Young Pinus Radiata Research Articles

Responses of a Non–N‐Limited Forest Plantation to the Application of Alkaline‐Stabilized Dewatered Dairy Factory Sludge

Amendment of forest soils with dewatered dairy factory sludge (DDFS), characterized by low heavy metal contents and high amounts of degradable C, can prevent the depletion of soil nutrients that results from intensive harvesting in forest plantations. However, this practice involves environmental risks when N supplies exceed the demand of plants or when the strong acidity of the soil favors the mobility of trace metals. These aspects were assessed in a young radiata pine plantation growing in a sandy, acidic, and organic N-rich soil for the 7 yr after application of a DDFS. The supply of limiting nutrients (mainly P, Mg, and Ca) provided by application of the DDFS, along with control of the ground vegetation, improved the nutritional status of the stand and led to increases in timber volume of more than 60 to 100%. Increases in soil inorganic N were observed during the first months after amendment. Data from soil incubation experiments revealed that some of the additional N was immobilized and, to a lesser extent, denitrified due to the readily available organic C content of the DDFS. Leaching and increased plant uptake of N were prevented by a combination of the latter processes and the low rate of nitrification. The strong acidity of the soil enhanced the availability of Mn and Zn to plants, although the maximum concentrations did not reach levels harmful to organisms. We conclude that although application of DDFS has positive effects on tree nutrition and growth and the environmental risks are low, repeated application may favor mobility of N and availability of heavy metals.

Acoustic measurements on standing trees, logs and green lumber

Acoustics provide opportunities for non-destructive evaluation of the mechanical properties of wood, especially stiffness. In this work, Fakopp 2D a time of flight (TOF) tool and WoodSpec a resonance-based system were used. In a scoping study on young Pinus radiata trees (aged 8–11) no systematic differences were found between the Fakopp acoustic velocity on opposite sides of young trees. These Fakopp values were then averaged and correlated with that from the equivalent log using WoodSpec. Finally stem and log values were correlated with acoustic velocity in outerwood and in corewood lumber. External measurements on the log (standing tree) correlated well with those for lumber cut adjacent to the bark and modestly for the corewood (R2 of 0.89 and 0.74, respectively). In a separate study, the acoustic velocities were measured on standing trees in three adjacent stands aged 8, 16 and 26 and the data were used to construct a “Russian Doll” model to demonstrate the enormous range in wood stiffness within and between trees. The stiffest 20% of the population was estimated to be 146, 87 and 76% stiffer than the poorest 20% in the corewood (age 8), intermediate (age 16) and outerwood zone (age 26) respectively.

Initial response on nutritional status of a young Pinus radiata D.Don plantation to wood-ash application

The aim of the present study was to evaluate the effects of the application of wood-bark ash as a amendment and fertilizer of a young plantation of Pinus radiata grown on an acid soil. Two different doses of ash (5.000 and 10.000 kg ha-1) and one dose of 8:24:16 NPK fertilizer (200 g in hole) were applied at establishment. The response of the soil solid fraction and foliar chemical composition was studied throughout 28 months. Fertilization of the soil with wood-bark ash produced an increase in soil pH, at the same time increasing the availability of Ca, Mg, P and K. Related to this increase, the needle levels of Ca and, in a lower extent, Mg were also higher. Possible diagnosis of vector analysis of foliar nutrient contents and concentrations showed that these two elements limited the species growth.

