total-N Content Research Articles

Upstream 2000 ha is the boundary of the stream water nitrogen and phosphorus saturation concentration threshold in the subtropical agricultural catchment

Catchment underlying surface conditions influence stream water nitrogen (N) and phosphorus (P) concentrations, but it is not known how much this characteristic affects N and P concentrations at different spatial and temporal scales, thus limiting the effectiveness of N and P controls at key spatial and temporal scales. Here, the area, elevation, mean slope gradient, and land use in eight subtropical hydrologically nested catchments were investigated, and the stream water total-N (TN) and total-P (TP) concentrations were observed from 2011 to 2017 to quantify the extent to which the underlying surface conditions of the catchment influenced stream water N and P levels. The stream water TN and TP concentrations were significantly higher in the dry season than in the wet season (2.79 vs. 2.35 mg N L-1 and 0.16 vs. 0.14 mg P L-1), indicating significant seasonal variation in the stream water N and P levels. The underlying surface conditions of the catchment, including area, elevation, mean slope gradient, and land use, were significantly correlated with the stream water N and P concentrations (p < 0.05) and explained 67.1%-90.3% of the total variation in the seasonal stream water N and P concentrations. The catchment area was the greatest determinant of stream water N and P levels, independently explaining 32.2–69.3% of the variation. Interestingly, the N and P concentrations were higher in the 2000 ha upstream catchments and decreased rapidly with increasing catchment area during both wet and dry seasons. This indicates that the saturation threshold for N and P concentrations in subtropical agricultural catchments was within the upstream 2000 ha. Therefore, an upstream catchment area of 2000 ha was likely the optimal spatial scale for implementing pollution control practices in agricultural catchments.

Tillage-residues affect mineral-associated organic matter on Vertisols in northern Mexico

Managing croplands for increased storage of soil organic matter (SOM) contributes to the development of resilient farming systems in a changing climate. We examined SOM dynamics in a wheat (Triticum durum L.) – maize (Zea mays L.) irrigated bed planting system established near Ciudad Obregón, Sonora, Mexico. Soil samples (0–15 cm) were collected from conventionally tilled raised beds (CTB) with all crop residues incorporated (CTB-I) and permanent raised beds (PB) with crop residues burned (PB-B), removed (PB-R), partly retained (PB-P) or fully retained (PB-K) receiving 0, 150 or 300 kg N ha−1, and analyzed for organic C (OC), total N (TN) and δ13C in whole-soil, light fraction (LF) and coarse- (sand) and fine- (silt and clay) mineral-associated organic matter (MAOM). Results indicated that PB-K and PB-B increased soil OC (p <0.05) in whole-soil relative to CTB-I, mainly through increases in sand- and silt-size MAOM, respectively. Similarly, N-fertilization increased soil OC and TN contents in whole-soil, coarse-MAOM and fine-MAOM, but not in the LF pool. Soil δ13C was higher (p <0.05) in PB-K (−20.18‰) relative to PB-B (−20.67‰), possibly due to the stabilization of partly decomposed maize-C in silt- and clay-size MAOM. Composition of SOM surveyed by CPMAS 13C NMR was not affected by tillage-residue management, and roughly consisted of 35% O-alkyl-C, 31% alkyl-C, 24% aromatic-C and 10% carboxyl-C. Our results indicate that long-term PB-K and PB-B adoption increased surface soil OC contents relative to CTB-I, even though pathways of SOM stabilization differed between systems. Under PB-K, accumulation of fine-MAOM was mostly related to straw-C inputs, whereas in PB-B it was closely associated to black-C precursors. Fine-MAOM appeared responsive to crop residue management, and should be therefore considered when analyzing mechanisms of SOM stabilization in irrigated croplands.

