Effects of liming and boron fertilization on boron uptake of Picea abies

The effects of liming on concentrations of boron and other elements in Norway spruce [Picea abies (L) Karst.] needles and in the mor humus layer were studied in long-term field experiments with and without B fertilizer on podzolic soils in Finland. Liming (2000+4000 kg ha^-1 last applied 12 years before sampling) decreased needle B concentrations in the four youngest needle age classes from 6–10 mg kg^-1 to 5 mg kg^-1. In boron fertilized plots the corresponding concentrations were 23–35 mg kg^-1 in control plots and 21–29 mg kg^-1 in limed plots. Both liming and B fertilizer decreased the Mn concentrations of needles. In the humus layer, total B concentration was increased by both lime and B fertilizer, and Ca and Mg concentrations and pH were still considerably higher in the limed plots than controls. Liming decreased the organic matter concentration in humus layer, whilst B fertilizer increased it.The results about B uptake were confirmed in a pot experiment, in which additionally the roles of increased soil pH and increased soil Ca concentration were separated by means of comparing the effects of CaCO₃ and CaSO₄. Two-year-old bare-rooted Norway spruce seedlings were grown in mor humus during the extension growth of the new shoot. The two doses of lime increased the pH of soil from 4.1 to 5.6 to 6.1, and correspondingly decreased the B concentrations in new needles from 22 to 12 to 9 mg kg^-1. However, CaSO₄ did not affect the pH of the soil or needle B concentrations. Hence the liming effect on boron availability in these soils appeared to be caused by the increased pH rather than increased calcium concentration.     

Advances in the positional cloning of nodulation genes in soybean

The effect of liming on the decomposition of Norway spruce needle litter was studied in 40–60-year-old Norway spruce stands. Finely-ground limestone had been spread about 30 years ago at a dose of 2 t ha^–1 and reliming was carried out about 20 yr later at a dose of 4 t ha^–1. Needle litter was collected from both control and limed plots, and it was placed in litter bags in the middle of the humus layer of the plot from which they originated, and similarly to the other plot in May. Litter bags were sampled after 4, 12 and 16 months. The site of origin of the needle litter, whether from control plot or from limed plot, affected mainly the early stages of decomposition. Initially the effect of liming was seen as decreased concentration of water soluble material and then, during decomposition, as decreased mass loss and decreased degradation of lignin, and increased C/N ratio. The incubation site, whether the control or the limed plot, did not affect decomposition significantly.Decomposition of Scots pine needles in a young Scots pine plantation was also studied. The treatments were: 2 t ha^–1 of finely-ground limestone and 2.5 t ha^–1 of bark ash spread 8 months before this study. The treatments did not affect decomposition much, but some stimulation of the treatments on decomposition was observed. Compared to spruce needles, the C/N ratio of pine seedles was lower, they contained less lignin and more water soluble material, and decomposed faster in the first summer.     

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.     

Nitrogen transformations in limed and nitrogen fertilized soil in Norway spruce stands

Nitrogen transformations in the soil, and the resulting changes in carbon and nitrogen compounds in soil percolate water, were studied in two stands of Norway spruce (Picea abies L.). Over the last 30 years the stands were repeatedly limed (total 6000 kg ha^–1), fertilized with nitrogen (total about 900 kg ha^–1), or both treatments together. Both aerobic incubations of soil samples in the laboratory, and intact soil core incubations in the field showed that in control plots ammonification widely predominated over nitrification. In both experiments nitrogen addition increased the formation of mineral-N. In one experiment separate lime and nitrogen treatments increased nitrification, in the other, only lime and nitrogen addition together had this effect. In one experiment immobilization of nitrogen to soil microbial biomass was lower in soil only treated with nitrogen. Soil percolate water was collected by means of lysimeters placed under the humus layer and 10 cm below in the mineral soil. Total N, NH₄-N and NO₃-N were measured, and dissolved organic nitrogen was fractioned according to molecular weight. NO₃-N concentrations in percolate water, collected under the humus layer, were higher in plots treated with N-fertilizer, especially when lime was also added. The treatments had no effect on the N concentrations in mineral soil. A considerable proportion of nitrogen was leached in organic form.     