Interpretation of foliar nutrient concentrations in young Pinus radiata D. Don plantations on abandoned agricultural lands in Galicia

The nutritional status of 14 4-5-yr-old Pinus radiata plantations on abandoned agricultural lands in Galicia (NW Spain) was studied. Nutritional status was assessed using macronutrient foliar analysis followed by the critical levels method, foliar nutrient ratios interpretation and the DRIS system. The relationships between foliar and soil nutrient levels and between annual growth and foliar and soil data were also analyzed. Mg and P deficiencies were the most common in foliage samples. Foliar N concentrations were always over the critical level and foliar N:P ratios were unbalanced in almost all sites. The annual height, diameter and volume growth were positively correlated with foliar P concentrations and negatively correlated with foliar N:P ratio. The P nutrition seems to play an important role in the plantation’s development. However, both, the high levels of available P in the soils, and the lack of a significant correlation between foliar and soil P levels, suggest that other factors, such the N excess or the soil pH, may interfere in the P assimilation. On the contrary, exchangeable soil Mg levels were not very high and were significantly correlated with foliar Mg. Thus, a positive growth response to Mg fertilization can be expected.

The influence of weed competition for light and water on growth and dry matter partitioning of young Pinus radiata, at a dryland site

Above-ground biomass growth and allocation was studied in juvenile Pinus radiata D. Don trees growing with and without competition from the woody weed broom ( Cytisus scoparius L.), at a dryland site, over a 2-year period. The relative significance of broom competition for light and water on seasonal growth of P. radiata was quantified using a growth modelling technique which effectively removed the confounding influences of season and initial tree size from analyses. Allometric regression analysis was used to separate size dependant changes in allocation from functional adjustments made in response to treatment. At the end of the second year, trees growing without broom had an above-ground biomass 25-fold greater than that of trees growing with broom. The presence of broom induced consistently more negative values of predawn needle water potential ( ψ e) in P. radiata over the 2-year period. Treatment differences were most pronounced during the first year when ψ e reached a minimum of −4 MPa in plots with broom, compared to a minimum of −1 MPa in plots without broom. Broom leaf area index increased markedly over the 2-year period, from average values of 0.76 m 2 m −2 in year 1 to 2.26 m 2 m −2 during year 2. During the first year, the strong link between ψ e and fractional biomass growth for trees in plots with broom ( r 2=0.91) suggests growth losses were almost entirely attributable to water deficit. Although ψ e was strongly related to fractional biomass growth over the second year ( r 2=0.71), values across a comparable range of ψ e, were on average 15% lower. Inclusion of a simple shading index explained this difference, suggesting broom restricted tree growth during the second year through competition for both light and water. Compared with P. radiata in weed-free plots, trees growing with broom allocated dry matter preferentially to stems (+8%) at the expense of foliage (−4%), roots (−2%) and branches (−2%). These findings on allocation confirm derivations based on pipe model theory and indicate that the root to shoot ratio in juvenile P. radiata remains relatively stable even under severe water deficit.

Modelling the influence of weed competition on the growth of young Pinus radiata at a dryland site

A water balance model was used to partition water loss and explain annual growth differences for 1-year-old Pinus radiata D. Don trees growing with and without competition from broom ( Cytisus scoparius L.) at a dryland site. Seasonal water deficits are characteristic of this site as annual precipitation is low (797 mm) and water storage within the stony soil is limited to approximately 70 mm. At the end of the second year, the presence of broom had reduced tree annual basal area increment by 10-fold compared with that in plots where broom had been removed. In both treatments, modelled root-zone water storage ( W) corresponded closely to measured values over the course of the year. Root-zone water storage in the treatment with broom fell to values close to minimum water storage ( W min) by mid-summer, and did not significantly increase again until late autumn. In contrast, W in the treatment without broom remained high until mid-summer then declined, almost reaching W min at the end of autumn. The lowest values of W in both treatments coincided with the driest late-summer to late-autumn period since 1960. Total annual evaporation in the treatment with broom was 92 mm higher than that for the treatment without broom. This higher rate was primarily due to wet canopy evaporation from the broom and, to a lesser extent, from increased rates of total transpiration within this treatment. Soil surface evaporation was the largest component of water loss in the treatment without broom, accounting for 47% of total annual precipitation. There was a clear relationship between the integral of root-zone water deficit and fractional basal area growth, suggesting losses in growth were almost entirely attributable to the development of a more pronounced water deficit in the treatment with broom. These findings highlight the importance of root-zone water storage in regulating productivity on dryland sites and indicate that water balance modelling provides a useful approach for predicting the influence of weed competition on tree growth.

