Nitrate Retention Capacity Research Articles

Climate controls on nitrate dynamics and gross nitrogen cycling response to nitrogen deposition in global forest soils

Understanding the patterns and controls regulating nitrogen (N) transformation and its response to N enrichment is critical to re-evaluating soil N limitation or availability and its environmental consequences. Nevertheless, how climatic conditions affect nitrate dynamics and the response of gross N cycling rates to N enrichment in forest soils is still only rudimentarily known. Through collecting and analyzing 4426-single and 769-paired observations from 231 15N labeling studies, we found that nitrification capacity [the ratio of gross autotrophic nitrification (GAN) to gross N mineralization (GNM)] was significantly lower in tropical/subtropical (19%) than in temperate (68%) forest soils, mainly due to the higher GNM and lower GAN in tropical/subtropical regions resulting from low C/N ratio and high precipitation, respectively. However, nitrate retention capacity [the ratio of dissimilatory nitrate reduction to ammonium (DNRA) plus gross nitrate immobilization (INO3) to gross nitrification] was significantly higher in tropical/subtropical (86%) than in temperate (54%) forest soils, mainly due to the higher precipitation and GNM of tropical/subtropical regions, which stimulated DNRA and INO3. As a result, the ratio of GAN to ammonium immobilization (INH4) was significantly higher in temperate than in tropical/subtropical soils. Climatic rather than edaphic factors control heterotrophic nitrification rate (GHN) in forest soils. GHN significantly increased with increasing temperature in temperate regions and with decreasing precipitation in tropical/subtropical regions. In temperate forest soils, gross N transformation rates were insensitive to N enrichment. In tropical/subtropical forests, however, N enrichment significantly stimulated GNM, GAN and GAN to INH4 ratio, but inhibited INH4 and INO3 due to reduced microbial biomass and pH. We propose that temperate forest soils have higher nitrification capacity and lower nitrate retention capacity, implying a higher potential risk of N losses. However, tropical/subtropical forest systems shift from a conservative to a leaky N-cycling system in response to N enrichment.

AquaZone: An Integrative Tool for Sustainable Fish Farm Zoning

Aquaculture is the fastest-growing animal food production sector and is expected to become increasingly important to meet future food demands. As a landlocked country, Austria’s self-sufficiency rate for fish is rather low with 6% in total and 48% for freshwater fish. Therefore, and in order to enable sustainable growth of the sector while avoiding negative impacts on the aquatic ecosystem and other uses, we developed aquaZone, a decision support tool for sustainable trout farm zoning. Thereby, 30 spatially explicit criteria related to environmental prerequisites, land use, legal constraints and water quality/quantity were defined, collected and classified according to their suitability for sustainable trout production. Criteria were combined in an integrative GIS-based modelling approach in order to perform the first countrywide and spatially-explicit zonation of suitable areas for aquaculture in Austria. Thereby, 7920 suitable areas with a mean size of 8.2 ha located in 1129 out of 5011 sub-basins (23%) were identified. The decision tree assigned the highest variable importance to water temperature, slope, agricultural unit, geology, nitrate retention capacity, fish region, minimum flow and pollution risk. These results should support decision making of investors and authorities in order to avoid conflicts and stranded investments at an early stage.

Dissimilatory nitrate reduction to ammonium dominates soil nitrate retention capacity in subtropical forests

The abundance, community composition and activity of key nitrogen (N)-cycling functional guilds were monitored at a site where coniferous Cunninghamia lanceolate and broadleaved Mytilaria laosensis were planted in 1993. Leaf cellulose, litter C/N ratio, leaf dry matter content, soil inorganic N content were significantly higher under C. lanceolata, while specific leaf area, litter production, litter magnesium, soil C and soil C/NO3− ratio were higher under M. laosensis. The 15N tracing experiment together with quantitative PCR revealed that autotrophic nitrification rates, as well as the abundances of ammonia-oxidizing archaea and comammox Nitrospira were significantly higher under C. lanceolate than M. laosensis. However, M. laosensis exhibited substantially higher nitrate retention capacity via dissimilatory nitrate reduction to ammonium (DNRA), accompanied by a significantly higher abundance of nrfA gene than C. lanceolate. The Illumina sequencing indicated that tree species markedly affected soil bacterial community composition regardless of the soil layers. Redundancy analysis suggested that litter C/N ratio was the most influential factor explaining functional gene abundances and bacterial communities. Taken together, our findings showed that M. laosensis improved soil N retention capacity mainly through inhibiting autotrophic nitrification while enhancing DNRA activity. This study highlights the importance of tree species identity in influencing the microbially-mediated N cycling and bacterial community composition.

