Showing papers on "Sowing published in 1998"

Stabilizing Rainfed Wheat Yields with Supplemental Irrigation and Nitrogen in a Mediterranean Climate

Abstract: The West Asia-North Africa (WANA) region, with a Mediterranean-type climate, has an increasing deficit in cereal production, especially bread wheat (Triticum aestivum L.). Rainfed cropping coincides with the relatively cool, rainy winter season, usually from October to May. Cereal yields are low and variable in response to inadequate and erratic seasonal rainfall and associated management factors, such as lack of N and late sowing. In an area where water is limited, small amounts of supplemental irrigation (SI) water can make up for the deficits in seasonal rain and potentially produce satisfactory yields. This field study (1992-1993 to 1995-1996) on a deep clay soil (a Calcixerollic Xerochrept) in northern Syria was conducted for four growing seasons to assess the effects of SI (rainfed, 1/3, 2/3, and full irrigation) combined with N rate (0, 50, 100, and 150 kg ha -1 ) and sowing date (early, normal, and late) on one traditional (Mexipak 65) and three improved bread wheat cultivars (Cham 4, Cham 6, Gomam). Yields of rainfed wheat varied with seasonal rainfall and its distribution, with all main factors having significant effects. A delay in the sowing date from November to January consistently reduced yields and the response to both SI and N. With irrigation, crop responses were generally significant up to 100 kg N ha -1 , while optimum response for rainfed conditions was with 50 kg N ha -1 . An addition of only limited irrigation (1/3 full irrigation) significantly increased yields, but near maximum yields were obtained by 2/3 of full irrigation. Responses to N and SI were greatest for the higher-yielding cultivars. Use efficiency for both water and N was greatly increased by SI. Thug with minimum irrigation during the winter growing season combined with appropriate management, inputs, and varieties, wheat output could be substantially and consistently increased In the semiarid Mediterranean zone. Production functions developed from this dataset can help predict the effects of changing any of these parameters in other locations in the region.

Winter Wheat Seedling Emergence from Deep Sowing Depths

Abstract: Growers in low-precipitation ( 100 mm. Coleoptile length was associated with emergence capability among both cultivars (r 2 = 0.71, P < 0.004) and advanced lines (r 2 = 0.62, P < 0.001). From deep sowing depths in this study: (i) cultivars and advanced lines with Rht 1 and Rht 2 reduced-height genes always emerged poorly compared with Moro; (ii) the Rht 3 reduced-height gene did not hamper emergence to the extent that Rht 1 and Rht 2 did; and (iii) several advanced experimental lines with long coleoptiles equaled or exceeded Moro for emergence.

Effects of Plant Growth-Promoting Rhizobacteria on Loblolly and Slash Pine Seedlings

Abstract: Loblolly and slash pine seed were inoculated at sowing with 1 of 12 different strains of plant growth-promoting rhizobacteria (PGPR) in the greenhouse. Time to germination and seedling densities were determined at 21 days, and seedling biomass was measured at 12 wk after sowing. All bacterial strains significantly increased the speed of seedling emergence over nontreated pine seed. By 12 wk, however, no differences in stand densities were observed between bacteria-treated and nontreated seed for either pine species. Postemergence damping-off was reduced in loblolly pine when seed was treated with 3 of the 12 bacterial strains; however, postemergence damping-off on slash pine seedlings was not affected by rhizobacteria. Treatment with rhizobacteria had a significant positive and negative effect on seedling growth and biomass, which depended on tree species. Loblolly pine shoot and root lengths, as well as the aboveand belowground biomass, were significantly reduced when seeds were treated with strains BS1 and BS2. In contrast, loblolly pine seeds treated with strains BS3, PM2, and INR7 significantly increased the below ground biomass of the seedling root systems. Slash pine seedlings had similar interactions with the bacterial strains. Strain BS1 significantly reduced shoot lengths compared with nontreated seeds, while strains 90-166, INR7, and SE49 increased shoot biomass. Slash pine root lengths and biomass were also reduced when treated with strains BS1 and BS2. Unlike loblolly pine, no bacterial strain increased slash pine root length or biomass. This study suggests that the effects of rhizobacteria inoculation on seedling emergence and plant growth are independent and that the effects are species specific. FOR. SCI. 44(1):139-144. Additional

