Defining the maximum nitrogen surplus in water management plans to recover nitrate polluted aquifers in Spain.

Nitrate pollution in aquifers is a global concern. Spain has developed a national strategy to recover nitrate polluted aquifers aligned with the European Union (EU) policies, specifically through the water planning under the EU Water Framework Directive. River basin management plans use PATRICAL model results to define the maximum nitrogen surplus in each polluted aquifer for the first time. The maximum nitrogen surplus allows to reach the good status in each aquifer and the model provides the number of years required. Around 30% of the aquifers in Spain is currently heavily polluted by nitrates. Model results show that 90% of these aquifers can be recovered in next 6-12 years by increasing nitrogen use efficiency and reducing nitrogen losses around 50%, which is in line with the EU Farm to Fork Strategy. The remaining aquifers require additional reductions to achieve the good status. In Spain this increase in nitrogen efficiency can be obtained with different measures including 30% reduction of current fertilization.

Effects of different drainage conditions on nitrogen losses of an agricultural sandy loam soil.

Prolonged waterlogging in agricultural fields has severe consequences for the crop development and growth, and could potentially lead to higher N losses. In this study, a 3.93 ha agricultural field in Denmark was separated into two parts of well-drained (WD) and poorly-drained (PD) based on the installation depth of the tile drains. The field was continuously monitored for drainage, soil water dynamics, nitrogen leaching through the drains, and grain dry matter and nitrogen yields in a 4-year period (2017-2020). Furthermore, denitrification potential of the top 1 m of the soil at both parts of the field was measured through the denitrifying enzyme activity assay, and a 1D Daisy model was utilized to capture the differences between water and nitrogen balances at WD and PD. Results indicated that on average over the 4 years, annual harvested nitrogen in the crops at PD was 14% lower compared to WD, with a significant reduction of 33% in 2017-2018, that coincided with the longest period of waterlogging at PD. Moreover, greater losses of nitrogen through leaching from drainage and other pathways were measured at the PD (109 kg N ha-1 ya-1) compared to the WD (95 kg N ha-1 ya-1). Based on the simulations, losses through preferential flow pathways to the drains dominated at PD and most of the denitrification is expected to occur within the topsoil. Future studies could significantly benefit from monitoring the redox dynamics in the top 30 cm of the PD soils, and increasing the depth of tiles drains by redrainage could reduce the N losses of poorly drained agricultural soils.

Low irrigation water minimizes the nitrate nitrogen losses without compromising the soil fertility, enzymatic activities and maize growth.

Nitrate nitrogen (NO3-_N) leaching increased with nitrogen (N) fertilization under high water supply to the field negatively affected the maize growth and performance. This study aimed to understand the mechanisms of NO3-_N leaching on a biochemical basis and its relationship with plant performance with 5 different doses (0, 200, 250, 300, 350 kg N ha- 1) of N fertilizers under low (60%; LW) and high (80%; HW) water holding capacity. Soil and plant enzymes were observed at different growth stages (V9, R1, R3, and R6) of the maize, whereas the leachates were collected at 10-days intervals from the sowing date. The LW had 10.15% lower NO3-_N leachate than HW, with correspondence increases in grain yield (25.57%), shoot (17.57%) and root (28.67%) dry matter. Irrespective of the irrigation water, RubisCo, glutamine synthase (GS), nitrate reductase (NR), nitrite reductase (NiR), and glutamate synthase (GOGAT) activities increased with increasing N fertilizer up to the V9 growth stage and decreased with approaching the maturity stage (R6) in maize. In HW irrigation, soil total N, GOGAT, soil nitrate (NO3-_N), leached nitrate (LNO3-_N), root N (RN), leaf N (LN) were positively correlated with N factors suggesting the higher losses of N through leaching (11.3%) compared to LW irrigation. However, the malondialdehyde (MDA), hydrogen peroxide (H2O2), superoxide (O2-), and proline were negatively correlated with the other enzymatic activities both under LW and HW irrigation. Thus, minimizing the NO3-_N leaching is possibly correlated with the LW and N300 combination without compromising the yield benefit and improving enzyme activities.

