Showing papers on "Sowing published in 2003"

Effects of Silicon on Growth of Wheat Under Drought

Abstract: Plants of wheat growing in pots with silicon (Si) applied before sowing had greater plant height, leaf area, and dry materials compared to those without Si applied in well watering conditions. Drought stress was applied by withholding watering for 12 days from 26‐day old seedlings. In the stress conditions, plants growing in Si‐applied soil could maintain higher relative water content (RWC), water potential and leaf area compared to those without Si applied. Moreover, the Si applied plant dry materials were not significantly changed by drought while those of plants growing in pots without Si applied were significantly decreased, and this was mainly due to growth inhibition of the shoots. Drought stressed wheat growing in pots with Si applied had a significantly greater leaf weight ratio (LWR) and lower specific leaf area (SLA) compared to those of stressed plants in the absence of applied Si. This demonstrates that the leaves of stressed plants growing in pots with Si applied were thicker compare...

Seed limitation and the regulation of community structure in oak savanna grassland

Abstract: Summary 1 We present results from a long-term sowing experiment conducted in nutrient-poor savanna grassland in eastern Minnesota. We examine the effects of a one-time seed addition of 23 grassland species on plant community dynamics and structure over eight growing seasons. 2 Our goals were to: (i) test the importance of seed availability in regulating plant colonization dynamics and species richness; (ii) assess both the initial effects of sowing on species diversity and community structure and whether these effects increased, persisted or dissipated over the long-term; and (iii) determine the long-term impacts of sown species on the structure and dynamics of the existing community, including effects on species diversity, the abundance of existing (non-sown) species, extinction rate and abundance hierarchy. 3 Sowing led to the successful establishment of several plant species that had not been present in the plots and to increased abundance of other species that were already present. 4 Sowing led to sustained, significant changes in community structure, including increased species richness, increased community evenness, and decreased absolute and relative abundance of non-sown species. Effects of sowing were large and significant 8 years after sowing, revealing the role of seed limitation in these grassland communities. 5 In total, the results suggest that dispersal limitations, species pools and local biotic processes interact to regulate plant community structure.

Seed priming winter wheat for germination, emergence, and yield

Abstract: Insufficient stand establishment of winter wheat (Triticum aestivum L.) is a major problem in the low-precipitation (<300 mm annual) dryland summer fallow region of the inland Pacific Northwest, USA. Low seed zone water potential, deep planting depths with 15 cm or more soil covering the seed, and soil crusting caused by rain before seedling emergence frequently impede winter wheat stands. A 2-yr study involving laboratory, greenhouse, and field components was conducted to determine seed priming effects on winter wheat germination, emergence, and grain yield. Two cultivars were used because of their strong (Edwin) and moderate (Madsen) emergence capabilities. Germination rate was measured in the laboratory by 44 treatment combinations (two cultivars × three priming durations × seven priming media + two checks). Germination rate differed between cultivars as well as by priming duration, priming media, and concentration of priming media. The most promising laboratory treatments were advanced to greenhouse and field experiments where emergence and grain yield (field only) were measured in 10 treatments (two cultivars × four priming media + two checks) from wheat planted deep with 16 cm of soil covering the seed. In the greenhouse, seed primed in potassium chloride (KCI), polyethylene glycol (PEG), and water led to enhanced emergence of Madsen, but not of Edwin, compared with checks. Rate and extent of seedling emergence was greater for Edwin compared with Madsen irrespective of priming media in three of four field plantings at Lind, WA. None of the seed priming media benefited field emergence or subsequent grain yield in either cultivar compared with checks. Overall, results suggest that seed priming has limited practical worth for enhancing emergence and yield of winter wheat planted deep into summer fallow.

Weeds in fields with contrasting conventional and genetically modified herbicide-tolerant crops. I. Effects on abundance and diversity.

