NITROGEN RATES AND ITS TIME OF APPLICATION INFLUENCE DRY MATTER PARTITIONING AND GRAIN YIELD IN MAIZE PLANTED AT LOW AND HIGH DENSITIES

Best nitrogen (N) management practices are most important for increasing maize (Zea mays L.) productivity and profitability in Northwest Pakistan. Field experiments were performed at the New Developmental Research Farm of NWFP Agricultural University, Peshawar during summer 2002 and 2003. Factorial experimental treatments were two plant densities (D₁ = 60,000 and D₂ = 100,000 plants ha^?1) and three N rates (N₁ = 60, N₂ = 120 and N₃ = 180 kg N ha^?1) as main plots, and six split N applications in different proportions at different growth stages of maize (cv. ‘Azam’) in two equal, three equal, three unequal, four equal, five equal and five unequal splits at sowing and with first, second, third, and fourth irrigation at two week intervals as subplots. Application of the higher N rate (180 kg ha^?1) with 4 to 5 splits significantly increased leaf, stem, ear, and total plant dry weight at silking and physiological maturity as well as grain yield plant^?1 at both low and high plant densities. Variation in dry matter partitioning and grain yield in maize due to fluctuation in the rainfall data of the two years suggests zonal specific effective N management practices for sustainable maize production in different agro-ecological zones of Northwest Pakistan.     

The amount,but not the proportion,of N2 fixation and transfers to neighboring plants varies across grassland soils

ABSTRACT

Biological nitrogen fixation (BNF) is an important nitrogen source for both N₂-fixers and their neighboring plants in natural and managed ecosystems. Biological N fixation can vary considerably depending on soil conditions, yet there is a lack of knowledge on the impact of varying soils on the contribution of N from N₂-fixers in mixed swards. In this study, the amount and proportion of BNF from red clover were assessed using three grassland soils. Three soil samples, Hallsworth (HH), Crediton (CN), and Halstow (HW) series, were collected from three grassland sites in Devon, UK. A pot experiment with ¹⁵N natural abundance was conducted to estimate BNF from red clover, and the proportion of N transferred from red clover to the non-N₂ fixing grass in a grass-clover system. The results showed that BNF in red clover sourced from atmosphere in the HH soil was 2.92 mg N plant^?1, which was significantly lower than that of the CN (6.18 mg N plant^?1) and HW (8.01 mg N plant^?1) soils. Nitrogen in grass sourced from BNF via belowground was 0.46 mg N plant^?1 in the HH soil, which was significantly greater than that in CN and HW soils. However, proportionally there were no significant differences in the percentage N content of both red clover and grass sourced from BNF via belowground among soils, at 65%, 67%, 65% and 35%, 27%, 31% in HH, CN, and HW, respectively. Our observations indicate that the amount of BNF by red clover varies among grassland soils, as does the amount of N sourced from BNF that is transferred to neighboring plants, which is linked to biomass production. Proportionally there was no difference among soils in N sourced from BNF in both the red clover plants and transferred to neighboring plants.     

Effects of Land Use Conversion from Native Forests to Exotic Plantations on Nitrogen and Phosphorus Retention in Catchments of Southern Chile

In six small catchments located at the Cordillera de la Costa in southern Chile (40° S), concentrations and fluxes of NO₃-N, NH₄-N, organic-N, total-N and total-P in bulk precipitation and runoff water were measured. The main objective of this study was to compare nitrogen and phosphorus retention of catchments with varying land cover of native forest and exotic plantations, in order to evaluate possible effects of land use change. Nitrate-N was the dominant fraction (>50%) of nitrogen loss, especially in the catchments dominated by exotic plantations. In the catchment with native forests, NO₃ ^? only contributed with 34% of the nitrogen loss and DON was the main output with 55%. Annual NO₃ ^? export was lower in the catchment with native forest compared to the catchments with exotic plantations where the streamflow output exceed the precipitation input. Average inputs of total-N were 2.6 kg ha^?1 year^?1 (DIN?=?1.4 kg ha^?1 year^?1, DON?=?1.2 kg ha^?1 year^?1) and outputs were 1.7 kg ha^?1 year^?1 (DIN?=?1.2 kg ha^?1 year^?1, DON?=?0.5 kg ha^?1 year^?1). Annual retention of total nitrogen fluctuated between 61% in a catchment dominated by native forests to 15% in catchments dominated by exotic plantations of Eucalyptus sp. Nitrogen retention was positively related with native forest coverage. The N retention capacity of the catchments could be both attributed to consequences of clear cutting practices and differences in vegetation cover.     

