Showing papers on "Sowing published in 2007"

The Happy Seeder enables direct drilling of wheat into rice stubble

Abstract: Lack of suitable machinery is a major constraint to direct drilling into combine-harvested rice residues due to the heavy straw load, and the presence of loose tough straw deposited by the harvester. Therefore, most rice stubbles are burnt in the mechanised rice–wheat systems of south Asia and Australia, as this is a rapid and cheap option, and allows for quick turn around between crops. As well as loss of organic matter and nutrients, rice stubble burning causes very serious and widespread air pollution in the north-west Indo-Gangetic Plains, where rice–wheat systems predominate. A novel approach with much promise is the Happy Seeder, which combines the stubble mulching and seed drilling functions in the one machine. The stubble is cut and picked up in front of the sowing tynes, which engage bare soil, and deposited behind the seed drill as mulch. Evaluation of the technology over 3 years in replicated experiments and farmers’ fields in Punjab, India, showed that establishment of wheat sown into rice residues with the Happy Seeder was comparable with establishment using conventional methods (straw burnt followed by direct drilling or cultivation before sowing) for sowings around the optimum time into stubbles up to 7.5 t/ha. For late sowings, plant density declined significantly at straw loads above 5 t/ha. The mulch also reduced weed biomass by ~60%, and reduced soil evaporation. Yield of wheat sown around the optimum time into rice residues, using the Happy Seeder, was comparable with or higher than yield after straw removal or burning, in replicated experiments and farmers’ fields, for straw loads up to 9 t/ha. In farmers’ fields there was an average yield increase of 9 and 11% in 2004–05 and 2005–06, respectively, compared with farmer practice. For sowings after the optimum time, yield declined significantly at straw loads greater than 7.5 t/ha. The Happy Seeder offers the means of drilling wheat into rice stubble without burning, eliminating air pollution and loss of nutrients and organic carbon due to burning, at the same time as maintaining or increasing yield.

Improving the performance of transplanted rice by seed priming

Abstract: Transplanting is the major method of rice cultivation in the world, in which seedlings are raised in nursery and then transplanted into well puddle and prepared fields. The traditional nursery sowing method is tedious and produces week seedlings that reduce the final yield due to high mortality. The potential of seed priming to improve the nursery seedlings and thus the transplanted rice was evaluated in the present study. The experiment was conducted in the rice growing area (31.45° N, 73.26° E, and 193 m) of Pakistan, during 2004–2005. Seed priming tools employed during the investigation included traditional soaking, hydropriming for 48 h, osmohardening with KCl or CaCl2 (Ψs −1.25 MPa) for 24 h (one cycle), 10 ppm ascorbate for 48 h or seed hardening for 24 h. Priming improved the initial seedling vigor and resulted in improved growth, yield and quality of transplanted fine rice while traditional soaking behaved similar to that of untreated control. Osmohardening with CaCl2 resulted in the best performance, followed by hardening, ascorbate priming and osmohardening with KCl. Osmohardening with CaCl2 produced 3.75 t ha−1 (control: 2.87 t ha−1) kernel yield, 11.40 t ha−1 (control: 10.03 t ha−1) straw yield and 24.57% (control: 22.27%) harvest index. The improved yield was attributed due to increase in the number of fertile tillers. Significant positive correlation was found between mean emergence time of nursery seedlings and kernel yield, nursery seedling dry weight and kernel yield, fertile tillers and kernel yield, and leaf area duration and kernel yield.

Characterization of Pythium spp. Associated with Corn and Soybean Seed and Seedling Disease in Ohio.

Abstract: Cool, moist conditions in combination with minimum tillage, earlier planting, and recent shifts in commercial fungicide seed-treatment active ingredients have led to an increase in corn (Zea mays) and soybean (Glycine max) seedling establishment problems. This situation resulted in an investigation of Pythium spp. associated with seed and seedling diseases. Samples of diseased corn and soybean seedlings were collected from 42 production fields in Ohio. All isolates of Pythium recovered were identified to species using morphological and molecular techniques and evaluated in an in vitro pathogenicity assay on both corn and soybean seed, and a subset of the isolates was tested for sensitivity to fungicides currently used as seed treatments. Eleven species and two distinct morphological groups of Pythium were identified, of which six species were moderately to highly pathogenic on corn seed and nine species were highly pathogenic on soybean seed. There was significant variation (P < 0.05) in sensitivity to mefenoxam, azoxystrobin, trifloxystrobin, and captan both across and within species. Multiple species of Pythium had the capacity to reduce germination of both corn and soybean seed. Results indicated that mefenoxam, azoxystrobin, trifloxystrobin, or captan, when used individually, may not inhibit all pathogenic species of Pythium found in Ohio soils.