Effects of molecular weight of polyaspartic acid on nitrogen use efficiency and crop yield.

BACKGROUND: In the past decades, ever-increasing fertilizer use has led to a continuous increase in agricultural output. However, serious waste of resources occurs because of the low utilization of fertilizers. Polyaspartic acid (PASP) is a biodegradable polymer that can be used as a fertilizer synergist in agricultural production to improve the nutrient utilization capacity of plants. For polymers, the molecular weight (MW) often affects their effectiveness. However, little information is available on the effects of PASP MW in agriculture, especially on nitrogen leaching and plant element uptake. RESULTS: This work was conducted to identify the effect of PASPs with three different MWs - PASP-1 (MW: 5517), PASP-2 (MW: 6934), and PASP-3 (MW: 7568) - on nitrogen leaching, lettuce growth, and wheat cultivation. The results revealed that PASP favored plant growth and nitrogen accumulation in the soil, independent of crop species. PASP with a higher MW improved yields and the agronomic characteristics of lettuce and wheat. Furthermore, apparent amelioration of nitrogen use efficiency for lettuce (7.6%, 12.8%, and 15.0%) and wheat (4.6%, 8.1%, and 9.2%) was observed in the treatments with PASP addition. The effects and merits of PASPs on preventing ammonium nitrogen leaching and improving lettuce and wheat productivity were as follows: PASP-3 > PASP-2 > PASP-1. CONCLUSION: The MW of PASP is an essential factor affecting inorganic nitrogen leaching and crop productivity, and PASP with a higher MW (7568) is recommended for application in agriculture. © 2022 Society of Chemical Industry.

Warming leads to more closed nitrogen cycling in nitrogen-rich tropical forests.

Warming may have profound effects on nitrogen (N) cycling by changing plant N demand and underground N supply. However, large uncertainty exists regarding how warming affects the integrated N dynamic in tropical forests. We translocated model plant-soil ecosystems from a high-altitude site (600 m) to low-altitude sites at 300 and 30 m to simulate warming by 1.0°C and 2.1°C, respectively, in tropical China. The effects of experimental warming on N components in plant, soil, leaching, and gas were studied over 6 years. Our results showed that foliar δ15 N values and inorganic N (NH4 -N and NO3 -N) leaching were decreased under warming, with greater decreases under 2.1°C of warming than under 1.0°C of warming. The 2.1°C of warming enhanced plant growth, plant N uptake, N resorption, and fine root biomass, suggesting higher plant N demand. Soil total N concentrations, NO3 -N concentrations, microbial biomass N and arbuscular mycorrhizal fungal abundance were decreased under 2.1°C of warming, which probably restricted bioavailable N supply and arbuscular mycorrhizal contribution of N supply to plants. These changes in plants, soils and leaching indicated more closed N cycling under warming, the magnitude of which varied over time. The closed N cycling became pronounced during the first 3 years of warming where the sustained reductions in soil inorganic N could not meet plant N demand. Subsequently, the closed N cycling gradually mitigated, as observed by attenuated positive responses of plant growth and less negative responses of microbial biomass N to warming during the last 3 years. Overall, the more closed N cycling under warming could facilitate ecosystem N retention and affect production in these tropical forests, but these effects would be eventually mitigated with long-term warming probably due to the restricted plant growth and microbial acclimation.

Leaching and runoff potential of nutrient and water losses in rice field as affected by alternate wetting and drying irrigation.