Elevated carbon dioxide level along with phosphorus application and cyanobacterial inoculation enhances nitrogen fixation and uptake in cowpea crop

Climate change, as a result of increase in the concentration of greenhouse gases, influences growth and productivity of leguminous crops. A study was carried out to analyse the impacts of elevated carbon dioxide (CO₂) and cyanobacterial inoculation on growth, N₂ fixation and N availability and uptake in cowpea crop, under different doses of phosphorus. Cowpea crop was grown under ambient (400 µmol mol^?1) and elevated (550 ± 20 µmol mol^?1) CO₂ levels using Free-Air Carbon dioxide Enrichment facility. Elevated CO₂ level increased chlorophyll content in leaves, improved nodulation and nitrogen fixation by the crop. Increase in P dose up to 16 mg kg^?1 soil enhanced nodule development and N₂ fixation under high CO₂ condition. Cyanobacterial inoculation increased nodule weight, leghaemoglobin content in nodules and total nitrogenase activity. Although nitrogen concentration in cowpea seeds decreased in high CO₂ treatment, higher N uptake was recorded. Under elevated CO₂ condition, cyanobacterial inoculation and higher P doses led to enhanced root growth and N₂ fixation and availability of soil nitrogen. The study illustrated the synergistic effect of high CO₂ and cyanobacterial inoculation in enhancing crop growth and availability of soil N, mediated by biological N₂ fixation in cowpea under different levels of P.     

PHOSPHORUS USE EFFICIENCY FOR SYMBIOTIC NITROGEN FIXATION VARIES AMONG COMMON BEAN RECOMBINANT INBRED LINES UNDER P DEFICIENCY

This study compared the growth, nodulation, phosphorus use efficiency and nitrogen (N₂) fixation by six recombinant inbred lines (RILs) of Phaseolus vulgaris (RILs 147, 28, 83, 34, 7, and 104). These RILs were inoculated with Rhizobium tropici CIAT899 and grown in an aerated nitrogen-free nutrient solution at deficient versus sufficient phosphorous supplies (75 vs. 250 μmol P plant^?1 week^?1) in a glasshouse. Our results show that plant growth, nodulation, and symbiotic nitrogen fixation were significantly affected by P deficiency for all RILs, whereas this adverse effect was more pronounced in RILs 147, 83, 28 and 7 than in RILs 34 and 104. Under P deficiency, RILs 34 and 104 showed higher efficiency than other RILs in the use of P for their symbiotic N nutrition. It is concluded that P utilization efficiency may be a useful selection criterion for genotypic adaptation of N₂-fixing legumes to low P soils.     

Sediment denitrification in waterways in a rice-paddy-dominated watershed in eastern China

Purpose

Rice-paddy-dominated watersheds in eastern China are intensively cultivated, and lands with two crops receive as much as 550–600 kg?ha^–1?year^–1 of nitrogen (N), mainly through the addition of N-based fertilizers. However, stream N concentrations have been found to be relatively low. Waterways in the watersheds are assumed to be effective “sinks” for N, minimizing its downstream movement. We directly measured net sediment denitrification rates in three types of waterways (ponds, streams/rivers, and a reservoir) and determined the key factors that control net sediment denitrification. Such information is essential for evaluating the impact of the agricultural N cycle on the quality of surface water.

