Increase In NO3-N Research Articles

Nitrogen Mineralization of Apple Orchard Soils in Regions of Western and South-Eastern Norway

The mineralization of nitrogen in apple orchard soil will increase the soil supply. An incubation study to test the soil potential and the validity of analytical methods was conducted at 3, 8, 15, and 20 °C for up to 128 days on soils from western and south-eastern Norway. Soils with the highest pH showed the highest mineralization. The mineralization increased with increasing temperature and time, but start-up N reduced mineralization. The mineralization cannot be estimated from standard soil chemical parameters because the different C/N ratio indicates organic material of different origin and quality. The increase in NO3-N started very quickly and ranged from 17 to 182% and 12 to 64% after 8 days at 3 °C and 20 °C, respectively. There was no correlation between total N in the soil and the amount of mineralized N. On average, the mineralization increased by 5–7% for a change of 1 °C in the interval from 8 to 15 °C in the soil. The chemical extraction method using heated KCl correlated well with the mineralization data. On average, the chemical method estimated 30 kg N ha−1, which corresponded to 0.48% of total N. Recommendations for N fertilization based on total N in the soil overestimate the contribution of plant-available N in most cases.

Agricultural intensification leads to higher nitrate levels in Lake Ontario tributaries

Eutrophication remains the most widespread water quality impairment globally and is commonly associated with excess nitrogen (N) and phosphorus (P) inputs to surface waters from agricultural runoff. In southern Ontario, Canada, increases in nitrate (NO3-N) concentrations as well as declines in total phosphorus (TP) concentration have been observed over the past four decades at predominantly agricultural watersheds, where major expansions in row crop production at the expense of pasture and forage have occurred. This study used a space-for-time approach to test whether ‘agricultural intensification’, herein defined as increases in row crop area (primarily corn-soybean-winter wheat rotation) at the expense of mixed livestock and forage/pasture, could explain increases in NO3-N and declines in TP over time. We found a clear, positive relationship between the extent of row crop area within watersheds and NO3-N losses, such that tributary NO3-N concentrations and export were predicted to increase by ~0.4 mg/L and ~130 kg/km2 respectively, for every 10% expansion in row crop area. There was also a significant positive relationship between row crop area and total dissolved phosphorus (TDP) concentration, but not export, and TP was not correlated with any form of landcover. Instead, TP was strongly associated with storm events, and was more sensitive to hydrologic condition than to landcover. These results suggest that pervasive shifts toward tile-drained corn and soybean production could explain increases in tributary NO3-N levels in this region. The relationship between changes in agriculture and P is less clear, but the significant association between dissolved P and row crop area suggests that increased adoption of reduced tillage practices and tile drainage may enhance subsurface losses of P.

The effect of forestry management activities on stream water quality within a headwater plantation Pinus radiata forest

Many long-term forestry water quality studies focus on the impact of the harvesting phase of forestry operations. As a result, the water quality impacts of other activities such as forest (re)planting, thinning and fertilising are less well understood. Here we report the results from 23 years of monthly water quality monitoring from a steep headwater catchment within the Waikato region, New Zealand. Three experimental sub-catchments were planted in different proportions of Pinus radiata (PW2 = 100%, K-Pine 57%; PW3 = 36%). PW2 and PW3 were historical pastoral sites in the first rotation of plantation forestry and K-Pine was harvested and subsequently planted in a second rotation of forestry. All sites underwent two phases of stand thinning six and eight years after planting. The most significant effect of forestry was the increase in nitrate-N (NO3-N) and total nitrogen (TN) concentrations in response to both stand planting and stand thinning operations. Planting resulted in significant increases in NO3-N, TN and DRP over a four-year planting period at PW2. Significant increases in NO3-N and TN were detected over a four-year thinning period, at all three experimental sites. We propose that stream NO3-N and TN concentrations increased in response to stand planting at PW2 because of the change in physical conditions (e.g. increased stream shading, proliferation of nitrogen fixing weeds and decreased spatial extent of seepage wetlands) caused by the change in land use. Increasing nitrogen concentrations due to decreasing stream runoff could also be contributing a factor. Any decrease in NO3-N and TN concentrations in response to increased uptake by the rapidly growing P. radiata appears to have been masked by these other factors. However, the increase in NO3-N and TN concentrations in response to stand thinning at all three experimental sites suggests that NO3-N uptake by growing trees is an important process. Over the entire forestry period, median NO3-N concentrations at PW2 (first rotation site) increased by a factor four (400–1590 µg l−1). The median NO3-N during the post-thinning period was also one order of magnitude higher than those measured at K-Pine (second rotation site) during the post-thinning period. We attribute these differences to the NO3-N legacy within soil and/or groundwater of the previous sheep and beef cattle grazing land use. Long-term use of the PW2 catchment for forestry may eventually reduce NO3-N concentrations to the lower levels measured at K-Pine. Therefore, while NO3-N concentrations and loads may increase in response to the establishment of plantation forestry we envisage that these will decline if plantation forestry continues beyond the first rotation. This research highlights: (i) the complex nature of the response of stream water quality to catchment land use changes, and (ii) the value of studies that monitor the impact of land use/cover change over the long-term.

