Modifying fertilizer rate and application method reduces environmental nitrogen losses and increases corn yield in Ontario

Distinguishing and quantifying the fate of nitrate in irrigation water and nitrate produced by ammonium nitrification

When the sources of nitrogen include not only ammonium (NH₄⁺) fertilizer (ANF) but also nitrate (NO₃^-) from groundwater and rainfall (NRI), if the proportions of various types of NO₃^- are still based on the amount of ANF, the corresponding calculation method may be complicated. This paper established a water flow-nitrogen migration transformation model for the unsaturated zone in grain-planting and vegetable-planting areas, and studied the migration and transformation of NH₄⁺ and NO₃^- in the unsaturated zone when ANF and NRI coexist. This paper proposed for the first time the proportional coefficient method (PCM) and hypothetical assignment method (HAM) to distinguish and quantify the fate proportions of NO₃^- from NO₃^- produced by NH₄⁺ nitrification (NNR) and NRI. The results showed that the PCM was more practical than the HAM in quantifying the fate of NO₃^- from different sources. If only the root absorption ratio was used to evaluate the degree of nutrient supply to crops, the ratios of root absorption were as high as 40% (44.75-50.85%). NRI provided more nutrients in grain-growing areas than those in vegetable-growing areas. If the sum of the proportion of other fates was regarded as the degree of groundwater NO₃^- mitigation through irrigation in the unsaturated zone, except for the ratio of NO₃^- leaching to groundwater, the proportion of NO₃^- pollution mitigation was as high as 57.89% (57.89-92.99%), and the mitigation ability of groundwater NO₃^- pollution in grain-growing areas was higher than that in vegetable-growing areas.

Global evaluation of inhibitor impacts on ammonia and nitrous oxide emissions from agricultural soils: A meta-analysis

Inhibitors are widely considered an efficient tool for reducing nitrogen (N) loss and improving N use efficiency, but their effectiveness is highly variable across agroecosystems. In this study, we synthesized 182 studies (222 sites) worldwide to evaluate the impacts of inhibitors (urease inhibitors [UI], nitrification inhibitors [NI] and combined inhibitors) on crop yields and gaseous N loss (ammonia [NH₃ ] and nitrous oxide [N₂ O] emissions) and explored their responses to different management and environmental factors including inhibitor application timing, fertilization regime, cropping system, water management, soil properties and climatic conditions using subgroup meta-analysis, meta-regression and multivariate analyses. The UI were most effective in enhancing crop yields (by 5%) and reducing NH₃ volatilization (by 51%), whereas NI were most effective at reducing N₂ O emissions (by 49%). The application of UI mitigates NH₃ loss and increases crop yields especially in high NH₃ -N loss scenarios, whereas NI application would minimize the net N₂ O emissions and the resultant environmental impacts especially in low NH₃ -N loss scenarios. Alternatively, the combined application of UI and NI enables producers to balance crop production and environmental conservation goals without pollution tradeoffs. The inhibitor efficacy for decreasing gaseous N loss was dependent upon soil and climatic conditions and management practices. Notably, both meta-regression and multivariate analyses suggest that inhibitors provide a greater opportunity for reducing fertilizer N inputs in high-N-surplus systems and presumably favor crop yield enhancement under soil N deficiency situations. The pursuit of an improved understanding of the interactions between plant-soil-climate-management systems and different types of inhibitors should continue to optimize the effectiveness of inhibitors for reducing environmental losses while increasing productivity.

Greenhouse gas emissions following biosolids application to farmland: Estimates from the DeNitrification and DeComposition model