Metarhizium anisopliae Seed Treatment Increases Yield of Field Corn When Applied for Wireworm Control

Abstract: In an effort to protect field corn (Zea mays L.) from wireworm (Agriotes obscurus L.) herbivory and yield loss, seeds were treated with conidia of Metarhizium anisopliae strain F52 alone or in combination with clothianidin or spinosad before planting at three farm fields in south coastal British Columbia, Canada. Corn seed treated with M. anisopliae conidia (main effect) resulted in significant increases in stand density (78% M. anisopliae treated vs. 67% no M. anisopliae) and stock and foliage area fresh wt. yield (9.6 Mg ha -1 M. anisopliae treated vs. 7.6 Mg ha -1 no M. anisopliae), and significantly increased plant (stock and foliage) fresh wt. when it was applied together with spinosad or with no additional agrichemical at one location. Spinosad had no effect on corn yield, whereas clothianidin caused a significant increase in plant stand density and yield. Wireworm cadavers showing M. anisopliae strain F52 growth were retrieved from treated plots, suggesting that the increase in yield may have been due to wireworm control. Laboratory experiments provided no evidence that the increase in stand density and yield from the M. anisopliae-treated corn seed was attributable to an increase in germination rate or root growth. We concluded that seed treatment with this fungus may be a novel method to increase stand density and yield of corn.

Potential effects of changes in mean climate and climate variability on the yield of winter and spring crops in Switzerland

Abstract: Climate change is expected to affect both the average level and the variability of crop yields. In this modelling study, we quantified mean and inter-annual variability of grain yield for maize Zea mays L., winter wheat Triticum spp. L. and winter canola Brassica napus L. for climatic conditions corresponding to current and doubled atmospheric CO2 concentrations. Climate scenarios with and without taking into account changes in the inter-annual variability of climate were developed from the output of a regional climate model for the time window 2071 to 2100. Climate change effects on the mean yield of maize and canola were consistently negative, but a positive impact was simulated for mean yield of winter wheat for elevated CO2 concentration. The coefficient of yield variation increased in the scenarios for maize and canola, but decreased for wheat. Higher thermal time requirements increased mean yield and reduced yield variability for all crops. Shifts in the sowing dates had a beneficial impact on the yield of maize, but not on the yield of canola and wheat. It is concluded that in the Alpine region, the potential effect of climate change is crop-specific. However, the introduction of new cultivars may provide means by which to maintain or even increase current productivity levels for most of the crops.

Effect of maize planting density on the performance of maize/soybean intercropping system in a guinea savannah agroecosystem

Abstract: Two field experiments were conducted during the 2004 early and late seasons at the Agricultural Vocational Training Centre, Otobi, Otukpo in the southern guinea savanna agro-ecological zone of Nigeria to evaluate the effects of maize planting density (38,000; 44,440 and 53,330 plants/ha) in intercrop with soybean varieties (TGX 1448-2E and Samsoy-2) on the growth, yield and productivity of the maize/soybean intercropping system. The soybean varieties were maintained at the optimum planting density of 266,660/ha in both sole and intercrops while sole maize (TZR-EW) plots were at the recommended planting density of 53,330 plants/ha. Samsoy -2 soybean plants were taller at the various ages of growth, had more leaves and attained 50% flowering earlier, produced more and heavier nodules than TGX 1448-2E but TGX 1448-2E produced significantly (P < 0.01) more pods and higher seed yield in both seasons. Intercropping reduced the number of soybean pods per plant by 46% in the early season and seed yield by 42 and 46% in the early and late seasons, respectively. Increasing maize planting density reduced soybean seed yield by 21 and 23% at maize planting density of 44,440 and 53,330 plants/ha, respectively, compared with intercropping at 38,000 maize plants/ha. Maize plant height and leaf production were not influenced by intercropping nor by maize planting density but in the late season, maize grain yield was highest with 53,330 maize density/TGX 1448-2E but lowest with 38,000 maize density/Samsoy-2 cropping. The productivity of the intercropping system indicated yield advantage of 2-63% as depicted by the LER 0f 1.02-1.63 showing efficient utilization of land resource by growing the crops together and this increased with maize planting density. The total monetary return was higher for the intercrops than the sole crops with the values highest with 53,330 maize density/TGX 1448-2E in both early (N293,171.80) and late (283,069.70) seasons. The implication of this is that farmers in the study area would earn more income growing the crops together. Key words: Maize planting density, soybean, intercropping, land equivalent ratio, monetary return.

