Nitrogen Fertilizer Application Research Articles

Biodiversity-safeguarding threshold for urea-fertilizer application on paddy fields: Protozoa-based toxicity tests

Urea is a widely applied fertilizer to enhance crop yields. Ecological risks associated with the excessive application of urea fertilizer threaten the paddy fields' sustainable agriculture and biodiversity preservation. There are no practical thresholds based on proven data on microbial communities. Protozoa are nitrogen-sensitive organisms. For the first time, this study conducted acute and chronic urea toxicity tests on eight species of organisms. The results indicate that Blepharisma sp. is the most sensitive species to urea exposure and is a suitable indicator for determining the safe threshold of urea. This study estimated the predicted no-effect concentration using species sensitivity distribution curves. Subsequently, it established the threshold for urea application in rice fields based on the fields' area and the surface water's height. The short-term safety threshold for urea in the studied paddy field with black soil is 87.7mg/L, equivalent to 43.85kg of urea per hectare for a single nitrogen fertilizer application. The long-term safety threshold is 5.02mg/L, representing the concentration for re-applicating urea. The biodiversity-safeguarding application threshold provides the basis for developing a urea fertilizer reduction protocol to safeguard the paddy fields' biodiversity.

A novel machine learning-driven approach for predicting nitrous oxide flux in precision managed agricultural systems

N2O, also known as nitrous oxide, is a greenhouse gas that is roughly 300 times more potent than CO2 and destroys the the stratospheric ozone layer causing climate change. One of the primary causes of the rapid increase of N2O in our ecosystem is the application of nitrogen fertilizer to agricultural land. This stimulates N2O emissions and accounts for approximately 5% of the global greenhouse gases, forcing harm to the environment and atmosphere (Aronson and Allison, 2012). Previous models severely underestimated N2O flux in various crops, causing inaccurate predictions to form. In our study, we utilized data from automated flux chambers to train and evaluate different machine-learning models to predict the field-level flux of N2O which assist farmers to predict fertilizer amounts to use. The best machine learning model, Random Forest, performed considerably better than the standard empirical and biophysical models by roughly 15%, and show promise in improving predictive accuracy and guiding sustainable agricultural practices.

Effects of soil acidification on humus, electric charge, and bacterial community diversity.

Soil acidification due to the long-term application of nitrogenous fertilizers and the consequent impact on crop growth have been frequently reported. The effects of acidification on soil humus, charge, and microbial communities need to be studied. In this experiment, fertilizer drenching was used to simulate the effects of multiple years of fertilizer application on the black soil. The results showed that 25years of soil acidification treatment resulted in a decrease of 8.97% in the content of stable humus and led to a decrease of 58% and 51.18% in the humic acid (HA) content and degree of humification (PQ) value in stable humus, respectively. In addition, soil acidification leads to a significant decrease in total negative charge (CEC8.2) and variable negative charge (CECv), with both decreasing by 63.28% and 88.67%, respectively, at 25years. Acidification treatments affected both soil microbial community abundance and diversity, with a significant decrease in Acidobacteriota and Gemmatimonadota abundance and an increase in Bacteroidia abundance and Acidobacteriota abundance at 25years.

Sugar transporter modulates nitrogen-determined tillering and yield formation in rice

Nitrogen (N) fertilizer application ensures crop production and food security worldwide. N-controlled boosting of shoot branching that is also referred as tillering can improve planting density for increasing grain yield of cereals. Here, we report that Sugar Transporter Protein 28 (OsSTP28) as a key regulator of N-responsive tillering and yield formation in rice. N supply inhibits the expression of OsSTP28, resulting in glucose accumulation in the apoplast of tiller buds, which in turn suppresses the expression of a transcriptional inhibitor ORYZA SATIVA HOMEOBOX 15 (OSH15) via an epigenetic mechanism to activate gibberellin 2-oxidases (GA2oxs)-facilitated gibberellin catabolism in shoot base. Thereby, OsSTP28-OSH15-GA2oxs module reduces the level of bioactive gibberellin in shoot base upon increased N supply, and consequently promotes tillering and grain yield. Moreover, we identify an elite allele of OsSTP28 that can effectively promote N-responsive tillering and yield formation, thus representing a valuable breeding target of N use efficiency improvement for agricultural sustainability.