Inefficient water management in rice paddy is responsible for a large quantity of water and nutrient loss, which causes tremendous economic and environmental costs. Yet, quantified data on the water and nutrient losses are limited. A study was conducted during 2018-2019 with an Aman (wet)-Boro (dry)-Aman (wet) rice rotation to evaluate the effect of water management on water and nutrient losses through different pathways. The treatments in 2018 Aman season were: (i) rainfed, (ii) I6D (irrigation after six days of ponded water disappearance), and (iii) I3D. In 2019, the Boro season had (i) I6D and (ii) I3D, and the Aman season had (i) rainfed, (ii) I9D, and (iii) I1D treatments. The water input and output from the studied lysimeters were measured daily, and samples from the leachates, ponded water, and topsoil were routinely analyzed for nutrient content. In both Aman seasons, the rainfed cultivation had lower percolation losses (38-44 % of total input) than other treatments (45-70 %). Evapotranspiration in the Boro season (5.4-5.9 mm/day) was higher than that in the Aman seasons (4.2-4.6 mm/day) because of the drier Boro season. Ammonium (NH4⁺-N) leached at 0.6-6.7 mg/L and nitrate (NO3⁻-N) 0.6-5.6 mg/L in these rice seasons. Phosphorus concentration ranged 0.04-0.37 mg/L in the leachates and 0.04-0.51 mg/L in the ponded water. The rainfed and I9D exerted higher nutrient leaching concentration in some events and less so for the I6D treatment than the I3D and I1D, possibly because of the better nitrification and preferential flow paths induced by the prolonged drying processes. However, the rainfed, I9D, and I6D had less leaching load than the I3D and I1D because the latter had larger percolation volume. For example, the I6D treatment in the Boro season reduced the N leaching load by 44 % and P load by 39 % compared with the I3D, and the I9D in 2019 Aman season had 42 and 13 % less N and P leaching load, respectively, than the I1D treatment. The findings will contribute to the effort of developing a sustainable and climate-resilient rice production system.

Effects of changes in throughfall on soil GHG fluxes under a mature temperate forest, northeastern China.

Climate change scenarios predict a change in the rainfall regimes for this current century, which has different impacts on soil greenhouse gas (GHG) fluxes. However, how changes in annual rainfall affect annual GHG fluxes of forest soils remain unknown. A six-year field experiment with -25% and -50% throughfall (TF) and +25% TF manipulation was performed to explore the mechanisms involving GHG fluxes under a mature temperate forest, northeastern China and to work out whether the TF effect sizes on annual soil GHG fluxes vary with dry and wet years. The results showed that both -25% TF and -50% TF treatments depressed annual soil nitrous oxide (N2O) and carbon dioxide (CO2) emissions but increased annual soil methane (CH4) uptake. A contrary pattern of annual soil GHG fluxes was observed in the +25% TF treatment. When annual TF input was decreased by 100 mm, annual soil N2O and CO2 emissions were decreased by 18.1 ± 3.1 mg N m-2 and by 39.4 ± 6.1 g C m-2 during the growing season, respectively, and annual soil CH4 uptake was increased by 11.5 ± 3.4 mg C m-2. Both -25% TF and -50% TF treatments reduced annual soil dissolved organic C (DOC) leaching by 29.3% and 45.6% and dissolved total N (DN) leaching by 30.8% and 39.6%, respectively. Contrary to annual soil N2O and CO2 emissions, annual soil CH4 uptake during the growing season significantly decreased with an increase in the annual leaching fluxes of soil DOC, inorganic N, and DN. Besides soil moisture and temperature and pH, soil GHG fluxes under manipulating TF condition were regulated by soil labile C and N status. Our findings indicated that the TF effect sizes on both annual GHG fluxes and net annual GHG balance (GWP) of forest soils varied with dry and wet years in northeastern China. The results highlight the importance of altered annual rainfall in regulating annual soil GHG fluxes and the GWP in temperate forests under global climate change.

Targeted set-aside: Benefits from reduced nitrogen loading in Danish aquatic environments.

