Nitrogen accumulation efficiency: Relationship between excess fertilizer and soil‐plant biological activity in winter wheat

The point at which nitrogen (N) applied approaches 100% recovery in the soil once plant and microbial sinks have been saturated has not been determined in winter wheat (Triticum aestivum L.) production systems. In dryland winter wheat, subsoil accumulation has not been found to occur until N rates exceed that required for maximum yield. Many conventional N rate experiments have not properly evaluated subsoil N accumulation due to the lack of equally spaced N rates at the high end of the spectrum over which accumulation is expected to occur. Therefore, the objectives of this study were to (i) determine when soil profile accumulation efficiencies reach 100% in continuous winter wheat production and (ii) to evaluate the potential for nitrate‐nitrogen (NO₃ ^‐N) leaching in continuous winter wheat when extremely high rates of fertilizer N are used. Two field experiments (T505 and T222) were conducted for two years using ten N rates (preplant‐incorporated) ranging from 0 to 5376 kg N ha¹. No additional preplant fertilizer was applied in the second year. Following the first and second year wheat harvest, soil cores were taken to 2.4 m and bulk density, ammonium‐nitrogen (NH₄‐N) and NO₃‐N were determined. Crop N‐use efficiency (NUE) (N uptake treated ‐ N uptake check/rate applied) and soil profile inorganic N accumulation efficiencies (NAE) [net inorganic N accumulation in the soil profile/(fertilizer applied ‐ net N removed in the crop)] changed with fertilizer rate and were inversely related. Priming (increased net mineralization of organic N pools when low rates of fertilizer N are applied) may have occurred since increased NUE was observed at low N rates. The highest N‐accumulation efficiencies were at N rates of 168 and 448 kg ha^‐1 in experiments T505 and T222, respectively. At both T222 and T505, no subsoil accumulation of NH₄‐N or NO₃‐N beyond 100 cm was observed for any of the N treatments when compared to the 0‐N check, even when N rates exceeded 448 kg ha^‐1.     

Crop Utilization of Nitrogen in Swine Lagoon Sludge

Swine lagoon sludge is commonly applied to soil as a source of nitrogen (N) for crop production but the fate of applied N not recovered from the soil by the receiver crop has received little attention. The objectives of this study were to (1) assess the yield and N accumulation responses of corn (Zea mays L.) and wheat (Triticum aestivum) to different levels of N applied as swine lagoon sludge, (2) quantify recovery of residual N accumulation by the second and third crops after sludge application, and (3) evaluate the effect of different sludge N rates on nitrate (NO₃-N) concentrations in the soil. Sludge N trials were conducted with wheat on two swine farms and with corn on one swine farm in the coastal plain of North Carolina. Agronomic optimum N rates for wheat grown at two locations was 360 kg total sludge N ha^?1 and the optimum N rate for corn at one location was 327 kg total sludge N ha^?1. Residual N recovered by subsequent wheat and corn crops following the corn crop that received lagoon sludge was 3 and 12 kg N ha^?1, respectively, on a whole-plant basis and 2 and 10 kg N ha^?1, respectively, on a grain basis at the agronomic optimum N rate for corn (327 kg sludge N ha^?1). From the 327 kg ha^?1 of sludge N applied to corn, 249 kg N ha^?1 were not recovered after harvest of three crops for grain. Accumulation in recalcitrant soil organic N pools, ammonia (NH₃) volatilization during sludge application, return of N in stover/straw to the soil, and leaching of NO₃ from the root zone probably account for much of the nonutilized N. At the agronomic sludge N rate for corn (327 kg N ha^?1), downward movement of NO₃-N through the soil was similar to that for the 168 kg N ha^?1 urea ammonium nitrate (UAN) treatment. Thus, potential N pollution of groundwater by land application of lagoon sludge would not exceed that caused by UAN application.     