OsSTP1 mediates sucrose allocation to regulate rice responses to different nitrogen supply levels

Improving the nitrogen use efficiency is an effective way to increase the yield of rice, and maintaining carbon-nitrogen balance is essential for the normal growth and development of rice. To investigate the impact of the sucrose transporter protein OsSTP1 on nitrogen absorption in rice, in this study, we constructed transgenic lines overexpressing the sucrose transporter gene OsSTP1 (OsSTP1-OE1, OsSTP1-OE2) and mutant transgenic lines (osstp1-1, osstp1-2) from the wild type TB309. Further, we conducted a hydroponic experiment with four nitrogen supply levels of free nitrogen (FN, 0 mg/L), low nitrogen (LN, 10 mg/L), normal nitrogen (NN, 40 mg/L), and high nitrogen (HN, 80 mg/L) to study the responses of each line to different nitrogen supply levels during the seedling stage. The results showed that compared with the wild type and mutant lines in the LN group, the OsSTP1-overexpressing lines exhibited significantly increased biomass, root length, and plant height, decreased soluble sugar content in the leaves, and increased soluble sugar content in the roots. The results indicate that the soluble sugars produced by leaf photosynthesis are transported to the roots through the phloem to promote root growth and nitrogen uptake, thus increasing the aboveground biomass. This study has identified that OsSTP1 can affect the long-distance transport of carbohydrates from source to sink to promote root growth, ultimately influencing rice's absorption and accumulation of nitrogen, improving nitrogen use efficiency and providing reference for reducing nitrogen fertilizer application.

Effect of nitrogen and phosphorus application on starch characteristics and quality of rice with different nitrogen efficiency

IntroductionThe application of nitrogen and phosphorus fertilizers is an important factors affecting the quality of rice, and different nitrogen-efficient rice varieties show significant differences in their response to nitrogen and phosphorus application.MethodsIn this experiment, a low-nitrogen-high efficiency variety (Deyou 4727) and a high-nitrogen-high efficiency variety (Jingyou 781) were selected, and the changes in rice quality and differences in starch structure under nitrogen–phosphorus interaction treatments were determined.ResultsAppearance, flavor, starch content and thermodynamic properties, endosperm cell arrangement, and starch granule morphology and size were significantly influenced by variety, nitrogen-phosphorus interactions, and their interaction effects. The effect of nitrogen fertilizer on quality was greater than that of phosphorus fertilizer. The whiteness and chalkiness rates of Deyou 4727 first decreased and then increased with increasing nitrogen fertilizer application, wheras the appearance quality of Jingyou 781 increased with increasing nitrogen fertilizer application. Starch crystallinity in Deyou 4727 first increased and then decreased with increasing nitrogen fertilizer application, whereas starch crystallinity in Jingyou 781 increased continuously with increasing nitrogen fertilizer application. The application of phosphorus fertilizer led to an increase in starch crystallinity in both nitrogen-efficient rice varieties, consistent with the response of different rice varieties to nitrogen and phosphorus in terms of appearance and chalkiness. With the increasing application of nitrogen and phosphorus fertilizers, the differences in the physicochemical properties and structure of starch became more significant.DiscussionHigh-nitrogen-efficient rice varieties can significantly improve appearance quality under high nitrogen conditions, and the interactions of medium-high nitrogen and low-medium phosphorus can lead to a significant decrease in starch thermal parameters and retention rate, thus improving rice cooking quality. Low-nitrogen-efficient rice varieties can also improve the quality of rice under low-medium-nitrogen conditions with appropriate application of phosphorus fertilizer.

Nitrogen input reduces the physical defense of rice plant against planthopper, Nilaparvata lugens (Hemiptera: Delphacidae).