Investigating nitrate retention capacity, elementary and mineral composition of Kalahari sandy soils at Mashare farm in Namibia, Okavango river basin

Kalahari sands which cover a large part of Southern Africa and extend into Central Africa are infertile and marginal soils for intensive agriculture. Therefore, high nitrogen fertilisation rates may degrade ecosystems of rivers with catchments covered by the Kalahari sands. A study on Mashare Farm located in the Okavango River basin showed that irrigated Kalahari sandy soils had a nitrate retention capacity, which enabled the soil to resist nitrate leaching in water saturated conditions. The irrigated soils were modified by agricultural activities; hence this study investigated if uncultivated and cultivated Kalahari sand soils had similar nitrate retention properties. The elementary composition of the soils was investigated for obtaining an insight into chemical properties that may be causing the nitrate retention capacity. A permeameter was used to leach out nitrates from irrigated and uncultivated soil samples, and nitrate concentrations were measured on the leaching effluent from the permeameter. Elemental analysis was done on the cultivated and the uncultivated soil samples using a Scanning Electron Microscope, a portable X-Ray Fluorescence analyzer, and an X-Ray Diffraction machine, and the later was also used for crystalline structure analyses. Sieve analyses confirmed that the Mashare's cultivated and uncultivated topsoils were similar, and both were similar to Botswana Kalahari topsoil. The irrigated and cultivated subsoil had a higher average nitrate retention capacity of 76% compared to 73% for the uncultivated subsoil. Both samples had the same elements, although the proportions were different. Both soil samples were dominated by a quartz mineral, but the field soil had traces of palygorskite. The presence of aluminum and transition metals outside the minerals structure, but as coatings on the quartz sand grains enhanced nitrate retention capacity properties of the Kalahari sand soils.

The fate of monsoonal atmospheric nitrate deposition in two forest catchments in Soyang lake watershed, South Korea: a mass balance and stable isotope approach

Over 60% of South Korea is covered by forests. Nitrate deposition plays an important role as nitrogen source in these forests. Nitrate input from deposition increases nitrogen availability leading initially to increases in productivity. However, later forests may become nitrogen saturated with nitrate leaching, denitrification and forest decline. Using a mass balance approach, we compared the atmospheric nitrate input and output by stream runoff in two forest sub-catchments, a deciduous and a mixed catchment, within the Soyang lake watershed, the main drinking water reservoir for the 20-million-person metropolis Seoul. A dual stable isotope approach was used to identify the origin of nitrate in stream discharge of the two sub-catchments. Extremely different monsoon seasons in 2013 and 2014 drove the nitrate discharge. Total nitrate-N export was closely related with rainfall events and intensities. Nitrate-N discharge at the deciduous forest was lower than nitrate-N deposition, thus sink conditions prevailed. Nitrate-N discharge at the mixed forest was consistently higher. During the heavy monsoon season of 2013 the mixed forest turned from a sink for atmospheric nitrate towards a source, i.e. nitrate amounts in the discharge were higher than atmospheric inputs. Nitrate isotopic compositions of stream water from both forests revealed soil nitrification as main nitrate source. However, under conditions of heavy monsoon rainfall direct runoff of atmospheric deposition nitrate was identified in the mixed forest. Lower nitrate assimilation capacities of conifers compared to broadleaf trees are probably the driver for a lower nitrate retention capacity making coniferous forests more prone to nitrate leaching.

