Showing papers on "Sowing published in 1997"

Seed Ageing and Smoke: Partner Cuesin the Amelioration of Seed Dormancyin Selected Australian Native Species

Abstract: Seed germination of many Australian native plant species has consistently proven to be fractious. With the discovery of smoke-mediated germination, it is now possible to better understand the heterogeneity in germination patterns for a wide range of species both in situ and ex situ. In the present study, over 180 species were examined as to viability and smoke responsiveness of freshly collected seed. Soil storage and a number of commonly used seed pre-treatments were employed in combination with smoke to examine both longevity in artificially constructed seed banks, and the role of seed ageing in improved germination. Methods of smoke application for commercial use were also investigated. Viability decline over 1 year varied between 10% and 80%. Reductions of as little as 15% were found to compromise the ability of a number of species to successfully recruit in consecutive seasons. When fresh seed was used,almost 70% of species tested responded positively to smoke whether applied prior to or after sowing. Variation in success between the two methods confirmed earlier conclusions that substances contained in plant-derived smoke may be inhibitory at high concentrations for particularly sensitive species. Only 10% of species under investigation recorded optimum germination with seed ageing alone but when smoke was applied as a treatment after soil storage, 60% of species responded positively. Implications for horticulture, rehabilitation, seed bank research and habitat management are discussed.

Kill Date of Vetch, Rye, and a Vetch–Rye Mixture: I. Cover Crop and Corn Nitrogen

Abstract: Spring kill date affects cover crop N content and N availability to subsequent no-till corn (Zea mays L.). This 2-yr study was conducted in 1990 and 1991 at Coastal Plain and Piedmont locations in Maryland to evaluate three cover crop kill dates, three corn planting dates, and four corn fertilizer N (FN) rates following hairy vetch (Vicia villosa Roth), cereal rye (Secale cereale L.) and a vetch-rye mixture. No-cover checks were included for each corn planting date. Fertilizer N rates were 0 to 202 kg ha -1 in the Piedmont and 0 to 270 kg ha -1 for the Coastal Plain. The vetch-rye mixture contained as much or more N than vetch, and more N than rye within each kill date. Cover crop biomass and N content increased for each delay in kill. In a 50-d period from late March until early May, vetch and the vetch-rye mixture accumulated about 2 kg N ha -1 d -1 , with total topgrowth N accumulation from 144 to 203 kg ha -1 over two locations and two years. Greatest rye N accumulation was 51 kg ha -1 . Corn N content ranged from 37 to 293 kg ha -1 , and was significantly affected by FN rate. Within FN rate, N content was greater following vetch or vetch-rye than following rye or no cover, particularly at low FN rates. Corn N content was greater if cover kill and corn planting were delayed until late April or mid-May. This was attributed to greater cover crop N production and mulching effects, and the timing of summer rainfall. Corn FN requirements were greatest following rye or no cover, intermediate following vetch-rye, and least following vetch. This demonstrates that cover crop species and kill date can be managed to conserve N with rye, supply N for the next crop with vetch, or provide both N conservation and N supply with vetch-rye mixture.

Weed suppression with Brassica green manure crops in green pea.

Abstract: Weed suppression in green pea was evaluated when green pea was planted after a fall planting of rapeseed, white mustard, rye, or wheat had been incorporated into the soil in spring. Tests were conducted at Mount Vernon, WA, in 1994 and 1995. Weed suppression in peas varied between different green manure crops. One month after planting, the highest weed population was in green pea following wheat, whereas the lowest was in green pea following rapeseed. Rye and white mustard suppressed early weeds relative to wheat by 25 and 30%, respectively. However, at harvest, weed density was similar in green pea planted after all green manure crops. Weed suppression improved when cultivation or metribuzin at 0.14 kg ha−1 was used in combination with white mustard, rapeseed, or rye. Pea population was not affected by green manure crops, except for rapeseed, which reduced pea population. In greenhouse experiments, white mustard added to the soil at 20 g per 400 g air dry soil reduced emergence of shepherd's-purse, kochia, and green foxtail by 97, 54, and 49%, respectively. Rapeseed suppressed emergence of shepherd's-purse, kochia, and green foxtail by 76, 25, and 25%, respectively.