Nitrogen (N) leaching from agricultural areas in the form of nitrate (NO3-) is one of the most dominant sources of eutrophication in coastal waters. This environmental pressure is expected to intensify with the predicted increase in food demand, highlighting the need for developing novel ways to reduce N loads from agriculture. This may be achieved by exploiting the spatial variation in N removal through denitrification in groundwater and surface water systems. Thus, agricultural intensification should occur in areas characterized by high N removal potential, whereas effective N-reduction measures such as setting aside agricultural land (set-aside) should be targeted towards areas characterized by low N removal. Simultaneously, setting aside agricultural land can potentially strengthen local nature areas. To reach the water quality targets defined by the EU Water Framework Directive (WFD), the Danish region has defined individual coastal N reduction goals for each of the existing Danish water catchments. With set-aside as an effective N-reduction measure the study aims were to: 1) evaluate the effect of targeting areas to set aside versus using no targeting and 2) evaluate whether different prioritization for targeting set-aside areas enhances multi-functionality of the landscape, while efficiently achieving the required N load reduction. Areas were selected according to three priority values: 1) high contribution to coastal N loads, 2) high nature value, and 3) low agricultural land rent. The combination of these three values per area defined three multifunctional scenarios: (GreenEnvi - N load dominates, TerreEco - nature dominates, AgroEcon - land rent dominates). Results indicate, that targeting areas with high N loads for set-aside is more beneficial (effective) for achieving multiple goals than blanket policies for entire countries (no targeting). Targeting requires only 23% of agricultural land compared to 35% when not targeting, leaving more land available for satisfying food demand. Moreover, multiple benefits can be achieved in surrounding environments by increasing set-aside to 25% according to the GreenEnvi scenario. The GreenEnvi scenario is also cheaper compared to targeting for only land rent.

Mycorrhizal fungi enhance plant nutrient acquisition and modulate nitrogen loss with variable water regimes.

Climate change will alter both the amount and pattern of precipitation and soil water availability, which will directly affect plant growth and nutrient acquisition, and potentially, ecosystem functions like nutrient cycling and losses as well. Given their role in facilitating plant nutrient acquisition and water stress resistance, arbuscular mycorrhizal (AM) fungi may modulate the effects of changing water availability on plants and ecosystem functions. The well-characterized mycorrhizal tomato (Solanum lycopersicum L.) genotype 76R (referred to as MYC+) and the mutant mycorrhiza-defective tomato genotype rmc were grown in microcosms in a glasshouse experiment manipulating both the pattern and amount of water supply in unsterilized field soil. Following 4 weeks of differing water regimes, we tested how AM fungi affected plant productivity and nutrient acquisition, short-term interception of a 15NH4+ pulse, and inorganic nitrogen (N) leaching from microcosms. AM fungi enhanced plant nutrient acquisition with both lower and more variable water availability, for instance increasing plant P uptake more with a pulsed water supply compared to a regular supply and increasing shoot N concentration more when lower water amounts were applied. Although uptake of the short-term 15NH4+ pulse was higher in rmc plants, possibly due to higher N demand, AM fungi subtly modulated NO3- leaching, decreasing losses by 54% at low and high water levels in the regular water regime, with small absolute amounts of NO3- leached (<1 kg N/ha). Since this study shows that AM fungi will likely be an important moderator of plant and ecosystem responses to adverse effects of more variable precipitation, management strategies that bolster AM fungal communities may in turn create systems that are more resilient to these changes.

Postfire nitrogen balance of Mediterranean shrublands: Direct combustion losses versus gaseous and leaching losses from the postfire soil mineral nitrogen flush.

Fire is a major factor controlling global carbon (C) and nitrogen (N) cycling. While direct C and N losses caused by combustion have been comparably well established, important knowledge gaps remain on postfire N losses. Here, we quantified both direct C and N combustion losses as well as postfire gaseous losses (N2 O, NO and N2 ) and N leaching after a high-intensity experimental fire in an old shrubland in central Spain. Combustion losses of C and N were 9.4 Mg C/ha and 129 kg N/ha, respectively, representing 66% and 58% of initial aboveground vegetation and litter stocks. Moreover, fire strongly increased soil mineral N concentrations by several magnitudes to a maximum of 44 kg N/ha 2 months after the fire, with N largely originating from dead soil microbes. Postfire soil emissions increased from 5.4 to 10.1 kg N ha-1  year-1 for N2 , from 1.1 to 1.9 kg N ha-1  year-1 for NO and from 0.05 to 0.2 kg N ha-1  year-1 for N2 O. Maximal leaching losses occurred 2 months after peak soil mineral N concentrations, but remained with 0.1 kg N ha-1  year-1 of minor importance for the postfire N mass balance. 15 N stable isotope labelling revealed that 33% of the mineral N produced by fire was incorporated in stable soil N pools, while the remainder was lost. Overall, our work reveals significant postfire N losses dominated by emissions of N2 that need to be considered when assessing fire effects on ecosystem N cycling and mass balance. We propose indirect N gas emissions factors for the first postfire year, equalling to 7.7% (N2 -N), 2.7% (NO-N) and 5.0% (N2 O-N) of the direct fire combustion losses of the respective N gas species.

