Greater Root Development Research Articles

Effect of Auger Size and Depth of Operation on Bulk Density, Cone Index, Germination, Root Length, Root Weight and Cob Weight for Maize Crop

Minimum tillage methods offer numerous benefits compared to conventional tillage, including reduced farm operations to establish a good seedbed. Spot tillage, in particular, has advantages such as preserving soil structure, preventing erosion, saving time and energy, and reducing input costs. For this study, the effect of different auger size (40, 50 & 70mm) which was operated by 12V DC motor at different depth of operations (80, 120 & 160mm) were determined. The different parameters were measured such as bulk density, cone index, germination percentage, root length, root weight and cob weight for maize crop (GAYMH-3) and same for traditional sowing method. The results showed that auger size (40, 50 & 70mm) and depth of operation (80, 120 & 160mm) significantly influenced bulk density as bulk density of the soil increased with depth and decrease with increase in auger size. The larger auger (70mm) resulting in lower values in bulk density due to more soil removal. However, cone index was not significantly affected by auger size (40, 50 & 70mm) and depth of operation (80, 120 & 160mm). Seed germination for maize was consistently around 90%, with no significant effects of auger size and depth of operation were observed. An auger size (70mm) was associated with shorter root lengths. Increasing depth resulted in greater root development, leading to longer roots was observed in small size augers. Larger auger size and deeper depths generally resulted in higher root weights. Cob weight increased with auger size (70mm) and deeper depths. Auger size and depth significantly impacted cob weight. Overall, results showed that auger having the size of 70mm and depth of operation at 160mm was desirable compared to other auger size in terms of lower bulk density and cone index but increased root weight and cob weight of maize crop.

No-Tillage System Can Improve Soybean Grain Production More Than Conventional Tillage System.

Soil management systems can directly interfere with crop yield via changes in the soil's physical and hydraulic properties. However, short- to medium-term experiments of conduction do not always demonstrate the modifications of the management systems in these properties. Thus, the aim of this study was to evaluate the physical properties of the soil in a long-term management system and to relate it to the storage and availability of water to plants, verifying its effect on soybean yield. The experiment was conducted in randomized blocks in a split-plot scheme with four replications. Plots were composed by soil management (conventional tillage and no-tillage), and subplots represented three soil depths (0.0-0.1, 0.1-0.2, and 0.2-0.4 m). The soil's physical and hydraulic properties, root development, and soybean yield were evaluated. The no-tillage system not only presented higher bulk density and soil resistance to compaction up to a depth of 0.2 m but also greater root development. This management also did not affect the process of water infiltration in the soil and presented an increase in soybean grain yield by 6.5%. The long-term no-tillage system (33 years) offers less risk of water stress to soybean plants; it contributes to greater grain yield of this crop when compared to the conventional tillage system.

Characteristics of the soil macropore and root architecture of alpine meadows during the seasonal freezing-thawing process and their impact on water transport in the Qinghai Lake watershed, northeastern Qinghai–Tibet Plateau

Low temperatures, freezing-thawing cycles, and short growing seasons characterize alpine soils. The mattic epipedon, a special diagnostic surface horizon with an intensive root network, is widely distributed in alpine ecosystems. Studies on the soil macropores and roots of the mattic epipedon layer in response to seasonal freezing-thawing processes on the Qinghai–Tibet Plateau are lacking. This study characterized the soil macropores and roots of alpine meadows during the seasonal freezing-thawing process using X-ray computed tomography and revealed the influence of soil macropores and roots structure on water transport in the mattic epipedon layer of the alpine meadows. The results showed that the soil pore distribution was more uniform during the unstable freezing stage (UFP) and the unstable thawing stage (UTP), whereas there was a clear mattic epipedon layer during the completely thawed stage (TP) and the completely frozen stage (FP). Soils in the TP stage had a higher total surface area density (0.1898 mm² mm⁻³), length density (225.28 mm mm⁻³), node density (1,592 no. mm⁻³), and connectivity (0.3144) of soil macropores than those in the UFP, UTP, and FP stages. In the TP stages, the density, surface area density, branch density, length density, and node density of roots had significant correlations with the macroporosity, surface area density, length density, node density, and tortuosity of soil macropores. In the FP stage, there were no correlations between the root and soil macropore characteristics. Vertical water is expected to move more readily through the mattic epipedon in the TP stage than in the UFP and UTP stages. Roots were the preferential pathways for water transport into the soil layer of the alpine meadow. Therefore, the mattic epipedon is a key layer for water and nutrient storage and plays an important role in the water-holding function of the Tibetan Plateau due to its greater root development.