Kill Date of Vetch, Rye, and a Vetch—Rye Mixture: II. Soil Moisture and Corn Yield

Abstract: Spring cover crop kill date effects on N and water availability to subsequent no-till corn (Zea mays L.) have not been studied. This 2-yr study was conducted in 1990 and 1991 at Coastal Plain and Piedmont locations in Maryland to evaluate soil moisture and corn responses to three cover crop kill dates, three corn planting dates, and four fertilizer N (FN) rates following cover crops of hairy vetch (Vicia villosa Roth), cereal rye (Secale cereale L.), and vetch-rye mixture. No-cover checks were included for each corn planting date. Corn yield ranged from 0.8 to 13.3 Mg ha -1 in 1990, and from 3.9 to 12.6 Mg ha -1 in 1991. Corn grain yield without FN was greatest following vetch or vetch-rye mixture. Late April or early May kill dates consistently resulted in greater corn yield than earlier kill dates, probably due to differences in N availability and moisture conservation. Cover crops killed late did not deplete surface soil moisture. The economic FN rate reflected N contributions and moisture conservation by each cover crop. At the Coastal Plain location, economic FN rates were 30 to 76 kg ha -1 for corn following vetch, 65 to 193 kg ha -1 following vetch-rye mixture, 161 to 247 kg ha -1 following rye, and 201 kg ha -1 following no cover crop. Similar rankings were observed for the Piedmont location, but maximum yield was lower following rye, and lower FN rates were required to attain that yield. Summer soil water conservation by cover crop residues was more important than spring moisture depletion by growing cover crops in determining final corn yield.

Superiority of Winter Sowing over Traditional Spring Sowing of Chickpea in the Mediterranean Region

Abstract: Chickpea (Cicer arietinum), when traditionally grown as a spring-sown crop in the Mediterranean region, often suffers from heat and moisture stress, resulting in low and unstable yields. In contrast, sowing the crop in winter with cultivars tolerant to cold and to ascochyta blight (caused by Ascochyta rabiei) minimizes the effects of terminal heat and drought stress and increases and stabilizes productivity. Therefore, a study was conducted with the objective of assessing the comparative seed yield advantage of winter over spring sowing in Mediterranean environments. Nineteen to 23 ascochyta blight-resistant and cold-tolerant breeding lines were compared in winter and spring sowing for 10 years (1983-93) at three locations in Syria and Lebanon. The set of lines used in this study differed each year. Averaged over 10 years, winter-sown chickpea produced 70% (692 kg ha-1) more seed yield than the spring-sown crop. The longer growing period of winter-sown chickpea resulted in higher biomass production, which contributed mainly toward increased seed yield. The yield potential of lines sown during winter was approximately 4000 kg ha-1, and yields were more stable than in the spring-sown crop. The correlation between seasonal rainfall and seed yield was positive and significant in both seasons. In 1988-89, when the Tel Hadya site experienced severe drought, the spring-sown crop resulted in virtually no seed yield, whereas the winter-sown crop produced an average yield of 542 kg ha-1 by a partial escape of the severe drought. Winter-sown plants were taller than those in the spring sowing, permitting harvesting by combines. Because of these advantages, winter sowing of chickpea is gaining popularity in the Mediterranean region

Nutritional, growth, and reproductive responses of maize (Zea mays L.) to arbuscular mycorrhizal inoculation during and after drought stress at tasselling

Abstract: The effects of root colonization by the arbuscular mycorrhizal (AM) fungus Glomus intraradices Schenck & Smith on nutritional, growth, and reproductive attributes of two tropical maize cultivars with different sensitivities to drought were studied. Freshly regenerated seeds of selection cycles 0 (cv. C0, drought-sensitive) and 8 (cv. C8, drought-resistant) of the lowland tropical maize population "Tuxpeno sequia" were used in this greenhouse experiment. Maize plants were subjected to drought stress for 3 weeks following tasselling (75–95 days after sowing) and rewatered for the subsequent 5 weeks until harvest. Mycorrhizal (M+) plants had significantly higher uptake of N, P, K, Mg, Mn, and Zn into grain than non-mycorrhizal (M–) plants under drought conditions. AM inoculation also produced significantly greater shoot masses in C0 and C8 regardless of the drought-stress treatment. In the sensitive cultivar C0, drought stress reduced the shoot mass and grain yield by 23% and 55%, respectively, when roots were not colonized, while the reductions were only 12% and 31%, respectively, with mycorrhizal association. In addition, the emergence of tassels and silks was earlier in M+ plants than in M– plants under drought conditions. Mycorrhizal response was more pronounced under both well-watered and drought conditions in C0 than in the C8 cultivar. The overall results suggest that AM inoculation affects host plant nutritional status and growth and thereby alters the reproductive behaviour of maize under drought conditions.

