NO3 Leaching Research Articles

Microbial N Transformations and N2O Emission after Simulated Grassland Cultivation: Effects of the Nitrification Inhibitor 3,4-Dimethylpyrazole Phosphate (DMPP).

Residue incorporation following grassland cultivation can lead to mobilization of large pools of N and potentially to significant N losses via leaching and N2O emissions. This study proposed a mitigation strategy of applying 3,4-dimethylpyrazole phosphate (DMPP) prior to grassland cultivation and investigated its efficacy in a laboratory incubation study. DMPP inhibited the growth and activity of ammonia-oxidizing bacteria but had no adverse effects on ammonia-oxidizing archaea and denitrifiers. DMPP can effectively reduce the potential for leaching of NO3- derived from residue decomposition, while the effect on reducing N2O emissions will be significant only when soil NO3- availability is limiting. Our findings provide insight into how DMPP affects soil nitrifier and denitrifier populations and have direct implications for improving N use efficiency and reducing environmental impacts during grassland cultivation.

Rye Cover Crop Effects on Direct and Indirect Nitrous Oxide Emissions

Core Ideas A rye cover crop in a Midwest corn–soybean rotation did not reduce direct N2O emissions. NO3 leaching and indirect N2O emissions were reduced with a winter rye cover crop. Large year‐to‐year variations in precipitation were a major determinant of N2O losses. Winter cover crops can have a pronounced effect on N cycling in agricultural ecosystems. By reducing available soil mineral N during active growth and by providing a substrate for denitrifying bacteria after they are killed, cover crops can potentially influence soil N2O emissions. However, there have been conflicting reports regarding cover crop effects on increasing or decreasing N2O emissions. In this study, direct soil emissions of N2O were measured for a 10‐yr period in a corn (Zea mays L.)–soybean [Glycine max (L.) Merr.] rotation, with and without a winter rye (Secale cereale L.) cover crop. Additionally, NO3 leaching losses during the period were measured and used to estimate indirect N2O emissions by applying the Intergovernmental Panel on Climate Change (IPCC) EF5 emission factor of 0.0075 kg N2O‐N kg−1 NO3–N leached. Direct N2O emissions measurements were measured using vented static chambers from March 2004 through December 2012. Annual N2O emissions in corn years were significantly greater than emissions in soybean years (P = 0.013). Under corn annual direct N2O emissions ranged from 2.3 to 12.5 kg N2O‐N ha−1 yr−1, and under soybean annual emissions ranged from 1.02 to 6.94 kg N2O‐N ha−1 yr−1. Cumulative direct N2O emissions were calculated each year by numerical integration and summed to compute 10‐yr cumulative emissions for the rotation. Total direct emissions during the 10‐yr period in the rye and no‐rye treatments were not significantly different. The rye cover crop did effect estimated indirect emissions (P = 0.046), which were 1.25 kg N2O‐N ha−1 yr−1 in the rye treatment and 2.69 kg N2O‐N ha−1 yr−1 in the no‐rye treatment. There was no significant difference (P = 0.155) between 10‐yr cumulative total N2O emissions (direct + indirect) of the rye cover crop treatment (55.7 kg N2O‐N ha−1) and the no cover crop treatment (63.8 kg N2O‐N ha−1).

English

The aim of this study was to determine the effects of increasing irrigation levels on the movement of nitrate and potassium in clay soil and on crop yields for the common bean irrigated by central pivot under Brazilian Cerrado conditions. The experiment was conducted in Urutai, Goias, Brazil, in Dystrophic Oxisol clayey soil in 2014. Four irrigation regimes were tested, which were equivalent to 50, 100, 150 and 200% of crop evapotranspiration (ETc), estimated using the Class A tank method. The plots were arranged in a randomized complete block design with four replications; the soil solution was evaluated seven times during the cycle. Potassium chloride with 58% K2O was used as the potassium source, and calcium nitrate with 15.5% total nitrogen (N) as the nitrogen source. To collect the soil solutions, extractors were installed at depths of 0.20, 0.40, 0.60, 0.80 and 1.00 m. The concentrations of nitrate (NO3-) and potassium (K+) were determined without filtering or digestion. At harvesting, the production components and yield were evaluated. The NO3- and K+ levels within the soil profile varied between treatments, showing nutrient leaching below the root system for the higher irrigation treatments. Therefore, the application of appropriate irrigation techniques should reduce the leaching of NO3- and K+ and lead to higher yields for the common bean. Key words: Bean, aspersion, water management, loss of NO3- and K+.