Nitrogen has important effects on plant growth and defense. Although studies on the alternation in plant chemical defense by nitrogen fertilization have been extensively reported, how it affects physical defense is poorly understood. Two rice (Oryza sativa L.) (Poales: Poaceae) varieties (LDQ7 and YLY1) were applied with varying nitrogen regimes (0.90 and 180kg ha-1) to study their physical defense against the brown planthopper (BPH) Nilaparvata lugens (Hemiptera: Delphacidae) in this study. Results of the electrical penetration graph showed that BPH searching and penetrating duration time was shortened with increasing nitrogen application. Also, the tubercle papicle of rice leaves decreased with increasing nitrogen application, while rice leaves' surface structure and waxy composition changed with increasing nitrogen application. In field experiments, BPH populations increased with the application of nitrogen fertilizer. These findings suggest that nitrogen input can affect plant-insect interactions by reducing the physical defense of plants, which provides new ideas for the organic combinations of yield increase and pest control in rice fields.

Effects of Different Straw Returning Periods and Nitrogen Fertilizer Combinations on Rice Roots and Yield in Saline–Sodic Soil

Straw return is an effective management practice for improving physical and chemical properties of saline–sodic soil in Northeast China. Straw decomposition and nutrient release are deeply influenced by soil and climatic factors. In Northeast China, straw decomposes slowly due to the long winter with low temperatures. Therefore, the season of straw return may be a key issue affecting rice. However, the impact of returning straw in different seasons on rice is disregarded and not commonly researched. We conducted a 2-year field experiment, including two residue management treatments: spring straw return treatment (SR) and autumn straw return treatment (AR), each containing five different N rates (0, 90, 180, 270, and 360 kg ha−1) as sub-treatments. The results reveal that, compared with the spring straw returning treatment, the autumn straw returning treatment significantly improved root morphology and root vigor and increased the number of spikes per unit area, which directly increased rice yield by 4.76% (2020) and 6.62% (2021). In addition, rice yield showed an increasing and then decreasing trend with the increase in N fertilizer application, and it was at its maximum when the N application rate was 270 kg ha−1. Compared to the spring straw return treatment, the autumn straw return treatment was able to reduce 31.46% (2020) and 38.48% (2021) of N fertilizer application without decreasing rice yield. Our findings demonstrate that straw return combined with nitrogen fertilization may be a promising management practice for improving rice root systems and yield in saline–sodic soils, and under the conditions of the autumn straw returning treatment, the best nitrogen fertilizer application rate was 270 kg ha−1.

Microbiomes-Plant Interactions and K-Humate Application for Salinity Stress Mitigation and Yield Enhancement in Wheat and Faba Bean in Egypt’s Northeastern Delta

Salinity, resulting from climate change and excessive mineral fertilization, burdens farmers and negatively impacts soil and water ecosystems in the Northeastern Nile Delta. Organic and biological approaches are crucial for addressing these issues. This study examined the effects of individual and combined inoculations with cyanobacteria, yeast, and Arbuscular Mycorrhizal Fungi (AMF), with or without K-Humate and reducing Nitrogen, phosphorus and potassium (NPK) mineral fertilizers application rates to crop quality of wheat and faba bean. In preliminary laboratory experiments, the interactive effects of these microbiomes on plant antioxidant and soil enzyme production were examined under salinity stress. Results showed that co-inoculation, especially with K-Humate, yielded superior outcomes compared to individual inoculations. These findings were validated by a field trial conducted in saline-alkaline soil in the Northeastern Nile Delta region. All biological treatments 25% of recommended doses, and enhancing salinity tolerance, increasing yield, and improving enhanced rhizosphere microbial activity, including soil enzyme activity, AMF colonization, spore density, and the total numbers of bacteria, cyanobacteria, and yeast. These effects were further amplified by K-Humate and were more pronounced with combined inoculations than with individual ones, leading to improved soil fertility and significant increases in both crop quantity and quality compared to control treatments. The triple treatment, combining cyanobacteria, yeast, and mycorrhizae in the presence of K-Humate while reducing the mineral NPK rate by 75%, achieved superior increases in the productivity of wheat grains and faba bean seeds, reaching 54.72% and 128.92%, respectively, compared to the 100% NPK mineral control. This treatment also significantly improved crop quality, with notable increases in nitrogen, potassium, phosphorus, and protein percentages in wheat grains and faba bean seeds. Microbiomes-interaction increased potassium uptake over sodium, enhancing the plant’s potassium/sodium ratio and improving salt stress tolerance. This approach reduces reliance on costly mineral fertilizers, enabling bio-organic farming in marginal lands, optimizing resource utilization, and preserving natural resources.