Determination of nitrate retention capacity of Kalahari sands using a permeameter: Case study of Mashare farm soil in the Okavango River basin

Namibian irrigators in Okavango River basin use high application rates of N fertilizers on Kalahari sandy soils which may leach nitrates and pollute water resources. The capacity of the sandy soils to retain the nitrates against leaching conditions of prolonged water saturation is not well understood. Therefore, in this study the sandy soil was tested for nitrate leaching rate and retention capacity using a constant head permeability meter in laboratory experiments. Eight samples were collected using a soil auger from one irrigated field. Four samples were top soil from 0 to 30 cm depth horizon and four were from the underlying 30–60 cm depth. A sieve analysis showed that the top layer had over 90% sand, less than 10% clay fraction and no silt fraction. The organic matter content in the top soil averaged 0.56% and subsoil had a calcrete gravel fraction. At a soil density of 1.4 g/cm3 the field's topsoil and subsoil had average permeability constants of 0.012 cm/s and 0.014 cm/s respectively. 3660 mg nitrate were applied to the 6 test samples, like irrigators' highest fertigation rates of 66 kg/ha. The nitrate concentration of effluent from the permeability meter was measured using a Eutech ion 6 + pH/mV meter and a nitrate ion selective electrode. The nitrate leachate concentration against time was a quadratic function with two distinct phases; a fast leaching rate with a steep gradient, until the topsoil and subsoil had lost about 21% and 29% respectively, and then a slower leaching rate close to a zero gradient. Under the constant saturation conditions, the slow leaching phase began after 8 and 7 h, for top and subsoil respectively. Therefore, for reducing nitrate leaching from the Kalahari sandy soils, a maximum fertigation rate of 45 kg/ha per single application was recommended for a calcium nitrate fertilizer.

Land-use type affects nitrate production and consumption pathways in subtropical acidic soils

The production and consumption pathways of nitrate (NO3−-N) are key factors for NO3−-N retention capacity (NR) in soils, especially in subtropical regions with high precipitation. This study was designed to examine the effect of land-use type on NO3−-N production and consumption pathways, in acidic soils in a subtropical region. Soils were collected from 5 differing land-use types: shrubland (SB), a eucalyptus plantation (ET), a sweet potato farm (SP), a citrus orchard (CO) and a mixed-vegetable farm (VE), in southeast China. In our study, SB was considered a natural system, ET was considered an artificial plantation system, and SP, CO and VE were considered agricultural systems. An incubation experiment was conducted with two 15N tracing treatments, and a numerical modeling method was applied to the experimental data to quantify gross N transformation rates. The results showed that 76% and 69% of NO3−-N was produced by heterotrophic nitrification (ONrec) in SB and ET respectively. Whereas, ONrec was negligible in SP, CO and VE, with >99% of NO3−-N produced by autotrophic nitrification. Dissimilatory NO3−-N reduction to NH4+-N (DNRA) had an important role in soil NO3−-N consumption in SB and ET, with >90% of NO3−-N produced in SB being simultaneously consumed via DNRA. However, DNRA was unimportant in SP, CO and VE. Nitrate immobilization and denitrification (INO3) was negligible for all land-use types. Soil NR under different land-use types was in the order SB > ET > SP ≈ CO ≈ VE. Although N fertilizer was applied at low rates, for only the following two years after planting eucalyptus saplings, the NR in ET was significantly lower than in SB (natural system). Nitrate retention capacity was negatively correlated with soil organic carbon (SOC) and total nitrogen (TN) concentrations, and positively correlated soil C:N and C: NO3−-N ratios. The lower NR in SP, CO and VE may therefore be due to higher SOC and TN concentrations and lower C:N and C:NO3−-N ratios in those soils relative to SB and ET soils. Our observations imply that ONrec and DNRA play an important role in soil NO3−-N production and consumption in SB and ET land-uses, but not in agricultural land-use (SP, CO and VE), within the subtropical region of China studied. These findings could contribute to a theoretical and practical framework for managing NO3−-N in subtropical acidic soils.

