Improve Fertilizer Use Research Articles

A mechanistic model for determining factors that influence inorganic nitrogen fate in corn cultivation.

Conventional practices for inorganic nitrogen fertilizer are highly inefficient leading to excess nitrogen in the environment. Excess environmental nitrogen induces ecological (e.g., hypoxia, eutrophication) and public health (e.g., nitrate contaminated drinking water) consequences, motivating adoption of management strategies to improve fertilizer use efficiency. Yet, how to limit the environmental impacts from inorganic nitrogen fertilizer while maintaining crop yields is a persistent challenge. The lack of empirical data on the fate and transport of nitrogen in an agriculture soil-crop system and how transport changes under varying conditions limits our ability to address this challenge. To this end, we developed a mechanistic model to assess how various parameters within a soil-crop system affect where nitrogen goes and inform how we can perturb the system to improve crop nitrogen content while reducing nitrogen emissions to the environment. The model evaluates nitrogen transport and distribution in the soil-corn plant system on a conventional Iowa corn farm. Simulations determine the amount of applied nitrogen fertilizer acquired by the crop root system, leached to groundwater, lost to tile drainage, and denitrified. Through scenario modeling, it was found that reducing application rates from 200 kg ha-1 to 160 kg ha-1 had limited impact on plant nitrogen content, while decreasing wasted nitrogen fertilizer by 25%. Delayed application until June significantly increased the f-NUE and denitrification while reducing the amount of fertilizer leached and exported through tile drainage. The value in a model like the one presented herein, is the ability to perturb the system through manipulation of variables representative of a specific scenario of interest to inform how one can improve crop-based nitrogen management.

Reuse of biogas sludge for the slow-release fertilizer production to improve fertilizer use efficiency and soil fertility

Fertilizer overuse causes negative impacts on the environment and crop yields. Therefore, the production of slow-release fertilizers from biogas sludge is a potential solution for waste reuse and sustainable use of fertilizers. Granular fertilizers containing primary macronutrients (N, P and K) were formulated using biogas sludge and supplementary chemical compounds before coating with a thin film of glutaraldehyde cross-linked gelatin. The coating films reduced the release rates of N and P effectively. The application of formulated biogas fertilizers resulted in the competitive yield and growth rate of mustard greens over the 45-days cultivation compared to the application of commercial fertilizers. Particularly, the application of coated biogas fertilizers led to less nutrient losses in drainage water while maintained a balanced supply of available nutrients and beneficial bacteria in soils. This study emphasizes the feasibility to reuse biogas sludge for slow-release fertilizers production in improving fertilizer use efficiency and soil fertility.

Optimizing rice yield, quality and nutrient use efficiency through combined application of nitrogen and potassium.

Reasonable nitrogen (N) and potassium (K) application rates can effectively improve fertilizer use efficiency, rice yield and quality. A two-year field experiment was conducted with combined application of three N rates (135, 180, and 225 kg ha-1, denoted as N1-N3) and four K rates (0, 90, 135, and 180 kg ha-1, denoted as K0-K3) using super indica hybrid rice cultivar Yixiangyou (YXY) 2115 to explore the effects of co-application of N and K on rice growth and development. The results indicated that the combined application of N and K had significantly interactive effects on dry matter (DM) accumulation, nutrients absorption, N harvest index (NHI), K harvest index (KHI), spikelets per panicle and most rice quality indexes. The highest total DM accumulation (17998.17-19432.47 kg ha-1) at maturity stage was obtained under N3K2. The effect of co-application of N and K on nutrients absorption and utilization varied between the two years and within each year. The highest total N and K accumulations at maturity stage were observed under N3K1 and N3K2, respectively, while the highest N recovery efficiency (NRE) and K recovery efficiency (KRE) were observed under N1K3. High expression levels of N and K metabolism-related genes in rice grains were observed under N3K2 or N3K3, consistent with N and K uptake. Co-application of N and K increased rice yield significantly and the highest yield (6745.02-7010.27 kg ha-1) was obtained under N2K2. As more N was gradually applied, rice appearance quality improved but milling, cooking and eating quality decreased. Although appropriate application of K could improve rice milling, cooking and eating quality, it reduced appearance quality. The optimal milling, cooking and eating quality were obtained under N1K2, while the best appearance quality was obtained under N3K0. Overall, a combination of 135-210 kg ha-1 N and 115-137 kg ha-1 K application rates was recommended for achieving relatively higher yield and better quality in rice production.