Residual nitrogen effects on wheat following legumes in the southern plains

Increasing nitrogen (N) fertilizer prices give rise to the question of N benefits from legumes in cropping systems in the Southern Great Plains. This study quantified wheat (Triticum aestivium L.) hay production and N uptake over seven years following six years of alfalfa (Medicago sativa L.), cicer milkvetch (Astragalus cicer L.), or grass (Old World bluestem, Bothriochloa ischaemum L.) production in western Oklahoma. Precipitation over the seven years averaged 550 mm·yr^‐1. The major residual N effects were measured within the first five years. On a fine sandy loam soil, wheat hay yields averaged 3,070 kg·ha^‐1·yr^‐1 over five years following alfalfa, 2,580 kg·ha^‐1·yr^‐1 following milkvetch, and 950 kg·ha^‐1·yr^‐1 following grass with N uptake attributed to the residual effect from legumes (calculated by the difference method) averaged 34 kg N ha^‐1·yr^‐1 from alfalfa and 25 kg·ha^‐1·yr^‐1 from milkvetch. On a deep loamy sand soil, wheat hay yields averaged 1,290 kg·ha^‐1·yr^‐1 over five years following alfalfa and 710 kg·ha^‐1·yr^‐1 following grass with N uptake attributed to the residual effect from alfalfa averaged 8 kg N ha^‐1·yr^‐1. Thus, the residual N effect attributed to legumes was substantial on the fine sandy loam soil and relatively small on the deep loamy sand soil.     

施用辐照处理的污水污泥对作物产量和土壤氮的影响

A field experiment was conducted to study the feasibility of irradiated and non-irradiated sewage sludge as a fertilizer for the growth of wheat and rice. The irradiated and non-irradiated sewage sludge were applied at rates of 0 (CK), 75, 150, 225 and 300 kg N ha^-1 for wheat, and 0 (CK), 112.5, 225, 337.5 and 450 kg N ha^-1 for rice, respectively. (NH₄)₂SO₄ at a rate of 150 kg N ha^-1 for wheat, and 225 kg N ha^-1 for rice were added to the control treatments. Additionally, 20 kg ¹⁵N ha^-1 in the form of (NH₄)₂SO₄ was added to each treatment for wheat to study the effect of sewage sludge on chemical nitrogen fertilizer recovery. The results showed that the irradiation of sewage sludge by gamma ray at a dosage of 5 kGy increased crop yield by 11%~27% as compared to the non-irradiated treatments. Irradiation stimulated mineralization of organic nitrogen in the sludge and improved seedling growth. It was found that addition of irradiated sludge could reduce the leaching loss of chemical nitrogen fertilizer. Both irradiated and non-irradiated sewage sludge could increase the content of soil total nitrogen. Based on the preliminary results, it was concluded that irradiated sewage sludge could partly substitute for chemical nitrogen fertilizer in crop production.     

Fate of fertilizer nitrogen.

Results are presented from a three year lysimeter investigation, employing single (¹⁵NH₄NO₃) and double (¹⁵NH₄¹⁵NO₃) labelled ammonium nitrate to study the uptake of soil and fertilizer nitrogen by cut ryegrass at 250, 500 and 900 kg N ha^?1 a^?1. Average annual recoveries of nitrogen were equivalent to 99,76 and 50% of the nitrogen added at 250, 500 and 900 kg N ha^?1, respectively. At 250 kg N ha^?1 the difference between the overall nitrogen recovery and the fertilizer recovery was almost entirely attributable to pool substitution resulting from mineralization/immobilization turnover (MIT). At 900 kg N ha^?1 both the low overall recovery of nitrogen and the low fertilizer recovery reflected the large excess of available nitrogen over crop requirements. No evidence of ‘priming’ was obtained. Analysis of the results from single and double labelled lysimeters using simultaneous equations indicated that at 250 kg N ha^?1,～70% of the nitrogen in the crop was derived from the ammonium pool. At 500 kg N ha^?1 this dropped to 64%, while at 900 kg N ha^?1 the figure was 59%. There was a suggestion that at the lower application rates, preferential uptake of ammonium was occurring but that as N supply exceeded crop requirements, nitrate was the major N source. Despite the preferential exploitation of the ammonium pool, at 250 and 500 kg N ha^?1 pool substitution resulting from MIT resulted in lower recoveries of fertilizer ammonium compared with fertilizer nitrate.     

