Showing papers on "Sowing published in 1993"

Towards the biological control of fungal and bacterial diseases of tomato using antagonistic Streptomyces spp.

Abstract: This investigation was designed to explore the potential of microbial antagonism in the control of some tomato diseases including bacterial, Fusarium and Verticillium wilts; early blight; bacterial canker. Three Streptomyces spp. were used: S. pulcher, S. canescens and S. citreofluorescens. The in vitro studies showed that an 80% concentration of the culture filtrate of either S. pulcher or S. canescens significantly inhibited spore germination, mycelial growth and spotulation of Fusarium oxysporum f.sp. lycopersici, Verticillium albo-atrum and Alternaria solani. The same concentration of filtrate of either S. pulcher or S. citreofluorescens was detrimental to the bacterial populations of Clavibacter michiganensis subsp. michiganensis and Pseudomonas solanacearum. The in vivo studies involved different treatments: soaking tomato seeds in filtrate of the antagonist prior to sowing, inoculation of the soil with the antagonist 7 days before sowing, and coating of tomato seeds with spores of the antagonist before sowing. The seed-coating treatment was the most effective in controlling all the pathogens at 42 and 63 days after sowing. Soil inoculation with the antagonist 7 days prior to sowing was less effective in controlling the tomato pathogens as compared to seed-coating. The seed-soaking treatment was the least effective in controlling the diseases concerned. The results also revealed that seed-coating with antagonistic Streptomyces spp. significantly improved tomato growth.

Nitrogen dynamics of tropical agroforestry and annual cropping systems

Abstract: The relative importance of the processes of SOM (maintenance of active soil organic matter) and SYNCHRONY (timing of release of organically-bound nutrients to coincide with crop demand) were assessed for their contribution to the maintenance of crop nitrogen availability in alley cropping. Alley cropping is a system of agroforestry where trees and crops are intercropped, the former being periodically pruned to produce mulch. Two maize alley cropping treatments, with Erythrina poeppigiana and with Gliricidia sepium , were compared to sole-cropped maize in an 8 yr old experiment at CATIE in Costa Rica. Maize productivity, maize N uptake, and N release from mulch and crop residue decomposition were measured each month during one cropping cycle. The effects of changes in active soil organic matter (SOM) on available N were assessed by measuring field N mineralization and the size of the microbial N pool through the cropping season. Two sub-treatments were introduced to assess the contribution of a current mulch application to maize N uptake (1) removing the mulch, and (2) applying 15 N labelled mulch. Monthly sampling of 15 N in the mulch, microbial biomass, and maize allowed assessment of the SYNCHRONY of mulch N release and crop uptake. Maize biomass and maize N content, N release from mulch and residue decomposition, and N mineralization were all higher in the alley crop than the sole crop by 2.2-, 2.8-, 5.0- and 2.1-fold respectively. Soil microbial N was not significantly different between treatments, but increased by 80% during the cropping season. Maize grown in the alley crop with the mulch removed contained only 3–15% less N at maturity. Similarly 15 N labelled mulch only contributed about 10% of crop N. The percentage contribution of mulch 15 N to the maize declined from 13–14% 30 days after planting to 8–11% 100 days after planting. Total recovery of mulch N by the maize was only about 10 kg ha −1 and almost all of this was taken up by 60 days after planting. The contribution of mulch N to weed N content declined from 15–24% 7 weeks after mulch application to 2–6% 9 months after application. Mulch N contributed only 3–5% of the microbial N pool at 40 days and this fell to zero by 105 days. The higher rates of N mineralization under the alley crop compared to rates under the sole crop led to faster establishment of the maize in the alley crop and maintained higher rates of N accumulation thereafter. These higher rates of N mineralization resulted from the build up of readily-mineralizable organic N in the soil over the 7 yrs of tree mulch application. The size of the microbial N pool was not to be related to nitrogen availability nor organic residue inputs. Mulch N released during a cropping season accounted for about 15% of the increase in N uptake by maize. Transfer of mulch N to the crop may have been restricted by the low incorporation of mulch N into the microbial biomass. The long-term build-up of the SOM reserve of mineralizable organic N was more important than the SYNCHRONY of mulch N release and crop uptake in determining the substantially higher productivity and N uptake in the alley crop compared to the sole crop.