The effect of drought and nitrogen fertiliser addition on nitrate leaching risk from a pasture soil; an assessment from a field experiment and modelling.

BACKGROUND: A combination of field experiment and modelling tested the hypothesis that dry summers increase the risk of nitrogen (N) leaching from pasture owing to a combination of: soil N accumulation in a dry summer; slow recovery of drought-affected pasture in the autumn; and the resultant inefficient use of fertiliser N by the pasture. RESULTS: In the experiment, pasture response to urea and apparent N recovery in autumn after the drought was half that of irrigated pasture (7 vs 13 kg dry matter kg-1 N; 28 vs 52% apparent recovery; P < 0.05). There was more soil mineral N at the start of drainage (P < 0.001) as a result of this inefficient fertiliser N use. Modelling of pasture growth in six different drought years demonstrated that subsequent N leaching risk after rewetting was inversely related to pasture N uptake during rewetting in the autumn. CONCLUSION: When the period between post-drought pasture recovery and the onset of drainage is short, N leaching risk increases. Nitrogen leaching is determined by the type of autumn (slow or fast growing conditions before drainage) and the amount of fertiliser N applied. The latter can be managed by a farmer, but the former cannot. © 2018 Society of Chemical Industry.

Analysis of water and nitrogen use efficiency for maize (Zea mays L.) grown on soft rock and sand compound soil.

BACKGROUND: Maize was grown on compound soils constituted from mixtures of soft rock and sand at different ratios, and water use efficiency (WUE), nitrogen use efficiency (NUE) and fertilizer nitrogen use efficiency (FNUE) were quantified. The data were used to assist in designing strategies for optimizing water and nitrogen management practices for maize on the substrates used. Maize was sown in composite soil prepared at three ratios of soft rock and sand (1:1, 1:2 and 1:5 v/v) in Mu Us Sandy Land, Yuyang district, Yulin city, China. Yields, amount of drainage, nitrogen (N) leaching, WUE and NUE were calculated. Then a water and nitrogen management model (WNMM) was calibrated and validated. RESULTS: No significant difference in evapotranspiration of maize was found among compound soils with soft rock/sand ratios of 1:1, 1:2 and 1:5, while water drainage increased significantly with increasing soft rock/sand ratio. WUE increased to 1.30 kg m-3 in compound soil with 1:2 soft rock/sand ratio. Nitrogen leaching and ammonia volatilization were the main reason for nitrogen loss, and N reduction mainly relied on crop uptake. NUE and FNUE could reach 33.1 and 24.9 kg kg-1 N respectively. Water drainage and nitrogen leaching occurred mostly during heavy rainfall or irrigation. Through a scenario analysis of different rainfall types, water and fertilizer management systems were formulated each year. CONCLUSION: This study shows that soft rock plays a key role in improving the WUE, NUE and FNUE of maize. © 2016 Society of Chemical Industry.

Effects of ditch-buried straw return on water percolation, nitrogen leaching and crop yields in a rice-wheat rotation system.

BACKGROUND: Crop residue management and nitrogen loss are two important environmental problems in the rice-wheat rotation system in China. This study investigated the effects of burial of straw on water percolation, nitrogen loss by leaching, crop growth and yield. Greenhouse mesocosm experiments were conducted over the course of three simulated cropping seasons in a rice1-wheat-rice2 rotation. RESULTS: Greater amounts of straw resulted in more water percolation, irrespective of crop season. Burial at 20 and 35 cm significantly reduced, but burial at 50 cm increased nitrogen leaching. Straw at 500 kg ha(-1) reduced, but at 1000 kg ha(-1) and at 1500 kg ha(-1) straw increased nitrogen leaching in three consecutive crop rotations. In addition, straw at 500 kg ha(-1) buried at 35 cm significantly increased yield and its components for both crops. CONCLUSIONS: This study suggests that N losses via leaching from the rice-wheat rotation may be reduced by the burial of the appropriate amount of straw at the appropriate depth. Greater amounts of buried straw, however, may promote nitrogen leaching and negatively affect crop growth and yields. Complementary field experiments must be performed to make specific agronomic recommendations.

