Effects of nutrient loading and fertilization at planting on growth and nutrient status of Lutz spruce (Picea x lutzii) seedlings during the first growing season in Iceland

The low availability of nitrogen (N) is believed to be one of the major limiting factors of forest regeneration in Iceland and frequently under Boreal conditions. Lutz spruce (Picea x lutzii Littl.) seedlings were nutrient loaded using four fertilization regimes in the end of nursery rotation in autumn 2008 and planted in the following spring, with or without a single dose of fertilizer, on two treeless sites in N-Iceland with contrasting soil fertility. Measurements were made after one growing season. The highest loading level without additional field fertilization increased new needle mass by 122% and 152%, for the poor and more fertile site, respectively. The highest loading level with field fertilization increased new needle mass equally, by 188% and 189%, for the poor and more fertile site, respectively. Retranslocation of N, from old needles to current needles, increased with more loading. However, it was clear that nutrient loading could not replace field fertilization, as the seedlings generally showed an additive response to field fertilization and nutrient loading; doing both always gave the best results in seedling performance. As the study only covers field establishment during the first year, the long-term effect of nutrient loading of Lutz spruce cannot be predicted. However, it was concluded that loading might provide an additional input for faster plantation establishment during the first growing season after planting.     

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.     

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.     

Biomass and nutrient allocation in Douglas-fir and amabilis fir seedlings: influence of growth rate and nutrition

Allocation of biomass and nutrients to shoots and roots was followed for three years in fast and slow growing populations of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco), a fast growing pioneer species, and amabilis fir (Abies amabilis Dougl. ex J. Forbes), a slow growing shade-tolerant species. Seedlings were grown for three seasons in five nutrient treatments containing varying proportions of nitrogen and phosphorus (N:P). In both species, growth was greatest in the 250:20 N:P treatment followed by the 100:60 and 100:20 treatments. Vector analysis showed that, in both species, relative to the 100:20 treatment, seedlings in the 20:20 treatment were N deficient and seedlings in the 100:4 treatment were P deficient, i.e., where deficiency is defined to mean that an increase in nutrient supply increases nutrient content, nutrient concentration and plant dry weight. Seedlings in the 100:60 treatment had a higher P content than seedlings in the 100:20 treatment but the same dry weight, indicative of what Timmer and Armstrong (1987) termed luxury consumption. No nutrient retranslocation was observed in either species until the third growing season. In Douglas-fir, the greatest percentage of nutrients was exported from one-year-old shoots between May and July of the third growing season to support new growth. The total amount and percent of nutrients retranslocated was higher in Douglas-fir than in amabilis fir. Amabilis fir seedlings also exported N and P from older shoots, but this was later partially replenished. In both species, P retranslocation was greatest in treatments with a high N:P ratio. Nitrogen retranslocation was greatest in amabilis fir seedlings in treatments with a low N:P ratio, and greatest in Douglas-fir seedlings in the 250:20 and 100:60 treatments. Potassium retranslocation was correlated with seedling size. Douglas-fir retranslocated more of its shoot N reserves into new growth at the expense of older needles when soil fertility was high and sinks were strong. Otherwise, both species preferentially translocated the elements in short supply. Thus, retranslocation varied with the ecological characteristics of species, the relative availability of soil nutrients and sink strength.     

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.     

Premature shoot growth termination allows nutrient loading of seedlings with an indeterminate growth strategy

Nutrient loading of nursery seedling stock of species with an indeterminate growth strategy is challenging and poorly understood. Here, we explore the use of two potential techniques for nutrient loading of trembling aspen (Populus tremuloides Michx.) seedlings: (1) exponential fertilization and (2) early shoot growth termination in order to divert assimilated nutrients and carbon to storage rather than to growth. In the first study, aspen seedlings were treated with either exponential or constant fertilization rates, both of which supplied the same amount of nutrients over the growing season. Exponential fertilization resulted in overall poor planting stock form (stunted seedling growth and weak root development) and produced only marginal improvements of nutrient status. As a result, the exponential fertilization regime studied cannot be recommended as a treatment for aspen seedlings. In the second study we treated seedlings with a 2 × 2 factorial combination of fertilization and shoot growth inhibitor (SGI) applications with the fertilizer treatments varying in terms of mid-season fertilizer concentrations. Seedlings with SGI application had much higher tissue nutrient and carbon reserve concentrations than seedlings without a SGI application. In addition, nutrient uptake appeared to be more efficient in SGI treated seedlings, which could potentially result in significant reductions of nutrient application rates during aspen seedling production in nurseries. Overall, early shoot growth termination using a SGI appears to be an effective technique to produce nutrient loaded aspen seedlings.     