Effects of agricultural production on phosphorus losses from paddy soils: a case study in the Taihu Lake Region of China

A field plot experiment was conducted on two types of paddy soils in the Taihu Lake Region of China from June 2000 through 2002 to assess phosphorus (P) losses by runoff and drainage flow and the effectiveness of rice–wheat double cropping on reducing P losses from paddy soils. Commercial NPK compound fertilizer and single superphosphate fertilizer were applied to furnish 0, 30, 150, and 300 kg P ha^–1 for rice season trials, and 0, 20, 80, and 160 kg P ha^–1 for wheat season trials. The experiments consisted of four replicates (plots of 5 × 6 m in a randomized block design) of each treatment in Argic stagnic anthrosols (Anzhen site) and six replicates in Cumulic stagnic anthrosols (Changshu site). P30 and P20 treatments (30 and 20 kg P ha^–1 in rice and wheat seasons, respectively) were considered as conventional P application rates in this area. Higher P treatments, such as P150 and P300 for rice and P80 and P160 for wheat, were intended to simulate the status of soil P in ~10–20 years with an application of P30 or P20 kg P ha^–1 each season. Results revealed that the average concentration of total P (TP) in runoff samples was 0.870 mg P l^–1 from P30 plots during the rice season, and 0.763 mg P l^–1 from P20 plots during the wheat season in both years at the Anzhen site, while it was 0.703 and 1.292 mg P l^–1, respectively, at the Changshu site. Average TP load (mass loss) at the Anzhen site with conventional P application rates was 220.9 and 439.5 g P ha^–1 during rice season in 2000/2001 and 2001/2002, respectively, but was 382.3 and 709.4g P ha^–1 during wheat season, respectively. Mass loss at the Changshu site was 140.4 and 165.7 g P ha^–1 during the rice season and 539.1 and 1184.6 g P ha^–1 during the wheat season, respectively. P losses from paddy soils were significantly greater during the wheat season, especially at the Changshu site, indicating that planting rice reduced P. Phosphate fertilizer levels significantly affected P concentrations and P loads in runoff both seasons. Both mean concentrations and average seasonal P loads from the P150/P80 plots were lower than that from the P300/P160 plots, but significantly higher than that from the P30/P20 and P0 plots. This implied that runoff P loads would be greatly increased in 10–20 years as a result of the accumulation of soil P if 50 kg P ha^–1 (rice season plus wheat season) is applied each year.     

Exchange of N-gases at the Höglwald Forest – A summary

During 4 years continuous measurements of N-trace gas exchange were carried out at the forest floor-atmosphere interface at the Höglwald Forest that is highly affected by atmospheric N-deposition. The measurements included spruce control, spruce limed and beech sites. Based on these field measurements and on intensive laboratory measurements of N₂-emissions from the soils of the beech and spruce control sites, a total balance of N-gas emissions was calculated. NO₂-deposition was in a range of –1.6 –2.9 kg N ha^–1 yr^–1 and no huge differences between the different sites could be demonstrated. In contrast to NO₂-deposition, NO- and N₂O-emissions showed a huge variability among the different sites. NO emissions were highest at the spruce control site (6.4–9.1 kg N ha^–1 yr^–1), lowest at the beech site (2.3–3.5 kg N ha^–1 yr^–1) and intermediate at the limed spruce site (3.4–5.4 kg N ha^–1 yr^–1). With regard to N₂O-emissions, the following ranking between the sites was found: beech (1.6–6.6 kg N ha^–1 yr^–1) >> spruce limed (0.7–4.0 kg N ha^–1 yr^–1) > spruce control (0.4–3.1 kg N ha^–1 yr^–1). Average N-trace gas emissions (NO, NO₂, N₂O) for the years 1994–1997 were 6.8 kg N ha^–1 yr^–1 at the spruce control site, 3.6 kg N ha^–1 yr^–1 at the limed spruce site and 4.5 kg N ha^–1 yr^–1 at the beech site. Considering N₂-losses, which were significantly higher at the beech (12.4 kg N ha^–1 yr^–1) than at the spruce control site (7.2 kg N ha^–1 yr^–1), the magnitude of total gaseous N losses, i.e. N₂-N + NO-N + NO₂-N + N₂O-N, could be calculated for the first time for a forest ecosystem. Total gaseous N-losses were 14.0 kg N ha^–1 yr^–1 at the spruce control site and 15.5 kg N ha^–1 yr^–1 at the beech site, respectively. In view of the huge interannual variability of N-trace gas fluxes and the pronounced site differences in N-gas emissions it is concluded that more research is needed in order to fully understand patterns of microbial N-cycling and N-gas production/emission in forest ecosystems and mechanisms of reactions of forest ecosystems to the ecological stress factor of atmospheric N-input.     