Nitrogen Balance in the Magruder Plots Following 109 Years in Continuous Winter Wheat

Abstract

The Magruder plots are the oldest continuous soil fertility wheat research plots in the Great Plains region, and are one of the oldest continuous soil fertility wheat plots in the world. They were initiated in 1892 by Alexander C. Magruder who was interested in the productivity of native prairie soils when sown continuously to winter wheat. This study reports on a simple estimate of nitrogen (N) balance in the Magruder plots, accounting for N applied, N removed in the grain, plant N loss, denitrification, non‐symbiotic N fixation, nitrate (NO₃ ^?) leaching, N applied in the rainfall, estimated total soil N (0–30 cm) at the beginning of the experiment and that measured in 2001. In the Manure plots, total soil N decreased from 6890 kg N ha^?1 in the surface 0–30 cm in 1892, to 3198 kg N ha^?1 in 2002. In the Check plots (no nutrients applied for 109 years) only 2411 kg N ha^?1 or 35% of the original total soil organic N remains. Nitrogen removed in the grain averaged 38.4 kg N ha^?1 yr^?1 and N additions (manure, N in rainfall, N via symbiotic N fixation) averaged 44.5 kg N ha^?1 yr^?1 in the Manure plots. Following 109 years, unaccounted N ranged from 229 to 1395 kg N ha^?1. On a by year basis, this would translate into 2–13 kg N ha^?1 yr^?1 that were unaccounted for, increasing with increased N application. For the Manure plots, the estimate of nitrogen use efficiency (NUE) (N removed in the grain, minus N removed in the grain of the Check plots, divided by the rate of N applied) was 32.8%, similar to the 33% NUE for world cereal production reported in 1999.     

Possibilities of using sewage sludge as nitrogen fertilizer for maize

Abstract

The objective of this study was to determine the effects of nitrogen fertilizer sources of ammonium sulphate and municipal sewage sludge on yield, N content and uptake of the maize (Zea mays L.). Nutrient and heavy metals were determined in soil and plant. The experiment with three sludge rates (256, 513 and 1026 kg total N ha^?1 or 9.5, 18.0 and 38.1 t ha^?1 sludge), two nitrogen rates (80 and 160 kg N ha^?1) and zero-N control were conducted on a clay loam soils under irrigated conditions in Eastern Anatolia region in Turkey. Treatments were arranged in a randomized complete block design with four replications. Yield, N content and total N uptake of maize increased significantly with sludge application. 9.5 t and 19.0 t ha^?1 sewage sludge applications did not significantly affect heavy metal content of leaf and grain. However, 38.1 t ha^?1 sludge applications increased leaf Pb and Zn. DTPA-extractable Cd, Cu, Fe, Pb and Zn concentrations of the soil increased at applications of 38.1 t ha^?1 sewage sludge, whereas applications of 9.5 t and 19.0 t ha^?1 sludge only resulted in elevated levels of Cu and Zn, We conclude that if sewage sludge is to be used in production of maize, applications rate up to 19 t ha^?1 could be accepted. However, this means also that the N requirement of maize crop is not covered by the sludge; therefore, the rest of nitrogen could be supplied as inorganic N.     

