density and root dry biomass at the 0–10 and 10–20 cm soil layers. Mineral fertilization, compared with no fertilization, significantly (P < 0.05) increased (by 34.7% to 44.6%) spring rape root biomass at the 0–10 cm soil layer and did not have any significant effect on root biomass at the 10–20 cm soil layer. Parabolic and statistically significant (P < 0.01) relationships exist between the above-ground dry biomass of oilseed rape and plant density. In the crop without fertilizers, the highest spring rape seed yield (2.31–2.38 t ha -1 ) was obtained at a crop density of 250.1–350 plants m -2 and in the crop with fertilizers – at a crop density of 100.1–200 plants m -2 (3.28–3.32 t ha -1 ). A trend of spring oilseed yield decrease with increasing crop density at investigated levels of fertilization was established. Mineral fertilization, compared with no fertilization, at all spring rape plant densities significantly (P < 0.05) (from 30.3% to 81.4%) increased rape seed yield. In the crop without fertilizers, spring rape seed yield significantly depended on the crop density (r 2 = 0.90, P < 0.05) and the above-ground dry biomass of rape at the flowering stage (r 2 = 0.67, P < 0.05). In the crop with fertilizers, rape seed yield was significantly influenced by the crop density (r 2 = 0.66, P < 0.05) and dry biomass of rape roots in the 0–10 cm soil layer at the flowering stage (r 2 = 0.86, P < 0.01).

Herbicide efficacy for control of annual ryegrass (Lolium rigidum Gaud.) is influenced more by wheat seeding rate than row spacing

Conservation cropping systems with no-till and stubble retention improve soil condition and water conservation. However, tillage is replaced by herbicides for weed control in these systems, increasing the threat of herbicide resistance. In the medium to high rainfall zones of the southern wheatbelt of Australia and under irrigation, wider row spacing is used to enable seeding into heavy stubble loads and to avoid stubble burning. Some evidence suggests that wider rows lead to reduced crop competitive ability and crop yields, greater herbicide dependence, and increased spread of resistance. Our aim was to test the hypothesis that increasing seeding rate compensated for reduced competitive ability at wider row spacings, especially when herbicide performance was suboptimal. We examined the impact of two wheat row spacings (18 and 36 cm) and five seeding rates (resulting in a range of densities of ~80–700 plants/m2) on control of Lolium rigidum with five rates of post-emergence application of diclofop-methyl (Hoegrass®), ranging from label rate to lower rates, over two growing seasons. In the presence of L. rigidum, wheat grain yield was unaffected by row spacing but was significantly reduced at low seeding rates, especially at lower herbicide rates. Lolium rigidum was suppressed at higher crop densities but was also unaffected by row spacing. Grain yield was maximised when post-emergence herbicide was applied at 60–100% of the recommended dose at wheat densities &gt;~300 plants/m2. Significant levels of the weed remained in the crop at anthesis in all treatments. Weed dry matter ranged from 525 g/m2 at low crop densities and with no herbicide to 150 g/m2 with the recommended rate of herbicide and high wheat densities. The implications of manipulating crop competitive ability to improve weed control are discussed, especially in conditions where herbicide performance is unreliable due to weeds developing herbicide resistance or adverse environmental conditions.

Sprouts seasonal elongation of two olive cultivars in a high-density orchard

The new high-density cropping systems (>1200 trees ha-1) represent a very interesting proposal for olive orchard profitability. It is crucial to know the morphology and the dynamics of sprout elongation of a cultivar in order to fully assess its suitability for a high-density olive orchard. For this reason we planned a research on two cultivars, Coratina and Arbequina, in a high-density orchard. The apical sprouts elongation of Arbequina early stopped at fruit set without a further step, while Coratina showed a little growth flux after pit hardening. Similar trends showed the lateral proleptic sprouts. Only the sylleptic sprouts of both cultivars had a second period of activity. In all cases, the sprouts elongation finished at the end of summer, when oil accumulation started. Coratina showed higher apical shoot growth and internodes mean length than Arbequina. On the contrary, Coratina showed lower lateral proleptic shoot growth and nodes number than Arbequina, but the same internodes mean length. No significant differences were observed between cultivars for growth, nodes number and internodes mean length of sylleptic shoots. The differences observed between the two cultivars could be explained considering their different vigour. The introduction of this innovative cropping system is allowed to register a considerable reduction of production costs. The result is a considerable increase in the economic performance of the olive grove and a consequent reduction in the unit cost for kg of oil. These data are very useful for varietal choice and field management in high-density orchards and then for new olive breeding programs.

Aumento da produção de grãos de pinhão-manso pela aplicação de benziladenina

O objetivo deste trabalho foi quantificar o florescimento e a produção de grãos de pinhão-manso (Jatropha curcas) em resposta à aplicação de benziladenina diretamente sobre inflorescências fechadas. O experimento foi realizado em campo, com plantas em idade produtiva, em cultivo adensado. Foram avaliados: número de flores femininas e masculinas por inflorescência, número de inflorescências e de cachos por planta, número de frutos por cacho, percentual de abortamento de frutos e produção por planta. O número de flores femininas aumentou pela aplicação do regulador vegetal, com incremento de 170% no número de frutos por cacho. Apesar do menor pegamento de frutos nas plantas tratadas, a aplicação da benziladenina aumentou a produção em 92%.