Weed control intensity effects on young radiata pine growth

An experiment was conducted to quantify the effect of different weed control intensities (WCI) during the first three growing seasons in a Pinus radiata plantation. At the end of the third growing season, results showed that stem volume index of check plants was similar to that of plants that received spot applications in the first and second year. On the other hand, when plots were treated with herbicide spot application (first year) plus band or total area application (second year), the stem volume index was two and three times larger, respectively. However, if the first year WCI consisted of total area application, the second and third year treatment had less effect on yield. The largest biomass yield was obtained when plots were submitted to total area WCI during the first and second year.

Foliar nutrient status and nutritional relationships of young Pinus radiata D. Don plantations in northwest Spain

Fifty-four plots of young Pinus radiata D. Don plantations on abandoned agricultural land in Galicia (northwest Spain) were selected for nutritional diagnosis. Nutritional status was assessed by foliar analysis using the critical levels method. The relationships between foliar nutrient concentrations and the plantation’s growth and survival and the topsoil physical and chemical properties were also analyzed. The most common deficiencies among plots were P and Mg. Foliar N concentrations were relatively high and generally they were above the critical level. Foliar N:P, N:K and N:Mg ratios were significantly unbalanced in 31, 44 and 17 out of 54 studied plots. Foliar P levels were significantly higher on sites with previous herbaceous land use and on soils with a finer texture, whereas foliar Mg levels were higher at low altitudes. Foliar nutrient levels were not significantly correlated with their respective soil levels except in the case of K. Foliar Ca and Mg concentrations correlated positively with topsoil pH. Growth correlated positively with foliar K and Mg concentrations and negatively with foliar N:P, N:K and N:Mg ratios. Percentage of dead and poor state plants were negatively correlated with foliar P, K and Ca levels and positively correlated with foliar N:P and N:Mg ratios. These results suggested that nitrogen may be in excess and may condition the uptake of other nutrients. Foliar N level was considered as an unfavorable parameter, whereas foliar P, K, Ca and Mg concentrations were considered as favorable parameters for P. radiata establishment in Galicia.

Effect of fertiliser and growth rate on angle of spiral grain in young Pinus radiata in Western Australia

Summary Spiral grain was measured on 36 ten-year-old P. radiata trees, from a fertiliser experiment in the south west of Western Australia, to examine the within-stem variation in spiral grain angle and to determine if spiral angles varied with fertiliser application and growth rate. Six discs were sampled from each tree, ranging from breast height (1.3 m) to 11 m up the stem. At all heights sampled in the stem, all trees exhibited a well-defined radial pattern of grain inclination that corresponded with the generally known pattern for this species. Maximum mean grain inclination (6.6°) occurred in annual growth ring three, after which the grain straightened steadily, to be at a minimum in growth rings nine and ten (0.8°), the oldest available in this study. There was no significant variation in spiral angle between treatments, or any significant relationship between spiral angle and height in the stem. Mean spiral angle for each growth ring at all heights in the stem were below the maximum 11.3° angle (1 in 5 slope) allowed in the Australian Standard AS 2858–1986 for F5 structural grade timber for P. radiata, and grain angles greater than 5° were restricted to the innermost five growth rings. There was a very weak positive linear relationship between growth rate and spiral angle. Growth rate explained only 14% of the variation in spiral angle and can therefore be considered to be of little consequence. The significance of these findings for plantation managers is in the knowledge that accelerated growth per se in the first ten years will not adversely affect wood quality by increasing spiral grain angle.