Subsoil retention of organic and inorganic nitrogen in a Brazilian savanna Oxisol

Abstract. Nitrogen (N) loss by leaching poses great challenges for N availability to crops as well as nitrate pollution of groundwater. Few studies address this issue with respect to the role of the subsoil in the deep and highly weathered savanna soils of the tropics, which exhibit different adsorption and drainage patterns to soils in temperate environments. In an Anionic Acrustox of the Brazilian savanna, the Cerrado, dynamics and budgets of applied N were studied in organic and inorganic soil pools of two maize (Zea mays L.) – soybean (Glycine max (L.) Merr.) rotations using ¹⁵N tracing. Labelled ammonium sulphate was applied at 10 kg N ha^?1 (with 10 atom%¹⁵N excess) to both maize and soybean at the beginning of the cropping season. Amounts and isotopic composition of N were determined in above‐ground biomass, soil, adsorbed mineral N, and in soil solution at 0.15, 0.3, 0.8, 1.2 and 2 m depths using suction lysimeters throughout one cropping season. The applied ammonium was rapidly nitrified or immobilized in soil organic matter, and recovery of applied ammonium in soil 2 weeks after application was negligible. Large amounts of nitrate were adsorbed in the subsoil (150–300 kg NO₃^?‐N ha^?1 per 2 m) matching total N uptake by the crops (130–400 kg N ha^?1). Throughout one cropping season, more applied N (49–77%; determined by ¹⁵N tracers) was immobilized in soil organic matter than was present as adsorbed nitrate (2–3%). Most of the applied N (71–96% of ¹⁵N recovery) was found in the subsoil at 0.15–2 m depth. This coincided with an increase with depth of dissolved organic N as a proportion of total dissolved N (39–63%). Hydrophilic organic N was the dominant fraction of dissolved organic N and was, together with nitrate, the most important carrier for applied N. Most of this N (>80%) was leached from the topsoil (0–0.15 m) during the first 30 days after application. Subsoil N retention as both adsorbed inorganic N, and especially soil organic N, was found to be of great importance in determining N losses, soil N depletion and the potential of nitrate contamination of groundwater.     

Effects of lime and sewage sludge on soil,pasture production,and tree growth in a six‐year‐old Populus canadensis Moench silvopastoral system

In many regions worldwide, silvopastoral systems are implemented to enable sustainable land use allowing short, medium, and long‐term economic returns. However, the short‐term production in silvopastoral systems is often limited due to nonappropriate soil‐fertility management. This study evaluated the effects of two doses of lime (0 and 2.5 t CaCO₃ ha^–1) and three sewage‐sludge treatments (0, 200, and 400 kg total N ha^–1 y^–1 applied in 2 consecutive years) on soil characteristics (soil pH, soil organic matter [SOM], soil nitrogen, cation‐exchange capacity [CEC]), pasture production, and tree growth in a silvopastoral system of Populus × canadensis Moench in Galicia, northern Spain during 6 years after establishment. Soil pH increased during the experimental period for all treatments, although this effect was more pronounced after lime application. Changes in SOM and soil nitrogen content were not consistent over time, but sewage‐sludge application seemed to result in higher values. Higher CEC was found for treatments with lime and sewage‐sludge application. Following incorporation of lime and sewage sludge, pasture production was significantly enhanced (cumulative pasture production 51.9 t DM ha^–1 for Lime/N400 compared to 39.0 t DM ha^–1 for No lime/N0). This higher pasture production also affected tree growth due to more severe competition between pasture and tree resulting in slower tree growth. Liming and application of sewage sludge are relevant measures to improve soil fertility and thereby optimizing the overall production of silvopastoral systems. However, it is important not to overintensify pasture production to ensure adequate tree growth.     

Increased plant nitrogen loss with increasing nitrogen applied in winter wheat observed with 15nitrogen

Nitrogen (N) fertilizer is generally the most costly input for winter wheat (Triticum aestivum L.) production. Therefore, it was important to maximize fertilizer use efficiency and minimize N losses to the environment. One of the mechanisms responsible for decreased N use efficiency (NUE) was plant N loss. The objectives of this experiment were to determine fertilizer N recovery in winter wheat when produced for forage and grain, and to quantify potential plant N losses from flowering to maturity in winter wheat. Two long‐term (>25 years) winter wheat (Triticum aestivum L.) N rate fertility experiments (Experiment 222 and Experiment 502) were selected to evaluate ¹⁵N fertilizer recovery. Percent ¹⁵N recovery was determined from all microplots in plant tissue at flowering, in the grain, and straw at harvest and in the soil. Fertilizer N(¹⁵NH₄ ¹⁵NO₃) was applied atratesof 0, 45, 90, and 135kg N ha^‐1 in Experiment 222, and 0, 22, 45, 67, 90, and 112 kg N ha^‐1 in Experiment 502. The ratio ofNO₃ ^‐to NH₄ ⁺ in wheat forage at flowering was positively correlated with estimated plant N loss. Estimated plant N loss (total N uptake in wheat at flowering minus N uptake in the grain and straw at maturity) ranged from a net gain of 12 kg N ha^‐1 to a loss of 42 kg N ha^‐1, and losses increased with increasing N applied.     

