Variation In Biomass Production Research Articles

Short-rotation forestry of birch, maple, poplar and willow in Flanders (Belgium) I—Biomass production after 4 years of tree growth

Abstract During the last three decades, oil crises, agricultural surpluses and global climate change enhanced the interest in short-rotation forestry (SRF). In this study, the biomass production of birch ( Betula pendula Roth), maple ( Acer pseudoplatanus L.—Tintigny), poplar ( Populus trichocarpa × deltoides —Hoogvorst) and willow ( Salix viminalis —Orm) growing under a short-rotation (SR) management system were compared after a 4 years period. The plantation was established on former agricultural land. The sandy soil had a mean pH of 4.5 and a mean carbon content of 1.0%. Survival rates after 4 years were 75.8%, 96.8%, 86.3% and 97.6% for birch, maple, poplar and willow, respectively. The mean actual annual biomass production for these four species amounted to 2.6, 1.2, 3.5 and 3.4 t DM ha −1 yr −1 , respectively. The large variation in biomass production at the different plots of the plantation could not be explained by the measured soil parameters. Biomass production results found here were in the lower range of values reported in literature. However, in contrast to most other studies, no weed control, fertilisation or irrigation was applied in this experiment. As marginal agricultural soils are suboptimal for the growth of poplar and willow, birch can be considered as a very interesting alternative for the establishment of SR plantations in Flanders.

Relationship of Leaf Stable Isotopes (δ13C and δ15N) to Biomass Production in Two Fertilized Merlot Vineyards

Grapevines (<i>Vitis vinifera</i> L.) are often cultivated under suboptimum conditions for both water and nutrients in order to enhance the quality of grapes for making wine. Since water supply and nitrogen nutrition are major determinants of photosynthetic activity, this study investigated the potential of leaf δ¹³C and δ¹⁵N to explain spatial variations in biomass production as a function of water use efficiency and fertilizer N uptake, respectively. The combined isotopic signal of the leaves, together with pruning weight, leaf nutrients, and soil properties, were measured in randomly selected field positions over two growing seasons in two fertilized, but different, Merlot vineyards. Significant correlations of surface soil properties and leaf nutrients with pruning weight were not great enough to explain spatial patterns in biomass production. In contrast, leaf δ¹³C and δ¹⁵N, when used as independent variables in multiple regression, explained 71% of the spatial variation of pruning weight across both fields and growing seasons. Most of the explained model variability was attributed to leaf δ¹⁵N (r² = 0.54), but within single years leaf δ¹³C was better correlated to biomass. The negative correlation between these two isotopes and pruning weight was high only within the vineyard that had steep topographic features and spatially variable growth patterns. It indicated a response of vines to adverse soil conditions by a progressive reduction of water use efficiency and an increase in fertilizer N uptake downslope from the low- to the high-biomass areas of this field. If these relationships persist in other fertilized and water-stressed fields, the isotopic signature of the leaves may be an important tool for application of site-specific management practices within single vineyards.

Modelling carbon dynamics in mixed grass–red clover swards

Growth and carbon dynamics in mixed grass–red clover leys were simulated using a growth model for pure stands based on radiation use, allocation within plant and loss of biomass. The model and its parameter values were taken from previous applications of the model to pure swards of grass and red clover grown in the same experiment at the same sites and years. The field data used comprised above-ground dry matter production and proportion of clover in a mixture of red clover ( Trifolium pratense L.), timothy ( Phleum pratense L.) and meadow fescue ( Festuca pratensis Huds.) in two seasonal growth cycles during two consecutive years, sampled at six sites in Central and Southern Sweden. On average for all fields, the proportion of clover decreased with increased nitrogen application. It increased from the first to the second cut, but decreased from the first to the second year. The model most often underestimated above-ground biomass when using proportion of clover and estimates of radiation use efficiency ( ε) and root allocation fraction ( b r) from values in the pure stands (Method 1). This discrepancy suggested that ε might be higher for the mixed stand than the pure stands. Values of ε and b r for the mixed stands were therefore derived by calibration to the observed above-ground biomass (Method 2). The radiation use efficiency ( ε) of the mixed stand was on average 6% higher than estimates of ε from pure stand values and proportion of clover. Overall, the variation in radiation use efficiency of mixed stands due to cutting and year was similar to that of pure stands of grass and clover, whereas the relationship to N treatment was weak and more similar to that of clover. The explanation that variations in biomass production were due to changes in root allocation seems reasonable. No variations in radiation use efficiency or root allocation fraction could be related to the proportion of clover. The variations due to cutting and year overwhelmed any such effect.