A no-tillage tomato production system using hairy vetch and subterranean clover mulches

Abstract: A novel approach is described for using two winter annual legumes - hairy vetch (Vicia villosa L. Roth.) and 'Mt. Barker' subterranean clover (Trifolium subterraneum L.) - as cover crops and plant mulches in tomato (Lycopersicon esculentum Mill.) production. The approach calls for sowing the cover crops in the fall in prepared beds, mowing the cover crops with a high-speed flail mower immediately before transplanting the tomato seedlings into the field in early May, and then transplanting the seedlings into the beds with minimal interruption of the soil or mulch cover. Plants in the vetch treatment with no tillage produced a higher yield than those grown under black polyethylene, paper, or no mulch in conventional systems. Both plant mulches delayed fruit maturity by approximately 10 days relative to black polyethylene mulch. The proposed approach eliminates tillage, reduces the need for applying synthetic fertilizers and herbicides, and is adapted to large- and small-scale tomato production in a low-input, no-tillage system. It also may be used to produce other vegetables

Differential responses of bread wheat characters to high temperature

Abstract: Agronomic and yield data were collected from two trials each containing 16 bread wheat genotypes, planted two years under late sowing conditions of high temperature (above 30° C) and one year under a normal sowing time environment. The aim was to study the character response and yield correlations with yield components and other characters under high temperature conditions with full irrigation. The results show that yield, seeds per spike, biomass, and plant height are more thermo-sensitive than spike number per square meter, 1000 kernel weight, and test weight. The grain-filling rate was more temperature-sensitive than days to anthesis and duration of grain-filling. Simple phenotypic correlation analysis indicated that yield was highly and positively correlated with seeds per spike, biomass, and harvest index (HI), independent of seasons and genotypes under high temperatures. The seeds per spike accounted for variation of yield ranging from 35.2 to 78.1%. Effect of earliness on the yield under high temperature was highly dependent on the temperature regime during the heading stage. Grains per spike, biomass, HI, and test weight could be considered potential selection criteria for yield under high temperature. Analysis of yields under normal and late sowing conditions failed to reveal any association between the yield potential in normal sowing date and the performance of varieties under high temperature.

Rice ( Oryza sativa L.) germplasm suitable for direct sowing under flooded soil surface

Abstract: Screening for rice germplasm which can establish seedling from flooded soil was conducted using 256 accessions of conserved germplasm from the International Rice Germplasm Center (IRGC) and 404 accessions from the International Network for Genetic Evaluation for Rice (INGER), IRRI. IRGC germplasm represented broad genetic diversity while INGER germplasm involved desirable agronomic characters. Seeds germinated for 2 d were planted at 25 mm depth in seedling trays. The trays were then submerged to a depth of 30–50 mm. Seedling establishment was evaluated by analyzing leaf development, seedling height, and percentage establishment 15 d after planting. Eight percent and 2% of IRGC and INGER germplasm, respectively, were identified statistically as superior to the control semidwarf IR varieties. Among the superior germplasm were those from Northeast India and Bangladesh which were adapted to deepwater and early summer rainfed lowland cultures. These could be utilized as parents in breeding programs which aim to develop varieties suitable for direct seeding technology (i.e., germinated seeds are sown under the surface of flooded soil).

