Differential foliar responses of northern hardwoods to fertilization

A 70-year-old thinned northeastern Fagus-Betula-Acer stand in the Adirondack Mountains of northern New York was fertilized with varying combinations of N, P, K, and lime in the spring of 1976.Betula alleghaniensis Brit.,Acer saccharum Marsh.,Acer rubrum L., andFagus grandifolia Ehrh. foliage was collected in the autumn for 1974 through 1977 and analyzed for foliage areas and weights, and levels of ash, N, P, K, Ca, Mg, Mn, Na, Fe, Zn, Al, Cu, and Co. Comparisons are made within species and among treatments, expressed as concentrations on a dry weight basis. Elemental composition is examined to determine the differential foliar responses to fertilization.Contribution of State University of New York College of Environmental Science and Forestry, Syracuse, New York, 13210.The authors are Graduate Research Assistant, Director of Huntington Forest, Technical Research Assistant, and Professor of Forest Soil Science (now deceased), SUNY, respectively.     

The growth and nutrients status of conifers on ash-treated cutaway peatland

Key message

Use of wood ash or a mixture of wood and oil shale ashes increases the concentrations of P and K in the assimilation organs of conifers and stimulates tree growth.

Abstract

The effect of fertilization with wood ash (10 and 15 t ha^?1) and a mixture of wood ash (10 t ha^?1) and oil shale ash (8 t ha^?1) on the growth (height, root collar diameter, biomass, biomass production) and nutrient concentrations in subsoil and needles of young Pinus sylvestris and Picea abies plants on the Puhatu (Northeast Estonia) cutaway peatland in the first 2 years were studied. After the second growing year differences in the average height growth of P. abies and P. sylvestris were statistically significantly higher on ash-treated plots than on the control plots (p < 0.05), being respectively 1.4–1.6 and 1.5–1.7 times greater than height growth of the control trees. The best results on root collar diameter were observed on mixture ash treatments: the root collars were 1.9 (P. abies) and 2.2 (P. sylvestris) times larger than of the control trees. The biomass of the two conifer species and the biomass production of P. sylvestris in 2012 was the greatest on the mixture ash treatments. Five months after fertilization with ashes the concentrations of P, K, Ca and Mg were higher on the treated plots than on the control plot. Although the concentrations of P and K in P. sylvestris needles rose after the treatment with ash, seedlings suffered from P and K deficiency. The concentrations of P and K in P. abies needles were on optimum. The P/N and the K/N ratios in needles were also improved compared to control trees needles.     

The growth and nutrient uptake of winter wheat

Summary Measurements with an ion selective electrode under winter wheat and in adjacent fallow soil, from April to July 1976, showed that nitrate concentrations were high in the 0–25 cm zone and correspondingly lower at 50 cm, because of the extreme drying conditions. Maximum differences in nitrate concentrations between cropped and fallow soil occurred at Feekes' stages 6, 10, and 11.1 indicating periods of maximum uptake by the crop (cf Ref.⁴).Dry matter weight of wheat, sampled biweekly, was maximum 15 days before maturity. The foliage senesced and lost weight from Feekes' stage 10.1 onwards. Nutrient concentrations in the foliage decreased from Feekes' stage 4, but N, P and Mg concentrations in the ears increased during Feekes' stage 11. N, P and Mg accumulated in the ears at the expense of the foliage during stage 11, maximum uptake occurring at stages 11.3, 11.1 and 11.2 respectively. In contrast, K and Ca uptake ceased at stages 10.1 and 10.5 respectively and then both were lost from the foliage in heavy showers.Rates of N uptake and soil nitrate depletion correlated significantly, enabling N uptake to be deduced approximately from thesein situ soil nitrate measurements.     