Soil fertility rehabilitation in young Pinus radiata D. Don. plantations from northern Spain after intensive site preparation

Soil fertility and tree nutrition of young Pinus radiata were examined four years after harvesting, site preparation and planting in a hilly area of northern Spain. Conventional stem-only harvesting was compared with highly mechanized techniques applied in the region, such as (a) whole-tree harvesting and humus layer removal, and (b) whole-tree harvesting and humus layer removal followed by down-slope deep ploughing. For the study, 58 plantations of Pinus radiata were selected which were located at sites with similar climatic conditions, on slopes often exceeding 35% and on soils with similar properties, developed from argillite. Whole-tree harvesting negatively affected the physical properties and fertility in the rooting soil layer over a period of some years, because of the severe soil disturbance and accelerated erosion which took place. Soils, whose bulk density was increased at the time of site preparation, still showed values high enough to be restrictive to tree growth after a period of four years. A very low rate of recovery was observed for organic matter, total N and S and exchangeable Ca, whose contents remained very low even four years after site preparation. In these soils, exchangeable K increased over this time, most probably as a consequence of the rapid release of this element from logging residues and soil organic matter decomposition. Intensive site preparation also affected the nutrition and growth of young trees. The removal of organic components and deep soil disturbance led to deficiencies of P, S and N in foliage, as well as potentially toxic levels of Mn, which were associated with symptoms of chlorosis, needle loss and poor growth.

Fate of applied phosphorus in an effluent-irrigated Pinus radiata plantation

We examined the fate of applied phosphorus (P) in a young Pinus radiata plantation in south-eastern Australia, spray-irrigated with secondary-treated municipal effluent. Measurements included changes (before irrigation, and after 5 years) in total P, total organic P, total inorganic P, labile P, and sorption and desorption characteristics. During the first 5 years a total of 363 kg/ha of P was applied at an average concentration of 5.4 mg/L. Irrigation changed the forms and distribution of P throughout the profile (0–1 m). Increases in labile inorganic P (membrane-exchangeable, bicarbonate-extractable, and in soil solution) were confined mostly to the 0–0.5 m horizon, and wholly within the 0–0.7 m horizon. In addition, large amounts of organic P (204 kg/ha) were mineralised within the surface 0.7 m, due to stimulation of decomposer activity by increased soil water. Mineralisation, therefore, provided a significant and additional input of inorganic P to soil. Irrigation and P additions changed both the placement and curvature of soil sorption isotherms. Retention capacity (0–0.5 m), calculated from P sorption isotherms, decreased by 180 kg/ha. Desorbable P, determined by sequential extraction with dilute acid, increased by 184 kg/ha. Thus, these 2 independent methods of measuring the changes in exchangeable P gave the same result. Of the total inorganic P added to the soil (in effluent and mineralised), 25% remained in the exchangeable form; the rest was retained unavailable for short-term exchange and migration through soil. After 5 years, fluxes (kg/ha) of P in the 0–0.7 m horizon were: input in effluent less storage in vegetation (323), change in total organic P (–204), change in total inorganic P (517), net change in total P (313). Thus, 97% of the net amount of P added in effluent was recovered in the surface 0.7 m. Results have implications for the way in which P retention capacity is calculated under effluent irrigation.