Nitrogen in the Baltic Sea: Long-term trends, a budget and decadal time lags in responses to declining inputs

The Baltic Sea Nitrogen (N) cycle has mainly changed due to increased N inputs from rivers and the atmosphere since the beginning of the 20th century. In order to better understand the complex N budget in the Baltic Sea we: 1) assembled a unique dataset from 255 stations (>390.000 observations) of water column total N (TN) concentrations to determine long-term changes, 2) constructed a simple TN budget, and 3) present possible scenarios for the time lag between a decrease in inputs and lower TN concentrations. We show that in most regions the water column TN pool increased from the 1970s up to the early 1990s where after it leveled off and in most cases have remained stable or started to decrease in the early 2000′s. The declines in TN were only generally evident in the nearshore areas (<12 nautical miles from the shoreline), which are more directly impacted by river inputs. The field data showed that the Baltic Sea water column TN pool has declined with 31 kiloton (kt) N y−1 in the period from 2011 until 2018, while the water column TN budget showed a decline of 48 kt N y−1. Using existing regional threshold concentrations for when the Baltic Sea is unaffected by eutrophication and their exceedance compared with regional TN levels found in our study, we show that a reduction of 28% compared with current levels is needed. This study reveals that all manageable TN inputs would need to be reduced by ̴ 50% before this reduction target (28%) for the water column can be reached within a ̴ 8 year period. However, as only 5% of the TN pool is contained in the water column, with the majority (95%) being in the top 0.2 m of the sediment, which exchanges N with the water column, the likely time lag is ̴ 20 times longer, with a minimum reduction of 20% leading to improvements in the open Baltic Sea after about 400 years. Our calculations show that recovery (“oligotrophication”) of the Baltic Sea is only possible for the water column within decadal timescales if the input reductions are considerably higher (e.g. 50%) than the current ambition of only 9%.

Mesocosm- and Field-Scale Evaluation of Lignocellulose- Amended Soil Treatment Areas for Removal of Nitrogen from Wastewater

Non-proprietary N-removal onsite wastewater treatment systems are less costly than proprietary systems, increasing the likelihood of adoption to lower N inputs to receiving waters. We assessed the capacity of non-proprietary lignocellulose-amended soil treatment areas (LCSTAs)—a 45-cm-deep layer of sand above a 45-cm-deep layer of sand and sawdust—to lower the concentration of total N (TN) in septic tank effluent (STE) at mesocosm and field scales. The mesocosm received wastewater for two years and had a median effluent TN concentration of 3.1 mg/L and TN removal of 60–100%, meeting regulatory standards of 19 mg/L or 50% removal. Removal varied inversely with temperature, and was lower below 10 °C. Removal was higher in the mesocosm than in five field sites monitored for 12–42 months. Median effluent TN concentration and removal met the standard in three continuously-occupied homes but not for two seasonally-occupied homes. Sites differed in temporal pattern of TN removal, and in four of five sites TN removal was greater—and effluent TN concentration lower—in the LCSTA than in a control STA containing only sand. The performance of non-proprietary LCSTAs was comparable to that for proprietary systems, suggesting that these may be a viable, more affordable alternative for lowering N inputs to receiving waters.

Soil organic C and total N as well as microbial biomass C and N affect aggregate stability in a chronosequence of Chinese fir plantations

Soil aggregation as one of the key processes can maintain soil quality. Revealing the relationships of soil aggregate stability with the relevant bio-chemical parameters could provide valuable guidance to maintain soil quality in the Chinese fir plantations. In this study, soil samples (0–20 cm and 20–40 cm depths) were collected from Chinese fir plantations with various stand ages (3 years, 9 years, 17 years, and 26 years) in Guangxi, China. Soil aggregates with four different sizes were obtained through the optimal moisture sieving method, including the >2 mm, 2-1 mm, 1–0.25 mm, and <0.25 mm fractions. For each fractions, the organic C (OC), total N (TN), microbial biomass C (MBC), microbial biomass N (MBN), and microbial respiration rate (MRR) were measured. Regardless of the Chinese fir plantation age, soil OC and TN contents were concentrated in the <0.25 mm fractions, while soil MBC, MBN, and MRR were relatively high in the 1–0.25 mm fractions compared with other fractions. Soil mean weight diameter (MWD) and geometric mean diameter (GMD) were higher in the 17-year Chinese fir plantations than other stand ages, which indicated stronger stability of soil aggregates in the 17-year Chinese fir plantations. In the process of Chinese fir planting, the peaks of soil OC, TN, MBC, MBN, and MRR were observed in the 17-year Chinese fir plantations. Based on the redundancy analysis (RDA) and Pearson's correlation analysis, soil aggregate stability was significantly positively correlated (P < 0.05) with the OC, TN, MBC, and MBN over time, particularly in the OC, which was the most important contributor of the chronological variation in soil aggregate stability. Overall, soil aggregate stability and aggregate-related OC, TN, MBC, and MBN are the highest in the 17-year Chinese fir plantations. With the growth of Chinese fir after 17 years, these factors decrease significantly. Therefore, it is necessary to adopt reasonable management methods (i.e., appropriate application of organic manure) to increase soil aggregate stability and maintain soil quality in Guangxi, China.