Nutrient Leaching and Retention in Riparian Soils as Influenced by Rice Husk Biochar Addition

Biochar application to agricultural soils has been reported to reduce nutrient leaching and ameliorate degraded soils. However, few studies exist that verify decreased nutrient leaching in biochar-amended riparian soils or that identify the mechanism for nutrient retention. Column leaching experiments were conducted to investigate the effects on nutrient leaching and retention of rice husk biochar additions at varying rates (0%, 1%, 2%, 5%, and 10% by weight) following application of fertilizer (NH4NO3 and KH2PO4) to a subtropical riparian soil from the Taihu Lake watershed of China over a 24-week incubation. We found that increasing levels of biochar decreased cumulative amounts of leachate NH4-N by 28 to 63%, NO3-N by 23% to 84% and dissolved organic nitrogen by 15% to 46%, while increasing leaching of PO4-P by 43% to 108%. Total nitrogen (N) and available phosphorus (P) contents significantly increased in the biochar-amended soil. The significant increase in soil microbial biomass N after biochar addition suggests that fertilizer N was retained by microbial cycling. The decrease in NH4-N and increase in NO3-N in biochar-amended soil imply that nitrification was enhanced with biochar addition. Biochar treatments increased soil available P due either to the release of soluble P from biochar or to enhanced P mineralization by soil microbial biomass. These results indicate that addition of biochar increased the capacity of the riparian soil studied to provide plant available nutrients and reduce N leaching.

Impact of wastewater treatment plant effluent on an urban river

ABSTRACTSewage treatment plant (STP) effluent has been used as ecological supplementary water in dry and polluted urban rivers. However, more consideration should be given to the impact of STP effluent on water quality and the environment. In this paper, a typical urban tributary river of Dianchi was selected to study the impact of STP effluent on water quality and plankton communities. Using a paired-sample t-test, factor analysis and canonical correspondence analysis, changes in water quality, plankton communities and their relationships were analyzed. The results showed that STP effluent decreased the concentrations of suspended solid, chemical oxygen demand, five-day biological oxygen demand (BOD5) and total phosphorus. However, it significantly increased the concentration of nitrate, total nitrogen and nitrate nitrogen (NO3-N). A distinct shift in the phytoplankton community from Chlorophyta (green algae) to Bacillariophyta (diatoms) occurred after the influx of STP effluent and further analysis indicated that this shift was primarily caused by the increase in NO3-N and facilitated by the seasonal rise in water temperature. Zooplankton communities were less sensitive to changes in water pollution condition than phytoplankton communities and the zooplankton community structure of the Chuanfang River was mainly influenced by water temperature.

Changes in Nitrogen Form in Paper Mill Wastewater Treated by Ozone Oxidation

Ozonizers will produce nitrogen oxides which can be dissolved into thewastewater as ozone is produced. This experiment, where ozonization process was employedas the post-treatment after the biological processes, aims to analyze the amountof nitrogen and its variation and transform rate in influents and effluents. Results showedthat after ozonization process, the concentrations of total nitrogen in effluents were higherthan the concentrations in influents (0.01~0.38 times higher). The concentrations ofnitrate nitrogen in effluents were also higher than the concentrations in influents, andaverage increased rate of NO3-N was 226.8%. Furthermore, the increase in the concentrationof NO3-N due to dissolution of NOx was 47.10% of total increase in NO3-N.