Materials and methods

The pond–stream–reservoir continuum was sampled every 2 months at nine sites in an agricultural watershed between November 2010 and December 2011. Net sediment N₂ fluxes/net sediment denitrification rates were determined by membrane inlet mass spectrometry and the N₂/Ar technique. A suite of parameters known to influence denitrification were also measured.

Results and discussion

Net denitrification rates ranged between 28.2?±?18.2 and 674.3?±?314.5 μmol N₂–N?m^–2?h^–1 for the streams, 23.7?±?23.9 and 121.2?±?38.7 μmol N₂–N?m^–2?h^–1 for the ponds, and 41.8?±?17.7 and 239.3?±?49.8 μmol N₂–N?m^–2?h^–1 for the reservoir. The mean net denitrification rate of the stream sites (173.2?±?248.4 μmol N₂–N?m^–2?h^–1) was significantly higher (p?<?0.001) than that of the pond sites (48.3?±?44.5 μmol N₂–N?m^–2?h^–1), and the three types of waterways all had significantly higher (p?<?0.01) mean net denitrification rates in summer than in other seasons. Linear regression and linear mixed effect model analysis showed that nitrate (NO₃ ^?–N) concentration in surface water was the primary controlling factor for net sediment denitrification, followed by water temperature. Using monitoring data on NO₃ ^?–N concentrations and temperature of the surface water of waterways and an established linear mixed effect model, total N removed through net sediment denitrification in the pond–stream–reservoir continuum was estimated at 46.8?±?24.0 t?year^–1 from July 2007 to June 2009, which was comparable with earlier estimates based on the mass balance method (34.3?±?12.7 t?year^–1), and accounted for 83.4 % of the total aquatic N. However, the total aquatic N was only 4.4 % of the total N input to the watershed, and thus most of the surplus N in the watershed was likely to be either denitrified or stored in soil.

Conclusions

High doses of N in a rice-paddy-dominated watershed did not lead to high stream N concentrations due to limited input of N into waterways and the high efficiency of waterways in removing N through denitrification.     

Cumulative Effect of Soil and Foliar Application of Nitrogen,Phosphorus, and Sulfur on Growth,Physico-Biochemical Parameters,Yield Attributes,and Fatty Acid Composition in Oil of Erucic Acid-Free Rapeseed-Mustard Genotypes

ABSTRACT

The feasibility of split (soil + foliar) applications of nitrogen (N) and phosphorus (P) and addition of a small quantity of sulfur (S) in the spray was tested for improving performance of rapeseed-mustard genotypes in a factorial randomized field experiment. Three genotypes (two erucic acid free, viz. Brassica napus L. cv. ‘Hyola PAC – 401’ and Brassica juncea L. Czern. and Coss. cv. ‘TERI (0E) M 21-Swarna’, and one best performing high yielding Brassica juncea L. cv. ‘Rohini’ as a check) were grown with four soil (B) plus foliar (F) applications of N, P, and S with uniform basal 30 kg potassium (K) ha^{? 1} (K₃₀), viz. (i) the optimum soil-applied treatment supplemented with the spray of deionized water (B_N90P30 + Fw) comprising control, (ii) B_N70P30 + F _N20, (iii) B_N70P28 + F_N20P2, and (iv) B_N70P28 + F_N20P2S2. Soil Plus foliar application of nutrients, particularly B_N70P28 + F_N20P2S2, improved their performance with respect to growth characteristics (shoot length plant^{? 1}, leaf number plant^{? 1}, area leaf^{? 1}, leaf area index, fresh weight plant^{? 1}, and dry weight plant^{? 1}), physico-biochemical parameters (net photosynthetic rate, stomatal conductance, carboxylation efficiency, water use efficiency, carbonic anhydrase activity, leaf NPK content, and N use efficiency), yield attributes (pod number plant^{? 1}, seed number pod^{? 1}, 1000-seed weight, seed yield ha^{? 1}, oil content, and oil yield ha^{? 1}), and fatty acid composition in oil of these genotypes. The cultivar ‘Hyola PAC-401’ performed best particularly with B_N70P28 + F_N20P2S2. The improvement in the response of genotypes to the split application of nutrients may be attributed to their ready availability through foliar application.     

