Showing papers on "Growing season published in 1985"

Ecology of a Grazing Ecosystem: The Serengeti

Abstract: Primary productivity and herbivory were studied in the Serengeti National Park, Tanzania, and Masai Mara Game Reserve, Kenya, during the annual cycle of 1974—1975, and wet—dry season transitions in 1976—1979. Basic state variables measured were aboveground plant biomass inside permanent and temporary fences, and outside fences. Productivity was calculated as the sum of positive plant biomass increments. Control productivity (cPn) was calculated from biomass dynamics inside permanent fences. Temporary fences were moved in concert with grazing by the region's abundant ungulates to estimate actual aboveground primary productivity (aPn). Primary productivity was highly stochastic with productive periods poorly synchronized even among nearby sites. Short—term productivities could be extremely high, exceeding 30 g°m—2°d—1. Grazing animals adjusted their densities in relation to grassland productivity. The average proportion of annual aPn that was consumed by herbivores was 0.66, with a minimum of 0.15 and a maximum of 0.94. Green forage was available everywhere late in the wet season in May but was available only at high rainfall sites in the northwest late in the dry season in November. By the end of the dry season, the residual plant biomass outside fences averaged only 8% of cPn. Nomadic grazers moved seasonally in response to grassland productivity. The growing season ranged from 76 d in low rainfall areas to virtually continuous in high rainfall areas. Annual cPn was linearly related to rainfall and averaged 357 g°m—2°yr—1 over the year and 1.89 g°m—2°d—1 during the growing season. Actual aPn was substantially greater than cPn at most sites, averaging 664 g°m—2°yr—1. Growing season aPn averaged 3.78 g°m—2°d—1. Grazing stimulated net primary productivity at most locations, with the maximum stimulation at intermediate grazing intensities. Stimulation was dependent upon soil moisture status at the time of grazing. Rain had a diminishing effect on primary productivity as the wet season progressed and plant biomass accumulated. Part of the stimulation of grassland productivity by grazing was due to maintenance of the vegetation in an immature, rapidly growing state similar to that at the beginning of the rainy season. Since grazers overrode rainfall—determined productivity patterns, aPn was more closely related to grazing intensity than to ranfall. Grazing was heavier on grasslands that were intrinsically more productive. Rate of energy flow per unit of plant biomass was much higher in grazed vegetation. Grazers ate green leaves almost exclusively during the wet season, but species composition of the diets of different grazers differed markedly. Diets of nomadic grazers were very different in the wet and dry seasons. Vegetation dried out rapidly at the onset of the dry season and dry plant tissues made up a substantial proportion of ungulate dry season diets. However, green forage commonly was more abundant in diets than in the vegetation. Grazing increased both forage quality and its rate of production. Zebras supplemented a high—bulk diet by eating the seeds of awnless grasses. The foraging patterns of different grazers were differentiated by several vegetation properties, including productivity, structure, and species composition, in a manner suggesting resource partitioning. The relationship between the stability of vegetation functional properties and community species diversity was positive in five of seven tests. Greater species diversity was associated with greater biomass stability through the seasons, greater resistance to grazing by a single species of ungulate in both the wet and dry seasons, and greater resilience after grazing. Species diversity was not associated with greater resistance to grazing by several ungulate species or to plant species extinction. Specific properties of trophic web members were identified that produced greater functional stability in more diverse communities. Fire does not appear to have important effects upon the functional properties of the grasslands except for a weak stimulation of productivity in the wet season immediately following dry season burning. Fire did have an important effect upon structural properties of the vegetation that would tend to regulate ungulate feeding. The ecology of neither the plants nor the animals in the Serengeti ecosystem can be understood in isolation; many traits of both suggest coevolution among trophic web members. The functional dynamics of the trophic web suggest that the acceleration of energy and nutrient flow rates due to intense herbivory has resulted in the development of an entire consumer food web due to additive fluxes rather than mere quasi—parasitic fluxes from plants to animals.

Tillering responses to enrichment of red light beneath the canopy in a humid natural grassland

Abstract: (1) Enrichment of red light at the base of dallisgrass (Paspalum dilatatum Poir.) and smutgrass (Sporobolus indices [L.] R.Br.) plants in a dense humid natural grassland was obtained by use of small light-emitting diodes around the crown of each grass plant. (2) Results of this study supported the hypothesis that modification in light quality by a dense grassland canopy was detrimental to tiller populations. Tillering rates were increased and tiller death delayed until the end of the growing season when additional red light was supplied to the crown of plants. (3) The photocontrol of axillary bud activity may be part of a system whereby the tiller dynamics would be related to resources availability. (4) These results also suggest that maintenance of a grass sward at a high leaf area index might not be a good management strategy for long-term productivity.

