Soil Water NO3 Research Articles

Nitrifying and denitrifying microbes exhibit distinct community structure and activity responses to different crop rotation systems in subtropical paddy soils

The adverse impacts of double-season rice cultivation on soil health and crop yield can be alleviated by crop rotation. However, the mechanisms by which biotic and abiotic factors influence microbial nitrogen cycling under different crop rotation systems remain unclear. Here, we evaluated the impact of crop rotation in paddy soils on the community abundance, composition, and activity of nitrifying microbes (ammonia-oxidizing archaea and bacteria (AOA and AOB)) and denitrifying microbes (nirK- and nirS-denitrifiers). A 6-year field experiment was performed with four crop rotation systems: (1) double rice as a control, (2) middle-season rice–fallow rotation (MR), (3) middle-season rice–oilseed rape rotation (MROR), and (4) middle-season rice–pak choi–oilseed rape rotation (MRPOR). AOB abundance increased significantly in MROR and MRPOR treatments, whereas AOA abundance decreased significantly in MROR. nirS gene abundance was significantly lower in MROR and MRPOR treatments, whereas nirK gene abundance was significantly lower in MR and MRPOR treatments. AOB and nirK gene community structures were significantly altered by crop rotation; this relationship was closely correlated with soil water content and NO3−-N concentration. For MROR and MRPOR treatments, potential nitrification activity was significantly increased and positively correlated with AOB abundance, whereas denitrification enzyme activity was significantly decreased and correlated with nirK and nirS community structure. Therefore, nitrifiers and denitrifiers exhibit distinct responses to crop rotation in paddy soils, which may influence microbial nitrogen cycling. These findings have practical implications for selecting appropriate cropping regimes.

Optimizing soil and fertilizer management strategy to facilitate sustainable development of wheat production in a semi-arid area: A 12-year in-situ study on the Loess Plateau

ContextThe low precipitation and low soil fertility in the Loess Plateau region of China limit the sustainable development of farmland. No-tillage, straw mulching, or planting green manure can improve soil water storage or soil quality. However, further research is needed to optimize these soil and fertilizer management strategies to maximize yield and effectively utilize resources. ObjectiveThe present study aimed to determine the optimal soil and fertilizer management strategies to maximize wheat growth and water/nitrogen utilization efficiency, while minimizing nitrogen fertilizer input. MethodsFive different soil and fertilizer treatments were tested on the Loess Plateau between 2009 and 2021, including traditional tillage followed by bare soil (CK), no-till with straw mulching (NTSM), no-till with straw mulching followed by leguminous green manure (OPT), and reductions in N fertilizer inputs of 10% (OPT10) and 20% (OPT20) under OPT. ResultsThe average results from 12 years of research revealed that the soil water content (SWC) and NO3–-N content in the 0–20 cm soil depth under OPT were higher by 4.3% and 13.4% compared to CK (P < 0.01), and the length and surface area of the wheat roots were higher by 20.9% and 11.0% (P < 0.01), respectively. Optimized soil and fertilizer management delayed leaf senescence and enhanced the antioxidant and photosynthetic capacities of the wheat crop. Compared with CK, the net photosynthetic rate and superoxide dismutase activity were 38.6% and 11.6% higher under OPT, respectively, and no significant differences were observed between OPT and OPT10. Optimized soil and fertilizer management promoted wheat yield formation, water and fertilizer use efficiency, and OPT obtained the highest yield (4497.3 kg ha−1), N uptake (138.7 kg ha−1), and water use efficiency (WUE, 13.3 kg ha−1). Compared with CK, OPT increased the wheat yield, N uptake, WUE, and WP by 21.5%, 16.7%, 16.6%, and 12.6%, respectively, and there were no significant differences between OPT10 and OPT. ConclusionsOptimizing the soil and fertilizer management strategies increased the soil water and NO3–-N contents, delayed leaf senescence, enhanced the leaf antioxidant and photosynthetic capacities, promoted wheat yield formation and efficient resource utilization. A 10% reduction in N fertilizer input based on no-till, straw mulching and green manure planting during the fallow period is an efficient soil and fertilizer management strategy for ensuring sustainable wheat production in semi-arid areas of the Loess Plateau. ImplicationsOur findings provide a reference for wheat production in semi-arid regions similar to the Loess Plateau throughout the world.