Effects of food quality,particularly nitrogen concentrations,of Eucalyptus blakelyi foliage on the growth of Paropsis atomaria larvae (Coleoptera: Chrysomelidae)

Five groups of E. blakelyi seedlings were differentially fertilized to obtain a range of N concentrations from 0.8–3.0% dry wt in the foliage. Groups of P. atomaria larvae were reared from eclosion to the prepupal stage on these seedlings. The effects on larval growth and development caused by foliar concentrations of N, moisture content, and tannins and leaf toughness were measured. Pupal dry weight and development time of P. atomaria did not differ between those reared on foliage with N levels of 1.7–3.0% but there was a significant decrease in pupal weight and increase in development time for individuals fed foliage with N below this level. Larvae fed foliage with an average of 0.8% N died before reaching instar III. Total dry matter consumption increased with a decrease in N concentration. Larval nitrogen utilization efficiency increased as foliar N level decreased until N reached a level somewhere between 1.7%–1.2% below which it decreased. There appeared to be an N concentration threshold above which P. atomaria larvae received adequate N by regulating consumption and nitrogen utilization efficiency but below which they could no longer accumulate enough N by compensation to maintain an optimum growth rate and development time. Effects of food quality variables on relative growth and consumption rates are presented and discussed.     

High nitrogen deposition may enhance growth of a new hybrid larch F1 growing at two phosphorus levels

A recently developed hybrid larch F₁ (F₁: Larix gmelinii var. japonica × L. kaempferi) is being planted widely in re- and afforestation projects in northeast Asia. Nitrogen (N) deposition to forest ecosystems has been rapidly increasing in this region, due mainly to industrialization and overuse of N fertilizer. Together with excess N, phosphorus (P) is considered to be the key determinant of tree growth in northeast Asia, because most soils have originated from immature volcanic ash. To predict the response of the F₁ to increasing N deposition and its relation with soil P availability related to immature volcanic ash soil in northern Japan, planting stocks of F₁ were grown in potted brown forest soil and categorised into eight treatments, comprising four N treatments covering the amount of N deposition observed and predicted in northeast Asia in combination with two P levels. N application increased the biomass and the light-saturated net photosynthetic rate (A _sat) of the F₁ at all concentrations. Despite expectations, P did not have any effect on these parameters. As N application increased the content of potassium (K), magnesium (Mg) and chlorophyll (Chl) in needles, a positive correlation was found between the content of N, K, P and A _sat. These results suggest that N deposition improves the growth of the hybrid larch F₁ at least by improving the needle N condition, as well as the concentration of other macronutrients in the initial stage of plantation.     

Changes in carbon, nutrients and stoichiometric relations under different soil depths, plant tissues and ages in black locust plantations

To investigate influences of forest plantations on soil nutrient properties, biomass accumulation, major nutrient elements (NPK) and their stoichiometric couplings in different tissues and aged plants, and correlations between major nutrient contents in soils and in foliage of plants, 5-, 10-, 15- and 20-year-old plantations of black locust (Robinia pseudoacacia L.) and farmland were selected. Black locust plantations increased soil organic carbon (SOC) and N stocks by 23–327 and 23–119 %, respectively, in the 0–10 cm top soil layer compared to those in farmland. Soil C:N, C:P, C:K, N:P, N:K and P:K ratios were 10.1, 22.9, 0.7, 2.2, 0.7 and 0.03, respectively. These ratios were higher in the 0–10 cm soil layer than those in the 10–20 cm soil layer and increased under older plantations. Higher C contents in stem, N contents in leaf, the largest C pools in stem and N pools in root in 20-year-old plantation were observed. Correspondingly, the highest C:N, C:P and C:K and the lowest N:P and N:K ratios in stem, decreased C:N and C:P ratios in older trees were found. No strong correlations were observed between element contents in soils and in leaves of black locust trees. These results suggest that black locust plantations can increase soil nutrient concentrations, SOC and N stocks resulting in changes in element stoichiometric relations. CNPK contents and their stoichiometries vary with tissues and tree ages of black locust. No strong coupling relations exist between major nutrient element contents in the top soil and in foliage of black locust.     

