Fertilizer-derived Nitrogen Research Articles

Humic Acids Incorporated into Urea at Different Proportions Increased Winter Wheat Yield and Optimized Fertilizer-Nitrogen Fate

Humic acids (HAs) incorporated into urea fertilizers are highly effective at increasing yield and decreasing fertilizer-derived nitrogen (N) loss from soil, but reports of the optimal proportion in fertilizers remain widely inconsistent. In this study, we examined the effects of urea enhanced with 0.2–5.0% HAs (UHAs) on the yield, biomass production, N uptake, and N residue in fluvo-aquic soil in winter wheat cultivated over two growing seasons from 2018 to 2020 in the North China Plain. UHAs application significantly enhanced wheat grain yield, aboveground dry biomass, total and fertilizer-derived N uptake by wheat, and residue in soil, while reducing the loss of fertilizer-derived N. Additionally, UHAs treatments increased fertilizer-N residues in soil, especially in the top 30 cm soil layer, which increased with the proportion of added HAs. These positive effects were attributed to a higher spike number under UHAs treatments compared to conventional urea. Clustering analysis of the different treatments showed that 0.2% HAs were more similar to conventional urea, while 0.5% had similar effects to HAs at higher proportions. UHAs application significantly enhanced wheat grain yield, mainly via increasing spike number, and optimized the fertilizer-N fate. Among UHAs treatments, 0.5% HAs showed the highest increase in economic benefit.

Modeling Nitrogen Uptake in Eight Common Leafy Vegetables in Red River Delta, Vietnam

Fertilizer originated nitrate excess in vegetables has attracted numerous studies for its effects on food quality. However, the relationship between plant nitrate accumulation and fertilizer-derived nitrogen (FTN) in the soil in continuous research is rarely reported. This study examines the impact of conventional ammonium fertilizer application (50.4 kg/ha) on the constant trend of soil nitrogen and plant nitrate uptake of 8 common leafy vegetables grown in Red Delta River, Vietnam. The vegetables reveal both FTN and plant nitrate took about 17 days to release from topsoil and plant. The trend of FTN is well fitted by a regression model (Decay model, R2=0.945, p<0.001), which shows the nitrogen loss rate of FTN range from 0.120-0.139 g N/day. Meanwhile, the trend of plant nitrate uptake fitted the quadratic equation (R2=0.889, p<0.01). Although the correlation between FTN and plant nitrate is weak, this study finds that autumn crops have a tighter relationship than summer crops (R=0.71 and R=0.46, respectively). It can be concluded that regression models could be suitable methods to observe the behavior of fertilizer nitrogen in soil and vegetable uptake.

Fertilizer-derived nitrogen use of two varieties of single-crop paddy rice: a free-air carbon dioxide enrichment study using polymer-coated 15N-labeled urea

ABSTRACT Atmospheric concentrations of carbon dioxide (CO2) have steadily increased over recent decades. The fertilization effect of elevated CO2 concentrations (E-[CO2]) is known to increase the biomass production and also the nitrogen (N) demand of paddy rice, which affects the rice N use efficiency. This study was conducted to elucidate the fertilizer-derived N use of paddy rice (Oryza sativa L.) for two varieties, japonica cv. Koshihikari and indica cv. Takanari, with and without E-[CO2] using a free-air CO2 enrichment (FACE) facility in central Japan. To quantify the fate of fertilizer-derived N directly, polymer-coated 15N-labeled urea was used with a one-shot application rate of 80 kg N ha–1 incorporated into the plowed layer at the basal fertilization before transplanting of rice seedlings. The biomass, total N concentrations, and 15N abundance in each part of the rice plants were measured at the panicle initiation, heading, and maturing stages. The total N content and 15N abundance in the soil were measured at the maturing stage to evaluate the N balance of the rice–soil system. While E-[CO2] significantly increased the whole plant biomass and the total N content in panicles, it did not increase the total N and the fertilizer-derived N content in the whole plant. The recovery efficiency (fertilizer-derived N in the whole plant to applied N, RE) ranged between 64.9% and 68.7%, and the agronomic efficiency (fertilizer-derived N in panicles to applied N, AE) ranged between 37.8% and 43.8%. The effect of CO2 on RE and AE was not significant. The REs, higher in Koshihikari, and the AEs, higher in Takanari indicated that Takanari preferentially allocated fertilizer-derived N to panicles. The REs, 69% at the maximum in this study, implies an upper limit of use efficiency of N fertilizer, even for polymer-coated (controlled-release) fertilizer. E-[CO2] significantly increased the rice N uptake from sources other than fertilizer, of which mineralization was the most-likely source. Monitoring of soil fertility and appropriate fertilization management are, therefore, necessary for sustainable rice production avoiding long-term decline in soil N fertility.