Plow layer management during the fallow season can enhance the wheat productivity and resource utilization in a semi-arid region

The soil quality is poor in the arid areas of Northwest China and planting green manure can improve the soil quality but it also increases the soil water consumption. Straw mulching in the wheat (Triticum aestivum L.) fallow season can improve the soil water content. It is unclear whether green manure can be planted in addition to straw mulching to improve the soil water content and quality. Therefore, a field experiment was conducted in the semi-arid area of the Loess Plateau in China from 2009 to 2017 with the following treatments; (1) traditional bare land in fallow season after plowing (CK), (2) no-tillage with straw mulching (NTSM), (3) and no-tillage with straw mulching and planting soybean as green manure (NTSGM). We determined the effects of these three treatments on the soil water, nutrients, and wheat productivity. Compared with CK, the average soil water contents in 0–100 cm soil depth increased by 11.1% and 3.6% under NTSM and NTSGM, respectively, during the soybean full bloom stage, and by 13.06% and 6.6% before wheat sowing. Compared with CK, the decomposition of green manure increased the NO3–-N contents in the 0–100 cm soil depth by 6.6% and 5.3% under NTSGM before wheat sowing and after harvesting, respectively, and NTSM and NTSGM significantly improved the soil nutrients, microbial biomass contents, and enzyme activities. The superior soil quality and water content under NTSM and NTSGM increased the fertilizer uptake and partial factor productivity. Compared with CK, the average precipitation storage efficiency, water use efficiency during the whole year, biomass, and wheat yield were 32.6%, 23.2%, 16.2%, and 21.6% higher under NTSGM, respectively. Therefore, NTSGM is an effective method for improving the soil water storage and NO3–-N contents before sowing wheat, as well as the water use efficiency, soil quality, utilization of nutrients, and wheat productivity in semi-arid areas of the Loess Plateau.

Distribution of ammonia oxidizers and their role in N2 O emissions in the reservoir riparian zone.

As a transitional boundary between terrestrial and aquatic ecosystems, the riparian zone is considered a hotspot for N2 O production because of the active nitrogen processes. Ammoxidation is an important microbial pathway for N2 O production, but the distribution of ammonia oxidizers under different land-use types in the reservoir riparian zone and what role they played in N2 O emissions are still not clear. We investigated spatiotemporal distributions of ammonia-oxidizing archaea (AOA) and bacteria (AOB) and their role in N2 O emissions in different land-use types along the riparian zone of Miyun Reservoir: grassland, sparse woods, and woodland. We found significant differences in both AOA abundance and AOB diversity indices among land-use types. AOA and AOB communities were significantly separated by different land-use types. The main drivers to determine the distribution of ammonia-oxidizing microbial community were soil water content, NH4 + , NO3 - , and total organic carbon (TOC). In situ N2 O flux was highest in woodland with a mean value of 12.28 μg/m2 ·h, and it was substantially decreased by 121% and 123% in sparse woods and grassland. TOC content was decreased by 20% and 40% in sparse woods and grassland compared with woodland, and it was significantly positively correlated with in situ N2 O flux. Meanwhile, AOB diversity indices were significantly correlated with in situ N2 O flux. These results showed that the heterogeneity of physicochemical properties among different land-use types affected the community of AOA and AOB in riparian zones. AOB not AOA, and community diversity rather than abundance, played a role in N2 O emissions.