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.     

Growth, allocation and tissue chemistry of Picea abies seedlings affected by nutrient supply during the second growing season

One-year-old Norway spruce (Picea abies (L.) Karst.) seedlings were grown hydroponically in a growth chamber to investigate the effects of low and high nutrient availability (LN; 0.25 mM N and HN; 2.50 mM N) on growth, biomass allocation and chemical composition of needles, stem and roots during the second growing season. Climatic conditions in the growth chamber simulated the mean growing season from May to early October in Flakaliden, northern Sweden. In the latter half of the growing season, biomass allocation changed in response to nutrient availability: increased root growth and decreased shoot growth led to higher root/shoot ratios in LN seedlings than in HN seedlings. At high nutrient availability, total biomass, especially stem biomass, increased, as did total nonstructural carbohydrate and nitrogen contents per seedling. Responses of stem chemistry to nutrient addition differed from those of adult trees of the same provenance. In HN seedlings, concentrations of alpha-cellulose, hemicellulose and lignin decreased in the secondary xylem. Our results illustrate the significance of retranslocation of stored nutrients to support new growth early in the season when root growth and nutrient uptake are still low. We conclude that nutrient availability alters allocation patterns, thereby influencing the success of 2-year-old Norway spruce seedlings at forest planting sites.     

The effect of carbon and nutrient loading during nursery culture on the growth of black spruce seedlings: a six-year field study

We tested the effects of exponential nutrient loading and springtime carbon loading during nursery culture on the field performance of black spruce (Picea mariana (Mill.) B.S.P.). Seedlings were grown from seed with a conventional, fixed dose fertilizer (10 mg N seedling⁻¹) or an exponential nutrient loading regime (75 mg N seedling⁻¹). The following spring, seedlings were exposed for two weeks to either ambient (370 ppm) or elevated levels of CO₂ (800 ppm) and then planted in the field; seedling growth was followed for the next six years. Exponential nutrient loading increased seedling height, stem diameter and leader growth, with the largest increases in height and leader length occurring in the first three years after outplanting. Carbon loading increased seedling height and leader length, but only in seedlings that had been exponentially nutrient loaded. A combination of carbon and nutrient loading increased shoot height 26%, stem diameter 37% and leader length 40% over trees that received neither treatment. These results demonstrate that the growth enhancement seen under exponential nutrient loading is maintained under field conditions for at least six years. Carbon loading just before outplanting was a useful supplement to nutrient loading, but was ineffective in the absence of nutrient loading.     

Exponential nutrient loading: a new fertilization technique to improve seedling performance on competitive sites

Reforestation efforts in Ontario have become increasingly more reliant on containerized planting stock since these seedlings are less costly to produce and plant than bare-root stock. Container seedlings, however, tend to be more susceptible to competing vegetation when planted on weed-prone sites often requiring release by chemical herbicides. We have developed cultural techniques to improve the competitiveness of containerized seedlings by promoting initial outplanting performance thus reducing the need for early vegetation control. The approach is based on two new preconditioning practices, exponential fertilization and nutrient loading, which induce a steady-state build up of nutrient reserves in seedlings for outplanting. Exponential nutrient loading integrates these practices with high dose fertilization inducing luxury consumption. Steady-state culture corresponds better with the competitive outplanting environment, since stable internal nutrient accumulation in the greenhouse phase conforms with steady-state nutrient uptake of natural exponentially growing vegetation in the field, and exponential nutrient delivery to container-restricted root systems also better simulates nutrient flux reached by expanding roots in a field soil with constant nutrient availability. Combined with nutrient loading, the higher nutrient reserves and improved nutrient balance in seedlings contribute to enhanced stress resistance and increased growth performance. This paper reviews the theory and practice of exponential nutrient loading during seedling culture, presents results of growth and nutritional responses of seedlings planted on competitive sites, and suggests appropriate criteria for quality testing of nutrient loaded stock.     

Steady-state nutrition of Pinus resinosa seedlings: response to nutrient loading, irrigation and hardening regimes

To test effects of fertilization on late-season growth and nutrient content of container-grown red pine (Pinus resinosa Ait.), seedlings were subjected to a factorial combination of two fertilization regimes (exponentially increasing concentrations providing 25 (1N) and 75 (3N) mg N seedling(-1), respectively) and two irrigation regimes (well-watered and water-stressed) followed by drought-hardening or nonhardening. The fertilization treatments gave rise to steady-state nutrition in the seedlings during the prehardening phase. The 3N treatment increased macronutrient uptake significantly more than dry matter production, particularly in the roots, giving rise to what has been called luxury consumption of nutrients, or nutrient loading. Nutrient loading was higher in well-watered seedlings than in water-stressed seedlings. Among well-watered seedlings, relative growth rate of nutrient-loaded seedlings was more sensitive to drought during the hardening phase than that of nonloaded seedlings. However, when watering was resumed at the end of the hardening treatment, the relative growth rate of the nutrient-loaded seedlings (421%) exceeded that of the nonloaded seedlings (213%). Nitrogen accumulation was also higher in nutrient-loaded seedlings than in nonloaded seedlings during the post-hardening phase.     