Nitrogen Fractions in Soil Fertilized with Waste Organic Materials

The aim of the study was to determine the effect of sewage sludge and composts produced from sewage sludge and municipal waste on the content of various forms of nitrogen in soil. The field experiment was carried out in 2004–2015. It included three crop rotations of the following plants: potato, spring barley, winter oilseed rape and winter wheat. The experiment consisted of the following treatments: control (without fertilization), NPK, manure (FYM), compost from municipal sewage sludge and straw (CSSS), composted sewage sludge (CSS), dried and granulated sewage sludge (DGSS), “Dano” compost produced from unsorted municipal waste (CUMW) and compost from municipal green waste (CMGW). Manure, composts and sewage sludge were applied once (10 t ha−1 of d.m.) or twice (5 t ha−1 of d.m.) in a crop rotation. It was significantly shown that the highest N-total content was in the soil fertilized with CUMW (compost produced from unsorted municipal waste). The soil fertilized with manure (FYM) contained the highest quantity of N-min. The prevalent pool of nitrogen (82.65–86.52%) consisted of N compounds not undergoing acid hydrolysis, and their smallest share was determined in the soil fertilized with NPK alone.

Conversion of alpine pastureland to artificial grassland altered CO2 and N2O emissions by decreasing C and N in different soil aggregates.

BackgroundThe impacts of land use on greenhouse gases (GHGs) emissions have been extensively studied. However, the underlying mechanisms on how soil aggregate structure, soil organic carbon (SOC) and total N (TN) distributions in different soil aggregate sizes influencing carbon dioxide (CO2), and nitrous oxide (N2O) emissions from alpine grassland ecosystems remain largely unexplored.MethodsA microcosm experiment was conducted to investigate the effect of land use change on CO2and N2O emissions from different soil aggregate fractions. Soil samples were collected from three land use types, i.e., non-grazing natural grassland (CK), grazing grassland (GG), and artificial grassland (GC) in the Bayinbuluk alpine pastureland. Soil aggregate fractionation was performed using a wet-sieving method. The variations of soil aggregate structure, SOC, and TN in different soil aggregates were measured. The fluxes of CO2 and N2O were measured by a gas chromatograph.ResultsCompared to CK and GG, GC treatment significantly decreased SOC (by 24.9–45.2%) and TN (by 20.6–41.6%) across all soil aggregate sizes, and altered their distributions among soil aggregate fractions. The cumulative emissions of CO2 and N2O in soil aggregate fractions in the treatments of CK and GG were 39.5–76.1% and 92.7–96.7% higher than in the GC treatment, respectively. Moreover, cumulative CO2emissions from different soil aggregate sizes in the treatments of CK and GG followed the order of small macroaggregates (2–0.25 mm) > large macroaggregates (> 2 mm) > micro aggregates (0.25–0.053 mm) > clay +silt (< 0.053 mm), whereas it decreased with aggregate sizes decreasing in the GC treatment. Additionally, soil CO2 emissions were positively correlated with SOC and TN contents. The highest cumulative N2O emission occurred in micro aggregates under the treatments of CK and GG, and N2O emissions among different aggregate sizes almost no significant difference under the GC treatment.ConclusionsConversion of natural grassland to artificial grassland changed the pattern of CO2 emissions from different soil aggregate fractions by deteriorating soil aggregate structure and altering soil SOC and TN distributions. Our findings will be helpful to develop a pragmatic management strategy for mitigating GHGs emissions from alpine grassland.