Long-term effectiveness of sowing high and low diversity seed mixtures to enhance plant community development on ex-arable fields

Abstract: Questions: How is succession on ex-arable land affected by sowing high and low diversity mixtures of grassland species as compared to natural succession? How long do effects persist? Location: Experimental plots installed in the Czech Republic, The Netherlands, Spain, Sweden and the United Kingdom. Methods: The experiment was established on ex-arable land, with five blocks, each containing three 10 m x 10 m experiment tal plots: natural colonization, a low- (four species) and high-diversity (15 species) seed mixture. Species composition and biomass was followed for eight years. Results: The sown plants considerably affected the whole successional pathway and the effects persisted during the whole eight year period. Whilst the proportion of sown species (characterized by their cover) increased during the study period, the number of sown species started to decrease from the third season onwards. Sowing caused suppression of natural colonizing species, and the sown plots had more biomass. These effects were on average larger in the high diversity mixtures. However, the low diversity replicate sown with the mixture that produced the largest biomass or largest suppression of natural colonizers fell within the range recorded at the five replicates of the high diversity plots. The natural colonization plots usually had the highest total species richness and lowest productivity at the end of the observation period. Conclusions: The effect of sowing demonstrated dispersal limitation as a factor controlling the rate of early secondary succession. Diversity was important primarily for its 'insurance effect': the high diversity mixtures were always able to compensate for the failure of some species.

Restoration of Prairie Community Structure and Ecosystem Function in an Abandoned Hayfield: A Sowing Experiment

Abstract: Using a multispecies seed sowing experiment, we investigated the roles of seed and microsite limitation in constraining the restoration of native prairie diversity and ecosystem function in an abandoned upland hayfield in northeastern Kansas. Seeds of 32 native and naturalized plant species from the regional pool were sown into undisturbed and experimentally disturbed field plots. After six growing seasons, experimental sowing led to major shifts in species and functional group composition, increases in native species abundance and floristic quality, declines in abundance of non-native species, and increases in plant diversity. These changes in community structure led to significant changes at the ecosystem level including increases in light capture, peak biomass, primary production, litter biomass, root biomass, and C storage in roots. Our findings reveal the importance of seed limitations in constraining the natural recovery of prairie vegetation, biodiversity, and ecosystem functioning in this grassland and confirm broadcast sowing as a useful tool for the restoration of upland hayfield sites.

Planting Date and Nitrogen Effects on Grain Yield and Protein Content of Spring Wheat

Abstract: High grain yield with adequate protein concentration is an important goal for spring wheat (Triticum aestivum L.) production. A field experiment conducted at two sites representing sandy loam and clay loam soils in Ottawa during 2003 and 2004 examined the effects of planting date and nitrogen (N) management on grain yield and grain protein concentration (GPC) in spring wheat. Cultivar AC Brio was planted at three dates at about 10 d intervals starting from the last week of April. Five N treatments were 0, 60, and 100 kg N ha 21 applied as preplant, 60140 (preplant 1 topdress at boot stage), and 60 1 40 kg N ha 21 (preplant 1 foliar spray at boot stage). Both planting date and N had significant effects on grain yield and GPC. When planting was delayed beyond mid-May, grain yield was reduced by 15 to 45% in three out of four site-years. However, GPC increased by 6 to 17% in all late planting dates than the early plantings. Grain yields were increased with N application, but there was no benefit due to split N application as topdress or foliar spray than a single application at 100 kg N ha 21 . Regardless of application method, GPC was greater with 100 kg N ha 21 than with 0 or 60 kg ha 21 , and GPC was more responsive to applied N in a sandy loam soil than in the clay loam soil. Results of this study suggest that it is likely to achieve the target GPC in spring wheat without a significant reduction in grain yield if wheat is planted before the middle of May, especially in clay loam soil.