Fate of Fertilizer Nitrogen as Affected by Time and Rate of Application on Corn

Abstract: Management of fertilizer N on corn (Zea mays L.) can greatly affect the efficiency ofN use and the potential for adverse environmental effects. Field studies were conducted on two nonirrigated southern Minnesota soils - a Webster clay loam (fine-loamy, mixed, mesic Typic Haplaquoll) and a Mt. Carroll silt loam (fine-silty, mixed, mesic Mollic Hapludalf) - to determine the effect of time and rate of N application on recovery of fertilizer-derived N (FDN) in corn grain and stover and in the soil. Nitrogen rates of 75 and 150 kg ha -1 on the Mt. Carroll soil and 100 and 200 kg ha -1 on the Webster were applied at planting or at the eight-leaf stage as (NH 4 ) 2 SO 4 to the same plots from 1982 to 1984. Enriched 15 N was applied to separate microplots each of the first 2 yr to allow measurement of FDN. Grain yield responded to applied N in 5 of 6 site-yr, but not to time of application. Uptake of FDN in grain was increased by higher N rate in all cases, but by delayed application in only one site-year. Total plant FDN recovery ranged from 31 to 60% at the low N rate and from 24 to 45% at the high rate. Both yields and FDN recovery were affected by unusually dry midseason conditions. Fertilizer-derived N recovery from the soil after harvest ranged from 25 to 56%, with a large proportion at the high N rate in inorganic forms, especially with the late application, which increased the potential for leaching losses. Residual uptake of FDN by grain ranged from 1 to 10% of the initial N rate. The difference method for estimating FDN recovery gave different results from the 15 N method, emphasizing the importance of examining both labeled and nonlabeled N pools for complete interpretation of 15 N studies.

Influence of crop management on take-all development and disease cycles on winter wheat.

Abstract: Wheat was assessed at four crop growth stages for take-all (Gaeumannomyces graminis var. tritici) in a series of field trials that studied the effects of five wheat management practices: sowing date, plant density, nitrogen fertilizer dose and form, and removal/burial of cereal straw. An equation expressing disease level as a function of degree days was fitted to the observed disease levels. This equation was based on take-all epidemiology and depended on two parameters reflecting the importance of the primary and secondary infection cycles, respectively. Early sowing always increased disease frequency via primary infection cycle; its influence on the secondary cycle was variable. Primary infection and earliness of disease onset were increased by high density; however, at mid-season take-all was positively correlated to the root number per plant, which was itself negatively correlated to plant density. At late stages of development, neither plant density nor root number per plant had any influenc...

Reduced and zero-tillage options for establishment of wheat after rice in South Asia

Abstract: One of the major constraints to higher production of wheat on the 12 million hectares of rice-wheat grown in the Indo-Gangetic flood plains of South Asia is late planting and resultant poor plant stands. Late planting results in a linear decline in yield potential equivalent to 1–1.5% loss ha-1 d-1 when planting occurs after November. Late harvest of the previous rice crop or long turnaround time from rice harvest to wheat planting are two major causes of late wheat planting. Reduced or zero-tillage options are proving effective in overcoming late planting and poor plant stands in the rice-wheat systems of Asia. This paper presents data on zero-tillage systems, ranging from surface seeding to planting with four-wheel tractor seed drills, resulting in higher yields at lower costs and savings in fuel use and tractor wear and tear. Reduced tillage systems include ‘data-using’ drills that combine land preparation and seeding in one operation. Both two and four-wheel tractors have been used to achieve good results. This paper concludes that conventional tillage systems can be replaced by more economic reduced tillage options. However, it is important with reduced tillage that soil moisture at seeding is maintained at a high enough level to keep soil strength low, as occurs in tilled soils. Some longer term research is needed to determine medium term positive or negative effects of reduced tillage on sustaining wheat yields.