Model predicting dynamics of biomass, structure and digestibility of herbage in managed permanent pastures. 2. Model evaluation

AbstractA mechanistic model, simulating the dynamics of production, structure and digestibility of managed permanent pastures, was developed. Its evaluation consisted of (i) studying model response to a range of grassland communities, cutting frequencies and site characteristics, and (ii) testing the model against experimental data, focusing on biomass accumulation and digestibility during three different cutting cycles, herbage production under a frequent cutting regime, and sward dynamics during the winter. The model realistically predicted the dynamics of biomass, structure and digestibility of herbage for various communities of permanent pastures, in different sites and under different management conditions for upland areas of the Auvergne region in France. The predicted responses to environmental conditions and cutting regimes were close to field observations and experimental results. Although the model successfully predicted the dynamics of average herbage production, it lacked precision in predicting the low biomass production observed in relation to the weather conditions found in a few specific years. The model was able to predict the dynamics of the sward during winter and is, therefore, fit for producing multiple‐year simulations. To improve the prediction of variability of biomass production and to predict the medium‐ to long‐term dynamics of permanent pastures, the model could be refined by adding seasonal and multiple‐year variation in nitrogen availability and in the proportion of grass functional groups in the grassland community.

Heritability and Correlations for Biomass Production and Allocation in White Spruce Seedlings

AbstractTree growth is a multidimensional trait and families vary for components of growth such as height, diameter, foliage and roots. Therefore, variation in tree growth is better studied by analysing biomass production and allocation than simple traits. In addition, biomass is better linked to products such as pulp and wood energy than simple traits. We analysed biomass of 3-year old open-pollinated greenhouse seedlings of white spruce to determine (1) heritability for biomass production and allocation to shoot and root components, (2) correlations between biomass traits, and biomass traits with primary traits, and (3) correlation between biomass production in the greenhouse and height growth for the same families in the field. The study had a randomised complete block design with single-tree plots, 30 blocks and 58 open-pollinated families. Individual-tree heritability (hi2) and family mean heritability (hf2) ranged from 0.200 to 0.333 and 0.374 to 0.516 for green weight, respectively. Likewise, hi2and hi2ranged from 0.186 to 0.359 and 0.352 to 0.536 for dry weight, respectively. Genetic correlation (ra) between green and dry weight ranged from 0.943 to 1.015, while rabetween shoot and root dry weight ranged from 0.947 to 0.955. In contrast, rabetween biomass traits and field height ranged from -0.403 to -0.124. Thus, we conclude (1) variation in biomass production and allocation exhibited low genetic basis, (2) testing and selection for green or dry weight should lead to similar genotypes, (3) biomass allocation may not be easily altered by selection and breeding, and (4) indirect early selection based on seedling biomass

Corrigendum to: Soil water extraction and biomass production by lucerne in the south of Western Australia