Asymbiotic and symbiotic seed germination of Eulophia alta (Orchidaceae)—preliminary evidence for the symbiotic culture advantage

Abstract: Eulophia alta (Linnaeus) Fawcett & Rendle seeds collected from the Florida Panther National Wildlife Refuge (Collier County, FL; FPNWR) were used in a screen of five asymbiotic orchid seed germination media to determine their effectiveness in promoting germination and protocorm development. In addition, 10 fungal isolates collected from the roots of E. alta at sites in the FPNWR, Highlands County (FL), and Goethe State Forest (Levy County, FL; GSF), and a fungal isolate from the roots of Spiranthes brevilabris collected from GSF were screened for their effectiveness at promoting in vitro symbiotic germination of E. alta seeds. After 18 weeks asymbiotic culture, seeds sown on PhytoTechnology Orchid Seed Sowing Medium germinated to a higher percentage (87.9%) and had a higher percentage of protocorms with developing protomeristems (32.7%) than seeds cultured on Knudson C, Malmgren Modified Terrestrial Orchid Medium, ½-strength Murashige & Skoog, or Vacin & Went Modified Orchid Medium. Significantly more leaf-bearing protocorms were observed on PhytoTechnology Orchid Seed Sowing Medium (0.8%) and Vacin & Went Modified Orchid Medium (1.3%) than other media tested. Of the fungi tested, one fungal isolate (Ealt-396) promoted germination to 69.0%, two isolates promoted germination to less than 0.75% and did not support further protocorm development, and eight isolates did not support germination. Seeds co-cultured in darkness with Ealt-396 grew more rapidly than asymbiotic seedlings following germination. In addition, co-cultured (=symbiotic) seedlings continued to develop more rapidly than asymbiotic seedlings upon transfer to 16/8 h light/dark photoperiod. Symbiotic seed culture of E. alta may be a more desirable method of propagation since protocorms develop more rapidly than seeds sown on asymbiotic media. Symbiotic seedlings may be more appropriate for reintroduction to natural areas than asymbiotic seedlings since symbiotic seedlings could serve to inoculate soils with a germination promoting mycobiont.

Root penetration rate - a benchmark to identify soil and plant limitations to rooting depth in wheat.

Abstract: Data on wheat rooting depth was compiled from 36 agronomic experiments conducted in southern NSW from 1990 to 2004. Rooting depth was measured by direct soil coring and observation of roots using core-break or root washing techniques. Maximum rooting depth varied from 80 to 180 cm and was influenced by the depth of soil wetting, soil type and the duration of the vegetative phase (sowing to anthesis) as determined by interactions of sowing date, variety and seasonal conditions. The root penetration rate (RPR cm/day), defined as (maximum root depth measured at or after anthesis) / (days from sowing to anthesis), emerged as a simple but unifying parameter which could be used to estimate the potential rooting depth of wheat on different soils. RPR, expressed on a thermal time basis, was highly correlated with that expressed on a simpler time basis (r = 0.92). Incomplete wetting of the soil profile reduced maximum rooting depth and RPR in 12 of the 36 crops studied, and root penetration in the subsoil was clearly restricted in soil layers with less than 45 to 50% plant available water. Soil type influenced the RPR. The average RPR for wheat was 1.13 ± 0.04 cm/day on Red Kandosols (n = 11), 1.01 ± 0.07 cm/day on a Red Sodosol (n = 3) and 0.79 ± 0.03 cm/day on Red Chromosols (n = 10). The RPR was relatively constant across cultivars and sowing dates within these soil types, although there was some evidence for a reduction in RPR with later sowing independent of time or thermal time. We suggest that the RPR (cm/day) established for wheat on various soil types provides a useful tool for wheat growers to estimate the rooting depth and available water and nutrients in-season. It also provides a benchmark to indicate potential subsoil limitations to crop growth, and for researchers investigating opportunities to increase the maximum rooting depth of wheat through management or breeding.