Nitrogen deposition and leaching in European forests — Preliminary results from a data compilation

Input-output fluxes of nitrogen (N) and other ecosystem data from 64 European forest ecosystem studies have been compiled in a database (ECOFEE). Sites with high N deposition (up to 64 kg N ha^–1yr^–1) were characterized by high input of ammonia/ammonium. The deposition of oxidized N was usually only 10 to 15 kg N ha^–1yr^–1 Of all the sites included, 60 % leached more than 5 kg N ha^–1yr^–1. Elevated nitrate leaching appeared at inputs above 10 kg N ha^–1yr^–1. At several sites with inputs of 15–25 kg N ha^–1yr^–1 nitrate leaching approached the N input, whereas ammonium dominated sites with high input still retained c. 50 % of the input.     

Soil Acidification Induced by Ammonium Sulphate Addition in a Norway Spruce Forest in Southwest Sweden

The contributions of different acidifying processes to the total protonload (TPL) of the soil in control plots (C) and ammonium sulphate treatedplots (NS) were studied in a Norway spruce stand in Southwest Sweden during 1988–1998. The annual deposition of inorganic nitrogen and sulphate was on average 18 kg N and 20 kg S ha^-1. In addition the NS treated plots received 100 kg N and 114 kg S ha^-1 annually. The amounts of nutrients added to the ecosystem by wet and dry deposition and the leaching at 50 cm depth were calculated. The net atmosphericproton load, the proton load by nitrogen transformations in the soil, the sulphate sorption/desorption in the soil and the excess base cation accumulation in biomass were calculated. There was no leaching of inorganic nitrogen from control plots during the study period. The net atmospheric proton deposition, originating from sulphuric and nitric acid deposition, was the main contributor to TPL in control plots. The addition of ammonium sulphate increased the leaching of ammonium, nitrate, sulphate, magnesium and calcium but not of potassium. The TPL in NS plots was about ten times that in control plots. The nitrogen transformation processes were the main contributors to TPL to NS soil, in the beginning by ammonium uptake and later also by nitrification. The pH decreased by 0.4 units in the mineral soil. The between-year variation in TPL during the eleven year period in C plots (200–1500 mol_c ha^-1 yr^-1) and in NS plots (1000–13000 mol_c ha^-1 yr^-1) was mainly dependent on the sorption or release of sulphate. Both in C and NS, the TPL was buffered mainly by dissolving solid aluminium compounds, most probably some Al(OH)₃ phase.     

CONTROLLED-RELEASE UREA FOR RICE PRODUCTION AND ITS ENVIRONMENTAL IMPLICATIONS

Controlled-release urea (CRU) and its placement method in rice production were investigated during 2007 and 2008 seasons. Controlled-release urea was applied at 62.5, 125, and 187.5 kg nitrogen (N) ha^?1, and the urea was 187.5 kg N ha^?1. All the CRU treatments were applied to the nursery beds once, and they were brought into the paddy field during transplanting, while the urea treatment was split into three applications from the plowing to the harvest. The results showed that rice seedlings with CRUs germinated and grow well and there was no salt damage at the nursery stage. The CRU treatment with 125 kg N ha^?1 had 33% less N than urea treatment (187.50 kg N ha^?1), but it produced significantly higher grain and straw yields, higher total N uptake and total apparent N uptake efficiency. In addition, all the CRU treatments effectively decreased floodwater ammonium (NH₄ ⁺)-N and nitrate (NO₃ ^?)-N concentrations, pH, and N runoff.     