The effect of fire on nutrient losses and cycling in aQuercus coccifera garrigue (southern France)

The effects of burning on plant nutrient budgets and rates of carbonic gas and particulate matter emission during fires were evaluated in aQuercus coccifera (garrigue) shrubland. Nutrient levels were determined in field-collected pre-fire vegetation and combustion residues. The losses (increased elemental transfer) were calculated as the difference between the quantity of an element in the fuel (combustible standing vegetation plus litter) before burning and that present in the postfire residues (ash). Weight losses of elements are correlated with weight losses of burnt plant biomass. The relative order of nutrient losses was: N>C>Na>Ca>P>K>Mg. Estimated losses of N, C and P from combustible plant matter exceeded 98, 97 and 79% respectively. Copious N, C and P volatilization during burning was promoted by high concentrations of these elements in foliage and fine woody biomass of the aboveground vegetation and leaf litter of the garrigue. Elements were principally removed in the smoke. The quantities of gaseous emissions of CO₂, CO and particulate matter produced were estimated.     

The Expression of Interionic Relationships in Pinus elliottii

The effects of factorial combinations of N, P and Mg on some of the interrelationships among nutrient ions as they occurred in seedlings of slash pine were investigated. In similar studies, true interactions have not always been differentiated from apparent interactions, the result of comparing foliage concentrations in plants with widely divergent growth rates. To prevent this, nutrient solutions were formulated to produce conditions ranging only from slight deficiency through luxury consumption. This relatively narrow range of nutrition allowed actual interactions to be separated from those changes in foliage concentration that are primarily a result of large differences in growth.

The needles were analyzed for total and soluble N and total P, K, Ca, Mg and Na. Each level of each nutrient variable had a significant effect on the concentration of 1 or more dissimilar elements. The familiar depressive effect of N on foliar P was observed; however this relationship was shown to be primarily the result of growth dilution rather than anion antagonism. Increased Mg did antagonistically reduce the uptake of Ca and, generally, K. Increments of P not required for growth stimulated uptake of N, Ca, Mg and K. No relationship was found between Mg supply and P accumulation.

     

Post-fallow decomposition of woody roots in the West African savanna

Potassium (K), calcium (Ca), iron (Fe) and aluminium (Al) release from Norway spruce (Picea abies Karsten), Scots pine (Pinus sylvestris L.) and silver birch (Betula pendula Roth.) logging residues (fine roots, foliage and small branches) were studied by means of litterbags over a period of three years in clear-cut area and adjacent uncut Norway spruce dominated mixed boreal forest in eastern Finland (63°51′ N, 28°58′ E, 220 m a.s.l) to determine the amounts and rates of release for these elements and to evaluate whether clear-cutting accelerates mineralization. Almost all K was released from logging residues already during the first year. Calcium was released from foliage and roots but accumulated in branches. Most of the roots Fe and Al content were released during three years while the absolute amounts of Fe and Al in branches and foliage generally increased with decomposition. The results indicate that mineralization is slightly accelerated as a result of clear-cutting since K from foliage and branches of all studied tree species and Ca from pine and spruce roots was released significantly faster at the clear-cut plot than at the forest plot. In three years the initial K pool in the logging residues declined by 90%, Ca by 8%, Fe by 55% and Al by 61% in the clear-cut area. These results indicate that Ca is retained a long time; but Fe, Al and in particular, K are soon released from logging residues. Fine roots of the logged trees release large amounts of Fe and Al and can significantly affect Fe and Al fluxes.     

Combustion influences on natural abundance nitrogen isotope ratio in soil and plants following a wildfire in a sub-alpine ecosystem