To understand the factors involved in lucerne reducing drainage below the root-zone and influencing lucerne biomass production and water extraction were analysed in the south of Western Australia. The lucerne was grown for 3 years before removal. The factors investigated as part of the water extraction analysis included the rate of advance of the extraction front or extraction front velocity (EFV, mm/day), the soil plant-available water-holding capacity (PAWC, mm/m soil), and the temporal change in soil water deficit (drainage buffer, mm). The drainage buffer is related to the EFV and PAWC. A site with deep sand had the highest EFV (mean of 9.2�mm/day) but the lowest PAWC (mean of 32�mm/m soil) to a depth of 4�m. In the duplex soils the EFV was 18.34% of the deep sand EFV and the PAWC was 60.222% higher than the deep sand PAWC to a depth of 1.6.2.1�m. The EFV was reduced by the higher clay content and sodicity in the B horizon of the duplex soils. The highest drainage buffer measurements occurred in the deep sand site and the better structured duplex soils and therefore these soils will have the greater effect on reducing drainage below the root-zone. However, lucerne was able to create a drainage buffer to at least a depth of 1.5�m over 3 years and therefore contribute to a reduced drainage even on the most sodic and saline sites. Low soil pH did not affect the drainage buffer as much as soil texture and structure. Variation in biomass production of lucerne-based pastures was positively related to rainfall and water use (taking into account soil water storage and drainage losses) across sites, explaining approximately 50% of the biomass variation. Rainfall and water use could therefore be used for predicting lucerne biomass production in Western Australia. Biomass water use efficiency was highest in spring (15 kg/ha.mm) and least during autumn (4.5 kg/ha.mm).

Soil water extraction and biomass production by lucerne in the south of Western Australia

To understand the factors involved in lucerne reducing drainage below the root-zone and influencing lucerne biomass production and water extraction were analysed in the south of Western Australia. The lucerne was grown for 3 years before removal. The factors investigated as part of the water extraction analysis included the rate of advance of the extraction front or extraction front velocity (EFV, mm/day), the soil plant-available water-holding capacity (PAWC, mm/m soil), and the temporal change in soil water deficit (drainage buffer, mm). The drainage buffer is related to the EFV and PAWC. A site with deep sand had the highest EFV (mean of 9.2 mm/day) but the lowest PAWC (mean of 32 mm/m soil) to a depth of 4 m. In the duplex soils the EFV was 18–34% of the deep sand EFV and the PAWC was 60–222% higher than the deep sand PAWC to a depth of 1.6–2.1 m. The EFV was reduced by the higher clay content and sodicity in the B horizon of the duplex soils. The highest drainage buffer measurements occurred in the deep sand site and the better structured duplex soils and therefore these soils will have the greater effect on reducing drainage below the root-zone. However, lucerne was able to create a drainage buffer to at least a depth of 1.5 m over 3 years and therefore contribute to a reduced drainage even on the most sodic and saline sites. Low soil pH did not affect the drainage buffer as much as soil texture and structure. Variation in biomass production of lucerne-based pastures was positively related to rainfall and water use (taking into account soil water storage and drainage losses) across sites, explaining approximately 50% of the biomass variation. Rainfall and water use could therefore be used for predicting lucerne biomass production in Western Australia. Biomass water use efficiency was highest in spring (15 kg/ha.mm) and least during autumn (4.5 kg/ha.mm).

Alteration of biomass and artemisinin production in Artemisia annua hairy roots by media sterilization method and sugars

Transformed root cultures of Artemisia annua grown in autoclaved medium show large variations in biomass and artemisinin production regardless of the culture conditions or clonal type. However, using filter-sterilized sugars singly or in combination while holding the carbon level in the medium constant resulted in an unexpected variability in biomass production and artemisinin yield. Autoclaving results in variable hydrolysis of sucrose in the culture medium. Subsequent experiments using combinations of filter-sterilized sugars at a constant total carbon level in the medium showed a stimulation of artemisinin production by glucose. Growth in sucrose was equivalent to growth in fructose and significantly better than in glucose. These results suggest that sugars may be affecting terpenoid metabolism not only as carbon sources, but also as signal molecules.

Relationship between grain yield and quality of durum wheats from different eras of breeding