Field observations on nitrogen catch crops. I. Potential and actual growth and nitrogen accumulation in relation to sowing date and crop species

Abstract: In temperate climates with a precipitation surplus during autumn and winter, nitrogen catch crops can help to reduce nitrogen losses from cropping systems by absorbing nitrogen from the soil and transfer it to a following main crop. The actual and potential accumulation of dry matter and nitrogen in catch crops were studied in the field during four seasons with winter rye (Secale cereale) and forage rape (Brassica napus ssp. oleifera (Metzg.) Sinsk) or oil radish (Raphanus sativus spp. oleiferus (DC.) Metzg.). Sowing dates were end of August and three and six weeks later. Potential nitrogen accumulation, Y (g m-2), could be summarized with Y = 96 −0.34 X, where X is the day number in the year of the sowing date (range: late August till end of September). Species were compared in their performance, looking at differences in specific leaf area, leaf weight ratio, leaf area ratio, light extinction and persistence during frost. The rate of dry matter accumulation in intervals of 14 days appeared to be determined primarily by the amount of radiation intercepted. A regression, forced through the origin, gave as a common slope 1.12 g dry matter accumulated per MJ intercepted global radiation, irrespective of season, species, sowing date or nitrogen treatment (period from ca. day 250 to day 310). From this result the inference is made that leaf expansion is a key process, determining the performance of catch crop species under varying environmental conditions.

Winter rye as a cover crop following soybean under conservation tillage

Abstract: Rotation of corn (Zea mays L.) with soybean [Glycine max (L.) Merr.] provides certain economic and environmental advantages over monoculture corn. Low soybean residue production and persistence, however, promote potentially excessive soil erosion following soybean harvest. An irrigated field experiment was conducted in eastern Nebraska for 4 yr (1990-1993) under various tillage treatments and N rates to evaluate the effects of a winter rye (Secale cereale L.) cover crop following soybean on (i) rye dry matter yield, (ii) surface residue cover for erosion protection, and (iii) corn establishment and production. The soil was a Sharpsburg silty clay loam (fine, montmorillonitic, mesic Typic Argiudolls). Treatments were (i) no-tillage and disk tillage; (ii) corn following soybean with a winter rye cover crop (CBR), corn following soybean without rye (CB) and corn following corn (CC); and (iii) 0, 50, 100, 150, and 300 kg N ha -1 (applied to corn). Rye aboveground dry matter yield, surface residue cover, and corn yield parameters were estimated. Rye dry matter yield ranged from 0.25 to 2.9 Mg ha -1 and was influenced by tillage, N rate, and weather conditions in different years. During the years of high rye dry matter yield, presence of rye in the corn-soybean system gave approximately 16% additional surface residue cover prior to planting through cultivation, compared with soybean residue alone. Surface cover by rye and soybean residues in CBR was equivalent to corn residue in CC under both disk and no-till management. In 1 of the 3 yr, corn plant population and grain yield were reduced following rye (CBR) compared with the no rye system (CB), possibly due to apparent allelopathic effects related to the age of rye. No significant difference in N response was observed between CBR and CB corn yields. In general, rotation of corn with soybean (with and without rye) resulted in an increase of approximately 27% in corn grain yield and N uptake over continuous corn. During the years of high rye dry matter production, rye accumulated approximately 45 kg N ha -1 through aboveground dry matter. Overall, including a winter rye cover crop in the corn-soybean rotation system was beneficial.