Municipal wastewater sludge may be processed into biosolids and applied to farmland for crop production, rather than be disposed of in landfills. Biosolids supply plant nutrients and increase soil organic carbon but also contribute to the production of greenhouse gases (GHGs). Computational models must therefore be refined to estimate the contribution of these gases to national GHG inventories. The DeNitrification and DeComposition (DNDC) model was evaluated for processes regulating crop growth, GHGs and soil C&N dynamics to determine its suitability for informing policy decision-making and advancing Canada's GHG inventory. Three years (2017-2019) of data were collected from replicated corn (Zea mays L.) plots in Quebec, Canada. The plots received 120 kg of available N ha^-1 y^-1 in mesophilic anaerobically digested biosolids, composted biosolids, alkaline-stabilized biosolids, urea, or combinations of these, while control plots were left unfertilized. Treatments receiving digested biosolids emitted more nitrous oxide (N₂O) during the growing season than other treatments, while carbon dioxide (CO₂) emissions were similar between treatments. After calibration, DNDC estimates were within the 95% confidence interval of the measured variables. Correlation coefficients (r) indicated discrepancies in trends between the estimated and measured values for daily CO₂ and N₂O emissions. These emissions were underestimated in the early and mid-growing season of 2018. They were more variable from plots fertilized with composted or alkaline-stabilized biosolids than from those with digested biosolids. Annual N₂O emissions (r = 0.8), crop yields (r = 0.5), and soil organic carbon (r = 0.4) were modelled with higher accuracy than cumulative CO₂ emissions (r = 0.3) and total soil N (r = 0.1). These findings suggest that DNDC is suitable for estimating field-scale N₂O emissions following biosolids application, but estimates of CO₂ emissions could be improved, perhaps by disaggregating the biosolids from the soil organic matter pools in the decomposition subroutines.

Economic and environmental nitrate leaching consequences of 4R nitrogen management practices including use of inhibitors for corn production in Ontario

Nitrate (NO₃^-) leaching has negative human and environmental health consequences that can be attributed to and mitigated by agricultural decision making. The purpose of this study is to examine the economic and environmental nitrogen (N) leaching reduction from 4R (Right Rate, Right Source, Right Time, Right Placement) agricultural management practices, including application methods, timing and rates, and the use of nitrification and urease inhibitors, for Ontario corn production. This study employed an integrated biophysical and economic GIS-based simulation model considering corn yields, prices, and production costs, and environmental losses, under historical weather scenarios, with NO₃^- leaching constraints. Reducing N application from historical to model optimized agronomic rates sharply lowered corn NO₃^- leaching from 75.3 to 24.9 kt N per year. Increasing model restrictions on corn NO₃^- leaching increased the use of broadcast and sidedress application methods compared to injection and lower overall production. They also increased the use of nitrification and urease inhibitors, which increased N use efficiency, because they allowed lower leaching from corn production, for a price. Leaching decreases from restrictions trade-off with ammonia (NH₃) volatilization increases, but there was no trade-off with nitrous oxide (N₂O) emissions. This highlighted the importance of considering net N losses and production trade-offs by policy decision-makers when developing N loss reduction strategies.

Spatial heterogeneity modeling of water quality based on random forest regression and model interpretation

A systematic understanding of the spatial distribution of water quality is critical for successful watershed management; however, the limited number of physical monitoring stations has restricted the evaluation of spatial water quality distribution and the identification of features impacting the water quality. To fill this gap, we developed a modeling process that employed the random forest regression (RFR) to model the water quality distribution for the Taihu Lake basin in Zhejiang Province, China, and adopted the Shapley Additive exPlanations (SHAP) method to interpret the underlying driving forces. We first used RFR to model three water quality parameters: permanganate index (COD_Mn), total phosphorus (TP), and total nitrogen (TN), based on 16 watershed features. We then applied the built models to generate water quality distribution maps for the basin, with the COD_Mn ranging from 1.39 to 6.40 mg/L, TP from 0.02 to 0.23 mg/L, and TN from 1.43 to 4.27 mg/L. These maps showed generally consistent patterns among the COD_Mn, TN, and TP with minor differences in the spatial distribution. The SHAP analysis showed that the TN was mainly affected by agricultural non-point sources, while the COD_Mn and TP were affected by agricultural and domestic sources. Due to differences in sewage collection and treatment between urban and rural areas, the water quality in highly populated urban areas was better than that in rural areas, which led to an unexpected positive relationship between water quality and population density. Overall, with the RFR models and SHAP interpretation, we obtained a continuous distribution pattern of the water quality and identified its driving forces in the basin. These findings provided important information to assist water quality restoration projects.

Response of area- and yield-scaled N2 O emissions from croplands to deep fertilization: a meta-analysis of soil, climate, and management factors

BACKGROUND

Nitrous oxide (N₂ O) is an important and persistent greenhouse gas making a significant contribution to global climate change. Deep fertilization has been demonstrated to increase crop yield and nutrient use efficiency by decreasing losses of volatilization and surface runoff. However, N₂ O emissions from croplands induced by deep fertilization are variable and mitigation strategies remain uncertain. This study aimed to (i) quantify the response of area-scaled (N₂ O emissions) and yield-scaled N₂ O emissions (N₂ O intensity) from croplands to deep fertilization, and (ii) identify the soil, climate, and management factors that mitigate N₂ O emissions and N₂ O intensity under deep fertilization.