This before-and-after-impact study uses the natural abundance N isotope ratio (δ¹⁵N) to investigate the effects of a wildfire on sub-alpine ecosystem properties and processes. We measured the ¹⁵N signatures of soil, charred organic material, ash and foliage in three sub-alpine plant communities (grassland, heathland and woodland) in south-eastern Australia. Surface bulk soil was temporarily enriched in ¹⁵N immediately after wildfire compared to charred organic material and ash in all plant communities. We associated the enrichment of bulk soil with fractionation of N during combustion and volatilization of N, a process that also explains the sequential enrichment of ¹⁵N of unburnt leaves > ash > charred organic material in relation to duration and intensity of heating. The rapid decline in ¹⁵N of bulk soil to pre-fire values indicates that depleted ash, containing considerable amounts of total N, was readily incorporated into the soil. Foliar δ¹⁵N also increased with values peaking 1 year post-fire. Foliar enrichment was foremost coupled with the release of enriched NH₄ ⁺ into the soil owing to isotopic discrimination during volatilization of soluble N and combustion of organic material. The mode of post-fire regeneration influenced foliar ¹⁵N enrichment in two species indicating use of different sources of N following fire. The use of natural abundance of ¹⁵N in soil, ash and foliage as a means of tracing transformation of N during wildfire has established the importance of combustion products as an important, albeit temporary source of inorganic N for plants regenerating after wildfire.     

Needle chemistry in young Norway spruce stands after application of crushed wood ash

Nutrient concentrations in current and 1-year-old needles were analyzed annually for 5 years after application of hardened wood ash in 1–4-year-old Norway spruce (Picea abies (L.) Karst.) stands within a range of climate and fertility gradients. At each site, 3000 kg ha^–1 hardened wood ash of two types, Nymölla and Perstorp, was applied in a randomized block design. Wood ash Nymölla contained 12 kg ha^–1 P, 30 kg ha^–1 K, 891 kg ha^–1 Ca, 72 kg ha^–1 Mg and wood ash Perstorp contained 12 kg ha^–1 P, 60 kg ha^–1 K, 486 kg ha^–1 Ca, and 60 kg ha^–1 Mg. The ash was intended to compensate for nutrients removed at the preceding harvest when logging residues were collected and removed from the site (whole-tree harvesting). The climate gradient included four climate zones throughout Sweden and each of these included a fertility gradient of three sites classified according to their ground vegetation type. There were no effects on nutrient concentrations in the needles 1 year after the application of wood ash. Five years after ash application, the concentrations of P, K and Ca in current and 1-year-old needles were higher than in the control plots. The results were consistent over all stands, irrespective of climate zone and fertility status. P and K concentrations were higher in spruce needles from plots treated with Perstorp wood ash, whereas Ca concentrations were higher in those of Nymölla treated plots. Analyses across all study sites revealed a treatment effect in terms of increased ratios of P:N, K:N and Ca:N in 1-year-old needles. The ratio P:N tended to increase with time in the Perstorp wood ash treatment compared with the control. The needle concentrations of Mg and S were not affected by the ash applications. The increase in needle nutrient concentrations after application of hardened wood ash suggests that wood ash recycling could be used in order to replace nutrients removed at whole-tree harvesting.     

Growth and uptake of N,P, K and B by Pinus radiata D. Don in response to applications of borax

Leader dieback associated with B deficiency in P. radiata D. Don plantations was treated with borax applied at rates of 50, 100 and 150 kg ha⁻¹. This initially increased B in foliage from 5 to 40, 80 and 110 μg g⁻¹ respectively, and was followed by a rapid decline and stabilisation at around 25 μg g⁻¹ for the duration of the study. Annual fluctuations in foliage B levels were strongly correlated with rainfall during the preceding spring and summer. Uptake of N, P and K increased as a result of applied B and comparison of the distribution of these nutrients in crowns of fertilized and unfertilised trees six years after application indicated continued uptake of these nutrients probably as a result of improved root growth due to B. Foliage concentrations of B like N, P and K, increased in young needles towards the upper crown and this, together with a decline in needle concentrations of B as foliage aged, indicated some redistribution of B from older to new foliage. A limit of 5 μg g⁻¹ was found below which little redistribution seems to occur. Application of B prevented further leader dieback, improved apical dominance and height growth and increased volume production by 25 m³ ha⁻¹ at age 8 years. Differences between application rates of B were not significant in terms of growth.     

