Leaf nutrient dynamics and nutrient resorption: a comparison between larch plantations and adjacent secondary forests in Northeast China

Aims Conversion of secondary forests to pure larch plantations is a common management practice driven by the increasing demand for timber production in Northeast China, resulting in a reduction in soil nutrient availability after a certain number of years following conversion. Nutrient resorption prior to leaf senescence was related to soil fertility, an important nutrient conservation strategy for plants, being especially significant in nutrient-poor habitats. However, the seasonal dynamics of leaf nutrients and nutrient resorption in response to secondary forest conversion to larch plantations is not well understood.Methods A comparative experiment between larch plantations (Larix spp.) and adjacent secondary forests (dominant tree species including Quercus mongolica, Acer mono, Juglans mandshurica and Fraxinus rhynchophylla) was conducted. We examined the variations in leaf nutrient (macronutrients: N, P, K, Ca and Mg; micronutrients: Cu and Zn) concentrations of these tree species during the growing season from May to October in 2013. Nutrient resorption efficiency and proficiency were compared between Larix spp. and the broadleaved species in the secondary forests.Important findings Results show that the seasonal variation of nutrient concentrations in leaves generally exhibited two trends, one was a downward trend for N, P, K, Cu and Zn, and another was an upward trend for Ca and Mg. The variations in foliar nutrient concentrations were mainly controlled by the developmental stage of leaves rather than by tree species. Resorption of the observed seven elements varied among the five tree species during leaf senescence. Nutrient resorption efficiency varied 6–75% of N, P, K, Mg, Cu and Zn, while Ca was not retranslocated in the senescing leaves of all species, and Mg was not retranslocated in Larix spp. Generally, Larix spp. tended to be more efficient and proficient (higher than 6–30% and 2–271% of nutrient resorption efficiency and resorption proficiency, respectively) in resorbing nutrients than the broadleaved species in the secondary forests, indicating that larch plantations had higher leaf nutrient resorption and thus nutrient use efficiency. Compared with Larix spp., more nutrients would remain in the leaf litter of the secondary forests, indicating an advantage of secondary forests in sustaining soil fertility. In contrast, the larch plantation would reuse internal nutrients rather than lose nutrients with litter fall and thus produce a positive feedback to soil nutrient availability. In summary, our results suggest that conversion from secondary forests to pure larch plantations would alter nutrient cycling through a plant-mediated pathway.     

Long term effects of manure, charcoal and mineral fertilization on crop production and fertility on a highly weathered Central Amazonian upland soil

Application of organic fertilizers and charcoal increase nutrient stocks in the rooting zone of crops, reduce nutrient leaching and thus improve crop production on acid and highly weathered tropical soils. In a field trial near Manaus (Brazil) 15 different amendment combinations based on equal amounts of carbon (C) applied through chicken manure (CM), compost, charcoal, and forest litter were tested during four cropping cycles with rice (Oryza sativa L.) and sorghum (Sorghum bicolor L.) in five replicates. CM amendments resulted in the highest (P < 0.05) cumulative crop yield (12.4 Mg ha⁻¹) over four seasons. Most importantly, surface soil pH, phosphorus (P), calcium (Ca), and magnesium (Mg) were significantly enhanced by CM. A single compost application produced fourfold more grain yield (P < 0.05) than plots mineral fertilized in split applications. Charcoal significantly improved plant growth and doubled grain production if fertilized with NPK in comparison to the NPK-fertilizer without charcoal (P < 0.05). The higher yields caused a significantly greater nutrient export in charcoal-amended fields, but available nutrients did not decrease to the same extent as on just mineral fertilized plots. Exchangeable soil aluminum (Al) was further reduced if mineral fertilizer was applied with charcoal (from 4.7 to 0 mg kg⁻¹). The resilience of soil organic matter (SOM) in charcoal amended plots (8 and 4% soil C loss, mineral fertilized or not fertilized, respectively) indicates the refractory nature of charcoal in comparison to SOM losses over 20 months in CM (27%), compost amended (27%), and control plots (25% loss).     