Differential accumulation patterns of phosphorus and potassium by canola cultivars compared to wheat

Abstract: The phosphorus (P) and potassium (K) accumulation patterns of canola (Brassica napus L) are poorly understood, although such information is essential for determining optimal P- and K-fertilizer strategies This study investigated the patterns of P and K uptake and distribution among plant organs of three early or midmaturing canola cultivars (Tribune, Trigold, and Boomer) differing in K efficiency compared to wheat (Triticum aestivum L cv Nyabing) Plants were grown in a glasshouse with nonlimiting P and K supply and harvested at eight growth stages until maturity Maximum P accumulation by all canola cultivars occurred during late flowering (GS 5,5; 84 d after sowing), whereas P accumulation in wheat plants peaked just prior to anthesis (Z59; 73 d after sowing) Maximum accumulation of K in canola cultivars Tribune and Trigold occurred 73 d after sowing (GS 4,8), but peaked earlier (61 d after sowing) in Boomer canola (GS 4,2) and Nyabing wheat (Z55) The results highlight the importance of early P and K supply to both species; however, the extended uptake of P and K by the canola cultivars Trigold and Tribune compared to wheat suggests that availability of soil P or K postflowering may be of more importance to canola than to wheat

Colonization by Arbuscular Mycorrhizal Fungi of Sorghum Leads to Reduced Germination and Subsequent Attachment and Emergence of Striga hermonthica

Abstract: TWO SORGHUM CULTIVARS: the Striga-tolerant S-35 and the Striga-sensitive CK60-B were grown with or without arbuscular mycorrhizal (AM) fungi, and with or without phosphorus addition. At 24 and 45 days after sowing (DAS) of sorghum, root exudates were collected and tested for effects on germination of preconditioned Striga hermonthica seeds. Root exudates from AM sorghum plants induced lower germination of S. hermonthica seeds than exudates from non-mycorrhizal sorghum. The magnitude of this effect depended on the cultivar and harvest time. A significantly (88-97%) lower germination of S. hermonthica seeds upon exposure to root exudates from AM S-35 plants was observed at both harvest times whereas for AM inoculated CK60-B plants a significantly (41%) lower germination was observed only at 45 DAS. The number of S. hermonthica seedlings attached to and emerged on both sorghum cultivars were also lower in mycorrhizal than in non-mycorrhizal plants. Again, this reduction was more pronounced with S-35 than with CK60-B plants. There was no effect of phosphorus addition on Striga seed germination, attachment or emergence. We hypothesize that the negative effect of mycorrhizal colonization on Striga germination and on subsequent attachment and emergence is mediated through the production of signaling molecules (strigolactones) for AM fungi and parasitic plants.

Increasing use efficiency of boron fertilisers by rescheduling the time and methods of application for crops in India

Abstract: Boron-deficiency is prevalent in light-textured acidic soil regions receiving high precipitation. Crop use efficiency of fertiliser B is also low under such B-leaching environments. For high leaching regimes, we hypothesised that the optimal timing and method of B application would vary with the crop sensitivity to B-deficiency and periods of peak demand for B. The aim of the present experiment was to vary the timing and method of B application to increase use efficiency on typical B-deficient Entisols. Mustard (Brassica campestris L.), wheat (Triticum aestivum L.) and potato (Solanum tuberosum L.) were the test crops. There were seven treatment combinations of B, applied either to soil or as foliar sprays at different doses and growth stages of the crops. Biomass and yield related characters of the crops at harvest, B concentration in plants and its uptake increased with B application being highest in mustard, followed by potato and wheat. Foliar application, in general had higher economic benefits than soil application. Split application of B either to soil (as basal and 25 days after sowing) or foliar sprays (at 25 and 40 and 25 and 45 days after sowing for mustard and potato, respectively) had an edge over a single application. For wheat, a single late application of B (at 45 or 60 days after sowing through soil or foliar spray, respectively) was more effective than the early or split application in increasing yields. Better use efficiency of B can thus be achieved if it is applied late for wheat but in splits over a longer period for mustard and potato with higher economic benefits.