Impact of long-term manure and mineral fertilization on yield and nutritive value of lucerne (Medicago sativa) in relation to changes in canopy structure

Fertilization management influences not only productivity but also the nutritive value of forage legumes. However, there have been few studies about these effects in long-term fertilization experiments. Our objectives were: (i) to compare the effects of mineral fertilization and organic manure on lucerne forage yield and leaf and stem nutritive value over a 2-year period following 60 years of different fertilization managements, and (ii) to investigate relationships among canopy structure traits and forage nutritive value in association with these fertilization treatments. The long-term fertilization experiment was established with four replications in the Czech Republic in 1955. Three levels of mineral N, P and K application (0:0:0, 39:24:109 and 91:31:146) were investigated, each with and without farmyard manure, resulting in six treatments. Lucerne stands were established in 2012 and 2013 in two strips. Forage yield was measured in two cuts in 2014 and 2015, respectively. Canopy structure traits and forage nutritive value (crude protein, ash, neutral detergent fibre (NDF) and NDF digestibility (NDFD) were analysed in the first cut in each year. Intensive mineral fertilization reduced lucerne nutritive value through a reduction in stem NDFD (-6%) and leaf weight ratio (-10 %) under higher forage productivity (+10 % of annual yield). Manure fertilization improved nutritive value of leaves and stems, with an associated increase in whole plant nutritive value as leaf proportion was maintained with increased yield (+8%). This positive response could be attributed to a soil environment effect: greater root development in soil that had received long-term manure fertilization probably reduced forage lignification and maintained leaf proportion in association with reduced drought stress. Long-term manure fertilization demonstrated potential for improvement of lucerne nutritive value despite the negative relationships between increased plant growth under higher nutrient supply and forage nutritive value.

Rootstocks and planting types on root architecture and vegetative vigor of ‘Pera’ sweet orange trees

ABSTRACT Root architecture affects plant growth and agricultural productions. Although it is related to genetic factors, soil physical limitations can affect the root system and volume of explored soil, compromising plant growth and fruit production. Considering the need to mitigate these restrictions, the objective of the present study was to evaluate two planting types (planting of protected seedlings and planting of seeds in definitive place) and two scion-rootstock combinations (‘Pera’ sweet orange, CNPMF D-6 selection, combined with ‘Santa Cruz Rangpur’ lime and ‘Sunki Tropical’ mandarin rootstocks). The experiment was conducted at the Lagoa do Coco Farm, Rio Real, BA, Brazil, in a Oxisol under rainfed conditions. Biometric, physiological, and soil water content evaluations were made during the experiment. Soil mechanical resistance to root penetration and root system characteristics were also evaluated. Roots were concentrated on the soil surface layers (0-0.40 m), extending horizontally up to 1.50 m from the plant, regardless of the management practices used. The total root length in each root diameter classes studied, root length density, and total root mean diameter were higher for planting of protected seedling, resulting in greater root development. Plants from ‘Pera’ sweet orange scion grafted on ‘Santa Cruz Rangpur’ lime rootstock had earlier production and were more vigorous. Soil structure affects root growth, and the root distribution up to 0.40 m depth is correlated with plant vigor, yield, and water status under rainfed conditions.

Effect of Water Stress during Grain Filling on Yield, Quality and Physiological Traits of Illpa and Rainbow Quinoa (Chenopodium quinoa Willd.) Cultivars.