Development of a linked forest productivity-soil process model

Abstract: A general model of linked carbon-nitrogen cycles in forest ecosystems as constrained by climate and geology is described. The model, written in FORTRAN, is based on the JABOWA model of Botkin et al. (1972) as revised by Solomon et al. (1984). The birth, growth, and death of all trees greater than 1.43-cm dbh in a 1/12-ha plot are simulated. The return of litter and its decomposition are also simulated. Sunlight is the driving variable. Growing season degree days, soil water availability, and actual annual evapotranspiration are calculated from monthly rainfalls and temperatures as well as soil field moisture capacity and wilting point. Decomposition and soil nitrogen availability are calculated from organic matter quantity and carbon chemistry, evapotranspiration, and degree of canopy closure. Light availability to each tree is a function of leaf biomass of all taller trees. Degree days and the availabilities of light and water constrain species reproduction. These, along with soil nitrogen availability, constrain tree growth and hence carbon accumulation in biomass. The probability of a tree's dying increases with age and slow growth. Leaf, root, and woody litter are returned to the soil at the end of each year to decay the following year. Parameters for 72more » upland species of eastern North America are taken from literature data. The model simulates species composition and ecosystem processes for most upland forests of eastern North America. 6 figs., 6 tabs.« less

Root characteristics of some temperate legume species and varieties on deep, free-draining entisols

Abstract: We report experiments comparing several legumes with the aim of distinguishing genotypic from environmental differences in those root parameters which influence water use and nutrition. Temperate crop and pasture legumes were grown on three xeric psamment soils at latitude 29¦S. in Western Australia to evaluate the relative root characteristics of different species. Sites had 428, 298 and 155 mm rainfall in the (winter) growing season. Maximum root depth was significantly different (P < 0.001) between genotypes, but non-significant between sites. Genetic control for maximum root depth is thus implied. This has significance for water use and plant production of these low water-storage sandy soils. Lupinus spp. extended their roots to an average 190 cm, Pisum sativum L. to only 65 cm, Triticum aestivum L. to 113 cm. The pasture species ranged from Vicia benghalensis L. (75 cm) and Trifolium spp. (69 cm) to Medicago spp. which averaged 92 cm. Lupins and wheat had less than 50% of their total root length (cm-1) in the top 20 cm, whereas other species all had over 70% of roots in that layer. Pasture legumes with high root density in that layer tend to dry sandy topsoils frequently, reducing nutrient availability and hence vegetative growth. Root density averaged only 0.045 for lupins, compared with 1.0 cm-2 for clovers. All total root lengths were low at maturity, compared with more favorable environments. Nevertheless, they were calculated to be adequate for water and mobile nutrient extraction from these sandy soils.

Evapotranspiration Crop Coefficients Predicted Using Growing-Degree-Days

Abstract: MONTHLY evapotranspiration (Et) of alfalfa (Medicago sativa L.), cotton (Gossypium hirsutum L.), corn (Zea mays L.), and sorghum (Sorghum bicolor (L) Moench) was measured in nonweighing lysimeters for various years and locations in New Mexico to evaluate the effects of various climatic conditions. Potential evapotranspiration (E0) was determined using Penman's equation, and a crop coefficient (the ratio of Et to E0) was determined for each month of the growing season for each crop. Growing-degree-days (G) were determined from temperature data. A third order polynomial crop curve, relating crop coefficient to cumulative G, was estimated for each crop. There was no statistical difference in the crop curve between locations in New Mexico. The coefficient of determination (r2) of the combined polynomial for alfalfa was 0.70. Accumulated G had less variability than calendar days in predicting the time duration to harvest for corn and sorghum, but not for cotton.

Sensitivity of boreal forests to possible climatic warming.