Long‐Term Effects of Controlled‐Release Urea on Crop Yields and Soil Fertility under Wheat–Corn Double Cropping Systems

The long‐term effects of controlled‐release urea (CRU) on crop yields and soil properties were investigated in lysimeters under wheat and corn rotation system from 2009 to 2014 in northern China. The CRU included polymer‐coated urea (PCU), sulfur‐coated urea (SCU), and polymer coating of sulfur‐coated urea (PSCU) was applied at 147, 210 kg N ha−1 for wheat and 262.5, 375 kg N ha−1 for corn and the urea was applied at 210 kg N ha−1 for wheat and 375 kg N ha−1 for corn. Results showed that the N release characteristics of three kinds of CRU in field condition were all closely matched to the N requirement of crops. Consequently, the CRU treatments improved wheat and corn yields by 3.2 to 10.1% and 4.9 to 11.1%, increased apparent N use efficiency by 45.9 to 53.8% in wheat, and 36.2 to 45.4% in corn, respectively, compared with urea. Furthermore, the PSCU achieved the highest and the most stable crop yields among CRU. Even reducing CRU rate by 30% produced the same yields as with the 100% rate of urea. In addition, soil total N and organic matter contents in CRU were effectively increased in the topsoil of 0 to 20 cm after 5 yr. Therefore, long‐term application of CRU had great potential to increase wheat–corn yields, N use efficiency, reduce application frequency, improve soil fertility, decrease the leaching of soil NO3−–N and NH4+–N, and also relieve soil pH decreased.Core Ideas The long‐term effect of controlled‐release urea on crop yield and soil chemical properties was studied. The N release rates of controlled‐release urea were closely matched to the demand for N during the whole growth periods of crops. The wheat and corn yields were increased by 3.2 to 10.1% and 4.9 to 11.1% by controlled‐release urea fertilization, compared with urea treatment.

Biochar impact on nitrate leaching in upland red soil, China

Positive effects of biochar on nitrate (NO3−–N) leaching have recently been demonstrated in many studies, which mainly focused on biochar mixed into soil samples in the laboratory. However, to our knowledge, studies on nitrate leaching from soil samples were directly taken from the field where biochar was added many years ago are relatively scarce. Therefore, a laboratory soil column method was used to study the influence of biochar on the process of vertical transport of nitrate. Breakthrough curves (BTCs) were obtained separately from each biochar treatment. The results were as follows: Biochar has a significant influence on the BTCs of NO3−–N. The initial time and total time increased incrementally with biochar application rate, whereas the cumulative amount of leached NO3−–N, peak concentration and water flux of the BTCs decreased at the same time. The C6 treatment (40 t/ha) significantly decreased the amount of leached NO3−–N. The measured values and simulated values obtained by CXTFIT 2.0 were highly significantly related, as shown by high correlation coefficients (r > 0.85**). A highly significant positive correlation (p < 0.01) was found between the initial time, total time and the application rate of biochar, while cumulative mass of leached NO3−–N, peak concentration and water flux showed a significant negative correlation (p < 0.01) with increasing biochar application rate. The results showed that the biochar added to soil could be an effective means of reducing nutrient leaching in soil column experiment in laboratory. CXTFIT 2.0 model was suitable in fitting the observed nitrate transport in upland red soils.