The total area under quinoa (Chenopodium quinoa Willd.) cultivation and the consumption of its grain have increased in recent years because of its nutritional properties and ability to grow under adverse conditions, such as drought. Climate change scenarios predict extended periods of drought and this has emphasized the need for new crops that are tolerant to these conditions. The main goal of this work was to evaluate crop yield and quality parameters and to characterize the physiology of two varieties of quinoa grown under water deficit in greenhouse conditions. Two varieties of quinoa from the Chilean coast (Rainbow) and altiplano (Illpa) were used, grown under full irrigation or two different levels of water deficit applied during the grain filling period. There were no marked differences in yield and quality parameters between treatments, but the root biomass was higher in plants grown under severe water deficit conditions compared to control. Photosynthesis, transpiration and stomatal conductance decreased with increased water stress in both cultivars, but the coastal variety showed higher water use efficiency and less discrimination of 13C under water deficit. This response was associated with greater root development and a better stomatal opening adjustment, especially in the case of Rainbow. The capacity of Rainbow to increase its osmoregulant content (compounds such as proline, glutamine, glutamate, K and Na) could enable a potential osmotic adjustment in this variety. Moreover, the lower stomatal opening and transpiration rates were also associated with higher leaf ABA concentration values detected in Rainbow. We found negative logarithmic relationships between stomatal conductance and leaf ABA concentration in both varieties, with significant R2 values of 0.50 and 0.22 in Rainbow and Illpa, respectively. These moderate-to-medium values suggest that, in addition to ABA signaling, other causes for stomatal closure in quinoa under drought such as hydraulic regulation may play a role. In conclusion, this work showed that two quinoa cultivars use different strategies in the face of water deficit stress, and these prevent decreases in grain yield and quality under drought conditions.

Evaluation of Different Types of Substrates in Cocoa Nursery (Theobroma Cacao L.)

This research was conducted at the experimental farm "La Maria" State Technical University of Quevedo, located at Km 7.5 Vía Quevedo - El Empalme, with the overall objective to determine the effect of different organic substrates on seedling growth cocoa nursery conditions. The specific objectives were to evaluate the growth of cocoa plants in different substrates study, identify the substrate that allows greater root development of seedlings of cacao and perform economic analysis of each of the treatments studied. The experiment was conducted under a completely randomized design with 10 treatments in three replicates and treatment means were compared with Duncan test at 95% probability. The treatments were: T1: 60% Bokashi + 40% black earth, T2: 60% Bokashi + 40% sawdust raft, T3: 60% Bokashi + 40% chaff burnt rice, T4: 40% Bokashi + 20% sawdust balsa + 20% black soil + 20% chaff burnt rice, T5: 60% vermicompost + 40% black earth, T6: 60% vermicompost + 40% sawdust raft, S7: 60% vermicompost + 40% chaff burnt rice, T8: 40% vermicompost + 20% black soil + 20% chaff burn rice + 20% sawdust raft, T9: 30% bokashi + 30% vermicompost + 20% black earth + 10% sawdust + 10% balsa burning rice chaff, T10: 75% + 25% black earth rice husks. The main results of this research it was observed that the planted in treating 9 (30% Bokashi, 30% vermicompost, 20% black soil, 10% sawdust balsa and 10% chaff burnt rice), was recorded 100% germination, plant also produced in this substrate were greater height, stem diameter, presence of leaves and root length. Treatment 10 (75% of black earth and 25% rice husks) produced the highest returns with 59.68% of the production of 1000 seedlings, meaning that for every dollar invested a profit of $ 0.60 was obtained for every dollar reversed, however, with treatment 9 (30% bokashi, 30% vermicompost + 20% black soil + 10% sawdust raft + 10% chaff burnt rice) plants showed better characteristics that are the basis for acceptance by the buyer, generating a return of 34.23%, as a result of higher production cost.

Effects of continuous spectrum LEDs used in indoor cultivation of two coniferous species Pinus sylvestris L. and Abies borisii-regis Mattf

ABSTRACTThe effects of four different continuous spectrum LED light qualities on the growth characteristics of Pinus sylvestris L. (PS) and Abies borisii-regis Mattf. (AB) seedlings were studied. The seedlings were exposed for 35 days inside growth chambers to G2 (high in red and far-red), AP67 (high in blue and far-red), AP67-ARCH (high in green), and NS2 (high in blue including a small percentage in the UV area) LEDs, as well as fluorescent light (FL) as Control. Each species showed a unique light-adapted response. G2 treatment stimulated needle formation of PS seedlings, while AB seedlings were unaffected. Hypocotyl elongation was promoted by FL; however, LEDs resulted in compact plants with greater root development, especially under the AP67-ARCH and AP67 spectra for PS and AB, respectively. In PS, AP67-ARCH and G2 significantly increased dry weight, while AB was affected significantly by AP67 and NS2. Furthermore, root growth potential of both species was better after LED pre-cultivation than the FL. Therefore, the use of continuous spectrum LEDs can enhance desirable quality characteristics of seedlings, which may be advantageous in large scale seedling production for reforestation.