The Effect of Reduced Nitrogen Fertilizer Application on japonica Rice Based on Volatile Metabolomics Analysis.

Nitrogen is critical for rice yield and quality, but its overuse can be detrimental to efficiency and the environment. To identify changes in the quality of rice in response to the reduced application of nitrogen fertilizer, we carried out a comprehensive metabolomics study of SuiJing 18 using volatile metabolomics methods. Our results showed that SuiJing 18 had a total of 358 volatile metabolites, mainly lipids (16.25%), terpenoids (15.41%), heterocyclic compounds (15.13%), and hydrocarbons (13.45%). SuiJing 18 underwent significant changes in response to the reduced application of nitrogen fertilizer. Key sweet volatile compounds such as 4-methyl-benzeneacetaldehyde, hexyl acetate, and 2-methylnaphthalene were present at significantly higher levels when nitrogen fertilizer was applied at a rate of 68 kg of pure nitrogen per hectare, and their flavor characteristics also differed significantly from the compounds resulting from the other two treatments. Focusing on 16 differential volatile metabolites, we further investigated their effects on flavor and quality, thus laying the foundation for a greater understanding of the biomarkers associated with changes in rice quality. This study contributes to a better understanding of the mechanisms underlying changes in rice quality after reduced nitrogen fertilizer application.

Transferability of models for predicting potato plant nitrogen content from remote sensing data and environmental variables across years and regions

The use of remote sensing technologies to monitor the nitrogen nutrient status of crops is gradually becoming a more sensible choice, as traditional methods are time-consuming, labor-intensive, and destructive. However, most predictive models utilizing remote sensing data are statistical rather than mechanistic, making them difficult to extend at interannual and regional scales. This study explored the interannual and regional transferability of the potato plant nitrogen content (PNC) prediction models, which combined environmental variables (EVs, e.g. temperature, precipitation, etc.) with proximal hyperspectral vegetation indices (VIs). Two methodologies were implemented to fuse EVs and VIs. The first involved a multiple regression analysis utilizing a multivariate linear model and a random forest approach, with VIs and EVs treated as independent variables, respectively. The second, a hierarchical linear model (HLM), employed EVs to dynamically adjust the relationship between VIs and PNC for different experimental sites. The predictive outcomes demonstrated that (i) the conventional method relying solely on optical VIs exhibited limited accuracy and stability in interannual and regional PNC forecasting; (ii) albeit the multivariate regression approach significantly enhanced model accuracy within the calibration set, its scalability across years and regions remained suboptimal; (iii) the HLM method exhibited high precision and scalability across years and regions, with R2, RMSE, and NRMSE values of 0.68, 0.50 %, and 19.68 % in the validation set, respectively. Those findings corroborate that using a two-tier HLM method can automatically adjust for discrepancies in VIs response to PNC through EVs, thereby enhancing the model's stability. Provided that remote sensing data and EVs are sustainably acquired over the potato growth cycle, it will provide a particularly promising approach to potato nitrogen diagnostics as a decision-making tool for regional application of nitrogen fertilizer.

Nitrogen-Fixing Gamma Proteobacteria Azotobacter vinelandii—A Blueprint for Nitrogen-Fixing Plants?

