Mechanisms for carbon and nutrient release and retention in beech forest gaps

Nutrient cycling and water balance in forest gaps has received little attention until now, although gap regeneration is important to natural dynamics of temperate forests. Gaps of 30 m diameter, cut in a mature beech forest, exhibited a distinct change in microclimatic conditions in comparison with the surrounding stand. Soil moisture in gaps remained very high throughout the observation period. Disruption of the N cycle in gaps led to substantial nitrate losses; seepage water nitrate concentrations were 10–18 mg NO₃-N L^-1. Excess nitrification was a significant cause of soil acidification and aluminium release. The pH in subsoil seepage water decreased by 0.25. Liming in gaps promoted the establishment of a herbaceous vegetation, which functioned as an important nutrient sink, and thus is recommended for tree regeneration in highly acidified forest ecosystems as it increases the resilience of the ecosystem to nutrient losses.     

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.     

Water balance of conifer logs in early stages of decomposition

Seasonal and long-term changes in the water balance of conifer logs during the first 8 years of decomposition were studied in an old-growth Pseudotsuga/Tsuga forest in the Oregon Cascade Mountains. Measurements were made of the moisture content of outer bark, inner bark, sapwood, and heartwood and of the flow of water into and out of logs of four species (Abies amabilis, Pseudotsuga menziesii, Thuja plicata, and Tsuga heterophylla). After the logs had decomposed from 1 to 2 years, 38–47% of the canopy throughfall landing upon them ran off the surface, 29–34% leached from the bottom, and 21–30% was absorbed and evaporated. After 8 years of decomposition, water entering and then leaching from logs increased 1.3 times while runoff decreased a similar amount. The proportion of water stored by and evaporated from logs in this study indicates that in old growth forests they may intercept 2–5% of the canopy throughfall to the forest floor and that, even in early stages of decomposition, they may affect the hydrological cycle of Pacific Northwest old-growth forests.This is paper 2945 of the Forest Research Laboratory, Oregon State University, Corvallis     

Rate of soil acidification under wheat in a semi-arid environment

The rate of acidification under wheat in south-eastern Australia was examined by measuring the fluxes of protons entering and leaving the soil, using the theoretical framework of Helyar and Porter (1989). Monthly proton budgets were estimated for the root zone (0–90 cm layer) and for the 0–25 and 25–90 cm layers. After an annual cycle, the root zone was alkalinized by 0.5 to 3.1 kmol OH^- ha^-1. The alkalinity originated from the mineralization of the organic anions contained in the organic matter. The budget was near neutrality in the 0–25 cm layer (range: –1.0 to 1.4 kmol H⁺ ha^-1), whereas there was net alkalinization in the 25–90 cm layer (1.7 to 2.3 kmol OH^- ha^-1). In the 0–25 cm layer, the acidity produced in autumn by mineralization of organic nitrogen was counterbalanced by the alkalinity released from crop residues. The main acidifying factor in this layer was leaching of NO₃ ^- during early winter (2.4 kmol H⁺ ha^-1). Nitrate added through leaching was the main alkalinizing factor in the 25–90 cm layer, as added NO₃ ^- was taken up by the roots or denitrified in this layer. Urea fertilization had almost no effect on the rate of acidification, as little NO₃ ^- was leached out of the root zone. The factors acidifying the soil under wheat were limited in this environment because of the small amout of NO₃ ^- leached and the retention of the crop residues.     

Effects of forest fertilization on nitrogen leaching and soil microbial properties in the Northern Calcareous Alps of Austria

Several boreal and alpine forests are depleted in nutrients due to acidification. Fertilization may be a remedy, but rapidly-soluble salts (N, P, K, Mg) may pose nitrate problems for the groundwater or decrease microbial activity.With the aim to investigate potential nitrogen leaching after fertilization we set up an experiment employing intact soil cores (11 cm diameter, 20–40 cm long) from a mixed forest and a Picea abies stand (soil type Rendsina) in the Northern Calcareous Alps of Austria. The cores were fertilized with a commercial NPK fertilizer or a methylene-urea-apatite-biotite (MuAB) fertilizer at a rate corresponding to 300 kg N ha^-1 and incubated for 28 weeks together with unfertilized controls. Both soil water (retrieved 5 cm below the soil surface) and leachate were analyzed for nitrate and ammonium in regular intervals. After the incubation, soil microbial biomass and basal repiration were determined and a nitrogen mineralization assay was performed.For the control, in the soil water and leachate maximum NH₄ ⁺ and NO₃ ^- concentrations of 5 and 11 mg N L^-1, respectively, were found. Compared to that, MuAB fertilizer resulted in a slow increase of NH₄ ⁺ and NO₃ ^- in the soil water (up to 11 and 35 mg N L^-1 respectively) and in the leachate (4 mg NH₄ ⁺-N L^-1 and 44 mg NO₃ ^--N L^-1). Highest nitrogen loads were found for the fast release NPK fertilizer, with NH₄ ⁺ and NO₃ ^- concentrations up to 170 and 270 mg N L^-1, respectively, in the soil water. NH₄ ⁺-N levels in the leachate remained below 5, while NO₃-N levels were up to 190 mg L^-1. Fast- release NPK caused a significant decrease of microbial biomass and basal respiration. These parameters were not affected by MuAB fertilizer.The results suggest that the MuAB fertilizer may be an ecologically appropriate alternative to fast-release mineral fertilizers for improving forest soils.     