Winter cover crops to minimize nitrate losses in intensive lettuce production

Abstract: A 2-year study conducted in Salinas, California in 1989–91 showed that soil nitrate (NO3–N) concentrations were reduced by cover crops during a short winter fallow period and that this practice can be compatible with year-round vegetable crop production schedules by planting and incorporating cover crops directly on the beds into which the lettuce crop will be direct seeded in the early spring. Cover crops grown the first year were oilseed radish (Raphanus sativus cv. Renova), white senf mustard (Brassica hirta cv. Martigena), white mustard (Brassica alba), Phacelia (Phacelia tanacetifolia cv. Phaci), rye (Secale cereale cv. Merced) and annual ryegrass (Lolium multiflorum). Only phacelia and Merced rye were included in the second year. In both years, all of the cover crops depleted soil NO3-N and soil moisture relative to the fallow control. Estimates of cover crop root length, based on core sampling to 60 cm soil depth, averaged 18800 m/m2 after 17 weeks of growth the first year and 12500 m/m2 after 13 weeks of growth the second year. Above-ground dry matter production averaged 449 g/m2 (12·8 g N/m2) the first year and 161 g/m2 (61 g N/m2) during a shorter growing period and under the more adverse growing conditions of the second year. Following cover crop incorporation with a rotary tiller, soil ammonium (NH4-N), N03-N and net mineralizable N (anaerobic incubation) peaked after c. 1 week, then gradually declined for 1 month. Cover-cropped plots sustained higher net mineralizable N levels than the fallow control after incorporation. Nitrate concentrations after spring rains were lower in soils left fallow during winter. The subsequent lettuce crop was not affected by cover crop treatment.

Seeding Methods Performance for Cereals, Rape, and Beans

Abstract: Drilling, band sowing, broadcast sowing, and precision drilling are dealt with. The uniformity of the sowing depth is described by its standard deviation. It is shown that the field emergence of small grains under average German conditions can be improved distinctly by seeding methods with a small standard deviation of the mean seeding depth.

The number of Bradyrhizobium sp. (Lupinus) applied to seed and its effect on rhizosphere colonization, nodulation and yield of lupin

Abstract: In field experiments we investigated the roles of inoculum potential of Bradyrhizobium sp. ( Lupinus ) and quantity of peat used to inoculate seed on the nodulation and yield of lupins. Within the range 0.125–3 times the Australian recommended rate of peat application (2.5 g peat kg −1 lupin seed), the amount of peat had no effect on nodulation or grain yield. In the first experiment, seven inoculum potentials were applied within the range log 10 0.32–6.28 bradyrhizobia per seed in 7, 10-fold increments which spanned the recommended rate of login 5.55 per seed. Inoculum potentials of log 10 6.27 and 5.27 improved the colonization of lupin rhizospheres and increased early nodulation, nodule number and nodule mass. Nodule mass was increased from 65 to 393 mg plant −1 at 43 days by increasing the inoculum from log 10 4.27 to 6.27 bradyrhizobia seed −1 . Grain yield and % N in the grain were not significantly different ( P > 0.05) between potentials of logio 4.27 and 6.27. In the second experiment, higher potentials of 6.80 and 7.28 further improved rhizosphere colonization and increased nodule mass. Studies of the survival of the inoculum, during inoculation, sowing and in the soil, identified a large mortality factor; 95% of bacteria died between inoculation and sowing and of those surviving, 83% died after 22.5 h in the soil. These observations have important implications for setting new standards for commercial inoculants and for emphasizing the care needed in handling inoculated seed to reduce the death of bradyrhizobia in the period between inoculation and sowing.

Population biology of Bacillus cereus UW85 in the rhizosphere of field-grown soybeans

Abstract: We studied the spatial and temporal distribution and abundance of the biocontrol agent Bacillus cereus UW85 in the rhizosphere of soybeans during two growing seasons in the field. For this study, we used a neomycin-resistant mutant, UW85nl, derived from UW85. UW85nl spores were applied to seeds and by 24 h after planting 72% of the spores had germinated. UW85nl colonized emerging radicles, but populations were 10–50-fold smaller on radicles than they were on seeds at planting. UW85nl population sizes in the rhizosphere of 10–35-day old plants were largest near the crown of the plant and smaller further from the crown. For example, in a 1989 experiment 21 days after planting, UW85nl populations were 158-fold larger 0–2 cm below the crown than they were 7–8 cm below the crown. UW85nl population sizes were largest right after planting, and by seed harvest they decreased to levels comparable to indigenous B. cereus populations on untreated roots; however, at harvest the entire B. cereus population on treated roots was neomycin resistant, whereas on untreated roots < 3% was neomycin resistant. The proportion of the heterotrophic bacterial population that was represented by UW85n 1 was generally largest right after planting and decreased at subsequent sampling times. Our results indicate that UW85nl grew and spread on soybean roots, and it persisted in the rhizosphere until seed harvest.

