Weed control increases nitrogen retranslocation and growth of white spruce seedlings on a reclaimed oil sands soil

Early establishment of seedlings in reclaimed oil sand areas is often limited by low nutrient and water availability due to factors such as strong understory vegetation competition. Management practices such as nursery fertilization and field weed control could help early establishment of planted seedlings and reclamation success. We investigated the effect of nursery nutrient loading and field weed control on the growth, nitrogen (N) retranslocation within seedling components, and plant N uptake from the soil for white spruce (Picea glauca [Moench] Voss) seedlings planted on a highly competitive reclaimed oil sands site for two years. Exponential fertilization during nursery production increased the root biomass but not the nutrient reserve in the seedling. In the field experiment, on average across the treatments, 78 and 49% of the total N demand of new tissue growth in the first and second year were met by N retranslocation, respectively. Though exponential fertilization did not affect N retranslocation, it increased the percent height and root collar diameter growth. Weed control increased not only the growth of seedlings by increasing soil N availability, but also N retranslocation within the seedlings in the second year after outplanting. We conclude that vegetation management by weed control is feasible in improving the early growth of white spruce seedlings planted on reclaimed soils and facilitate tree establishment in the oil sands region. Optimization of the nursery exponential N fertilization regime for white spruce may further help with early revegetation of reclaimed oil sands sites.     

Nutrient loading of forest tree seedlings to promote stress resistance and field performance: a Mediterranean perspective

The planting environment of Mediterranean areas is highly challenging as summer drought and winter frost jeopardize survival, and soil infertility limits establishment success. We review the potential for seedling nutrient loading to alleviate these post-planting stresses. A growing body of evidence indicates that nitrogen (N) rich seedlings have improved field performance in Mediterranean environments, due to their ability to grow new roots rapidly and out-compete weeds. In addition, frost resistance during hardening is crucial for relatively cold inland nurseries; recent research shows a positive relationship between N and shoot frost resistance though a knowledge gap exists regarding the influence of nutrition on root frost resistance. Some new evidence also implicates phosphorus as an important driver of seedling response in the Mediterranean due to its influence on root growth and physiology. Nutrient status influences other functional attributes critical to survival in Mediterranean areas, such as drought tolerance, root hydraulic conductivity, and mycorrhization. In light of the apparent benefits of high nutrient reserves for seedling performance in Mediterranean areas, we also review techniques for nursery nutrient loading. Exponential fertilization can be applied when species’ growth patterns match this application regime. However, many Mediterranean species exhibit episodic growth indicating that constant or fall fertilization could be more effective in reaching loading. In particular, late-season fertilization has shown good potential to avert nutrient dilution in the fall and increase frost resistance. Several needs for future research are identified, with special emphasis on the necessity to match fertilization regimes to species ecological traits and planting conditions.     

Two provenances of Quercus ilex ssp. ballota (Desf) Samp. nursery seedlings have different response to frost tolerance and autumn fertilization

Despite evidences that Holm oak has a high plasticity and great adaptability, there is limited or contradictory knowledge of the morphological and physiological variability of this species. Holm oak has been widely used for reforestation projects in Mediterranean areas, but has frequently shown poor field performance. We hypothesized that Holm oak has inter-population differences in physiological responses to abiotic stressors that could affect reforestation success. The influence of nursery culture on the characteristics of Holm oaks from different provenances has not been explored in depth. Thus, we studied the effect of nursery autumn fertilization on morphological traits, frost tolerance, root growth potential, and nutritional status of two Spanish provenances of Holm oak, La Alcarria (a region with inland Mediterranean climate) and Sierra Morena Occidental (a region with a warm coastal Mediterranean climate). There were significant differences between the provenances in frost tolerance, biomass allocation, and leaf nutrient content, suggesting a role of genetic factors. The leaves of seedlings from La Alcarria had less visual damage at ?12°C than seedlings from the warmer provenance (45% vs. 92%). Seedlings from La Alcarria, compared to those from Sierra Morena, had higher leaf P concentration (0.17% vs. 0.15%), greater stem diameter (3.1?mm vs. 2.7?mm), lower shoot-to-root dry mass ratio (0.46 vs. 0.53), and lower slenderness (4.03 vs. 5.31). For both provenances, N autumn fertilization improved growth, root growth potential, cold hardiness, and nutritional status of seedlings. We suggest that forest reforestation programs should consider to a greater extent Holm oak provenances and their tolerances to different abiotic stressors.     