Long-term predictions of ecosystem acidification and recovery

This paper considers the long-term (500year) consequences of continued acid deposition, using a small forested catchment in S. England as an example. The MAGIC acidification model was calibrated to the catchment using data for the year 2000, and run backwards in time for 200years, and forwards for 500. Validation data for model predictions were provided by various stream and soil measurements made between 1977 and 2013. The model hindcast suggests that pre-industrial stream conditions were very different from those measured in 2000. Acid Neutralising Capacity (ANC) was +150μeqL−1 and pH7.1: there was little nitrate (NO3). By the year 2000, acid deposition had reduced the pH to 4.2 and ANC to c. −100μeqL−1, and NO3 was increasing in the stream. The future state of the catchment was modelled using actual deposition reductions up to 2013, and then based on current emission reduction commitments. This leads to substantial recovery, to pH6.1, ANC +43μeqL−1, though it takes c. 250years. Then, however, steady acidification resumes, due to continued N accumulation in the catchment and leaching of NO3. Soil data collected using identical methods in 1978 and 2013 show that MAGIC correctly predicts the direction of change, but the observed data show more extreme changes – reasons for this are discussed. Three cycles of forest growth were modelled – this reduces NO3 output substantially during the active growth phase, and increases stream pH and ANC, but acidifies the soil which continues to accumulate nitrogen. The assumptions behind these results are discussed, and it is concluded that unmanaged ecosystems will not return to a pre-industrial state in the foreseeable future.

Key unknowns in nitrogen budget for oil palm plantations. A review

Nitrogen (N) losses in agroecosystems are a major environmental and economic issue. This issue is particularly pronounced in oil palm cultivation because oil palm production area is expected to increase to 12 Mha by 2050. N fertilization in oil palm plantations is mainly provided by mineral fertilizers, palm oil mill by-products, and biological fixation using legume cover crops. N loss has a major environmental impact during cultivation. For instance, 48.7 % of the greenhouse gases emitted to produce 1 t of palm oil fruit are due to N fertilization. Actually, there is little comprehensive knowledge on how to calculate N budgets in oil palm plantation in order to optimize fertilization, taking into account N leaching and N gases emissions. Here we modeled knowledge about all N fluxes in an oil palm field following standard management practices of industrial plantations, on a mineral soil, from planting to felling after a 25-year-growth cycle. The largest fluxes are internal fluxes, such as oil palm uptake, with 40–380 kg N ha−1 year−1, and the decomposition of felled palms at the end of the cycle, with 465–642 kg N ha−1. The largest losses are emissions of NH3 and leaching of NO3−, corresponding to 0.1–42 % and 1–34 % of mineral N applied, respectively. The most uncertain and least documented fluxes are N losses such as N2O, NOx, N2 emissions, leaching, NH3 volatilization, and runoff. The most critical conditions for N losses occur during the immature phase when young palms uptake is low and during the mature phase in areas with sparse soil cover or receiving high amounts of fertilizers. Data is lacking about the effects of management practices on NO3− leaching and N2O/NOx emissions in those critical conditions.

A modeling study on mitigation of N2O emissions and NO3 leaching at different agricultural sites across Europe using LandscapeDNDC

The identification of site-specific agricultural management practices in order to maximize yield while minimizing environmental nitrogen losses remains in the center of environmental pollution research. Here, we used the biogeochemical model LandscapeDNDC to explore different agricultural practices with regard to their potential to reduce soil N2O emissions and NO3 leaching while maintaining yields. In a first step, the model was tested against observations of N2O emissions, NO3 leaching, soil micrometeorology as well as crop growth for eight European cropland and grassland sites. Across sites, LandscapeDNDC predicts very well mean N2O emissions (r2=0.99) and simulates the magnitude and general temporal dynamics of soil inorganic nitrogen pools. For the assessment of site-specific mitigation potentials of environmental nitrogen losses a Monte Carlo optimization technique considering different agricultural management options (i.e., timing of planting, harvest and fertilization, amount of applied fertilizer as well as residue management) was used. The identified optimized field management practices reduce N2O emissions and NO3 leaching from croplands on average by 21% and 31%, respectively. Likewise, average reductions of 55% for N2O emissions and 16% for NO3 leaching are estimated for grasslands. For mitigating environmental loss - while maintaining yield levels - it was most important to reduce fertilizer application rates by in average 10%. Our analyses indicate that yield scaled N2O emissions and NO3 leaching indicate possible improvements of nitrogen use efficiencies in European farming systems. Moreover, the applied optimization approach can be used also in a prognostic way to predict optimal timings and fertilization options (rates and splitting) upon accurate weather forecasts combined with the knowledge of modeled soil nutrient availability and plant nitrogen demand.