Impacts of chemical fertilizer reduction on grain yield: A case study of China.

Reducing fertilizer usage is a crucial measure for achieving high-quality development in Chinese agriculture. Utilizing panel data from 31 Chinese provinces spanning from 2004 to 2019, this study empirically analyzes the dynamic relationship between fertilizer application and grain production, exploring the underlying mechanisms. The study findings reveal that the application of fertilizers maintains a positive impact on grain production. The two variables will demonstrate a dynamic alternation between "strong decoupling" and "retreat decoupling," suggesting that grain production may either increase or gradually decline, while fertilizer application exhibits a decreasing trend. Mechanism analysis reveals a distinct substitution relationship between fertilizer use efficiency and application quantity. Increasing fertilizer use efficiency while reducing application quantity still facilitates the stable and increased production of grains. Heterogeneity analysis indicates that the efficiency of fertilizer use has a more pronounced impact on grain yield in the eastern and western regions. Increasing fertilizer quantity is detrimental to wheat yield but has a promoting effect on corn yield. However, in the main grain-producing areas, increasing fertilizer quantity can enhance wheat yield but is unfavorable for the overall grain yield. Additionally, nitrogen fertilizer input has exceeded the optimal level compared to potassium fertilizer. Continuously increasing nitrogen fertilizer input will hinder the increase in grain yield. Therefore, there is a need to shift from the notion of "more fertilizer is better" and focus on improving fertilizer use efficiency to transition from the emphasis on "quantity" to "quality" of fertilizer application.

NITROGEN USE EFFICIENCY IN SUNFLOWER (HELIANTHUS ANNUUS L.) INFLUENCED BY VARIOUS FERTIGATION AND BED PLANTING TECHNIQUES

Low nitrogen fertilizer use efficiency and high losses of nitrogen are the critical challenges being faced by sunflower grower. To address these concerns, an experiment was carried out during spring 2021 at the Agronomic research area of the Agriculture University, Faisalabad. The randomized complete block design experiment was used with three replications under split plot arrangement. The 5m x 3m net plot size was kept with sowing procedures retained in the main plot and nitrogen application techniques kept in the sub plot. The experiment was planted on 20-02-2021. The matured crop was reaped on 18 June, 2021 manually. The single row hand drill was used to sow sunflower crop. The 75 cm line to line and 25 cm plant to plant distance was maintained. The results indicated that plant population ranged from 73 to 74 with maximum plant height of 174.33 cm, stem diameter (3.70 cm), head diameter (23.13 cm), number of achenes per head (1237.6), 1000-achene weight (68.17 g), highest biological yield (10.92 t ha-1), achene yield (3.22 t ha-1), harvest index (29.48 %) and protein contents (29.03 %) was observed in treatment where nitrogen was applied by fertigation method and sunflower was sown on beds. But maximum oil contents (41.78 %) were observed where nitrogen was side dressed and flat sowing technique was adopted for crop sowing. It is found that use of fertigation method of nitrogen application and bed planting techniques proved to be the best combination for improving growth, yield & yield relating attributes and improve fertilizer use efficiency with lower nitrogen losses for sunflower (Hybrid-33) under agro-climatic conditions of Faisalabad.

Comprehensive study of on-the-go sensing and variable rate application of liquid nitrogenous fertilizer