Assessing impacts of rainfall intensity and slope on dissolved and adsorbed nitrogen loss under bare loessial soil by simulated rainfalls

Nitrogen is of key importance to sustain modern agriculture but how to accurately quantify the loss forms of fertilizer-derived nitrogen has been a challenge for bare loessial soil. We employ 30 simulated rainfalls to evaluate effects of rainfall intensity (45, 60, 75, 90, 105 and 120 mm/h) and slope gradient (5°, 10°, 15°, 20° and 25°) on dissolved and adsorbed nitrogen loss. Here, we show that there was an overall increasing trend of runoff yield with increased rainfall intensity and also an overall increasing trend of sediment yield with increased slope gradient. TN loss at different slopes was more concentrated under rainfall intensities of 45 mm/h and 60 mm/h and more dispersed under rainfall intensities of 75–120 mm/h. t-Test results showed that there were no significant differences for 6 TN samples at each slope (p > 0.05) and 5 TN samples at each rainfall intensity (p > 0.05). All NO3−-N concentration had a slight declining trend at the beginning of runoff yield and then gradually tended to be gentle with the prolongation of rainfall duration. All NH4+-N concentration first showed a sharp decreasing trend and then relatively levelled off with the prolongation of rainfall duration, but it was different and unstable for different rainfall intensities, especially in the first 10 min. Adsorbed TN under bare loess soil occupied 7.0–82.0% of TN loss with an average of 58.6%, while dissolved TN accounted for 18.0–93.0% with an average of 41.4%. NO3−-N and NH4+-N concentrations respectively accounted for 11.8–73.2% and 1.5–13.3% of TN loss under all combinations of rainfall intensity and slope. There were significant differences in variation trends among NO3−-N, NH4+-N and TN loss load under various rainfall intensities and slopes, but they all presented an overall upward trend with increased rainfall intensity. Our results provide the underlying insights needed to guide nitrogen loss control in sloping land of the loess hilly region.

NITROGEN LOSS BY EROSION FROM MECHANICALLY TILLED AND UNTILLED SOIL UNDER SUCCESSIVE SIMULATED RAINFALLS

The description of the fate of fertilizer-derived nitrogen (N) in agricultural systems is an essential tool to enhance management practices that maximize nutrient use by crops and minimize losses. Soil erosion causes loss of nutrients such as N, causing negative effects on surface and ground water quality, aside from losses in agricultural productivity by soil depletion. Studies correlating the percentage of fertilizer-derived N (FDN) with soil erosion rates and the factors involved in this process are scarce. The losses of soil and fertilizer-derived N by water erosion in soil under conventional tillage and no tillage under different rainfall intensities were quantified, identifying the intervening factors that increase loss. The experiment was carried out on plots (3.5 × 11 m) with two treatments and three replications, under simulated rainfall. The treatments consisted of soil with and soil without tillage. Three successive rainfalls were applied in intervals of 24 h, at intensities of 30 mm/h, 30 mm/h and 70 mm/h. The applied N fertilizer was isotopically labeled (15N) and incorporated into the soil in a line perpendicular to the plot length. Tillage absence resulted in higher soil losses and higher total nitrogen losses (TN) by erosion induced by the rainfalls. The FDN losses followed another pattern, since FDN contributions were highest from tilled plots, even when soil and TN losses were lowest, i.e., the smaller the amount of eroded sediment, the greater the percentage of FDN associated with these. Rain intensity did not affect the FDN loss, and losses were greatest after less intense rainfalls in both treatments.