The availability of fixed nitrogen limits overall agricultural crop production worldwide. The so-called modern “green revolution” catalyzed by the widespread application of nitrogenous fertilizer has propelled global population growth. It has led to imbalances in global biogeochemical nitrogen cycling, resulting in a “nitrogen problem” that is growing at a similar trajectory to the “carbon problem”. As a result of the increasing imbalances in nitrogen cycling and additional environmental problems such as soil acidification, there is renewed and increasing interest in increasing the contributions of biological nitrogen fixation to reduce the inputs of nitrogenous fertilizers in agriculture. Interestingly, biological nitrogen fixation, or life’s ability to convert atmospheric dinitrogen to ammonia, is restricted to microbial life and not associated with any known eukaryotes. It is not clear why plants never evolved the ability to fix nitrogen and rather form associations with nitrogen-fixing microorganisms. Perhaps it is because of the large energy demand of the process, the oxygen sensitivity of the enzymatic apparatus, or simply failure to encounter the appropriate selective pressure. Whatever the reason, it is clear that this ability of crop plants, especially cereals, would transform modern agriculture once again. Successfully engineering plants will require creating an oxygen-free niche that can supply ample energy in a tightly regulated manner to minimize energy waste and ensure the ammonia produced is assimilated. Nitrogen-fixing aerobic bacteria can perhaps provide a blueprint for engineering nitrogen-fixing plants. This short review discusses the key features of robust nitrogen fixation in the model nitrogen-fixing aerobe, gamma proteobacteria Azotobacter vinelandii, in the context of the basic requirements for engineering nitrogen-fixing plants.

Nutrient Use Efficiency and Cucumber Productivity as a Function of the Nitrogen Fertilization Rate and the Wood Fiber Content in Growing Media.

A peat substrate is made from peat from drained peatlands, which is a limited resource. A realistic estimate is that 50% of the world's wetlands have been lost. Peat is used in horticulture, especially for the cultivation of vegetables in greenhouses. The consequences of peatland exploitation are an increase in the greenhouse effect and a decrease in carbon stocks. Wood fiber can be used as an alternative to peat. The chemical properties of growing media interact and change continuously due to the small volume of growing media, which is limited by the growing container. This study aims to gain new knowledge on the impact of nutrient changes in the microbial degradation of carbon compounds in wood fiber and mixtures with a peat substrate on the content and uptake of nutrients required by plants. The cucumber (Cucumis sativus L.) variety 'Dirigent H' developed in the Netherlands was cultivated in growing media of a peat substrate and wood fiber: (1) peat substrate (PS); (2) wood fiber (WF); (3) wood fiber and peat substrate 50/50 v/v (WF/PS 50/50); (4) wood fiber and peat substrate 25/75 v/v (WF/PS 25/75). The rates of fertilization were the following: (1) conventional fertilization (CF); (2) 13 g N per plant (N13); (3) 23 g N per plant (N23); (4) 30 g N per plant (N30). The experiment was carried out with three replications. As the amount of wood fiber increased, the humidity and pH of the growing media increased. The fertilization of the cucumbers with different quantities of nitrogen influenced the nutrient uptake. The plants grown in the 50/50 and 25/75 growing media had the best Cu uptake when fertilized with N23. When the plants grown in the wood fiber media and the 50/50 media were fertilized with N13, N23, and N30, the Mn content in the growing media at the end of the growing season was significantly lower than the Mn content in the media with conventional fertilization. Thus, nitrogen improved the uptake of Mn by the plants grown not only in the wood fiber, but also in the combinations with a peat substrate. Growing plants in wood fiber and fertilizing them with N13 can result in the optimum uptake of micronutrients. The number and biomass of cucumber fruits per plant were influenced by the amount of wood fiber in the growing media and the application of nitrogen fertilizer. The highest number of fruits and biomass of fruits per plant obtained were significantly higher when the cucumbers were grown in WF/PS 50/50 growing media with additional N13 fertilization.