Stem deformity inPinus radiata plantations in south-eastern Australia

Plantations of radiata pine (P. radiata D.Don) on soils previously under legume based pastures have a high incidence of stem deformity compared with forest soils. A comparison of soil properties and tree nutrition of 5 to 7 year-old radiata pine on former pastures in the first part of the study showed that stem deformity was strongly correlated with mineralisation of soil N and in particular with nitrification. Other soil properties that have changed as a result of pasture improvement, e.g. pH, available P and Mn, were only partially correlated with stem deformity. In the second part of the study, the role of N availability and other soil properties in the expression of deformity was further investigated in a separate field experiment on soils formerly under native eucalypt forest, tobacco cropping, and improved pasture. Young radiata pine plantings were treated with lime, phosphorus, and nitrogen applied as urea and sodium nitrate. Liming increased soil pH by around 1.5 units, raised exchangeable Ca2+ and decreased available Mn. Soil mineral N content was only marginally affected by liming. Superphosphate increased soil available P and raised levels of P in foliage. Changes in soil pH, availability of P, Mn, and B did not affect growth or stem deformity at any of the sites. In contrast, application of N fertilisers at 200 and 600 kg N ha-1 increased mineral N content and stimulated nitrification, particularly at the forest site. The high rate of N fertiliser increased basal area at the forest site by 45%, but also raised the level of stem deformity from 12% to 56%. At the tobacco and pasture sites, this treatment did not increase growth and did not significantly raise stem deformity above the already high basic level of deformity (63%). Implications of stem deformity in young plantations of radiata pine on potential utilisation later in the rotation are discussed.

Rainfall interception by trees and slash in a young Pinus radiata D. Don stand

Rainfall interception by trees and slash was measured for 1 year in a 9 m tall, 7-year-old Pinus radiata D. Don stand, thinned to 450 trees ha −1 and pruned to heights up to 5 m. Tree leaf and slash surface area indices, on a one-sided area basis, were 1.7 and 3.5, respectively. Slash surface area was principally (about 90%) comprised of leaves. A total of 1154 mm of rain was recorded on 163 days during 336 events. Median event size and rainfall intensity were 0.8 mm and 0.4 mm h −1, respectively. The measured fraction of rainfall intercepted by the tree canopy was 0.19. Stemflow was linearly related to rainfall, with maximum values (for rainfall of 91.4 mm) of 6.3 and 7.6 mm for trees that had been pruned to heights of 2–3 m and 3–5 m, respectively. Slash covered 60% of the ground, with interception being 11% of rainfall on a stand basis. Wetness sensors, located within the base of the tree canopy, were wet for 26% of the time. The fraction of wetness duration during darkness nearly coincided with the time fraction of dark hours. This result and the equal probability of rainfall throughout the day showed the importance of night-time interception and evaporation. Estimates of stand aerodynamic conductance for water vapour transfer, derived from six night-time canopy drying events, were proportional to wind speed and varied from 0.05 to 0.33 m s −1 (corresponding wind speeds were 1.2 ms −1 and 6.0 ms −1, respectively). During these events, there was no radiative energy so that evaporation was driven by convective energy, with vapour pressure deficit being typically 0.1 kPa. The effect of rainfall interception on the forest water balance was examined using a biophysical water balance model with parameters derived from the stand measurements. Although there was generally satisfactory agreement between modelled and independently measured two-weekly soil water storage over the year, annual evaporation of rainfall intercepted by the tree canopy modelled with the Penman equation was only 9% of rainfall (100 mm). This is attributed largely to an underestimation of wet tree canopy evaporation -during 15 days of higher-intensity rain when daily falls exceeded 20 mm. For the remaining 148 rain days, modelled wet tree canopy evaporation was generally close to the measured 19% of rainfall. Modelled annual wet canopy evaporation emanating from the slash was 116 mm (10% of rainfall). Modelled annual tree transpiration and understorey evaporation during fine periods were 367 and 328 mm. respectively. Annual soil drainage/water yield was 270 mm. Implications for the management of water yield from forested catchments are discussed.

Effects of slash and litter management on fluxes of nitrogen and tree growth in a young Pinusradiata plantation