Nitrogen dynamics under corn fields in the Red River Valley of North Dakota

AbstractExcessive applications of fertilizer N in corn (Zea mays L.) has profound environmental and economic consequences. Corn grain yield, N losses, N2O denitrification, NH3 volatilization, and soil water NO3 concentration at 60‐cm depth were collected for eight corn fields in the Red River Valley of North Dakota. Relationships of soil and management factors with cumulative N2O and NH3 losses were studied. Grain yield varied from 3.58 to 5.66 Mg ha–1. Cumulative NH3 and N2O losses were ranged between 1.0–2.4 kg ha–1 and 24.7–150 g N2O‐N ha–1, respectively. Soil organic matter (SOM; r = .94, p = .001), clay (r = .94, p = .001), and initial inorganic N (0–60 cm) content (r = .83, p = .01) had a positive relationship with cumulative N2O losses. Cumulative NH3 had a negative relationship with soil pH (r2 = .63, p = .01). Results indicate that soil properties such as, SOM, clay concentration, and initial profile N had a control over N losses.

Assessment of nitrification and urease inhibitors on nitrate leaching in corn (Zea mays L.)

Agricultural ecosystems are one of the largest global contributors to nitrate (NO3−) contamination of surface- and groundwater through fertilizer application. Improved fertilizer practices are needed to manage crop nutrient supply in corn (Zea mays L.) while minimizing impacts to clean water reserves. The goal of this study was to compare current nitrogen (N) fertilizer practices (urea at planting) with “packages” of improved management practices (a combination of right timing and product) that farmers potentially use. We conducted measurements in a continuous corn system from November 2015 to May 2017 at a large field scale (four 4 ha plots). Nitrate concentration was measured below the root zone and drainage estimated using a soil water budget approach in which evapotranspiration was measured using the eddy covariance method. The objective was to compare NO3−-N leaching from fields receiving urea vs. urea + combination of nitrification and urease inhibitors (NUI) fertilizer applications at planting, urea–ammonium nitrate (UAN) vs. UAN + NUI applied at sidedress, and a combination of these practices: urea + NUI at planting vs. UAN at sidedress. Drainage was only significant in the non-growing season. Neither fertilizer products applied with NUI at planting or sidedress proved to significantly reduce NO3−-N leaching. The combination of delaying fertilization to sidedress and applying UAN significantly reduced the soil water NO3−-N concentration compared with urea + NUI at planting (mean of 5.2 vs. 6.7 mg L−1) but only in 2015–2016. Based on these results, applying UAN at sidedress is recommended, although additional study years are needed to confirm those results.

A Sharp Decline in Nitrogen Input in a N‐Saturated Subtropical Forest Causes an Instantaneous Reduction in Nitrogen Leaching

AbstractIn China, as in other parts of the world, the emission and deposition of reactive nitrogen (N) have been reduced in recent years. Several decades of elevated N deposition in southwest China (40 to 60 kg ha−1 year−1) have resulted in extreme cases of N saturation, where N outputs are nearly equal to N inputs. Doubling N inputs using either NH4NO3or NaNO3fertilizer in a subtropical forest in Tieshanping, near Chongqing city in southwest China, caused an immediate doubling of N leaching (as NO3−). Reducing N inputs to ambient atmospheric deposition levels after 10 years of fertilization led to a rapid decrease in soil water NO3−concentration to levels similar to those in the reference plots that had not receive N fertilizer application. NO3−leaching via the soil water in the NH4NO3plots was even lower than that in the NaNO3plots or the reference plots, confirming the finding of a previous N‐fertilizing experiment that found that NH4+deposition, in contrast to NO3−deposition, increased N retention in the forest ecosystem. The N sink remained for at least 2 years after the cessation of N addition. Even with reduced N inputs, ambient atmospheric N deposition caused significant acidification, buffered partly by SO42−sorption. Therefore, further abatement of reactive N emissions is necessary in the future.