Mineral nutrient imbalances and arginine concentrations in needles of Picea abies (L.) Karst. from two areas with different levels of airborne deposition

Summary This study evaluated the utility of free arginine concentrations as a possible alternative to mineral nutrient concentrations as an indicator of mineral nutrient imbalances in Norway spruce [Picea abies (L.) Karst.]. The concentrations of mineral nutrients and arginine were measured in the needles of spruce trees from two areas in Sweden, one with high (15–30 kg ha^–1 year^–1) airborne N deposition, and one with lower (1–4 kg ha^–1 year^–1) deposition. The spruce needles from the area with high deposition in southern Sweden had elevated concentrations of free arginine, especially on peat sites. No increase in concentrations was found in the low deposition area in northern Sweden. The arginine concentrations on different sampling occasions were consistent for each site and for individual trees. Trees on peat sites in the south seemed to suffer from P deficiency in relation to N availability. A tendency for K deficiency in needles from peat sites was also found. Needles from trees on mor plots showed acceptable levels of these nutrient elements. Sites in the northern area showed low N concentrations, but the ratios between the different mineral elements analyzed in this study and N were within ranges normally found. A low P/N ratio correlated to high free arginine concentration. The threshold for elevated arginine concentrations is crossed when P/N ratios drop below 0.07–0.08. A tendency for increased arginine levels when ratios between N and the other mineral elements are low was also found, although it was not as strong as that for the P/N ratio. The results are discussed in relation to mineral nutrient imbalances in spruce stands caused by airborne deposition.     

Competition in tree row agroforestry systems. 2. Distribution, dynamics and uptake of soil inorganic N

The effect of tree row species on the distribution of soil inorganic N and the biomass growth and N uptake of trees and crops was investigated beneath a Grevillea robustaA. Cunn. ex R. Br. (grevillea) tree row and Senna spectabilisDC. (senna) hedgerow grown with Zea mays L. (maize) and a sole maize crop, during one cropping season. The hypothesis was that a tree with a large nutrient uptake would have a greater competitive effect upon coexisting plants than a tree that takes up less and internally cycles nutrients. The field study was conducted on a kaolinitic Oxisol in the sub-humid highlands of western Kenya. Soil nitrate and ammonium were measured to 300 cm depth and 525 cm distance from the tree rows, before and after maize cropping. Ammonium concentrations were small and did not change significantly during the cropping season. There was > 8 mg nitrate kg^–1 in the upper 60 cm and at 90–180 cm depth at the start of the season, except within 300 cm of the senna hedgerow where concentrations were smaller. During the season, nitrate in the grevillea-maize system only decreased in the upper 60 cm, whereas nitrate decreased at almost every depth and distance from the senna hedgerow. Inorganic N (nitrate plus ammonium) decreased by 94 kg ha^–1 in the senna-maize system and 33 kg ha^–1 in the grevillea-maize system.The aboveground N content of the trees increased by 23 kg ha^–1 for grevillea and 39 kg ha^–1 for senna. Nitrogen uptake by maize was 85 kg ha^–1 when grown with grevillea and 65 kg ha^–1 with senna. Assuming a mineralisation input of 50 kg N ha^–1season^–1, the decrease in inorganic soil N approximately equalled plant N uptake in the grevillea-maize system, but exceeded that in the senna-maize system. Pruning and litter fall removed about 14 kg N ha^–1 a^–1 from grevillea, and > 75 kg N ha^–1 a^–1 from senna. The removal of pruned material from an agroforestry system may lead to nutrient mining and a decline in productivity.     