Mid-Rotation Silviculture Timing Influences Nitrogen Mineralization of Loblolly Pine Plantations in the Mid-South USA

Intensively managed loblolly pine (Pinus taeda L.) plantations often develop nutrient deficiencies near mid-rotation. Common silvicultural treatments for improving stand nutrition at this stage include thinning, fertilization, and vegetation control. It is important to better understand the influence of timing fertilization and vegetation control in relation to thinning as part of improving the efficiency of these practices. The objective of this study was to determine the effects of fertilization and vegetation control conducted within a year prior to thinning and within a year after thinning on soil N supply in mid-rotation loblolly pine plantations on a gradient of soil textures. Net N mineralization (Nmin) and exchangeable N were measured monthly. Fertilization increased annual Nmin at all sites irrespective of timing relative to thinning, with the increase more pronounced when combined with vegetation control. This finding suggests some management flexibility in the timing of mid-rotation fertilization relative to thinning for increasing soil N supply. However, the site with the highest total soil N and the lowest C:N ratio was more prone to NO3-N increases after fertilization conducted pre- and post-thinning. At all sites, fertilization with vegetation control promoted increases in NO3-N when done after thinning, which may indicate that this practice increased soil N supply to levels that exceeded stand N demand.

Assessment of Environmentally Harmful Nitrogen Surplus by 0.01 M Calcium Chloride Soil Extractant in Long-Term Experiments

Calcium chloride–extractable (1:10 soil/solution ratio, w/v) nitrate nitrogen (NO3-N), ammonium nitrogen (NH4-N), organic nitrogen (EON), and Ntotal fractions were measured in two long-term experiments. Both experiments are located in the Great Hungarian Plain. The first experiment was established on a Luvic Phaeozem soil and the second experiment was on a Calcic Chernozem soil. Researchers investigated the effects of long-term fertilization and irrigation on the amounts of nitrogen (N) fractions. Nitrogen rates caused significant increase in NO3-N and Ntotal fractions. These fractions were in close correlation (r = 0.87; r = 0.88) with nitrogen balance. The nitrate content of the 200-cm-deep soil layer of soils under different nitrogen- and water-supply conditions were also studied. As an effect of N overfertilization, the maximum nitrate accumulation on nonirrigated plots occurred in the 200-cm depth, whereas on irrigated plots a nitrate accumulation layer could not be observed in the 200-cm-deep soil layer.

A meta-analysis of the effects of clearcut and variable-retention harvesting on soil nitrogen fluxes in boreal and temperate forests

One of the assumed advantages of variable-retention (VR) harvesting over clearcut harvesting is reduced postharvest leaching losses of nitrogen. We test this assumption by synthesizing results from long-term field trials in a meta-analysis. Overall, clearcutting significantly increased soil NO3-N concentration, NO3-N as a proportion of soluble inorganic nitrogen (SIN), N concentration in leachates, N flux, nitrification rates, and pH, but not total N, NH4-N, SIN concentration, ammonification, or N mineralization rate. The proportion of soil NO3-N in deciduous forests increased immediately and returned to preharvest levels within five years; the effect was delayed in coniferous forests, but levels remained elevated for several years. Deciduous leaf litter decomposed faster and needle litter decomposed more slowly on clearcut sites than in uncut forests. Single-tree selection caused smaller changes in NO3-N than removal of groups of trees (i.e., gap creation) and led to smaller increases in NO3-N as a proportion of SIN than clearcut harvesting. High levels of retention (>70%) were required to maintain uncut stand N-cycling characteristics. Postharvest NO3-N levels could be predicted from NO3-N availability in the uncut forests.