Variable rate technology (VRT) provides a sustainable, efficient, and cost-effective nutrient application option. A pioneered study is carried out to develop a variable rate liquid fertilizer application system to detect on-the-go deficiency of Nitrogen within a field and apply it according to the requirement of crop. The system includes microcontroller, nitrogen sensor (i.e. Green-seeker sensor), proportional solenoid valve, pressure relief valve, pump, battery, etc. Microcontroller receives a signal from Green-seeker sensor and it transmits to the proportional solenoid valve (PSV). The PSV opening is change based on the prescribed nutritional dose. The experimental study is conducted on groundnut crop. The experiment is carried out for different level of fertilizer (N1-150, N2– 200, N3-250, and N4-300 l ha−1) as well as different operating speed is 3, 4, 5 km h−1 to estimate actual fertilizer dropped (AFD), % error, droplet size, droplet density (DD), uniformity coefficient (UC), and spray deposition. The response time of the system is in the range of 1.12 s to 1.80 s. It is observed from the experimental study that the error in the fertilizer to be dropped and AFD increases with increase in the speed of operation. The percentage error is found to be 2.73 %, which is the lowest one, at 3 km h−1 operating speed. The maximum droplet size is found to be 272.5 μm at 5 km h−1 forward speed and 300 l ha−1 nitrogen application rate, whereas minimum droplet size is found to be 241.23 μm at 3 km h−1 forward speed and 150 l ha−1 nitrogen application rate. The present study proposes maximum of 24.30 % saving in the fertilizer application for groundnut crop. Thus, the present system improved fertilizer use efficiency, profitability while minimizing environmental hazards.

Bibliometric and literature review of the development of mineral fertilizers.

Mineral fertilizers are a new type of sustainable fertilizers, containing natural ores as the primary raw material with various nutrients and organic matters. This study combines two methods of bibliometric analysis to comprehensively review the progress of mineral fertilizers from 2000 to 2021. The results showed that the research on mineral fertilizers has increased in the past 21years, especially after 2014. Developed countries studied mineral fertilizers more extensively than developing countries, but some developing countries, such as China and India, are also paying attention to this area in recent years. Chinese Academic of Sciences, Agriculture and Agri-Food Canada, and Chinese Academy of Agricultural Sciences were the main publishing institutions. Nutrient elements, changes in soil properties, and the effects on promoting crop growth were the main contents of the research. Still, such issues as bioremediation, soil environment improvement, and crop resistance are becoming hot spots. The field of mineral fertilizers showed a strong interdisciplinary nature and an increasingly comprehensive research perspective. The goal is that this synthesis will be used as a starting point for a broader study on responsible environmental management and research on improving fertilizer use efficiency.

Water and Nitrogen Balance under Various Water and Fertilizer Regulation Modes

A experiment was conducted at the Jiangxi Province Center Station of Irrigation Experiment from 2019 to 2021 to study the water and nitrogen balance under water and fertilizer regulation modes. The study aimed to propose a recommended mode for paddy fields that could save water, control pollution, reduce gas emission, and improve fertilizer use efficiency. This study examined the impact of different irrigation methods and nitrogen application levels on water saving and emission reduction in paddy fields. The experiment included six treatments, which involved two irrigation methods (intermittent irrigation and flooding irrigation, referred to as W1 and W0, respectively) and three application rates of nitrogen fertilizer (0 kg/ha, 135 kg/ha, 180 kg/ha, referred to as N0, N1 and N2, respectively). The study found that irrigation methods had a significant effect on the amount of irrigation, drainage, leakage, nitrogen load from drainage, soil nitrification potential, and ammonia volatilization. The results showed that compared to flooding irrigation, intermittent irrigation reduced the amount of irrigation, drainage, leakage and nitrogen load from drainage by an average of 25.98%, 16.03%, 8.43% and 10.86%, respectively. However, the study also found that the nitrification potential and ammonia volatilization increased by an average of 6.45% and 4.32%, respectively. Fertilization levels had a significant effect on drainage nitrogen load, early soil nitrification potential and ammonia volatilization. Compared with the treatment of N2 (180 kg N/ha), the drainage nitrogen load under the treatment of N1 (135 kg N/ha) decreased by 10.86% on average, while nitrification potential and ammonia volatilization increased by 38.74% and 3.33%, respectively. In terms of nitrogen output, the amount of nitrogen absorbed by crops was the largest, followed by the nitrogen load from field drainage, then ammonia volatilization, and then denitrification. Considering the goals of water saving, emission reduction, and the efficient utilization of water and fertilizer in paddy fields, the optimal water and fertilizer regulation mode was the W1N1 mode (intermittent irrigation combined with reduced nitrogen fertilizer application rate, 135 kg N/ha).