Nutrient Distribution Indicated Whole-Tree Harvesting as a Possible Factor Restricting the Sustainable Productivity of a Poplar Plantation System in China

We evaluated the biomass and contents of five major macronutrients (N, P, K, Ca and Mg) in 10-year-old poplar trees (Populus deltoids Bartr. cv. “Lux”), and determined their nutrient use efficiencies (NUEs) at Zhoushan Forestry Farm (32°20′ N, 119°40′ E), Jiangsu province, in eastern China. The above- and below-ground biomass of poplar trees was 161.7 t ha^-1, of which 53.3% was stemwood. The nutrient contents in the aboveground part were as follows: 415.1 kg N ha^-1, 29.7 kg P ha^-1, 352.0 kg K ha^-1, 1083.0 kg Ca ha^-1, and 89.8 kg Mg ha^-1. The highest nutrient contents were in stembark, followed by branches, roots, stemwood, and foliage. The NUEs of the aboveground parts of poplar for N, P, K, Ca and Mg were 0.313, 4.377, 0.369, 0.120, 1.448 t dry biomass kg^-1 nutrient, respectively, while those of stemwood were 1.294, 33.154, 1.253, 0.667, and 3.328 t dry biomass kg^-1, respectively. The cycling coefficients, defined as the percentage of annual nutrient return in annual nutrient uptake, of N, P, K, Ca and Mg for the aboveground part were 87, 95, 69, 92, and 84%, respectively. Based on the NUE and nutrient cycling characteristics, shifting from whole-tree harvesting to stemwood-only harvesting and appropriately extending the harvest rotation could prevent site deterioration and support sustainable productivity of poplar plantation systems.     

锐齿栎林个体光合器官生长与营养季节动态

锐齿栎林单叶面积和干重的季节生长呈不同的S型曲线,叶面积叶干重比的季节变化呈不完全S型.叶从萌动到落叶持续约160d,展叶第1周,叶重量绝对增长快于叶面积的增加,之后相反.叶季节变化表现为叶面积增长迅速且持续时间较短,叶重量增加相对缓慢且持续时间较长.刚展叶时N、P、K含量很高,展叶期明显下降,落叶前最低,Ca含量季节变化则相反;Mg含量展叶期较高,之后逐渐下降且趋于稳定.叶N、P、K、Mg间呈显著的正相关,前者与Ca间呈显著的负相关.叶在生长期内具有较高的N/P、N/K,且其季节变化比单个元素含量更稳定;展叶初期K/Ca很高,之后变化逐渐稳定;叶K/Mg的季节变化趋于降低.展叶第1周叶N、P、K和Mg积累量迅速增加,继而缓慢增加,第45～50天达峰值,之后逐渐降低;Ca积累随叶龄的增加一直处于上升的趋势.叶内N、P、K、Mg和Ca积累量与叶的生长发育期有密切的关系.     

生态恢复对马尾松叶片化学计量及氮磷转移的影响

为了解生态恢复对侵蚀红壤恢复的马尾松林叶片碳氮磷化学计量及氮磷养分转移的影响,在福建省长汀县河田镇典型侵蚀红壤区选取恢复13、30、33a的马尾松林为研究对象,并以未治理侵蚀地(CK1)和次生林(CK2)分别作为恢复前和恢复后的对照,通过测定马尾松叶片的碳、氮、磷含量,计算其计量比,内稳性指数和氮磷转移率,分析了侵蚀红壤生长的马尾松养分限制与养分转移的关系。结果表明:在侵蚀红壤恢复过程中,马尾松1年龄叶片C、N、P含量及1年龄叶片C∶N、C∶P、N∶P变化较小,这与马尾松较高的内稳性有关(N和P内稳性指数分别为7.57和3.89)。所有实验地马尾松1年龄叶片N∶P处于11.0—13.4之间,表明马尾松的生长受N、P共同限制,其中马尾松叶片N转移率显著低于P转移率,这与生态恢复过程中马尾松养分利用效率、生长需求以及土壤养分供应状况有关。1年龄叶片C∶N、C∶P分别与马尾松N、P转移率成负相关关系,当马尾松叶片C∶N、C∶P较低时,表明N、P利用效率较低,叶片衰老时更多的N和P被转移利用;反之,则N、P利用效率较高,转移率低。同时,C∶N、C∶P分别与树高、胸径成显著负相关关系,即马尾松生长对N、P的需求同样会影响化学计量比的变化,从而影响养分转移。虽然侵蚀地生态恢复过程中土壤N、P含量增加,但仍较贫瘠,不足以满足马尾松的生长,马尾松养分转移率较高,因此,为了提高侵蚀地恢复的马尾松林的生产力,建议下一步恢复措施中适当施加N肥和P肥。该研究将侵蚀红壤不同生态恢复年限的马尾松叶片C、N、P化学计量及养分转移结合,有助于全面、系统地揭示生态恢复过程马尾松林的养分循环,对指导侵蚀红壤恢复和提高马尾松生产力具有重要意义。     