Temporal patterns of soil nutrients in a Panamanian moist forest revealed by ion-exchange resin and experimental irrigation

The effect of seasonal water availability on soil nutrients and soil N transformations was investigated by irrigating two large plots of mature tropical forest on Barro Colorado Island (BCI), Panama, during the dry season for five consecutive years. Methods included (i) nutrient accumulation by ion-exchange resins placed on the surface of the mineral soil for contiguous 21-day periods, (ii) monthly mineral soil (0–10 cm) extractions and incubations for inorganic N and P concentrations, and (iii) leaching loss of nutrients from leaf litter samples. Rates of nutrient accumulation by the resins showed a great deal of variation between sampling dates and among years in control plots; albeit, seasonal patterns were slight, except for the highest Ca values near the end of the wet season and inorganic P (P_i) and SO₄ values that peaked during the dry season. Irrigation had remarkably little effect on nutrient accumulation rates by resins, except for an increase in Mg and Na values, but did affect the timing in the temporal variation in K, Na, N_i and P_i values. In contrast, inorganic N (N_i) and P_i pools and N transformation rates in the mineral soil hardly varied among sampling dates and did not show any response to irrigation. We hypothesize that the timing of leaf litterfall and nutrient leaching from forest floor litter can set up temporal patterns in the levels of soil nutrient at the surface of the mineral soil, but the temporal patterns essentially disappear with depth in the mineral soil.     

Zinc-biochemical co-fertilization improves rice performance and reduces nutrient surplus under semi-arid environmental conditions

Biofertilizers are a promising approach to substantially improve nutrient recovery and crop production. Moreover, zinc (Zn) deficiency is one of the key abiotic factors limiting global rice production. However, the effect of Zn-biochemical co-fertilization on rice production and nutrients recovery and surplus under semi-arid environmental conditions is not fully obvious. Two years field experiment was conducted to evaluate the effect of Zn-biochemical (nitrogen “N”, phosphorus “P”, and potassium “K”) co-fertilization on yield and yield components, physico-chemical characteristics, and nutrient recovery and surplus as well as farm profitability of four rice (Oryza sativa L.) cultivars treated with two Zn levels (no Zn application, and 600 mg chelated Zn L^?1 as a foliar application) and six fertilization regimes (no fertilizers application, biofertilizers, 25% NPK plus biofertilizers, 50% NPK plus biofertilizers, 75% NPK plus biofertilizers, and 100% NPK). Biofertilizers mixture (cerealin, phosphorine, and potassiomage) were used. The results revealed that chemical constituents, growth attributes, yield, yield components, nutrients uptake (N, P, K, and Zn), and nutrients recovery (N, P, and K) significantly increased due to Zn foliar application. Biofertilizers replacement for 25% of inorganic NPK combined with Zn provides the highest nutrients uptake through increasing N, P, and K recovery by 57–94%, 61–128%, and 45–69%, respectively in the four rice cultivars compared with 100% NPK treatment. This improvement in nutrients uptake and recovery was attributed to decrease nutrients surplus by 64–78%, 46–53%, and 50–59%, respectively. Additionally, Zn-biochemical co-fertilization improves growth attributes, yield, and yield components of rice cultivars through producing more contents of chlorophyll a and b, carotenoids, total carbohydrates, and total amino acids than using 100% NPK alone. All previous characteristics significantly affected by the cultivated rice variety. The net return under the treatment of 75% NPK plus biofertilizers plus Zn foliar application was 21.5–27.5% higher than the treatment of 100% NPK. Therefore, our findings suggest that biofertilizers replacement for 25% of inorganic NPK combined with Zn foliar application supplies a financially attractive choice to substantially enhance nutrient recovery and production of rice, while effectively reducing nutrients loss.     

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.     

Influence of Norway spruce seedlings on the nutrient availability in mineral soil and forest floor material