Fall fertilization enhanced nitrogen storage and translocation in Larix olgensis seedlings

Fall nutrient loading of deciduous forest nursery seedlings is of special interest because of foliage abscission and varied translocation patterns. For non-deciduous seedlings in the nursery, fall fertilization typically can reverse nutrient dilution and possibly increase nutrient reserves; however, this technique has received little attention with deciduous conifer trees that translocate nutrients before abscising foliage. We evaluated how fall nitrogen (N) fertilization affected N storage and translocation in the deciduous conifer Olga Bay larch (Larix olgensis Henry) seedlings during the hardening period. Seedlings were supplied with 25 mg N seedling^?1 for 15 weeks before hardening and fall fertilization treatments began with a three week application period of K¹⁵NO₃ at 0, 5, 10 and 15 mg N seedling^?1. During the hardening period, fall N fertilization had little effect on seedling morphology. The N concentration and content of needles decreased dramatically as needles abscised, while that of stems and roots increased. Six weeks after fall N fertilization ceased, all seedlings translocated similar net N from their needles. For the control seedlings, this accounted for 84 % of the N stored in stems and roots. For fall fertilized seedlings, however, the proportion of N stored in stems and roots translocated from needles accounted for only 41–61 % of the total because of absorption of fall fertilizer that was translocated directly to stems and roots. Six weeks after fall fertilization, the distribution pattern of N concentration and content in seedlings was found in this order: stems > fine roots > coarse roots > needles. Our results suggest that providing deciduous conifer seedlings N during hardening, in this case Olga Bay larch, is a way to promote nutrient loading during nursery production.     

Field Performance of Three Stock Sizes of Douglas-fir Container Seedlings Grown with Slow-release Fertilizer in the Nursery Growing Medium

Containerized coastal Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) seedlings were grown with conventional soluble fertilizer and supplemented with one of four slow-release fertilizers (SRF treatments) or unsupplemented (control treatment). Seedlings were outplanted to two sites in 1998. At the time of outplanting, SRF incorporated into the growing medium resulted in larger seedlings with higher foliar nutrient concentrations as compared to conventionally fertilized seedlings. After four growing seasons, SRF-amended seedlings at both sites had significantly greater height, basal stem diameter, and stem volume, with increases up to 19, 21, and 73%, respectively, as compared to conventionally fertilized seedlings. Additionally, three stock sizes were compared at one of the sites. Increasing stock size resulted in increased growth during the first two seasons, enabling larger stock to maintain their size advantage. Seedling responses to SRF are attributed to larger initial size, increased internal nutrient reserves at planting, and continued fertilization after planting.     

A strategy for tree-perennial crop productivity: nursery phase nutrient additions in cocoa-shade agroforestry systems

Shade tolerant species response to nutrient additions and light regulation by canopy trees in perennial agroforestry systems has been well documented. However, accelerated early growth, particularly in cocoa-shade systems, may be offset by competition for limited resources on nutrient poor sites. To date, few agroforestry management strategies focus on nutrient manipulation of the shade tree component or strategies for precision nutrient application. Our research objective was to diagnose interactions between nutrient supplied shade trees intercropped with cocoa. We established greenhouse trials in Kwadaso, Ghana cultivating Terminalia superba seedlings with four fertility treatment levels: conventional rate (current practices) under linear additions, and half, full and double conventional rate under exponential additions (steady-state nutrition) to determine maximal growth and nutrient uptake. After 4 months of additions in the nursery, pre-fertilized T. superba seedlings were then out-planted into field trials with cocoa seedlings. After 4 months of intercropping, cocoa associated with half rate exponentially supplied T. superba had significantly larger leaf area, greater leaf number, and higher nutrition (N and P uptake) than cocoa associated with full rate conventionally supplied T. superba. This may be attributed to (1) more favorable light conditions under these taller shade seedlings and (2) the internal use of nutrients associated with exponentially supplied T. superba seedlings, which lowered stress on native soil resources. The latter is corroborated with our findings on soil fertility status. This strategy focused on reducing fertilizer inputs and developing precise plant nutrition technology for on-farm use. Our findings suggest that shade seedlings under steady state nutrition can mitigate early growth competition in the field.     