Determinants of tree species preference for foraging by insectivorous birds in a novel Prosopis–Leucaena woodland in Puerto Rico: the role of foliage palatability

The foliage palatability hypothesis predicts that avian insectivores will preferentially forage in tree species with the greatest abundance of their arthropod prey, which in turn are associated with the tree’s foliage nutrition and palatability. We tested this hypothesis in a novel Prosopis–Leucaena woodland in Puerto Rico by determining foraging preferences of five insectivorous bird species for six tree species (five alien, one native) and relating preferences to foliage arthropod biomass and leaf chemistry. The most frequently preferred tree species for foraging were the alien Prosopis juliflora (preferred by five bird species) and Pithecellobium dulce (preferred by four bird species). Both species had high foliage arthropod biomass, high N content, low lignin/N ratios, and low hemicellulose content. Compounds, previously known to affect herbivore responses to Albizia lebbeck and Leucaena leucocephala, may explain low arthropod biomass despite high N content in Albizia and avoidance of Leucaena by four bird species despite its high arthropod biomass. The native Bucida buceras had tough leaves with low N content, low arthropod biomass, and only one bird species showed a weak preference for foraging in it. Biomass of predaceous arthropods showed strong negative correlations with the ratios of lignin/N and hemicellulose/N. Some alien tree species had highly palatable foliage with high arthropod biomass and hence were preferred for foraging by avian insectivores as predicted by the foliage palatability hypothesis. High foliage palatability of some alien tree species may weaken the effect of enemy release in some novel plant communities.     

Towards Miscanthus combustion quality improvement: the role of flowering and senescence

In commercially grown Miscanthus × giganteus, despite imposing a yield penalty, postwinter harvests improve quality criteria for thermal conversion and crop sustainability through remobilization of nutrients to the underground rhizome. We examined 16 Miscanthus genotypes with different flowering and senescence times for variation in N, P, K, moisture, ash, Cl and Si contents, hypothesizing that early flowering and senescence could result in improved biomass quality and/or enable an earlier harvest of biomass (in autumn at peak yield). Ideal crop characteristics at harvest are low N and P to reduce future fertilizer inputs, low K and Cl to reduce corrosion in boilers, low moisture to reduce spoilage and transportation costs, and low Si and ash to reduce slagging and consequent operational downtime. Stems and leaves were harvested during summer, autumn and then the following spring after overwinter ripening. In spring, stem contents of N were 30–60 mg kg^?1, P were 203–1132 mg kg^?1, K were 290–4098 mg kg^?1, Cl were 10–23 mg kg^?1 and moisture were 12–38%. Notably, late senescence resulted in increased N, P, K, Cl, moisture and ash contents, and should therefore be avoided for thermochemical conversion. Flowering and senescence led to overall improved combustion quality, where flowered genotypes tended towards lower P, K, Cl and moisture contents; marginally less, or similar, N, Si and ash contents; and a similar higher heating value, compared to those that had not flowered. Such genotypes could potentially be harvested in the autumn. However, one genotype that did not flower in our trial exhibited sufficiently low N and K content in autumn to meet the ENplus wood pellet standards for those traits, and some of the lowest P, moisture and ash contents in our trial, and is thus a target for future research and breeding.     