Life cycle inventory-based analysis of greenhouse gas emissions from arable land farming systems in Hokkaido,northern Japan

Abstract

To assess their impacts on net global warming, total greenhouse gas emissions (mainly CO₂, N₂O and CH₄) from agricultural production in arable land cropping systems in the Tokachi region of Hokkaido, Japan, were estimated using life cycle inventory (LCI) analysis. The LCI data included CO₂ emissions from on-farm and off-farm fossil fuel consumption, soil CO₂ emissions induced by the decomposition of soil organic matter, direct and indirect N₂O emissions from arable lands and CH₄ uptake by soils, which were then aggregated in CO₂-equivalents. Under plow-based conventional tillage (CT) cropping systems for winter wheat, sugar beet, adzuki bean, potato and cabbage, on-farm CO₂ emissions from fuel-consuming operations such as tractor-based field operations, truck transportation and mechanical grain drying ranged from 0.424 Mg CO₂ ha^?1 year^?1 for adzuki bean to 0.826 Mg CO₂ ha^?1 year^?1 for winter wheat. Off-farm CO₂ emissions resulting from the use of agricultural materials such as chemical fertilizers, biocides (pesticides and herbicides) and agricultural machines were estimated by input–output tables to range from 0.800 Mg CO₂ ha^?1 year^?1 for winter wheat to 1.724 Mg CO₂ ha^?1 year^?1 for sugar beet. Direct N₂O emissions previously measured in an Andosol field of this region showed a positive correlation with N fertilizer application rates. These emissions, expressed in CO₂-equivalents, ranged from 0.041 Mg CO₂ ha^?1 year^?1 for potato to 0.382 Mg CO₂ ha^?1 year^?1 for cabbage. Indirect N₂O emissions resulting from N leaching and surface runoff were estimated to range from 0.069 Mg CO₂ ha^?1 year^?1 for adzuki bean to 0.381 Mg CO₂ ha^?1 year^?1 for cabbage. The rates of CH₄ removal from the atmosphere by soil uptake were equivalent to only 0.020–0.042 Mg CO₂ ha^?1 year^?1. From the difference in the total soil C pools (0–20 cm depth) between 1981 and 2001, annual CO₂ emissions from the CT and reduced tillage (RT) soils were estimated to be 4.91 and 3.81 Mg CO₂ ha^?1 year^?1, respectively. In total, CO₂-equivalent greenhouse gas emissions under CT cropping systems in the Tokachi region of Hokkaido amounted to 6.97, 7.62, 6.44, 6.64 and 7.49 Mg CO₂ ha^?1 year^?1 for winter wheat, sugar beet, adzuki bean, potato and cabbage production, respectively. Overall, soil-derived CO₂ emissions accounted for a large proportion (64–76%) of the total greenhouse gas emissions. This illustrates that soil management practices that enhance C sequestration in soil may be an effective means to mitigate large greenhouse gas emissions from arable land cropping systems such as those in the Tokachi region of northern Japan. Under RT cropping systems, plowing after harvesting was omitted, and total greenhouse gas emissions from winter wheat, sugar beet and adzuki bean could be reduced by 18%, 4% and 18%, respectively, mainly as a result of a lower soil organic matter decomposition rate in the RT soil and a saving on the fuels used for plowing.     