Changes in mycorrhiza development in maize induced by crop management practices

Abstract: We selected three crop production practices; crop rotation, tillage and phosphorus fertilization, all known to affect arbuscular mycorrhiza (AM) development, to study early AM intraradical colonization in maize. Half of the plots were planted during the first year with either a host (maize, Zea mays L.) or a non-host (canola, Brassica napus L.) crop, and all of them with maize for the second year. Tillage and P fertilization treatments were applied to the plots in the second year. Mycorrhiza development in maize was measured in pot culture bioassays conducted before planting and after harvest of the previous and the subsequent crops, and in the field during the second crop season. Previous cropping of a soil with canola (Brassica napus L.), a non-host plant species, delayed mycorrhiza development of maize in a bioassay conducted with that soil in comparison with a previous cropping cycle with maize (Zea mays L.) or with the original plant species in the field site, bromegrass (Bromus inermis Leys.) and alfalfa (Medicago sativa L.). The delay in mycorrhiza development after cropping with canola was also observed in samples taken from the field and in a bioassay, both conducted at the beginning of the subsequent cropping cycle. Tillage had, on average, little effect on intraradical colonization either in the field or in the bioassays. Phosphorus fertilization also had little effect on mycorrhiza development in the field. Crop rotation with a non-host had the strongest effect on intraradical mycorrhiza development of the three practices studied.

Corn Response to Cover Crop Species, Spring Desiccation Time, and Residue Management

Abstract: Cover crops are integral parts of whole farm systems that indude corn (Zea mays L.), but there is a lack of synchrony between cover crop N release and corn N uptake. This synchrony may be enhanced by varying the cover crop spring desiccation time and subsequent residue management. A field study was established to determine (i) the effect of rye (Secale cereale L.), hairy vetch (Vicia villosa Roth), and rye + hairy vetch spring desiccation timing on cover crop biomass, N content, and C:N ratio and (ii) the effect of the cover crop species, spring desiccation timing, and residue management on soil moisture content, soil mineral N concentration, corn tissue N concentration, and corn grain yield. Chemical desiccation times were either the boot stage of rye (approximately 3 wk prior to corn planting) or the early flowering stage of hairy vetch (several days prior to corn planting) for all three cover crop treatments. Three cover crop residue management treatments were implemented several days after each chemical desiccation : no further treatment (control), cover crop residue mowed (mow), or cover crop residue mowed and disked (mow + disk). All cover crops increased in biomass accumulation, but only hairy vetch increased in N content between desiccation times. Cover crop N availability was more important for corn yield potential than cover crop soil moisture conservation. Corn yields were higher following hairy vetch than following rye and rye + hairy vetch, due to greater N availability from hairy vetch residue. Corn N concentrations and yields were not influenced by desiccation time following hairy vetch, indicating that hairy vetch should be allowed to grow until immediately prior to corn planting, to permit maximum N accumulation. However, corn N concentrations and yields were higher with early desiccation than late desiccation following rye and rye + hairy vetch, indicating that cover crops including rye should be desiccated several weeks before corn planting, Mowing may be an alternative cover crop management technique that enhances the synchrony of cover crop N release with corn N need and uptake while maintaining a moisture conserving mulch.

Assessment of weed and crop fitness in cover crop residues for integrated weed management

Abstract: Cover crop residues are not widely used for weed control because, as a stand-alone tactic, they do not effectively suppress all weeds and their duration of weed control is too short. Field experiments were conducted in 1995 and 1996, under both irrigated and rainfed conditions, to quantify Amaranthus spp., Setaria spp., and soybean emergence and growth in residues of fall-planted, spring-killed barley, rye, triticale, wheat, and hairy vetch. For both weed species, seedling emergence was reduced 3 wk after soybean planting by rye and wheat residues (≥ 2, 170 kg ha−1) in 1996. In 1996, Amaranthus spp. canopy volume was reduced 38 to 71% by residues 3 wk after planting. Likewise, Setaria spp. canopy biomass was reduced 37 to 97% in residues 5 wk after planting over both years. The response comparison index was used to identify frequency by which weed growth was placed at a disadvantage relative to soybean growth. Amaranthus spp. and Setaria spp. growth suppressions 3 to 5 wk after planting indicate potential times for intervention with other integrated weed management tactics such as reduced postemergence herbicide rates and interrow cultivation.

Size and composition of the weed seedbank under different management systems for continuous maize cropping.