Oil Content and Fatty Acid Composition of Some Safflower (Carthamus tinctorius L.) Varieties Sown in Spring and Winter

Abstract: Oil content and fatty acid composition were examined for Yenice (spineless), Dincer (spineless) and Remzibey-05 (spiny) saf- flower varieties planted winter and spring seasons in 2004-2005. Oil content was affected by sowing time and variety. Oil content in three varieties ranged from 24.53 % to 28.47 % in winter sowing and from 21.23 % to 25.76 % in spring sowing. A significant sowing time x variety interaction for oil content was not observed. The sowing time x variety interaction was not significant for all fatty acids examined. Only the stearic acid among major fatty acids (palmitic, stearic oleic, and linoleic acids) and the linolenic acid were influenced (P<0.01 and P<0.05, respectively) by sowing time. The stearic acid content in varieties increased with the ratio of 0.18 % in winter sowing time. The linolenic acid was higher of 0.02 % in spring sowing. It was recorded that there was a negative correlation between the palmitic and the stearic acids in winter (r= -0.063) and spring (r= -0.806, P<0.01) sowings. Also, there was an inverse relationship (r= - 0.999, P<0.01) between the oleic and linoleic acids in both all varieties and two sowing times. The results of the study have been demonstrated the sowing time and variety may have an important effect on oil quality and content of safflower seed. Therefore, winter sowing time may be recommended in Ankara conditions.

Surface-soil responses to paraplowing of long-term no-tillage cropland in the Southern Piedmont USA

Abstract: The type of conservation-tillage management employed could impact surface-soil properties, which could subsequently affect relationships between soil and water quality, as well as with soil C sequestration and greenhouse gas emissions. We determined soil bulk density, organic C and N fractions, plant-available N, and extractable P on Typic Kanhapludults throughout a 7-year period, in which four long-term (>10 years), no-tillage (NT) water catchments (1.3–2.7 ha each) were divided into two treatments: (1) continuation of NT and (2) paraplowing (PP) in autumn (a form of non-inversion deep ripping) with NT planting. Both summer [cotton (Gossypium hirsutum L.), maize (Zea mays L.), sorghum (Sorghum bicolor L. Moench), soybean (Glycine max L. Merr.)] and winter [wheat (Triticum aestivum L.), barley (Hordeum vulgare L.), rye (Secale cereale L.), crimson clover (Trifolium incarnatum L.)] crops were NT planted throughout the study under each management system. Soil bulk density was reduced with PP compared with NT by as much as 0.15 Mg m � 3 , but the extent of reduction was inversely related to the time lag between PP operation and sampling event. Soil organic C became significantly enriched with time during this study under NT (0.49 Mg C ha � 1 year � 1 ), but not under PP, in which poultry litter was applied equivalent to 5.7 Mg ha � 1 year � 1 to all water catchments. Soil maintained a highly stratified depth distribution of organic C and N fractions and extractable P under both NT and PP. Inability to perform the PP operation in the last year of this study resulted in rapid convergence of soil bulk density between tillage systems, suggesting that PP had <1-year effectiveness on soil loosening. The high energy cost of PP (ca. 30 kW shank � 1 ) and the lack of sustained improvement in surface-soil properties put into question the value of PP for improving upon long-term NT management in sandy loam and sandy clay loam Ultisols of the Southern Piedmont USA, unless large effects on crop yield, water quality, or other ecosystem processes warrant its use. Published by Elsevier B.V.

Traffic alternatives for harvesting soybean (Glycine max L.) : Effect on yields and soil under a direct sowing system

Abstract: This initially high level of soil compaction in some direct sowing systems might suggest that the impact of subsequent traffic would be minimal, but data have not been consistent. Soil compaction is caused by the high traffic intensity and weight of tractor and combines in harvest operations, especially when these operations are carried out on wet soil or with high-pressure tyres. Traffic effects on the yield of soybean and on some physical soil properties were studied over a period of 3 years. After this period, the reduction of traffic intensity from 38 to 15 Mg km −1 ha −1 produced an increase on the yields of 29.2% from the base year improving the incomes by US$134 ha −1 besides the reduction of fuel consumption of 35.5%. With the results obtained in this work it can be assumed that traffic reduction at harvest has a good potential to increase yields and reduce soil compaction under direct sowing system on the Rolling Pampa Region, Argentina.