Leachate Composition of Temperate Agricultural Soils in Response to Biochar Application

Biochar (BC) as a soil amendment has found considerable interest in global agriculture and food production. However, BC application to agricultural soils requires knowledge about side-effects on leachate composition potentially affecting deeper soil layers and groundwater. We investigated the effects of BC application on leachate water characteristics in a greenhouse pot experiment with two crops cultivated in series, mustard (Sinapis alba L., cv. Serval) and barley (Hordeum vulgare L., cv. Xanadu). The experiment was set up with three agricultural soils (Planosol, Cambisol, Chernozem), four different BC types, derived from three different feedstocks (wheat straw, woodchips, and vineyard pruning), added at two application rates of 1 % (w/w) and 3 % (w/w). Leachate sampling was performed five times from November 2010 to May 2011 by excess watering. The leachates were analyzed for their pH, electrical conductivity (EC), as well as their nitrate (NO3 −), dissolved phosphorus (PDISS), potassium (K+), and dissolved organic carbon (DOC) concentrations. The application of all BCs caused a significant pH increase in the leachates; EC increased most noticeably in the straw biochar treatment. All BC types significantly decreased leachate NO3 − loads (by up to 80 % for woodchip-derived BC) compared to the control, while PDiss and K+ loads most significantly increased in the straw-derived BC treatment. The results show that BC may be suitable as soil amendment in soils prone to NO3 − leaching; moreover, whereas straw-derived BC in particular may support soil nutrient status by introducing P and K.

Polymer Coated Urea in Turfgrass Maintains Vigor and Mitigates Nitrogen's Environmental Impacts

Polymer coated urea (PCU) is a N fertilizer which, when added to moist soil, uses temperature-controlled diffusion to regulate N release in matching plant demand and mitigate environmental losses. Uncoated urea and PCU were compared for their effects on gaseous (N2O and NH3) and aqueous (NO3-) N environmental losses in cool season turfgrass over the entire PCU N-release period. Field studies were conducted on established turfgrass sites with mixtures of Kentucky bluegrass (Poa pratensis L.) and perennial ryegrass (Lolium perenne L.) in sand and loam soils. Each study compared 0 kg N ha-1 (control) to 200 kg N ha-1 applied as either urea or PCU (Duration 45CR®). Application of urea resulted in 127–476% more evolution of measured N2O into the atmosphere, whereas PCU was similar to background emission levels from the control. Compared to urea, PCU reduced NH3 emissions by 41–49% and N2O emissions by 45–73%, while improving growth and verdure compared to the control. Differences in leachate NO3- among urea, PCU and control were inconclusive. This improvement in N management to ameliorate atmospheric losses of N using PCU will contribute to conserving natural resources and mitigating environmental impacts of N fertilization in turfgrass.