Abstract: The size and composition of the weed seedbank after 5 years of maize (Zea mays L.) continuous cropping under four crop management systems was evaluated. The management systems included a conventional system (ploughing, full-rate fertilization, broadcast pre-emergence herbicides), an organic system (ploughing, organic fertilization, physical weed control), a reduced-input system (rotary harrowing, low-rate fertilization, physical post-emergence herbicides) and a strip-cultivation system (non-tillage, banded fertilization and herbicides at sowing, broadcast top-dress fertilization and post-emergence herbicides). Seedbank sampling was performed after maize harvest by taking 270 soil cores per management system at depths of 0-10, 10-20 and 20-30 cm. Weed seedbank size was largest under the organic system (100 761 seeds m -2 ) and smallest under the conventional system (27 601 seeds m -2 ). Differences among maize management systems depended mainly upon weed control efficacy rather than upon tillage effects. Four of the eight major weed species showed differential responses to tillage and weed control methods carried out within maize management systems. Canonical discriminant analysis showed that maize management systems based upon reduced tillage had more characteristic weeds than systems based upon ploughing. Amaranthus retroflexus L., Chenopodium album L., Digitaria sanguinalis L. and Solanum nigrum L. were the most troublesome weeds for the cropping system under study; their relative importance in the seedbank usually varied according to maize management system.

Effect of proximity factors on competition between winter wheat (triticum aestivum) and italian ryegrass (lolium multiflorum)

Abstract: Density and spatial arrangement (rectangularity) effects on the competitive relationships, yield performance, and dynamics in canopy dominance of winter wheat and Italian ryegrass were evaluated using two addition series experiments. In experiment 1, combinations of six densities of each species formed the treatment matrix of addition series. In experiment 2, each species was tested at four densities and three rectangularities (RE) of winter wheat. In monocultures, crop density (plants per square meter) explained 82 to 85% of the total variation in the per-plant biomass of winter wheat in experiment 1. In mixtures of crop and weed, initial wheat density (N1) and initial ryegrass density (N2) and interaction of N1 and N2 explained 74 to 80% of the total variation in the per-plant biomass of winter wheat and 68 to 79% of Italian ryegrass in experiment 1. Intraspecific competition was apparent between 15 and 90 days after emergence (DAE) in winter wheat and between 90 and 170 DAE in Italian ryegrass. In mixtures, RE influenced plant size of Italian ryegrass up to 50 DAE only. Maximum winter wheat intraspecific competition occurred at 170 DAE, but maximum interspecific competition occurred during reproductive stages in mixtures. High RE increased seed yield, seed size, and harvest index of winter wheat and reduced biomass of Italian ryegrass. Grain yield of winter wheat was reduced up to 92% by competition from ryegrass. Even nine ryegrass plants in 100 winter wheat plants m−2 reduced winter wheat grain yield by 33%. However, the extent of loss in winter wheat grain yield was less in RE 16 (wider spacing) than in RE 1 (square planting) or 4 (close row spacing). Winter wheat was the stronger competitor during vegetative stages, but Italian ryegrass became the stronger competitor during the reproductive stages of development. Winter wheat leaves dominated at the top canopy during the vegetative stage, but ryegrass dominated at the top canopy during the reproductive stages. In the top canopy of mixtures at 200 DAE, the leaf area indices (LAI) of ryegrass was 6.6 times greater than winter wheat at RE 1 compared to only 1.6 times at RE 16. Greater LAI of Italian ryegrass in the top canopy reduced photosynthetically active radiation available to winter wheat by 68% at booting stage.

Sustaining productivity of a Vertisol at Warra, Queensland, with fertilisers, no-tillage, or legumes. 5. Wheat yields, nitrogen benefits and water-use efficiency of chickpea-wheat rotation