How inhibiting nitrification affects nitrogen cycle and reduces environmental impacts of anthropogenic nitrogen input.

Anthropogenic activities, and in particular the use of synthetic nitrogen (N) fertilizer, have doubled global annual reactive N inputs in the past 50-100 years, causing deleterious effects on the environment through increased N leaching and nitrous oxide (N2 O) and ammonia (NH3 ) emissions. Leaching and gaseous losses of N are greatly controlled by the net rate of microbial nitrification. Extensive experiments have been conducted to develop ways to inhibit this process through use of nitrification inhibitors (NI) in combination with fertilizers. Yet, no study has comprehensively assessed how inhibiting nitrification affects both hydrologic and gaseous losses of N and plant nitrogen use efficiency. We synthesized the results of 62 NI field studies and evaluated how NI application altered N cycle and ecosystem services in N-enriched systems. Our results showed that inhibiting nitrification by NI application increased NH3 emission (mean: 20%, 95% confidential interval: 33-67%), but reduced dissolved inorganic N leaching (-48%, -56% to -38%), N2 O emission (-44%, -48% to -39%) and NO emission (-24%, -38% to -8%). This amounted to a net reduction of 16.5% in the total N release to the environment. Inhibiting nitrification also increased plant N recovery (58%, 34-93%) and productivity of grain (9%, 6-13%), straw (15%, 12-18%), vegetable (5%, 0-10%) and pasture hay (14%, 8-20%). The cost and benefit analysis showed that the economic benefit of reducing N's environmental impacts offsets the cost of NI application. Applying NI along with N fertilizer could bring additional revenues of $163 ha(-1)  yr(-1) for a maize farm, equivalent to 8.95% increase in revenues. Our findings showed that NIs could create a win-win scenario that reduces the negative impact of N leaching and greenhouse gas production, while increases the agricultural output. However, NI's potential negative impacts, such as increase in NH3 emission and the risk of NI contamination, should be fully considered before large-scale application.

Salt as a mitigation option for decreasing nitrogen leaching losses from grazed pastures.

BACKGROUND: The main source of nitrogen (N) leaching from grazed pastures is animal urine with a high N deposition rate (i.e. per urine patch), particularly between late summer and early winter. Salt is a potential mitigation option as a diuretic to induce greater drinking-water intake, increase urination frequency, decrease urine N concentration and urine N deposition rate, and thereby potentially decrease N leaching. This hypothesis was tested in three phases: a cattle metabolism stall study to examine effects of salt supplementation rate on water consumption, urination frequency and urine N concentration; a grazing trial to assess effects of salt (150 g per heifer per day) on urination frequency; and a lysimeter study on effects of urine N rate on N leaching. RESULTS: Salt supplementation increased cattle water intake. Urination frequency increased by up to 69%, with a similar decrease in urine N deposition rate and no change in individual urination volume. Under field grazing, sensors showed increased urination frequency by 17%. Lysimeter studies showed a proportionally greater decrease in N leaching with decreased urine N rate. Modelling revealed that this could decrease per-hectare N leaching by 10-22%. CONCLUSIONS: Salt supplementation increases cattle water intake and urination frequency, resulting in a lower urine N deposition rate and proportionally greater decrease in urine N leaching. Strategic salt supplementation in autumn/early winter with feed is a practical mitigation option to decrease N leaching in grazed pastures.

Atmospheric deposition and soil water chemistry in Swedish forests since 1985 - Effects of reduced emissions of sulphur and nitrogen.