Timing nitrogen applications for corn in a winter legume conservation-tillage system

Abstract: Fertilizer N efficiency of corn (L.) in conservation-tillage systems with winter legumes such as crimson clover (L.) can possibly be improved by better synchronization of legume-N release, fectftizer-N application time, and crop demand for N. The objective of this 3-yr (1986-1988) field experiment was to determine the effect of N application time on dry matter accumulation, N uptake, and grain yield of corn grown in a winter legume conservation-tillage system. Corn was planted with unit planters into crimson clover residue following in-row subsoiling. The clover was killed at midbloom every year. Treatments were a factorial arrangement of fertilizer N rates and application time. Nitrogen as NHNO was broadcast at rotes of 34, 67, and 134 kg ha. Zero-N checks were also included in both clover and rye (L.) plots. Application times were at planting, or 3, 6, or 9 wk later. In addition, split applications (1/3 at planting and the remainder 6 wk later) of the 67 and 134 kg N ha rates were included. In 2 of 3 yr, dry matter accumulation was not affected by N application time. In 1987, however, dry matter production was greater when N was applied at planting compared to split applications or applications later than 3 wk after planting. Application time affected N uptake patterns during the growing season, but generally did not affect total N uptake at the end of the season. With the exception of the first year, split N applications resuited in equivalent or reduced N uptake compared to application of all N at planting. Based on linear regression models, maximum yield was obtained with 134, 116, and 93 kg N ha in 1987, 1988, and 1989, respectively. After the first year, applying N later than 6 wk after planting reduced grain yield and split applications of N were not effective in increasing grain yield. These results suggest that the fertilizer N requirement of corn grown in winter legume conservationtillage systems on Coastal Plain softs decreases with successive years in the system and that the optimum management practice for conservation of N, energy, time, and labor would be to apply all fertilizer N at planting.

Influence of genotype, sowing date, and seeding rate on wheat development and yield

Abstract: A 3-year study was conducted to measure the effect of sowing time and seeding rate on the development and yield of wheat (Triticum aestivum L.) grown under high-yielding conditions in north-eastern Victoria. A range of wheat cultivars with different development responses, including 'winter' types, was used in 2 experiments in each season. High grain yields for dryland wheat were measured in the first 2 seasons (1985-86), and in 1985, near-optimal water use efficiencies (>18 kg/ha. mm effective rainfall) were obtained. In the third season (1987) grain yield was limited by adverse climatic conditions-in the me- and post-anthesis period. In each season, grain yield declined with delay in sowing time. In 1985 there was a loss of 200-250 kg grain/ha for each week's delay in sowing time. In 1987, yield loss with delayed sowing was 50-110 kg grain/ha. In each season, cultivars with late or midseason maturity development gave the highest mean yields, and the use of these maturity types allowed earlier sowing, in mid April. However, with late sowing of wheat there was a trend for early maturity types to give higher yields, and so the use of 2 wheat cultivars with distinct maturity development responses to climate is recommended. If only 1 wheat cultivar is to be used, then a late maturity type is recommended. Higher wheat yields were also obtained as spike density increased, as a result of higher seeding rates. Our data suggest that in the higher rainfall region of north-eastern Victoria, a spike density of about 500 spikes/m2 is required to optimise wheat yields.

The role of seedbank and sown seeds in the restoration of an English flood‐meadow

Abstract: . In 1985 an opportunity arose to make use of an area (referred to as Somerford Mead) which had recently been used for intensive grass or cereal production but which originally had been a permanent hay-meadow. Situated on circum- neutral alluvial soils over limestone gravel, it is in close proximity to the River Thames and to species-rich flood meadows, including Oxey Mead (Fig. 1). This paper describes the early stages of an experiment to recreate a ‘typical’ flood-meadow community using seed harvested from Oxey Mead. Before sowing the seed, soil samples were taken and seedling emergence suggested that little of the original flood-meadow seed bank survived. Although Oxey Mead was known to contain at least 57 species, germination of samples of the sown seed in the glasshouse was confined to 12 species. All except Bromus commutatus and Trisetum flavescens and an additional nine Oxey Mead species were recorded in the field, together with 24 arable weed/ruderal species. Soil-nutrient contents (N, P and K) were high; so the restoration of this flood-meadow using only management techniques (hay cutting at the end of June and aftermath grazing) and the local seed bank would take a long time. The use of Alopecuros pratensis-Sanguisorba officinalis seed mixture was justified by the accelerated succession on Somerford Mead towards the parent community.