Dicyandiamide effects on nitrification and total inorganic soil nitrogen in sandy soils

Abstract

Inhibition of nitrification in soil results in a decreased ratio of nitrate‐nitrogen (NO₃‐N) to ammonium‐nitrogen (NH₄‐N). If the conditions for NO₃‐N loss by leaching or denitrification exist, nitrification inhibitors should increase concentrations of total inorganic soil nitrogen (N) (TISN) (NH₄‐N + NO₃‐N). This can then result in plants taking up more N and developing more crop yield or biomass. This study examined whether inhibition of nitrification by dicyandiamide (DCD) would result in increased concentrations of TISN under field conditions. The effects of DCD on soil N were evaluated in hyperthermic sandy soils planted to potato (Solanum tuberosum L., cv. Atlantic). Treatments were factorial combinations of N as ammonium nitrate (NH₄NO₃) at 67, 134, and 202 kg N ha^‐1 and DCD at 0, 5.6, and 11.2 kg DCD ha^‐1. Soil NH₄‐N, NO₃‐N, and TISN concentrations were determined for up to five potato growth stages at two locations for two years for a total of 16 determinations (cases), i.e., four were not determined. The N form ratio [NO₃‐N/(NH₄‐N + NO₃‐N] x 100 was decreased in 10 of 16 cases, indicating that nitrification was inhibited by DCD. With two of these 10 cases, TISN concentration increased, but with four others, TISN concentration decreased with at least one N rate. With four of these 10 cases, inhibition of nitrification had no effect on TISN concentration. Under the conditions of these field studies, DCD inhibited nitrification more often than not. Inhibition of nitrification was, however, more likely to reduce TISN concentration than to increase it. This may have been due to DCD effects on immobization of applied NH₄‐N.     

Nitrat‐Austräge auf intensiv und extensiv beweidetem Grünland,erfasst mittels Saugkerzen‐ und Nmin‐Beprobung I Einfluss der Beweidungsintensität

Nitrate leaching from intensively and extensively grazed grassland measured with suction cup samplers and sampling of soil mineral‐N I Influence of pasture management Leaching of nitrate (NO₃^—) from two differently managed cattle pastures was determined over four winters between 1993 and 1997 using ceramic suction cup samplers (with min. 34 cups ha^—1); additionally, vertical soil mineral‐N content in 0—0.9 m (N_min) was measured at the beginning and end of two winters (with min. 70 different sample cores ha^—1). The experimental site in the highlands north‐east of Cologne, Germany, is characterized by high annual precipitation (av. 1,362 mm between 1993 and 1996). An intensive continuous grazing management (1.3 ha, fertilized with 250 kg N ha^—1 yr^—1, average stocking density 4.9 LU ha^—1, = [I]) was tested against an extensive continuous grazing system (2.2 ha, av. 2.9 LU ha^—1; no N‐fertilizer but an estimated proportion of Trifolium repens up to 15 % of total dry matter in the final year, = [E]). The results can be summarized as follows: (1) Mean leaching losses of NO₃‐N, estimated from suction cup sampling and balance of drainage volume, were 85 kg NO₃‐N ha^—1 [I] and 15 kg NO₃‐N ha^—1 [E] during three wet winters with drainage volumes between 399 and 890 mm; in a dry winter with 105 mm calculated percolation, nitrate leaching decreased by a factor of 5 for both grazing treatments. (2) Although the amount of mineral N in soil (N_min) sampled in late autumn showed differences between intensive and extensive grazing, the N_min method permits no certain indication of the risk of NO₃ leaching. For example, during the winter period 1994/95 a reduction of mineral N in the soil (0—0.9 m) in both grazing treatments was found (—33 [I] / —8 [E] kg NO₃‐N ha^—1 and —26 [I] / —21 [E] kg NH₄‐N ha^—1) whereas during the winter 1996/97 an increase in almost all mean mineral N values occurred (+10 [I] / +2 [E] kg NO₃‐N ha^—1 and +10 [I] / —10 [E] kg NH₄‐N ha^—1). (3) In spite of the differences between both methods, the experiment shows that NO₃‐N leaching under extensive grazing could be reduced almost to levels close to those under mown grassland.     