Abstract: We compared the seedbanks, seed rains, plant densities and biomasses of weeds under two contrasting systems of management in beet, maize and spring oilseed rape. Weed seedbank and plant density were measured at the same locations in two subsequent seasons. About 60 fields were sown with each crop. Each field was split, one half being sown with a conventional variety managed according to the farmer's normal practice, the other half being sown with a genetically modified herbicide-tolerant (GMHT) variety, with weeds controlled by a broad-spectrum herbicide. In beet and rape, plant densities shortly after sowing were higher in the GMHT treatment. Following weed control in conventional beet, plant densities were approximately one-fifth of those in GMHT beet. In both beet and rape, this effect was reversed after the first application of broad-spectrum herbicide, so that late-season plant densities were lower in the GMHT treatments. Biomass and seed rain in GMHT crops were between one-third and one-sixth of those in conventional treatments. The effects of differing weed-seed returns in these two crops persisted in the seedbank: densities following the GMHT treatment were about 20% lower than those following the conventional treatment. The effect of growing maize was quite different. Weed density was higher throughout the season in the GMHT treatment. Late-season biomass was 82% higher and seed rain was 87% higher than in the conventional treatment. The difference was not subsequently detectable in the seedbank because the total seed return was low after both treatments. In all three crops, weed diversity was little affected by the treatment, except for transient effects immediately following herbicide application.

Annual losses of weed seeds due to predation in organic cereal fields

Abstract: 1. Post-dispersal seed losses in annual arable weed species are poorly quantified, but may be of significance for natural population control, especially if they can be manipulated. We hypothesized that weed seed predation on the soil surface was significant, so we measured rates in the field to estimate annual seed losses due to predation. 2. Temporal patterns of weed seed losses due to predation ('demand') as well as weed seed production ('supply') were measured from May to June until harvest in August 1999 and 2000 during 2-week exposure periods in four organic cereal fields in the Netherlands. The proportion of weed seeds lost to predators M-i (number of seeds consumed per number of seeds exposed per 14 days) was measured, using cards containing seeds of Stellaria media, Chenopodium album or Avena fatua. Seed production, Y-i (number of seeds per m 2 per 14 days), was measured in 2000, using seed traps. 3. Annual seed loss due to predation, (M) over bar (number of seeds consumed per number of seeds produced per year), was calculated based on M-i and the exposure period of seeds to predators, starting with seed shed and ending with seed burial. The importance of the length of the exposure period on total seed loss was explored using a model. 4. The temporal trend in M-i was consistent among farms and years: high in June and early July, lower in the second half of July and negligible in August and after harvest. Total seed production varied considerably among fields, i.e. 800-16 000 seeds per m(2) per year. The timing of peak seed production also varied substantially. 5. Calculated (M) over bar ranged from 32% to 70%, when assuming continuous exposure of seeds to predators from seed shed till crop harvest. When exposure was limited to 2 or 4 weeks after seed shed, (M) over bar decreased to 18-57% or 28-67%, respectively. Differences between fields and weed species were mainly due to differences in the timing of seed shed. 6. Synthesis and applications. Our results suggest that seed predation in organic cereal fields is an important factor shaping the population dynamics of arable weeds. A combination of environmental conditions (hot and dry weather) and agricultural practices (an early crop sowing) can advance weed phenology and postpone seed burial, resulting in higher proportions of weed seed loss to predation in cereals.

Soil microbial community, fertility, vegetation and diversity as targets in the restoration management of a meadow grassland