The effects of slash and litter management practices on soil water and temperature, fluxes of mineral N, needle water potential, and tree nutrition and growth were studied in a young Pinusradiata D. Don plantation growing on a sandy Podzol in southeastern Australia. Treatments were slash and litter retained (SL), litter only retained (L), litter ploughed (LP), and slash and litter removed (SLR). Soils without slash or litter cover (LP and SLR) were up to 4 °C warmer on average than soils overlaid by slash or litter and were subjected to greater extremes of temperature. Treatments had relatively little effect on soil water content and needle water potential in trees. Carbon in surface soil increased from 1.14 to 1.83% after incorporation of litter by ploughing, but decreased to 1.37% during the next 40 months. Smaller but significant decreases in C also occurred in other treatments. LP and SLR led to the highest rates of N mineralization in the 1st year. During the first 3 years after clear-felling, rates of N mineralization increased in SL, L, and LP but decreased in SLR. During the 4th year, rates of N mineralization were low (20–30 kg N•ha−1•year−1) in all treatments. Over 4 years, 211, 170, 210, and 147 kg N•ha−1 were mineralized in treatments SL, L, LP, and SLR, respectively. Rates of mineralization and leaching were strongly correlated (R2 = 0.82) and leaching below 30 cm accounted for 75–85% of N mineralized irrespective of treatment. Incorporation of litter by ploughing doubled concentrations of mineral N during the first summer after planting and increased early tree growth. However, rates of N mineralization in the slash and litter treatments, which were high compared with potential rates of uptake, were weakly correlated with tree growth. Factors controlling N supply were of little consequence for tree growth during this early phase of plantation establishment.

Partitioning evapotranspiration into tree and understorey components in two young pinus radiata D. Don stands

The tree and understorey components of latent heat flux density ( LE) in two young Pinus radiata D. Don stands at different stages of commercial management were measured on two consecutive fine autumn days in each stand when there was no soil water deficit. LE was determined from the difference between available energy ( A) and sensible heat flux density ( H) measured using eddy covariance. Contributing LE from understorey ( LE u) and trees ( LE t) was estimated using small weighing lysimeters and the Penman-Monteith equation, respectively. There was generally good agreement between ( A- H) and ( LE t+ LE u). LE t was strongly determined by stomatal conductance, vapour pressure deficit and leaf area index ( a t). Tree canopy conductances were of a similar magnitude in the two stands but were an order of magnitude less than corresponding values of aerodynamic conductance. In both stands, the daily contribution of LE u to forest LE was considerable. LE u was nearly equal to LE t in a 4-year-old stand which had not been pruned or thinned since establishment, but in a nearby 7-year-old stand, LE u was 30% less than LE t. In the 7-year-old stand, the presence of woody debris from pruning and thinning operations covering c. 60% of the understorey was responsible for the comparative reduction in LE u. Equilibrium LE u was estimated in the 7-year-old stand and overall was 43% less than measured LE u. Vertical wind statistics, determined near ground level in the relatively open 7-year-old stand, indicated that gusts regularly penetrated from above the forest to the understorey. These results suggest that forest management effects on the available energy and turbulence regimes below the tree canopy can be important determinants of LE u.

Influence of fertilizer timing on seasonal nutrient uptake and dry-matter production by young Pinus radiata in southern western Australia

Seasonal changes in above ground dry-matter, nitrogen (N), and phosphorus (P) accumulation were measured following application of N and P in autumn or spring to 1-year-old Pinus radiata (D. Don). Dry-matter production and nutrient accumulation were measured eight times over two years following fertilization. All trees produced dry-matter throughout the year, but during the summer, fertilized trees produced more dry-matter than unfertilized trees. In contrast to dry-matter production, nutrient accumulation showed a distinctly seasonal pattern with maximum accumulation of N and P occurring in winter and spring, when rainfall and soil moisture were highest. Accumulation of N and P either slowed markedly or ceased during summer depending on fertilizer treatment. Continued dry-matter production during summer, when nutrient accumulation was low, resulted in the decline of N and P concentrations in needles, branches and stems of all trees. This indicated that nutrients required for new growth during summer were mobilized from existing foliage and wood. Fertilization increased the concentrations of N and P in foliage and wood, and these higher concentrations persisted through summer. Spring fertilization increased N accumulation to a greater extent than autumn fertilization, this effect lasting two years. The greater dry-matter production by fertilized trees during summer indicated that growth during summer was limited by nutrient supply.