Wheat Planting Date Effects on Soil Water Extraction and Grain Yield

Abstract: Due to a wide range of irrigated and dryland production systems and highly variable weather, planting date of winter wheat (Triticum aestivum L.) grown in the Southern High Plains varies from August to November. A 2-yr field study was conducted at Bushland, TX, to evaluate planting date effects on soil water extraction and grain yield. 'TAM 107' wheat was planted in late August to simulate a grazed production system, early October to represent an optimum date for grain production, and early November on preirrigated Pullman clay loam soil (fine mixed thermic Torrertic Paleustoll) and grown to maturity without further irrigation. Gravimetric soil water content to 3.6 m depth was determined at the beginning and end of winter dormancy and at anthesis [...]

Impact of fire on Picea mariana and Pinus banksiana seedlings in subarctic lichen woodlands

Abstract: . The demography of Picea mariana (black spruce) and Pinus banksiana (jack pine) seedlings was monitored through five censuses over 13 months in four different seed bed types after fire of four severity levels in lichen woodland. Most seeds germinated just before early frost in late summer 1990 or immediately after snow thaw in early spring 1991; the germination rate subsequently decreased. For both species, germination rate decreased along a gradient of fire severity. The proportion of Pinus seeds that produced a seedling surviving 13 months after sowing was 4.3 % and 0.4 % respectively in the intact lichen mat and in the mineral soil seed bed type. For Picea these values are 3.2 % and 0.2 % respectively. The low germination rate in a severely burned seed bed type appeared to be associated with the formation of a water-repellent crust at the soil surface following the fire. Seedlings were contagiously distributed and were more frequent in flat and hollow microsites, where there is probably more water available than on bumps or among pebbles. Properties of experimentally burned seed bed types may differ from those under natural fires where regeneration by seed generally occurs following dispersal. However, the high germination rate observed in the intact lichen mat suggests that scattered lichen woodland patches may respond to increased seed input by a higher frequency of seedling establishment.

Changes in potential seed longevity and seedling growth during seed development and maturation in marrow

Abstract: Marrow (Cucurbita pepo L.) seed quality was monitored during seed development and maturation in 2 years. Mass maturity (end of the seed-filling phase) was attained 61–63 d and 54 d after anthesis in 1989 and 1990, respectively, when seed moisture contents had declined to 40–48% (wet basis). Considerable dormancy was encountered during standard germination tests, but was overcome by decoating the seeds. The ability of dried, decoated seeds to germinate normally in standard tests reached near maximal values shortly after mass maturity; these values were more or less maintained in seeds from subsequent harvests. Maximum seed longevity in air-dry storage was detected in seeds harvested 24 d (1989) and 26–31 d (1990) after mass maturity. Seedling dry weights 15 d after sowing were greatest for seeds harvested 2–22 d (basal fruits) or 14 d (apical fruits) after mass maturity in 1989, and were positively correlated (P 0.25) in 1990, but absolute seedling size did (P<0.005); seeds harvested 21–31 d after mass maturity had the greatest seedling weight and also growth rate (in absolute terms) at any one time after sowing. Decline in seed quality (when assessed by both potential seed longevity and seedling growth) was not detected until the final harvest interval in 1990 (85–90 d after anthesis, 31–36 d after mass maturity). These results for marrow contradict both aspects of the general hypothesis that seed quality is maximal at the end of the seed-filling phase and that viability and vigour begin to decline thereafter.

