Showing papers on "Sowing published in 1989"
TL;DR: N2 fixation and its potential contribution to increasing soil total N were estimated in field-grown crops of lupin and pea in 21 trials at 10 locations in New South Wales and Victoria, during 1984 to 1987.
Abstract: N2 fixation and its potential contribution to increasing soil total N were estimated in field-grown crops of lupin and pea in 21 trials at 10 locations in New South Wales and Victoria, during 1984 to 1987. Chickpea, faba bean and annual medic were included at some sites. Across experiments there were differences in annual rainfall (267 to 646 mm), soil N (0.02 to 0.20%), soil pH (CaCl2,4.3 to 8.0) and sowing date (24 April to 16 June). Most experiments were conducted on acidic (pH < 4.8) red-earth, the others on grey-cracking clay or sandy soil, both of higher pH The differing sites, seasons, and sowing time contributed to variation in legume biomass (2.02 to 14.33 t/ha) and total N (45 to 297 kg N/ha), and the amount of N harvested with grain (8 to 153 kg N/ha), which were related.Lupin fixed an average of 65% of total crop N, and pea 61%, but there was considerable variation about these averages (20 to 97%). Significant differences in % N2 fixation between legumes within sites were few. The amount of N2 fixed averaged 98.5 kg N/ha by lupin and 80.5 kg N/ha by pea, varying 26 to 288 kg N/ha and 16 to 177 kg N/ha, respectively. Variation in proportional and total N2 fixation was associated with biomass, soil mineral N, and sowing date. N2 fixation increased with more biomass and declined with higher soil mineral N, and later sowing (lupin). Each additional tonne of dry matter increased fixed N by c. 20 kg N/ha. Differences in amounts of fixed N between legumes within sites were due primarily to biomass differences.N2fixed by lupin contributed an average of 38.2 kg N/ha to soil N, and by pea, 17.9 kg N/ha. The contribution was variable, -41 to 135 kg N/ha (lupin) and -32 to 96 kg N/ha (pea), and correlated with proportional and total N2 fixation. Positive increase to soil total N occurred when lupin fixed at least 50% of its crop N, and pea 65%. This occurred in most crops. Legumes frequently used less of the available soil N than cereals.
137 citations
TL;DR: This chapter elaborates seed coatings and treatments, and their effects on plant establishment, and finds that the degree of attraction or repulsion by the seed coating can have large effects on the germination of coated seeds.
Abstract: Publisher Summary This chapter elaborates seed coatings and treatments, and their effects on plant establishment. Seed coating is a mechanism of applying needed materials in such a way that they affect the seed or soil at the seed–soil interface. Seed coating provides an opportunity to package effective quantities of materials such that they can influence the microenvironment of each seed. The treatment of seeds with fungicides and/or insecticides is a relatively common practice compared to other coatings. The most commonly applied seed coatings are those in which a trace quantity of fungicide and/or insecticide is applied to seeds in such a way that this small quantity is evenly distributed among the seeds. The process of seed coating usually involves the use of adhesives to bind materials to the surface of seeds. It is found that the degree of attraction or repulsion of moisture by the seed coating can have large effects on the germination of coated seeds. The mechanical planting of seeds is facilitated by having seeds that are of uniform size and shape, have sufficient size and weight to be easily separated mechanically, and flow readily without clumping together. The incorporation of nutrients in seed coatings provides a unique opportunity to supply each sown seedling with an accurately controlled quantity of nutrient that may be preferentially available to the sown species and less available to any neighboring weed species.
130 citations
TL;DR: It is concluded that seed yield of both DT and INDT soybean in subtropical latitudes is optimized by May seeding, high PPD, and use of square planting patterns as approximated by narrow-row culture.
Abstract: Narrowrow compared to conventional wide-row plantings have consistently produced higher seed yields in the Northern USA, where early maturity groups (MG) and indeterminate (INDT) types are commonly used. Node and pod numbers leaf area index (LAI), crop growth rate (CGR), total biomass, and seed yields were significantly increased (per unit land area) with increasing plant population density (PPD) up to a certain PPD, depending on spatial arrangement.We conclude that seed yield of both DT and INDT soybean in subtropical latitudes is optimized by May seeding, high PPD (40 plants m -2 ), and use of square planting patterns as approximated by narrow-row culture
120 citations
TL;DR: High biomass-accumulation was associated with long growth-duration, especially the duration of grain-filling and thus high cumulative radiation interception, and with high radiation-use efficiency, and the possibility for yield improvement for cereals in the semi-arid tropics.