Nitrous oxide and nitric oxide fluxes from cornfield,grassland, pasture and forest in a watershed in Southern Hokkaido,Japan

Abstract

To develop an advanced method for estimating nitrous oxide (N₂O) emission from an agricultural watershed, we used a closed-chamber technique to measure seasonal N₂O and nitric oxide (NO) fluxes in cornfields, grassland, pastures and forests at the Shizunai Experimental Livestock Farm (467 ha) in southern Hokkaido, Japan. From 2000 to 2004, N₂O and NO fluxes ranged from –137 to 8,920 µg N m^?2 h^?1 and from –12.1 to 185 µg N m^?2 h^?1, respectively. Most N₂O/NO ratios calculated on the basis of these N₂O and NO fluxes ranged between 1 and 100, and the log-normal N₂O/NO ratio was positively correlated with the log-normal N₂O fluxes (r ² = 0.346, P < 0.01). These high N₂O fluxes, therefore, resulted from increased denitrification activity. Annual N₂O emission rates ranged from –1.0 to 81 kg N ha^?1 year^?1 (average = 6.6 kg N ha^?1). As these emission values varied greatly and included extremely high values, we divided them into two groups: normal values (i.e. values lower than the overall average) and high values (i.e. values higher than average). The normal data were significantly positively correlated with N input (r ² = 0.61, P < 0.01) and the “higher” data from ungrazed fields were significantly positively correlated with N surplus (r ² = 0.96, P < 0.05). The calculated probability that a high N₂O flux would occur was weakly and positively correlated with precipitation from May to August. This probability can be used to represent annual variation in N₂O emission rates and to reduce the uncertainty in N₂O estimation.     

Zeolite influences on nitrate leaching,nitrogen-use efficiency,yield and yield components of canola in sandy soil

With regard to the low cation-exchange capacity and large saturated hydraulic conductivity of sandy soils, a field experiment was carried out in 2006–2007 to determine the impact of zeolite on nitrogen leaching and canola production. Four nitrogen (N) rates (0, 90, 180, and 270 kg ha^–1) and three zeolite amounts (3, 6 and 9 t ha^?1) were included as treatments. The results demonstrated that the highest growth parameters and seed yield were attained with 270 kg N ha^?1 and 9 t zeolite ha^?1. However, the highest and the lowest seed protein percentage and oil content were obtained with 270 kg N ha^?1 accompanied by 9 t zeolite ha^?1, respectively. Nitrate concentration in drained water was affected by nitrogen and zeolite. The lowest and highest leached nitrate values were found in control without N and zeolite (N₀Z₀) and in treatments with the highest N supply without zeolite (N₂₇₀Z₀), respectively. In general, nitrogen-use efficiency decreased with an increase in N supply. Application of 9 t zeolite ha^?1 showed higher nitrogen use efficiency than other zeolite amounts. Also, application of more N fertilizer in soil reduced nitrogen uptake efficiency. In total, application of 270 kg N ha^?1 and 9 t zeolite ha^?1 could be suggested as superior treatment.     

Impacts of nitrogen addition on the carbon balance in a temperate semiarid grassland ecosystem

Understanding carbon (C) cycling and sequestration in vegetation and soils, and their responses to nitrogen (N) deposition, is important for quantifying ecosystem responses to global climate change. Here, we describe a 2-year study of the C balance in a temperate grassland in northern China. We measured net ecosystem CO₂ exchange (NEE), net ecosystem production (NEP), and C sequestration rates in treatments with N addition ranging from 0 to 25 g N m^?2 year^?1. High N addition significantly increased ecosystem C sequestration, whose rates ranged from 122.06 g C m^?2 year^?1 (control) to 259.67 g C m^?2 year^?1 (25 g N). Cumulative NEE during the growing season decreased significantly at high and medium N addition, with values ranging from ?95.86 g C m^?2 (25 g N) to 0.15 g C m^?2 (5 g N). Only the highest N rate increased significantly cumulative soil microbial respiration compared with the control in the dry 2014 growing season. High N addition significantly increased net primary production (NPP) and NEP in both years, and NEP ranged from ?5.83 to 128.32 g C m^?2. The C input from litter decomposition was significant and must be quantified to accurately estimate NPP. Measuring C sequestration and NEP together may allow tracking of the effects of N addition on grassland C budgets. Overall, adding 25 or 10 g N m^?2 year^?1 improved the CO₂ sink of the grassland ecosystem, and increased grassland C sequestration.     