Trends for the atmospheric deposition of sulphur (S) and inorganic nitrogen (inorg-N) to forests and changes in the forest soil water chemistry in Sweden have been assessed since 1985, with special focus on the last 25 years, based on measurements within the Swedish Throughfall Monitoring Network (SWETHRO). The reductions in the deposition of S and inorg-N in the southern part of Sweden corresponded relatively well with the pollutant emission reductions for S and inorg-N from both EU27 + UK and Sweden during 1996/97-2021/22. For northern Sweden the deposition of S and inorg-N decreased to a lesser extent than both European and Swedish emissions. The bulk deposition of NO3-N has decreased more than the deposition of NH4-N over the last 25-year period, which is consistent with the much larger emission reductions for NOx compared to NH3 from EU27 + UK and Sweden. The S concentrations in the soil water, at 50 cm below soil surface, have decreased during the last 25 years, however somewhat less than the S deposition. At sites with low ANC and pH in the beginning of the period, the increase in ANC was generally greater and the increase in pH was smaller, but at sites with high pH and ANC above zero, the increase in pH was dominant, in line with the nonlinear relationship between pH and ANC in the soil water. The incidence of elevated concentrations of NO3-N in the soil water was highest in southwest Sweden, ranging between 4 and 19 % of all measuring occasions since 1985/86. The reduced deposition of N over the 35-year period was not reflected in the incidence of elevated concentrations of NO3-N in the soil water over time.

Reducing nitrogen leaching using wood vinegar treated in urea-fertilized soil.

Wood vinegar (WV) is known to retard the release of ammonium (NH4+) from urea by inhibiting urea hydrolysis. However, the effect of WV on nitrogen leaching in soil is not known, and there are few studies on the effect of WV on microbial activity although WV exhibits antibacterial properties against pathogens in agriculture. Therefore, the purpose of this study was to investigate the effect of WV on controlling nitrogen leaching and soil microbial activity. Soils were treated with urea and WV, and the available inorganic nitrogen concentrations in the soil were compared with those from soils treated with N-(n-butyl)thiophosphoric triamide (NBPT), a commonly used urease inhibitor. The nitrate concentration in the soil was significantly decreased in the WV treatment, although the ammonium concentration was not affected by the WV treatment. Basal soil respiration was significantly increased in the WV and NBPT treatments although the microbial biomass was increased in the urea only treatment. The ammonium nitrogen concentration in the leachate was not significantly different in the WV and urea-treated soil compared to the urea-only treatment. However, the nitrate leaching increased in the soil treated only with urea at 16 days after the treatment although there was no statistically significant difference in the total leached nitrate. Therefore, WV can be used to reduce nitrogen leaching and enhance soil microbial activity.

Determining optimal range of reduction rates for nitrogen fertilization based on responses of vegetable yield and nitrogen losses to reduced nitrogen fertilizer application.

Vegetable production is commonly accompanied by high nitrogen fertilizer rates but low nitrogen use efficiency in China. Reduced fertilization has been frequently recommended in existing studies as an efficient measurement to avoid large amount of nutrient loss and subsequent nonpoint source pollution. However, the reported responses of vegetable yield and nitrogen losses to reduced fertilization rates varied in a large range, which has resulted into large uncertainties in the potential benefits of those recommended reduction rates. Thus, we constructed the relationship between responses of nitrogen losses and vegetable yield to reduced nitrogen fertilization rates to determine the optimal range of reduction rates for nitrogen fertilization in a proportional form based on data reported in literatures across China's mainland, and evaluated the roles of greenhouse, managing options, and vegetable species on the responses. The relationships were constructed separately for 4 subregions: Northern arid and semiarid, loess plateau regions (NSL), Temperate monsoon zone (TMZ), Southeast monsoon zone (SMZ), Southwest zone (SWZ). The optimal nitrogen fertilizer reduction range for the TMZ, SMZ and SWZ were 51 % to 67 %, 40 % to 66 % and 54 % to 80 %, respectively and no reduction for NSL. Vegetable yields were not be sacrificed when fertilizations were reduced within the optimal ranges. Greenhouse and managing options showed no significant effect on the responses of both vegetable yield and nitrogen losses by the optimal reduction range but vegetable species played a relatively important role on the responses of vegetable yield. This indicated that the optimal reduction rates can be effective on reducing nitrogen loss in both open-field and greenhouse conditions across China's mainland without extra managing options. Therefore, the optimal reduction rates can still serve as a good starting point for making regional plans of nitrogen reduction that help balancing the chasing of high vegetable yield and low nitrogen loss.