Abstract: Summary. In this study, the benefits of chickpea–wheat rotation compared with continuous wheat cropping (wheat–wheat rotation) were evaluated for their effects on soil nitrate nitrogen, wheat grain yields and grain protein concentrations, and water-use efficiency at Warra, southern Queensland from 1988 to 1996. Benefits in terms of wheat grain yields varied, from 17% in 1993 to 61% in 1990, with a mean increase in grain yield of 40% (825 kg/ha). Wheat grain protein concentration increased from 9.4% in a wheat–wheat rotation to 10.7% in a chickpea–wheat rotation, almost a 14% increase in grain protein. There was a mean increase in soil nitrate nitrogen of 35 kg N/ha.1.2 m after 6 months of fallow following chickpea (85 kg N/ha) compared with continuous wheat cropping (50 kg N/ha). This was reflected in additional nitrogen in the wheat grain (20 kg N/ha) and above-ground plant biomass (25 kg N/ha) following chickpea. Water-use efficiency by wheat increased from a mean value of 9.2 kg grain/ha. mm in a wheat–wheat rotation to 11.7 kg grain/ha.mm in a chickpea–wheat rotation. The water-use efficiency values were closely correlated with presowing nitrate nitrogen, and showed no marked distinction between the 2 cropping sequences. Although presowing available water in soil in May was similar in both the chickpea–wheat rotation and the wheat–wheat rotation in all years except 1996, wheat in the former used about 20 mm additional water and enhanced water-use efficiency. Thus, by improving soil fertility through restorative practices such as incorporating chickpea in rotation, water-use efficiency can be enhanced and consequently water runoff losses reduced. Furthermore, beneficial effects of chickpea in rotation with cereals could be enhanced by early to mid sowing (May–mid June) of chickpea, accompanied by zero tillage practice. Wheat of ‘Prime Hard’ grade protein (≥13%) could be obtained in chickpea–wheat rotation by supplementary application of fertiliser N to wheat. In this study, incidence of crown rot of wheat caused by Fusarium graminearum was negligible, and incidence and severity of common root rot of wheat caused by Bipolaris sorokiniana were essentially similar in both cropping sequences and inversely related to the available water in soil at sowing. No other soil-borne disease was observed. Therefore, beneficial effects of chickpea on wheat yields and grain protein were primarily due to additional nitrate nitrogen following the legume crop and consequently better water-use efficiency.

Moisture conservation for rainfed wheat production with alternative mulches and conservation tillage in the hills of north-west India

Abstract: In the hills of north–west India, maize (Zeamays L.)-wheat (Triticumaestivum L.) is the dominant cropping system. However, rainfed wheat suffers from lack of optimum moisture at sowing. Field experiments were conducted for 3 years on a silty clay loam (Typic Hapludalf) to evaluate the effectiveness of mulches and conservation tillage for rainfed wheat in mitigating this problem. The treatments were ten factorial combinations of five mulch-tillage practices and two nitrogen levels (N60 and N120 kg ha−1). Mulch treatments consisted of application of 10 Mg ha−1 (dry weight basis), to previous standing maize, of either wild sage (Lantanacamara L.) or eupatorium (Eupatoriumadenophorum Sprengel) in combination with either conventional or conservation (minium) tillage prior to wheat sowing. These alternative practices were compared to the conventional farmer practice of soil tillage after harvest of maize with no mulch. The application of these weed mulches to standing maize maintained friable soil structure owing to a five fold higher mean population of earthworms underneath mulch. Mulches resulted in 0.06–0.10 m3 m−3 higher moisture in the seed-zone when wheat was sown compared with the conventional farmer practice of soil tillage after maize harvest. Mulch-conservation tillage treatments favourably moderated the hydro-thermal regime for growing a wheat crop. The mean root mass density under these treatments at wheat flowering was higher by 1.27–1.40 times over the conventional farmer practice during the 3 year study. Conservation tillage holds promise because it does not require elaborate tillage and may ultimately reduce animal draught in the hilly regions. Recycling available organic materials having no fodder value coupled with conservation tillage may help enrich the soil environment in the long-term. The practice also offers gainful use of these obnoxious weeds that cause great menace in grass and forest lands in the region.

Stimulatory effects of sodium and calcium hypochlorite, pre‐chilling and cytokinins on the germination of Cypripedium macranthos seed in vitro