Effects of Demand-driven Fertilization on Nutrient Use,Root:Plant Ratio and Field Performance of Betula pendula and Picea abies

Norway spruce [Picea abies (L.) Karst.] and silver birch (Betula pendula Roth) seedlings were grown for one season under three different fertilization regimens in the forest nursery. During the first 50 days the seedlings were grown in a glasshouse, and thereafter outdoors until the beginning of September. Finally, the plants were exposed to 16 h nights in the glasshouse throughout September. When the seedlings were supplied with fertilizers at a rate adjusted to expected plant demand (R_O), less than half as much of each nutrient was applied as in a conventional regimen (R_C), in which equal amounts were supplied per unit time during the growth season, yet the plants still looked healthy. Utilization of N increased by almost 50% in spruce when supply was adjusted to plant demand. In the third treatment (R_L), nutrients were supplied as in the R_O treatment, but at a growth-limiting rate. These plants were loaded with nutrients at the end of the season and had higher root:plant ratios, i.e. root weight in relation to total plant weight, compared with the other treatments. The nutrient status of the plants was not growth limiting at the end of the growing season in any of the treatments. The plants given the different treatments differed in size at planting out, but they had similar heights after 3 yrs in the field. This indicates that the root:plant ratio may be important for growth performance, provided that nutrient status is not at a growth-limiting level. This study suggests that the use of fertilizers can be considerably reduced in Swedish forest nurseries.     

Why seedlings survive: influence of plant attributes

Seedling survival and successful forest restoration involves many silvicultural practices. One important aspect of a successful forest restoration program is planting quality seedlings with high survival capability. Thus the nursery needs to create seedlings with plant attributes that allow for the best chance of success once a seedling is field planted. Since the mid-twentieth century, research foresters have critically examined plant attributes that confer improved seedling survival to field site conditions. This review describes the value of commonly measured seedling quality material (i.e. shoot height, stem diameter, root mass, shoot to root ratio, drought resistance, mineral nutrient status) and performance (i.e. freezing tolerance and root growth) plant attributes defined as important in answering the question of why seedlings survive after planting. Desirable levels of these plant attributes can increase the speed with which seedlings overcome planting stress, become ‘coupled’ to the forest restoration site, thereby ensuring successful seedling establishment. Although planting seedlings with these desirable plant attributes does not guarantee high survival rates; planting seedlings with desirable plant attributes increases chances for survival after field planting.     

Summer planting performance of white spruce 1 + 0 container seedlings affected by nursery short-day treatment

Impacts of nursery short-day treatments on the survival, growth and needle damage of about 5,000 1 + 0 container white spruce (Picea glauca [Moench] Voss) seedlings from a single seedlot were studied for two growing seasons following planting on July 22, 1999 at four boreal reforestation sites in Northern Alberta, Canada of varying soil texture, drainage, aspect, slope, and slope position. Each site was separated into two areas that were site-prepared by either ripping or mounding. When seedlings reached a height of about 20 cm under normal greenhouse growth conditions, the seedlings from different germination dates over a 7-week period were exposed to one of five different conditioning treatments (T), mainly through varying the duration of 12-h short-day exposure to 0 (T0), 3 (T3), 7 (T7), 10 (T10), or 15 (T15) days followed by different periods of reduced N supply. N-reduction produced few differences in needle nutrient concentrations and so was not considered a likely cause of differences in field performance. The treatments progressively (from T0 to T15) increased tolerance to drought and frost, and resulted in a similar seedling size for T3, T7 and T10 (planting height of 21 cm and ground diameter of 2.9 mm) although T0 seedlings were smaller (20 cm) and T15 taller (24 cm). The weather in 1999 was dry, particularly in the weeks immediately before and after planting, but relatively moist and favorable in 2000 and 2001 apart from one major frost event (−7°C) in May 2000. Survival, growth and needle damage varied substantially among sites and short-day treatments, and the treatment differences were largely consistent across the four sites. In general the growth was better on the ripped than on the mounded areas. Seedlings in T7 (intermediate tolerance) survived and grew best in the first year but T0 (actively growing) did best during the second year. After 2 years, no differences were observed among T0, T3 and T7 in mortality (18%) and total height growth (15 cm). However, T10 and T15 had higher mortality (24 and 43%), and lower height growth (12 and 10 cm, respectively). The percentage of seedlings showing very severe needle damage after 2 years increased from T0 through T15 (14–33%). New root egress in the field also differed significantly among treatments and was positively and highly correlated with survival rate and growth. These results suggest that a longer short-day regime, as in T10 or T15, may be counterproductive and a shorter regime may be more effective in improving the performance of summer-planted white spruce seedlings.     