Abstract: 1. The enhancement of biodiversity in meadow grassland, an environmental aim of European agricultural policy, requires definition of appropriate management regimes and the rate at which they enhance biodiversity and change ecosystem properties. We describe vegetation changes in a 10-year trial on mesotrophic grassland that was previously agriculturally improved, plus change in the soil microbial community and fertility, important factors that influence biodiversity. 2. Management treatments were three hay-cut dates, plus two mineral fertilizer, two seed addition and two farmyard manure (FYM) applications. Treatment combinations included the traditional management regime (21 July hay-cut date, no mineral fertilizer, autumn grazing with cattle, spring grazing with sheep), modern variants of this (14 June hay-cut date, mineral fertilizer) and exceptional historic variants (1 September hay-cut date). 3. Sowing seed increased species richness and, in the absence of fertilizer and FYM, produced a plant community similar to Geranium sylvaticum–Anthoxanthum odouratum grassland. The greatest cover of sown species was found in seeded treatments, cut for hay on 21 July, in the absence of mineral fertilizer. The target plant community (MG3b grassland) was most rapidly achieved with a 21 July hay cut. Initial decrease in Ellenberg fertility scores only persisted in the 21 July and 1 September cut dates when mineral fertilizer was absent. Soil phosphate was lowest in the joint absence of mineral fertilizer and FYM. 4. There were few treatment effects on the soil microflora. Bacterial biomass was reduced when FYM was applied with the 14 June cut date, but increased when FYM was applied with the 1 September cut date. Fungal biomass decreased when mineral fertilizer was applied. 5. Increased species richness, primarily through an increase in legumes, stress-tolerant and stress-tolerant ruderal plant strategists, was associated with an increase in soil fungi and the abundance of fungi relative to bacteria. All these were associated with seed addition to unfertilized plots cut on 21 July, in the absence of FYM, indicating a functional role for individual species. 6. Synthesis and applications. The enhancement of biodiversity in meadow grassland is a long-term (> 10-year) secondary succession, most rapidly achieved in the absence of mineral fertilizer by cutting for hay in mid-July and autumn grazing with cattle. The sowing of key functional species, i.e. legumes and Rhinanthus minor, was important in facilitating the staged colonization of other sown species.

Modelling the emergence response of weed seeds to burial depth: interactions with seed density, weight and shape

Abstract: Summary 1 Weeds play an important role in arable and horticultural habitats, and models are being developed to improve our understanding of their population dynamics. The position of a weed seed in the soil profile influences the probability of a seed germinating, emerging successfully and its relative time of emergence. Identifying a relationship between the shape or weight of a seed and its ability to emerge from depth may allow the development of generic models. The aim of this study was to quantify seed response to burial depth, to improve the wider application of existing seedling emergence models. 2 A field experiment used weed seeds sown at different depths and densities in a standard substrate. In addition, two laboratory studies used pre-germinated seeds of the same range of species, buried at a range of depths in optimum conditions using the same substrate. These studies explored the effects of seed size, shape and sowing density on seedling emergence and also enabled reserve-dependent pre-emergence mortality to be quantified. 3 The largest and heaviest of the seeds tested overall, Veronica hederifolia, emerged from the greatest depth (8 cm). In contrast, Tripleurospermum inodorum and Veronica arvensis, the two smallest species, showed a sharp decline when burial exceeded 1 cm. However, the link between seed shape or weight and the ability to emerge from depth suggests a complex relationship. Given optimum conditions, some species (Stellaria media and Chenopodium album) have the physical reserves to emerge from a wider range of burial depths than normally observed in the field, suggesting an ability to exploit opportunities when they occur. 4 For some species, emergence was reduced at high seed densities (e.g. Veronica arvensis). These responses may be associated with traits that have evolved to counteract sibling competition. 5 Synthesis and applications. Generic models identifying the maximum depths for seed germination and emergence have a number of practical applications. For example, they can be used to target cultivation to deplete the weed seed bank or to prescribe the optimum depth of mulches to favour certain species. Our model showed that, in general, larger-seeded species emerged from deeper in the soil, but the relationship between seed size and shape and emergence was complex, possibly species specific. Our germination data may also assist our understanding of the relative importance of different causes of seed losses, particularly from different zones of the soil profile, such as the soil surface. Understanding the component processes of seed behaviour and germination is essential to developing sustainable weed management practices in agriculture and horticulture, and the work reported here contributes to a larger programme modelling weed seed bank population dynamics.

Simulating evolution of glyphosate resistance in Lolium rigidum II: past, present and future glyphosate use in Australian cropping