Long-term effects on soil-water nitrogen and pH of clearcutting and simulated disc trenching of previously nitrogen-fertilised pine plots

Forest fertilisation with nitrogen (N) typically increases N leaching for 1–2 years. Some studies have reported effects also after clearcutting. This study presents an analysis of soil-water chemistry data from the 3rd to the 15th year after clearcutting of fertilised experimental plots on a low-fertility site in Sweden. Before clearcutting in 1987, study plots had been fertilised with NH4NO3 in 1967, 1974, and 1981, resulting in total applications ranging from 0 to 1800 kg N·ha−1. In 1989, disc trenching was simulated by manual digging on small subplots within the fertilised main plots. Soil-water samples were collected at a depth of 50 cm. Previous N fertilisation and site preparation, respectively, affected (p &lt; 0.05) the total N and NO3–-N concentrations and pH of soil water, but no statistical interaction between fertilisation and site preparation was found. The NO3–-N concentration was elevated for total N applications above 720 kg·ha−1 (mean NO3–-N concentration of 0.93 mg·L−1 for 1080 kg N·ha−1, 1.6 mg·L−1 for 1440 kg N·ha−1, and 2.4 mg·L−1 for 1800 kg N·ha−1 compared with 0.20 mg·L−1 for the control) and lower after simulated disc trenching (0.63 mg·L−1) than in nontrenched soil (1.3 mg·L−1). The elevations in the soil-water NO3–-N concentration for the fertiliser treatments seemed to be related to changes in the soil N store created by previous fertilisation.

Impact of Shrub Willow (Salix spp.) as a Potential Bioenergy Feedstock on Water Quality and Greenhouse Gas Emissions

The development of shrub willow as a bioenergy feedstock contributes to renewable energy portfolios in many countries with temperate climates and marginal croplands. As willow is developed commercially in the US Northeast, there is a need to better understand its impact on water quality and greenhouse gas (GHG) emissions compared to alternative land uses (e.g., corn, hay). We measured the impact of cultivated willow of various ages (2 and 5 years) and management strategies (fertilized vs. unfertilized) compared to corn and hay on water table depth, soil water NO3 − and PO4 3− concentrations, and N2O, CH4, and CO2 fluxes at the soil-atmosphere interface during a drier than normal year in heavy clay soils with marginal agricultural value in upstate New York, USA. Soil water concentrations resulted in higher PO4 3− in willow and higher NO3 − in corn and hay, although willow is unlikely to negatively impact water quality with respect to phosphorus due to shorter periods of hydrologic connectivity in willow and hay than in corn. Gas fluxes varied spatially and temporally with hot moments of CH4 and N2O in corn and hay and seasonally variable CO2 in willow. While CH4 did not vary between fields, N2O was higher in corn and hay, and CO2 in willow, resulting in no net difference between CO2 equivalent (CH4, CO2, and N2O) emissions between fields. Converting marginal cropland on clay soils from corn or hay to willow left overall GHG emissions unaffected, slightly increased PO4 3−, and decreased NO3 − concentrations in soil water.

Drip irrigation lateral spacing and mulching affects the wetting pattern, shoot-root regulation, and yield of maize in a sand-layered soil

Soil with a 20–60cm thick subsoil (60–90cm below the surface) sand layer has been recently reclaimed to exploit its grain production potential in an arid region in northwest China. A 2-year field study was conducted in the Hetao irrigation district to investigate the effects of lateral spacing and soil mulching methods under drip irrigation on the soil moisture, NO3−, shoot-root regulation, and water use efficiency (WUE) of spring maize. The Christiansen uniformity coefficient (Cus) was adopted to evaluate soil moisture and NO3− distribution, which was calculated with soil water content and NO3− concentration. The four studied treatments consisted of two irrigation lateral-spacings (A1: 1.0m, A2: 0.5m) and two film-covering modes (M1: fully mulched, M2: partially mulched) were arranged.Soil moisture was most affected by mulch coverage (full or half surface coverage) under low frequency irrigation lateral spacing (adjacent to or between crop rows) under high frequency irrigation. Lateral spacing exerted a notable influence on soil moisture at a 20cm depth, while the mulching method influenced soil moisture mainly at 40cm. Irrigation frequency and close lateral spacing can effectively enhance Cus. Based on our observations, a decrease in the Cus of soil NO3− may occur under frequent fertigation, particularly when irrigation laterals are between crop rows. The mulching method can play an important role in improving the concentration and Cus of soil NO3−, while the A2 treatments can slow the decrease of the Cus of soil NO3− under frequent fertigation. Root length density (RLD) under A1 treatments were lower close to lateral while higher away from lateral than A2 treatments. Close lateral spacing can result in high hundred gain weight (HGW) and high harvest index (HI) while exerting a more conspicuous effect than the mulching method by extending the grain filling stage.Frequent fertigation (i.e. once every three days) after jointing is preferentially recommended in a sand-layered field. A1M2 should be chosen for higher HI and low cost. If frequent fertigation is infeasible, A2M1 can be a good choice under low frequency fertigation.