RESULTS

Compared with the control, deep fertilization increased N₂ O emissions by 18.6% (P < 0.001) but decreased N₂ O intensity by 20.1% (P = 0.018). By adopting deep fertilization, N₂ O emissions could be significantly mitigated in rice-paddies soils (-48.8%), with fertilizer depth > 10 cm (-33.0%), and with fertilizer N amount > 200 kg N ha^-1 (-8.2%). N₂ O intensity following deep fertilization significantly decreased in soils with pH ≤6 (-22.5%), at sites with precipitation of 500-1000 mm (-25.5%), in rice-paddies soils (-53.0%), with the method of mixed fertilizer in the control (-21.2%), and with fertilizer depth > 10 cm (-33.6%).

CONCLUSION

This study provides a basis for assessing the effect of deep fertilization on N₂ O emissions and provides potential measures to mitigate N₂ O emissions associated with deep fertilization practices.

Effects of Adapted N-Fertilisation Strategies on Nitrate Leaching and Yield Performance of Arable Crops in North-Western Germany

Groundwater pollution with nitrate is a big challenge for drinking water abstraction in regions with intensive agricultural land-use, specifically with high livestock densities on sandy soils in humid climates. Karst aquifers with high water flow velocities are extremely vulnerable to this problem. To cope with this situation, a field trial with an installation of ceramic suction cups under a randomised block design with a typical north-German cropping sequence of silage maize–winter wheat–winter barley was established in a karst water protection zone. Over three years, reduced nitrogen (N) application rates and N type (mineral or combined organic + mineral fertilisation) were tested for their effects on crop yields and leachate water quality below the root zone. Results showed no significant reductions in crop yields with 10/20% reduced N rates for cereals/maize and only slight reductions in cereal protein content. Nitrate concentration from adapted N rates was significantly lower in treatments with an application of organic fertilisers (−7.74 mg NO3-N l−1) with greatest potential after cultivation of maize; in only mineral fertilised plots the effect was smaller (−3.80 mg NO3-N l−1). Cumulative leaching losses were positively correlated with post-harvest soil mineral nitrogen content but even in unfertilised control plots losses >50 kg N ha−1 were observed in some crop-years. Reduced N rates led to decreased leaching losses of 14% (6.3 kg N ha−1 a−1) with mineral and 29% (20.1 kg N ha−1 a−1) with organic + mineral fertilisation on average overall cops and years. The presented study revealed the general potential of adapted fertilisation strategies with moderately reduced N applications (−10/−20%) to increase leachate water quality without affecting significantly crop yields. However, regionally typical after-effects from yearlong high N surpluses in livestock intensive farming systems are a limiting factor.

Probabilistic carcinogenic and non-carcinogenic risk assessment of heavy metal ingestion through consumption of different walnut cultivars: An Iranian study

The heavy metal levels in six walnut cultivars from five geographical zones of Iran were measured. An assessment of risks was conducted by calculating the Target Hazard Quotient (THQ) and Incremental Lifetime Cancer Risk (ILCR) by use of the Monte Carlo simulation method. The highest amounts of As and Pb were reported in Farouj samples. Also, the highest levels of Cr, Zn, Cu and Mn were determined in samples collected from Tuyserkan. Accordingly, 50th and 95th ILCRs for general population due to consumption of walnut were 1.03 × 10^-4 and 3.11 × 10^-4 (for As), 4.10 × 10^-6 and 1.1 × 10^-5 (for Cr) and 4.71 × 10^-9 and 1.05 × 10^-8 (for Pb), respectively. In addition, the 50th and 95th centiles of the HIs for walnut ingestion by Iranians were 1.02 and 2.05, respectively, indicating a minor chance of non-cancer effects. Based on the calculated 95% ILCR, dietary exposure to As through the consumption of walnut poses a risk to Iranian consumer health. However, ILCR values of other heavy metals (HMs) were in acceptable ranges (ILCR < 1 × 10^-4), representing no toxicological concern for consumers. The most significantly influential parameters were determined by sensitivity analysis during the MCS. According to THQ and ILCR methods, concentration was the most sensitive parameters. For THQ method the concentration effects were ranged from 72.4 to 85.1%. Moreover, for ILCR method the effects of concentration in As, Cr, and Pb were 87.1, 79.1 and 83.54%, respectively.