Nitrous oxide flux from komatsuna (Brassica rapa) vegetated soil: a comparison between biogas digested liquid and chemical fertilizer

Biogas production generates digested slurry as a by-product. It can be used as fertilizer especially after its conversion into digested liquid. A microcosm-based study was conducted in order to compare the effects of single application of digested liquid or chemical fertilizer on N₂O flux and crop yield of komatsuna vegetable. Analysis revealed that digested liquid-treated soils released almost equal cumulative N₂O (0.43 g?N m^?2) compared to chemical fertilizer (0.39 g?N m^?2). The uncropped soils treated with the digested liquid and chemical fertilizer released more N₂O compared to corresponding cropped soils. The N₂O emission factor and soil mineral N contents were similar for the digested liquid and chemical fertilizer-treated soils. Plant biomass in the first crop after digested liquid application was significantly higher (5.59 g plant^?1) than that after applied chemical fertilizer (4.78 g plant^?1); but there was no significant difference for the second crop. Nitrogen agronomic efficiency was improved by the digested liquid compared to chemical fertilizer. This study indicates that cumulative N₂O flux was similar after application of the digested liquid and chemical fertilizer, while the overall yield from both croppings was increased in the digested liquid-treated soil compared to chemical fertilizer-treated soil.     

Emergence Rate,Yield, and Nitrogen-Use Efficiency of Sunflowers (Helianthus annuus) Vary with Soil Salinity and Amount of Nitrogen Applied

For understanding the effects of soil salinity and nitrogen (N) fertilizer on the emergence rate, yield, and nitrogen-use efficiency (NUE) of sunflowers, complete block design studies were conducted in Hetao Irrigation District, China. Four levels of soil salinity (electrical conductivity [EC_e] = 2.44–29.23 dS m^?1) and three levels of N fertilization (90–180 kg ha^?1) were applied to thirty-six microplots. Soil salinity significantly affected sunflower growth (P < 0.05). High salinity (EC_e = 9.03–18.06 dS m^?1) reduced emergence rate by 24.5 percent, seed yield by 31.0 percent, hundred-kernel weight by 15.2 percent, and biological yield by 27.4 percent, but it increased the harvest index by 0.9 percent relative to low salinity (EC_e = 2.44–4.44 dS m^?1). Application of N fertilizer alleviated some of the adverse effects of salinity, especially in highly saline soils. We suggest that moderate (135 kg ha^?1) and high (180 kg ha^?1) levels of N fertilization could provide the maximum benefit in low- to moderate-salinity and high- or severe-salinity fields, respectively, in Hetao Irrigation District and similar sunflower-growing areas.     

Standardization of media and nutrient concentration for coleus (Plectranthus barbatus Andr.) under substrate culture

Coleus (Plectranthus barbatus Andr.) is a medicinal herb whose roots contain forskolin. Incidences of soil-borne diseases, wilt complex and nematodes are the major limiting factors for growing this crop under soil media. Hence, an investigation was initiated for the standardization of soilless growth media and nutrient solution concentration in coleus. Coco peat, vermiculite, sand and their combinations were used as potting media with different concentrations of nutrients based on the recommended dose of fertilizers for soil media (1,080 mg plant^?1 nitrogen, 960 mg plant^?1 phosphorous and 1200 mg plant^?1 potassium). Among the different media and nutrients, plants grown under coco peat media with 80% of the recommended dose of fertilizer for soil (864 mg plant^?1 nitrogen, 768 mg plant^?1 phosphorous and 960 mg plant^?1 potassium) recorded significantly higher root yield (17.10 tha^?1) and quality parameters (0.98% forskolin). Benefit–cost ratio was also recorded maximum (4.25) in the same treatment.     