Interplay between nutrients, water, root growth and productivity in young plantations

Development of plantations from planting to canopy closure is characterised both by high vulnerability to competition and great opportunity for maximising production through innovative silviculture. To illustrate the links between process-based knowledge and management decisions, three key issues are analysed competition for site resources: opportunity for and consequence of rapid development of canopy during free-growing stage; and the production and configuration of the root system. Although empirical studies on weed competition have resulted in practical management prescriptions, further improvement calls for experiments in which the intensity of competition is manipulated and equal attention is paid to the dynamics of both water and nutrients. Even in relatively dry environments, intensive silvicultural practices can lead to rapid development of a stand and early canopy closure, which especially influences depletion and recharge of available soil water. The role of individual nutrients on canopy development and water-use efficiency at a stand level needs to be studied. New results suggest that fine-root production may not be a major sink for assimilates in young Pinus radiata stands grown under stressful conditions, and greater attention needs to be focused on root function in relation to root geometry and distribution in deeper parts of the profile.

Chemical control of epicormic shoots on 4 year oldPinus radiataD. Don

Summary Epicormic or adventitious shoots often develop in young Pinus radiata D. Don plantations following pruning and thinning operations. Chemical control of epicormic shoots was investigated in a trial near Busselton in the South West of Western Australia, as an alternative to mechanical or silvicultural means of removal. Diquat (200 g/1) applied at 3 ml/1 and monosodium methyl arsenate (800 g/1) applied at 24 ml/1 killed epicormic shoots without significantly affecting the health and growth of trees.

Role of weeds in the management of nitrogen in a young Pinus radiata plantation

Pinus radiata trees were grown on a podzolized sandy soil at a second rotation site under the following treatments: total weed control, total weed control plus ammonium nitrate, strip weed control and no weed control. During the first two summers after planting the differences in needle water potential between trees under no, strip or total weed control were very small. Despite similar rates of net N-mineralization in strip and total weed control treatments, which averaged 64 kg ha−1 yr−1 in the 0–15 cm soil depth, weeds in the strip weed control treatment reduced soil mineral-N concentrations by 50–80%, leaching of N by the end of the first growing season by 45%, foliar-N concentrations by 4–14% and stem biomass at 20 months after planting by 46%. Although N-uptake by above-ground vegetation (trees plus weeds) was 49% higher in the strip weed control treatment, the amount of N apportioned to trees during the first 20 months after planting was reduced from 15.5 to 9.0 kg ha−1. These effects of weeds were even more pronounced in the no weed control treatment. Since weeds had little effect on the needle water potential of trees and the annual rates of N-mineralization, but adversely affected N-uptake by trees, results indicate that weeds directly competed with trees for N, and thereby aggravated N-deficiency in trees. Application of ammonium nitrate after complete weed control increased foliar-N concentrations, and N-uptake and growth of trees, but also induced severe stem deformation.

An appraisal of the in situ soil-core technique for measuring nitrogen uptake by a young Pinus radiata plantation

N uptake by a weed-free Pinus radiata plantation growing on a sandy podzol between 8 and 37 months after planting was measured by an in situ soil-core technique and by biomass harvesting. As estimated by both techniques, N uptake ranged from 1 kg ha −1 between 8 and 15 months of age, to about 30 kg ha −1 between 26 and 37 months. There was close quantitative agreement between the two techniques for two of the four measurement periods, and reasonable and poor agreement for the other two periods. Over the entire 8–37 months, N uptake was estimated to be 61.6 and 51.2 kg ha −1 for the soil-core and harvest techniques, respectively. An ancillary experiment indicated that the frequency of core sampling (every 4–16 wk) did not greatly affect estimated rates of N mineralization. The in situ soil-core technique is useful for measuring annual N uptake by young P. radiata, but there is uncertainty about its value in estimating seasonal uptake.