Limited nitrate retention capacity in the Upper Mississippi River

The Mississippi River and other large rivers have the potential to regulate nitrogen export from terrestrial landscapes, and thus mitigate eutrophication in downstream aquatic ecosystems. In large rivers, human-constructed impoundments and connected backwaters may facilitate nitrogen removal; however, the capacity of these features is poorly quantified and incompletely incorporated into model frameworks. Using a high-resolution and spatially intensive sampling technique, we assessed the contribution of individual navigation pools, as well as impounded open waters and backwater wetlands within them, to overall nitrate retention by mapping the entire length (1370 km) of the Upper Mississippi River (UMR) main channel. Based on this single spatial survey of water chemistry, the river appeared to act primarily as a passive nitrate transporter, retaining only 12.5% of the incoming load, most of which occurred in the upper 150 km of the river, which includes the largest and only naturally impounded reach of the river. Although reservoirs typically are nitrogen sinks, our data indicate that UMR dams do not impede river flows to the extent necessary to promote substantial changes in water residence times and subsequent nitrogen removal. Backwaters routinely had lower nitrate concentrations than the main channel, but their limited hydrologic connectivity to the through-flowing river channel constrained their influence on downstream export. As a whole, the UMR did not remove a substantial proportion of its nitrate load despite optimal N removal conditions, numerous impoundments, and the presence of extensive backwater habitats. These results suggest that efforts to reduce delivery of nitrogen to the Gulf of Mexico should emphasize mitigation strategies that target upland nutrient sources rather than relying on removal within the Mississippi River.

Soil gross nitrogen transformations in responses to land use conversion in a subtropical karst region

Gross nitrogen (N) transformations can provide important information for assessing indigenous soil N supply capacity and soil nitrate leaching potential. The current study aimed to assess the variation of gross N transformations in response to conversion of maize-soybean fields to sugarcane, mulberry, and forage grass fields in a subtropical karst region of southwest China. Mature forests were included for comparison. Gross rates of N mineralization (GNM) were highest in the forests, intermediate in the maize-soybean and forage grass fields, and lowest in the sugarcane and mulberry fields, suggesting capacity of indigenous soil N supply derived from organic N mineralization was lowered after conversion to sugarcane and mulberry fields. The relative high indigenous soil N supply capacity in the maize-soybean fields was obtained at the cost of soil organic N depletion. Gross nitrification (GN) rates were highest in the forests, intermediate in the forage grass fields and lowest in the other three agricultural land use types. The nitrate retention capacity (24.1 ± 2.0% on average) was similar among the five land use types, implying that nitrate leaching potential was not changed after land use conversion. Microbial biomass N exerted significant direct effects on the rates of N mineralization, nitrification, ammonium immobilization and nitrate immobilization. Soil organic carbon, total N and exchangeable magnesium had significant indirect effects on these N transformation rates. Our findings suggest that forage grass cultivation instead of other agricultural land uses should be recommended from the perspective of increasing indigenous soil N supply while not depleting soil organic N pool.

Soil Gross Nitrogen Transformations in Typical Karst and Nonkarst Forests, Southwest China

AbstractSoil gross nitrogen (N) transformations are crucial for assessing forest N status. Although there is evidence suggesting that the N cycle is open in the karst forest, southwest China, process‐based investigation of gross soil N transformations is limited. In the current study, gross soil N transformations were investigated using 15N isotope dilution and 15N tracer techniques in a typical karst forest with calcareous soil (Calcareous lithosols) in comparison with an adjacent nonkarst forest with red soil (Haplic acrisol).The gross rates of N mineralization, nitrification, dissimilatory nitrate reduction to ammonium (DNRA), and nitrate immobilization were significantly greater in the karst forest. Ammonium immobilization was comparable to gross N mineralization, so that ammonium could be efficiently conserved in the nonkarst forest. Meanwhile, the produced nitrate was mostly retained via DNRA and nitrate immobilization. This resulted in a negligible net nitrate production in the nonkarst forest. In contrast, ammonium immobilization rate only accounted for half of gross N mineralization rate in the karst forest. The nitrate retention capacity is relatively low, with 41.6 ± 4.2% of the produced nitrate being retained via DNRA and nitrate immobilization. Due to relatively low nitrate retention capacity, nitrate was accumulated in the karst forest soil. Our results indicate that the nonkarst forest with red soil holds a very conservative N cycle, but the N cycle in the karst forest is leaky.