Impact of social networks on fertilizer use efficiency in China: Evidence from kiwifruit production in Shaanxi province.

Improving fertilizer use efficiency (FUE) is an effective way to reduce the fertilizer use and non-point source pollution in agriculture production in China. Existing research related to fertilizer use efficiency ignores the impact of famers' social networks, which can significantly affect the fertilizer use and its efficiency. This paper analyzed the impact of social networks on fertilizer use efficiency and the mediator effect of green fertilization technology adoption, based on the calculation of fertilizer use efficiency of 569 kiwifruit farmers in Shaanxi province of China surveyed in 2021 by using stochastic frontier method. The results show that the FUE of kiwifruit production ranged within 0.1027-0.9945, with an average value of 0.333, which showed great variability, and fertilizer input had an average 66.7% reduction potential without reducing output. Social networks and its four dimensions all had a significant positive impact on FUE, in which network trust and network learning had a greater impact on FUE. Farmers' adoption of green fertilization technology played a positive mediator effect in the process of social networks influencing their fertilizer use efficiency, which was mainly promoted by network trust and learning. Farmers' experience in agricultural production, joining the cooperative, the quantity of village agricultural supply points had a significant positive impact on fertilizer use efficiency, while age and gentle of the head of household had a significant negative impact of fertilizer use efficiency. Planting scale had a U-shape impact on FUE. Policies aimed at improving FUE and reducing non-point source pollution should, therefore, focus on improving the social networks of farmers, especially young farmers, strengthening network trust, promoting network learning, network reciprocity and network interaction, strengthening the research and development and extension of green fertilization technology, encouraging farmers to join agricultural cooperative, improving village production conditions, guiding sustainable agricultural production.

Effects of Nitrogen Applications on Transpiration, Physiological, and Growth Characteristics of Sugarcane (Saccharum spp.)

Improving fertilizer and water use efficiencies is an important strategy in agricultural production. This study aimed to evaluate the effect of nitrogen fertilization on the daily whole-plant transpiration, growth, and physiological activities of sugarcane. The pot experiment was conducted under glass-house conditions. Five treatments of various nitrogen application rates (0, 4, 8, 12, and 16mM) were assigned in a randomized complete block design with three replications. The result showed that higher nitrogen applications led to higher growth, physiological, and biomass parameters. Nevertheless, biomass nitrogen use efficiency and photosynthetic water use efficiency declined because of applying nitrogen at higher rates. During the first weeks of plant growth, no significant differences in plant height, leaf number, SPAD, and whole-plant transpiration among nitrogen treatments indicated that higher nitrogen added was not necessary during this time. Nitrogen and water use efficiencies could be improved if the remaining soil nitrogen and crop growth stage nitrogen requirements are estimated in cultivation practice.

Nanofertilizers: Types, Delivery and Advantages in Agricultural Sustainability

In an alarming tale of agricultural excess, the relentless overuse of chemical fertilizers in modern farming methods have wreaked havoc on the once-fertile soil, mercilessly depleting its vital nutrients while inflicting irreparable harm on the delicate balance of the surrounding ecosystem. The excessive use of such fertilizers leaves residue on agricultural products, pollutes the environment, upsets agrarian ecosystems, and lowers soil quality. Furthermore, a significant proportion of the nutrient content, including nitrogen, phosphorus, and potassium, is lost from the soil (50–70%) before being utilized. Nanofertilizers, on the other hand, use nanoparticles to control the release of nutrients, making them more efficient and cost-effective than traditional fertilizers. Nanofertilizers comprise one or more plant nutrients within nanoparticles where at least 50% of the particles are smaller than 100 nanometers. Carbon nanotubes, graphene, and quantum dots are some examples of the types of nanomaterials used in the production of nanofertilizers. Nanofertilizers are a new generation of fertilizers that utilize advanced nanotechnology to provide an efficient and sustainable method of fertilizing crops. They are designed to deliver plant nutrients in a controlled manner, ensuring that the nutrients are gradually released over an extended period, thus providing a steady supply of essential elements to the plants. The controlled-release system is more efficient than traditional fertilizers, as it reduces the need for frequent application and the amount of fertilizer. These nanomaterials have a high surface area-to-volume ratio, making them ideal for holding and releasing nutrients. Naturally occurring nanoparticles are found in various sources, including volcanic ash, ocean, and biological matter such as viruses and dust. However, regarding large-scale production, relying solely on naturally occurring nanoparticles may not be sufficient or practical. In agriculture, nanotechnology has been primarily used to increase crop production while minimizing losses and activating plant defense mechanisms against pests, insects, and other environmental challenges. Furthermore, nanofertilizers can reduce runoff and nutrient leaching into the environment, improving environmental sustainability. They can also improve fertilizer use efficiency, leading to higher crop yields and reducing the overall cost of fertilizer application. Nanofertilizers are especially beneficial in areas where traditional fertilizers are inefficient or ineffective. Nanofertilizers can provide a more efficient and cost-effective way to fertilize crops while reducing the environmental impact of fertilizer application. They are the product of promising new technology that can help to meet the increasing demand for food and improve agricultural sustainability. Currently, nanofertilizers face limitations, including higher costs of production and potential environmental and safety concerns due to the use of nanomaterials, while further research is needed to fully understand their long-term effects on soil health, crop growth, and the environment.