Phalaris minor seedbank studies: longevity, seedling emergence and seed production as affected by tillage regime

Abstract: Summary Studies were conducted to investigate seed longevity, seedling emergence and seed production of the weed Phalaris minor in wheat in northern India. The longevity of P. minor seeds buried in bags in the field was often limited to less than 1 year, although many seeds buried at 30 cm depth in a rice–wheat rotation remained viable for longer. The application of direct seeding in wheat reduced the seedling emergence rate of P. minor, when compared with conventional ploughing and sowing. However, a larger P. minor seedbank in the upper soil layer in plots under direct seeding partly reversed this positive effect in one of the two studies. Besides differences in relative distribution of weed seeds through the soil profile, it was likely that other factors such as reduced soil disturbance and soil characteristics associated with the application of direct seeding were also involved in regulating the emergence rate. Mature P. minor plants in wheat were found to invest a stable part (27%) of their aboveground biomass in seed, so that total seed weight was strongly linearly correlated with the aboveground biomass of the mother plant. Individual seed weight, however, was little affected by the weight of the mother plant.

Impact of Water Stress on Maize Grown Off-Season in a Subtropical Environment

Abstract: During the last decade, the production of off-season maize has increased in several regions of Brazil. Growing maize during this season, with sowing from January through April, imposes several climatic risks that can impact crop yield. This is mainly caused by the high variability of precipitation and the probability of frost during the reproduction phases. High production risks are also partially due to the use of cultivars that are not adapted to the local environmental conditions. The goal of this study was to evaluate crop growth and development and associated yield, yield components and water use efficiency (WUE) for maize hybrids with different maturity ratings grown off-season in a subtropical environment under both rainfed and irrigated conditions. Three experiments were conducted in 2001 and 2002 in Piracicaba, state of Sao Paulo, Brazil with four hybrids of different maturity duration, AG9010 (very short season), DAS C032 and Exceler (short season) and DKB 333B (normal season). Leaf area index (LAI), plant height and dry matter were measured approximately every 18 days. Under rainfed conditions, the soil water content in the deeper layers was reduced, suggesting that the extension of the roots into these layers was a response to soil water limitations. On average, WUE varied from 1.45 kg m -3 under rainfed conditions to 1.69 kg m -3 under irrigated conditions during 2001. The average yield varied from 4209 kg ha -1 for the hybrids grown under rainfed conditions to 5594 kg ha -1 under irrigated conditions during 2001. Yield reductions under rainfed conditions were affected by the genotype. For the hybrid DKB 333B with a normal maturity, yield was reduced by 25.6 % while the short maturity hybrid Exceler was the least impacted by soil water limitations with a yield reduction of only 8.4 %. To decrease the risk of yield loss, the application of supplemental irrigation should be considered by local farmers, provided that this practice is not restricted by either economic considerations or the availability of sufficient water resources.

Cultivar and Seeding Rate Effects on the Competitive Ability of Spring Cereals Grown under Organic Production in Northern Canada

Abstract: Organically managed production systems often experience greater weed pressure than their conventional counterparts, potentially causing yield losses and increased weed seed build-up. The use of competitive crop cultivars and the cultural practice of increasing seeding rates may moderate such production constraints. Field trials were conducted at two organically managed locations in Alberta, Canada for 2 yr to determine the effect of competition with tame oat (Avena sativa L.), cultivar, and crop seeding rate (300 and 600 seeds m -2 ) on the competitive ability and agronomic performance of Canadian spring wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.). Cultivars were selected based on their differing heights, tillering capacities, and times to maturity. Simulated weed competition from tame oat reduced grain yield by an average of 27%. Barley cultivars were generally more competitive than wheat cultivars. Height and early maturity were more closely associated with weed suppression and yield maintenance than tillering capacity. The modem semidwarf CDC Go was the highest yielding wheat cultivar, but was a poor weed suppressor. Doubling the seeding rate increased grain yield and weed suppression. This effect was not cultivar specific, which implies that doubling the seeding rate may be a generally effective method of overcoming yield losses and weed seed build-up associated with increased weed populations under organic production.