Abstract: Summary Glyphosate is a key component of weed control strategies in Australia and worldwide. Despite widespread and frequent use, evolved resistance to glyphosate is rare. A herbicide resistance model, parameterized for Lolium rigidum has been used to perform a number of simulations to compare predicted rates of evolution of glyphosate resistance under past, present and projected future use strategies. In a 30-year wheat, lupin, wheat, oilseed rape crop rotation with minimum tillage (100% shallow depth soil disturbance at sowing) and annual use of glyphosate pre-sowing, L. rigidum control was sustainable with no predicted glyphosate resistance. When the crop establishment system was changed to annual no-tillage (15% soil disturbance at sowing), glyphosate resistance was predicted in 90% of populations, with resistance becoming apparent after between 10 and 18 years when sowing was delayed. Resistance was predicted in 20% of populations after 25–30 years with early sowing. Risks of glyphosate resistance could be reduced by rotating between no-tillage and minimum-tillage establishment systems, or by rotating between glyphosate and paraquat for pre-sowing weed control. The double knockdown strategy (sequential full rate applications of glyphosate and paraquat) reduced risks of glyphosate and paraquat resistance to <2%. Introduction of glyphosate-resistant oilseed rape significantly increased predicted risks of glyphosate resistance in no-tillage systems even when the double knockdown was practised. These increased risks could be offset by high crop sowing rates and weed seed collection at harvest. When no selective herbicides were available in wheat crops, the introduction of glyphosate-resistant oilseed rape necessitated a return to a minimum-tillage crop establishment system.

Planting Date Influence on Dual-Purpose Winter Wheat Forage Yield, Grain Yield, and Test Weight

Abstract: The use of winter wheat (Triticum aestivum L.) as a dual-purpose forage and grain crop is important to the agricultural economies of the Southern Great Plains of the USA. Planting date is an important management factor in determining the economic success of a dual-purpose winter wheat enterprise. The overall objective of the research reported in this paper is to determine the economic optimal planting date for dual-purpose winter wheat production. The specific objectives are to determine wheat fall-winter forage yield, wheat grain yield, and wheat test weight response to planting date for dual-purpose winter wheat production. Field studies were conducted in north central Oklahoma from 1991-1992 through 1999-2000. The impact of alternative planting dates on dual-purpose wheat fall-winter forage yield, grain yield, and test weight was estimated. Estimated response functions illustrate that delaying the planting date from 10 to 30 September resulted in an 18% increase in expected grain yield, a 68% decrease in expected fall-winter forage yield, and only a 0.5% increase in expected test weight. Optimal planting date is sensitive to the relative value of wheat fall-winter forage and wheat grain, but not sensitive to wheat test weight discount schedules. When the value of wheat forage is high relative to the value of grain, it is more profitable to plant early to increase expected forage yield. Alternatively, when the value of grain is high relative to the value of forage, later planting generates greater net returns.

Cover crop, tillage, and herbicide effects on weeds, soil properties, microbial populations, and soybean yield

Abstract: A field study was conducted during 1997 to 2001 on a Dundee silt loam soil at Stoneville, MS, to examine the effects of rye and crimson clover residues on weeds, soil properties, soil microbial populations, and soybean yield in conventional tillage (CT) and no-tillage (NT) systems with preemergence (PRE)-only, postemergence (POST)-only, and PRE plus POST herbicide programs. Rye and crimson clover were planted in October, desiccated in April, and tilled (CT plots only) before planting soybean. Both cover-crop residues reduced density of barnyardgrass, broadleaf signalgrass, browntop millet, entireleaf morningglory, and hyssop spurge but did not affect yellow nutsedge at 7 wk after soybean planting (WAP) in the absence of herbicides. Densities of these weed species were generally lower with PRE-only, POST-only, and PRE plus POST applications than with no-herbicide treatment. Total weed dry biomass was lower when comparing CT (1,570 kg ha−1) with NT (1,970 kg ha−1), rye (1,520 kg ha−1) with crimson ...

The effects of depth and fluctuating soil moisture on the emergence of eight annual and six perennial plant species

Abstract: Weed seedling emergence is partially dependent on biotic and abiotic conditions directly surrounding the seed. When environmental conditions are appropriate, seed germination and emergence occurs. We studied the impact of seeding depth (surface, 1 to 2, 3 to 4, and 6 to 7 cm) and fluctuating soil moisture regimes (field capacity [FC]–1/3FC–FC; FC–1/6FC–FC) on percent weed emergence in a greenhouse. At FC, wild mustard and field pennycress had the greatest percent emergence when seeds were placed on or near the soil surface, whereas percent emergence of barnyardgrass and round-leaved mallow was unaffected by seeding depth. All the perennials tested had the greatest percent emergence at FC when seeds were placed near or on the soil surface, except for common milkweed which only emerged below the soil surface. When soil moisture levels fluctuated, surface seeds of barnyardgrass, catchweed bedstraw, green foxtail, wheat, and wild oat had less emergence than seeds below the soil surface; field pennycr...