Abstract: General circulation models indicate substantial CO2 warming in high latitudes In these regions, which include the boreal coniferous forests, the activity of ecosystems is largely controlled by temperature The effective temperature sum (degree-days) is used in this study for describing the regional variability in the productivity of boreal ecosystems Although the concept is simple, it takes into account two basic factors: the length of the growing season and the day-to-day level of activity of the ecosystem This study examines which areas in the boreal coniferous forests would be most sensitive to a possible climatic warming The data used in the study are for Finland A regression is estimated between regional forest growth rate and effective temperature sum A climatic warming is assumed and the corresponding growth response is calculated, using the regression, for northern and southern areas, and for maritime and continental areas The response is expressed in terms of (i) absolute increase in growth (grams per m2 per year) and (ii) relative increase in growth The results indicate that a given climatic warming would yield the greatest absolute increase in growth in warm (ie southern) and maritime parts of the biome In terms of the relative growth response the sensitivity would increase northward and toward maritime areas

Clonal growth in Typha latifolia: population dynamics and demography of the ramets.

Abstract: (1) Ramet demography and growth in a mature natural population of Typha latifolia shoots in south-central Michigan, U.S.A. were studied. Records of 1981 individuallytagged shoots, observed at 1or 2-week intervals for two growing seasons, included height, number of leaves and status of each leaf. Biomass was determined by harvesting replicate plots. (2) Shoots emerged in three main pulses each year, resulting in three major cohorts. These pulses were timed similarly in 2 years. The first cohort emerged in early spring, grew throughout the summer and senesced completely in late autumn. The second emerged in midsummer; 82% (year 1) and 76% (year 2) of these shoots senesced completely in autumn, while the remainder resumed growth the following spring. The third emerged in late summer and early autumn; 78% (year 1) and 92% (year 2) of all its shoots resumed growth the following spring. (3) Shoot mortality within 3 weeks of emergence was minor (13%, year 1; 6%. year 2). (4) The ranges in live shoot density were very similar for the 2 years: 12 7-43 9 shoots m-2 in year 1 v. 11 2-41-9 shoots m-2 in year 2. In year 1, however, live shoot density increased gradually throughout the growing season, while in year 2 a rapid increase in shoot density resulted in a density of 40.1 shoots m-2 by mid-May. This density was maintained throughout the second growing season. (5) Because the density of shootsv growing from early spring was 60% greater in year 2 than in year 1, we were able to evaluate the applicability of genet-based, density-mediated competition theory (based on eight expected consequences) to ramet-level populations. We conclude that density-mediated competition does not regulate ramet populations in mature stands of T. latifolia.

Photosynthesis and Dry Matter Production in C3 and C4 Pasture Plants, With Special Emphasis on Tropical C3 Legumes and C4 Grasses

Abstract: The nature of C3 and C4 pasture plants is described, and the potential biomass productivity is discussed. Then differences in net annual production and crop growth rates of C3 and C4 pasture plants are analysed in terms of the interception of solar radiation and the efficiency of its conversion to dry matter. Finally, the components of photosynthetic production of tropical C4 grasses and tropical C3 legumes are compared with their growth rates and dry matter yields in the subtropics. The higher crop growth rates of tropical C4 grasses compared with C3 pasture plants, whether they are of temperate or tropical origin, seem to be due mainly to higher leaf net photosynthetic rates and to the absence of photorespiration associated with possession of the C4 pathway. However, light utilization efficiencies are probably also higher in C4 grasses. In addition to these two characteristics, the longer growing season of C4 grasses in the warm conditions of the tropics contributes to their higher net annual production of dry matter. There is a close association between possession of the C4 pathway, higher rates of photosynthesis and growth, and higher dry matter yields when tropical C4 pasture grasses are compared with tropical C3 legumes in a subtropical climate.

Seasonal Carbon and Water Balances of Soybeans Grown Under Stress Treatments in Sunlit Chambers