Biochar impact on nitrate leaching as influenced by native soil organic carbon in an Inceptisol of central India

Biochar is anticipated to be an effective mitigation option to nitrate leaching. However, the extent to which its effectiveness is influenced by native soil organic carbon (SOC) is not known. Thus, the present study was conducted to investigate the interactive effect of native SOC and biochar amendment on leaching of nitrate and total dissolved salts (TDS) using a laboratory column experiment. The study was conducted in a loamy (Mixed Hyperthermic Udic Ustocrept) soil of central India, with three native SOC levels, four levels of biochar amendment, and three replications, in a factorial design. The three native total SOC levels were 1.18% (C1), 0.97% (C2) and 0.79% total SOC (C3) and four biochar amendment levels were 0 (B0, control), 5 (B5), 10 (B10) and 20 (B20) g biochar kg−1 of air dry soil. Repacked soil columns (40cm height and 11cm internal diameter) were leached with deionized water once a week for 15 consecutive weeks. Nitrate in form of KNO3 was added at the rate equivalent to 100mgkg−1 soil (220kgha−1) at each application in the 1st, 9th and 12th week. Leaching of NO3−-N and TDS significantly reduced with increase in native SOC content (p<0.01) and increase in amount of biochar (p<0.01) amendment. However, interaction effect was significant only for the TDS flux. At higher SOC content, leaching of NO3 - N and TDS of the leachate were significantly lower. As compared to C1 soil, total NO3−-N leached in C3 soil was higher by 40, 45, 37 and 11% under B0, B5, B10 and B20 biochar amendment levels indicating biochar application at the rate of 20gkg−1 soil (B20) could mitigate nitrate leaching by 29% in the low carbon (C3) soil. Differential behaviour of biochar at different SOC level was observed with regard to NO3−-N and TDS leaching. The effectiveness of higher dose of biochar (B20) in mitigating NO3− leaching was higher in soils with low SOC level. The best biochar treatment (B20) could reduce NO3−-N leaching by 14% under C1, as compared to 23 and 32% under C2 and C3 soils. Increased sorption and water retention under high biochar treatments might be responsible for reduced NO3 leaching.

Drivers of nitrogen dynamics in ecologically based agriculture revealed by long-term, high-frequency field measurements.

Nitrogen (N) loss from agriculture impacts ecosystems worldwide. One strategy to mitigate these losses, ecologically based nutrient management (ENM), seeks to recouple carbon (C) and N cycles to reduce environmental losses and supply N to cash crops. However, our capacity to apply ENM is limited by a lack of field-based high-resolution data on N dynamics in actual production contexts. We used data from a five-year study of organic cropping systems to investigate soil inorganic N (SIN) variability and nitrate (NO3-) leaching in ENM. Four production systems initiated in 2007 and 2008 in central Pennsylvania varied in crop rotation, timing and intensity of tillage, inclusion of fallow periods, and N inputs. Extractable SIN was measured fortnightly from March through November throughout the experiment, and NO3- N concentration below the rooting zone was sampled with lysimeters during the first year of the 2008 start. We used recursive partitioning models to assess the importance of management and environmental factors to SIN variability and NO3- leaching and identify interactions between influential variables. Air temperature and tillage were the most important drivers of SIN across systems. The highest SIN concentrations occurred when the average air temperature three weeks prior to measurement was above 21 degrees C. Above this temperature and within 109 days of moldboard plowing, average SIN concentrations were 22.1 mg N/kg soil; 109 days or more past plowing average SIN dropped to 7.7 mg N/kg soil. Other drivers of SIN dynamics were N available from manure and cover crops. Highest average leachate NO3- N concentrations (15.2 ppm) occurred in fall and winter when SIN was above 4.9 mg/kg six weeks prior to leachate collection. Late season tillage operations leading to elevated SIN and leachate NO3- N concentrations were a strategy to reduce weeds while meeting consumer demand for organic products. Thus, while tillage that incorporates organic N inputs preceding cash crops can promote synchrony of N mineralization and crop demand, late or post-season tillage promotes NO3 leaching by stimulating SIN pulses that are asynchronous with plant uptake.