A greenhouse experiment was performed to evaluate the effect of Norway spruce (Picea abies (L.) Karst.) seedlings on net nutrient availability in five different growing media containing F- or H-layer and mineral soil originating from a haplic podzol in northern Sweden. The initial total amounts of eight nutrient elements (N, K, P, Ca, Mg, Mn, Fe, Zn) and exchangeable amounts of the same elements were analyzed in pots with or without spruce seedlings. In the planted pots seedling nutrient uptake was also estimated. After 26 weeks, higher net nutrient availability with seedlings was found in 25 out of the 40 (62%) growing media and nutrient element combinations. A positive seedling effect on net nutrient availability might be explained by rhizodeposition stimulating the soil microorganism activity and accelerating the weathering of minerals or by seedling roots promoting the nutrient providing processes through changes in soil chemical and physical properties. Nitrogen availability was primarily affected by what part of the forest floor the growing medium contained although the positive response to seedling presence was apparent. The positive net availability response of P, Ca, Mg, Mn, Fe and Zn to seedling presence was on the other hand relatively strong. In the case of P, K, and Zn the growing medium composition (if the F- and H-layer was pure or mixed with mineral soil) was also an important factor for the estimated net availability. Pure F-and H-layer provided greater P- and K-availability while the availability of Zn increased when mineral soil was added. The influence of growing plants ought to be considered when soil samples are used for assessing the nutrient availability.     

Effects of nitrogen fertilization of grapefruit trees on soil acidification and nutrient availability in a Riviera fine sand

Nitrogen (N) fertilizer applied in the NH4+ form results in some degree of soil acidification, which could influence nutrient availability to plants and nutrient losses through leaching. Effects of various N rates (0 – 168 kg N ha-1 yr-1) on soil acidification and nutrient availability were investigated in a Riviera fine sand with 26-year-old white Marsh grapefruit (Citrus paradisi MacFadyen) trees. Soil pH significantly decreased with increasing NH4–N rates. Application of 112 kg N ha-1 yr-1 for four years decreased the pH by 0.7 to 1.7 unit. Soil acidification was greater when the NH4+ form of N fertilizer was applied as dry soluble granular material compared to fertigation or controlled release forms. The marked effect of NH4–N fertilization on the pH of the Riviera fine sand was due to its low buffering capacity. Soil acidification increased the concentration of extractable Fe and P but decreased that of K, Zn and Mn. Soil pH was positively correlated with concentration of Ca, but negatively with concentrations of Fe, Mn and Zn in six-month-old spring flush leaves of the grapefruit trees. Leaf P concentrations, however, were poorly correlated with soil pH. This study also demonstrated an increase in leaching of P and K below the grapefruit trees rootzone with a decrease in soil pH.     

Effects of irrigation and balanced fertilization on nutrient cycling in a Douglas fir stand

The effects on growth and nutrient status of an increased availability of all major nutrients was studied in a 40 year old Douglas fir stand. The nutrient amounts were applied by daily sprinkling and were in fixed, optimal proportions to the estimated annual uptake of N. Irrigation was included to avoid drought stress. The nutrient applications were also done in combination with a lower NH₄ load, realized under a roof that was placed above the ground. According to nutritional standards nitrogen supply was optimal and was related to the moderately high atmospheric N inputs. Nutrition of P, K and in some years Ca seemed critical.In all four studied growing seasons water additions resulted in a growth increase, of 30 to 40%. Irrigation decreased needle fall. Nutrient applications increased the needle concentrations of P and K considerably, but this did not result in a growth enhancement. Fertilization also increased K and P in shedded needles. Only minor leaching losses were calculated. The recovery in trees of fertilizer K and P was maximally 15%. Input-output budgets suggested that P was strongly retained in the soil. The decrease in NH₄ load had slightly decreased N availability and soil acidification, and seemed to enhance tree growth. The use of tree growth as a parameter to evaluate the effects of an improved nutritional balance is discussed.     

Use of plant residues for improving soil fertility, pod nutrients, root growth and pod weight of okra (Abelmoschus esculentum L)