Rational Nitrogen Reduction Helps Mitigate the Nitrogen Pollution Risk While Ensuring Rice Growth in a Tropical Rice–Crayfish Coculture System

The incorporation of aquaculture feed within a rice–crayfish coculture system significantly enhances nitrogen cycling, thereby diminishing the reliance on chemical fertilizers. However, this benefit is often overlooked in practice, and farmers continue to use large quantities of chemical fertilizers to maximize production, resulting in excessive soil fertility and water nitrogen pollution. Thus, avoiding nitrogen pollution in rice–crayfish coculture systems has become a pressing issue. In this study, we conducted a two-year experiment with two rice cultivars, and a 33.3% reduction in nitrogen fertilizer in a rice–crayfish coculture system (RC), to systematically analyze the overall nitrogen balance, rice nitrogen nutrition, and soil fertility, as compared with a rice monoculture system (RM). Our findings revealed the following: (1) Under the 33.3% reduction in nitrogen fertilizer, the nitrogen surplus in the rice–crayfish coculture system was comparable to that in the rice monoculture, and was controlled at an environmental safety level. (2) Nitrogen utilization efficiency and the accumulation of nitrogen in the rice–crayfish coculture were comparable to those in the rice monoculture. The nitrogen cycle in this system was able to provide the nitrogen required for rice growth after nitrogen fertilizer reduction. (3) The rice–crayfish coculture significantly improved the overall soil fertility and the effectiveness of soil nitrogen nutrition. Furthermore, cutting off the application of nitrogen fertilizer after the mid-tillering stage effectively controlled the total nitrogen content in soil after rice maturity. In conclusion, reducing nitrogen fertilizer in a rice–crayfish coculture system is feasible and beneficial. It ensures rice production, reduces the risk of excessive nitrogen surplus and surface pollution, and promotes a greener, more environmentally friendly paddy field ecosystem.

The impact of nitrogen Fertilizer application on air Pollution: Evidence from China

We examine the effects of nitrogen fertilizer application on air pollution in China. Distinct from the existing literature that tends to utilize field sampling method, we construct a comprehensive panel dataset and discover that 1 g nitrogen increase in fertilizer correlates with a rise of 0.55 μg/m³ in PM2.5 concentrations. Additionally, heterogenous results across the crops indicate that rice and corn crops exacerbate air pollution, whereas the impact of nitrogen fertilizer on wheat remains ambiguous, and these effects predominantly emerge during the initial growth stages. Our findings also suggest that while the nitrogen fertilizer contributes to heightened levels of PM2.5 and SO2, it conversely leads to a reduction in ozone concentrations, which is not provided by existing studies.

The combined nitrogen and phosphorus fertilizer application reduced soil multifunctionality in Qinghai-Tibet plateau grasslands, China

The impact of nitrogen (N) and phosphorus (P) fertilizer inputs on soil nutrient cycling and ecological function processes has garnered significant attention. Soil multifunctionality primarily refers to the soil's ability to perform multiple functions simultaneously, particularly the functions related to the genes involved in carbon (C), nitrogen (N), and phosphorus (P) cycles, which are critical for ecosystem sustainability. Despite this, the effects of N and P fertilizers on the expression of genes involved in soil carbon (C), nitrogen (N), and phosphorus (P) cycles, and their consequent influence on soil multifunctionality, remain unclear. To investigate this, we conducted a long-term nine-year experiment. The experimental site was fenced to prevent grazing and included four treatments: Control (no fertilizer), N (10 g N m−2 y−1, urea), P (5 g P m−2 y−1, Ca(H2PO4)2), and NP (10 g N and 5 g P m−2 y−1, urea and Ca(H2PO4)2). We examined the effects of these treatments on soil microbial functional gene abundance and multifunctionality. Our findings revealed that N addition altered the composition of soil microbial functional genes but did not affect functional diversity. Both N and P inputs, as well as their combination, negatively impacted soil carbon fixation and the genes encoding enzymes for the degradation of starch, hemicellulose, cellulose, and chitin. N input also disrupted soil nitrogen and phosphorus cycling by inhibiting the expression of soil denitrification genes (nirS and nosZ), phytate hydrolase gene (cphy), and a phosphatase gene (phoD). Additionally, P input significantly inhibited functional genes involved in soil nitrification, denitrification, ammonification, nitrogen fixation, and ammonia oxidation processes. It also adversely affected phytate synthesis and degradation. The combined N and P inputs had a substantial negative impact on soil nitrification (hao), denitrification (narG, nirK, nirS, and norZ), ammonification (gdh), nitrogen fixation, annamox, and nitrogen reduction, and inhibited the expression of soil phosphorus cycle genes. Long-term phosphorus application was found to have a more detrimental effect on soil multifunctionality compared to nitrogen application. Furthermore, our study showed that vegetation diversity and abundance are crucial drivers of soil carbon, nitrogen, and phosphorus cycling functional genes and multifunctionality. We concluded that N and P inputs alter soil multifunctionality by influencing vegetation diversity; therefore, maintaining vegetation diversity is essential for sustaining soil multifunctionality.