CHANGES IN THE DISSOLVED NITROGEN POOL ACROSS LAND COVER GRADIENTS IN WISCONSIN STREAMS

Increases in anthropogenic nitrogen fixation have resulted in wide-scale enrichment of aquatic ecosystems. Existing biogeochemical theory suggests that N enrichment is associated with increasing concentrations of nitrate; however, dissolved organic nitrogen (DON) is often a major component of the total dissolved nitrogen (TDN) pool in streams and rivers, and its concentration can be significantly elevated in human-influenced basins. We examined N concentrations during summer base flow conditions in 324 Wisconsin streams to determine whether DON was a significant component of TDN and how its relative contribution changed across a gradient of increasing human (agriculture and urban) land use for 84 of these sites. Total dissolved nitrogen varied from 0.09 to 20.74 mg/L, and although DON was significantly higher in human-dominated basins relative to forested and mixed-cover basins, its concentration increased relatively slowly in response to increasing human land cover. This limited response reflected a replacement of wetland-derived DON in low-N streams by anthropogenic sources in human-dominated sites, such that net changes in DON were small across the land use gradient. Nitrate-N increased exponentially in response to greater human land cover, and NH4-N and NO2-N were present at low levels. Nitrite-N exceeded NH4-N at 20% of sites and reached a maximum concentration of 0.10 mg/L. This examination suggests that basic mechanisms driving N losses from old-growth forests subject to N saturation also shape the summertime N pool in Wisconsin streams, in addition to other processes dictated by landscape context. The overwhelming role of human land use in determining the relative and absolute composition of the summertime N pool included (1) rapid increases in NO3-N, (2) limited changes in DON, and (3) the unexpected occurrence of NO2-N. High (>3 mg/L) TDN conditions dominated by NO3-N, regardless of landscape context or forms of N inputs, indicate a state of "N hypersaturation", which appears to be increasingly common in human-influenced streams and rivers. Many sites in agriculturally rich areas had NO2-N and NO3-N concentrations that, if sustained, are at chronically toxic levels for sensitive aquatic biota, suggesting that N enrichment now has local consequences for resident stream biota in addition to contributing to coastal eutrophication.

Soil chemical changes following manure application on irrigated alfalfa and rainfed timothy in southern Alberta

In areas within Alberta where suitable cultivated land is not available, or for convenience, the use of forage land is an alternative for manure application. However, there is limited research on the effects of manure on forage land in the province. The objective of this 5-yr study was to determine the effects of manure on soil chemical properties of forage land. Cattle (Bos taurus L.) and hog (Sus scrofa L.) manures were applied at five rates on irrigated alfalfa ( Medicago sativa L.) and on rainfed timothy(Phleum pratense L.) sites. Treatments were replicated four times and arranged in a randomized complete block design. Soil samples (0 to 15, 15 to 30, 30 to 60, 60 to 90, 90 to 120, and 120 to 150 cm) were collected each spring prior to manure application. Manure application on forage land significantly affected soil chemical properties such as increases in NO3-N, PO4-P, K, Na, and electrical conductivity. There was also evidence of accumulation and some downward movement of NO3-N, Na, and K below 15 cm. The higher manure application rates used in this study (>31 Mg ha-1 cattle manure and >42 Mg ha-1 hog manure; wet weight) are not sustainable in terms of potential environmental risk, such as leaching of NO3-N to groundwater, loss of P in runoff water, and increased soil salinity. Appropriate application rates should be based on crop nutrient requirements and management practices that include regular manure and soil testing. Key words: Alfalfa, timothy, manure, hog, cattle, soil nutrients, electrical conductivity

Mineral N dynamics, leaching and nitrous oxide losses under maize following two-year improved fallows on a sandy loam soil in Zimbabwe