94 citations
TL;DR: Results indicate that weeds directly competed with trees for N, and thereby aggravated N-deficiency in trees, and therefore affected N-uptake by trees.
Abstract: Pinus radiata trees were grown on a podzolized sandy soil at a second rotation site under the following treatments: total weed control, total weed control plus ammonium nitrate, strip weed control and no weed control. During the first two summers after planting the differences in needle water potential between trees under no, strip or total weed control were very small. Despite similar rates of net N-mineralization in strip and total weed control treatments, which averaged 64 kg ha−1 yr−1 in the 0–15 cm soil depth, weeds in the strip weed control treatment reduced soil mineral-N concentrations by 50–80%, leaching of N by the end of the first growing season by 45%, foliar-N concentrations by 4–14% and stem biomass at 20 months after planting by 46%. Although N-uptake by above-ground vegetation (trees plus weeds) was 49% higher in the strip weed control treatment, the amount of N apportioned to trees during the first 20 months after planting was reduced from 15.5 to 9.0 kg ha−1. These effects of weeds were even more pronounced in the no weed control treatment. Since weeds had little effect on the needle water potential of trees and the annual rates of N-mineralization, but adversely affected N-uptake by trees, results indicate that weeds directly competed with trees for N, and thereby aggravated N-deficiency in trees. Application of ammonium nitrate after complete weed control increased foliar-N concentrations, and N-uptake and growth of trees, but also induced severe stem deformation.
91 citations
TL;DR: In this paper, a locally developed and validated crop growth model for wheat, SIMTAG, using historic daily weather data, was used to simulate wheat crops at four locations in northern Syria.
83 citations
TL;DR: In this paper, the effects of chopped wheat residue and unchopped crop residues of wheat (Triticum aestivum L.) and rice ( Oryza sativa L.) in corn ( Zea mays L.) rotations on grain yield and soil properties were investigated in 27 field experiments during 9 years.
79 citations
TL;DR: Seeds were significantly higher in narrow rows than in the wide rows and seed yield per plant was most uniform at the 25-cm row spacing and became more variable as row width increased, while weight of aerial plant parts during the mid seed-fill growth period (R5) increased with decreasing row spacings.
Abstract: Information is needed to characterize soybean [ (L.) Merr.] plant responses where cultural practices and environmental conditions are maintained at a level conducive to high yield. Field studies were conducted in 1985 and 1986 to determine the effect of row spacing and plant population on seed yield and yield components of soybean. Two determinate Maturity Group V cultivars, Essex and Deltapine 105, were grown at three row spacings of 25, 51, and 76 cm and three plant populations of 260 200, 390 400, and 520 400 plants ha. Seed yield was significantly higher in narrow rows (25 and 51 cm) than in the wide rows (76 cm) with the 25-cm row spacing averaging 10% higher than the 76-cm row spacing (3740 vs. 3361 kg ha). There was a row spacing × cultivar interaction due mainly to a greater reduction in seed yield of Essex than Deltapine 105 as row width increased. Weight of aerial plant parts during the mid seed-fill growth period (R5) increased with decreasing row spacings. Plant number in plots with 76-cm row spacing decreased approximately 23% between planting and harvest whereas, the plant number in 51- and 25-cm row spacings decreased only 7 and 3% respectively during the growing season. Seed yield per plant was most uniform at the 25-cm row spacing and became more variable as row width increased
78 citations
TL;DR: The negative effect of wheat stubble on cotton stand establishment can apparently be overcome by; limiting the amount of aboveground residues that ara incorporated into the seedbed during planting, increasing the seeding rates, and planting tolerant cultivars.