Intercepted Solar Radiation during Seed Filling Determines Sunflower Weight per Seed and Oil Concentration

Abstract: A reduction in intercepted photosynthetically active radiation (PAR) during a short period of seed filling could affect weight per seed and oil concentration in sunflower (Helianthus annuus L.) depending when the reduction occurs. The main objectives of this work were (i) to determine the period of time during which intercepted PAR most influences final weight per seed and oil concentration, and (ii) to establish and validate relationships between intercepted PAR during such a period and oil yield components. Intercepted PAR was modified by shading (0, 50, or 80%) field grown crops during different periods of seed filling. Data from published and unpublished field experiments, in which intercepted PAR per plant was changed during the entire seed filling period by shading, thinning to reduce plant population, or both, were also used. All experiments were performed under adequate water and nutrient conditions. A reduction in intercepted PAR during 7 to 10 d of seed filling affected weight per seed and oil concentration. The developmental interval during which final weight per seed and oil concentration were best accounted for by accumulated intercepted PAR (r 2 > 0.805) began at 250°C d and ended at 450°C days after flowering (DAF). The established relationships were validated with independent data. The relationships obtained in this work help to explain the effects of environment and crop management (sowing date, location, year) on oil yield variation.

Effects of Injected Liquid Cattle Manure on Growth and Yield of Winter Wheat and Soil Characteristics

Abstract: Liquid cattle (Bos taurus) manure should be applied to soils in such a manner that would improve soil fertility and crop production without causing salinity problems or increasing NO - 3 levels. This study investigated the influence of liquid cattle manure on winter wheat (Triticum aestivum L. cv. Yecora) germination, growth, and nutrient utilization. Four treatments were applied in the same plots in a 4-yr field experiment with winter wheat: (i) application of 40 Mg ha -1 yr -1 liquid dairy cattle manure (wet weight basis) before sowing; (ii) single application of 120 and 26 kg ha -1 yr -1 N and P, respectively, as inorganic fertilizers before sowing; (iii) as in ii, but with split application of N, half the amount before sowing and the rest at tillering; and (iv) no fertilization. The biological evaluators used to compare the effect of the treatments were (i) number of seedlings per square meter at tillering for the first year only and (ii) dry biomass at heading and harvest; plant concentration and uptake of N, P, and K; and grain yield for every year of experimentation. The results showed that application of manure did not affect seed germination but resulted in a significant increase in dry biomass at the two growth stages and in grain yield and nutrient uptake, similar to the inorganic N and P fertilization. The amounts of soil available NO 3 -N and P were significantly increased while at the end of the field experiment, soil salinity, organic C, and total N levels remained unchanged.

Evaluating physicochemical constraints of Calcarosols on wheat yield in the Victorian southern Mallee

Abstract: Soil salinity, sodicity, and high extractable boron (B) are thought to reduce wheat yields on alkaline soils of south-eastern Australia; however, little quantitative information on yield penalties to edaphic constraints is available. The relationships between wheat yield of a B-tolerant cultivar and soil physicochemical conditions in the Victorian Mallee were explored using ridge regression analysis, using natural variation in the field. Wheat yields in the survey ranged from 1.3 to 6.1 Mg/ha, with low yields attributed to inadequate soil water supply during pre-anthesis growth. Crop sequences, fallow–wheat, and pulse–wheat left greatest soil water prior to sowing of the wheat crop, and lucerne–wheat the least. A descriptive model explained 54% of variation in wheat yield, with rainfall around anthesis, available soil water in the 0.10–0.40 m layer, nitrate in the 0–0.10 m layer at sowing and salinity, and sodicity in the 0.60–1.00 m layers being important factors. Subsoil salinity (ECe) and sodicity (ESP) appear to be effective surrogates for estimating the likelihood of water extraction in the deep subsoil. The analyses suggest that subsoils need to have an ECe <8 dS/m and ESP < 19% for crops to make use of water deep in the profile. Although soluble B ranged from 2 to 52 mg/kg in the 0.60–1.00 m layer of the alkaline soils considered, B appeared to have little correlation with root growth, water extraction, or yield of wheat, which has been attributed to B-tolerance of the cultivar tested and/or the overbearing effect of high Na+ in these soils.