Root Development of Nitrogen Catch Crops and of a Succeeding Crop of Broccoli

Abstract: The root development of seven catch crop species, and of a broccoli crop following catch crops, was followed by a minirhizotron technique. Large differences in root growth patterns were found among the catch crops. Fodder radish already had a rooting depth of 112 cm 49 days after sowing, whereas Italian ryegrass did not reach this depth until 175 days after sowing. The catch crops with a fast establishment of deep rooting also reduced the mineral nitrogen content in the subsoil most. Broccoli showed a significantly higher root density in the subsoil when grown after narrow-leaved lupin and lower after winter rape than where no catch crop had been grown. The main reason for these differences appeared to be the distribution of mineral nitrogen in the soil.

Compatibility of imidacloprid with fungicides as a seed-treatment control of Russian wheat aphid (Homoptera: Aphididae) and effect on germination, growth, and yield of wheat and barley

Abstract: Imidacloprid insecticide, applied as a seed treatment, singly or in combination with fungicides (carboxin-thiram, triadimenol-captan, and tebuconazole-thiram), protected growing plants of wheat and barley from developing infestations of Russian wheat aphid, Diuraphis noxia (Mordvilko) for 27-85 d after planting based on four greenhouse and four field trials. There were no compatibility problems in insecticide performance by combining imidacloprid with fungicides on the seed. Imidacloprid significantly reduced plant damage by D. noxia in all trials and increased yields in three of three field trials where plots were entirely infested. As a seed treatment, imidacloprid offers an environmentally safer approach to the control of D. noxia than is possible with wide-spectrum aerial or in-furrow granular insecticide treatments.

Biological and physical factors influencing Acacia constricta and Prosopis velutina establishment in the Sonoran Desert.

Abstract: Over the past century woody plants have increased in abundance on sites formerly occupied by grasslands in the Sonoran Desert. Woody plant invasion has been associated with a multitude of biological and physical factors. This study was conducted to determine temperature, soil, fire, rodent, and livestock effects on the germination and establishment of whitethorn acacia (Acacia constricta Benth.) and velvet mesquite (Prosopis velutina (Woot.) Sarg.). Optimum termination temperatures for both shrubs ranged from 26 to 31 degrees C, and seedling emergence was greatest from seed sown at 1 to 2 cm depths in sandy loam soil. Merriams kangaroo rats (Dipodomys merriami) fed seeds in the laboratory removed seed coats and planted embryos at 2 to 4 cm depths in a sandy loam soil. Prescribed fire killed 100% of seed placed on the soil surface but had no measurable effect on the germination of seed planted at 2 cm. After passage by sheep, about 6% of the A. constricta and 13% of the P. velutina seeds germinated while after passage by cattle, only 1% of the A. constricta and 3% of the P. velutina seed terminated. Embryo planting by rodents may improve survival efficiencies for these legunminous shrub seedlings, but seed consumption and passage by sheep and cattle appear to adversely affect seed germination. Dipodomys merriami, rather than domestic livestock, may be responsible for the spread of these shrubs in the Sonoran Desert.

Big Bluestem and Switchgrass Establishment as Influenced by Seed Priming

Abstract: Seed dormancy and slow seedling development often limit estab lishment of warm-season grass stands. Establishment of seedlings with two solid matrix seed priming (SMP) treatments [2-d moistened (17°C) and 14-d wet-chill (4°C)] was compared with untreated seed of 'Kaw' and 'Pawnee' big bluestem (Andropogon gerardii Vitman) and 'Path-finder' and 'Cave-in-Rock' switchgrass (Panicum virgatum L.) in greehouse and field experiments. In two greenhouse studies, seedling emergence was monitored from 7 to 26 d after planting and numher of adventitious roots were monitored from 2 to 5 wk after planting. Field experiments were initiated on 19 Apr. 1988, 3 June 1988, and 23 May 1989, on a Sharpsburg silty clay loam (fine montmorillonitic, mesic, Typic Argiudolls) [...]