Abstract: Emergence was reduced by an average of 9% for Paymaster 404 and 21% for Acala A246 when wheat stubble residues were present in the seedbed. The allelopathic effect of wheat stubble indirectly influenced lint yield by affecting population densities. The negative effect of wheat stubble on cotton stand establishment can apparently be overcome by; limiting the amount of aboveground residues that ara incorporated into the seedbed during planting, increasing the seeding rates, and planting tolerant cultivars
74 citations
TL;DR: Growth and water use of kabuli-type chickpea was measured during the 1982/83 and 1983/84 growing seasons in northern Syria under rainfed conditions and comparison between seasons showed that the relations could not be used predictively.
Abstract: Growth and water use of kabuli-type chickpea was measured during the 1982/83 and 1983/84 growing seasons in northern Syria under rainfed conditions. Winter-sown (November) and springsown (March) crops of cv. ILC 482 were grown in 1982/83 while in 1983/84 spring-sown crops of contrasting genotypes (ILC 482, ILC 1929 and ILC 3279) were compared.In 1982/83, shoot dry matter and seed yields of the winter-sown crop were almost twice those of the spring-sown crop although the water use of both crops was almost the same. Root growth of both crops was most rapid before flowering but continued until maturity (early June) in the winter-sown and until mid to late pod filling (also early June) in the spring-sown crop. Root dry weight (c. 45 g/m2) and length (c. 45 cm/cm2) were similar in both crops during pod filling.In 1983/84, shoot weight, root weight and root length were similar in all genotypes but the later maturity of ILC 3279 resulted in lower seed yield and hence harvest index, and greater water use.The root length density decreased approximately logarithmically with depth in the soil profile although comparison between seasons and with other published results showed that the relations could not be used predictively. Water use efficiency was poorer in the second, drier season and was almost doubled by winter sowing.
71 citations
TL;DR: Investigation of the effects of seed density, relative frequency, and relative planting date on the emergence of seedlings in the species Senecio vulgaris, Capsella bursa-pastoris, and Poa annua found that the probability of emergence significantly decreased with an increase in total seed density.
Abstract: The interactions between seeds in the soil are poorly understood. We per- formed greenhouse experiments to investigate the effects of seed density, relative frequency, and relative planting date on the emergence of seedlings in the species Senecio vulgaris, Capsella bursa-pastoris, and Poa annua. We found that for both Poa and Senecio, the probability of emergence significantly decreased with an increase in total seed density. Neither the density of conspecifics nor heterospecifics alone could explain this decline in the probability of emergence. We also found that, for all three species studied, the rate of emergence accelerated in the presence of previously planted seeds. A second experiment indicated that this acceleration involves a response to leachate from previously germinated seeds.
Journal Article•
TL;DR: Plants fertilized with moderate and high N levels in the greenhouse produced larger early yields in the filed, but there was no effect of N or P level applied inThe greenhouse on total yield.
Abstract: «Pik-Red» tomato (Lycopersicon esculentum Mill.) transplants grown in the greenhouse were fertilized with three levels of N and P. Nitrogen at 400 mg•liter −1 and P at 30 mg•liter −1 had produced the largest transplants at 5 weeks after sowing. Nitrogen at 100 mg•liter −1 produced the largest root: shoot ratio. Phosphorus had no effect on root: shoot ratios. Plants fertilized with moderate and high N levels in the greenhouse produced larger early yields in the filed, but there was no effect of N or P level applied in the greenhouse on total yield. Four- and 5-week-old plants produced greatest total yields
TL;DR: If direct effects of poor vigour seed on yield through reduced establishment are avoided by adjusting sowing rates so that recommended rates of establishment are achieved, then there will probably be little or no effect of seed vigour in final yield, providing normal germination in the laboratory test is 85% or more, and sowing in the spring is not delayed.
TL;DR: The proportion of the legume in the harvested material was much lower than expected from the seed ratios and Digestibility and crude protein content were highest in the mixtures of triticale and peas.
Abstract: Two small-grained cereals, Mulga oats and a triticale line, and two legumes, local vetch and local peas, were grown in pure stands and in mixtures at various cereal: legume seed ratios (20:80, 40:60, 60:40 and 80:20) for three successive cropping years, 1981/82 to 1983/84, at Laxia and Dromolaxia, Cyprus, in each year.The cereal pure stands produced, on average, more dry matter, 8·40 t/ha, and more digestible organic matter, 4·12 t/ha, than the legume pure stands, 3·68 and 2·18 t/ha, respectively. On average, total dry matter production decreased linearly as the seed proportion of the legume component in the mixture increased. The proportion of the legume in the harvested material was much lower than expected from the seed ratios. The highest proportion of legume was seen in the mixtures of peas with triticale and ranged from 8·1 to 35·5% at the various sowing rates. Digestibility and crude protein content were highest in the mixtures of triticale and peas.