Assessing the effect of late-season fertilization on Holm oak plant quality: insights from morpho–nutritional characterizations and water relations parameters

Forest restoration projects with Holm oak (Quercus ilex) have had limited success, mostly due to water stress after planting and poor plant quality. Recent studies indicated that large and nutrient rich plants perform better in Mediterranean areas, suggesting that late-season fertilization may improve plant quality and field performance. The purpose of this study was to assess the effect of late-season fertilization on the quality of Holm oak seedlings, as determined by morphological, nutritional, and water relations analyses. We grew Holm oak nursery seedlings under 5 different late-season fertilization regimes and then analyzed morphological characteristics, nutritional status, and water relations parameters of the fertilization groups at the end of the nursery period. We also analyzed the effect of fertilization on nutritional status by use of vector nomograms. Our results indicated that late-season NPK fertilization improved shoot and root growth, and the overall nutritional status of seedlings. The lack of late-season fertilization leads to nutrient deficiency in plants, whilst the application of imbalanced fertilization treatments may trigger nutrient luxury consumption and nutrient dilution, pointing out the importance of NPK proportions in the fertilizer. Moreover, late-season fertilization with nitrogen might improve the drought resistance of seedling by enhancing their osmotic adjustment.     

Is nitrogen fertilization in the nursery a suitable tool for enhancing the performance of Mediterranean oak plantations?

Mediterranean oaks frequently have poor performance in forest restoration projects. We analyzed if nitrogen (N) fertilization during nursery cultivation enhances the outplanting performance of two ecologically distinct oaks, Quercus coccifera L. an evergreen shrub, and Quercus faginea L., a deciduous tree. Additionally, we compared the sufficiency N levels of both oaks and if root growth capacity (RGC) and photosynthesis testing at low air temperature better discriminated among fertilization treatments than testing at mild temperature. Plants were cultivated under five N fertilization rates (0, 30, 75, 150 and 200 mg N plant^?1) for one growing season. At the end of the cultivation period several plant material and performance attributes were measured. RGC and photosynthesis were assessed at mild temperature and cool conditions in Q. coccifera, while in Q. faginea these attributes were only analyzed at mild temperature conditions. Q. coccifera seedlings were transplanted into four terraces that imposed increasing drought stress, while Q. faginea seedlings were transplanted into an abandoned wheat cropland. Sufficiency level was higher for the tree (150 mg N plant^?1) than for the shrub (75 mg N plant^?1) Nitrogen-deprived Q. coccifera plants had higher frost damage than remaining treatments, which did not differ among them. Fertilization in Q. faginea did not affect photosynthesis rate but it delayed leaf senescence and abscission. RGC increased with fertilization in both species. Testing temperature did not change the effect of fertilization on RGC in Q. coccifera. Photosynthesis in cool conditions discriminated N-deprived seedlings from the remaining treatments, but treatments did not differ in photosynthesis at mild temperature. Fertilization enhanced outplanting survival in Q. coccifera, primarily in the terraces imposing stronger drought stress, while fertilization only increased growth in the terraces imposing mild drought stress. Overall, survival and growth was positively related to seedling size at planting in both oaks. Additionally, Q. coccifera survival was also positively related to RGC in the harsh planting conditions. Field growth was positively related to RGC and plant N concentration in both oaks but the relation was weak or nonexistent under harsh conditions in Q. coccifera. We conclude that fertilization in the nursery is an important tool for improving the success of oak plantations in Mediterranean continental sites, and that large and N-rich seedling have greater field performance than small and low tissue N concentration seedlings, especially in harsh field sites.     