Nutrient requirements of exotic tree species in Zimbabwe

Pot and field experiments were conducted in the greenhouse and at three field sites (Marondera, Domboshawa and Makoholi) in Zimbabwe to examine the effects of soils and fertilizers on nutrient uptake and growth of 6 exotic tree species (Eucalyptus camaldulensis, E. grandis, E. tereticornis, Leucaena leucocephala, Casuarina cunninghamiana, and Acacia holosericea). Plant growth, N and P contents of all species were increased by the application of N, P, K and micronutrient fertilizers. The effect of individual nutrients (N, P, K and micronutrients) and their combination on Eucalyptus species was further investigated in a pot experiment using soil from Domboshawa. Eucalyptus species responded only to N application and no significant interactions were found between N and the other elements. Nutrient uptake results showed that E. camaldulensis and E. tereticornis removed more cations than the N-fixing trees but only in the fertilized treatments. L. leucocephala and C. cunninghamiana were higher in P, but no clear trends were observed for N. Plant growth and nutrient uptake by E. camaldulensis. C. cunninghamiana and A. holosericea were assessed in the field at the three sites. Plant species grown in the Marondera site had greater height and diameter at breast height (DBH) than those in the two other sites. These results followed trends in soil nutrient contents. The analysis of foliage revealed differences in the nutrient concentration of leaves from different trees, but no effect of site was found. The interrelationships between plant characteristics, soil and foliage nutrients were examined. In a pot experiment, mineral N was the only variable correlated with growth response and nutrient uptake, while in the field the only significant correlation was obtained with soil pH.     

Effectiveness of wood ash containing charcoal as a fertilizer for a forest plantation in a temperate region

Amendment of forest soils with mixed wood ash (MWA) generated in biomass power plants can prevent the depletion of soil nutrients that results from the intensive harvesting of forest plantations. Unlike fly wood ash, MWA contains charcoal and is characterized by a lower release of nutrients, so that it might be useful as a long term source of nutrients and soil organic matter. However, in order to use MWA as a fertilizer in forest systems, its effectiveness as regards supplying P and N must be improved. These aspects were studied in a 4 year-trial carried out in a Pinus radiata plantation. MWA was added alone or with mineral P, and the results were compared with those obtained with a combination of Ca(OH)₂ and mineral P. The application of MWA together with mineral P fertilizer increased the nutrient supply to the trees, as revealed by the changes in nutrient concentrations, lower values of resorption efficiencies and improved tree growth. The results showed that the amounts of Ca, Mg and K supplied by the MWA were suitable for maintenance of soil reserves. However, the presence of charcoal may have decreased the availability of P. The application of the MWA led to lower soil N mineralization rates and mineral N concentrations, which may affect N-limited systems. The use of density-dependent single tree increment models enabled the positive effects on tree growth of fertilization and thinning to be distinguished. For the treatments supplemented with mineral P, multiplicative factors of 1.13 to 1.15 can be applied to obtain post-thinning predictions of 4-year single-tree basal area increments. Although MWA can be used as a long term source of nutrients, charcoal temporarily reduces the availability of P and N.     

Effects of Soil Nutrients and Moisture on Root/Shoot Ratios in Lolium perenne L. and Trifolium repens L

The dry weights of foliage and roots (excluding stembases) werecompared in a 3³x2² factorial experiment with Lolium perenneL. and Trifolium repens L. grown in pots with three nitrogen(0–300 ppm N), phosphorus (0–300 ppm P), and soilmoisture (pF 3.2, pF 2.4, and waterlogged) treatments, eachduplicated. Root/shoot ratios were influenced significantly (P < 0.001)by N, P, and W (soil moisture), but these main effects werequalified by highly significant first-order interactions andsecond-order interactions which included N and P. The lowestR/S ratios occurred where N, P, and W were all non-limiting,and the highest where there was an imbalance of these factors. The explanation suggested is that a decrease in the availabilityof N, P, or W causes an increase in the relative weight of roots,but in the presence of N, P, or W deficiency an increase inany one of these factors causes a further increase in the R/Sratio by increasing the relative efficiency of the foliage.