TL;DR: Solarization controlled broom-rape and other weeds in the following two seasons when the soil was left undisturbed during the season of the treatment.
Abstract: Summary. Experiments were conducted between 1985 and 1988 to evaluate the effect of duration and time of solarization on the control of two broom rapes (Orobanche aegyptiaca Pers., O. crenata Forsk.) and other weeds common in the fields of faba bean (Vicia faba L.) and lentil (Lens culinaris Medik.) in West Asia. Solarization was performed by applying clear polyethylene sheet to the soil for 0, 10, 20, or 40 days in 1985/86, 0, 30, or 40 days in 1986/87 and 0, 20, 30, 40 or 50 days in 1987/88 during the hot season (July and August) and for 50 days immediately before sowing during milder weather (September and October) in 1986/87. Best control was obtained with solarization for 30–50 days in the hot season. Maximum soil temperature under polyethylene at 5 cm was 55°C in 1985, 48°C in 1986 and 57°C in 1987. Broomrape dry weight decreased in the first experiment by more than 90% in both faba bean and lentil fields. Solarization controlled broom-rape and other weeds in the following two seasons when the soil was left undisturbed during the season of the treatment.
TL;DR: In this experiment moderately high populations of each crop were found to be necessary to obtain beneficial yields from the mixtures and semi-additive mixtures, with 67% of eachcrop's pure stand population, appeared most appropriate.
Abstract: The growth and development of maize and soya bean when grown in mixtures in different proportions and arrangements were studied at Samaru (11° 11' N, 38° E) and Yandev (07° 23' N, 09° 10' E) in the savannah belts of Nigeria. The crops were sown in both pure and mixed stands. The pure-stand densities were 513 plants/m2 for maize and 20·15 plants/m2 for soya bean. Mixtures were made in three proportions: additive (100:100), containing 100% of the sole crop population of each crop; semi-additive (67:67), containing 67% of each crop's sole population; and replacement (67:33 and 33:67), containing 67% of one crop's population to the other's 33%. The mixtures were formed either on the same ridge (in-ridge) or on different ridges (alternate ridge).Maize grain yield at Samuru was not significantly reduced in mixtures except where its proportion was reduced to 33% of its sole crop density. Seed yields in soya bean were significantly reduced in all mixtures, and when associated with maize density of not greater than 67%, soya bean was capable of 50% of its sole crop yield. At Yandev, late planting coupled with inadequate rainfall in the month following planting depressed seed yields in both crops, the sole crop yields being only 1·53 t/ha in maize and 0·24 t/ha in soya bean. Also maize appeared to be adversely affected in the mixtures at this location, the yields being significantly reduced in the mixtures irrespective of planting ratios.All mixtures, except 100:100 at Yandev, proved beneficial by producing land equivalent ratio (LER) values greater than one, while 67:67 proportions made higher gross returns than any of the sole crops at Samaru. In this experiment moderately high populations of each crop were found to be necessary to obtain beneficial yields from the mixtures. In this regard semi-additive mixtures, with 67% of each crop's pure stand population, appeared most appropriate.Incidence of maize streak was significantly lower in alternate ridge mixtures; otherwise the crop in the mixtures seemed to be little affected by pattern of plant arrangement; while soya bean was quite sensitive, its flowering and podding being significantly delayed in in-ridge mixtures at Yandev. The legume yields in this mixture were also slightly, though not significantly, adversely affected. Thus alternate ridge arrangement was more favourable.
TL;DR: Embryo maturation with abscisic acid (ABA) gave 48% conversion in soil under growth chamber conditions and 64% conversion was obtained under greenhouse conditions, when humidified air was used to prevent soil surface drying.