Influence of Planting Date and Seeding Rate on Winter Wheat Grain Yield and Yield Components

Abstract: Winter wheat (Triticum aestivum L.) is commonly seeded over a 60-d period in the Midwest depending on crop rotation options, weather, and other farm operations. This study was conducted to determine whether winter wheat seeding rates should be altered depending on planing date and cultivar. Seeding date and planting rate responses of the cultivars, Merrimac and Cardinal, were evaluated at the University of Wisconsin Arlington Research Station during the 1988 to 1991 growing seasons. Eight planting dates ranged from 24 August to 3 November and seeding rates were 14, 28, 42, and 56 seeds/sq ft. Grain yield and yield components were influenced by all variables and specific interactions. Heads per square feet and kernel weight, two primary yield components, decreased as seeding was delayed after 12 September [...]

Germination and establishment of Themeda triandra (kangaroo grass) as affected by soil and seed characteristics

Abstract: The seed supply of Themeda triandra, syn. T. australis (kangaroo grass), for revegetation purposes may always be limited given the biological constraints on its production. It is important, therefore, that available seed be used efficiently by maximising germination and establishment. In two glasshouse experiments, we investigated the effects of various soil and seed factors and their interactions on germination and establishment of seeds sown on the soil surface and at depth. Maximum germination was achieved by either de-awning seeds and burying them manually at 1 cm depth or by sowing awned seeds on the soil surface in the vicinity of cracks or stones which allowed up to 96% of the seeds to bury themselves by natural means. Diurnal fluctuations in relative humidity of only 30% caused the 4-6 cm long geniculate awns to twist hygroscopically, thereby propelling the seeds along the soil surface and increasing their chances of becoming buried in favourable or 'safe' microsites for germination. A bitumen-coated straw mulch improved germination of de-awned seeds by maintaining high moisture content in the top 2 cm of soil, but inhibited the movement of awned seeds along the soil surface and their entry into safe microsites for germination. The data are discussed in terms of maximising germination and seedling establishment of Themeda, determining the most appropriate seed harvesting and cleaning methods, and selecting sowing methods which are most likely to be effective.

Interseeded forage legume potential as winter ground cover, nitrogen source, and competitor

Abstract: Legume winter ground covers may contribute to row crop systems by providing protection from wind and precipitation and by releasing N to the subsequent row crop, but to attain effective size, these legumes must begin growth well before the winter. A 3-yr study was conducted to evaluate the performance of four commonly used forage legumes interseeded into corn (Zea mays L.). Alfalfa (Medicago sativa L.), yellow sweetclover (Melilotus officinalis Lam.), red clover (Trifolium pratense L.), and alsike clover (T. hybridum L.) were seeded in a mix consisting of equal seed numbers (pure live seed) from each species. Seeding dates were (i) at corn planting and (ii) at last cultivation. Control treatments were nonseeded. Two levels of weed control also were evaluated [...]

Cotton Yield and Fiber Quality Response to Green Manures and Nitrogen

Abstract: The quantity and availability of N from green manures will considerably affect the N management of a succeeding cotton (Gossypium hirsutum L.) crop. This study was conducted to determine the N supplying capacity of crimson clover (Trifolium incarnatum L.), Austrian winter pea [Pisum sativum subsp. arvense (L.) Poir.], and rye (Secale cereale L.) to cotton and their influence on cotton yield and fiber properties. Green manure treatments (and a fallow check) with fertilizer N levels of 0, 56, 112, and 168 kg ha −1 were compared for 3 yr on a Norfolk loamy sand (fine-loamy, siliceous, thermic Typic Kandiudult). Soil moisture at planting was similar among the four green manure treatments. At the 0 N level, the legumes generally had higher soil NO 3 -N than rye or fallow [...]

Lentil domestication: On the quality of evidence and arguments

Abstract: The current views on lentil domestication are based on biological attributes of the wild progenitorLens culinaris ssp. orientalis and on assumptions which have never been tested. Seed dormancy, a major factor in the adaptation of ssp.orientalis to its natural habitat, makes it inappropriate for cultivation, because poor germination causes seed yield following cultivation to be equal to the amount of sown seeds. Higher yield, resulting from the evolution of a non-dormant type can be obtained only after five or six cycles of unprofitable cultivation. It is doubtful that incipient farmers would have undertaken such an endeavor without preexisting knowledge that non-dormant types could eventually be obtained. Experiments involving the sowing of wild lentil would have been much more successful if the non-dormant types were present in appreciable quantities in the seed stock. Establishment of that type in the natural population would have required a period of seven to eight years with favorable growing conditions allowing the non-dormant type to become widespread in the population, followed by massive predation by man reducing the hazard of a population explosion. The close similarity between isozyme profiles of the cultivated lentil and its wild progenitor indicates that lentil cultivation was attempted with seeds derived from different populations and in different areas.