Caracterização da produtividade do funcho (Foeniculum vulgare Mill.) no sertão de Sergipe

Com o objetivo de avaliar a produtividade e qualidade do funcho (Foeniculum vulgare Mill.) produzido nas condições edafoclimáticas de Sergipe, foi conduzido cultivo orgânico de funcho em Frei Paulo-SE. Em junho de 2008 e de 2009, início do período de chuvas, foram instalados plantios por meio de mudas. Adicionalmente, em dezembro de 2010 foi realizada colheita de frutos a partir de plantas obtidas após poda drástica e rebrota. Foi realizada colheita de frutos e determinação da produtividade de dezembro a janeiro de 2008, 2009 e em dezembro de 2010. Verificou-se produtividade de 720 Kg.ha-1, no primeiro plantio e de 349 Kg.ha-1 no plantio de 2009. As plantas obtidas por rebrota em 2010 resultaram em produtividade de 589 Kg.ha-1. Sugere-se que a maior produtividade verificada no primeiro ano seja decorrente da maior precipitação média e conseqüente maior disponibilidade de água. A produtividade verificada nas plantas que rebrotaram em 2010 foi também superior a verificada em 2009, o que pode ser explicado tanto em função da maior precipitação, quanto em função do provável maior desenvolvimento das raízes e maior número de ramos após poda, devido à quebra da dominância apical. Esses dados sugerem importância da disponibilidade hídrica na determinação da produtividade na região e explicam a variação na produtividade verificada. A massa seca dos frutos (5, 29 g para 1000 frutos) e o alto teor de óleo essencial verificado (3,2%), assim como a composição do óleo, revelam a alta qualidade dos frutos produzidos na região.

Root distribution and yield responses of wheat/maize intercropping to alternate irrigation in the arid areas of northwest China

A field experiment was conducted to investigate the effects of alternate irrigation (AI) on root distribution and yield of wheat (Triticum aestivum L.)/maize (Zea mays L.) intercropping system during the period of 2007–2009 in an oasis of arid north-west China. Five treatments, i.e. sole wheat with conventional irrigation (W), sole maize with alternate irrigation (AM), sole maize with conventional irrigation (CM), wheat/maize intercropping with alternate irrigation (AW/M), and wheat/maize intercropping with conventional irrigation (CW/M). The results showed that root growth was significantly enhanced by alternate irrigation (AI), root weight density (RWD), root length density (RLD) and root-shoot ratios (R/S) in AI treatments were all higher than those in conventional irrigation (CI) treatments. Moreover, intercropped wheat and maize also had a greater root development at a majority of soil depths than wheat and maize in monoculture. In three years, AW/M always achieved the highest total seed yield under different treatments. Higher yield and reduced irrigation resulted in higher water use efficiency (WUE) for the AW/M treatment. Our results suggest that AI should be a useful water-saving irrigation method on wheat/maize intercropping in arid oasis field where intercropping planting is decreased because of limited water resource.

Integrated Nitrogen and Phosphorus Management in Rice Under Flood-Prone Lowland Situation

ABSTRACT Crop survival as influenced by integrated N management (INM) in rice variety ‘Gayatri’ was studied following 10 days of complete submergence at maximum tillering stage during 2003 and 2004 in the Central Rice Research Institute, Cuttack, India. Organic N sources such as farmyard manure (FYM) and Sesbania aculeate were included in INM along with fertilizers N and P. Crops with the combined organics of FYM and Sesbania survived better after submergence, which was attributed to higher biomass production, less tiller mortality, greater root development, and higher critical N content in leaf, as compared with other treatments. These crops produced significantly higher grain yield (2.97 and 3.09t ha−1 in 2003 and 2004) compared with those with application of FYM (2.48 and 2.61 t ha−1), use of Sesbania (2.24 and 2.35 t ha−1) and chemical fertilizer N (1.98 and 2.07 t ha−1) alone. In both the years, application of P also led to higher grain yields (2.40 and 2.52 t ha−1) compared with no application of P (2.19 and 2.29 t ha−1). Interaction of INM with P showed that application of P with the combined organics increased grain yield by 13.1–13.7%, followed by that with FYM (10.16–12.2%), Sesbania (8.37–8.89%), and fertilizer N (7.33–8.04%). In both the years, greater nutrient utilization as evidenced by N use efficiency (29.2 and 29.7 kg grain per kg N ha−1), N uptake (54.0 and 57.0 kg ha−1), and N recovery (35.0 and 41.5%) was attributed to the crops with combined organics. P use efficiency (10.5 and 11.5 kg grain per kg P ha−1), P uptake (14.9 and 16.5 kg ha−1), and P recovery (28.5 and 31.5%) were higher in the treatments with applied P. Thus the study revealed that application of both FYM and Sesbania in combination with fertilizers N and P in rice improved crop growth resulting in increased grain yield and nutrient utilization in flood-prone situations. Therefore, it is recommended to follow INM that included FYM and Sesbania in combination with both fertilizers N and P in rice cultivation for increasing grain yield in flood-prone lowland situations.