Abstract: Cypripedium macranthos is a wild orchid that is becoming endangered. Efficient methods for its propagation from seed, which is indispensable for conservation, production and breeding, have not been reported. The effects of sodium and calcium hypochlorite, pre-chilling and cytokinins on the germination of seeds of Cypripedium macranthos Swartz were examined. The duration of treatment with a solution of hypochlorite prior to sowing was one of the critical factors that affected germination. Approximately 70% of seeds that had been treated with either a solution of NaClO that contained 0.5% available chlorine for 60 min or with one of Ca(ClO)2 with 3.2% available chlorine for 7 h, germinated after 3 months of culture at 20°C, subsequent to 2 months chilling at 4°C. Chilling seeds at 4°C prior to culture at 20°C was another factor that stimulated germination. Even chilling for 2 weeks had a promotive effect on germination, and chilling for 2 months enhanced it most effectively: the frequency of germination was 67% after 3 months of culture at 20°C. However, the promotive effects of chilling on germination were reduced by holding seeds at 20°C for 3 and 6 weeks prior to chilling treatment. Germination of 58-70% was achieved by the addition of 1 µM cytokinin to the medium, while the frequency was only 17% in cytokinin-free medium. We report a reproducible and efficient method for enhancing seed germination of C. macranthos, which involves treatment with hypochlorite prior to sowing, and the combination of chilling at 4°C prior to germination and exposure to a cytokinin.

Yields, weeds, pests and soil nitrogen in a white cabbage-living mulch system.

Abstract: The purpose of the present studies was to screen for suitable cover crops and seeding rates and investigate the influence of non-suppressed and mechanically suppressed living mulch on white cabbage yield, weed growth, pest damage and green manuring effects. Because no differences in weed suppression between the species/cultivars were found in the first experiment, Trifolium repens L. cv. Pertina, which had least negative impact on cabbage yield was chosen for the second experiment. In addition, Trifolium subterraneum L. cv. Geraldton was included. The competition between cover crop and cabbage was considerable in the second experiment. Mowing once or twice did not improve cabbage yield compared with unmowed treatments. A considerable increase in cabbage yield was achieved both in subclover and white clover by rototilling between the rows 6 weeks after transplanting. The cover crops did not reduce weed biomass or number of weeds early in the season compared with monoculture, but weed biomass in lat...

Residue management and minimum tillage systems for soybean following wheat

Abstract: The acceptance of no-till systems for soybean [Glycine max (L.) Merr.] production following winter wheat (Triticum aestivum L.) on fine-textured soils in Ontario has been hampered by soybean yield reductions due to unfavorable seedbed conditions. This research was conducted to identify alternative tillage and residue management systems that will enhance emergence, growth, and yield of soybean following winter wheat. Seven tillage and residue management systems, comprising fall moldboard plow, fall chisel plow, fall disk only, fall zone-till, no-till, no-till (with wheat straw baled), and no-till (with wheat straw and stubble removed), were evaluated following winter wheat on fine-textured soils from 1994 to 1996 at six different sites near Centralia and Wyoming in southwestern Ontario. Spring soil moisture was lower in the fall tillage treatments than in no-till with wheat residue, but moisture differences did not vary among fall tillage treatments. No-till seedbeds had the highest soil moisture contents, the lowest proportion of fine soil aggregates (<5 mm in diameter), and the greatest penetrometer resistance. No-fill soybean growth was delayed and yields were reduced as the level of wheat residue left after planting increased. Soybean seed yield was negatively correlated with surface residue cover, but positively correlated with soil aggregates <5 mm in diameter at all sites. Fall zone-till and fall disk systems generally improved in-row seedbed conditions (higher fine soil aggregates and lower soil resistance), and increased seed yields by 5 to 29% relative to no-till treatments. Fall zone-till and fall tandem disk systems were the best conservation tillage alternatives to fall moldboard plowing.

Relating Preseason Soil Nitrogen to Maize Yield in Tree Legume-Maize Rotations

Abstract: Legumes can be an important source of N for cereals in tropical, subsistence farming systems that use little or no fertilizers. Out objective was to identify measures of soil N availability, following growth of diverse legumes, that correlated with yield of a subsequent unfertilized maize (Zea mays L.) crop. Unfertilized maize followed nine 3-yr-old systems (six monocultures of planted trees legumes, a groundnut [Arachis hypogea L.]-maize-soybean [Glycine max (L.) Merr.] rotation, an uncultivated fallow with natural regrowth of vegetation, and unfertilized maize monoculture) in two experiments on a Ustic Rhodustalf in eastern Zambia. Total soil C and N before maize planting were not related to grain yield of maize. Preseason soil inorganic N (NO 3 + NH 4 ), aerobic N mineralization, and light-fraction N (N in macroorganic matter, 150-2000 μm and <1.37 Mg m 3 ) at 0- to 15-cm depth correlated (P < 0.01) with maize grain yield. Preseason inorganic N combined with light-fraction N accounted for 59% of the variance in maize grain yield. The predictahility of maize yield was slightly improved (64% of the variance) by including the population of the parasitic weed striga [Striga asiatica (L.) Kuntze] with preseason inorganic N and light-fraction N. The results suggest that yield of unfertilized, rain-fed maize following different rotational systems on a N-limiting soil in an area with monomodal rainfall was strongly related to the additive effects of preseason soil inorganic N and a soil N fraction related to N mineralization.