Abstract: Conversion (plant production) was obtained from direct-planting alfalfa somatic embryos and encapsulated somatic embryos (artificial seeds) of alfalfa into a growth chamber and greenhouse. The embryos were planted in a commercial soil potting mix under nonsterile conditions in a manner similar to zygotic seed. Embryo maturation with abscisic acid (ABA), prior to planting, gave 48% conversion in soil under growth chamber conditions. Under greenhouse conditions, 64% conversion was obtained when humidified air was used to prevent soil surface drying. Previously, conversion in soil was between 0–6% without the ABA maturation treatment. The replacement of ABA with mannitol or combinations of mannitol and ABA during maturation resulted in lower conversion in the growth chamber than with ABA alone. ABA may be promoting the accumulation of embryo storage reserves such as proteins and carbohydrates for growth after planting in the soil environment.
TL;DR: It is concluded that almost all of the offspring originated from widely scatterhoarded seeds around seed sources of red squirrels and the distribution of the children were ultimately decided by the fate of the scattered seeds.
TL;DR: By increasing biomass, as well as biomass production per unit water used, winter planting offers a promising avenue towards increasing sunflower yields in rainfed cropping systems of mediterranean climates.
TL;DR: In this paper, the CERES-Maize model was used to simulate the growth and grain yield of a Brazilian maize hybrid, DINA 10.5, based on available soil, crop and weather data.
TL;DR: In this article, the authors assess the influence of plant growth habit, planting pattern (inter and intra-row spacings), and seeding date on light interception and vegetative and reproductive growth, development, and yield of peanut.
TL;DR: At normal farm lupin plant densities, the biological plough effect was estimated to improve wheat yields by substantially less than the benefits from nitrogen fixation and breaks in disease cycles, Nevertheless, it still suggests that l upin stand densities should be maintained or increased in crop rotations on compacted sands.
Abstract: Summary. The effects of the density of lupin (Lupinus angustifolius L. cv. Illyarrie) taproots on a following wheat crop (Tritium aestivum L. cv. Gutha) were investigated on a compacted, earthy sand soil near Geraldton, Western Australia. In 1985, plots were sown to lupins at densities ranging from 35 to 220 plants m-2. Because peak lupin biomass varied by less than 25%, and 100 kg N ha-1 of mineral fertiliser was supplied to the wheat, the effects of variation in residual N from the lupins were considered to be minimal. In 1986, all plots were split for shallow or deep tillage and wheat sown. There were no effects of tillage or lupin density on stored soil water at sowing. Growth and yield ofwheat on the shallow tilled plots increased linearly with lupin plant density in the previous year, to equal or better wheat yields on the deep tilled plots, which were unaffected by lupin density. At normal farm lupin plant densities, the biological plough effect was estimated to improve wheat yields by 100 kg ha-1, substantially less than the benefits from nitrogen fixation and breaks in disease cycles. Nevertheless, it still suggests that lupin stand densities should be maintained or increased in crop rotations on compacted sands.
Journal Article•
TL;DR: Delayed sowing later than April may result in serious crop yield loss due to the second generation larvae of B. fusca in Awassa, and high infestation by secondgeneration larvae appeared to be connected with the high biotic potential of the moths of the first, non‐diapause generation.
Abstract: The relationship between sowing date and the maize stalk borer, Busseola fusca (Fuller) in terms of infestation rate, and crop damage was studied using ten successive sowing dates between April and July in 1985 and 1986. Different degrees of infestation by B. fusca were recorded from all sowing dates. Early sowing in April and the early part of May had significantly lower infestations of first generation larvae. Levels of infestation by second generation larvae were significantly higher on late sowing dates. High infestation by second generation larvae appeared to be connected with the high biotic potential of the moths of the first, non‐diapause generation. Second generation larvae caused crop loss ranging from 22–5 to 100% while it was only 0–22.6% due to the first generation. In conclusion, delay of sowing later than April may result in serious crop yield loss due to the second generation larvae of B. fusca in Awassa.
TL;DR: In this paper, the authors evaluated the influence of several black nightshade-free periods on cotton yield, reproduction of black night shade, and longevity of weed seeds in soil.