First-year growth response of cold-stored,nursery-grown aspen planting stock

This research examined the first year growth characteristics of cold stored and transplanted nursery-produced aspen (Populus tremuloides) seedlings (container and bareroot (BR)) and compared it to the growth of seedlings that had not been transplanted (established from germinants in the field) and therefore had an unrestricted root system (UR). Prior to planting, nursery-produced seedlings were placed in cold storage (−3°C) and root growth potential (RGP) and total non-structural carbohydrate (TNC) root reserves were tested at 0, 10, 75 and after 150 (container) and 190 days (BR) of storage. Both container and BR stock had much lower root to shoot ratios (RSRs) and root carbohydrate reserves compared to UR seedlings after 170 days. During storage, root reserves in container stock declined faster than in the BR and UR seedlings. RGP in all nursery stock was the highest after 75 days of storage, while longer storage resulted in shoot dieback and reduced root growth. After the first growing season, UR seedlings were one tenth the size of the nursery stock; however, in the second growing season they had no stem dieback and grew twice the height and stem diameter. The higher RSRs and root reserves in the UR seedlings was likely caused by early bud set in its first year of growth. This suggests that inducing bud set earlier in the growing regime might allow seedlings to increase root mass and carbohydrate reserves.     

Nutrition and bud removal affect biomass and nutrient allocation in Douglas-fir and western red cedar

Seedlings of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) and western red cedar (Thuja plicata J. Donn ex D. Don) were grown at high (250 mg l(-1)) and low (20 mg l(-1)) nitrogen (N) supply for a year. Before the second growing season, half of the seedlings in each nutrient treatment were allocated to the other treatment. Half of the seedlings in each nutrient treatment then had all growing points removed. Biomass and N, phosphorus (P) and potassium (K) concentrations of old and new shoots and roots were measured three times in the second year to test the interaction of current-year and previous-year nutrient supply on biomass and nutrient allocation in these two species with different growth habits. Pruned seedlings served as controls. Unpruned seedlings of both species increased in height throughout the second growing season, except for Douglas-fir in the N250 --> N20 treatment. Repeated pruning did not prevent new shoot growth, but resulted in a 12 to 52% reduction in biomass of new shoots and new and old roots. Seedlings receiving a low N supply in the first growing season were more severely affected by pruning than seedings receiving a high N supply. Growth was reduced more by pruning in western red cedar than in Douglas-fir. Concentrations of N, P and K were higher in pruned seedlings than in unpruned seedlings. Although dry weights of all plant parts in all treatments increased throughout the second growing season, some retranslocation of N, P and K was observed from old shoots of both species in the N250 --> N20 and N20 --> N20 treatments after August. Quantities of N, P and K retranslocated were greatest in seedlings grown the previous year in the high-N treatment.     

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.     

Fall fertilization of Holm oak affects N and P dynamics,root growth potential,and post-planting phenology and growth

• Introduction   

For Holm oak (Quercus ilex L.), a flush growing species, nutrient loading during the growing season is difficult and can lead to a low nutrient status of the seedlings. To provide insights about Holm oak nutrient dynamics during fall in the nursery and subsequent planting performance, a factorial nursery experiment was conducted in a mild fall–winter area testing the effects of timing of fertilization (early and late fall) and rate (two doses of a NPK fertilizer that applied 28 and 56 mg N per seedling), followed by an experimental plantation.     

Organic matter amendments to a calcareous forest nursery soil

Organic amendments were added to a southwestern United States forest nursery sandy loam soil to determine the effects on soil nutrient reserves and subsequent growth of 1.5+0 ponderosa pine (Pinus ponderosa Laws.) seedlings. Treatments included irradiated sewage sludge, peat moss and pine bark each at 67 t/ha, sawdust at 43 t/ha, and a control that received no organic matter. Sludge caused immediate increases in soil nutrients, especially N and P. Sawdust resulted in near complete N immobilization 45 d after application. Peat moss and bark did not significantly alter soil nutrients. All treatment effects disappeared within 6 months of application.Amendments did not significantly alter seedling survival, biomass or yield (caliper 3 mm). Seedling biomass was positively correlated with early soil nutrient status, but growth was not significantly improved. The modest, short-term nutritional benefits indicate single applications of organic amendments are ineffective in improving the nutrient status of sandy nursery soils of the Southwest.     

林业苗圃地连作和轮作对苗木生长及土壤肥力影响的研究

研究了林业圃地连作与轮作培育杉木、酸枣、厚朴等苗木的生长状况及土壤肥力的变化。结果表明:用水稻等作物与杉木轮作后,杉木苗生长状况改善,土壤有效养分和速效养分增加。