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"Nitrogen fertilizers"
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Crop rotations for increased soil carbon
More diverse crop rotations have been promoted for their potential to remediate the range of ecosystem services compromised by biologically simplified grain-based agroecosystems, including increasing soil organic carbon (SOC). We hypothesized that functional diversity offers a more predictive means of characterizing the impact of crop rotations on SOC concentrations than species diversity per se. Furthermore, we hypothesized that functional diversity can either increase or decrease SOC depending on its associated carbon (C) input to soil. We compiled a database of 27 cropping system sites and 169 cropping systems, recorded the species and functional diversity of crop rotations, SOC concentrations (g C kg/soil), nitrogen (N) fertilizer applications (kg N·ha−1·yr−1), and estimated C input to soil (Mg C·ha−1·yr−1). We categorized crop rotations into three broad categories: grain-only rotations, grain rotations with cover crops, and grain rotations with perennial crops. We divided the grain-only rotations into two sub-categories: cereal-only rotations and those that included both cereals and a legume grain. We compared changes in SOC and C input using mean effect sizes and 95% bootstrapped confidence intervals. Cover cropped and perennial cropped rotations, relative to grain-only rotations, increased C input by 42% and 23% and SOC concentrations by 6.3% and 12.5%, respectively. Within grain-only rotations, cereal + legume grain rotations decreased total C input (−16%), root C input (−12%), and SOC (−5.3%) relative to cereal-only rotations. We found no effect of species diversity on SOC within grain-only rotations. N fertilizer rates mediated the effect of functional diversity on SOC within grain-only crop rotations: at low N fertilizer rates (≤75 kg N·ha−1·yr−1), the decrease in SOC with cereal + legume grain rotations was less than at high N fertilizer rates. Our results show that increasing the functional diversity of crop rotations is more likely to increase SOC concentrations if it is accompanied by an increase in C input. Functionally diverse perennial and cover cropped rotations increased both C input and SOC concentrations, potentially by exploiting niches in time that would otherwise be unproductive, that is, increasing the “perenniality” of crop rotations.
Journal Article
The California nitrogen assessment : challenges and solutions for people, agriculture, and the environment
\"Nitrogen is indispensable to all life on Earth. However, humans now dominate the nitrogen cycle and nitrogen emissions resulting from human activity involve real costs: water and air pollution, climate change, and detrimental effects for human health, biodiversity, and natural habitat. Too little nitrogen limits ecosystem processes, while too much nitrogen transforms ecosystems profoundly. The California Nitrogen Assessment is the first comprehensive accounting of nitrogen flows, practices, and policies for California; encompassing all nitrogen flows--not just those associated with agriculture--and their impacts on ecosystem services and human wellbeing. How California handles issues of nitrogen will be of interest nationally and internationally, and the goal of the assessment is to more effectively link science with action and to produce information that informs both future policy and solutions to nitrogen pollution. This book also provides a model for application of integrated ecosystem assessment methods at regional and state (sub-national) levels.\"--Provided by publisher.
Book
Nitrogen fertilizer replacement values of organic amendments: determination and prediction
The nitrogen fertilizer replacement value (NFRV) quantifies the value of organic amendments as a nitrogen (N) fertilizer, and is commonly defined as the extent to which organic fertilizer N can replace mineral fertilizer N. NFRVs can be calculated by comparing the crop N uptake from equal N application rates of mineral and organic fertilizer, or by comparing the N rates of both fertilizers needed to obtain equal crop N uptake. Currently, NFRVs are mainly known for animal manure, whereas other organic waste products may become available as fertilizer products in the future. In this study, a pot experiment with spring wheat was performed to (1) assess NFRVs of a range of organic amendments; (2) compare NFRVs based on equal N application with NFRVs based on equal N uptake; and (3) assess which product characteristics explain observed variation. Observed NFRVs varied between 6.2 and 78.8%, with the lowest value for raw food waste and the highest for fishmeal. NFRVs were overestimated when calculated based on equal N application rate (with on average 6.9% point), and more so at high N application rate (9.0% point). NFRVs should therefore be calculated based on equal N uptake from organic and mineral fertilizers. Nitrogen concentration of the organic fertilizer provided the best explanation of variation observed in NFRVs (R
2
= 0.86). These findings give valuable insights into the large variation in value of organic waste streams as organic fertilizer and can support decisions on sustainable N application rates, to increase crop N uptake and reduce N losses to the environment.