Abstract: SOME agricultural research issues require that engineers provide continuous monitoring and treatment control of plant environments over seasonal time frames under field-like conditions. In such a system, complete mass balances of C02 and H20 were maintained on six soybean canopies grown in sunlight at two C02 treatment levels, 330 and 660 pmiol mol '.In each set of C02 treatments, the three canopies were differentially watered to create one non-stressed canopy and two water stressed canopies. Seasonal balances were based on daily integrated values of transpiration, daytime C02 exchange and nighttime C02 exchange. Canopies were completely harvested for total biomass and yield determinations at the end of the growing season. Final biomass and yield were increased by C02 enrichment and decreased by water stress. The water stressed high C02 treatments yielded more than the continuously well watered low C02 treatment. On average, the high C02 canopies transpired about 10% less water over the season than did the low C02 canopies. Cumulative seasonal net CO, exchange rate correlated linearly and positively with seasonal biomass accumulation (R = 0.99) and seed yield (R = 0.95). A simple linear correlation between seasonal transpiration and yield (or biomass accumulation) did not hold across C02 treatments (R = 0.16). However, when C02 treatments were separated, yield showed a strong correlation with seasonal transpiration for low C02 (R — 0.95) and high C02 (R = 0.99) conditions. These whole canopy results are based on the continuous competent operation of the environmental chamber systems throughout the 108 day season and confirm the unique utility of this research tool.

The effects of simulated daylight and shade-light on vegetative and reproductive growth in kiwifruit and grapevine

Abstract: SummaryPlants of kiwifruit, female cv Hayward and male cv Matua, and grapevine cv Muller Thurgau were grown in controlled environments, which simulated the daylength and temperature of a typical New Zealand fruit production region, for the whole of one growing season to study the influence of light environment on vegetative growth and reproductive development. The controlled environments differed in the distribution of their short-wave radiation: comparisons were made between high and low photosynthetic photon flux density (PPFD) and high and low red:far-red ratios. The red:far-red ratio did not have a large effect on either vegetative or fruit growth during the first season or on flowering in the following season. Elongation of some organs was increased with low red:far-red ratio which simulated the radiation quality of shade-light. In contrast, low PPFD reduced specific leaf area and pruning weight, although it did not have a large effect on other apsects of vegetative growth, and severely decreased fru...

Determination of growing season soil water deficits on a forested slope using water balance analysis

Abstract: Coefficients for the calculation of soil water balance components at seven sites on a forested slope were determined using only measurements of daily solar irradiance, maximum and minimum air temperature and rainfall, and weekly root zone soil water content during a 2-year period. Site parameters required were root zone depth, soil water retention characteristics, and rainfall interception coefficients. Based on daytime net radiation, the Priestley–Taylor evapotranspiration coefficient (α) was found to be 0.73 ± 0.07, which is similar to values reported in other conifer forest studies. Growing season water deficit increased with decreasing root zone water storage capacity, which was mainly a function of root zone depth. A comparison between high and low elevations on the slope showed 100-year site indices ranging from 17 to 53 m corresponding to growing season soil water deficits during the driest year of the study, ranging from 79 to 4 mm. Basal area annual increments were found to be correlated with soi...

Development of populations of rhizobium trifolii and nodulation of subterranean clover following the cropping phase in crop-pasture rotations in southeastern Australia

Abstract: Soil samples taken from 28 sites following varying periods of cropping in a crop-pasture rotation contained very low populations of Rhizobium trifolii . Populations were less than 10 3 g −1 R. trifolii of soil for 89% of the sites and were significantly correlated with soil pH. Application of lime resulted in a build-up of R. trifolii in the absence of the host legume, subterranean clover, but when inoculated clover seed was sown the populations built up to satisfactory levels after the first season's growth, regardless of soil pH. The number of nodules per plant was increased by the application of lime, but the plants growing in unlimed soil had fewer, larger nodules. The increase in nodulation with lime on these low-calcium acid soils persisted to the third growing season.

Compaction of a swelling clay soil by agricultural traffic; effects upon conditions for growth of winter cereals and evidence for some recovery of structure

Abstract: SUMMARY A swelling stagnogley soil remained unwheeled or was uniformly wheeled by a combine harvester and a tractor in two successive autumns before direct drilling winter cereals. Combine wheeling of the soil at its wettest condition caused the largest loss of soil porosity. The autumn and spring of the second growing season for the winter cereals were wetter than long term average. The smaller porosity in the wheeled soil, created lower soil redox potential and smaller oxygen flux as well as greater soil strength and larger amounts of available water, but little difference in soil temperature. The crop in the wheeled soil had fewer plants, less root and a lighter yield than in the unwheeled soil. The wheeled soil recovered some porosity and lost strength after wetting and drying during the second growing season, whereas soil freezing had very little effect. This restructuring was sufficient to reverse some of the detrimental effects of compacting the soil.