High protein content and a ‘strong’ gluten are required in durum wheat (Triticumturgidum L. var. durum) to process semolina into a suitable final pasta product. The variation in grain protein content and quality realized through breeding and the concomitant variation in biomass production and partitioning have been analyzed by comparing in a 2-year field trial, four groups of cultivars released in different eras and areas of breeding. Three groups of cultivars represented the evolution of the Italian germplasm from the first landraces and genealogical selections (Group 1) to the cultivars constituted by crossing Mediterranean types with Syriacum types (Group 2), and the modern dwarf and semi-dwarf cultivars (Group 3). Group 4 was an ICARDA collection of breeding lines bred for adaptation to high altitudes. The measured traits included both biomass production and its partitioning to the grain, and total nitrogen uptake and its partitioning to the grain. Grain protein percentage, gluten content and gluten index were utilized as quality traits. Breeding resulted in an increased earliness, reduced height without significant decreases in total biomass, and improved partitioning. The concomitant total nitrogen uptake did not change, whereas the changed biomass partitioning caused a parallel change in nitrogen partitioning, with an increase in nitrogen harvest index from 0.41 to 0.59. The lower protein percentage in the grains of modern cultivars was therefore not due to a reduced nitrogen uptake, nor to a lower NHI or to less milligram of nitrogen per grain, but to the dilution effect caused by the heavier grains of modern cultivars. A notable increase in gluten index was observed in the modern cultivars, reflecting an improvement in the pasta-making quality of grain proteins.

Eficiência de utilização de nutrientes e sustentabilidade da produção em procedências de Eucalyptus grandis e Eucalyptus saligna em sítios florestais do estado de São Paulo

A eficiência de utilização de nutrientes (EUN) e o crescimento de três procedências de Eucalyptus grandis e de três de E. saligna foram avaliados, aos 78 meses de idade, nos municípios de Angatuba, Itapetininga, Paraibuna, São Miguel Aracanjo e São José dos Campos, Estado de São Paulo. Houve variação na produção de biomassa entre os municípios, sendo as maiores produtividades observadas em São Miguel Aracanjo, seguido por Paraibuna, com os demais municípios constituindo um terceiro grupo. Dentro dos municípios não houve diferença entre materiais genéticos na produção de biomassa, exceto em São Miguel Arcanjo. Os materiais genéticos mostraram variações na EUN entre locais. Observou-se maior EUN de E. grandis em relação ao E. saligna para N, P e Mg, não havendo diferenças apreciáveis de eficiência entre as duas espécies para Ca e K. A alta EUN não está necessariamente ligada à alta produtividade. O Ca e o K são os nutrientes que mais poderão limitar a produtividade do próximo ciclo, quando se considera a colheita do tronco. Entretanto, esta limitação pode ser substancialmente reduzida, principalmente para o Ca, se a colheita for realizada apenas do lenho.

Effect of Sowing Technique on Growth of Undersown Crop and Yield of Spring Barley

Undersowing a main crop enables establishment of a catch crop in areas characterized by a short post‐harvest period before the onset of winter. Techniques with lower costs than conventional undersowing by separate drilling are often regarded as unreliable. Undersowing by drilling after sowing spring barley (Hordeum vulgare L.) was compared with broadcast sowing simultaneously with drilling barley. Various implements were coupled behind the combined drill in cases where seed was broadcast: a press‐wheel attachment, a long‐tined harrow and a cage roller. A fourth treatment did not include an implement coupled behind the drill. The undersown crop was sown as a seed mixture of 3 kg ha–1 red clover (Trifolium pratense L.) and 6 kg ha–1 meadow fescue (Festuca pratensis Hudson). The numbers of plants and weeds and the plant height were measured five times during the growing season. Above‐ground biomass of the undersown species was determined at barley harvest and in late autumn. Grain yield of spring barley was recorded. Drilling resulted in the highest yield of undersown crop when an early summer drought occurred, but broadcasting in combination with use of seed covering equipment led to the least variation in biomass production over the 4 years the experiment was conducted. The relative proportion of meadow fescue in the crop was low in three years, and lower when broadcast than when drilled. Barley grain yield was highest when the seed was broadcast and seed covering equipment was used. Use of a cage roller increased weed biomass, but press‐wheels and a long‐tined harrow did not. Separate rolling after undersowing increased undersown crop yield in one year, but decreased grain yield in some cases.