Riparian zones attenuate nitrogen loss following bark beetle‐induced lodgepole pine mortality

AbstractA North American bark beetle infestation has killed billions of trees, increasing soil nitrogen and raising concern for N loss impacts on downstream ecosystems and water resources. There is surprisingly little evidence of stream N response in large basins, which may result from surviving vegetation uptake, gaseous loss, or dilution by streamflow from unimpacted stands. Observations are lacking along hydrologic flow paths connecting soils with streams, challenging our ability to determine where and how attenuation occurs. Here we quantified biogeochemical concentrations and fluxes at a lodgepole pine‐dominated site where bark beetle infestation killed 50–60% of trees. We used nested observations along hydrologic flow paths connecting hillslope soils to streams of up to third order. We found soil water NO3 concentrations increased 100‐fold compared to prior research at this and nearby southeast Wyoming sites. Nitrogen was lost below the major rooting zone to hillslope groundwater, where dissolved organic nitrogen (DON) increased by 3–10 times (mean 1.65 mg L−1) and NO3‐N increased more than 100‐fold (3.68 mg L−1) compared to preinfestation concentrations. Most of this N was removed as hillslope groundwater drained through riparian soils, and NO3 remained low in streams. DON entering the stream decreased 50% within 5 km downstream, to concentrations typical of unimpacted subalpine streams (~0.3 mg L−1). Although beetle outbreak caused hillslope N losses similar to other disturbances, up to 5.5 kg ha−1y−1, riparian and in‐stream removal limited headwater catchment export to &lt;1 kg ha−1y−1. These observations suggest riparian removal was the dominant mechanism preventing hillslope N loss from impacting streams.

Soil properties, greenhouse gas emissions and crop yield under compost, biochar and co-composted biochar in two tropical agronomic systems

The addition of organic amendments to agricultural soils has the potential to increase crop yields, reduce dependence on inorganic fertilizers and improve soil condition and resilience. We evaluated the effect of biochar (B), compost (C) and co-composted biochar (COMBI) on the soil properties, crop yield and greenhouse gas emissions from a banana and a papaya plantation in tropical Australia in the first harvest cycle. Biochar, compost and COMBI organic amendments improved soil properties, including significant increases in soil water content, CEC, K, Ca, NO3, NH4 and soil carbon content. However, increases in soil nutrient content and improvements in physical properties did not translate to improved fruit yield. Counter to our expectations, banana crop yield (weight per bunch) was reduced by 18%, 12% and 24% by B, C and COMBI additions respectively, and no significant effect was observed on the papaya crop yield. Soil efflux of CO2 was elevated by addition of C and COMBI amendments, likely due to an increase in labile carbon for microbial processing. Our data indicate a reduction in N2O flux in treatments containing biochar. The application of B, C and COMBI amendments had a generally positive effect on soil properties, but this did not translate into a crop productivity increase in this study. The benefits to soil nutrient content, soil carbon storage and N2O emission reduction need to be carefully weighed against potentially deleterious effects on crop yield, at least in the short-term.