Foliar nutrient dynamics, growth, and nutrient use efficiency of Hamamelis virginiana in three forest microsites

Abstract: To determine the relative importance of soil moisture and soil nutrient availability in determining levels of nutrient use efficiency, seasonal nutrient dynamics and growth rates were determined for individuals of Hamamelis virginiana L., an understory tree, in three forest microsites. The mixed oak site had the lowest levels of soil nutrients and moisture, the mixed mesophytic site the highest nutrient availability, and the valley bottom the highest moisture levels. Foliar nitrogen and phosphorus levels declined over the season in all trees, while calcium levels increased with time. Relative growth rates did not differ significantly among sites, though growth varied inversely with tree mass. Proportional nitrogen resorption was highest in trees at the fertile mesophytic site. Phosphorus and calcium use efficiency were higher at the infertile mixed oak site than the others, and phosphorus resorption was highest in trees from the mixed oak site. Projected nitrogen uptake needs for the next growing season w...

Phosphorus Relationships in Potato Plants

Abstract: Maximum potato (Solanum tuberosum L.) tuber yields occur when an active plant canopy is maintained until normal plant maturation. Plaid nutrient concentrations and uptake rates play a major role in maintaining an active plant top. The objectives of this study were to relate the plant P concentrations to the P and dry matter balance between tuber and total plant growth needs. Growth analysis data, plant and leaf total P concentrations and content, and the petiole soluble P concentrations were obtained on a 10-to 14-day sampling interval from P fertilization treatments in replicated field studies. The P concentration of the plant tops was significantly related to the petiole soluble P concentration and the P concentration of the active leaves. Total plant P uptake and dry matter production rates were not adequate for the tuber growth rate when the total P concentrations of the tops and active leaves were less than 2.2 g P kg-1. Soluble P concentrations in the fourth petiole down from the growing tip were less than 1000 and 700 mg kg-1 when P uptake and dry matter production rates were not adequate for tuber growth, respectively. Final tuber yields increased from 30 to 70 Mg ha-1 as the number of growing days past tuber set increased from 10 to 60 days for which the P concentration of the tops was above 2.2 g P kg-1. The petiole soluble P concentration decreased during the growing season following a semi-logarithmic relationship. This relationship enabled the prediction of the petiole soluble P concentration for the rest of the growing season and could be used to predict when to apply supplemental P fertilizer.

Fluctuations in the length of the growing season in minnesota

Abstract: Fluctuations in growing season length and in the dates of the last spring freeze and first fall freeze between 1899 and 1982 were studied for five rural Minnesota stations with long, high quality records. A general increase in growing season length was found, but there was substantial variation in the pattern of fluctuations among the stations. The increase in growing season length is not clearly and uniformly related to changes in the dates of first and last freezes. The interannual variability of growing season duration is on the order of the increase in duration so that the change would not be readily apparent to a casual observer. Our results do not correspond well with certain other studies of growing season length nor with fluctuations in hemispheric mean temperature. We conclude that extreme care must be used in extrapolating results of growing season length studies in space and in relating them to mean temperature fluctuations.

Delayed emergence of four conifer species on postfire seedbeds in eastern Canada

Abstract: This study compares the emergence of jack pine (Pinusbanksiana Lamb.), eastern white pine (Pinusstrobus L.), black spruce (Piceamariana (Mill.) B.S.P.) and balsam fir (Abiesbalsamea (L.). Mill.) for three seasons after sowing on two postfire seedbeds to test the hypothesis that conifer species differ in their ability to store viable seeds in the soil. Less than 20% of all viable seeds produced emergent seedlings in the first growing season. Emergence continued in the second growing season but not in the third. No viable seeds of any species were found at the end of the experiment. During the second growing season (July 1), the emergence of jack pine was greatest at the warmer and drier site but at the cooler and moister site, large numbers of black spruce emerged; by the end of the second season jack pine seedlings predominated at both sites. Although this delayed emergence accounted for <3% of the viable jack pine seeds sown, this percentage would be sufficient to produce a dense stand given normal postf...