One-Year Monitoring of Daily Earthworm Cast Production: Surface Cast Contribution to Soil Fertility in a Subtropical Forest

The process of earthworm casting plays an important role in soil fertility. The contributions of earthworm casts to soil nutrients dynamics cannot be fully understood unless the temporal changes in earthworm cast production and the related nutrient resource pools are explored in the field. Here, we recorded the daily surface cast production of earthworms and monthly change patterns of carbon (C), nitrogen (N) and phosphorous (P) in casts in a subtropical plantation for one year and compared the nutrient concentrations and microbial community traits (structure and bacterial activity) in casts with those in bulk soils. Our objectives were to characterize the temporal patterns of earthworm cast production and the C and nutrients in casts and to assess the potential contribution of earthworm casts to soil fertility. The results showed that the annual surface cast production at the study site was 8.3 tons ha−1; monthly cast production was &gt;80 g m−2 during April to November and &lt;30 g m−2 during December to March. The annual outputs of total organic C (TOC), total N (TN) and total P (TP) in surface casts were 68.10, 4.84 and 0.38 g m−2, respectively; the annual outputs of available P (AP), NH4+-N and NO3−-N were 22.4, 147.0 and 61.3 mg m−2, respectively. The concentrations of TOC and TN in casts were higher during warm months, but NH4+-N was higher during cold months, while both the concentrations of TP and AP in casts were constant throughout the year. The nutrient concentrations were 1.6–4.3-fold greater, and the microbial biomass C and N contents were 7–8-fold greater in earthworm casts than those in bulk soils. However, the bacterial stress index (BSI) was significantly greater in casts than in the bulk soil, which implies that bacteria in casts were under stress. Accordingly, the ratio of fungal to bacterial biomass (F/B) was significantly higher in casts than in the bulk soil. Earthworm casting activity can process forest soil into a “new soil”, which forms large amounts of earthworm-induced hotspots of soil fertility. These resource pools in casts, with monthly fluctuated C and N and constant P, could be more readily accessed by fungi rather than bacteria. Earthworm casting activity potentially changes both the nutrients available and the interactions of plants and rhizosphere microbiota.

Runoff-related nutrient loss affected by fertilization and cultivation in sloping croplands: An 11-year observation under natural rainfall

Fertilization and cultivation play important roles in affecting nitrogen (N) and phosphorus (P) losses from sloping croplands. However, the extent and magnitude of these effects are still unknown. Fifteen plots (8 m in length, 4 m in width) were constructed in a representative purple sloping cropland (15°) to determine the fertilization and cultivation effects on runoff-related N and P losses from 2008 to 2018. Five treatments (3 replications for each), including no fertilizer with downslope cultivation (CK), combined manure and chemical fertilizers with downslope cultivation (T1), chemical fertilizer with downslope cultivation (T2), 1.5-fold chemical fertilizer with downslope cultivation (T3), and chemical fertilizer with contour cultivation (T4), were examined. The results showed that there were significant differences in runoff depth, sediment yield, total N (TN) and total P (TP) loss amounts among the five treatments (P < 0.05). The loss amounts of TN, nitrate-nitrogen (NO3-N), ammonium-nitrogen (NH4-N) and TP were the highest in CK and lowest in T4. T1 presented lower TN and TP losses than T2. Total dissolved N (TDN) accounted for 57.97–70.34% of TN loss while total dissolved P accounted for 18.74–31.28% of TP loss in runoff, demonstrating that TDN and particulate P dominated the N and P losses. Runoff depth exhibited significant positive correlations with TN, NO3-N, and NH4-N concentrations (P < 0.05). Our results highlighted that manure application and contour cultivation markedly reduced the N and P losses in sloping croplands, and the risk of N loss caused by unit erosive rainfall decreased with the monitoring years.