Abstract: Black nightshade plants were controlled by hoeing in the same cotton plots each year (1982 to 1986) for 3 to 15 weeks after crop emergence to evaluate the influence of several black nightshade-free periods on cotton yield, reproduction of black nightshade, and longevity of weed seeds in soil. Similar information, although limited, was also collected for Palmer amaranth that escaped the initial herbicidal treatment each year. Except for 1982, black nightshade competing with cotton for the duration of the growing season in nonhoed plots severely reduced yields (60 to 100%), with greatest yield reductions (82 to 100%) occurring in 1983 and 1984 when 0.5 to 0.7 cm of rain fell within 10 days after cotton planting. When combined with cultivation, a 3-week nightshade-free period at cotton planting was of sufficient duration to protect cotton yields. Weed seed production for all hoed treatments was less than 1% of the nonhoed treatment, and after five consecutive cotton crops (1982 to 1986), the amount of both black nightshade and Palmer amaranth seeds in soil was similar for all hoed treatments. These populations were 60 to 80% and 95 to 97% less than beginning populations of black nightshade and Palmer amaranth in 1982, respectively. After 5 yr of continuous treatments, cotton was grown in 1987, with standard cultivation as the only method of weed control, to evaluate how the weed-free periods in 1982 to 1986 influenced weed seed populations in the soil and the resultant effect on weed competition and cotton yields. Reduction of cotton yields in 1987, in the absence of weed-free periods, indicated that black nightshade seed survival in soil appears to be sufficiently long for ample establishment of this weed to compete with cotton. Thus, fields will have to be kept weed free for greater than 5 yr to reduce black nightshade populations to a level that will not reduce cotton yields.
TL;DR: Under the stress conditions that occurred in the early planting date in 1982 and 1983 following no-tillage, the high- vigor seed lots had significantly greater emergence than low-vigor seedLots.
Abstract: The low- and medium-vigor seed lots had consistently lower emergence than high-vigor seed lots in all tillage systems and planting dates. Emergence following conventional tillage was consistently greater than emergence following all no-tillage treatments; however, this difference was significant only at the early planting date in 1982 and 1983. Under the stress conditions that occurred in the early planting date in 1982 and 1983 following no-tillage, the high-vigor seed lots had significantly greater emergence than low-vigor seed lots . Thus, selecting seed lots with high germination and vigor would be beneficial for early plantings in no-tillage systems
TL;DR: It is concluded that the application of osmoconditioning of seeds to commercial production is limited to its effects on germination and early growth alone.
Journal Article•
TL;DR: Subclover mulches show some potential for suppressing weeds and increasing soil organic matter, and vegetable yields varied in tests, depending on how the mulch was managed.
Abstract: Subclover mulches, which grow from fall through spring then die back before crop planting, show some potential for suppressing weeds and increasing soil organic matter. Vegetable yields varied in tests, depending on how the mulch was managed.
01 Jan 1989
TL;DR: Experiments proved that the disk-harrowing of rhizomes was a useful method of establishing A. arenaria and the cause of the replant failures on reconstructed dunes was investigated, which means that erosion control can become very costly.
Abstract: Introduction This study deals with the establishment, growth, and degeneration of Ammophila arenaria (marram grass), a grass species that dominates the vegetation in coastal foredunes. Following natural establishment from rhizomes on high parts of the beach A.arenaria reduces wind velocity, which results in the accretion of windblown sand and the formation of dunes. A. arenaria grows vigorously in mobile dunes where fresh sand is deposited by wind, but it disappears from the vegetation when these dunes become stabilized. Because of its ability to stabilize the sand, A. arenaria is often used in dunes to control erosion. It is planted according to a long practicised manual technique, using culms that are collected from stands at the foredune. When foredunes are reconstructed, however, (e.g. after storms) the establishment of A. arenaria is often unsuccessful, which means that erosion control can become very costly. This study was carried out to develop new methods of establishing A. arenaria and to investigate the cause of the replant failures on reconstructed dunes. In addition, experiments were carried out to eludicate the relationship between the colonization of windblown sand and the vigour of A. arenaria . Establishment Two alternative methods were developed: (1) the sowing of seeds, which is rarely practiced and (2) the disk-harrowing of rhizomes, which has not previously been applied. Experiments showed that seeds hardly germinate at constant temperatures. A high rate of germination can be achieved with fluctuating high temperatures, but at