Rate of accumulation and emission of N2, N2O and CH4 from a flooded rice soil

In a field experiment using microplots, a flooded Crowley silt loam (Typic Albaqualfs) rice soil was fertilized with ¹⁵N labelled (60–74 atom %) urea and KNO₃. Emission of N₂, N₂O and CH₄ and accumulation in soil were measured for 21 d after fertilizer application.Emission of ¹⁵N₂-N measured from the urea and KNO₃ treated plots ranged from <15 to 570 and from 330 to 3,420 g ha^–1 d^–1, respectively. Entrapped ¹⁵N₂-N in the urea treated microplots was significantly lower (<15 g to 2.1 kg ha^–1) on all sampling dates compared to the ¹⁵N₂-N gas accumulation in the KNO₃ treated plots (6.4 to 31.5 kg ha^–1). Emissions of N₂O-N were low and did not exceed 4 g ha^–1 d^–1. Fluxes of CH₄ from the fertilizer and control plots were low and never exceeded 33 g ha^–1 d^–1. Maximum accumulation of CH₄ in the flooded soil measured 460 and 195 g ha^–1 for the urea and KNO₃ treatments, respectively.     

Long term effect of liming and fertilization on ectomycorrhizal colonization and tree growth in old Scots pine (Pinus sylvestris L.) stands

In this study, we surveyed the long term effects of liming and fertilizing in old Scots pine stands on the ectomycorrhiza (ECM) colonization, tree growth and needle nutrient concentration 35 years later. Four mature stands of Scots pine on low productive mineral soil were limed in 1959 and 1964 with total doses of limestone ranging from 3 to 15 Mg ha^?1 and fertilized with nitrogen (N) in 1970. Thirty-five years after the first liming treatment, all stands were analysed for tree growth and needle nutrient concentrations and two of the stands were also analysed for ECM colonization. ECM colonization increased significantly with liming from 61.5% in the control plots to 88% in the plot with the highest limestone dose. ECM colonization increased with increasing pH in the humus layer from 62% colonization at pH?=?3.5 to 90% at pH?=?6.5 and decreased with increasing amount of extractable phosphorus (P) in the humus. Liming did not affect the frequencies of different ECM morphotypes or dead short root tips, the fine root biomass or necromass. ECM colonization was uncorrelated with needle nutrient concentrations or tree increment. Liming did not significantly affect tree growth. However, nutrient concentrations of current-year needles were affected by prior liming. Ca concentrations in current-year needles increased from approximately 15 mg g^?1 in control treatments to more than 30 mg g^?1 in limed plots, whereas concentrations of Mn, Al, Fe, and in two stands, B, decreased due to liming. In conclusion, liming with doses up to 15 Mg ha^?1 was detectable in stands 35 years after treatment. The liming significantly increased the ECM colonization of Scots pine fine roots, increased the needle nutrient concentration of Ca and decreased the needle concentrations of Mn, Al, and Fe.     

Comparative efficacy of Beauveria bassiana, Bacillus thuringiensis, and aldicarb for control of Colorado potato beetle in an irrigated desert agroecosystem and their effects on biodiversity

Five weekly applications of Beauveria bassiana (Balsamo) Vuillemin, a genetically engineered isolate of Bacillus thuringiensis Berliner (Raven^®), and aldicarb (Temik^®) were compared for control of Colorado potato beetle, Leptinotarsa decemlineata (Say) in an irrigated desert cropping system. B. thuringiensis was applied using low and high label rates (1.17 and 7.0 l ha^–1). B. bassiana was applied at 5×10¹³ spores ha^–1. Aldicarb (Rh^one-Poulenc), applied at 3.37 kg a.i. ha^–1 provided the greatest beetle control and potato yields (45 metric tons ha^–1), but overall lowest biodiversity in nontarget organisms, particularly predatory Heteroptera. Low and high rates of B. thuringiensis produced fair to excellent beetle control, yielded 33 and 40 metric tons ha^–1 and enabled good survival in predatory Heteroptera and other nontargets. Plots treated with B. bassiana resulted in poor control of beetles prior to row closure after which fair to good control was achieved. Yield in the Beauveria-treated plots was 33 metric tons ha^–1 and effect on biodiversity was comparable to the Bt-treated plots. The lowest number of overwintering adult L. decemlineata was found in the plots treated with bacteria and fungi (0.68–0.84 adults/0.03 m^–3 of soil) and the highest was found in control and aldicarb plots (3.44 and 1.84 adults/0.03 m³ of soil). Aphids and leafhoppers showed higher densities in plots treated with microbial control agents, but were eliminated from plots treated with aldicarb.     