Effect of ammonium nitrogen on pepper grown under soilless culture

The response of pepper (Capsicum annuum L.) to Ammonium-N was studied in a multispan greenhouse under soilless culture using coir fiber as substrate. Ammonium-N application rates were 0, 2, 4, 6 and 8 mM with a total-N concentration of 13 mM. The total content of the rest of all macronutrients in the nutrient solution was maintained from the beginning of the experiment until the end. The highest water uptake was recorded at 2 mM ammonium concentration in the nutrient solution. Compared to nitrate, ammonium nitrogen caused a decrease in nitrate absorption, but led to an increase when applying 8 mM ammonium. Despite a progressive increase in ammonium content in the nutrient solution, potassium absorption was constant below the ammonium concentration of 8 mM. Under a high N-NH4 content (from 6 to 8 mM) in the nutrient solution, high toxicity was found, deriving in the appearance of deformed or noncommercial fruits. There was a significant benefit by the use of ammonium as a component in the nutrient solution. The optimum yield ammonium concentrations were found in the range from 2 to 4 mM. Nevertheless, concentrations higher than 6 mM led into a decrease in commercial production, with the production of increasing deformed fruit, out of size and/or blossom-end rot.

Characteristics of Runoff-related Total Nitrogen and Phosphorus Losses Under Long-term Fertilization and Cultivation on Purple Soil Sloping Croplands

To elucidate the effects of long-term fertilization and cultivation on runoff rates and runoff-related nitrogen (N) and phosphorus (P) losses, the following five treatments were established on sloping purple soil cropland:① no fertilizer with downslope tillage (CK), ② combined application of manure and fertilizer with downslope tillage (T1), ③ chemical fertilizers with downslope tillage (T2), ④ chemical fertilizer with increasing fertilization with downslope tillage (T3), and ⑤ chemical fertilizer with contour tillage (T4). The runoff rate, runoff-related total N (TN), and total P (TP) concentrations and their loss rates from 104 erosive rainfall events were determined for the period 2008-2019. Results showed that although runoff rates were not significantly different among the fertilization treatments (P>0.05), runoff was markedly lower in fertilization treatments than in the CK treatment (P<0.05). Runoff-related TN concentrations were significantly higher in the CK compared to the fertilization treatments (P<0.05), while there were no significant differences among the T2, T3, and T4 treatments, which had higher concentrations than the T1 treatment. Runoff-related TP concentrations were significantly higher from the T1, T2, and T3 treatments than the CK treatment (P<0.05), and were significantly lower in the T4 than the CK treatment (P<0.05). TN loss rates were not significantly different among the fertilization treatments (P>0.05), but were all lower than the CK treatment (P<0.05). Furthermore, TP loss rates were not significantly different among the downslope treatments (P>0.05), but were all higher than the contour treatment (P<0.05). Runoff rates showed no significant relationships with TN and TP concentrations in the CK, T1, and T2 treatments but were significantly negatively linearly correlated in T3 (P<0.05) and significantly positively linearly correlated in T4 (P<0.05). These results potentially provide scientific guidance for the prevention and control of agricultural non-point source pollution on sloping croplands in the purple soil area.

Context is Everything: Interacting Inputs and Landscape Characteristics Control Stream Nitrogen.

To understand the environmental and anthropogenic drivers of stream nitrogen (N) concentrations across the conterminous US, we combined summer low-flow data from 4997 streams with watershed information across three survey periods (2000-2014) of the US EPA's National Rivers and Streams Assessment. Watershed N inputs explained 51% of the variation in log-transformed stream total N (TN) concentrations. Both N source and input rates influenced stream NO3/TN ratios and N concentrations. Streams dominated by oxidized N forms (NO3/TN ratio > 0.50) were more strongly responsive to the N input rate compared to streams dominated by other N forms. NO3 proportional contribution increased with N inputs, supporting N saturation-enhanced NO3 export to aquatic ecosystems. By combining information about N inputs with climatic and landscape factors, random forest models of stream N concentrations explained 70, 58, and 60% of the spatial variation in stream concentrations of TN, dissolved inorganic N, and total organic N, respectively. The strength and direction of relationships between watershed drivers and stream N concentrations and forms varied with N input intensity. Model results for high N input watersheds not only indicated potential contributions from contaminated groundwater to high stream N concentrations but also the mitigating role of wetlands.