Modified exponential nitrogen loading to promote morphological quality and nutrient storage of bareroot-cultured Quercus rubra and Quercus alba seedlings

Abstract

Exponential nutrient loading has been used to improve nursery fertilizer uptake efficiency of conifer seedlings, but the technique has received little attention in the culture of temperate deciduous hardwoods. This study examined responses of northern red oak (Quercus rubra L.) and white oak (Q. alba L.) seedlings to modified exponential nitrogen loading during bareroot nursery culture using a broad range of nutrient supply from 0 to 3.35 g nitrogen (N) per plant per season for 18 weeks in Indiana, USA. Seedling growth and nutritional parameters followed a curvilinear pattern that ranged from deficiency to toxicity with increased fertilization consistent with trends depicted in the proposed model for nutrient loading. Fertilization increased plant dry mass by 113–260% for red oak and 49–144% for white oak. Severe nutrient deficiency occurred under indigenous soil fertility, and limited phosphorus and potassium uptake were found to inhibit seedling growth at higher N supply. The sufficiency and optimum rates were determined to be 0.84 and 1.68 g N per seedling per season, respectively, under the current cultural conditions. Fertilization at 1.68 g N per plant increased N content by 40% in red oak and 35% in white oak. This approach may be used to help refine nursery fertilization practices in hardwood culture to produce high-quality seedlings for field planting.     

Autumn Fertilization in the Nursery Affects Growth of Picea abies Container Seedlings After Transplanting

Second-year Norway spruce seedlings [Picea abies (L.) Karst.] grown in containers were divided into three fertilization levels in August [5, 15 and 25 mg nitrogen (N) seedling^?1]. The resulting foliar concentrations of N were 11.0, 13.1 and 15.8 g kg^?1, respectively. Seedling height (mean 26.0 cm) did not differ among treatments. The next spring, the seedlings were tested in two experiments. (1) The seedlings were transplanted into pots containing sandy soil in the greenhouse, where they were fertilized with either pure water or nutrient solution (22 mg N l^?1). (2) The outplanting performance of the autumn-fertilized seedlings was tested on a sandy field. In the greenhouse experiment, the autumn fertilization level affected height growth and root egress of the seedlings significantly, but less than fertilization with a nutrient solution after planting. In the field experiment, during the first season after transplanting shoot growth of the seedlings increased with the level of autumn fertilization. After the second and third seasons, the seedling stem volume was highest with the highest level of autumn fertilization. These results suggest that, by improving the preplanting nutrient status of seedlings, the growth of shoot, stem diameter and root biomass can be enhanced after planting, especially on nutrient-poor soils. However, heavier autumn fertilization than that used here may yield a greater and more persistent increment in growth.     

Effect of nitrogen fertilizer on biomass production and nodulation behavior of Pongamia pinnata Pierre seedlings under nursery conditions

At the seedling stage, a small amount of N is required to boost growth of leguminous plants. A pot experiment was conducted to observe the effect of N fertilizer on various growth parameters and nodulation behavior of Pongamia pinnata under nursery conditions. After the establishment of seedlings, four nitrogen treatments, 0, 40, 80 and 100 kg·ha^?1 N were applied in two equal splits. Monthly observations were taken for the morphological parameters viz. plant height, collar diameter, leaf number, root length, root shoot ratio, nodule number and weight per plant. Maximum plant height was recorded after application of N at 40 kg·ha^?1. Seasonally, the difference in collar diameter in rainy season was significantly higher than in winter or summer. However, more leaves were produced per plant at N-40 and N-100 treatments in winter and rainy seasons. Higher root length was recorded in rainy season than in winter or summer. Root biomass was higher than for stems or leaves. Seasonal effects of N-80 and N-40 treatments on leaf dry weight were significantly higher than for N-100 or N-0. Stem dry weight was higher at N-40 than at other treatments in winter and summer seasons. Root:shoot ratio was higher throughout winter to early summer. Nodule biomass was 2–3 times higher in rainy season compared to winter or summer. Maximum nodule number and biomass per plant were highest at N-40, followed by N-0, N-80 and N-100 treatments. New nodule formation started from June to the end of September. Maximum biomass per plant was recorded at N-40, followed by N-80, N-100 and N-0. Nitrogen treatment effect and seasonal behaviour interaction were not significant. Significantly higher numbers of nodules per plant were recorded in rainy season followed by summer and winter for all treatments. Higher nitrogen doses suppressed growth while lower doses promoted growth in Pongamia pinnata. Therefore, the lower nitrogen dose i.e., N-40 Kg·ha^?1 applied in two equal splits was suitable at the initial nursery stage for the increase in nodulation and biomass production.     