Cheek-pouch dispersal of seeds by Japanese monkeys (Macaca fuscata yakui) on Yakushima Island, Japan

Abstract: Seed dispersal by Japanese monkeys (Macaca fuscata yakui) via cheek-pouch was studied in a warm temperate evergreen forest on Yakushima Island. Plant list was compiled based on a study during 1986–1995, of which troops of monkeys have been habituated without artificial feeding. We followed the well-habituated monkeys in 1993 and 1994 to observe the feeding behavior and their treatments of fruits and seeds, and collected seeds dispersed by monkeys to record the distance carried from the mother trees. We checked the difference of germination ratio between seeds dispersed via cheek-pouch and seeds taken from mother trees by sowing experiments. Seeds and acorns of 22 species were observed to be dispersed via cheek-pouch of monkeys. Among them, three species with acorns were never dispersed via feces, and 15 species with drupes were seldom dispersed via feces. Plant species of which seeds are dispersed only via cheek-pouch had larger seeds than those of dispersed both via cheek-pouch and via feces, and typically had only one or two seeds in a fruit. As for one of cheek-pouch dispersal species,Persea thunbergii, the mean distance when seeds were carried from the mother trees via cheek-pouch was 19.7 m, and the maximum distance was as long as 105 m although more than 80% of seeds were dispersed within 30 m from mother trees. And 82% of seeds dispersed via cheek-pouch germinated. The easy separation of seeds from other parts of the fruit seems to facilitate cheek-pouch dispersal more than dispersal via feces. Cheek-pouch dispersal by monkeys has possibly enhanced the natural selection for larger seeds which bring forth larger seedlings with high shade-tolerance. In conclusion, cheek-pouch dispersal by monkeys is quite an important mode for trees in the mature stand in a warm temperate evergreen forest on Yakushima Island.

Priming Effect of Rice Seeds on Seedling Establishment under Adverse Soil Conditions

Abstract: An experiment was carried out to find out the priming effects of rice seeds, Oryza sativa L. (cv. Ilpumbyeo) on. the seedling establishment and early emergence under excess soil moisture conditions. Seeds were primed by soaking in -0.6 MPa polyethylene glycol (PEG) solution at 25~circC for 4 days. The primed seeds were sown in soils with various soil moistures (60, 80, 100, 120, and 140% field capacity) at 17 and 25~circC , respectively. Germination and emergence rates, plumule height, and radicle length of primed seeds were higher than those of untreated seeds at any soil moisture and temperature examined. The time from planting to 50% germination (T50 ) of primed seeds was less than that of untreated seeds by 0.9～3.7 days. Germination rate, emergence rate, plumule height, and radicle length were highest at the soil moisture of 80% field capacity among the soil moistures. Priming effects of rice seeds on germination and emergence rates were more prominent under the unfavorable soil moistures (60, 100, 120, and 140% field capacity) than those under the optimum soil moisture condition (80% field capacity). However, priming effects on seedling growth were greater at near optimum soil moisture compared with too lower or higher soil moistures. Therefore, these findings suggest that priming of rice seeds may be a useful way for better seedling establishment under the adverse soil conditions.

Responses of faba bean (Vicia faba L.) to sowing rate in south-western Australia. I. Seed yield and economic optimum plant density