ANALISIS KUALITAS TANAH PADA LAHAN TEGALAN BERPASIR DI DAS MIKRO SUPITURUNG, KABUPATEN KEDIRI, JAWA TIMUR

Soil quality is the ability of soil that plays a role in maintaining plant productivity, preserving and maintaining water availability and supporting human activities. Soil quality assessment is measured based on indicators that describe important soil processes based on the physical, chemical and biological properties of the soil. The level of soil quality in a plot of land is assessed based on the soil quality index. This research was conducted from August to December 2020 in the Supiturung Micro Watershed, Kediri Regency, East Java using a graphical survey method based on the Land Map Unit. Soil samples were taken at a depth of 0-20 cm at each observation point (20 points) for analysis in the laboratory. Soil quality indicators are determined based on key soil properties with the Minimum Data Set (MDS) method, with soil quality indicators from soil physical properties including texture, bulk density, porosity and soil chemical properties including pH, available-P, exchangeable-K, total-N, organic-C. Soil quality index was calculated by weighting soil quality indicators with criteria which divided into 5 classes, i.e. (i) very low class (0.00-0.19), (ii) low (0.20-0.39), (iii) moderate (0.40-0.59), (iv) good (0.60-0.79) and (v) very good (0.80-1.00). The results showed that the soil in land unit 2 had different limiting factor values on the percentage of sand and dust from the soil texture, the total-N content of the soil and the organic-C content of the soil which caused differences in soil quality. There are two indicators of soil quality, namely the percentage of dust from the soil texture and the total N content of the soil which has the most influence on the soil quality index.

Potential test of non-symbiotic nitrogen-fixing bacteria in increasing nitrogen in Andisol soil

Nitrogen (N) is one of the elements most needed by plants and widely distributed in nature. Nitrogen fixation can occur symbiotic or non-symbiotic by soil microbes. This research aimed to examine the potential of N-fixing microbes in increasing the availability of N in the soil. This research was conducted at the Soil Biology Laboratory of Faculty of Agriculture, Universitas Sumatera Utara. The results showed that the ability of microbes to increase the availability of N in the soil was varied. The population of N-fixing bacteria increased during 4 weeks of incubation. All bacterial isolates which incubated on Andisol soil were able to increase soil N-total content by around 9.4% -15.6%. The isolate with the most potential to increase soil N-total content was B6 isolate with an increase in total N content by 15.6%.

Mineralization of Nitrogen Forms in Soil Cultivated with Yellow Melon under Organic and Mineral Fertilization

ABSTRACT The association of mineral and organic fertilization is a nitrogen supply system for the melon crop. Nitrogen (N) fractionation is an important tool to understand its dynamics in the soil and the contribution of each fraction to N bioavailability. This study aimed to evaluate the effects of organic and mineral fertilization on organic and inorganic forms of soil N of the cultivation of yellow melon. The experiment was conducted in the Experimental Field of Pacajus, belonging to Embrapa Agroindústria Tropical, in soil classified as Red Yellow Argisol. The experimental design was a split-plot randomized block. Fertilizer application was the main plot treatment and sampling time was arranged as subplots. The experimental results indicated that only organic fertilization was sufficient to significantly increase the total-N content (varying from 1,127 mg kg−1 to 967 mg kg−1) compared to only mineral fertilization (951 mg kg−1) and organic N represented 92 ± 2% of the total-N. In addition, the higher hydrolyzable N content was observed in the treatment with only bovine manure application (542 mg kg−1) which represents an N source for the mineralization and subsequent inorganic N for plants. Our results reveal that organic fertilization is efficient for long-term fertility management, increasing melon productivity.