Fertilizer and Irrigation Management Effects on Nitrous Oxide Emissions and Nitrate Leaching

Irrigation and N fertilizer management are important factors affecting crop yield, N fertilizer recovery efficiency, and N losses as nitrous oxide (N2O) and nitrate (NO3−). Split application of conventional urea (split‐U) and/or one‐time application of products designed to perform as enhanced‐efficiency N fertilizers may mitigate N losses. The objective of this study was to compare the effects of controlled‐release polymer‐coated urea (PCU), stabilized urea with urease and nitrification inhibitors (IU) and split‐U on direct soil‐to‐atmosphere N2O emissions, NO3− leaching, and yield for fully irrigated and minimum‐irrigated corn in loamy sand. Indirect N2O emissions due to NO3− leaching were estimated using published emission factors (EF5). Split‐U increased yield and N uptake compared with preplant‐applied PCU or IU and decreased NO3− leaching compared with PCU. Direct N2O emissions were significantly less with IU or split‐U than with PCU, and there was a trend for greater emissions with split‐U than with IU (P = 0.08). Irrigation significantly increased NO3− leaching during the growing season but had no significant effect on direct N2O emissions. After accounting for significantly increased yields with irrigation, however, N losses expressed on a yield basis did not differ and in some cases decreased with irrigation. Post‐harvest soil N and soil‐water NO3− in spring showed the potential for greater N leaching in minimum‐irrigated than fully irrigated plots. Indirect emissions due to NO3− leaching were estimated to be 79 to 117% of direct emissions using the default value of EF5, thus signifying the potential importance of indirect emissions in evaluating management effects on N2O emissions.

Investigation into preferential flow in natural unsaturated soils with field multiple-tracer infiltration experiments and the active region model

Preferential flow in natural unsaturated soils is common, but difficult to characterize and predict. The major objective of this research is to investigate the preferential flow patterns with field-scale multiple-tracer infiltration experiments and to evaluate the capability of the active region model (ARM) in predicting the field-scale preferential flow and transport processes. For this purpose, the mixture solutions of iodine and bromide, iodine and nitrate, and again iodine and bromide, as the tracing solutes, were applied sequentially in two plots in natural unsaturated loam soil to illustrate the flow and transport processes. The distributions of soil water content and concentrations of applied tracing solutes (NO3- and Br−) were measured after experiments and predicted using ARM and the mobile–immobile region model (MIM). The relative root mean square errors (RRMSE) between those predictions (from ARM and MIM) and measured results were calculated for quantitatively evaluating the prediction accuracy and comparing the modeling efficiency of the two models. Both field observations and the ARM predictions indicated that there were macropores in Plot 1 but not in Plot 2, and the macropores in Plot 1 were mainly in the top 20cm soil layer. The mixture solutions transported in the top 20cm soil layer in Plot 1 were mainly from the soil surface directly and less affected by the macropore flow, while the preferential flow in the soil layer below 20cm was considerably affected by the macropores and more applied mixture solutions were delivered into the deep soil layer quickly. Compared to the mixture solutions applied in the first and third steps, more mixture solution applied in the second step was transported to the deep soil layer by macropores, corresponding to obvious peaks of soil water content and NO3- concentration distributions observed in the deep soil layer in Plot 1. On the other hand, unstable flow was the major preferential flow behavior in Plot 2, inducing no obvious peaks of soil water content and solutes (NO3- and Br−) concentrations observed in the infiltrated soil profile. The comparisons between predicted and observed results in Plot 2 indicated that the ARM captured the overall behavior of unstable flow and associated tracer transport better than the MIM; however, to well characterize the macropore flow process, the ARM needs to be improved to include the effects of macropores.

Woody Vegetation Removal Stimulates Riparian and Benthic Denitrification in Tallgrass Prairie

Expansion of woody vegetation into areas that were historically grass-dominated is a significant contemporary threat to grasslands, including native tallgrass prairie ecosystems of the Midwestern United States. In tallgrass prairie, much of this woody expansion is concentrated in riparian zones with potential impacts on biogeochemical processes there. Although the effects of woody riparian vegetation on denitrification in both riparian soils and streams have been well studied in naturally wooded ecosystems, less is known about the impacts of woody vegetation encroachment in ecosystems that were historically dominated by herbaceous vegetation. Here, we analyze the effect of afforestation and subsequent woody plant removal on riparian and benthic denitrification. Denitrification rates in riparian soil and selected benthic compartments were measured seasonally in naturally grass-dominated riparian zones, woody encroached riparian zones, and riparian zones with woody vegetation removed in two separate watersheds. Riparian soil denitrification was highly seasonal, with the greatest rates in early spring. Benthic denitrification also exhibited high temporal variability, but no seasonality. Soil denitrification rates were greatest in riparian zones where woody vegetation was removed. Additionally, concentrations of nitrate, carbon, and soil moisture (indicative of potential anoxia) were greatest in wood removal soils. Differences in the presence and abundance of benthic compartments reflected riparian vegetation, and may have indirectly affected denitrification in streams. Riparian soil denitrification increased with soil water content and NO3 - . Management of tallgrass prairies that includes removal of woody vegetation encroaching on riparian areas may alter biogeochemical cycling by increasing nitrogen removed via denitrification while the restored riparian zones return to a natural grass-dominated state.