Seed yield and yield stability of determinate and indeterminate autumn-sown white lupins ( Lupinus albus ) grown at different locations in France and the UK

Abstract: The seed yields and maturity dates of an indeterminate cultivar (Lunoble) and a determinate line (CH304/70) of Lupinus albus L. were measured at three locations in France (Lusignan, Dijon and Gotheron) and at Rothamsted, UK, in 1989/90 and 1990/91. Different combinations of sowing dates, plant densities and irrigation treatments were tested at some sites. Averaged over all sites, CH304/70 yielded more than Lunoble (3.26 v. 2.98 t/ha) but there were significant genotype x location interactions for yield and date of maturity. Both genotypes gave similar yields at the three locations in France (3.13 and 3.06 t/ha, respectively) (.)

Colonization of pea (Pisum sativum L.) taproots by Pseudomonas fluorescens: effect of soil temperature and bacterial motility.

Abstract: Root colonization by introduced strains of Pseudomonas fluorescens was examined to determine if temperature and bacterial motility affect the distribution of bacteria along the taproot of peas. Seeds coated with strain PRA25rif were sown in soil held at a constant soil-water matric potential of −6 kPa and temperatures of 16, 20, 24 and 28°C. After 7 days, 1 cm segments of the epicotyl (0–1 cm above the seed) and taproot (0–5 cm below the seed) and the seed were assayed for bacterial populations by dilution plating. A significant ( P P = 0.68). Of the temperatures tested, the temperature optimal for root colonization was 16°C, whereas root growth was most rapid at 24°C. The bacterium was never recovered from taproot segments > 3 cm below the seed, indicating that transport of this strain with the growing root, even when roots grew slowly, was not a major means of dispersal in the pea rhizosphere. The effect of bacterial motility on root colonization was assessed with P. fluorescens strains WCS374(Tn5) (motile) and LWM74-30 (non-flagellated, non-motile mutant) at 24°C with both a constant soil-water matric potential of −6kPa and with 27.2 mm of water added 4 days after planting. Seven days after planting the epicotyl, seed and 1 cm taproot segments 0–18 cm below the seed were assayed as above for bacterial populations. Neither the motile nor the non-motile strain was recovered > 3 cm below the seed under tatic conditions. However, both strains were recovered 14–16 cm below the seed 3 days after water was added, indicating that passive movement with water flow, and not motility, played a large role in bacterial dispersal in this system.

Environmental and Agronomic Effects on the Growth of Four Peanut Cultivars in a Sub-tropical Environment. I. Dry Matter Accumulation and Radiation Use Efficiency

Abstract: Four peanut cultivars of Spanish or Virginia botanical type and varying time to maturity were grown at a range of plant densities (44 000 to 352 000 plants ha-1) and spatial arrangements under irrigated conditions in sub-tropical southern Queensland, Australia. Total and pod dry matter production of the very early maturing Spanish cultivar Chico showed strong positive responses to increased plant density up to the highest density tested. Responses were less pronounced for the later maturing Spanish cultivar McCubbin and were minimal for the Virginia cultivars Early Bunch and Mani Pintar. All cultivars were insensitive to spatial arrangements. Accumulation of total dry matter, adjusted for the higher synthesis costs of oil and protein during seed filling, was well correlated to intercepted photosynthetically active radiation (PAR). Much of the variation in dry matter production among cultivars and plant populations could be accounted for by the effects of differing leaf area duration on cumulative intercepted PAR. Radiation use efficiency was negatively associated with the canopy extinction coefficient (k) within most sowing dates, and also negatively associated with minimum temperature across sowing dates for all cultivars except Mani Pintar.Crecimiento y eficacia del use de radiacion en el mani