Long-term fate of nitrate fertilizer in agricultural soils

Increasing diffuse nitrate loading of surface waters and groundwater has emerged as a major problem in many agricultural areas of the world, resulting in contamination of drinking water resources in aquifers as well as eutrophication of freshwaters and coastal marine ecosystems. Although empirical correlations between application rates of N fertilizers to agricultural soils and nitrate contamination of adjacent hydrological systems have been demonstrated, the transit times of fertilizer N in the pedosphere-hydrosphere system are poorly understood. We investigated the fate of isotopically labeled nitrogen fertilizers in a three-decade-long in situ tracer experiment that quantified not only fertilizer N uptake by plants and retention in soils, but also determined to which extent and over which time periods fertilizer N stored in soil organic matter is rereleased for either uptake in crops or export into the hydrosphere. We found that 61-65% of the applied fertilizers N were taken up by plants, whereas 12-15% of the labeled fertilizer N were still residing in the soil organic matter more than a quarter century after tracer application. Between 8-12% of the applied fertilizer had leaked toward the hydrosphere during the 30-y observation period. We predict that additional exports of (15)N-labeled nitrate from the tracer application in 1982 toward the hydrosphere will continue for at least another five decades. Therefore, attempts to reduce agricultural nitrate contamination of aquatic systems must consider the long-term legacy of past applications of synthetic fertilizers in agricultural systems and the nitrogen retention capacity of agricultural soils.

Potential urea-derived nitrogen losses caused by ammonia volatilization and nitrogen leaching in a rainfed semiarid region, China

In the rainfed semiarid region of the China Loess Plateau, rainfall is concentrated in the growing season and usually occurs in large storms. This makes for a high risk for fertilizer-derived nitrogen losses. However, relatively little attention has been given to fertilizer efficiency in this region. In this study, ammonia volatilization at natural field conditions as affected by urea-application rate was measured to evaluate the potential ammonia volatilization losses. Nitrogen-leaching potential in the 0–100 cm soil profile as affected by urea-application rate and -application depth for different rainfall-simulated irrigation regimes (two irrigation volumes: 70 and 105 mm; two irrigation methods: single irrigation and three-split irrigation) was also investigated. Results showed that the low initial soil moisture content at the crop-planting stage and a strong following rainfall made ammonia volatilization of low importance from an agricultural management perspective. The stock percentage of urea-derived nitrogen in the soil profile was significantly affected by irrigation method and irrigation volume but not by urea-application rate. Generally, the 105 mm irrigation volume and the single-irrigation method had a lower percentage of applied nitrogen remaining in the soil profile. The results of this rainfall-simulated irrigation investigation indicated that heavy rainfall, especially occurring in large storms, in this area increased the risk of nitrogen leaching. We recommend that split applications of urea should be adopted instead of a conventional lumped (single) application to reduce nitrogen losses in this rainfed semiarid region.

Linkages between coral assemblages and coral proxies of terrestrial exposure along a cross-shelf gradient on the southern Great Barrier Reef

Coral core records, combined with measurements of coral community structure, were used to assess the long-term impact of multiple environmental stressors on reef assemblages along an environmental gradient. Multiple proxies (luminescent lines, Ba/Ca, δ15N) that reflect different environmental conditions (freshwater discharge, sediment delivery to the nearshore, nutrient availability and transformations) were measured in Porites coral cores collected from nearshore reefs at increasing distance from the intensively agricultural region of Mackay (Queensland, Australia). The corals provide a record (1968–2002) of the frequency and intensity of exposure to terrestrial runoff and fertilizer-derived nitrogen and were used to assess how the present-day coral community composition may have been influenced by flood-related disturbance. Reefs closest to the mainland (5–32 km offshore) were characterized by low hard coral cover (≤10%), with no significant differences among locations. Distinct annual luminescent lines and elevated Ba/Ca values (4.98 ± 0.63 μmol mol−1; mean ± SD) in the most inshore corals (Round Top Island; 5 km offshore) indicated chronic, sub-annual exposure to freshwater and resuspended terrestrial sediment that may have historically prevented reef formation. By contrast, corals from Keswick Island (32 km offshore) indicated episodic, high-magnitude exposure to Pioneer River discharge during extreme flood events (e.g., 1974, 1991), with strongly luminescent lines and substantially enriched coral skeletal δ15N (12–14‰). The reef assemblages at Keswick and St. Bees islands were categorically different from all other locations, with high fleshy macroalgal cover (80.1 ± 7.2% and 62.7 ± 7.1%, respective mean ± SE) overgrowing dead reef matrix. Coral records from Scawfell Island (51 km offshore) indicated little exposure to Pioneer catchment influence: all locations from Scawfell and further offshore had total hard and soft coral cover comparable to largely undisturbed nearshore to middle shelf reefs of the southern Great Barrier Reef.