Nitrate leaching under maize cropping systems in Po Valley (Italy)

Intensive crop production in Po Valley (Northern Italy) is associated to high risk of nitrate leaching. A multi-year monitoring of soil solution nitrogen was conducted at 6 sites under the ordinary farm management of maize crop ( Zea mays L.) in order to assess NO 3–N leaching. The amount of N fertilizer (organic + mineral) varied from 209 to 801 kg N ha −1 year −1. Maize biomass ranged from 15 to 32 t ha −1 and N removal from 150 to 400 kg ha −1. Soil water solution was sampled at five depths along the soil profile (from 0.3 to 1.5 m) at time intervals of 7–30 days using suction cups. Soil water content (SWC) was measured daily by TDR at the same depths of suction cups. Soil water NO 3–N concentrations varied from 0 to 110 mg L −1, with the highest concentrations measured after fertilizer application. Once validated on measured SWC data, SWAP model was applied to estimate the drainage flux. Annual leaching was calculated by multiplying drainage flux by soil water NO 3–N concentration. N Leaching ranged from 14 to 321 kg ha −1 year −1, according to fertilization, crop N removal, rainfall, irrigation management, and it was mainly affected by N surplus.

The effects of phytophagous insects on water and soil nutrient concentrations and fluxes through forest stands of the Level II monitoring network in the UK

The effects of insect defoliators on throughfall and soil nutrient fluxes were studied in coniferous and deciduous stands at five UK intensive monitoring plots (1998 to 2008). Links were found between the dissolved organic carbon (DOC), nitrogen (N) and potassium (K) fluxes through the forest system to biological activity within the canopy. Underlying soil type determined the leaching or accumulation of these elements. Under oak, monitored at two sites, frass from caterpillars of Tortrix viridana and Operophtera brumata added direct deposition of ~ 16 kg ha −1extra N during defoliation. Peaks of nitrate (NO 3–N) flux between 5 and 9 kg ha −1 (×5 usual winter values) were recorded in consecutive years in shallow soil waters. Synchronous rises in deep soil NO 3–N fluxes at the Grizedale sandy site indicate downward flushing, not seen at the clay site. Under three Sitka spruce stands, generation of honeydew (DOC) was attributed to two aphid species ( Elatobium abietinum and Cinara pilicornis) with distinctive feeding strategies. Throughfall DOC showed mean annual fluxes (6 seasons) ~ 45–60 kg ha −1 compared with rainfall values of 14–22 kg ha −1. Increases of total N in throughfall and NO 3–N fluxes in shallow soil solution were detected — soil water fluxes reached 8 kg ha −1 in Llyn Brianne, ~ 25 kg ha −1 in Tummel, and ~ 40 kg NO 3–N ha −1 in Coalburn. At Tummel, on sandy soil, NO 3–N leaching showed increased concentration at depth, attributed to microbiological activity within the soil. By contrast, at Coalburn and Llyn Brianne, sites on peaty gleys, soil water NO 3–N was retained mostly within the humus layer. Soil type is thus key to predicting N movement and retention patterns. These long term analyses show important direct and indirect effects of phytophagous insects in forest ecosystems, on above and below ground processes affecting tree growth, soil condition, vegetation and water quality.