Productivity and complementarity in grassland microcosms of varying diversity

Several researchers have hypothesized that, through various mechanisms, loss of species and functional group richness from a plant community will affect the magnitude and interannual variability of productivity. To test this hypothesis, I conducted a microcosm study of California grassland communities that differed in species richness. I grew cohorts of microcosms that simulated undisturbed grassland (in one year) and gopher‐disturbed grassland (in two consecutive years). As the number of species per functional group decreased from 4 to 1, biomass production remained constant in all three cohorts. As species richness decreased from 16 to 1 (or 8 to 1, in either case including a drop in functional group richness), productivity declined in one of the cohorts. In this cohort, productivity of one polyculture marginally exceeded that of the most productive monoculture. Resource complementarity and a type of selection effect may have each contributed to the observed diversity‐productivity relationships. Results suggest the existence of a selection effect that involves species that are highly productive in mixtures, rather than in monoculture. Over two seasons, species and functional group richness did not affect the interannual variability of biomass production. Comparisons of interannual changes in the productivity of monocultures and polycultures suggested that, in some polycultures, increased water availability might have relieved interspecific competition more than intraspecific competition. Based on results from this experiment and other manipulative experiments, I develop a framework to explain the relationship between species richness and productivity in terrestrial plant communities. The framework highlights the importance of environmental variation in shaping the diversity/productivity relationship.

Characterization of core collection of lentil germplasm for phenology, morphology, seed and straw yields

Increasing and maintaining crop residues in predominantly cereal-based rotations of the US Pacific Northwest is critical to controlling soil erosion. The core collection of lentil (Lens culinaris Medik.) germplasm comprising 287 accessions was evaluated for variation in phenological, morphological and growth parameters including seed yields and residue amounts over a two-year period under conventional tillage and no-till conditions. The objectives of this study were (i) assess lentil genetic variation in germplasm for variation in biomass production and seed yield, (ii) assess the relationship of phenological and morphological traits with biomass and seed yield and (iii) identify high biomass producing germplasm for use as parents in the breeding program. Days to flowering and days to maturity ranged from 31 to 78 and from 71 to 106 days, respectively. Time to flowering in terms of cumulative heat units was a more efficient measurement than days to flowering. Plant height and plant canopy width had a significant association with total biomass, seed yield and residue amounts. Total biomass ranged from 788–6389 kg ha−1 under conventional tillage, while the range under no-till conditions was 1045–6195 kg ha−1. Most of the lines with higher biomass also produced the highest seed yields and residue amounts. Overall, only one accession produced more residue than `Laird'. In the more favorable environment of 1997, six accessions exceeded the control cultivars, `Laird' and `Indianhead', for residue amounts, and seven and twenty-four accessions exceeded control cultivars, `Pardina' and `Brewer', for seed yield. Results indicated that plant height, canopy width at maturity and seed yield explained most of the variation in biomass and residue production. Large seeded germplasm consistently had a longer reproductive growth period than small seeded accessions and had 17%, 7% and 21% more biomass, seed yield and residue, respectively. Our data indicated significant variation in lentil germplasm for biomass, seed yield and residue amounts to warrant their use in the breeding program.

Observational evidence that diversity may increase productivity in Mediterranean shrublands

This paper reports field observational evidence on the diversity-biomass production relationship from eastern Mediterranean shrublands dominated by Cistus salviifolius. The main results are: (1) plant diversity and ecosystem primary production are positively correlated in the Cistus shrublands, which are multigrowth form systems; (2) the taxonomic and growth form diversity in Cistus shrublands suggests that there is strong differentiation along the structural niche axis, and thus functional redundancy is weak; (3) the performance of the dominant Cistus in terms of biomass production did not affect the overall diversity-biomass production of the studied communities.