Enhancing root systems of waiting-bed strawberry plants grown on substrates

SummaryTo find techniques to improve root system development of waiting-bed strawberry plants ‘Camarosa’ grown in substrates, the influence of two substrates (peat and coconut coir dust), or plants from three waiting-beds at different altitudes, and of root treatments with different plant growth regulators (naphthalenacetic acid at 25, 50 and 75 mg g–1; indolebutyric acid at 10, 20 and 30 mg g–1; l-triacontanol at 0.02, 0.04 and 0.06 mg g–1) by dipping runners prior to planting, were studied in two experiments in the 1997–98 and 1998–99 seasons. In both years, plants from high elevation beds (HE) produced the greatest root development, and plants from medium elevation beds (ME) produced more new roots than those from low elevation beds (LE). Root development of plants grown in peat was greater than those grown in coconut coir dust in the first experiment and only on the first measuring dates (one month after planting). This difference was particularly high in plants from high or medium elevation nurseries, when the degree of root development was greater. No differences between substrates were observed in the second experiment. Treatments with the different growth regulators tested, at any of the concentrations used, did not improve root development on average for the other factors.

A comparison between minirhizotron and soil coring methods of estimating root distribution in young almond trees under trickle irrigation

SummaryThe minirhizotron method and the soil coring method were used to study the development of the root system (down to 105 cm) of almond trees cv. Atocha on ‘Pestaneta’ almond rootstock. The study was carried out during the first years of development of the trees under trickle irrigation. Most of the roots (about 80%) developed within the wetted zone of the trickle line in the top 60 cm of soil. The greatest root length density (RLD) was within 30 cm of the soil surface but decreased rapidly with depth. Outside the wetted zone, the greatest root development occurred at about 60 cm depth. When the RLD values obtained by the minirhizotron and soil coring methods were compared, the former was seen to underestimate the RLD values particularly in the top layers of soil so much so that the root distribution patterns established by the methods were not comparable. However, a significant relationship was established between the measurements obtained by both methods at different soil depths.

Water relations, gas exchange and morphological development of fall- and spring-planted yellow cypress stecklings

Yellow cypress ( Chamaecyparis nootkatensis (D.Don) Spach) stecklings (stock derived from rooted cuttings) were fall-(September 1990) and spring-planted (April, 1991) on a coastal reforestation site in British Columbia to determine the influence of planting season and various nursery cultural treatments on steckling establishment, growth and survival. Gas exchange and water relations measurements were made in the first year after planting, with morphological development monitored during the first and second year. A randomized complete block design (6 blocks) was used and influence of planting season was analyzed as an independent factor from the nursery cultural treatments. Nursery cultural treatment means within each plant-time population were similar ( t-test, α = 0.05), with no effect on steckling physiology during the first growing season. Moisture stress nursery cultural treatments produced smaller stecklings (e.g. shoot height, diameter, root and shoot dry weights) than well-watered treatments, but morphological differences disappeared after the first year. Water relation parameters indicated that fall-planted stock had greater turgor maintenance than spring-planted stock throughout the first growing season (e.g. fall ≥ spring in predawn and minimum shoot water potentials, total and utilized turgor; fall ≥ spring in osmotic potential at saturation and turgor loss point, and relative water content at turgor loss point). Spring-planted stecklings had greater maximum net photosynthesis under optimum conditions in a controlled environment, but had lower net photosynthesis under low air temperature conditions in the field, compared with fall-planted stecklings. Fall-planted stecklings had greater stomatal conductance under all measured field climatic conditions, except moderate conditions when both populations had similar stomatal conductance. Shortly after fall planting, extreme environmental conditions (i.e. soil surface temperatures of 42°C, evaporative demand > 4 kPa and steckling minimum shoot water potentials of − 1.61 ± 0.04 MPa) resulted in high fall-planted steckling mortality. As a result, survival rates measured 8 weeks after spring planting were 82.9% and 99.8% for fall- and spring-planted stecklings, respectively. Thereafter, spring planting, mortality was low and similar between the two plant-time populations. Fall-planted stecklings had greater root development early in the first growing season, but by season end, spring-planted stecklings had greater root development. At the end of the second growing season, both populations were similar in shoot development, though spring-planted stecklings had greater root development.