Effect of soil-applied NPK fertilizers on severity of black spot disease (Alternaria brassicae) and yield of oilseed rape

Effect of soil application of eight combinations of NPK fertilizers on the severity of black spot disease (BSD), caused by Alternaria brassicae (Sacc.) Berk., and yield of short duration oilseed rape (Brassica campestris L) were investigated under both pot and field conditions in 1987–88, 1988–89 and 1990–91. The severity of BSD was significantly greater (36–48%) on plants grown in ground treated with NP (N 90 kg ha^–1+P 40 kg ha^–1) applied as urea and single superphosphate respectively than on plants from the unfertilized control (NoPoKo) (o). However, the severity of BSD was significantly smaller (25–33%) when K (40 kg ha^–1) was applied as muriate of potash than in plants from control and NP treatments. The effect of NK (N 90 kg ha^–1+K 40 kg ha^–1) in decreasing the severity of BSD was increasingly more pronounced than the effects of PK (P 40 kg ha^–1+K 40 kg ha^–1), NP and K (40 kg ha^–1) applications. The decrease in the severity of BSD due to K was due to increased production in plants of phenolics which inhibited conidial germination and decreased sporulation of A. brassicae.The decrease in the severity of BSD due to NK application gave consistently increased seed yield 68% more than those of control and other treatments. The K-fertilized plants also showed increased resistance to lodging, increased 1000-seed weight and decreased seed infection. Seeds obtained from K-fertilized plants showed good seed germinability and vigorous seeding growth.     

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.     

Algal nitrogen fixation on temperate arable fields

Summary N₂-fixation by algae on the Broadbalk continuous wheat experiment was measured over a two year period using the acetylene reduction technique. The plots studied receive spring fertilizer treatments including farmyard manure and combinations of nitrochalk and Na, P, K and Mg which have remained much the same since the experiment started in 1843.Nitrogen applied at 196 kg ha^–1 in spring suppressed algal N₂-fixation until late in the season but at lower levels (48 kg N ha^–1) the denser plant canopy increased both surface moisture and fixation. Herbicide treatment decreased fixation on plots of moderate nutritional status early in the season but had little effect on unfertilised plots where weed cover was sparse. On plots where weed and crop cover was very dense herbicide treatment increased fixation in August.Algal N₂-ase activity, assayed by C₂H₂ reduction, continued throughout the night at a rate which averaged 33% of the midday value. Laboratory experiments indicate that dark fixation is very temperature sensitive and this value may represent a maximum. Algal crust in the field dried to 4.5–6.8% H₂O content became active 3 1/2 h after rewetting and reached a steady state after 7 h which represented only 6–22% of that at the previous maximum suggesting that many cells had been killed.In a year with average rainfall algae on plots receiving 48 kg N ha^–1 were estimated to fix 25–28 kg N ha^–1 and plots without fertiliser 13–19 kg N ha^–1. Algal fixation appeared to make a substantial contribution to the continuing fertility of unfertilised plots.     