Effect of the type of environmental stress on the emergence of sunflower (Helianthus annus L.), soybean (Glycine max (L.) Merril) and maize (Zea mays L.) seeds with different levels of vigor

Abstract: Sowing is a critical time in the cycle of a crop and the seeds are frequently exposed to adverse conditions that may compromise the establishment of seedlings in the field. on this basis, the objective of the present study was to determine the effect of types of environmental stress on the emergence of sunflower, maize and soybean seeds with different levels of vigor. High vigor seeds were artificially aged in order to obtain medium and low vigor seeds and then they were sown in clay soil in plastic boxes and submitted to the following types of environmental stress during the germination process : 1) high temperature (35degreesC), 2) low temperature (15 or 18degreesC), 3) water excess (Psi > -0.0001 MPa), 4) water deficiency (Psi approximately equal to -1.1; -1.2 and -0.6 MPa for sunflower, maize and soybean, respectively), 5) sowing at a depth of 7 cm and 6) pathogenic infection of sunflower seeds with Alternaria helianthi, of maize seeds with Fusarium moniliforme and of soybean seeds with Colletotrichum dematium, var. truncata. The results were compared to those obtained with controls sown under optimal condition. It was concluded that: 1) the effect of seed vigor on emergence depends on the type of enviromental stress to which the seeds are exposed, 2) the stress to which the the seeds demonstrated highest sensitivity varied with species and 3) high temperature stress was the one that most impaired the emergence of the three species.

Seed production and germination in two rare and three common co-occurring Acacia species from south-east Australia

Abstract: Seed set, size, viability and germination requirements were investigated for two rare (Acacia ausfeldii and A. williamsonii) and three common (A. pycnantha, A. genistifolia and A. paradoxa) co-occurring congeners in box-ironbark eucalypt forests near Bendigo, south-east Australia to investigate correlates of rarity. Seed size was significantly smaller for the two rare species and germinants were less able to emerge from deeper sowing depths than were the larger seeded common congeners. All species had a strong heat-stimulated germination response. While the rare A. ausfeldii showed strong germination only at the highest temperature treatment (100°C), the common and widespread A. pycnantha showed strong germination across a broad range of temperatures (60-100°C), likely to be experienced by soil-stored seeds during a fire. Seed viability, number of seeds per plant, and number of firm, aborted and eaten seeds per pod varied between species, but the pattern of variation was not related to rarity. Small seed size and a very specific temperature requirement for germination may help to explain rarity in A. ausfeldii, and to a lesser extent in A. williamsonii. Fires are often patchy and heating of the soil is likely to be highly spatially variable, so species with germination responses to a broad range of temperatures have an advantage over those that respond only to a narrow range. A narrower range of soil depths from which seeds can emerge will further reduce the proportion of the seed bank that might recruit following fire. Human impacts on species habitats, such as fragmentation, loss of topsoil through mining, timber harvesting, grazing and urbanization, and consequent reduction in fire intensity, are likely to have further contributed to rarity in these species. The role of pollination and other factors in relation to population size is the subject of further investigation.

Response of Lentil (Lens culinaris Medik) to Plant Density, Sowing Date, Phosphorus Fertilization and Ethephon Application in the Absence of Moisture Stress

Abstract: Lentil (Lenus culinaris Medik) is a major grain legume crop in many developing countries in West Asia, North Africa and many other areas of the world. The effects of sowing date (1 January, 15 January and 2 February), plant density (80, 100 and 120 plants m -2 ), phosphorus level (0, 17.5, 35.0 and 52.5 kg Pha -1 ) and ethephon application [(1500 p.p.m. ethephon (2-chloroethel phosphonic acid) applied 30 days after sowing] were investigated in the semiarid region in the north of Jordan. High yields were obtained for early sowing (1 January), high plant density (120 plants m -2 ), and high phosphorus application rate (52.5 kg P ha -1 ). Yield and yield components were not affected by ethephon application 30 days after sowing.