Effects of 28-homobrassinolide on yields of wheat, rice, groundnut, mustard, potato and cotton

Abstract: Yield responses of some economically important crop plants due to foliar applications of low concentrations of 28-homobrassinolide (HBR) were studied in experiments conducted at research stations and in farmers' fields in India during 1989–95. Foliar sprays of different concentrations of HBR were applied at tillering and spike/panicle initiation in wheat (0·5 and 1·0 mg/l) and rice (0·25, 0·50 and 1·00 mg/l); at flowering and pegging in groundnut (0·25 and 0·50 mg/l); 30 and 45 days after sowing (DAS) in mustard (0·25 and 0·50 mg/l); 25 and 35 days after emergence in potato (0·25 and 0·50 mg/l); and 30, 50, 70 DAS in cotton (0·1 and 1·0 mg/l). The HBR treatments significantly (P<0·05 and P<0·01) increased grain yields in wheat, rice and mustard, pod yields in groundnut, tuber yields in potato and seed cotton yields, over control. The extent of yield improvement due to HBR was influenced by crop species, concentration of HBR, plant growth stage at application and frequency of application.

Accumulation of Seed Vigour During Development and Maturation

Abstract: Physiological maturity (PM, maximum accumulation of dry seed weight) represents maximum yield in grain crops and is proposed to represent maximum seed quality (germination and vigour) for planting purposes of all crops We investigated the relationship of seed maturation to seed quality for five agronomic and four horticultural crops in several field environments Annual evaluations of several soyabean (Glycine max (L) Merr) cultivars were made from 1982 to 1992, while one single cross hybrid of maize (Zea mays L) was tested from 1985 to 1994 All other crops were evaluated for two production years, except wheat (Triticum aestivum L em Thell) with one year High seed viability occurred first (early in development) for all crops and was followed by maximum standard germination at or before PM in all crops except tomato (Lycopersicon esculentum Mill) and pepper (Capsicum spp) Maximum seed vigour occurred at or slightly before PM in crops harvested as dry seed, but after PM for crops with seed harvested from fleshy fruits (tomato, pepper) When soyabean and maize plants were stressed by defoliation, drought or high temperatures during seed development, seed maturation was accelerated, but maximum seed vigour occurred at or before PM Thus, the maximum expression of seed vigour was closely related to the occurrence of PM in all crops harvested as dry seed

Base Temperature and Growing-Degree-Hour Requirements for the Emergence of Canola

Abstract: Spring canola (Brassica napus L. and B. rapa L.) is sometimes planted when soil temperatures are below the optimum, causing farmers to have stand losses because of seed rotting in cold soil. Knowledge of the growing-degree hours (GDH) required for emergence of canola from different planting depths could help producers decide when and how deep to plant this crop. Out objectives were to quantify the base temperature (the minimum temperature required) for emergence, the number of GDH required for initial emergence of five cultivars of spring and winter canola, and to evaluate temperature x planting depth interactions of spring canola. 'Alto', 'Global', Tobin', 'Crystal', and 'Glacier' cultivars were planted 1 cm deep into pots of Weld silt loam (fine, montmorillonitic, mesic aridic Paleustolls). Pots were incubated at 0, 2, 4, and 16°C. Seedlings emerged were counted daily for all temperatures and twice daily during rapid emergence at 16°C. Simple-linear and segmented-nonlinear-regression were used to determine base temperatures and GDH requirements for initial emergence. Calculated base temperatures were between 0.4 and 1.2°C. Regardless of the constant temperature regime, emergence began between 1560 and 1940 GDH for the spring canola. Winter canola emerged at 1600 to 2800 GDH. Two cultivars (Tobin and Global) were also planted at 1-, 2-, 2.5-, 3-, and 4-cm depths and incubated at 4, 8, 12, and 16°C to investigate planting depth x temperature interactions. A reduction in emergence, as a function of an interaction between temperature and planting depth, was found for Global but not Tobin at the temperatures and planting depths used in this study. A match between the accumulated heat units in early spring for a location and the GDH required for initial emergence of the spring cultivars tested can be used to determine early spring canola planting dates. This analysis indicates that severe reductions in stand are possible when canola is planted at soil temperatures that are sustained much below 8°C. The heat unit approach used allows for the transfer of the relationships developed in this study to other locations.