Impact of a forage legume or nitrogen fertilizer application on ammonia volatilization and nitrous oxide emissions in Brachiaria pastures

ABSTRACT The largest proportion of greenhouse gas (GHG) emissions in the Agriculture sector of the Brazilian national GHG inventory is derived from the large (>200 million head) herd of cattle. The greatest contribution to these emissions comes from the enteric methane from cattle, but the direct and indirect emissions of nitrous oxide (N 2 O) from cattle excreta and N fertilizer are responsible for approximately 9 % of all national anthropogenic GHG emissions. Ammonia (NH 3 ) can be volatilized from N fertilizer and cattle excreta and deposited in sites remote from the source, constituting an indirect source of N 2 O. This study aimed to determine whether direct N 2 O emissions and NH 3 volatilization from N-fertilized pastures were greater than those derived from a mixed grass-legume pasture without N fertilizer addition. Emissions of N 2 O and NH 3 from excreta and N fertilizer from a Palisade grass (Urochloa brizantha cv. Marandu) monoculture fertilized with 2 × 60 kg N ha -1 yr -1 urea were compared to those from a mixed Palisade grass-forage peanut (Arachis pintoi) pasture. Dung and urine were collected from these cattle, and NH 3 losses and N 2 O emissions from the excreta and from N fertilizer were monitored using static chamber techniques. Volatilization of NH 3 and N 2 O emissions were found to be greater from urine than from dung. Ammonia losses from excreta and urea fertilizer were low, not exceeding 6.8, 1.1, and 4.7 % of the N applied as urine, dung, and fertilizer, respectively. The N 2 O emissions showed a tendency to be greater for the urine from the N-fertilized compared to the mixed grass-legume pasture, and the N 2 O emissions from the urine of the N-fertilized pasture ranged from 0.08 to 0.94 % of applied urine N. The N 2 O emission from the N fertilizer was at maximum 0.46 % of the applied N. The direct N 2 O emissions and the loss of NH 3 by volatilization (indirect N 2 O emission) from the excreta of cattle grazing the mixed grass-legume pasture were similar to, or lower than, the grazed grass monoculture fertilized with 120 kg N ha -1 yr -1 . As the mixed pasture received no N fertilizer and hence no GHG emission from its manufacture or application, introducing forage peanut to the Urochloa brizantha pastures shows potential to be responsible for lower GHG emissions than the N fertilized grass pasture.