Impacts of nursery cultural treatments on stress tolerance in 1 + 0 container white spruce (<Emphasis Type="Italic">Picea glauca</Emphasis> [Moench] Voss) seedlings for summer-planting

Impacts of nursery cultural treatments (T) on stress tolerance of greenhouse-grown 1 + 0 container white spruce (Picea glauca [Moench] Voss) seedlings (mean height 24 cm, root collar diameter 3.1 mm) for summer planting were studied. Seedlings were subjected to 12-h short-day treatments of 0 (T0), 3 (T3), 7 (T7), 10 (T10), or 15 (T15) days, followed by 0, 7, 17, 40, or 46 days of reduced N supply, respectively. Relevant physiological and morphological factors were examined concurrently. Foliar N concentrations exceeded optimal levels and differed little among treatments, suggesting a minor confounding role for N reduction. Both frost and drought tolerance increased incrementally from T0 through T15. Electrolyte leakage index decreased steadily from T0 (25% for roots, 17% for needles) to T15 (1% for roots, 2% for needles) after 2-h exposure of fine roots to − 2°C and of needles to − 8°C. Withholding soil watering for 19 days caused 80% mortality among seedlings in T0, 50% in T3, and < 10% in T7–T15. The transpiration decline curve suggested that enhanced drought tolerance was largely attributable to quicker stomatal closure during water stress and lower cuticular transpiration rate. The treatments increased root growth capacity on a per-seedling, but not per-root-mass, basis. Needle primordia were developed in all T7-T15 seedlings but not in T0 and T3 treatments, suggesting that nurseries may need no more than 7 days of blackout application for conditioning spruce seedlings for summer planting. Shoot dry weight fraction increased gradually from T0 through T15 and was linearly correlated with needle specific weight and frost tolerance, and may thus be useful in monitoring progress of conditioning treatments.     

Performance and nutrient dynamics of holm oak (<Emphasis Type="Italic">Quercus ilex</Emphasis> L.) seedlings in relation to nursery nutrient loading and post-transplant fertility

Holm oak (Quercus ilex L.) seedlings were exponentially (E) nutrient loaded using incremental increases in fertilizer addition or conventionally (C) fertilized using a constant fertilizer rate during nursery culture. The fertility treatments (mg N plant⁻¹) were control (0), 25E, 100E, and 100C. Subsequently, 1-year-old plants were transplanted under simulated soil fertility gradients in a greenhouse to evaluate effects of nutrient loading and post-transplant fertility on seedling performance. Post-transplant fertility consisted of fertilizing plants at two rates (0 vs. 200 mg N plant⁻¹). A water-soluble fertilizer 20-20-20 was supplied in both nursery and post-transplant experiments. Nutrient loading increased plant N content by 73% in 100E and by 75% in 100C relative to controls, although no significant differences were detected between constant and exponential fertilization regimes at the 100 mg N plant⁻¹ rate. When transplanted, nutrient loading promoted post-transplant root growth relative to shoot, implicating potential to confer competitive advantage to loaded holm oak seedlings after trans-planting. In contrast, post-transplant fertility increased new shoot dry mass by 140% as well as N, P and K content relative to controls. Results suggest that holm oak seedlings can be successfully nutrient loaded in the nursery at higher fertility rates, improving its potential to extend new roots, but alternative fertilization regimes and schedules that better fit nutrient availability to the growth rhythm and conservative strategy of this species must be tested.     

Do harrowing and fertilisation at middle rotation improve tree growth and site quality in <Emphasis Type="Italic">Eucalyptus globulus</Emphasis> Labill. plantations in Mediterranean conditions?