99/01334 Clonal variability in biomass production and conversion efficiency of poplar during the establishment year of a short rotation coppice plantation : Deraedt, W. and Ceulemans, R. Biomass and Bioenergy, 1998, 15, (4/5), 391–398

99/01334 Clonal variability in biomass production and conversion efficiency of poplar during the establishment year of a short rotation coppice plantation : Deraedt, W. and Ceulemans, R. Biomass and Bioenergy, 1998, 15, (4/5), 391–398

Clonal variability in biomass production and conversion efficiency of poplar during the establishment year of a short rotation coppice plantation

A high density, intensively managed field trial with 17 different poplar ( Populus) clones was established in April 1996 in Boom (province of Antwerpen, Belgium) on a former waste disposal site. All plants were cut back at the end of the establishment year and the above ground biomass production, as well as carbon concentration were measured. Significant clonal variation was observed in overall mortality rates and length of the growing season. Mortality rates ranged from 2 to 55% due to difficult soil conditions. Based on incoming available photosynthetically active radiation, length of growing season and above ground biomass production, conversion efficiency ratios were calculated. These were rather low, ranging from 0.002 to 0.041 g MJ −1, with the highest values calculated for the poplar clone Hoogvorst. The carbon concentration of the wood ranged from 46 to 47%, with 3.2 to 5.5% remaining in the ash. Net photosynthesis measurements were made in the field during mid-summer and revealed significant clonal differences in maximum photosynthetic rate and carboxylation efficiency. Clonal differences in net photosynthetic rate, length of growing season, mortality and biomass production rate are relevant to overall carbon uptake rates of short rotation biomass plantations.

Variability of traits associated with phosphorus efficiency in wild and cultivated genotypes of common bean

Genetic variation in plant growth under limited phosphorus (P) supply is necessary to obtain more productive cultivars on low P-available soils. Two pot experiments were conducted to evaluate the variability of some traits associated with efficiency of P absorption and utilization in wild and cultivated genotypes of common bean (Phaseolus vulgaris L.) under biological N2 fixation. At two P levels (20 and 80 mg P kg-1 soil, P1 and P2, respectively), 20 wild and 6 cultivated genotypes were grown in Experiment 1, and 4 wild and 27 cultivated genotypes were grown in Experiment 2. Plants were harvested at flowering, but in Experiment 1 wild accessions that did not flower were harvested at the beginning of leaf senescence. In Experiment 1, part of the genotypic variability of wild accessions was attributed to a less homogeneous ontogenetic stage at harvest, whereas in Experiment 2 some variation in biomass production was due to distinct phenologies of cultivated genotypes. Wild lines did not seem more tolerant to low P conditions, but the genotypic variation observed suggests these materials as a source of genetic diversity. Part of the variation in the root area and root efficiency ratio (total P content:root area) was compensatory, resulting in narrow genotypic differences in the total P content. The total P content and root efficiency ratio presented a wider amplitude of variation at P2 than at P1, and P uptake was more influenced by P supply than root production. Since the genotype × P level interaction was not significant for shoot biomass and shoot P concentration in Experiment 2, P utilization efficiency may be a useful selection criterion for cultivars between limited and adequate P supply. Within the sample of genetic diversity evaluated herein, there was large genotypic variability for traits related to P efficiency among wild and cultivated genotypes of common bean.

‘Effective growing days’: a simple predictive model of the response of herbaceous plant growth in a Mediterranean ecosystem to variation in rainfall and phosphorus availability

1 Herbaceous plant production on many Mediterranean soils is severely restricted by nutrient deficiency. On such a shallow, phosphorus‐deficient soil in the western Galilee of Israel with an average annual rainfall &gt;800 mm, a single addition of phosphorus fertilizer consistently increased herbaceous plant production in a community dominated by the dwarf shrub Sarcopoterium spinosum by a factor of 2.8–3.8 over 7 years. Regardless of phosphorus addition, interannual variation of the herbaceous vegetation remained high (C.V. = 0.33). A simple model based on climate data was developed to explain the continuing interannual variation in biomass production. 2 This interannual variation is accounted for by an ‘effective growing day’ index, G, based on an estimate of the number of days throughout the growing season during which the available water in the rooting zone can balance the current potential evaporation demand. The validity of this approach was tested on data from 7 consecutive years. 3 At given phosphate (P) availability levels, the index G was found to be highly correlated with both seasonal biomass production and P uptake of the herbaceous plant, but the regression lines intersected the G axis far to the right of the origin. 4 When the adverse effect of the winter climate on growing conditions was taken into account, the regression lines passed close to the origin. Annual biomass production and P uptake could then be well described as linear functions of G with the slope related to availability of P. 5 Average intraseasonal trends gave G‐values which were better predictors of both biomass production and P‐uptake than annual weather (temperature or potential evaporation) fluctuations. 6 Both shoot biomass and P uptake were strongly influenced by growing conditions in autumn (beginning of growing season) and in spring (main growing season), but plant production was more sensitive than P uptake to growing conditions in autumn and vice versa in spring. 7 The close relationship between G and P uptake at different P availability levels indicates that availability of P did not diminish for at least 7 years after a single application of 4.5–9.0 g m−2 P as superphosphate. Nutrient cycling, secondary effects of the dominant legume species, and small losses of P from the ecosystem are proposed as possible reasons for this phenomenon.