Appropriate Analysis and Interpretation Approaches to Determine Fertilizer-derived Nitrogen in Plant Tissues

Two approaches for estimating the amount of nitrogen (N) in plant tissues derived from labeled fertilizer were evaluated for two tissue types (root and shoot) in three different genera. In the first, atom percentage values obtained by mass spectrometry were converted to the portion of N derived from the fertilizer (NDFF). In the second, the slope of the regression line for the relationship between total N and labeled fertilizer N was used to represent the incremental increase in fertilizer N for each unit increase in total N. These two approaches were applied to data collected during container experiments. Unless a plot of total N versus labeled fertilizer N passes through the origin, conventional ratio-based estimates of the amount of NDFF for plants or tissues are often misleading. When nonzero intercepts occur, NDFF is dependent on the size (total N content) of the tissue or plant. Nonzero intercepts were frequently encountered. An analysis of regression lines describing the relationship between total N gain and fertilizer N produces a different interpretation than evaluations of the NDFF for treatment means. When an analysis of covariance was used to account for differences in total N between tissues and genera, results were generally consistent with the graphical observations and regression analysis. If only ratio-based approaches are used, it is difficult to determine if there are real physiological differences among treatments, genera, and tissues or if differences in NDFF are size-related. Because the data easily can be analyzed several ways, simultaneously evaluating data with ratio-based NDFF, covariates, and regression is appropriate.

The effect of fertilizer placement on nitrogen uptake and yield of wheat and maize in Chinese loess soils

Field trials were carried out to study the fate of15N-labelled urea applied to summer maize and winter wheat in loess soils in Shaanxi Province, north-west China. In the maize experiment, nitrogen was applied at rates of 0 or 210 kg N ha−1, either as a surface application, mixed uniformly with the top 0.15 m of soil, or placed in holes 0.1 m deep adjacent to each plant and then covered with soil. In the wheat experiment, nitrogen was applied at rates of 0, 75 or 150 kg N ha−1, either to the surface, or incorporated by mixing with the top 0.15 m, or placed in a band at 0.15 m depth. Measurements were made of crop N uptake, residual fertilizer N and soil mineral N. The total above-ground dry matter yield of maize varied between 7.6 and 11.9 t ha−1. The crop recovery of fertilizer N following point placement was 25% of that applied, which was higher than that from the surface application (18%) or incorporation by mixing (18%). The total grain yield of wheat varied between 4.3 and 4.7 t ha−1. In the surface applications, the recovery of fertilizer-derived nitrogen (25%) was considerably lower than that from the mixing treatments and banded placements (33 and 36%). The fertilizer N application rate had a significant effect on grain and total dry matter yield, as well as on total N uptake and grain N contents. The main mechanism for loss of N appeared to be by ammonia volatilization, rather than leaching. High mineral N concentrations remained in the soil at harvest, following both crops, demonstrating a potential for significant reductions in N application rates without associated loss in yield.

Isotopic fractionation accompanying fertilizer nitrogen transformations in soil and trees of a Scots spine ecosystem

Foliage from a mature stand of Scots pine (Pinus sylvestris L.) receiving increasing doses of ammonium nitrate and urea nitrogen was assayed during the five subsequent growing seasons for total N concentration and 15N abundance. The aim of the study was to examine the potential of the δ15N technique to provide estimates on fertilizer N recovery and its fate in the ecosystem. The 15N abundance in the foliage increased in proportion to the dose of fertilizer application. This was generally owing to the fact that the δ15N of the fertilizer N was significantly higher than that in the soil inorganic-N pool, as well as in the needle biomass of the Scots pine trees on the nonfertilized plots. Due to 15N isotope discrimination occurring during N transformations in soil the relationship was however not very close. Calculations based on the principle of isotope dilution yielded only rough and, in some cases, even misleading estimates of the fraction of the fertilizer-derived nitrogen (Ndff) in the needles. This was especially the case for the urea-N, which undergoes significant isotopic fractionation during the process of ammonia volatilization and possibly microbial NH4+ assimilation in soil. Over five growing seasons, foliar total N concentration peaked at the end of the second season while the 15N abundance continued to increase. Although large methodological errors may be involved when interpreting natural 15N abundance, the measurement of δ15N seems to provide semi-quantitative information about fertilizer N accumulation and transformation processes in coniferous ecosystems. A better understanding of the tree and soil processes causing isotopic fractionation is a prerequisite for correct interpretation of 15N data.