Nitrogen Balance and Fertigation Use Efficiency in a Field Coffee Crop

Brazil is a major world coffee producer, using increasing quantities of nitrogen (N) fertilizer as the monoculture expands across the savannas. The fate and efficiency of this fertilizer N were evaluated for one complete cropping cycle using ¹⁵N tracer, permitting an N balance at harvest. Annual rates of 200, 400, 600, and 800 kg N ha^?1 year^?1 of ¹⁵N-labeled urea and an unfertilized control were applied every 14 days via fertigation. The N concentration, percentage of N derived from fertilizer, quantity of N derived from fertilizer, and percentage of nitrogen derived from fertilizer per N rate was assessed for 8-year-old coffee trees. The most efficient N use was with 200 kg ha^?1 year^?1 because it presented the lowest losses and highest N recoveries in the crop. Conversely, the least sustainable rate was 800 kg ha^?1 year^?1, which presented the greatest losses and the lowest N recovery in the whole plant.     

Effect of different nitrogen-potassium concentrations on growth and flowering of chrysanthemum in a drip hydroponic system

Different concentrations of Nitrogen (N) and Potassium (K) at vegetative and flowering stages were evaluated to optimizing their levels for high quality performance of Chrysanthemum morifolium Ramat. cv. ‘Mother Teresa’ grown in soilless media mixture (cocopeat:perlite:vermiculite = 3:1:1) in a non-recovery drip hydroponic system. The treatments consisted of five nutrient solution concentrations (NSC), having N (50, 100, 150, 200 and 250 ppm) and K levels (40, 80, 120, 160 and 200 ppm) during vegetative stage, whereas during reproductive stage, the N and K levels were 40, 80, 120, 160 and 200 ppm, and 60, 110, 160, 210 and 260 ppm, respectively. The performance of chrysanthemum improved with increasing levels of N-K concentration. The nutrient concentration (NSC-V) of N₂₅₀ + K₂₀₀ during vegetative and N₂₀₀ + K₂₆₀ during reproductive stage produced highest (153) number of flowers, plant height (31.5 cm), plant canopy (35 cm) and flower sprays (21) per plant proved to be the best treatment.     

Dry and Wet Deposition of Nitrogen Emitted in Buenos Aires City to Waters of de la Plata River

Dry and wet deposition of atmospheric nitrogen species (NO₂ and HNO₃) coming from nitrogen oxides emissions in Buenos Aires city to surface waters of de la Plata River were estimated. Atmospheric dispersion models DAUMOD-RD (v.2) and CALPUFF were applied to area and point sources, respectively. These models were run considering 1 year of hourly meteorological data. Emission information included a typical diurnal variation of area source emissions. Annual atmospheric nitrogen (N–NO₂?+?N–HNO₃) deposition to 1,763 km² of the river was 35,600 kg-N year^?1. Dry deposition processes accounted for 89% of this value. The small contribution of wet deposition was a consequence of the very few cases (5%) of rain events during offshore wind conditions. Monthly dry deposition to 1,763 km² of the river varied from 1,628 kg-N month^?1 in February to 3,799 kg-N month^?1 in December, following the monthly occurrence of offshore winds. Monthly wet deposition varied from 1 kg-N month^?1 in June to 1,162 kg-N month^?1 in February. These results came from the combination of favorable conditions for formation of HNO₃ and the occurrence of precipitation during offshore wind situations. Spatial distribution of annual atmospheric N deposition showed a strong coastal gradient. Deposition values reached a maximum of 137.1 kg-N km^?2 year^?1 near the shoreline, which was reduced to the half at 4 km from the coast.     