The effect of wood ash, sawdust, ground cocoa husk, spent grain and rice bran upon root development, ash content, pod yield and nutrient status and soil fertility for okra (Abelmoschus esculentum L NHAe 47 variety) was studied. The five organic fertilizer treatments were compared to chemical fertilizer (400kg/ha/crop NPK 15-15-15) and unfertilized controls in four field experiments replicated four times in a randomized complete block design. The results showed that the application of 6tha(-1) of plant residues increased (P<0.05) the soil N, P, K, Ca, Mg, pH, and SOM; pod N, P, K, Ca, Mg and ash; root length; and pod yield of okra in all four experiments relative to the control treatment. For instance, spent grain treatment increased the okra pod yield by 99%, 33%, 50%, 49%, 65% and 67% compared to control, NPK, wood ash, cocoa husk, rice bran and sawdust treatments respectively. In the stepwise regression, out of the total R(2) value of 0.83 for the soil nutrients to the pod yield of okra; soil N accounted for 50% of the soil fertility improvement and yield of okra. Spent grain, wood ash and cocoa husk were the most effective in improving okra pod weight, pod nutrients, ash content, root length and soil fertility whereas the rice bran and sawdust were the least effective. This was because the spent grain, wood ash and cocoa husk had lower C/N ratio and higher nutrient composition than rice bran and sawdust, thus, the former enhanced an increase in pod nutrients, composition for better human dietary intake, increased the root length, pod weight of okra and improved soil fertility and plant nutrition crop. The significance of the increases in okra mineral nutrition concentration by plant residues is that consumers will consume more of these minerals in their meals and monetarily spend less for purchasing vitamins and mineral supplement drugs to meet health requirements. In addition, the increase in plant nutrition and soil fertility would help to reduce the high cost of buying synthetic inorganic fertilizers and maintain the long term productivity of soils for sustainable cultivation of okra.     

Nutrient cycling in Pinus sylvestris stands in eastern Finland

Nutrient cycling within three Pinus sylvestris stands was studied in eastern Finland. The aim of the study was to determine annual fluxes and distribution of N, P, K, Ca, Mg, Zn, Fe, B, and Al in the research stands. Special emphasis was put on determining the importance of different fluxes, especially the internal cycle within the trees in satisfying the tree nutrient requirements for biomass production. The following nutrient fluxes were included, input; free precipitation and throughfall, output; percolation through soil profile, biological cycle; nutrient uptake from soil, retranslocation within trees, return to soil in litterfall, release by litter decomposition. The distribution of nutrients was determined in above- and belowground tree compartments, in ground and field vegetation, and in soil.The nitrogen use efficiencies were 181, 211 and 191 g of tree aboveground dry matter produced per g of N supplied by uptake and retranslocation in the sapling, pole stage and mature stands, respectively. Field vegetation was more efficient in nitrogen use than trees. Stand belowground/aboveground and fine root/coarse root biomass ratios decreased with tree age. With only slightly higher fine root biomass, almost three times more nitrogen had to be taken-up from soil for biomass production in the mature stand than in the sapling stand.The annual input-output balances of most nutrients were positive; throughfall contained more nutrients than was lost in mineral soil leachate. The sulphate flux contributed to the leaching of cations, especially magnesium, from soil in the mature stand.Retranslocation supplied 17–42% of the annual N, P and K requirements for tree aboveground biomass production. Precipitation and throughfall were important in transferring K and Mg, and also N in the sapling stand. Litterfall was an important pathway for N, Ca, Mg and micro nutrients, especially in the oldest stands.     

Nitrogen enrichment regulates calcium sources in forests

Nitrogen (N) is a key nutrient that shapes cycles of other essential elements in forests, including calcium (Ca). When N availability exceeds ecosystem demands, excess N can stimulate Ca leaching and deplete Ca from soils. Over the long term, these processes may alter the proportion of available Ca that is derived from atmospheric deposition vs. bedrock weathering, which has fundamental consequences for ecosystem properties and nutrient supply. We evaluated how landscape variation in soil N, reflecting long‐term legacies of biological N fixation, influenced plant and soil Ca availability and ecosystem Ca sources across 22 temperate forests in Oregon. We also examined interactions between soil N and bedrock Ca using soil N gradients on contrasting basaltic vs. sedimentary bedrock that differed 17‐fold in underlying Ca content. We found that low‐N forests on Ca‐rich basaltic bedrock relied strongly on Ca from weathering, but that soil N enrichment depleted readily weatherable mineral Ca and shifted forest reliance toward atmospheric Ca. Forests on Ca‐poor sedimentary bedrock relied more consistently on atmospheric Ca across all levels of soil N enrichment. The broad importance of atmospheric Ca was unexpected given active regional uplift and erosion that are thought to rejuvenate weathering supply of soil minerals. Despite different Ca sources to forests on basaltic vs. sedimentary bedrock, we observed consistent declines in plant and soil Ca availability with increasing N, regardless of the Ca content of underlying bedrock. Thus, traditional measures of Ca availability in foliage and soil exchangeable pools may poorly reflect long‐term Ca sources that sustain soil fertility. We conclude that long‐term soil N enrichment can deplete available Ca and cause forests to rely increasingly on Ca from atmospheric deposition, which may limit ecosystem Ca supply in an increasingly N‐rich world.     