Effective barley grass (Hordeum spp.) control in annual medics with 2,2-DPA herbicide

The ability of 2,2-dichloropropionic acid (2,2-DPA) to control annual grasses was examined in a 4-year-old medic (Medicago polymorpha var. brevispina cv. Circle Valley) pasture. Six rates of 2,2-DPA with and without spray adjuvants (1% spray oil + 0.25% wetting agent) were used: 0.37, 0.56, 0.74, 1.11, 1.48, 2.22 kg a.i./ha. The pasture was sprayed in July at the 4-true-leaf stage of the medic, after identifying and counting grasses and medics. Plants were counted again after spraying and grass seed heads were counted in spring. At the end of the season, medic seed yields were obtained. Nine annual pasture legumes were later evaluated for their tolerance to 2.22 kg 2,2-DPA/ha at 3 growth stages [post plant, pre-emergence (PPPE); 3-5-true-leaf stage; flowering] under weed-free conditions. A rate of 1.11 kg 2,2-DPAJha was found to reduce barley grass density by 85%. Efficacy was improved, however, with higher rates and/or the addition of spray adjuvants. Because of low silvergrass (Vulpia spp.) and ryegrass (Lolium rigidurn) plant numbers, it was not possible to assess whether 2,2-DPA controlled these species effectively. There was no effect of herbicide on medic seed yields, seed weight, seed number per pod, or seed germination. Medic seed yields were well correlated with plant density of medic but not with herbicide rates. There was a wide variation in biomass production of the 9 pasture legumes in the evaluation of tolerance, when assessed by visual rating and seed yield, with significant biomass and yield reductions at all timings of application of 2,2-DPA. Subterranean clover (Trifoliurn subterraneum L.) was the most severely affected. Generally, medic species tolerated 2,2-DPA well. Serena was the most susceptible medic cultivar at any treatment time, with seed yield reductions at the first 2 times of application. The results suggest that 2,2-DPA could be used safely on annual medics for the control of barley grass, and possibly other annual grasses.

Influence of mineral nutrient availability on growth of tree seedlings from the tropical deciduous forest

The effects of different nutrient availabilities on growth and biomass partitioning in seedlings from the tropical deciduous forest in Mexico were compared. The tree species studied were Heliocarpus pallidus, a species associated with disturbed parts of the forest, and Caesalpinia eriotachys, Jacquinia pungens and Recchia mexicana, species from mature, undisturbed habitats. The tropical deciduous tree seedlings were grown in pure silica sand for 50 days inside growth chambers under four nutrient regimes; 5, 20, 100 and 200% Long Ashton nutrient solutions. Data showed contrasting responses among species to different nutrient availabilities. Except Jacquinia pungens, all species had increased growth and productivity as nutrient level increased from 5 to 100%; however, no significant differences in these parameters were detected between 100 and 200% in all species. Compared with mature forest species, pioneer species showed higher variations in biomass production, relative growth rate and net assimilation rate. In contrast to mature forest species, root/ shoot ratios in Heliocarpus pallidus were greater and thus showed higher biomass allocation to roots when nutrient supply was limited. This response suggests higher phenotypic plasticity in pioneer species. Species from mature parts of the forest (Caesalpinia eriostachys, Recchia mexicana) showed less dependency on nutrient supply than pioneer species. These responses appear to support observations from studies with temperate plants investigating growth responses to soil fertility.