Nitrogen Fixation,Soil Nitrogen Availability,and Biomass in Pure and Mixed Plantations of Alder and Pine in Central Korea

ABSTRACT

Rates of nitrogen (N) fixation, soil N availability, and aboveground biomass were measured in 27-year-old pure and mixed Alnus hirsuta and Pinus koraiensis plantations in central Korea. Nodule biomass and N fixation were 179.3 kg ha^{? 1} and 46.6 kg ha^{? 1}yr^{? 1} for the pure A. hirsuta plantation (PA) and 95.2 kg ha^{? 1} and 41.1 kg ha^{? 1}yr^{? 1} for the mixed A. hirsuta + P. koraiensis plantation (MAP), respectively. A. hirsuta seemed to provide more than two thirds of annual N requirement for P. koraiensis.Rates of acetylene reduction were significantly related to soil temperature (R² = 0.51, P < 0.001), but not to soil moisture content. Total inorganic N [ammonium (NH₄ ⁺)plus nitrate (NO₃ ^?)] availability measured using ion exchange bags were significantly higher under PA (27.91 μ g-N bag^{? 1}) and MAP (31.34 μ g-N bag^{? 1}) than under the pure P. koraiensis plantation (PP) (14.31 μ g-N bag^{? 1}). Especially soils under the influence of A. hirsuta showed at least 2 fold increase in resin total inorganic N concentrations. Total aboveground biomass (Mg ha^{? 1}) was 147.3 for PA, 145.8 for MAP, and 174.8 for PP, respectively, and was not significantly different among plantations. A. hirsuta significantly increased soil N availability; however, the influence of N fixation on aboveground biomass was not significant for the study plantations.     

Input-Output Budgets of Inorganic Nitrogen for 24 Forest Watersheds in the Northeastern United States: A Review

Input-output budgets for dissolved inorganic nitrogen (DIN) are summarized for 24 small watersheds at 15 locations in the northeasternUnited States. The study watersheds are completely forested, free of recent physical disturbances, and span a geographical region bounded by West Virginia on the south and west, and Maine on the north and east. Total N budgets are not presented; however, fluxes of inorganic N in precipitation and streamwater dominate inputs and outputs of N at these watersheds. The range in inputs of DIN in wet-only precipitation from nearby National Atmospheric Deposition Program (NADP) sites was 2.7 to 8.1 kg N ha^-1 yr^-1 (mean = 6.4 kg N ha^-1 yr^-1; median = 7.0 kg N ha^-1 yr^-1). Outputs of DIN in streamwater ranged from 0.1 to 5.7 kg N ha^-1 yr^-1 (mean = 2.0 kg N ha^-1 yr^-1; median = 1.7 kg N ha^-1 yr^-1). Precipitation inputs of DIN exceeded outputs in streamwater at all watersheds, with net retention of DIN ranging from 1.2 to 7.3 kg N ha^-1 yr^-1 (mean = 4.4 kg N ha^-1 yr^-1; median = 4.6 kg N ha^-1 yr^-1). Outputs of DIN in streamwater were predominantly NO₃-N (mean = 89%; median = 94%). Wet deposition of DIN was not significantly related to DIN outputs in streamwater for these watersheds. Watershed characteristics such as hydrology, vegetation type, and land-use history affect DIN losses and may mask any relationship between inputs and outputs. Consequently, these factors need to be included in the development of indices and simulation models for predicting 'nitrogen saturation' and other ecological processes.     