Nitrate retention capacity of milldam-impacted legacy sediments and relict A horizon soils

Abstract. While eutrophication is often attributed to contemporary nutrient pollution, there is growing evidence that past practices, like the accumulation of legacy sediment behind historic milldams, are also important. Given their prevalence, there is a critical need to understand how N flows through, and is retained in, legacy sediments to improve predictions and management of N transport from uplands to streams in the context of climatic variability and land-use change. Our goal was to determine how nitrate (NO3−) is cycled through the soil of a legacy-sediment-strewn stream before and after soil drying. We extracted 10.16 cm radius intact soil columns that extended 30 cm into each of the three significant soil horizons at Big Spring Run (BSR) in Lancaster, Pennsylvania: surface legacy sediment characterized by a newly developing mineral A horizon soil, mid-layer legacy sediment consisting of mineral B horizon soil and a dark, organic-rich, buried relict A horizon soil. Columns were first preincubated at field capacity and then isotopically labeled nitrate (15NO3−) was added and allowed to drain to estimate retention. The columns were then air-dried and subsequently rewet with N-free water and allowed to drain to quantify the drought-induced loss of 15NO3− from the different horizons. We found the highest initial 15N retention in the mid-layer legacy sediment (17 ± 4 %) and buried relict A soil (14 ± 3 %) horizons, with significantly lower retention in the surface legacy sediment (6 ± 1 %) horizon. As expected, rewetting dry soil resulted in 15N losses in all horizons, with the greatest losses in the buried relict A horizon soil, followed by the mid-layer legacy sediment and surface legacy sediment horizons. The 15N remaining in the soil following the post-drought leaching was highest in the mid-layer legacy sediment, intermediate in the surface legacy sediment, and lowest in the buried relict A horizon soil. Fluctuations in the water table at BSR which affect saturation of the buried relict A horizon soil could lead to great loses of NO3− from the soil, while vertical flow through the legacy-sediment-rich soil profile that originates in the surface has the potential to retain more NO3−. Restoration that seeks to reconnect the groundwater and surface water, which will decrease the number of drying–rewetting events imposed on the relict A horizon soils, could initially lead to increased losses of NO3− to nearby stream waters.

Low nitrate retention capacity in calcareous soil under woodland in the karst region of southwestern China

A 15N-tracing study was conducted to investigate the gross N transformation rates involved in the production and consumption of NH4+ and NO3− in karst region soils (a calcareous and a red soil) from southwest China under woodland. The gross mineralization rate of organic N to NH4+ was much lower in calcareous soil (3.71 mg N kg−1 d−1) than in red soil (5.57 mg N kg−1 d−1), while the total gross nitrification rate was significantly higher in calcareous soil (5.80 mg N kg−1 d−1) than in red soil (0.70 mg N kg−1 d−1). Microbial NO3− immobilization accounted for 2.9% and 153% of the total nitrification in calcareous soil and red soils respectively. Thus the calcareous soils in the karst region have a low biological N retention capacity and high N losses, which are further aggravated by the high precipitation and fractured soil structure.

Nitrate retention under sugarcane in wet tropical Queensland deep soil profiles

Nitrate leaching below the crop root-zone in variable charge soils may be adsorbed at anion exchange sites, thereby temporarily reducing the risk of contamination of water bodies. The objectives of this study were (i) to investigate whether nitrate adsorption, accumulation, and retention in the Johnstone River Catchment of Far North Queensland wet tropics is widespread; (ii) to assess the capacity of soil in the Johnstone River Catchment to retain nitrate; and (iii) to deduce the consequences of nitrate adsorption/desorption on contamination of water bodies. Soil cores ranging from 8 to 12.5 m depth were taken from 28 sites across the catchment, representing 9 Ferrosol soil types under sugarcane (Saccharum officinarum-S) cultivation for at least 50 years and from rainforest. The cores were segmented at 0.5-m depth increments and subsamples were analysed for nitrate-N, cation and anion exchange capacities, pH, exchangeable cations (Ca, Mg, K, Na), soil organic C, electrical conductivity, sulfate-S, and chloride. Nitrate-N concentration under sugarcane ranged from 0 to 72.5 mg/kg, compared with 0 to 0.31 mg/kg under rainforest, both Pin Gin soils. The average N load in 1–12 m depth across 19 highly oxidic profiles of the Pin Gin soil series was 1550 kg/ha, compared with 185 kg/ha under 8 non-Pin Gin soils and 11 kg/ha in rainforest on a Pin Gin soil. Most of the nitrate retention was observed at depth of 2–12 m, particularly at 4–10 m, indicating that the accumulation was well below the crop root-zone. The average maximum potential nitrate retention capacity was 10.8 t/ha for the Pin Gin and 4.7 t/ha for the non-Pin Gin soil. Compared with the current N load, the soils still possess a large capacity to adsorb and retain nitrate in profiles. Retention of large quantities of the leached nitrate deep in most of the profiles has reduced the risk of contamination of water bodies. However, computations show that substantial quantities of the nitrate leached below the root-zone were not adsorbed and remain unaccounted for. This unaccounted nitrate might have entered both on- and off-site water bodies and/or have been denitrified.