The fate of the added N on a sandy loam soil was determined in an improved fallow - maize sequence field experiment in Zimbabwe. Pre-season mineral N was determined in 20 cm sections to 120 cm depth by soil auguring in seven land use systems. Thereafter, sequential soil auguring was done at two-week intervals in plots that previously had 2-year fallows of Acacia angustissima, Sesbania sesban and unfertilized maize to determine mineral N dynamics. Using the static chamber technique, N2O fluxes were also determined in the same plots. Pre-season NH4-N concentrations were > 12 kg N ha-1 in the 0-20 cm layer for treatments that had a pronounced litter layer. NO 3-N concentrations below 60 cm depth were 10 kg N ha-1 layer-1 in the control plots where maize had been cultivated each year. There was a flush of NO 3-N in the Sesbania and Acacia plots with the first rains. Topsoil NO3-N had increased to > 29 kg N ha-1 by the time of establishing the maize crop. This increase in NO3-N in the topsoil was not sustained as concentrations decreased rapidly within three weeks of maize planting, to amounts of 8.6 kg N ha-1 and 11.2 kg N ha -1 for the Sesbania and Acacia plots, respectively. Total NO 3-N leaching losses from the 0-40 cm layer ranged from 29-40 kg ha-1 for Sesbania and Acacia plots within two weeks when 104 mm rainfall was received to an already fully recharged soil profile. Nitrate then accumulated below the 40 cm depth during early season when the maize had not developed a sufficient root length density to effectively capture nutrients. At one week after planting maize, N2O fluxes of 12.3 g N2O-N ha-1 day-1 from Sesbania plots were about twice as high as those from Acacia, and about seven times the 1.6 g N2O-N ha -1 day-1 from maize monoculture. This was at the time when mineral N was at its peak in the topsoil. The unfertilized maize showed consistently low N2O emissions, which never exceeded 2 g N 2O-N ha-1 day-1 for all the eight sampling dates. The decrease of mineral N concentration in the topsoil resulted in reduced N2O fluxes, despite very high soil moisture conditions. Total N2O-N emissions were greatest for Sesbania plots with 0.3 kg ha -1 lost in 56 days. We conclude that, under high rainfall conditions, there is an inherent problem in managing mineral N originating from mineralization of organic materials as it accumulates at the onset of rains, and is susceptible to leaching before the crop root system develops. We did not quantify nitric oxide and N2 gas emissions, but it is unlikely that total gaseous N losses would be significant and contribute to poor N recovery that has been widely reported.

Upland active acid sulfate soils from construction of new Stafford County, Virginia, USA, Airport

This paper reports on a situation where severe active acid sulfate soils were brought into existence by the construction of a new (opened in 2002) airport in Stafford County, VA, approximately 60 km south-west of Washington, DC. About 290 ha of new land surface was brought into existence that consisted of both scalped land surfaces on steep slopes, and spoil (fill), some of which was graded to provide level land surfaces for paved runways. Over 150 ha of ultra acidic (pH <3.5 at soil surface) post-construction acid sulfate soils remained barren for over 2 years before the acid sulfate soil situation was properly recognised. Construction took place in an originally dissected landscape with about 30 m of local relief. The construction was designed to balance the cut and fill areas so that soil materials would not need to be taken from the area or brought to it from other locations. This resulted in some deep cuts (scalped surfaces) in the higher parts of the landscapes, which retained slopes of about 25%. Great difficulty was encountered in establishing vegetation on these surfaces. The exposed sulfidic materials were dense, commonly on steep slopes, and developed low pHs, some <pH 2, after exposure. After a dry period in the autumn of 2001, sulfuric horizons crusted over with bitter hydrated sulfate salt minerals had formed in the surface of sulfidic materials originally exposed in 1999. By X-ray diffraction, halotrychite, Fe2+Al2(SO4)4.22H2O, was identified as a main white salt mineral and copiapite group minerals, e.g. Al2/3Fe3+4(SO4)6(OH)2.20H2O for aluminocopiapite, were identified as a yellow salt minerals. Information about, and photographs of, the site, soils, and drainage waters are presented, including examples of deleterious environmental impacts. Intensive reclamation/revegetation measures were initiated in 2002. These involved the application of high rates of lime stabilised biosolids (sewage sludge) incorporated to a depth of about 0.15 m to neutralise acidity and add organic matter and nutrients to the soils. These measures permitted the establishment of acid- and salt-tolerant grasses on the acid sulfate soils and caused dramatic increases in pH and drops in Fe and Al levels in stream waters leaving the site. However, they also caused initial large increases in ammonia/ammonium-N in the waters and subsequent increases in NO3-N in the waters. Experience with this and other similar sites demonstrates the need for engineers involved with earth-moving construction activities to be educated in the principles of acid sulfate soils so that the number of such disturbances that result in the creation of active acid sulfate soils can be lessened or, preferably, eliminated. Plans for recognition and reclamation of acid sulfate soil situations should be built into the construction plans and designs when it is necessary to disturb sulfidic materials.