KARAKTERISTIK SIFAT KIMIA TANAH DAN KANDUNGAN MERKURI PADA LAHAN BEKAS TAMBANG EMAS DAN LAHAN PERKEBUNAN KELAPA SAWIT (Elaeis guineensis Jacq.)

The present study was conducted in Tebing Tinggi Village, Pulau Punjung Sub-district, Dharmasraya District was motivated by a desire to exploit land resources, especially open access land that was formerly a gold mine by cultivating oil palm plants. The objectives of this study were to determine the characteristics of soil chemical properties, the soil fertility level, and the level of mercury (Hg) contamination in former gold mining land by compared with the soil chemical fertility of oil palm plantations. The research method was a survey by purposive sampling. The Soil sampling for analysis of soil chemical properties was carried out by drilling of 0-40 cm deep with 12 sample points divided into 4 locations, where 3 locations in the former gold mine area that were grouped into three segments, namely segments 1, 2 and 3 and one location was in oil palm land. The parameters of soil chemical properties observed were pH, Al-dd, C-organic, C / N Ratio, N, P, K and Hg (Mercury). The results of this research, shows that the characteristics of soil chemical properties in the former gold mining area have decreased the level of soil fertility, characterized by the very low pH value and C-organic content, ​​so that the nutrients contained in the land are very limited when compared to the soil fertility in oil palm land. This is indicated by the fact that the oil palm land has a high C-organic content and a moderate level of N-total content. The utilization of the land resources of the former gold mine, it is necessary to do land improvementsin terms of soil physically, chemically and biologically.

Effectiveness of Advanced Nitrogen-Removal Onsite Wastewater Treatment Systems in a New England Coastal Community

Wastewater is a major source of nitrogen (N) to groundwater and coastal waterbodies, threatening both environmental and public health. Advanced N-removal onsite wastewater treatment systems (OWTS) are used to reduce effluent N concentration; however, few studies have assessed their effectiveness. We evaluated the total N (TN) concentration of effluent from 50 advanced N-removal OWTS in Charlestown, Rhode Island, USA for 3 years. We quantified differences in effectiveness as a function of N-removal technology and home occupancy pattern (seasonal vs. year-round use), and examined the relationship between wastewater properties and TN concentration. RX30 systems produced the lowest median TN concentration (mg N/L) (13.2), followed by FAST (13.4), AX20 (14.9), and Norweco (33.8). Compliance with the state’s regulatory standard for effluent TN concentration (19 mg N/L) was highest for RX30 systems (78%), followed by AX20 (73%), FAST (67%), and Norweco (0%). Occupancy pattern did not affect effluent TN concentration. Variation in TN concentration was driven by ammonium and nitrate for all technologies, and also by temperature for FAST and pH for Norweco. Median daily (g N/day) and annual (kg N/yr) N loads were significantly higher for year-round (5.3 and 2.3) than for seasonal (3.7 and 0.41) systems, likely due to differences in volume of wastewater treated. Our results suggest that advanced N-removal OWTS vary in their compliance with the state regulatory standard for effluent TN and can withstand long periods of non-use without compromising effectiveness. Nevertheless, systems used year-round do produce a higher daily and annual N load than seasonally-used systems.

Phenotypical evidence of effective amelioration of ammonium-inhibited plant (root) growth by exogenous low urea

Ammonium and nitrate are major soil inorganic-nitrogen sources for plant growth, but many species cultivated with even low millimolar NH4+ as a sole N form display a growth retardation. To date, critical biological components and applicable approaches involved in the effective enhancement of NH4+ tolerance remain to be thoroughly explored. Here, we report phenotypical traits of urea-dependent improvement of NH4+-suppressed plant/root growth. Urea at 0.1 mM was sufficient to remarkably stimulate NH4+ (3 mM)-fed cotton growth, showing a 2.5∼4-fold increase in shoot- and root-biomass and total root-length, 20 % higher GS activity, 18 % less NH4+-accumulation in roots, and a comparable plant total-N content compared to the control, implying a novel role for urea in cotton NH4+detoxification. A similar phenomenon was observed in tobacco and rice. Moreover, comparisons between twelve NH4+-grown Arabidopsis accessions revealed a great degree of natural variation in their root-growth response to low urea, with WAR and Blh-1 exhibiting the most significant increase in primary- and lateral-root length and numbers, and Sav-0 and Edi-0 being the most insensitive. Such phenotypical evidence suggests a common ability of plants to accommodate NH4+-stress by responding to exogenous urea, providing a novel aspect for further understanding the process of urea-dependent plant NH4+ tolerance.