low temperatures the seeds required stratification in order to germinate. In the field the seeds germinated well if they had been sown during the winter, which was probably because of natural stratification. Seeds can be sown mechanically while afterwards the sand surface needs to be stabilized. For this purpose straw proved to be more effective for seedbed stabilization than spraid compost. Rhizomes (i.e. vertical underground stems) were collected from the foredune by mechanical sieving of the sand. Experiments proved that the disk-harrowing of rhizomes was a useful method of establishing A. arenaria provided that the sand surface was temporarily stabilized with straw or planted bundles of reed (chapter 2). Growth Field experiments showed that higher sowing rates and higher planting densities of rhizomes resulted in higher numbers of seedlings and primary shoots. However, after one growing season production of biomass and numbers of tillers appeared to be independent of the initial density. Application of slow-release NPK fertilizer (Osmocote, 12 to 14 months active at 21 °C) increased dry matter yield and numbers of tillers (chapter 2). In a large-scale field experiment, rhizomes and a combination of planted culms and rhizomes produced more biomass and percentage cover than a sown stand during the first growing season. The lowest dry matter yield and percentage cover were obtained with traditionally planted culms. All plantings had been supplied with the same amount of slow- release NPK fertilizer. In the second year, however, the highest production was recorded for planted culms and for seeds in combination with compost. During these two years less than 5 per cent of the total area had to be replanted. All methods, therefore, were satisfactory in terms of sand stabilization. The influence of uncontrolled factors was demonstrated by a 100 per cent higher production from a one-year-old stand in 1986 compared to 1987. The origin of the culms and rhizomes also influenced growth. Culms or rhizomes that had been collected from a stable dune with degenerated A.arenaria produced less dry matter and percentage cover than when the plant material was obtained from a mobile dune which was covered by vigorous plants (chapter 3). Degeneration Growth of seedlings of A.arenaria was strongly reduced in sand from the root zone of a foredune, when compared to growth in fresh (sea) sand. However, no differences occurred when both sand samples were sterilized prior to planting of the seedlings. In sea sand, growth was equal to that in sterilized sand. It was concluded, therefore, that the rhizosphere of A. arenaria contained harmful soil organisms (chapter 4). In order to trace the nature of these organisms, biocides (bactericides, a nematicide, and fungicides) were applied to rhizosphere sand, which was planted with seedlings of A.arenaria. Bacteria were not supposed to be involved in the degeneration of A. arenaria , as bactericides did not affect plant growth. The nematicides effectively eliminated endoparasitic nematodes ( Heterodera avenae group, Meloidogyne maritima , and Pratylenchus sp.) and the application led to increased plant growth. Fungicides also enhanced growth, however, they also eliminated the nematodes H. avenae and M. maritima. It was concluded that nematodes were involved in the growth reduction and degeneration of A. arenaria, but the involvement of soil fungi could not be established unequivocally. Results of a preliminary inoculation experiment suggested that a complex of soil fungi and nematodes is responsible for the degeneration of A. arenaria (chapters 5 and 8). The harmful soil organisms from a certain location reduced growth of local, as well as of foreign populations of A. arenaria. The growth of Calammophila baltica (purple, or hybrid marram grass, a sterile bastard of A. arenaria x Calamagrostis epigejos ) was also reduced by harmful soil organisms, but less than A. arenaria (chapters 4 and 6). In three Dutch coastal dune systems harmful soil organisms were detected in the root zones of stable, as well as of mobile foredunes (degenerating and vigorous A. arenaria , respectively), but not in beach sand. The relation between sand deposition by wind and vigorous growth of A. arenaria was explained by supposing that windblown sand, originating from the beach, enables A. arenaria to escape harmful soil organisms (chapter 6). However, within one year after plants had produced new roots in fresh windblown sand, the root system became colonized by harmful soil organisms (chapter 7). If harmful organisms were present in the sand prior to root growth, root hair formation was reduced severely and the branching of the roots was stimulated (chapter 7). This deformation of the root system by harmful soil organisms is assumed to be related to the degeneration of A. arenaria. A reduced uptake function and a shallow placement of the root system due to attack by harmful soil organisms in stable dunes increases the susceptibility of the plants to stress of drought, high soil temperatures, and shortage of nutrients. It is concluded that the degeneration of A. arenaria in stable dunes is caused by a combination of harmful biotic factors and abiotic stress.