Water quality of the Modder River, South Africa

The Modder River is a relatively small river in the central region of the Free State Province, South Africa and has a mean annual runoff of 184 × 106m3. Botshabelo is a city, which has developed in the catchment area of the river, and its sewage outflows are discharged into the Klein Modder, a tributary of the Modder River. This study was conducted in order to determine the influence of Botshabelo's sewage outflow on the water quality of the river. It was determined that the Modder and Klein Modder Rivers do not generally follow distinctive seasonal patterns in terms of chemical parameters, although NO3-N and PO4-P concentrations usually increase with increasing flow and conductivity decreases with increasing flow. Physical parameters such as turbidity, flow and temperature did however follow distinctive seasonal patterns from February 1996 to December 1997, as did phytoplankton growth. Low chlorophyll-a concentrations were exhibited in the winter and higher concentrations during spring. In the Klein Modder River, algal blooms occurred more frequently, and the algal biomass was higher than in the Modder River. This could be ascribed to the higher nutrient concentrations and lower flow velocities in the former. The inflow of the Klein Modder River into the Modder River caused on average, 112% increase in PO4-P, 171% increase in NO3-N, 50% increase in chlorophyll-a concentration, and 230% increase in E. coli counts.

Producing Nitrate-free Endive Heads: Effect of Nitrogen Form on Growth, Yield, and Ion Composition of Endive

In a growth chamber, endive (Cichorium endivia L. var. crispum Hegi) plants were grown using a solution culture method to evaluate the influence of four ammonium : nitrate (NH4-N : NO3-N) percentage ratios (100:0, 70:30, 30:70, and 0:100) on growth (leaf area, dry mass, crop growth rate, relative growth rate, and net assimilation rate), yield characteristics (head and root fresh mass and root length), quality (dry matter, nitrogen, and nitrate), and inorganic ion content. No symptoms of NH4+ toxicity were detected in endive plants 8 weeks after beginning nutrient treatments. Moreover, by feeding N in mixed form, the growth indices increased compared to indices from feeding with any of the two N forms alone. Ammonium-fed plants produced nitrate-free heads with a fresh mass (171 g) similar to nitrate-fed plants. Compared to the other treatments, the heads of NH4+-fed plants were darker green and more succulent. Mixed N improved yield but caused a remarkable accumulation of nitrate in heads. Following an increase in NO3-N from 30% to 70% in the nutrient solution, head fresh mass rose from 196 to 231 g and NO3- concentration more than doubled (from 2.4 to 6.1 g·kg-1 fresh mass). With 100% of NO3-N, NO3- concentration was 5.5 g·kg-1 fresh mass. With higher NO3-N percentages in the nutrient solution, the difference in the concentration of inorganic cations and anions increased, but K+ concentration was also high in ammonium-fed plants (on average 77 g·kg-1 dry mass). Head total N accumulation was increased by the presence of NH4+ in the nutrient solution and decreased with 100% NO3-N. From the commercial viewpoint, the produce obtained from 100% NH4-N was good, with the value-added factor of the absence of nitrate. This may be an extremely remarkable factor because of the commercial limits on the allowable nitrate content in leafy vegetables already enforced by many European countries and those the European Union is going to adopt in a directive.

679 (PS 5) Evaluation of Hand Held, Flat Electrode pH, Electrical Conductivity, Potassium, and Nitrate Meters

Cardy flat electrode pH, electrical conductivity, potassium and nitrate meters were evaluated for their application to greenhouse solution and media testing. The pH, EC, K, and NO3-N levels in 7 recirculated nutrient solution reservoirs were monitored weekly for 8 weeks using Cardy meters and standard methods. Regression analysis of the results of the Cardy meters against those of standard methods resulted in slopes of 0.64, 0.94, 1.05 and 1.03 for pH, EC, NO3-N and K respectively. Saturated media extract (SME) samples of a peat-based medium were diluted to provide concentrations of 10 to 200 mg·liter-1 NO3-N. The regression equation describing the relationship between the colorimetric and Cardy determinations was: ppm NO3-N = 0.86 * Cardy ppm NO3-N + 11.1 (R2=0.98). In a separate experiment, KNO3 and Ca(NO3)2 were added to a commercial peat-based medium to provide 27 to 490 mg·liter-1 NO3-N using the SME method. The regression equation describing the relationship between the colorimetric and Cardy determinations was: ppm NO3-N = 1.05 * Cardy ppm NO3-N -2.05 (R2=0.98). Chloride in the range of 0 to 1400 mg·liter-1 resulted in a 0.02 mg·liter-1 increase in NO3-N with every 1 mg·liter-1 increase in chloride.