Advances in the Study of NO3− Immobilization by Microbes in Agricultural Soils

The extensive application of nitrogen (N) fertilizers in agriculture has resulted in a considerable accumulation of N in the soil, particularly nitrate (NO3−), which can be easily lost to the surrounding environments through leaching and denitrification. Improving the immobilization of NO3− by soil microorganisms in agriculture is crucial to improve soil N retention capacity and reduce the risk of NO3− loss. In this paper, we reviewed the significance of microbial immobilization of soil NO3− in soil N retention, the techniques to quantify soil gross microbial NO3− immobilization rate, and its influencing factors. Specifically, we discussed the respective contribution of fungi and bacteria in soil NO3− retention, and we clarified that the incorporation of organic materials is of vital importance in enhancing soil microbial NO3− immobilization capacities in agricultural soils. However, there is still a lack of research on the utilization of NO3− by microorganisms of different functional groups in soil due to the limited techniques. In the future, attention should be paid to how to regulate the microbial NO3− immobilization to make soil NO3− supply capacity match better with the crop N demand, thereby improving N use efficiency and reducing NO3− losses.

Grain Crop Yield Prediction Using Machine Learning Based on UAV Remote Sensing: A Systematic Literature Review

Preharvest crop yield estimation is crucial for achieving food security and managing crop growth. Unmanned aerial vehicles (UAVs) can quickly and accurately acquire field crop growth data and are important mediums for collecting agricultural remote sensing data. With the rapid development of machine learning, especially deep learning, research on yield estimation based on UAV remote sensing data and machine learning has achieved excellent results. This paper systematically reviews the current research of yield estimation research based on UAV remote sensing and machine learning through a search of 76 articles, covering aspects such as the grain crops studied, research questions, data collection, feature selection, optimal yield estimation models, and optimal growth periods for yield estimation. Through visual and narrative analysis, the conclusion covers all the proposed research questions. Wheat, corn, rice, and soybeans are the main research objects, and the mechanisms of nitrogen fertilizer application, irrigation, crop variety diversity, and gene diversity have received widespread attention. In the modeling process, feature selection is the key to improving the robustness and accuracy of the model. Whether based on single modal features or multimodal features for yield estimation research, multispectral images are the main source of feature information. The optimal yield estimation model may vary depending on the selected features and the period of data collection, but random forest and convolutional neural networks still perform the best in most cases. Finally, this study delves into the challenges currently faced in terms of data volume, feature selection and optimization, determining the optimal growth period, algorithm selection and application, and the limitations of UAVs. Further research is needed in areas such as data augmentation, feature engineering, algorithm improvement, and real-time yield estimation in the future.

Metals geochemistry and ecological risk assessment in lateritic soils and their transfer to tea plants

ABSTRACT Tea plant cultivation has been demonstrated to change the physicochemical properties of soils and metal bioavailability. The present study reported the geochemistry of four selected metals (Fe, Mn, Cr, and Ni) in lateritic soil cores regarding various depths cultivated with tea plants of different ages (3, 6, and 10 years old). The ecological risk and bioaccumulation of these metals in tea plants were also evaluated. The results indicate the acidic property of tea plant cultivation soils (pH < 4.5) and highlight further soil acidification due to long-term cultivation. The soils were strongly affected by farming methods and showed high levels (average from all soil cores) of total organic carbon contents (4.0% w/w), total nitrogen (2806 mg kg−1), and total phosphorus (1730 mg kg−1). We suggest that the selected metals originated naturally, supported by a high percentage in residual fractions from the results of soil sequential extraction (over 95% for Mn, Fe, and Ni and ∼ 90% for Cr). These metals exhibited no ecological risk to the adjacent environment. Mn showed the highest bioavailability, possibly due to the acidic soils and nitrogen fertiliser applications, increasing the release of Mn from soils. Mn also exhibited the highest bioconcentration factor (BCF) among four metals and 2.4 ÷ 6.5-folds higher BCFs in tea leaves than in roots. Despite the dominant content of Fe in soils (average of 20% w/w), Fe indicated lower amounts in tea leaves than Mn (average of 513 mg kg−1 vs 1354 mg kg−1). This could be attributed to the formation of Fe-rich root coatings on the tea plant root surface as a barrier to prevent Fe from translocating to other higher tea plant parts. Ni and Cr, as potentially toxic metals, were found at the lowest contents in tea leaves with low BCFs, indicating consumer safety in terms of exposure by these metals.