Nitrogen benefits of lupins, field pea, and chickpea to wheat production in south-eastern Australia

Abstract: Nitrogen balances of narrow leaf lupin (Lupinus angustifolius L.), albus lupin (L. albus L.), field pea (Pisum sativum L.), chickpea (Cicer arietinum L.), and barley (Hordeum vulgare L.) sown over a range of dates were examined in 1992 in a rotation study at Wagga Wagga, NSW. Each N budget included assessment of dependence on fixed as opposed to soil N, peak aboveground biomass N, and N removed as grain or returned as unharvested aboveground crop residues. N balances of wheat sown across the plots in 1993 were assessed similarly in terms of biomass and grain yield. Yields, N2 fixation, and crop residue N balances of the legumes were markedly influenced by sowing time, and superior performance of lupins over other species was related to higher biomass production and proportional dependence on N2 fixation, together with a poorer harvest index. Residual N balances in aboveground biomass after harvest of the 1992 crops were significantly correlated with soil mineral N at 1993 sowing and with biomass and grain N yields of the resulting wheat crop. Best mean fixation and grain N yield came from albus lupin. Wheat grain N yields following the 2 lupins were some 20% greater than after fiield pea and chickpea and 3 times greater than after barley. Net soil N balance based solely on aboveground returns of N of legumes in 1992 through to harvest of wheat in 1993 was least for narrow leaf lupin-wheat ( –20 kg N/ha), followed by albus lupin-wheat ( –44), chickpea-wheat ( –74), and field pea-wheat ( –96). Corresponding combined grain N yields (legume+wheat) from the 4 rotations were 269, 361, 178, and 229 kg N/ha, respectively. The barley-wheat rotation yielded a similarly computed soil N deficit of 67 kg/ha. Data are discussed in relation to other studies on legume-based rotations.

Use of allelopathic extracts of sorghum and sunflower herbage for weed control in wheat

Abstract: A field trial to investigate the feasibility of using water extracts of allelopathic crops viz. sorghum and sunflower as a natural weed control approach for wheat crop, was carried out during Rabi 1995-96. Mature sorghum and sunflower herbage were used for preparing water extracts. The water extracts in 100% and 50% concentrations, were sprayed 30 days after sowing of wheat crop while control plots received no spray. Spraying sorghum and sunflower 100% water extracts decreased total weed dry weight up to 53% & 53% and they suppressed biomass of individual weed species as Rumex dentatis 74% and 73%, Chenopodium album 38% and 26% Coronopus didymus by 62% and 42% and Fumaria parviflora by 40% and 33%, respectively. Sorghum 100% extract increased wheat grain yield by 14% while sunflower 100% extract by 7%.

Innovative propagation methods in seed tuber multiplication programmes

Abstract: The production of large volumes of vitroplantlets and greenhouse tubers for increasing the rate of multiplication at the start of seed programmes provides the opportunity of reducing the total number of field generations grown before the seed moves into commerce. This implementation is especially useful for countries where high quality potato seed tubers cannot be produced because there are no vector-free production areas. This review covers the following steps: a) laboratory production of microplantlets and microtubers; b) minituber production in the glasshouse; c) storage and dormancy of micro- and minitubers; d) field performance of micro- and minitubers compared with conventional seed tubers; e) incorporation of the mentioned propagules in seed production systems. Many optimized protocols are already available for propagating plantlets, inducing microtubers and obtaining minitubers in the glasshouse at all periods of the year. Advanced molecular approaches techniques (RFLP and RAPD) to detect genetic variation in the progeny of these propagules have been described. Investigations carried out in this field have shown genetic stability, with the propagules usually reproducing plants true-to-type and tubers without deviants. By contrast, variations were demonstrated in DNA extracted from old suspension cell culture. Field trials assessed a lower yield potential crops from in vitro propagules compared with conventional seed tubers., mainly due to slow early crop development and the failure of plants caused by early stress after emergence. This may cause problems when the growing season is short because of the necessity for planting late to avoid night frosts and the mandatory haulm killing dates, common in many seed producing areas. Strategies for improving the field performance of micro- and minitubers are discussed. The most promising crop husbandry techniques appear to be: a) using tubers of a suitable physiological age, properly presprouted and encapsulated; b) optimizing the time application of fertilizer and irrigation, and c) using floating films. Outside the classical seed tuber areas of Northern Europe where the length of the growing period for pre-basic seed is usually not more than 80 days, the growing season is long enough to obtain reasonable yields even from micro- and minitubers.