Effect of five tree crops and a cover crop in multi-strata agroforestry at two fertilization levels on soil fertility and soil solution chemistry in central Amazonia

The spatio-temporal patterns of soil fertility and soil solution chemistry in a multi-strata agroforestry system with perennial crops were analysed as indicators for the effects of crop species and management measures on soil conditions under permanent agriculture in central Amazonia. The study was carried out in a plantation with locally important tree crop species and a leguminous cover crop at two fertilization levels on a xanthic Ferralsol. Soil fertility to 2 m soil depth was evaluated 3.5 years after the establishment of the plantation, and soil solution chemistry at 10, 60 and 200 cm soil depth was monitored over 2 years. Several soil fertility characteristics exhibited spatial patterns within the multi-strata plots which reflected the differing properties of the plant species and their management, including the fertilizer input. Significant differences between species could be detected to 150 cm depth, and between fertilization treatments to 200 cm depth. Favourable effects on nutrient availability in the soil were found for annatto (Bixa orellana) (P, K) and cupuaçu (Theobroma grandiflorum) (Ca, Mg) in comparison with peach palm (Bactris gasipaes) and Brazil nut (Bertholletia excelsa). Nutrient concentrations of the soil solution showed pronounced fluctuations in the topsoil, corresponding to fertilizer applications. Large nutrient concentrations in the soil solution were accompanied by increased concentrations of aluminium and low pH values, caused by exchange reactions between fertilizer and sorbed acidity and reinforced by the acidifying effect of nitrification. The soil solution under the leguminous cover crop Pueraria phaseoloides had relatively large N concentrations during periods when those under the tree crops were small, and this could partly explain why no yield responses to N fertilization were observed at this site.     

Early stages of root and leaf decomposition in Hawaiian forests: effects of nutrient availability

We examined the effects of soil nutrient availability and tissue chemistry on decomposition of both fine roots (<2 mm diameter) and leaves in three sites along a forest chronosequence in the Hawaiian Islands. These sites form a natural fertility gradient, with the youngest and oldest sites having lower nutrient availability than the intermediate-aged site. Nitrogen (N) limits aboveground net primary productivity (ANPP) in the youngest site, while phosphorus (P) limits ANPP in the oldest site. Both root and leaf litter decomposed most slowly in the 4.1-Myear-old site. We also investigated root decomposition in fertilized plots at the youngest and oldest sites; when roots were produced and decomposed in fertilized plots, root decomposition rates increased with N and P additions at the 4.1-Myear-old site. At the 300-year-old site, however, root decomposition rates did not respond to N or P additions. Roots decomposed faster than leaves at the more infertile sites, in part because of lower lignin-to-nitrogen ratios in roots than in leaf litter. Decomposing roots immobilized more nutrients than did decomposing leaves, and may serve an important role in retaining nutrients in these forests. Received: 30 November 1998 / Accepted: 12 August 1999     

Reversibility of Soil Productivity Decline with Organic Matter of Differing Quality Along a Degradation Gradient