Effects of the type of forest alteration on gross nitrogen mineralization in soils of southern India

Change in land-use practices can result in major shifts in the cycling of various elements, particularly nitrogen (N), which is prone to anthropogenic perturbations. For quantifying these shifts, accurate measurements of rates of biogeochemical transformations of N are needed. We used the (15N) isotope dilution technique to understand the effects of the types of forest alteration on (N) transformation rates by comparing gross N mineralization and ammonium (NH4+) consumption rates in soils of a managed forest, an unmanaged forest, and a rubber plantation in Kerala, India. Overall, nitrate (NO3−) dominated soils of the managed and unmanaged forests, whereas soils in the rubber plantation showed relatively higher NH4+ concentration. Total N (TN) and total organic carbon (TOC) concentrations were the highest under the rubber canopy (TN: 1.49 ± 0.02 mg N g−1; TOC: 7.96 ± 0.86 mg C g−1). In soils of all three forest types, gross N mineralization rates were higher compared to NH4+ consumption rates. Despite high TN and TOC concentrations, the rates of gross N mineralization and NH4+ consumption were considerably lower in the rubber plantation (mineralization: 1.08 ± 0.08 mg N kg−1 d−1; consumption: 0.85 ± 0.09 mg N kg−1 d−) compared to the managed (mineralization: 3.71 ± 0.35 mg N kg−1 d−1; consumption: 2.20 ± 1.41 mg N kg−1 d−1) and unmanaged (mineralization: 2.20 ± 1.07 mg N kg−1 d−1; consumption: 1.39 ± 0.27 mg N kg−1 d−1) forests. The lower NH4+ consumption rates in the rubber plantation led to significantly higher (p < 0.05) residence time of NH4+ (~ 4 days) compared to the managed and unmanaged forests (< 2 days), possibly contributing to acidification of rubber soils (pH ~ 4.8). These results together suggest that replacement of naturally grown forests with a mono-cropped plantation such as rubber negatively impact rates of N transformation processes in tropical soils and imply that change in tree species composition of naturally grown forests can adversely affect soil microbial activity. We recommend intercropping these plantations with commercial crops to maintain soil microbial diversity and biogeochemical cycling for sustainable forest management.

Keragaman Mikroflora, Mikrofauna, Kandungan C-organik, dan Total N Tanah Sawah Akibat Aplikasi Azolla dan Pupuk Hayati

This study was conducted to determine the effect of Azolla pinnata and biofertilizers (Azotobacter and Phosphate Solubilizing Bacteria) on the total microflora, microfauna, organic C, N-total soil, and C/N ratio of soil in lowland rice. The study was carried out in the SPLPP experimental field (Agricultural Research and Development Research Studio) of the Faculty of Agriculture, Padjadjaran University, Jelekong Village, Ciparay, Bandung Regency, West Java, with an altitude of 628 meters above the sea level. The experimental design used was factorial randomized block design consisted of two factors and repeated four times. The first factor was the provision of Azolla with two levels: without Azolla and 3 tons ha-1 of Azolla pinnata. The second factor was the provision of biofertilizer with three levels, without biofertilizer, 5 L ha-1 biofertilizer, and 10 L ha-1 biofertilizer. The results showed that there was an interaction between A. pinnata with biofertilizer on the increase in the total bacterial population. Total fungus, microfauna (nematodes), and soils N-total content did not increase with the addition of Azolla or biofertilizers. Independently A. pinnata increased soil C-organic matter while biofertilizer 10 L ha-1 increased the total population of actinomycetes.