Absolute environmental sustainability assessment of rice in Pakistan using a planetary boundary-based approach

The increasing anthropogenic pressure with high food demands requires fundamental changes in global food production practices while respecting the environmental and resource limits of the Earth. Half of the world population consume rice as a staple food which is grown in more than a hundred countries. This study aimed at evaluating the environmental repercussions of rice production in Pakistan following a novel approach. The adopted methodology, planetary boundary-based life cycle assessment, enabled the evaluation of the sustainable limits while respecting the carrying capacity of the Earth. The results revealed that the rice production had considerable impacts in terms of global warming (5632 ± 17.8 % kg CO2 eq), freshwater eutrophication (0.67 ± 43.5 % kg P eq), and water use (3928 ± 12.7 % m3) per tonne of milled rice; contributing to the triple planetary crisis, viz., global warming and nutrient pollution as well as unsustainable use of valuable resources. Field emissions due to microbial activity of methanogenic bacteria, fossil-based irrigation processes, and agrochemical applications were identified as the hotspots. Sensitivity analysis revealed that yield increment could be a beneficial approach to reduce environmental burdens; particularly where the impacts were surpassing the sustainable limits. Furthermore, sensitivity and uncertainty analyses also confirmed the obtained results for most of the impact categories (global warming, freshwater eutrophication, and water use) were significantly higher than the considered sustainable limits. Environmentally friendly irrigation systems, improved fertilizer use efficiency, and short-duration rice varieties with higher yield were recommended due to the substantial impacts reduction potential.

Prediction of soybean yield cultivated under subtropical conditions using artificial neural networks

AbstractMathematical models that incorporate biotic and abiotic attributes are important tools for improving fertilizer use efficiency and reducing production costs for soybean [Glycine max (L.) Merrill] crop. In this study, artificial neural networks (ANNs) were used to estimate soybean grain yield (GY) under subtropical conditions in Brazil from plant morphological and nutritional data collected from 16 cultivars in two growing seasons. The ANNs were adequately trained, with a mean squared error of approximately 10−5 between the outputs obtained (via ANN) and desired (via experimental field), equivalent to a mean percentage error of 70.1 kg ha−1 (1.6%), confirming their efficacy as a tool to estimate GY. Smaller plant height, higher foliar calcium, magnesium and chlorophyll concentrations, and greater numbers of grains per pod and branches per plant were associated with higher GY, whereas oil content, crude protein content, and foliar manganese and potassium concentrations had no predicted effects on GY.