Soil conditions and regeneration after clear felling of a Pinus sylvestris L. stand in a nitrogen experiment,Central Sweden

Forest N fertilization is a common practice in areas of Sweden that are not affected by high levels of N deposition. The environmental consequences of high N input to closed forests are fairly well known, but the long-term effects following clear-felling are a lot less well known. Thus, residual effects on soil and planted seedlings of previous N additions at an experimental N gradient 11 years after clear-felling were studied at a naturally nutrient-poor forest site in central Sweden. The experimental N gradient had been established by three repeated applications (in 1967, 1974 and 1981) of six dosages of NH₄NO₃ with increments of 120 kg N ha^–1. Thus, in total, the applied N dose ranged between 0 and 1800 kg N ha^–1. The study examined extractable base cations and P, soil pH, total-N, total-C, net N-mineralization and potential nitrification in four soil horizons (the humus layer, and 0–5, 5–10 and 10–20 cm in the mineral soil). We also measured the survival and growth of planted Pinus sylvestris L. seedlings. The applied N had no effect on the amounts of extractable-P or base cations in the soil. The soil pH decreased with increasing N dose in the deeper soil horizons, while in the humus the pH showed a weak but statistically significant increase due to the N application. Both total-C and total-N increased as a result of the N application, while the C/N ratio decreased. In the humus layer and the uppermost mineral soil layer NH₄ ⁺ was the major inorganic N source, in contrast to the lowest mineral soil horizon where NO₃ ^– dominated. For most of the studied horizons, there was a positive linear relationship between applied N dose and amount of inorganic N. Both net N-mineralization and potential nitrification showed increases with increasing N dose. As for the plants, no difference in survival or growth was found between the different N treatments. For doses generally applied in forest fertilization no significant differences in any of the studied properties were found.     

Effect of nitrogen and light on nutrient concentrations and associated physiological responses in birch and fir seedlings

We grew seedlings of two co-occurring high elevation tree species in controlled light and nitrogen (N) environments to examine the effect on foliar N and P concentrations and the resulting correlation with photosynthesis and growth. Foliar N concentrations in both heart-leaf paper birch (Betula cordifolia) and balsam fir (Abies balsamea) seedlings were greater in low light treatments than in high light treatments. P concentrations, however, were lower in birch and fir foliage grown in low light than in high light. N-availability had no effect on foliar N in birch but tended to increase N concentration in fir needles at all but 100% ambient light. N-availability had no effect on P concentration in fir seedlings, but high N decreased foliar P in birch. There was a positive relationship between foliar N-concentration (mg g^–1) and mass-based maximum photosynthetic rate (Asat) in birch seedlings and a corresponding growth response to increased N-availability (suggesting N-limitation). Fir photosynthesis exhibited a positive correlation up to 22 mg g^–1 – N and a negative correlation above that point, suggesting that high N concentrations may be detrimental to photosynthesis in the fir seedlings. There was no significant effect of N-treatment on growth.     

The effect of liming on quantity and chemical composition of soil organic matter in a pine forest in Berlin,Germany

The study was carried out in a 40-yr old pine plantation on a Cambic Arenosol within the urban area of Berlin. Lime application (6.1 t ha^-1) has led to a pH increase in the forest floor from 3.3 to 5.5 within one year and to a strong stimulation of macrofaunal and microbiological activity. Three years after liming, the C:N ratio of the forest floor decreased from 28 to 25 and P, Pb, Zn, Cu and Cd concentrations in organic matter increased significantly. The organic C pool of the forest floor was almost 7 t ha^-1 lower in the limed plot which is attributed to increased microbial respiration. In the mineral soil too, C-pools are lower in the limed plot, amounting to 13.2 t ha^-1 or 14% less than in the control. C:N ratios have narrowed significantly from 27–29 to 23 in 10–30 cm depth. The humic acid fraction is lower throughout the limed profile while the percentage of fulvic acids has increased significantly below 10 cm. The results point to severe losses of organic matter and to profound changes in its composition. This may be of consequences for site quality and leaching processes.     