Nitrate accumulation under cropping in the Ferrosols of Far North Queensland wet tropics

Recent research on the fate of applied fertiliser N in the Ferrosols of the wet tropics of Far North Queensland (FNQ) has shown that the nitrate leaching below the crop root-zone is a major pathway of N loss from paddocks. Information on the fate of this nitrate is essential to develop best N fertiliser management practices and for the long-term sustainability of land and water resources. Because of the ability of Ferrosols to adsorb anions in the soil matrix, it was speculated that the leached nitrate may be accumulating at depth in the Ferrosol profiles. The objectives of this study were to (i) verify whether the leached nitrate has been accumulating in the Ferrosols under the major cropping systems in the Johnstone River Catchment (JRC) of FNQ, and (ii) provide preliminary estimates for nitrate retention capacity of the Ferrosols. Soil cores to a depth of 10 m were taken from under sugarcane (Saccharum officinarum-S), banana (Musa (AAA group, Cavendish subgroup) cv. Williams), dairy pasture, and rainforest in JRC during August 1995. The cores were segmented at 0.5-m depth increments and soil samples were analysed for nitrate- and ammonium-N, cation- (CEC) and anion- (AEC) exchange capacities, pH, Ca2+ , Mg 2+ , K + , Na + , and Cl – . Nitrate-N concentration under sugarcane was as high as 33 mg/kg, compared with 6.9 mg/kg for banana, 0.3 mg/kg under rainforest, and that under pasture was below detection limit. Nitrate-N load in the top 10 m of the profiles under sugarcane ranged from 345 to 1875 kg nitrate-N/ha compared with 145 kg/ ha for banana, and 21 kg/ha under rainforest. Most of the nitrate accumulation was found between 2 and 8 m, i.e. well below the crop root-zone. From 7% to 70% of the nitrate that leached below crop root-zone was retained at depths >1 m. In general, Cl – and total cation (TC = sum of Ca2+ , Mg 2+ , K + , and Na + ) concentrations in the profiles under cropping were higher than those under rainforest, and the pH under sugarcane was more acidic. Simple correlation analysis indicated associations existed between the accumulated nitrate and Cl – , pH, AEC, or TC. The estimated nitrate holding capacity of the Ferrosols ranged from 17 to 32 t N/ha. The results show that large quantities of the nitrate that leached below crop root-zone have accumulated at depth under long-term sugarcane and banana cropping in the Ferrosols of FNQ.

Retenção de nitrato num solo de carga variável, influenciada por adubação fosfatada e calagem

O presente trabalho teve como objetivo avaliar o efeito da aplicação de fósforo e de calcário sobre a capacidade de retenção de nitrato (CRN) de um solo de carga variável. Entre 1982 e 1989, um Latossolo Vermelho-Escuro argiloso de cerrado foi cultivado com milho, trigo, arroz e feijão (2, 4, 5 e 6 cultivos, respectivamente), recebendo adubação fosfatada (total de 1530 kg/ha de P2O5: 90 kg/ha por cultivo) ou adubação fosfatada+calagem (5,5 t/ha de calcário dolomítico: 2,5 e 3,0 t/ha em 1982 e 1985, respectivamente). Testes realizados em amostras coletadas em 1991 mostraram que o solo apresentava CRN negativa (exclusão do nitrato) na camada arável (0-20 cm), e positiva e crescente com a profundidade, nas camadas subjacentes. Os tratamentos diminuíram a CRN original do solo na camada de 20-60 cm, sendo esse efeito mais intenso no tratamento com calagem. A adubação fosfatada e, especialmente, a calagem, exerceram considerável efeito residual sobre a capacidade de retenção de nitrato do latossolo estudado.