Nitrogenous fertilizers and earthworm populations in agricultural soils

The influence of various inorganic and organic fertilizers was assessed in three long-term “classical” experiments and two short-term field experiments, one on grass and one on wheat. The long-term experiments included Broadbalk which had grown continuous wheat since 1843, Barnfield, continuous root crops since 1843 and Park Grass, continuous grass since 1836. Annual fertilizer treatments were farmyard manure (48 and 96 kg N ha^?1), various forms of inorganic nitrogen (48, 96, 144 and 192 kg N ha^?1), liquid and solid sewage sludge and sewage cake in a wide range of doses.In the three arable experiments, all species of earthworms were more numerous in plots treated with organic fertilizers than in untreated plots.There was a strong positive correlation (r = 0.9825) between amounts of inorganic N applied and populations of earthworms. Plots receiving both inorganic and organic N had the largest populations of earthworms.The effects of both inorganic and organic N were much less on earthworm populations in grassland than on those in arable crops, even in the long-term experiments, and there was some evidence of adverse effects when an excessive amount of liquid sludge was applied in a single dose.Effects of organic fertilizers were greater on populations of Lumbricus terrestris than on those of Allolobophora longa, A. caliginosa or A. chorotica.     

Simulation of Increased Nitrogen Deposition to a Montane Forest Ecosystem: Partitioning of the Added 15N

Nitrogen (N) was added over two years to a spruce-dominated (Picea abies) montane forest at Alptal, central Switzerland. A solution of ammonium nitrate (NH₄NO₂) was frequently sprinkled on the forest floor (1500 m²) to simulate an additional input of 30 kg N ha^-1 yr^-1 over the ambient 12 kg bulk inorganic N deposition. The added nitrogen was labelled with ¹⁵NH₄ ¹⁵NO₃ during the first year. Results are compared to a control plot. Neither the trees nor the ground vegetation showed any increase in their N content. Only 4.1% of N in the ground vegetation came from the N addition. Current-year needles contained 11 mg N g^-1 dry weight, of which only 2% was from labelled N; older needles had approximately half as much ¹⁵N. The uptake from the treatment was therefore very small. Redistribution of N also took place in the trunks: 1 to 2-year-old wood contained 0.7% labelled N, tree rings dating back 3 to 14 years contained 0.4%. Altogether, the above-ground vegetation took up 12% of the labelled N. Most ¹⁵N was recovered in the soil: 13% in litter and roots, 63% in the sieved soil. Nitrate leaching accounted for 10%. Factors thought to be influencing N uptake are discussed in relation to plant use of N and soil conditions.     

Nitrogen mineralization in histosols of the everglades agricultural area

Abstract

A long‐term soil incubation and column nutrient leaching study was conducted to determine nitrogen (N)‐mineralization rates of selected Florida Histosols with drained and intermittent‐flooded conditions. Five surface soils from the Everglades Agricultural Area (EAA) were packed in columns (5‐cm i.d. containing the 0‐ to 15‐cm depth of each soil) and leached with 0.01M CaC12 followed by distilled water every 25 d for 1 yr. Drained columns were treated with a minus‐nitrogen‐phosphorus (NP) solution followed by applying ‐0.97 MPa tension to remove excess solution. Flooded columns received the same minus‐NP solution, but were flooded to a depth of 3 cm. Both treatments were incubated for 25‐d periods, solution sampled, and treatments reapplied. Because flooding conditions could not be maintained during the sampling period, this treatment is referred to as intermittent flooded. The ammonium‐nitrogen (NH₄ ⁺‐N) released from drained soils accounted for less than 6% of the total soluble N released from all soils, compared to more than 30% released from flooded soils. There were no differences in the amounts of soluble organic N from drained and intermittent flooded soils. Total soluble N from the surface 15‐cm of drained soils ranged from 217 to 509 kg‐ha^‐1yr^‐1, with 50 to 67% released as nitrate‐nitrogen (NO₃ ^‐‐N). In contrast, total soluble N released from flooded soils ranged from 168 to 345 kg‐ha^‐1yr^‐1, with less than 3% released as NO₃ ^‐‐N.