Variation in Yield Gap Induced by Nitrogen,Phosphorus and Potassium Fertilizer in North China Plain

A field experiment was conducted under a wheat-maize rotation system from 1990 to 2006 in North China Plain (NCP) to determine the effects of N, P and K on yield and yield gap. There were five treatments: NPK, PK, NK, NP and a control. Average wheat and maize yields were the highest in the NPK treatment, followed by those in the NP plots among all treatments. For wheat and maize yield, a significant increasing trend over time was found in the NPK-treated plots and a decreasing trend in the NK-treated plots. In the absence of N or P, wheat and maize yields were significantly lower than those in the NPK treatment. For both crops, the increasing rate of the yield gap was the highest in the P omission plots, i.e., 189.1 kg ha⁻¹ yr⁻¹ for wheat and 560.6 kg ha⁻¹ yr⁻¹ for maize. The cumulative omission of P fertilizer induced a deficit in the soil available N and extractable P concentrations for maize. The P fertilizer was more pivotal in long-term wheat and maize growth and soil fertility conservation in NCP, although the N fertilizer input was important for both crops growth. The crop response to K fertilizers was much lower than that to N or P fertilizers, but for maize, the cumulative omission of K fertilizer decreased the yield by 26% and increased the yield gap at a rate of 322.7 kg ha⁻¹ yr⁻¹. The soil indigenous K supply was not sufficiently high to meet maize K requirement over a long period. The proper application of K fertilizers is necessary for maize production in the region. Thus, the appropriate application of N and P fertilizers for the growth of both crops, while regularly combining K fertilizers for maize growth, is absolutely necessary for sustainable crop production in the NCP.     

Effects of base cation fertilization on the nutrient status,free amino acids and some carbon fractions of the leaves of sugar maple (Acer saccharum Marsh.)

A study was conducted in the Lower Laurentians of southern Quebec to test the hypothesis that base cation fertilization would improve the nutrient status of declining sugar maples (Acer saccharum Marsh.) and alter the partitioning of leaf C and N. Six 40×40 m plots were delineated in an 80 year old stand of sugar maple. Three plots received a mixture of fertilizer and liming materials (500 kg ha^–1 of K₂SO₄, 250 kg ha^–1 of CaCO₃ and 250 kg ha^–1 of CaMg(CO₂)₂) in the spring of 1989. Leaves from mid crown of dominant or co-dominant maples were sampled monthly during the 1990 growing season. Trees were cored in 1992 to measure their response in diameter growth. Fertilization increased diameter growth and foliar K concentration of trees but reduced foliar Ca concentration. Fertilization resulted in lower starch concentrations and higher ratios of soluble sugars to starch in June and September, and in higher free amino acid concentrations but lower ratio of total non-structural carbohydrates to free amino acids in September. Leaf proline concentration was correlated with leaf starch concentration (r=0.39). The results suggest that amelioration of K deficiencies in sugar maple through fertilization with a mixture of base cations can increase tree growth and affect the seasonal dynamics of foliar C and N pools.Abbreviations FAA free amino acids - TNC total non-structural carbohydrates     

Effect of exposure to fluoride,nitrogen compounds and SO2 on the numbers of spruce shoot aphids on Norway spruce seedlings

Summary Development of spruce shoot aphid (Cinara pilicornis Hartig) populations was monitored in natural and artificial infestations of Norway spruce (Picea abies Karst.) seedlings, exposed to air pollutants in an experimental field. The pollutants, applied both singly and in mixtures, were gaseous sulphur dioxide, NaF (30 mg l^-1 F) and Ca(NO₃)₂ or (NH₄)₂SO₄ in aqueous solutions (200 mg l^-1 N). Aphid numbers on 10 seedlings in each treatment and two control plots were counted at 2-week intervals. At the beginning of the experiment aphid numbers did not differ between treatments. Aphid populations peaked in late June and early July. All the pollutants and their combinations significantly increased the numbers of aphids per seedling. Four apterous females were transferred to spruce seedlings which were growing in containers in the same plots. After 4–5 weeks aphid numbers were significantly higher in the fluoride treatment and in the combined treatment of fluoride, nitrogen and SO₂. The pollution treatments did not have a significant effect on shoot growth. Concentrations of F and S in needles were higher in treatments involving these pollutants. There were no significant differences in the concentrations of free amino acids in shoot stems between control and fluoride treatment. However, the relatively low concentration of arginine in the F treatment at the end of the growing season might indicate disturbances in the nitrogen metabolism of spruce seedlings.