Competitive ability and tolerance of organically grown wheat cultivars to natural weed infestations.

Abstract: Summary Competitive ability of a traditional winter wheat cultivar (Maris Widgeon) was compared with two modem cultivars (Hereward and Genesis) when grown organically in each of four seasons in Gloucestershire, UK. In two seasons, cultivars were compared at two sowing dates (September and October or November). Cv. Maris Widgeon was the tallest cultivar and intercepted most photosynthetically active radiation (PAR), particularly if sown early. Cv. Hereward was taller than cv. Genesis when sown early. Cv. Maris Widgeon accumulated most nitrogen and dry matter early in the season (until the end of March) when sown early, but not when sown late. Relative nitrogen and dry matter accumulation by cultivars later in the season depended on season and sowing date. In one season cv. Maris Widgeon had significantly more early season ground cover. Cultivars did not differ significantly in early tiller production. Although most of these indirect measures of competitive ability were greater for the older variety cv. Maris Widgeon, infestation of Veronica spp. was greater in plots of this cultivar than in plots of either one or both of the shorter cultivars in two successive seasons. In the 1993/94 season, the soil seedbank from plots previously cropped with cv. Maris Widgeon produced more seedlings of Sinapis awensis. In the 1994 / 95 season, cv. Maris Widgeon plots contained less weed in terms of ground cover, numbers, dry matter and nitrogen than the other cultivars, and soil sampled from plots previously cropped with cv. Hereward sown late gave rise to larger numbers of weeds than cv. Maris Widgeon. Sowing date affected weed burdens and emergence to a much greater extent than wheat cultivar. In years and sowing date treatments with relatively low weed presence the shorter cultivars tended to yield more than cv. Maris Widgeon. When weed burdens were severe cv. Maris Widgeon yields were equal to or greater than those of either cvs Hereward or Genesis. The results suggest that the traditional tall cv. Maris Widgeon could be used beneficially to tolerate weeds in organic systems when high weed infestations were anticipated, but could not be relied upon to suppress weed development, and in some circumstances could actually encourage certain species.

Horizontal movement of seeds following tine and plough cultivation : implications for spatial dynamics of weed infestations

Abstract: Summary Horizontal movement of seeds by different cultivators was investigated in three experiments. Seeds of barley (Hordeum vulgare L.), field bean (Vicia faba L.) and oilseed rape (Brassica napus L.) were positioned on the soil surface or buried 0.1 m deep prior to cultivation, Seed movement was assessed by counting germinated seedlings. The type of tine implement used significantly affected mean seed movement, with surface-sown seeds being moved significantly further than buried seeds. Primary cultivation with flexi- or spring-tine machines moved seeds further than straight-tine or power harrow implements. However, there was no overall difference between plough and flexi-tine mean seed movement. A single pass with a tine attached to a seed drili moved seeds less than the two passes with tine plus seed drill, but the first pass had the greatest effect. Small oilseed rape seeds moved significantly further than larger barley or field bean seeds. More than 84% of seeds moved ≤ 1m from the source: no seeds were observed>4.8m in a forward direction or >0.2m backwards from the source, In a fourth experiment, plots containing seeds of Sinapis arvensis L. were cultivated in alternate directions in successive years, The results broadly validated the findings of the previous experiments Quantifying the horizontal movement of weed seeds is important to the understanding of the spatial dynamics of weed patches and thus in the prediction of future weed distributions.

Transplant Stress Index: A proposed method of quantifying planting check

Abstract: This paper demonstrates a simple way of estimating the intensity and duration of planting check by examining height growth patterns. A “transplant stress index” is determined by the relationship between initial seedling height and subsequent height growth. This index is defined as the slope of a linear relationship between initial height and height increment. If the slope is negative, the plants (as a population) are said to be experiencing planting check. When the slope is approximately zero, the stock is said to be recovering from planting check. A steep positive slope suggests the stock has recovered from planting check. TSI values were determined for several conifers including Pinus elliottii Engelm. var. elliottii, Pinus taeda L., Pinus radiata D. Don, Picea sitchensis (Bongard) Carriere, and Larix× eurolepis Henry.