Influence of nursery culture on western red cedar

Western red cedar (Thuja plicata Donn) seedlings from six nursery cultural treatments (i.e., long-day wet (LDW), long-day moderate (LDM), long-day dry (LDD), short-day wet (SDW), short-day moderate (SDM) and short-day dry (SDD)) were fall- and spring-planted on a field site in coastal British Columbia. Fall-planted seedlings were monitored for freezing tolerance (expressed as the temperatures causing 50% foliage electrolyte leakage, II50) throughout the fall, winter and early spring. Both fall- and spring-planted populations were monitored for morphological development over the first growing season. Short-day, compared to long-day, treatments were either greater or comparable in freezing tolerance (lower II50 temperatures) throughout the fall and winter and deacclimated slower in spring. The SDD treatment had the greatest decrease in II50 in response to freezing temperature events. All treatments had similar seasonal minimum II50 temperatures, measured just prior to deacclimation in late winter and early spring. One month after spring field planting, LDW seedlings had the greatest root development among fall-planted treatments, while SDM and SDD seedlings had the greatest root development among spring-planted treatments. The fall-, compared to spring-planted seedlings, had greater root development and diameter, but had shorter height one month after spring field planting. Both populations had identical shoot growth over the first season. However, fall-planted SDW seedlings continued to grow in height during a dry period in late summer while height growth of all other fall and spring treatments slowed or stopped. At the end of the growing season, SDW seedlings had the greatest shoot and root development among fall-planted treatments while LDW seedlings had the greatest morphological development among spring-planted treatments. In general, fall-planted seedlings were shorter in height, but larger in diameter and greater in root development than spring-planted seedlings. All treatments had similar survival rates (98–100%) for both fall- and spring-planted seedlings at season end.

Interior spruce seedlings compared with emblings produced from somatic embryogenesis. II. Stock quality assessment prior to field planting

Interior spruce (Piceaglauca (Moench) Voss × Piceaengelmannii Parry) seedlings and emblings produced through somatic embryogenesis tissue culture were removed from frozen storage and tested with a stock quality assessment procedure prior to spring planting. Seedlings, compared with emblings, had greater height as well as shoot and root dry weights. Seedlings and emblings had similar root-collar diameter, buds per total shoot length, and needle primordia in their terminal buds. Seedlings and emblings had similar shoot form (i.e., branch quotient) and balance between their shoot and root system (i.e., plant water balance ratio). Emblings, compared with seedlings, had a lower osmotic potential at turgor loss point and symplastic fraction, plus a higher dry weight fraction and total turgor. Seedlings and emblings had similar osmotic potential at saturation and relative water content at turgor loss point. Seedlings and emblings had similar resistance to water movement through the plant–atmosphere continuum (Rpac) at 22 °C root temperature, though emblings had greater Rpac at 7.5 °C root temperature. Seedlings had greater net photosynthesis (Pn) than emblings over a 14-day period at both 7.5 and 22 °C root temperatures. Seedlings, compared with emblings, had greater root development over a 14-day period at 22 °C root temperature, though they had low and similar root development at 7.5 °C root temperature. Both Pn and needle conductance (gwv) decreased as predawn shoot water potential (Ψpd) declined in seedlings and emblings. Nearly complete stomatal closure occurred at Ψpd less than −1.5 MPa, while similarly low Pn readings (seedlings: −0.01 ± 0.04 μmol•m−2•s−1; emblings: 0.02 + 0.04 μmol•m−2•s−1) occurred between a Ψpd of −1.0 and −2.0 MPa. A performance potential index (PPI), which combines material and performance attributes in a comprehensive characterization of field performance potential, indicated that seedlings had a better PPI under optimum environmental conditions. However, seedlings and emblings had similar PPI under low temperature and drought conditions.