Journal Article
Fate of fertilizer nitrogen from a winter wheat field under film mulching and straw retention practices
A comprehensive understanding of the transformation, migration and loss pathways of nitrogen (N) fertilizer was pivotal for optimum nutrient management. Three different cultivation practices (conventional cultivation, plastic film mulching and straw retention) and N rates (0, 144 and 180 kg N ha
−1
) were assigned as the main plots and split plots separately in a split-plot design during 2017–2020. Moreover
15
N-labeled urea was used in each microplot to trace the fertilizer N fate. The results showed that the N recovery efficiencies with plastic film mulching, straw retention and conventional cultivation were 44–46%, 34–37% and 43–44% in the first season. However, it sharply decreased in the next two seasons. The N residual rates in straw retention and plastic film mulching were 21–26% and 20–27% after three wheat seasons, which were higher than that in conventional cultivation. Furthermore, residual nitrate nitrogen was detected in the deep profiles in plastic film mulching and straw retention at the third season. The ammonia volatilization sourced from fertilizer was 3–5 kg ha
−1
in the first season and accounted for 2–3% of the total applied N. Overall, plastic film mulching treatment increased fertilizer N utilization by plants and residual fertilizer N in soil, and reduced unidentified fertilizer N. Although, straw retention depressed fertilizer N uptake by plants, it improved the N budget and had the potential to reduce N input. Accordingly, plastic film mulching and straw retention are recommended in dryland wheat cropping systems. However, we should pay attention to the residual plastic pollution in the practice.
Journal Article
Response of symbiotic and asymbiotic nitrogen-fixing microorganisms to nitrogen fertilizer application
PurposeBiological nitrogen fixation (BNF) plays an important role in nitrogen cycling by transferring atmospheric dinitrogen to the soil. BNF is performed by symbiotic and asymbiotic nitrogen-fixing microorganisms. However, the abundance, activity, and community structure of diazotrophs under different nitrogen fertilizer application rates and how root exudates influence diazotrophs remain unclear.Materials and methods15N-N2 and 13C-CO2 labeling, DNA-based stable isotope probing (SIP), and molecular biological techniques were used in this study. The abundance, activity, and structure of symbiotic and asymbiotic diazotrophs under different nitrogen fertilizer applications in paddy soil were investigated.Results and discussionWe found that the nitrogen fixation capacity in milk vetch (Astragalus sinicus L.) and nifH gene abundance in the root nodules were significantly higher in the low-nitrogen treatment than in the control (zero) and high-nitrogen treatments. Nitrogen-fixing bacteria were abundant in the soils with a high biodiversity. Soil nifH gene sequences were dominated by α-, β-, and δ-proteobacteria, as well as by Cyanobacteria. The relative abundance of α-proteobacteria was lower, and the relative abundance of Cyanobacteria was higher under high nitrogen. Incubation of soil with 13CO2 and subsequent DNA-SIP analysis demonstrated that OTU65 from α-proteobacteria was relatively more abundant in heavy fractions of the 13C-labeled soils than that in the unlabeled soils, indicating that α-proteobacteria may prefer rhizodeposition carbon to other organic carbon. However, OTU24 and OTU73 from δ-proteobacteria had relatively high abundances in light fractions both in the 13C-labeled and unlabeled samples, indicating that δ-proteobacteria may prefer other soil organic carbon to rhizodeposition carbon.ConclusionsThe results suggested that soil N availability and rhizodeposition strongly modified the microbial communities of nitrogen-fixing bacteria. Moderate nitrogen application increased the symbiotic biological N fixing activity in the Astragalus sinicus L. rhizosphere. The BNF activity in the legume-rhizobia system is regulated by the exchange of organic C and N nutrient between the host plant and N-fixing bacteria.
Journal Article
Deep nitrogen fertilizer placement improves the yield of summer maize (Zea mays L.) by enhancing its photosynthetic performance after silking
Background
Effective nitrogen (N) fertilizer management can improve photosynthetic performance of maize and enhance the grain yield. However, the effects of the deep placement of N on post-silking photosynthetic performance in maize and its relationship with grain filling are limited. The study was a split-plot design with N application rates as the main plots and N placement depths as sub-plots. The N application rates consisted of 225, 191.25, and 157.5 kg ha
− 1
and N placement depths consisted of 5 and 15 cm, respectively. The growth parameters, photosynthetic capacity, subcellular ultrastructure, antioxidant system in maize leaves, and grain filling characteristics were measured.