Effects of harrowing and fertilisation on tree growth, understory vegetation, forest floor litter and soil properties were studied in a field experiment installed in a 5-year-old first rotation eucalypt plantation. The treatments were harrowing (H), fertilisation (F), harrowing and fertilisation (HF) and a control without any treatments (C), with four replicates. Tree growth, root mass, tree nutrition status, understory vegetation, mass of forest floor litter and soil physical and chemical properties were monitored till the end of the rotation (stand was 14-year old). Effects of treatments on tree growth, root mass and timber production were not significant. Root nutrient concentration differed between treatments only few months after the beginning of the experiment, while differences regarding specific root length and area were observed during the first year. Harrowing (H and HF) led to significantly smaller biomass of understory vegetation (<13.4 g m⁻²) than other treatments (33−61 g m⁻²) during the first 3 years, but at the end of the experiment differences were less important. Forest floor litter mass after 3 years and at the end of the experiment were similar among treatments. Soil bulk density significantly decreased by harrowing (H and HF treatments), but 16 months after treatments were similar. Although soil chemical properties were not significantly affected by treatments, a decrease in base cations occurred during the rotation period. Fertiliser application is a questionable practice under the economic point of view, whereas harrowing can reduce the fuel load only during a short period, without negative effects on productivity and soil quality.     

Growth of Nursery-grown Bamboo Inoculated with Arbuscular Mycorrhizal Fungi and Plant Growth Promoting Rhizobacteria in two Tropical Soil Typeswith and without Fertilizer Application

A nursery experiment was conducted to assess the effect of bioinoculants (Glomus aggregatum, Bacillus polymixa, Azospirillum brasilense) on seedling growth promotion of bamboo (Dendrocalamus strictus (Roxb.) Nees.) in two soil types (alfisol, vertisol) with or without fertilizer application. Bamboo seedlings were grown in the presence or absence of bioinoculants either individually or in all combinations for 180 days in field soil under tropical nursery conditions. Shoot, rhizome and root length, dry masses, nutrient concentrations and arbuscular mycorrhizal (AM) colonized root lengths were determined at harvest. Under the experimental condition tested combined inoculation of AM fungi, PSB and A. brasilense resulted in maximum growth response both under fertilized and unfertilized conditions in both soil types. Fertilizer application enhanced the efficiencies of N, P and K uptake, whereas reduced their usage efficiencies. Though soil type did not affect microbial inoculation response, fertilizer application significantly affected plant response to microbial inoculation.     

Minimizing nutrient leaching and improving nutrient use efficiency of Liriodendron tulipifera and Larix leptolepis in a container nursery system

Fertilization is essential to seedling production in nursery culture, but excessive fertilization can contaminate surface and ground water around the nursery. The optimal fertilization practice is that which maximizes seedling growth and minimizes nutrient loss. We tested three fertilization strategies: (1) constant fertilization (2) a three-stage rate, and (3) exponential fertilization on Liriodendron tulipifera and Larix leptolepis containerized seedlings. Growth performance, nutrient uptake, and nutrient loss in leaching were measured. Height, root collar diameter, and dry weight of both species were not significantly different among treatments even though the nutrient supply of the exponential treatment was half that of the constant and three-stage treatments. Generally, nutrient losses in leached solutions were higher in constant and three-stage than the exponential treatment. Nutrient use efficiency was calculated as the ratio of the nutrient content of the seedlings to the amount of nutrient applied to the containers. The nitrogen use efficiency in the constant, three-stage, and exponential treatments was 63, 61, and 85% for yellow poplar, respectively, and 35, 30, and 53% for larch. Similar results were obtained for phosphorus and potassium. Thus, the exponential treatment had the highest nutrient use efficiency as well as the least nutrient loss. Adjusting fertilization rates can reduce soil and water contamination around the nursery without compromising growth performance, which reduces both producer’s investments and environmental impacts.     

Influence of nutrient supply on spring frost hardiness and time of bud break in Norway spruce (Picea abies (L.) Karst.) seedlings

When spring frosts occur on recently planted forest sites, severe damage may occur to the seedlings. The aim of the present study was to test how different low levels of nutrient concentrations in Norway spruce (Picea abies (L.) Karst.) seedlings affected spring frost hardiness and time of bud break. Seedlings were grown in a greenhouse for one season and supplied with fertiliser containing 22, 43 and 72 mg N l^–1, respectively. The treatments resulted in needle nitrogen concentrations ranging from 0.9 to 1.8% in autumn. After winter storage at 0 °C, bud break was recorded on seedlings growing in the greenhouse, outdoors and in growth chambers at 12 °C and at 17 °C. Freezing tests were performed on seedlings directly removed from winter storage and following one week growth in the greenhouse. Seedlings receiving fertiliser with 43 mg N l^–1 had less freezing injury than the two other fertilisation treatments in the present study. The earliest bud break occurred in seedlings receiving 72 mg N l^–1.     