Soil mineral nitrogen changes following prescribed burning in ponderosa pine

In a ponderosa pine (Pinus ponderosa Laws.) forest near Flagstaff, AZ, USA, there was a striking pattern in forest characteristics, consisting of substands of old-growth trees (28–120 cm diameter at breast height (dbh) and 200–500 years old) and of saplings (1.5–10 cm dbh and 60–70 years old) in a matrix of pole-sized trees (10–28 cm dbh and 60–100 years old). Tree size and forest floor mass decreased from old-growth to pole to sapling substands, but soluble N (as KCl extractable inorganic N) in the mineral soil did not vary substantially among substands before prescribed burning.Prescribed burning had little immediate impact on the overstory but substantially decreased the forest floor mass, with the greatest absolute and relative decreases being in the old-growth substands. Immediately after burning, ammonium-nitrogen (NH4-N) increased from 2.3 to 45.1 mg kg−1 in the old-growth substands, from 1.3 to 26.7 mg kg−1 in the pole substands, and from 1.3 to 8.3 mg kg−1 in the sapling substands. These differences in NH4-N among the substand types are directly correlated with differences in the initial forest floor weight and the amount of forest floor burned. Nitrate-nitrogen (NO3-N) was not changed immediately after burning.By 1 year after burning, NH4-N had declined substantially with only the old-growth substands being significantly higher than controls (30.0 versus 2.56 mg kg−1). Much of this decline showed up as an increase in NO3-N, particularly for the old-growth substands where NO3-N was 18.6 mg kg−1 on burned plots compared with 0.03 mg kg−1 on controls.These results support the conclusion that while increases in NH4-N are an immediate effect of burning (most likely from NH4-N produced by pyrolysis of forest floor material), nitrate increases, which occur later, are most likely caused by nitrification of the high NH4-N produced immediately after burning.A preliminary budgetary analysis for the mineral soil showed an immediate increase in inorganic N of 34.3 kg ha−1 in old-growth substands, 14.7 kg ha−1 in pole substands, and 4.0 kg ha−1 in sapling substands. Because these increases appear to have been transferred directly to the mineral soil from the forest floor, previous studies which have not accounted for this phenomenon may have somewhat overestimated N volatization losses from burning.

Evaluation of methods of measurement of nitrogen in poultry and animal manures

Kjeldahl nitrogen (N), total N and forms of inorganic N (ammoniacal (NH4)-N, nitrate (NO3)-N and nitrite (NO2)-N) were measured in a range of animal manures. The manures include fresh samples of poultry manure, sheep manure, horse manure, dairy slurry and pig slurry and composted poultry manure. Kjeldahl N was measured by standard micro-Kjeldahl digestion. For total N measurements, NO3-N and NO2-N were recovered during Kjeldahl digestion by pretreatments with various oxidizing and reducing agents. Inorganic forms of N were measured by extraction with 2M KCl solution. Kjeldahl digestion alone allowed measurement only of organic N and NH4-N. Amongst various modifications to the Kjeldahl, pretreatment with either acidified (H2SO4) Zn-CrK(SO4)2 or acidified (H2SO4) reduced Fe achieved complete recovery of NO3-N. Nitrite N was only recovered by first oxidising the NO 2 - to NO 3 - with KMnO4 followed by reduction to NH4-N with acidified (H2SO4) reduced Fe. More than 95% of the total N in fresh animal manure was present as organic N and NH4-N which were recovered by the standard Kjeldahl digestion. In the case of fresh manures there was no difference between the amount of total N measured by the Kjeldahl digestion and its modified methods. However composting of poultry manure or drying of poultry manure, pig slurry and dairy slurry resulted in an increase in NO3-N which was not recovered during Kjeldahl digestion alone. Under these conditions the total N could be measured by pretreating the samples with KMnO4 and reduced Fe prior to Kjeldahl digestion. Drying of animal manures caused a decrease in organic N and NH4-N, especially in poultry, pig and dairy manures. There was a slight increase in NO3-N; but most of the decrease in N content with drying was attributed to the volatilization loss of ammonia (NH3). Amongst various drying methods examined air drying caused maximum loss of N as NH3 whereas freeze drying caused minimum loss of N. This suggests that fresh animal manures can be freeze dried for analysis of N which causes minimum loss of N.