In the highlands of Western Kenya, we investigated the reversibility of soil productivity decline with increasing length of continuous maize cultivation over 100 years (corresponding to decreasing soil organic carbon (SOC) and nutrient contents) using organic matter additions of differing quality and stability as a function of soil texture and inorganic nitrogen (N) additions. The ability of additions of labile organic matter (green and animal manure) to improve productivity primarily by enhanced nutrient availability was contrasted with the ability of stable organic matter (biochar and sawdust) to improve productivity by enhancing SOC. Maize productivity declined by 66% during the first 35 years of continuous cropping after forest clearing. Productivity remained at a low level of 3.0 t grain ha^-1 across the chronosequence stretching up to 105 years of continuous cultivation despite full N–phosphorus (P)–potassium (K) fertilization (120–100–100 kg ha⁻¹). Application of organic resources reversed the productivity decline by increasing yields by 57–167%, whereby responses to nutrient-rich green manure were 110% greater than those from nutrient-poor sawdust. Productivity at the most degraded sites (80–105 years since forest clearing) increased in response to green manure to a greater extent than the yields at the least degraded sites (5 years since forest clearing), both with full N–P–K fertilization. Biochar additions at the most degraded sites doubled maize yield (equaling responses to green manure additions in some instances) that were not fully explained by nutrient availability, suggesting improvement of factors other than plant nutrition. There was no detectable influence of texture (soils with either 11–14 or 45–49% clay) when low quality organic matter was applied (sawdust, biochar), whereas productivity was 8, 15, and 39% greater (P < 0.05) on sandier than heavier textured soils with high quality organic matter (green and animal manure) or only inorganic nutrient additions, respectively. Across the entire degradation range, organic matter additions decreased the need for additional inorganic fertilizer N irrespective of the quality of the organic matter. For low quality organic resources (biochar and sawdust), crop yields were increasingly responsive to inorganic N fertilization with increasing soil degradation. On the other hand, fertilizer N additions did not improve soil productivity when high quality organic inputs were applied. Even with the tested full N–P–K fertilization, adding organic matter to soil was required for restoring soil productivity and most effective in the most degraded sites through both nutrient delivery (with green manure) and improvement of SOC (with biochar).     

Nutrient changes in direct-seeded submerged rice soils with varying nutrio-environments

Summary Nutrient changes in submerged rice soil were studied in soil-water-plant ecosystem in direct-seeded rice crop. Continuous removal of nutrients by the crop resulted in ultimate decrease in the availability of NH₄–N, P, K, Ca, Mg, Mn, Zn and Cu. However, there was a slight increase in Fe availability in soil with increase in period of submergence and crop growth. The data was subjected to statistical function fittings to study the nature of changes. Depending on the R²% values, quadratic type was the best fit for pH, available NH₄–N, K, Mg, Fe, Mn and Cu, whereas logarithmic type was the best fit for available P, Ca and Zn. No response was noticed to the application of P and K. Highest correlation coefficient between grain yield and NH₄–N in soil was obtained at the panicle initiation stage indicating that limiting nitrogen during this period might affect grain yield to the maximum extent compared to tiller initiation and maximum tillering stages.     

Aboveground nutrient cycling and forest development on poor sandy soil

The aboveground nutrient turnover of three ecosystems representing the main stages of heathland forest succession in NW Germany was investigated in a comparative study with regard to nutrient availability of the soil and light availability below the canopy. It was expected that nutrient availability would play a decisive role in forest development on nutrient poor acidic soil. The results show that the input of nutrients into the Calluna heathland is higher than the annual aboveground turnover of N, P, Ca, Mg, and K via litterfall. Compared to the pioneering birch-pine forest, the annual aboveground turnover of nutrients within the Calluna heathland, and therefore the nutrient availability is very low, while the light availability below the canopy is high. The increasing productivity of the growing successional forest is combined with an increasing nutrient turnover, mainly via litter fall. As a result, the increasing nutrient availability favours shade tolerant species with a higher nutrient demand at the late stages of succession. Consequently, the presumed terminal stage of succession, the oak-beech forest, is characterized by low light availability below the canopy and higher nutrient supply according to the resource-ratio hypothesis of Tilman (1985, 1986, 1988).     

Soil fertility of afforested arable land compared to continuously

In Finland, over 220,000 ha of arable land has been afforested in recent decades. To meet the goals of forest management on afforested fields, information on the effects of former agricultural land use on soil fertility is needed. In this study, we examine the soil fertility of 12 former arable fields afforested either 10 or 60–70 years ago with Norway spruce (Picea abies (L.) Karst.) and adjacent sites that have been forested continuously. Volumetric soil samples were collected from the organic soil layer and from mineral soil to a depth of 40 cm. Soil samples were analyzed for pH, bulk density, organic matter content and amounts of nutrients (Kjeldahl N, extractable P, K, Ca, Mg, Zn and B). On afforested fields, amounts of nutrients in the mineral soil, especially in 10-year-old afforestations, were higher than on continuously forested sites. In the organic layer plus the 0–40 cm soil layer, the 10-year-old afforestations had 68% more N, 41% more P, 83% more K, 252% more Ca, 6% more Mg, 61% more Zn and 33% more B than the continuously forested sites at a comparable soil depth. In the 60–70-year-old afforestations, the differences were significant only for N, Ca and Zn (20% more N, 121% more Ca and 115% more Zn than on the continuously forested sites). The effects of agriculture on amounts of nutrients were most clearly detected in the former plough layer (0–20 cm) of the 10-year-old afforestations and in the top layer (0–10 cm) of the older afforestations. Amounts of nutrients in the organic layer of the afforested sites were lower, but their concentrations were higher than in the continuously forested sites. On the 10-year-old afforestations, the bulk density of the mineral soil tended to be lower and the organic matter content higher than on the continuously forested sites. On both young and old afforestations, soil pH was higher than on the continuously forest sites. According to these results, changes in soil properties caused by agriculture have increased the soil fertility and therefore probably also the site index. The results also suggest that changes in soil properties due to agricultural land use are quite long lasting.     