Nitrogen saturation, soil acidification, and ecological effects in a subtropical pine forest on acid soil in southwest China

AbstractElevated anthropogenic nitrogen (N) deposition has caused nitrate (NO3−) leaching, an indication of N saturation, in several temperate and boreal forests across the Northern Hemisphere. So far, the occurrence of N saturation in subtropical forests and its effects on the chemistry of the typically highly weathered soils, forest growth, and biodiversity have received little attention. Here we investigated N saturation and the effects of chronically high N inputs on soil and vegetation in a typical, subtropical Masson pine (Pinus massoniana) forest at Tieshanping, southwest China. Seven years of N flux data obtained in ambient conditions and in response to field manipulation, including a doubling of N input either as ammonium nitrate (NH4NO3) or as sodium nitrate (NaNO3) solution, resulted in a unique set of N balance data. Our data showed extreme N saturation with near‐quantitative leaching of NO3−, by far the dominant form of dissolved inorganic N in soil water. Even after 7 years, NH4+, added as NH4NO3, was nearly fully converted to NO3−, thus giving rise to a major acid input into the soil. Despite the large acid input, the decrease in soil pH was insignificant, due to pH buffering caused by Al3+ mobilization and enhanced SO42− adsorption. In response to the NH4NO3‐induced increase in soil acidification and N availability, ground vegetation showed significant reduction of abundance and diversity, while Masson pine growth further declined. By contrast, addition of NaNO3 did not cause soil acidification. The comparison of NH4NO3 treatment and NaNO3 treatment indicated that pine growth decline was mainly attributed to acidification‐induced nutrient imbalance, while the loss in abundance of major ground species was the combining effect of N saturation and acidification. Therefore, N emission control is of primary importance to curb further acidification and eutrophication of forest soils in much of subtropical south China.

Gross nitrogen transformations in black soil under different land uses and management systems

In this study, the 15N isotope pool dilution technique was used to investigate the gross N transformation rates in black cropland soils that had been subjected to different fertilization treatments [no fertilizer application (NF), N and P applications (NP), and N and P applications with composted pig manure (NPM)] compared to a neighboring grassland soil in northeast China. The results showed that gross N mineralization and immobilization rates were significantly higher in grassland soils than in cropland soils, whereas the reverse was true for gross nitrification rates, which led to a higher gross nitrification rate/ammonium immobilization rate in cropland soils compared to grassland soils. Long-term applications of chemical fertilizer increased the gross rates of mineralization, immobilization, and nitrification compared to the no fertilizer treatment, and this effect was more prominent when combined with application of organic manure. However, the ratio of gross nitrification rate to ammonium immobilization rate in the NPM treatment decreased compared to the NP and NF treatments, which suggested that converting grassland to cropland reduced the potential release and conservation of N and promoted N loss via NO3− leaching, whereas appropriate management practices, such as the combined application of chemical fertilizer and pig manure, could increase N retention and decrease the production and leaching of NO3−.

High-resolution quantification of root dynamics in split-nutrient rhizoslides reveals rapid and strong proliferation of maize roots in response to local high nitrogen.

The plant's root system is highly plastic, and can respond to environmental stimuli such as high nitrogen (N) in patches. A root may respond to an N patch by selective placement of new lateral roots, and therewith increases root N uptake. This may be a desirable trait in breeding programmes, since it decreases NO3(-) leaching and N2O emission. Roots of maize (Zea mays L.) were grown without N in split-nutrient rhizoslides. One side of the slides was exposed to high N after 15 d of root development, and root elongation was measured for another 15 d, described in a time course model and parameterized. The elongation rates of crown axile roots on the N-treated side of the plant followed a logistic increase to a maximum of 5.3cm d(-1); 95% of the maximum were reached within 4 d. At the same time, on the untreated side, axile root elongation dropped linearly to 1.2cm d(-1) within 6.4 d and stayed constant thereafter. Twice as many lateral roots were formed on the crown axis on the N side compared to the untreated side. Most strikingly, the elongation rates of laterals of the N side increased linearly with most of the roots reaching an asymptote ~8 d after start of the N treatment. By contrast, laterals on the side without N did not show any detectable elongation beyond the first day after their emergence. We conclude that split-nutrient rhizoslides have great potential to improve our knowledge about nitrogen responsiveness and selection for contrasting genotypes.