Comparative effects of bark and peat based composts on the occurrence of vine weevil larvae and the growth of containerized polyanthus

A series of experiments was conducted to investigate the effect of inclusion of bark in potting composts on the numbers of vine weevil larvae on polyanthus plants. In 1989 more larvae were recovered from plants grown in peat compost than those grown in bark but these results were reversed when the study was repeated in 1990. Numbers of larvae also increased with higher ratios of bark:peat in composts but declined as the size fraction of bark used increased. The degree to which bark was composted did not appear to materially affect the numbers of vine weevil recovered. A strong, positive, relationship between larval numbers and foliage dry weight was found. Similarly, larval numbers were bigger with greater root development in bark composts. The results are discussed and it is suggested that the use of bark may promote more vigorous growth in polyanthus and thus enable plants to support more larvae.

MEDIA COMPOSITION, IBA, AND NODE POSITION AFFECT ROOTING OF CLEMATIS CUTTINGS.

Five cuttings from different node positions on stock plants were taken from each of 3 Clematis cultivars (Jackmani, Contesse de Bouchard, and Gypsy Queen) and Clematis purpurea plena elegans. Actively growing plants with 5 nodes were acquired. Node number increased from 1 at the base of the plant to 5 at the tip of the plant. Cuttings were treated with or without 0.1% IBA (indole-3-butyric acid) and placed in 1 of 5 different media: 100% washed sand (WS), 50% washed sand and 50% sphagnum peat (WP), 50% sphagnum peat and 50% perlite (SP), 100%) perlite (PT), or 50% sphagnum peat plus 25% perlite plus 25% vermiculite (PV). Rooting date, primary and secondary root number, and root dry weight were collected after 8 weeks. `Gypsy Queen' showed the earliest rooting with the greatest root development. Jackmani showed the worst rooting. Media WS and PT showed the best rooting whereas WP and SP showed the worst. Cuttings taken from the first 3 nodes rooted the best. As node position increased root number and dry weight decreased and time to root increased. Application of IBA had no significant effect on time to root or degree of rooting.

Influence of dormancy induction treatments on western hemlock seedlings. II. Physiological and morphological response during the first growing season on a reforestation site

Western hemlock (Tsugaheterophylla (Raf.) Sarg.) seedlings from four dormancy induction treatments (DIT) (i.e., long-day dry, long-day wet, short-day dry, short-day wet) were planted on a coastal reforestation site in British Columbia and monitored for physiological response and morphological development over the first growing season. Seedlings in all DIT showed a similar net photosynthetic, needle conductance, and shoot water potential response to seasonal low temperature, non droughty, and late summer drought conditions. Pressure–volume analysis at the beginning of the growing season (late February) showed short-day wet seedlings to have lower saturated and turgor loss point osmotic potentials than other DIT, while at the end of the growing season (October) there was no osmotic potential difference between DIT. At the end of the growing season, short-day wet seedlings had a much lower maximum modulus of elasticity than other DIT, indicating their shoots were still elongating. Morphological assessment 1 month after field planting showed short-day DIT seedlings had less needle damage and greater root development in response to continuous low temperature exposure. Four months after planting, long-day wet seedlings had the greatest shoot (i.e., height, root collar diameter) and root development in response to mild temperatures and high soil moisture conditions. Eight months after planting, survival was between 95 and 97% for all DIT. Long-day DIT seedlings had the greatest height and all DIT had similar root collar diameter and root development. Short-day DIT seedlings had the best shoot/soil roots ratio. Short-day wet seedlings had the least number of stem units per centimetre of new shoot development throughout the growing season. Results are discussed in reference to stock quality assessment presented in the first paper of this series.

Responses of Nitrate-Fed and Nitrogen-Fixing Soybeans to Progressive Water Stress

Soybean plants, receiving nitrate-N or dependent on nitrogen fixation, were subjected to progressive water deprivation under controlled environmental conditions in a growth room. Comparative studies were carried out with respect to well-watered, control plants. Stressed, nitrate-fed plants had relatively greater root development, higher transpiration rates per unit leaf area, lower threshold values of leaf water potential for stomatal closure and osmotic adjustment in upper leaves. Therefore, these plants were adopting mechanisms to achieve stress tolerance. In contrast, stressed, nitrogen-fixing plants adopted mechanisms orientated to avoid stress: lower transpiration rates, stomatal closure at higher leaf water potentials, and delayed onset of osmotic adjustment. Root development in these plants stopped under more severe stress. Nitrogen-fixing plants were more conservative in terms of water use than nitrate-fed plants.