Seasonal nutrient dynamics of Solidago altissima (Compositae)

Abstract: ABRAHAMSON, W. G. AND K. D. MCCREA (Dept. Biology, Bucknell University, Lewisburg, PA 17837). Seasonal nutrient dynamics of Solidago altissima (Compositae). Bull. Torrey Bot. Club 112:414-420, 1985.-The pattern of biomass distribution, and the concentrations of N, P, K, Ca, and Mg were determined by standard methods in goldenrod ramets throughout the annual growing-dormancy cycle. In spring, N, P, K, and Mg were translocated to new rhizomes over a month before ramets emerged and, with the exception of Mg, the concentrations of these elements rapidly declined in above-ground organs after ramet emergence. Although there was a continuous uptake of all five elements from soil reserves during the growing season, there was little autumn retranslocation of nutrients from above-ground to below-ground organs. The mineral element allocation patterns were stable during the growing season except for the principal trade-off between the major sinks of leaves and inflorescences for N, P, K, and Mg and between stems and inflorescences for Ca. The data show that S. altissima is efficient in its use of nutrients, thus reducing the amounts of nutrients required from soil reserves. This, in part, may explain the broad site tolerance of tall goldenrod.

Weed control using herbicides in short-rotation intensively cultured poplar plantations.

Abstract: Summarizes a series of studies that investigated chemical weed control from time of planting to the end of the second growing season. The studies confirm the importance of weed control with preemergents at the time of planting and the importance of additional weed control before the start of the second growing season.

The effect of fire severity level on postfire recovery of hazel and raspberry in east-central Alberta

Abstract: A study of the effects of fire on the regrowth of beaked hazel (Corylus cornuta Marsh.) and wild red raspberry (Rubus strigosus Michx.) was carried out in Elk Island National Park, Alberta. Shrubs growing under an aspen stand were subjected to five levels of fire severity by artificially adjusting the fuel load on small plots within a larger prescribed fire. Effects studied included mortality, number of stem sprouts, height growth of sprouts, and number of leaves per sprout, all during the first growing season, and biomass after the second season. Generally, fire killed the shrub stems at all severity levels. Variation in fire severity had little significant effect on regrowth, except that lower levels seemed to favor higher numbers of hazel sprouts and increased raspberry height growth.

Seasonal changes in the within-crown distribution of the aphid Cinara pini on Scots pine

Abstract: The within-tree distribution of Cinara pini L. was studied on five, 18-yr-old Scots pine trees at about weekly intervals throughout the growing season. Aphid emigration and mortality from natural enemies were reduced by placing cages around the trees. Aphids were aggregated on the young internodes in the top parts of the crown during early summer, and on the older internodes in the lower parts of the crown during late summer. Seasonal changes in the within-tree distribution of the aphids are discussed in relation to the phenology of translocation streams in the tree. Both quantitative and qualitative changes take place in the phloem sap of Scots pine during the course of the growing season which correlate well with changes in aphid distribution patterns.

Soil temperature under zero tillage systems for wheat in saskatchewan

Abstract: Soil temperature profiles and the aerial growth of wheat were characterized over portions of the growing season in 1980 and 1981 under zero and conventional tillage systems in a semi-arid region of Saskatchewan. Differences in maximum and minimum soil temperature, accumulative heat sums and thermal diffusivity over the 2.5-cm to 20-cm soil depth were related to variations in surface crop residues, soil moisture and crop canopy. Generally, maximum soil temperatures were 1–5 °C lower under zero tillage compared to conventional tillage during the first 30 days of crop growth for spring wheat. Similar soil temperature differences were evident between winter wheat zero tilled on stubble or chemical fallow during the period of early spring growth. Subsequent differences in crop canopy (shoot height), between tillage systems, tended to modify the soil temperature profile. Soil temperature differences were not associated with differences in yields of spring or winter wheat. Key words: Soil temperature, soil therm...

Growth and regeneration of field horsetail (Equisetum arvense).

Abstract: Growth and regeneration of field horsetail (Equi- setum arvense L. #3 EQUAR) were investigated under field and greenhouse conditions. Field horsetail produced shoots during the entire summer but its growth was detrimentally affected by the presence of corn (Zea mays L.). Field horse- tail regrew as well whether it had been hoed once or 16 times during the growing season; and during the subsequent sum- mer, there were no significant differences between horsetail growth in plots kept weed-free the previous growing season and in plots where field horsetail grew freely. In the green- house, rhizome segments 1 cm long placed 15 cm deep easily regenerated plants. Simulations were done using the growth and regenerative ability of field horsetail to estimate its potential spread in agricultural fields. The results of these simulations indicate that this weed can infest a hectare within 6 yr of its introduction into a new area. Additional index words. Cultivation, mowing, EQUAR.