Simulation of spatial and temporal variation of nitrate leaching in the vadose zone of alluvial regions on a large regional scale.

Excessive use of fertilizers presents a significant threat to groundwater safety. To mitigate nitrate leaching and ensure the sustainable utilization of groundwater resources, it is crucial to quantify the spatial heterogeneity of nitrogen leaching and its drivers. Therefore, accurate modeling of deep nitrate leaching at large regional scales is necessary. In this study, we have created a computational framework to analyze the transport of unsaturated zone water and nitrate at a regional scale. The framework is based on a process-oriented, watershed-scale computational model that segments the study area into a grid system, with each grid modeled using Richards-based advection-diffusion equations for water and solutes. The research model estimated nitrate nitrogen leaching, accumulation, and denitrification in the vadose zone of agricultural fields in the Baiyangdian watershed, which is a typical agricultural region with complex land use and soil deposition conditions in the North China Plain. The results showed that there were significant spatial differences in nitrate N leaching, denitrification and accumulation with values of 0-388 kg/ha/year, 30-177 kg/ha/year and 75-4778 kg/ha. Groundwater recharge in the wheat/maize, vegetable, and cotton area exhibited a negative correlation with nitrate N accumulation while showing a positive correlation with nitrate N leaching. Nitrate nitrogen distribution indicated spatial heterogeneity, attributable mainly to the heterogeneity in soil texture, structure, and land use. With nitrate nitrogen leaching and denitrification levels reaching 327-388 kg/ha/year and 133-175 kg/ha/year, respectively, vegetable fields pose a direct threat to groundwater. Meanwhile, wheat/maize fields showed the greatest nitrate nitrogen accumulation, ranging from 624 to 4778 kg/ha. This excessive buildup of nitrate in these fields presents a potential hazard to groundwater quality. Soil texture in the root zone had a greater influence on the amount of nitrate leaching and denitrification than soil texture below the root zone. Deeper soil texture (>2 m) was found to mainly control total nitrate accumulation in the vadose zone. To assess nitrate leaching, denitrification, and accumulation at a regional scale within the deep vadose zone, a process-oriented model was developed, considering the intricate associations among land usage, soil texture, and biochemical reactions.

Dune soil nitrogen leaching for Chinese-yam cultivation: Impact of microbe-decomposable slow-release fertilizer.

Chinese yam production is thriving in Aomori Prefecture, a cold and snowy region in Japan. Recently, there has been an increasing risk of nitrogen leaching in Chinese-yam fields, which consist of sandy soil, due to localized torrential rain. The relationships between the type of fertilizer used for Chinese-yam cultivation, the amount of nitrogen (N) leaching, and the timing of leaching remain unknown. Therefore, this study aimed to fill this knowledge gap by investigating the effects of different fertilizers (fast-acting and/or slow-release fertilizer) and irrigation practices (conventional and/or excessive irrigation) in order to mitigate the detrimental impact of nitrogen leaching on groundwater quality. An enhanced mathematical model and the spatiotemporal dynamics of inorganic nitrogen concentration in soil pore water were evaluated the negative impact of nitrogen leaching on the groundwater environment was evaluated. The results showed that the combined use of slow-release fertilizers could significantly reduce nitrate-nitrogen concentration in soil-water, especially during the harvest season. This study demonstrated that cultivating Chinese yam with a fertilizer application system that includes the use of slow-release fertilizer can diminish the negative impact of nitrogen leaching on the groundwater environment, contributing to our understanding of sustainable agricultural practices in regions facing similar environmental challenges. Therefore, our findings represent an important advancement providing new approaches to maintaining productivity while mitigating the adverse impacts on groundwater environments, as well as offering guidelines for agricultural practices in regions facing similar environmental challenges.