Monitoring and modelling draining and resident soil water nitrate concentrations to estimate leaching losses

Abstract Quantifying nitrogen (N) losses below the root zone is highly challenging due to uncertainties associated with estimating drainage fluxes and solute concentrations in the leachate. Active and passive soil water samplers provide solute concentrations but give limited information on water fluxes. Mechanistic models are used to estimate leaching, but require calibration with measured data to ensure their reliability. Data from a drainage lysimeter trial under irrigation in which soil profile nitrate (NO3−) concentrations were monitored using wetting front detectors (passive sampler) and ceramic suction cups (active sampler) were compared to NO3− concentrations in draining and resident soil water as simulated by the research version of the Soil Water Balance model (SWB-Sci). SWB-Sci is a daily time-step, cascading soil water and solute balance model that provides draining NO3− concentrations by accounting for incomplete solute mixing. As hypothesized, suction cup concentrations aligned closely with resident soil water concentrations, while wetting front detector concentrations aligned closely with draining soil water NO3− concentrations. These results demonstrate the power of combining monitoring and modelling to estimate NO3− leaching losses. Access to measured draining and resident NO3− concentrations, especially when complemented with modelled fluxes, can contribute greatly to achieving improved production and environmental objectives.

Soil and Groundwater Nitrogen Response to Invasion by an Exotic Nitrogen‐Fixing Shrub

Autumn-olive (Elaeagnus umbellata Thunb.) is an invasive, exotic shrub that has become naturalized in the eastern United States and can fix nitrogen (N) via a symbiotic relationship with the actinomycete Frankia. Fixed N could potentially influence nutrient cycling rates and N leaching into soil water and groundwater. In situ net N mineralization, net nitrification, and net ammonification rates, as well as soil water and groundwater nitrate N (NO(3)-N) and ammonium N (NH(4)-N) concentrations, were measured under autumn-olive-dominated and herbaceous open field areas in southern Illinois. Soil net N mineralization and net nitrification rates were higher under autumn-olive compared with open field (p < 0.05) and could be driven, in part, by the relatively low C/N ratio (11.41 +/- 0.29) of autumn-olive foliage and subsequent litter. Autumn-olive stands also had greater soil water NO(3)-N (p = 0.003), but soil water NH(4)-N concentrations were similar between autumn-olive and open field. Groundwater NO(3)-N and NH(4)-N concentrations were similar beneath both types of vegetation. Groundwater NO(3)-N concentrations did not reflect patterns in soil N mineralization and soil water NO(3)-N most likely due to a weak hydrologic connection between soil water and groundwater. The increased N levels in soil and soil water indicate that abandoned agroecosystems invaded by autumn-olive may be net sources of N to adjacent terrestrial and aquatic systems rather than net sinks.

Surfactant Use to Improve Soil Water Distribution and Reduce Nitrate Leaching in Potatoes

Recent evaluations of soil water use by potato (Solanum tuberosum L.) plants have confirmed that a dry zone develops mid to late in the growing season when potatoes were grown in a ridge and furrow system under sprinkler irrigation on some sandy soils. Although trickle irrigation has been shown to reduce the dry zone in potato hills, a more cost- and labor-effective solution could be the use of a surfactant to change soil water surface tension and thereby promote more uniform water distribution into hills. Water content in surfactant-treated potato hills was compared with no-surfactant―treated hills using data from time domain reflectometry probes collected at 15-minute intervals. In addition, nitrate-nitrogen (NO 3 ― N) concentration in soil water collected 1 m below the crop row with porous cup samplers was evaluated to assess NO 3 ― N leaching below the root zone of potatoes. Data from surfactant applications at 9.35 L ha ―1 at planting with the seed piece in 1998, 1999, and 2003 through 2005 generally resulted in significantly increased movement of water into the dry portion of potato hills and in many cases decreased soil water NO 3 ― concentrations at a depth of 1 m beneath potato hills. Comparison of several surfactants suggested that water movement into the dry zone can be accomplished with a number of different products. Some trends of increased potato yield with surfactant applications as compared with no surfactant were noted in a few cases; but in all cases (P = 0.16―0.24), these were not statistically significant at the 95% level.