The effects of SO2 and O3 fumigation on acid deposition and foliar leaching in the Liphook forest fumigation experiment

The ambient pollution climate at the Liphook forest fumigation site, where coniferous trees were fumigated with SO₂ and O₃, for 4 years under field conditions, was characteristic of the fringes of the areas where pollutant effects are a problem. Experimental treatments increased SO₂ concentrations to levels more characteristic of Eastern Europe, and summer O₃ concentrations by 30%. Deposition of SO₂ to the soil between the trees (inferred from shallow lysimeters) was significant, the deposition velocity being 2–1 mms^?1. Deposition to Scots pine and Sitka spruce canopies was greater, deposition velocities being 8.5 and 9.4 mm s^?1, respectively. These high values may perhaps be explained by co-deposition with NH₃. Calculations assume that dry deposition was the sole source of SO₄^2? gain in throughfall, and that there was no significant retention by the trees. There was a trend for O₃ to enhance SO₂ deposition to both soil and trees. Fumigation with SO₂ led to a significant increase in leaching of cations from foliage. Each species neutralized about 63% of the dry-deposited SO₂, predominantly by ion exchange for Ca and K. Equations are provided which allow calculation of foliar leaching given SO₂ concentrations or SO₄^2? deposition. Fumigation increased the rate of nutrient cycling considerably, without affecting foliar concentrations or damaging the trees. Ozone treatments did not enhance foliar leaching, calling into question some suggested mechanisms for the causes of forest decline.     

Wheat and soil bromide dynamics after fumigation with methyl bromide in a mediterranean climate

Summary Soil and wheat bromide dynamics are studied in methyl bromide-fumigated plots in a Mediterranean climate. Bromide residues range between 5 to 10 ppm in the fumigated soil and they are distributed to a depth of 50–60 cm, where a compacted layer exists, in accordance with soil organic matter and moisture distribution. The total amount of bromide in soil is 5.8 gm⁻² up to a depth of 1 m and it remains almost constant during the wheat growth period. The plant bromide concentration decreases throughout the development of spring wheat. The bromide distribution in the different plant organs was identical in the two years studied and it is correlated with the chloride content. Fumigation increases the phosphorus concentration in wheat and does not affect sulphur and chloride. Though the bromide concentration in the fumigated soils is high, the levels in the plants growing in it do not cause scorched areas. This may be due to antagonic Br/Cl and Br/NO₃ effects.     

Effects of differentiated applications of fertilizer N on leaching losses and distribution of inorganic N in the soil

Summary Nitrogen fertilizer was applied to field plots at rates of 0, 50, 100, 150 and 200 N kg/ha yr, in order to determine the effects of differentiated N applications on drainage water and groundwater quality. Water samples, collected monthly or bimonthly from 1974 to 1983, were analysed for inorganic and total N content. In order to see the impact of residual N on leaching losses, soil samples were collected to a depth of 2 m in the N0, N100 and N200 plots, usually in September and April. Leaching of nitrate was moderate to the N100 level but increased substantially with increasing fertilization, up to 91 N kg/(ha-yr) for the highest application rate (N200), during the wet year of 1980/81. The losses were greatest during the fall, mainly due to high levels of N remaining in the soil after harvest combined with high precipitation. The N content of the groundwater did not show any significant correlation to the fertilization intensity. A buildup of inorganic N in the soil occurred only when excessive amounts of fertilizer were applied (N200), while the contents of the N0 and N100 treatments fluctuated around states of balance, approximately 45 and 70 N kg/ha respectively. Spring rape followed by winter wheat showed a great ability to reduce N contents in the tile effluent from highly fertilized plots (N150 and N200), even though the plots had received excessive amounts of fertilizer for several years. Results of this experiment in central Sweden demonstrate the importance of applying nitrogen fertilizer in balance with crop needs and of maintaining a growing crop cover as much of the time as possible in order to minimize water pollution.     

The role of cattle in the volatile loss of nitrogen from a shortgrass steppe

The cycling and volatile loss of N derived from cattle urine at upland and lowland sites within the shortgrass steppe of eastern Colorado was studied, using¹⁵N-labelled urea as an N source. Losses of NH ₀ ³ were determined by direct measurement and by difference. Losses were higher from coarse (27% summer, 12% winter) than from fine textured (0–2%) soils. Immobilization and plant uptake of N accounted for significant amounts of added N. Extrapolating our plot measurements to a typical pasture, using spatially and temporally stratified urine deposition data, losses from upland sites were calculated to be 0.016 g N · m^-2 · y^-1, while losses from lowland sites were negligible. This resulted in an average loss of 0.011 g N · m^-2 · y^-1 for a pasture divided 70:30 between uplands and lowlands. The loss of urine N calculated assuming no spatial stratification would be sevenfold higher (0.076 g N · m^-2 · y^-1). Losses of NH ₀ ³ from urine, animal biomass removal, and NH₂O loss totaled only 0.07 g N · m^-2 · y^-1 , or about 25% of wet deposition input. We calculated a potential loss of NH ₀ ³ from senescing vegetation of 0.26 g N · m^-2 · y^-1, an order of magnitude larger than all other losses combined.     

Effects of rainfall on the use of foliar analysis for diagnosing boron toxicity in field-grown wheat

The effect of rain on foliage elemental composition, especially B, was assessed using samples of wheat collected at three harvests from a field trial conducted in soil containing excessive levels of B. Moderate rainfall substantially decreased both the B concentration and content of whole shoots and young leaves. The change in B concentration due to rain suggests that foliar analysis is unreliable for diagnosing B toxicity. For the other elements examined (Ca, Cu, Mg, Mn, Mg, P, S, Zn), rainfall had little effect.