Container characteristics influence Pinus pinea seedling development in the nursery and field

The growth and development of Pinus pinea seedlings grown in different containers was followed through one growing season in the nursery and 3 years following outplanting in the field. The variables studied in the nursery were height, diameter, biomass of shoots and roots, nutrient uptake and root density. The measured field variables, height and diameter increment and survival, were correlated with the nursery variables. Container volume had the greatest influence on plant morphology. Containers with larger rooting volume had seedlings with larger height and diameter, greater nutrient content, and better field performance. Growing density was correlated with seedling morphology and nutrient concentration in the nursery. Among the variables that influenced container volume, the diameter of the container was the most important, while the depth of the container had a minor influence on seedling morphology.The best indicator of seedling development in the nursery was the ratio of container depth to container diameter, and the optimum ratio was 4. All containers produced seedlings with some root spiralling, including those containers with ribs. There was no relationship between either the number of spiralling roots or the angle of spiralling and container characteristics. Furthermore, root spiralling did not influence seedling performance following outplanting. Root density (root biomass/cm³) was inversely correlated with container volume but there was no correlation with either depth or growing density. The largest plants were produced with container volumes of 300–400 cm³, depth/diameter ratios of 4, and growing densities of 200–300 seedlings/m². These growing conditions will result in larger Pinus pinea seedlings coming out of the nursery, which will increase growth following outplanting.     

Growth regulation of Scots pine seedlings with different fertilizer compositions and regimes

Scots pine (Pinus sylvestris L.) seedlings were grown in containers filled with peat, using two different fertilizers and three different fertilizer regimes. Seedling shoot and root growth and shoot content of nitrogen, potassium and phosphorus were followed in the nursery and after outplanting in the field. Attempts to regulate growth rate by an exponential nutrient supply were not successful, but the root/shoot ratio was influenced by the fertilization regime. Internal nitrogen concentration was stable only for seedlings with low relative growth rate, while seedlings with high nutrient supply in the nursery showed strong nutrient dilution in the shoot after planting.     

Effects of mulching materials on nitrogen mineralization,nitrogen availability and poplar growth on degraded agricultural soil

Nitrogen (N) is usually the most limiting nutrient in degraded agricultural soils and affects the growth and ecological function of poplar (Populus spp.) plantations. We hypothesized that application of organic mulch would improve soil nitrogen availability and increase tree growth, while the quality of mulching materials would alter the supply of essential nutrients. In this study, poplar plantations were established in 2004 and two experiments were established in the field. The fresh above-ground biomass of cogongrass (Imperata cylindrica (L.) P. Beauv.), oak (Quercus fabri Hance), Chinese coriaria (Coriaria nepalensis Wallich) and brackenfern (Pteridium aquilinum (L.) Kuhn. var. latiusculum (Desv.) Underw. ex Heller) in the current year was selected as mulching materials, and mulches were annually applied at the rate of 5.0 kg/m² in the N mineralization experiment and 20,000 kg/ha in growth and nutrient availability experiment. Additions of fresh biomass significantly improved annual net N-mineralization estimates and the mulching treatments increased the cumulative N mineralized over the incubation period by 22–30%. However, a significant difference in the cumulative N mineralized was not observed among the mulched treatments, even if the cumulative N mineralized in the treatment mulched with oak (QF) was 5.9, 3.3 and 2.2% greater than that of treatments with brackenfern (PA), Chinese coriaria (CN) and cogongrass (IC), respectively. Application of fresh biomass mulch markedly affected soil available N contents and growth performance of poplar plantations. The mulching treatments with QF, IC, PA and CN increased annual means of available N concentration by 39.0, 29.0, 29.6 and 39.7% respectively. At the end of the fifth growing season, the average height of poplar plantations in treatments mulched with QF, IC, PA and CN was 46.8, 14.9, 42.6 and 57.4% greater than that in Check (CK-no mulch), while mean DBH increased by 35.4, 12.5, 33.3 and 52.1%, respectively. Overall, the productivity was enhanced in mulched plots at the end of the third growing season. Compared with CK, the treatments mulched with QF, IC, PA and CN increased total biomass by 97.4, 96.4, 63.1 and 81.6%, respectively. Based on the results of this study, annual application of 20,000 kg/ha fresh woody biomass would be recommended for soil improvement in young poplar plantations growing on a degraded agricultural soil.