Abstract: Sowing rate in∞uences plant establishment, growth, seed yield, and the profltability of a crop. However, there is limited published information on the optimum sowing rate and plant density for faba bean in Australia. The response of the growth and seed yield of faba bean (cv. Fiord) to sowing rate (70{270 kg/ha) was examined in 19 fleld experiments conducted over 3 years in south-western Australia. The economic optimum plant density was estimated at each site by fltting an asymptotic model to the data and calculating the point where the cost of extra seed equalled the return from additional seed yield, allowing a 10% opportunity cost for the extra investment. On average across all sites and seasons, only 71% of the seeds sown emerged. Increasing sowing rate resulted in more dry matter production at flrst ∞ower and at maturity, and at about half of the sites there was a small trend of reduced harvest index. In general, the mean number of seeds per pod (1¢8{2¢6) and mean seed weight (32{45 g/100 seeds) were unafiected by sowing rate. As sowing rate increased, the number of pods per plant (5{35) generally decreased, but this was compensated by the large plant population and more pods per unit area. The asymptotic models fltted to the seed yield data accounted for 15{81% of the variance. In 8 experiments, the models indicated that yield was continuing to increase substantially as sowing rate increased at the largest sowing rate treatment. The estimated optimum plant densities in these experiments were beyond the range of the data or had large standard errors and, hence, were excluded from any further consideration. Among the remaining 11 experiments, the estimated optimum plant densities varied from 31 to 63 plants/m 2 , with a mean of 45 plants/m 2 . This study demonstrates that targeting sowing rates greater than the current commercial practice for faba bean in southern Australia of 15{30 plants/m 2 results in more yield and proflt. Additional experiments are required with sowing rates in excess of 270 kg/ha to estimate accurately the optimum plant density for faba bean. Fungal diseases were either absent or controlled with fungicides in these experiments but the interactions between disease, time of sowing, and sowing rates also deserve further attention.

Growth, seed yield and water use of faba bean (Vicia faba L.) in a short-season Mediterranean-type environment

Abstract: Summary. A number of studies conducted in Western Australia have shown that faba bean has considerable potential as a pulse crop in the low to medium rainfall cropping regions (300–450 mm/year). However, its yield is variable and can be low in seasons when rainfall is less than average. Traits associated with the adaptation of 10 diverse faba bean genotypes to low rainfall, Mediterranean-type environments were evaluated at Merredin in south-western Australia over 2 contrasting seasons. Plant density was varied with seed size to ensure all genotypes achieved similar canopy development and dry matter production. Time to flowering appeared to be the most important trait influencing seed yield of faba bean in this environment. Seed yield was significantly correlated with time to 50% first flower in 1994 and 1995 (r2 = 0.61 and 0.82 respectively, P<0.01). In the dry 1994 season, rapid leaf area development in ACC286 allowed a greater absorption of photosynthetically active radiation resulting in more dry matter accumulation than other genotypes. ACC286 also had greater root length density at 20–30 cm depth compared with Icarus and the standard cultivar Fiord. There were no significant differences in total water use between the genotypes examined, although the pattern of water use varied markedly. The ratio of pre- to post-flowering water use was about 1:1 in the early flowering and high yielding ACC286 and 2.6 :1 for the late maturing, low yielding Icarus. Seed yield and harvest index were positively correlated with post-flowering water use (r2 = 0.75 and 0.71 respectively). Above-average rainfall in 1995 resulted in increased yield of all genotypes, particularly ACC286 which again produced the highest yields. Early flowering genotypes with rapid dry matter accumulation in the seedling stages (such as ACC286) could widen the adaptation of faba bean to low rainfall, Mediterranean-type environments and situations where sowing is delayed.

Variability and trends in sowing dates across the Australian wheatbelt

Abstract: As sowing dates are critical for appropriate yield forecasting, a national survey of Australian wheat farmers was undertaken. This revealed that wheat sowing generally takes 2-4 weeks to complete between the middle of May and the middle of June. Distinct regional differences occur in the way sowing is completed and these are related to soil and climatic effects. In Western Australia, sowing follows a more distinct gbreak in the season" and the midpoint of farm sowing is fairly uniform across cropping areas. As one progresses into south-eastern and then north-eastern cropping areas the spatial variability in sowing increases. The combination of fallowing practices, unreliable autumn rainfall, and heavier soils (that delay operations when conditions are wet or dry), all add to the variability in sowing date and sowing duration in north-eastern areas. The range of midpoint in sowing (between years) generally decreases as the progression is made from a farm, to a State, to a national scale. Reduced variability at a national scale is enhanced by broad-scale weather patterns causing sowing opportunities to contrast markedly on different sides of the country. During the 1980s, sowing progressed a day earlier per year at a national scale. The most pronounced changes occurred in Queensland and Western Australia, where a 2-3-week shift to earlier sowing was recorded. Coinciding with this was a trend in all areas to reduced or minimum tillage techniques. Late opening rains in South Australia restricted early sowing opportunities during this time.