Risk of environmental contamination by the active ingredient imidacloprid used for corn seed dressing. Preliminary results

Abstract: Aim of the study was to detect the possible loss of a.i. imidacloprid through the fan drain of pneumatic seed drills during corn sowing operations. The experiment regarded Gaucho ® dressed corn seeds. In order to detect air contamination, paper filters were positioned at the air output of the fan; in addition grass and flower samples from green areas near fields were collected immediately after the corn had been sown. Residues of imidacloprid were found both in the paper filters and in the grass and flowers samples. Quantity of imidacloprid in the paper filters increased with increasing exposure times. The results confirm that the air is contaminated by a.i. imidacloprid during normal sowing operations using Gaucho ® dressed corn seeds.

Soybean Cyst Nematode Reduces Soybean Yield Without Causing Obvious Aboveground Symptoms.

Abstract: Field experiments were conducted at locations in northern and southern Illinois, central Iowa, and central Missouri from 1997 to 1999 to investigate the effects of Heterodera glycines on soybean growth, development, and yield. A wide range of infestation levels was present at all locations. Two locally adapted cultivars, one resistant to H. glycines, were grown at each location. Cultivars were planted in alternating four-row strips with 76 cm between rows. For each cultivar, 20 1-m-long single-row plots were sampled every 2 weeks starting 4 weeks after planting. Infection by H. glycines reduced plant height and leaf and stem weight on the resistant cultivars in the first 12 weeks after planting, and delayed pod and seed development 12 to 14 weeks after planting. Biomass accumulation was not reduced on the susceptible cultivars until 10 weeks after planting; reduction in pod and seed development occurred throughout the reproductive stages. Susceptible cultivars produced significantly lower yields than resistant cultivars, but the yield reductions were not accompanied by visually detectable symptoms.

Impact of Rye Cover Crop and Herbicides on Weeds, Yield, and Net Return in Narrow-Row Transgenic and Conventional Soybean (Glycine max) 1

Abstract: A field study was conducted during 1999, 2000, and 2001 at Stoneville, MS, on a Dundee silty clay loam to determine the impact of a rye cover crop with one or two postemergence (POST) herbicide applications on weed control, yield, and net return in narrow-row glyphosate-resistant, glufosinate-resistant, and conventional soybean systems. Cover crop systems included no-cover crop conventional tillage (CT), no-cover crop no-tillage (NT), and rye NT, all with early POST (EPOST), EPOST followed by late POST (LPOST), and no-herbicide weed management. Weed control and net return among glyphosate-resistant, glufosinate-resistant, and conventional soybean systems were similar. One POST ($111/ha) application of herbicides was more profitable than two POST ($79/ha) applications regardless of soybean cultivar and cover crop system. Rye residue reduced total weed density by 9 and 27% and biomass by 19 and 38% compared with no-cover crop CT and NT, respectively. In the rye cover crop, input costs were higher because of the additional cost of seed, planting, and rye desiccation. The additional cost resulted in a lower net return with the rye cover crop ($29/ha) compared with the no-cover crop CT ($84/ha) or NT ($87/ha) system, even though soybean yield in the rye cover crop system was comparable to that from the no-cover crop CT and NT systems. These results showed that because of additional cost, rye cover crop-based soybean production was less profitable compared with existing no-cover crop-based production systems. Nomenclature: Acifluorfen; bentazon; chlorimuron; clethodim; glufosinate; glyphosate; barnyard- grass, Echinochloa crus-galli(L.) Beauv. # 3 ECHCG; browntop millet, Brachiaria ramosa(L.) Stapf # PANRA; hemp sesbania, Sesbania exaltata (Raf.) Rydb. ex A. W. Hill # SEBEX; pitted morning- glory, Ipomoea lacunosa L. # IPOLA; prickly sida, Sida spinosa L. # SIDSP; sicklepod, Senna obtusifolia (L.) Irwin and Barneby # CASOB; smooth pigweed, Amaranthus hybridusL. # AMACH; rye, Secale cereale L. 'Elbon'; soybean, Glycine max (L.) Merr. 'DP 3588', 'DP 5806 RR', 'A 5547 LL'. Additional Index words: Conventional tillage, herbicide, integrated weed management, mulch, net return, no-tillage, transgenic soybean, weed biomass, weed density. Abbreviations: CT, conventional tillage; EPOST, early postemergence; LPOST, late postemergence; NT, no-tillage; POST, postemergence; WAP, weeks after planting.