Phenotypic Plasticity of Spiny Amaranth (Amaranthus spinosus) and Longfruited Primrose-Willow (Ludwigia octovalvis) in Response to Rice Interference

The growth of spiny amaranth and longfruited primrose-willow was studied by growing them alone and in competition with 4 and 12 rice (cv. RC222) plants. Interference with 12 rice plants reduced the height of spiny amaranth beyond 6 wk after planting. The height of longfruited primrose-willow was significantly reduced by the crop interference starting from 4 wk after planting. Both weed species showed the ability to reduce the effects of rice interference by increasing leaf area, leaf and stem biomass in the upper half of the plant, and specific stem length. At 9 wk after planting, for example, longfruited primrose-willow had 89 and 99% leaf biomass in the upper half of the plant when grown with 4 and 12 rice plants compared with only 34% when grown alone. These values for spiny amaranth were 15, 29, and 72% when grown alone, with 4 rice plants, and 12 rice plants, respectively. Despite such plasticity, spiny amaranth's aboveground biomass at final harvest was reduced by 34 and 70% when grown with 4 and 12 rice plants, respectively, compared with its biomass without crop interference. The corresponding values for longfruited primrose-willow were 92 and 98%, respectively. These results suggest that uniform and high crop density could be an important tool to reduce competition from these weeds in direct-seeded rice.

Competition of sorghum cultivars and densities with Japanese millet (Echinochloa esculenta)

Field studies were conducted at two locations in southern Queensland, Australia during the 2003–2004 and 2004–2005 growing seasons to determine the differential competitiveness of sorghum (Sorghum bicolor L. Moench) cultivars and crop densities against weeds and the sorghum yield loss due to weeds. Weed competition was investigated by growing sorghum in the presence or absence of a model grass weed, Japanese millet (Echinochloa esculenta). The correlation analyses showed that the early growth traits (height, shoot biomass, and daily growth rate of the shoot biomass) of sorghum adversely affected the height, biomass, and seed production of millet, as measured at maturity. “MR Goldrush” and “Bonus MR” were the most competitive cultivars, resulting in reduced weed biomass, weed density, and weed seed production. The density of sorghum also had a significant effect on the crop's ability to compete with millet. When compared to the density of 4.5 plants per m2, sorghum that was planted at 7.5 plants per m2 suppressed the density, biomass, and seed production of millet by 22%, 27% and 38%, respectively. Millet caused a significant yield loss in comparison with the weed‐free plots. The combined weed‐suppressive effects of the competitive cultivars, such as MR Goldrush, and high crop densities minimized the yield losses from the weeds. These results indicate that sorghum competition against grass weeds can be improved by choosing competitive cultivars and by using a high crop density of &gt;7.5 plants per m2. These non‐chemical options should be included in an integrated weed management program for better weed management, particularly where the control options are limited by the evolution of herbicide resistance.

Performance of prohexadione-calcium on shoot growth and fruit quality of apple — Effect of spray surfactants

Vegetative growth control of apples (Malus × domestica Borkh.) is necessary to maintain a balance between growth and cropping. Pruning is a labour-intensive management practice to achieve this and intrinsically stimulates new growth. Prohexadione-calcium (PC) is a plant bio-regulator that effectively regulat es the shoot extension growth of apples and other tree fruits. Previous research has demonstrated that its efficacy can vary based on the use of spray surfactants and adjuvants. This study investigated the efficacy of two rates of Apogee™, the commercial form of PC, used in combination with the spray surfactants Sylgard 309 and LI 700, on extension shoot growth and yield parameters. Experiments were conducted in Ontario on Empire and Nova Scotia on Royal Court™ Cortland apples. Treatments of 0, 75 or 125 mg L-1 PC, with and without either 0.5% (vol/vol.) LI 700 surfactant or 0.05% (vol/vol) Sylgard 309 surfactant were applied to Empire trees, and 75 or 125 mg L-1 PC, with or without 0.5% (vol/vol) LI 700, were applied to Royal Court™ trees. An untreated control treatment was also included for comparison purposes. A total of two sprays were applied to the Empire trees and a total of three sprays were applied to the Royal Court™ trees. PC significantly decreased the vegetative growth of Empire and Royal Court™ trees by approximately 18 to 44%, respectively, and the efficacy of PC was enhanced when combined with either Sylgard 309 or LI 700 surfactant. No additional benefit in vegetative growth control was gained when using Apogee™ at rates of 125 mg L-1 PC, relative to 75 mg L-1 PC. The rate of Apogee™ did not influence the number of fruit or yield per tree or mean fruit size of either cultivar. For Empire, LI 700 and Sylgard 309 significantly reduced the number of fruit per tree, resulting in lower yields and crop densities. In addition, higher mean fruit weights, and a greater distribution of fruit in the larger size categories were observed for LI 700. Fruit from Royal Court trees treated with the highest rate of Apogee™ had higher crop densities, poorer coloured fruit, and a higher percentage of fruit less than 60 mm in diameter. These data provide support for the use of alternative surfactants with Apogee™ other than those listed on the US and Canadian product labels. Key words: Apogee™, Empire, Cortland, Regalis, calcium 3-oxido-5-oxo-4-propionylcyclohex-3-enecarboxylate, surfactant