A rapid method for estimating labile carbon and nitrogen pools in Mollisols under no-tillage

The objective of this study was to adapt the partial chemical digestion method for estimation of labile soil organic matter pools by evaluating the effect of different digestion times in Mollisols of the Argentine Pampas. The soils were sampled from nine agricultural fields under no-tillage at the 0–20 cm depth. A chemical method was performed through partial soil digestion with dilute sulphuric acid at 100°C on the basis of four digestion times: 1 (N_d1), 2 (N_d2), 4 (N_d4) and 6 (N_d6) hours. Soil organic carbon (C) and nitrogen (N) fractions were determined. The extracted organic N (N_d) ranged from 0.076 g kg^?1 to 0.273 g kg^?1, with a mean of 0.154 g kg^?1. Statistically, the means for each digestion time indicated highly significant differences (P = 0.008). High correlations were found between N_d for different times and labile C and N fractions. However, the best fit prediction was observed between N_d2 and soil total carbohydrates (CHt), with a high coefficient of determination (R² = 0.94). Partial chemical digestion for 2 h can be used as a rapid indicator to accurately predict CHt. Because of its speed and simplicity, this method may also be useful for rapid soil quality assessments.     

Changes in soil bacterial communities in an evergreen broad-leaved forest in east China following 4 years of nitrogen addition

Purpose

Evergreen broad-leaved forest ecosystems are common in east China, where they are both ecologically and economically important. However, nitrogen (N) addition over many years has had a detrimental effect on these ecosystems. The objective of this research was to evaluate the effect of 4 years of N addition on microbial communities in an evergreen broad-leaved forest in southern Anhui, China.

Materials and methods

Allochthonous N in the form of aqueous NH₄NO₃ and phosphorus (P) in the form of Ca(H₂PO₄)₂·H₂O were applied at three doses with a control (CK, stream water only without fertilizer): low-N (50 kg N ha^?1 year^?1), high-N (100 kg N ha^?1 year^?1) and high-N+P (100 kg N ha^?1 year^?1 + 50 kg P ha^?1 year^?1). Quantitative PCR analysis of microbial community size and Illumina platform-based sequencing analysis of the V3-V4 16S rRNA gene region were performed to characterize soil bacterial community abundance, structure, and diversity.

Results and discussion

Bacterial diversity was increased in low-N and high-N treatments and decreased in the high-N+P treatment, but α-diversity indices were not significantly affected by N additions. Proteobacteria, Acidobacteria, and Actinobacteria were the predominant phyla in all treatments, and the relative abundance of different genera varied among treatments. Only soil pH (P = 0.051) showed a weak correlation with the bacterial community in CK and low-N treatment.

Conclusions

The composition of the bacterial community and the abundance of different phyla were significantly altered by N addition. The results of the present study indicate that soil bacterial communities in subtropical evergreen broad-leaved forest are, to a certain extent, resilient to changes derived from N additions.

     

Temporal in situ dynamics of N<Subscript>2</Subscript>O reductase activity as affected by nitrogen fertilization and implications for the N<Subscript>2</Subscript>O/(N<Subscript>2</Subscript>O + N<Subscript>2</Subscript>) product ratio and N<Subscript>2</Subscript>O mitigation

In vitro, high nitrate (NO₃ ^?) concentrations significantly inhibit N₂O reductase activity. However, little information is available on the in situ temporal effects of excessive N fertilization on soil N₂O reductase activity and the regulation of the N₂O/(N₂ + N₂O) product ratio in agricultural soil. This study examined the monthly in situ dynamics of NO₃ ^? concentration, N₂O reductase activity, and N₂O/(N₂ + N₂O) product ratio for 2 years in loamy soil that had received either continuous N fertilizer at 400 kg N ha^?1 year^?1 for 15 years (N400) or no N fertilizers (CK). N₂O reductase activity was significantly lower under the N400 treatment than under the CK and correlated negatively with soil NO₃ ^? concentration. The decrease in N₂O reductase activity resulted in the N₂O/(N₂ + N₂O) product ratio increasing. These results demonstrate that excessive N fertilization has the potential to increase N₂O emissions by reducing N₂O reductase activity in soils. These results highlight the need for N₂O mitigation options to embrace the reduction of soil NO₃ ^? concentrations.