Modelling inorganic nitrogen in runoff: Seasonal dynamics at four European catchments as simulated by the MAGIC model

Nitrogen (N) deposition is globally considered as a major threat to ecosystem functioning with important consequences for biodiversity, carbon sequestration and N retention. Lowered N retention as manifested by elevated concentrations of inorganic N in surface waters indicates ecosystem N saturation. Nitrate (NO3) concentrations in runoff from semi-natural catchments typically show an annual cycle, with low concentrations during the summer and high concentrations during the winter. Process-oriented catchment-scale biogeochemical models provide tools for simulation and testing changes in surface water and soil chemistry in response to changes in sulphur (S) and N deposition and climate. Here we examine the ability of MAGIC to simulate the observed monthly as well as the long-term trends over 10–35years of inorganic N concentrations in streamwaters from four monitored headwater catchments in Europe: Čertovo Lake in the Czech Republic, Afon Gwy at Plynlimon, UK, Storgama, Norway and G2 NITREX at Gårdsjön, Sweden. The balance between N inputs (mineralization+deposition) and microbial immobilization and plant uptake defined the seasonal pattern of NO3 leaching. N mineralization and N uptake were assumed to be governed by temperature, described by Q10 functions. Seasonality in NO3 concentration and fluxes were satisfactorily reproduced at three sites (R2 of predicted vs. modelled concentrations varied between 0.32 and 0.47 and for fluxes between 0.36 and 0.88). The model was less successful in reproducing the observed NO3 concentrations and fluxes at the experimental N addition site G2 NITREX (R2=0.01 and R2=0.19, respectively). In contrast to the three monitored sites, Gårdsjön is in a state of change from a N-limited to N-rich ecosystem due to 20years of experimental N addition. At Gårdsjön the measured NO3 seasonal pattern did not follow typical annual cycle for reasons which are not well understood, and thus not simulated by the model. CapsuleThe MAGIC model is able to simulate NO3 leaching on a monthly as well as an annual basis, and thus to reproduce the seasonal and short-term variations in N dynamics.

Multifunctional landscapes: Site characterization and field-scale design to incorporate biomass production into an agricultural system

Current and future demand for food, feed, fiber, and energy require novel approaches to land management, which demands that multifunctional landscapes are created to integrate various ecosystem functions into a sustainable land use. We developed an approach to design such landscapes at a field scale to minimize concerns of land use change, water quality, and greenhouse gas emissions associated with production of food and bioenergy. This study leverages concepts of nutrient recovery and phytoremediation to place bioenergy crops on the landscape to recover nutrients released to watersheds by commodity crops. Crop placement is determined by evaluating spatial variability of: 1) soils, 2) surface flow pathways, 3) shallow groundwater flow gradients, 4) subsurface nitrate concentrations, and 5) primary crop yield. A 0.8 ha bioenergy buffer was designed within a 6.5 ha field to intercept concentrated surface flow, capture and use nitrate leachate, and minimize use of productive areas. Denitrification-Decomposition (DNDC) simulations show that on average, a switchgrass (Panicum Virgatum L.) or willow (Salix spp.) buffer within this catchment according to this design could reduce annual leached NO3 by 61 or 59% and N2O emission by 5.5 or 10.8%, respectively, produce 8.7 or 9.7 Mg ha−1 of biomass respectively, and displace 6.7 Mg ha−1 of corn (Zea mays L.) grain. Therefore, placement of bioenergy crops has the potential to increase environmental sustainability when the pairing of location and crop type result in minimal disruption of current food production systems and provides additional environmental benefits.