Vegetation Dynamics in Amazonian Treefall Gaps

In a 1—ha plot of old—growth tierra firme forest near San Carlos de Rio Negro, Venezuela (northwest Amazon Basin), 88 trees ≥ 10 cm dbh out of 786 die over a 10—yr period. Most deaths resulted in the formation of small (5—100 m2) canopy openings (gaps). Occasionally, large gaps are formed in this region when strong winds topple many trees together. In five small (single—treefall) gaps and one large (multiple—treefall) gap we studied changes in soil fertility and nutrient leaching, and also plant establishment, mortality, and growth during the first 4 yr following gap formation. Gaps were divided into four zones, or microhabitats: a trunk zone, an open zone (between bole and forest edge), a crown zone, and a root—pitzone. Sampling was conducted in each microhabitat. Soil nutrient levels in single—treefall gaps did not differ in a predictable fashion in response to microhabitat within gap of gap age. Moreover, except for a small, short—term increase in NO3—N, leaching losses from single—treefall gaps did not differ from forest levels. Advance regeneration plays a dominant role n treefall gap succession at San Carlos. Under closed forest, advance regeneration has a mean annual survivorship of °80%; height growth is only a few centimetres a year, and leaf retention times frequently exceed 4 yr. Four years after gap formation, advance regeneration accounted for 97% of all trees ≥ 1 m tall in the single—treefall gaps and 83% of all trees in the multiple—treefall gap. Almost all trees in both gap types were of primary forest species; pioneer trees comprised only a small fraction of the regrowth. In general, microhabitat within gaps did not influence plant density, or plant establishment and mortality patterns. However, mortality was much higher for individuals that germinated after gap formation than for individuals present as advance regeneration. Plant growth within treefall gaps was influenced by gap size, gap microhabitat type, gap age, and plant size. Seedlings and saplings of forest trees in the multiple—treefall gap grew three times as fast as those in the single—treefall gaps. Within single—treefall gaps, height growth was greater in the trunk and open zones than in the crown zone, and trees generally grew more slowly as gaps aged. Furthermore, tree growth was positively correlated with tree size, causing the size differential between trees of different heights to expand as gaps aged. As San Carlos, tree seedlings do not grow to the canopy during a single gap event; rather, canopy closure occurs by growth of larger pole—sized trees that survived treefalls or by lateral expansion of bordering subcanopy trees. Our results indicate that neither gap size, microhabitat with gaps, nor gap age have measurable effects on nutrient loss, nor do they appear to affect plant density, plant establishment, or plant mortality. Size, microhabitat, and temporal affects are minimized, in large part, because of the great importance of advance regeneration in gap succession.

Agricultural chemicals in ground water: Extent and implications

AbstractThe accelerated use of agricultural chemicals over the past 20–30 years has increased production and generally has been profitable, but it has also had an adverse impact on ground water quality in many major agricultural areas. The contamination of ground water, related to nitrogen fertilizers and pesticides, from widespread, routine land application, as well as from point sources has become a serious concern. Ground water contamination also impairs surface water quality. Research, world-wide, has shown increases in NO3-N in ground water concurrent with major increases in N-fertilization. Many shallow ground water supplies now exceed recommended NO3-N drinking water standards. While many sources contribute N into the environment, synthetic fertilizers have become the major component. There are clear economic incentives to improve management; harvested crops often account for less than 50 percent of the purchased fertilizer inputs. Pesticides are appearing in ground water with unanticipated frequency, and while their concentrations are generally below acute toxic levels, many are of concern for possible chronic effects. Such widespread contamination is of real concern because of the potential for long-term and widespread exposure of the public through drinking water. Surveys of farmers indicate a desire to improve management practices and reduce chemical inputs. Promoting the principles of alternative, sustainable agriculture is a necessary element in the resolution of these problems.