Is primary production in holm oak forests nutrient limited?

Correlations between primary production and patterns of nutrient use and nutrient availability were investigated in 18 plots in closed holm oak (Quercus ilex L.) stands in the Montseny mountains (NE Spain), searching for evidence of nutrient limitation on primary production. The plots spanned a range of altitudes and slope aspects within a catchment. Nutrients considered were nitrogen (N), phosphorus (P), potassium (K) and magnesium (Mg) in plant samples, and the above plus calcium (Ca) and sodium (Na) in the soil. Primary production was found by summing the annual aboveground biomass increment to the annual litterfall. Across plots, primary production was correlated with the annual return of nutrients in litterfall, but this relationship probably arose from the common effects of the amount of litterfall on both primary production and nutrient return, and not from any nutrient limitation. Primary production was not significantly correlated with nutrient concentrations in mature leaves nor leaf litterfall, nor with absolute or relative foliar retranslocation of nutrients before leaf abscission, nor with the concentration and content (kg/ha) of total N, extractable P, and exchangeable K, Mg, Ca and Na in the upper mineral soil. We conclude that there is no correlational evidence that primary production is nutrient limited in this holm oak forest.     

不同施肥模式下潮棕壤稻田的速效养分状况和水稻的养分分配

研究了不同施肥模式下下辽河平原潮棕壤稻田土壤速效养分的供应能力及水稻的养分分配.结果表明:各处理0～20 cm速效养分供应能力均高于20～40 cm,其变异也大于20～40 cm(速效氮除外);有机、无机肥相结合有利于提高土壤速效养分的供应能力;水稻氮和磷的分配主要集中在籽实中,钾的分配则主要集中在秸秆中.采用秸秆还田措施有利于缓解钾肥资源的不足,保持钾素的循环再利用,维持土壤钾库,减少钾肥投入,降低农业生产成本,减轻环境污染.     

Nutrient limitation of plant growth on the floodplain of the Narran River, Australia: growth experiments and a pilot soil survey

Water resource development has altered the hydrological regime on the Lower Balonne River in Queensland, Australia. Concerns have been raised about possible impacts to floodplain plant communities, which support a pastoral industry and a range of native fauna. Water and nutrients commonly limit plant growth in south central Queensland, where the climate is semi-arid and the soils are infertile. Floodplain plant productivity is boosted by inundation with water, but the role of flooding in nutrient provision is not known. Growth experiments and a pilot soil survey were conducted to help determine if soil nutrient deficiencies exist and if regular flooding is required to maintain floodplain soil fertility. Soils were sampled from areas representing three flood frequency classes: high, moderate, and low. Chemical extractions were performed as a surrogate for `bioavailable' nutrients. Soil nitrogen (N) but not phosphorus (P) limited the growth of seedlings of wheat (Triticum aestivum L. Gardia) based on responses to nutrient additions: plants supplied with N had greater shoot length and total biomass than plants without N. Clear evidence of an effect of flood frequency on fertility was not revealed. Neither soil P, soil N, nor plant growth varied significantly with flood frequency. However, this analysis had low statistical power. There were trends for greater biomass of seedlings grown on moderately flooded soils and thinner roots for seedlings grown on frequently flooded soils, but neither of these growth responses was clearly linked to nutrient limitation. Nevertheless, the possibility that flooding provides a nutrient subsidy to plants cannot be ruled out because of a number of factors, including the statistical power of this analysis and the possibility that short-term nutrient subsidies occur with floods.