Results
Increasing the N placement depth counteracted the adverse effects of reduced N availability on the leaf area index, leaf area duration, and photosynthetic performance of plants. Compared to 225 kg N ha
− 1
applied underground at 5 cm, a 15% reduction in the N application rate at 15 cm reduced oxidative stress through the activation of antioxidative enzymes, which enabled plants to maintain their chloroplast ultrastructure, achieving 20.7% higher chlorophyll content, 7.8% higher photosynthetic rate per unit of leaf area, and 5.6% higher leaf area index during the later growth period. It also facilitated enhancing the growth rate during maximum filling and extending the active filling duration of grains.
Conclusions
Overall, reducing the recommended N application rate of 225 kg ha
− 1
by 15% but applying it at a depth of 15 cm might delay plant senescence and extend grain filling active time, improved photosynthetic performance in late growth period, and finally increased grain weight and grain yield of maize.
Journal Article
Impact of N application rate on tea (Camellia sinensis) growth and soil bacterial and fungi communities
Purpose
Applying excessive N is a common strategy in tea plantations. Fungal and bacterial responses to N fertiliser addition in tea plantations, especially their relationship with tea growth, quality, and soil microbiome composition, remain unclear.
Methods
We performed a field experiment using different N fertiliser application rates for 5 years (2016‒2020) in a tea-producing region of China.
Results
The N application rate of 360 kg ha
−1
y
−1
achieved the highest tea yield and quality. Bacterial diversity and community responses to N addition were more apparent than fungal diversity and community responses. Partial least square path modelling suggested that N addition directly affected the diversity and communities of bacteria and fungi and indirectly affected bacterial community and fungal diversity by altering soil contents. N fertiliser application contributed to tea growth but did not maintain high microbial diversity.
Conclusion
Fungal alpha and beta diversity had a greater effect on tea yield and quality than bacterial diversity; therefore, more attention should be given to fungi such as ligninolytic and cellulolytic taxa, which play a stable role in nutrient cycling and organic matter decomposition in tea plantations, favouring tea growth in the long term.
Journal Article
Agricultural Non-Point Source Pollution in China: Causes and Mitigation Measures
Non-point source (NPS) pollution has been increasingly serious in China since the 1990s. The increases of agricultural NPS pollution in China is evaluated for the period 2000−2008 by surveying the literature on water and soil pollution from fertilizers and pesticides, and assessing the surplus nitrogen balance within provinces. The main causes for NPS pollution were excessive inputs of nitrogen fertilizer and pesticides, which were partly the result of the inadequate agricultural extension services and the rapid expansion of intensive livestock production with little of waste management. The annual application of synthetic nitrogen fertilizers and pesticides in China increased by 50.7 and 119.7%, respectively, during 1991−2008. The mitigation measures to reduce NPS pollution include: correct distortion in fertilizer prices; improve incentives for the recycling of organic manure; provide farmers with better information on the sound use of agro-chemicals; and tighten the regulations and national standards on organic waste disposal and pesticides use.
Journal Article
Nitrogen rate impacts on tropical maize nitrogen use efficiency and soil nitrogen depletion in eastern and southern Africa
Sub-Saharan Africa is facing food security challenges due, in part, to decades of soil nitrogen (N) depletion. Applying N fertilizer could increase crop yields and replenish soil N pools. From 2010 to 2015, field experiments conducted in Embu and Kiboko, Kenya and Harare, Zimbabwe investigated yield and N uptake response of six maize (
Zea mays
L.) hybrids to four N fertilizer rates (0 to 160 kg N ha
−1
) in continuous maize production systems. The N recovery efficiency (NRE), cumulative N balance, and soil N content in the upper 0.9 m of soil following the final harvest were determined at each N rate. Plant and soil responses to N fertilizer applications did not differ amongst hybrids. Across locations and N rates, NRE ranged from 0.4 to 1.8 kg kg
−1
. Higher NRE values in Kiboko and Harare occurred at lower post-harvest soil inorganic N levels. The excessively high NRE value of 1.8 kg kg
−1
at 40 kg N ha
−1
in Harare suggested that maize hybrids deplete soil inorganic N most at low N rates. Still, negative cumulative N balances indicated that inorganic soil N depletion occurred at all N rates in Embu and Harare (up to − 193 and − 167 kg N ha
−1
, respectively) and at the 40 kg N ha
−1
rate in Kiboko (− 72 kg N ha
−1
). Overall, maize N uptake exceeded fertilizer N applied and so, while yields increased, soil N pools were not replenished, especially at low total soil N levels (< 10,000 kg N ha
−1
in top 0.9 m).
Journal Article