Biocontrol of Fusarium and Verticillium Wilt of Tomato by Penicillium oxalicum under Greenhouse and Field Conditions

Abstract: Treatments with conidia of Penicillium oxalicum produced in a solid-state fermentation system were applied at similar densities (6 x 10 6 spores/g seedbed substrate) to tomato seedbeds in water suspensions (Tl: 5 days before sowing, or T2: 7 days before transplanting; 15 days after sowing), or in mixture with the production substrate (T3: 7 days before transplanting; 15 days after sowing). Treatments T2 and T3 significantly (P = 0.05) reduced fusarium wilt of tomato in both greenhouse (artificial inoculation) (33 and 28%, respectively) and field conditions (naturally infested soils) (51 and 72%, respectively), while treatment Tl was efficient only in greenhouse (52%). Verticillium wilt disease reduction was obtained with T3 in two field experiments (56 and 46%, respectively), while Tl and T2 reduced disease only in one field experiment (52% for both T1 and T2). Treatment with conidia of P. oxalicum plus fermentation substrate (T3) resulted in better establishment of a stable and effective population of P. oxalicum in seedbed soil and rhizosphere providing populations of approx. 10 7 CFU/g soil before transplanting. Results indicate that it will be necessary to apply P. oxalicum at a rate of approx. 10 6 -10 7 CFU/g in seedbed substrate and rhizosphere before transplanting for effective control of fusarium and verticillium wilt of tomato, and that formulation of P. oxalicum has a substantial influence on its efficacy.

Spatial and temporal distribution of soil inorganic nitrogen concentration in potato hills

Abstract: The purpose of this study was to determine the spatial and temporal variation in soil inorganic N concentration in the potato hill, and to discuss the implications of this variation on soil sampling strategies. The experiment was conducted in 1999 and 2000 using four treatments: bare soil with no N fertilizer applied, and a potato crop with no fertilizer N added, with 180 kg N ha-1 applied at planting, or with 120 kg N ha-1 applied at planting plus 60 kg N ha-1 applied at hilling. Elevated (above background) soil NH4+-N concentrations were measured for 40 or more days after planting, therefore in-season sampling should be done for both soil NO3−-N and NH4+-N. There was a period of up to 50 days between planting and rapid crop N uptake during which loss of NO3−-N from the root zone could occur. Split fertilizer application reduced the risk of NO3−-N loss during this time, but resulted in reduced tuber yield in 1999. Strong vertical variation in soil inorganic N concentration was measured in the potato hill...

Assessing winter wheat responses to climate change scenarios: a simulation study in the u.s. great plains

Abstract: Hard red winter wheat (Triticum aestivum L.) is a major crop in the Great Plains region of the U.S. The goal of this assessment effort was to investigate the influence of two contrasting global climate change projections (U.K. Hadley Center for Climate Prediction and Research and Canadian Centre for Climate Modelling and Analysis) on the yield and percent kernel nitrogen content of winter wheat at three locations in Nebraska. These three locations represent sub-humid and semi arid areas and the transition between these areas and are also representative of major portions of the winter wheat growing areas of the central Great Plains. Climate scenarios based on each of the projections for each location were developed using the LARS-WG weather generator along with data from automated weather stations. CERES-Wheat was used to simulate the responses for two contrasting cultivars of wheat using two sowing dates. The first sowing date represented current sowing dates appropriate for each location. The second sowing date was later and represents the approximate date when the mean air temperature from the climate scenarios is the same as the mean air temperature from the actual climate data at the current sowing dates. The yield and percent kernel nitrogen content using the two climate scenarios generally decrease going from the sub-humid eastern to the semi arid western parts of Nebraska. Results from these simulations indicate that yield and percent kernel nitrogen content using the two climate scenarios could not both be maintained at levels currently simulated. Protein content (directly related to kernel nitrogen content) and end-use quality are the primary determinants for the use of hard red winter wheat in baked goods. Nitrogen management and new cultivars, which can enhance the uptake and translocation of nitrogen, will be proactive steps to meet the challenges of global climate change as represented by these climate scenarios.