Crop Utilization of Nitrogen in Swine Lagoon Sludge

Swine lagoon sludge is commonly applied to soil as a source of nitrogen (N) for crop production but the fate of applied N not recovered from the soil by the receiver crop has received little attention. The objectives of this study were to (1) assess the yield and N accumulation responses of corn (Zea mays L.) and wheat (Triticum aestivum) to different levels of N applied as swine lagoon sludge, (2) quantify recovery of residual N accumulation by the second and third crops after sludge application, and (3) evaluate the effect of different sludge N rates on nitrate (NO3-N) concentrations in the soil. Sludge N trials were conducted with wheat on two swine farms and with corn on one swine farm in the coastal plain of North Carolina. Agronomic optimum N rates for wheat grown at two locations was 360 kg total sludge N ha−1 and the optimum N rate for corn at one location was 327 kg total sludge N ha−1. Residual N recovered by subsequent wheat and corn crops following the corn crop that received lagoon sludge was 3 and 12 kg N ha−1, respectively, on a whole-plant basis and 2 and 10 kg N ha−1, respectively, on a grain basis at the agronomic optimum N rate for corn (327 kg sludge N ha−1). From the 327 kg ha−1 of sludge N applied to corn, 249 kg N ha−1 were not recovered after harvest of three crops for grain. Accumulation in recalcitrant soil organic N pools, ammonia (NH3) volatilization during sludge application, return of N in stover/straw to the soil, and leaching of NO3 from the root zone probably account for much of the nonutilized N. At the agronomic sludge N rate for corn (327 kg N ha−1), downward movement of NO3-N through the soil was similar to that for the 168 kg N ha−1 urea ammonium nitrate (UAN) treatment. Thus, potential N pollution of groundwater by land application of lagoon sludge would not exceed that caused by UAN application.

Microbial denitrification dominates nitrate losses from forest ecosystems

Denitrification removes fixed nitrogen (N) from the biosphere, thereby restricting the availability of this key limiting nutrient for terrestrial plant productivity. This microbially driven process has been exceedingly difficult to measure, however, given the large background of nitrogen gas (N2) in the atmosphere and vexing scaling issues associated with heterogeneous soil systems. Here, we use natural abundance of N and oxygen isotopes in nitrate (NO3 (-)) to examine dentrification rates across six forest sites in southern China and central Japan, which span temperate to tropical climates, as well as various stand ages and N deposition regimes. Our multiple stable isotope approach across soil to watershed scales shows that traditional techniques underestimate terrestrial denitrification fluxes by up to 98%, with annual losses of 5.6-30.1 kg of N per hectare via this gaseous pathway. These N export fluxes are up to sixfold higher than NO3 (-) leaching, pointing to widespread dominance of denitrification in removing NO3 (-) from forest ecosystems across a range of conditions. Further, we report that the loss of NO3 (-) to denitrification decreased in comparison to leaching pathways in sites with the highest rates of anthropogenic N deposition.

Potential to assess nitrate leaching vulnerability of irrigated cropland

Irrigated cropland represents the largest source of groundwater nitrate (NO3) pollution in the Central Valley (CV) of California. Mitigation, through the use of best management practices that maximize crop nitrogen use efficiency (NUE), will be most effective in reducing pollution if used where the risk of NO3 leaching loss is greatest. The University of California9s Nitrate Groundwater Pollution Hazard Index (HI) tool was used to map the risk of NO3 leaching below the rootzone in irrigated fields in a portion of the CV. The HI is an expert system that calculates an index value based on soil properties, crop characteristics, and type of irrigation system in use. Depth to groundwater, aquifer recharge rate, and actual farm management practices (e.g., rate of nitrogen [N] fertilizer applied) are not considered in the calculation. Application of the HI to 1,318,000 ha (3,256,848 ac) of irrigated cropland in the four southernmost counties of the CV revealed that 31% of the area is at high risk of NO3 leaching loss if not managed carefully. Adoption of drip or microsprinkler irrigation on all orchards, vineyards, and vegetable fields would decrease the area rated as most vulnerable from 31% to 20% of the area analyzed. Crop fields on permeable soils and/or irrigated by surface gravity methods contributed the most to the area at high risk. The HI can help the USDA, regulatory agencies, and Cooperative Extension target regulatory, research, and education efforts.