Effect and Mechanism of Rice-Pasture Rotation Systems on Yield Increase and Runoff Reduction under Different Fertilizer Treatments

This study investigated the effects of crop rotations and different ratios of dairy manure fertilizer on nitrogen loss and rice yield in the Erhai Lake basin. Two kinds of herbages were set in the rotation: Ryegrass (Lolium multiflorum cv.‘Tetragold’) (R) and Villose Vetch (Vicia villosa var. Glabresens) (V). The experiment involved two-year field tests with nine management treatments. The results showed that the rice-Vicia villosa rotation with 70% chemical and 30% dairy cattle manure fertilization increased rice yield significantly, while reducing nitrogen runoff losses and increasing microbial abundance with nitrification and nitrogen fixation. The microbial abundance varied among tested soils, with Alphaproteobacteria, Rhodopseudomonas, Rhizobiales, Bradyrhizobium, and Azotobacter Vinelandii being the highest in 70% chemical fertilizer + 30% manure rice Villose Vetch (R-V) to ameliorate plant growth and strengthen the efficiency of nutrient uptake, whereas that of Planctomycete was comparatively lower to promote long-term N stabilization in soil. The 70% F—30% M R-V treatment also significantly decreased nitrate reductase and ammonia monooxygenase enzyme activity, potentially improving fertilizer use efficiency, and reducing gaseous losses. The LEfSe analysis results indicated that 70% F—30% M R-V fertilizers significantly enhanced the abundances of metabolic genes related to energy and nitrogen. These findings suggested that appropriate agricultural management using rice-Vicia villosa rotation and 70% chemical + 30% dairy cattle manure fertilization can improve the soil quality and sustainability of agroecosystems.

Role of Biologicals in Enhancing Nutrient Efficiency in Corn and Soybean

National, state, and regional corn and soybean yields continue to set new production records, and with and these higher yields come a larger nutrient requirement per land area. Improvements in fertilize use efficiency are needed to sustain high yields while mitigating off-target nutrient movement. Are biologicals the key? There has been a surge of biological products coming to market with claims to enhance soil nutrient supply and/or improve fertilizer use efficiency. However, not all products are created equal, and each performs in a unique way, resulting in questions of which product types work, where and how they work, and most importantly, what other management practices help realize the full economic benefit of these biological products. Earn 1 CEU in Nutrient Management by reading this article and taking the quiz at https://web.sciencesocieties.org/Learning-Center/Courses.

Climate Resilient Agriculture Practices - The Future of Farming

Climate-resilient agriculture (CRA) harnesses the intrinsic roots of agricultural and oxen production systems to generate increased long-term yields and farm income through sustainability. This review paper aims to draw attention to climate-resilient farming practices for medicinal plants and other cereal crops. There are several techniques and strategies that can be used to adapt to climate change, including yield-tolerant strains in poultry and cattle, Feed administration, irrigation, Agro-consulting and clay organic carbon. Governmental climate change adaptation programs such as the National Action Plan on Climate Change (NAPCC), the Pradhan Mantri Krishi Sinchayee Yojana (PMKSY), the Indian Council of Agricultural Research (ICAR), the Paramparagat Krishi Vikas Yojana and the Mahatma Gandhi National Rural Employment Guarantee Act (MGNREGA) continue to be implemented. Agriculture in India offers a living for the bulk of the populace and should never be disregarded. Increased demand for quantity, healthful food and diversity, as well as globalization effects and rising median income, would be revealed by India's growing population, globalization effects and increasing median income. Nutrient deficiencies in Indian soils, Imbalanced fertilizer application and Lack of Nitrogen-fixing crops have all caused significant climatic stress in India and the rest of the world. Various programs and policies, such as the Soil Health (Vitality) Card Scheme, are in place to improve fertilizer use efficiency. This cultivation practice pays attention to maintaining the environmental balance and bio-dynamization of agricultural systems so that ethical yield can be obtained.

Magnetized Water Irrigation Alleviates Emitter Clogging of a Drip Fertigation System

Drip fertigation systems are a new technology to alleviate water shortages and improve fertilizer use efficiency. Emitter clogging is the main obstacle to their application. However, few efficient, safe, and environmentally friendly methods are available to alleviate clogging. In this study, we explored the effects of magnetized water irrigation on emitter clogging at different fertilization levels. Field experiments were conducted to study the patterns and clogging characteristics of drip irrigation systems during two planting seasons. The results showed that with an increase in fertilizer application, clogging of the emitter was aggravated. Magnetization treatment effectively relieved emitter clogging, which increased the average discharge variation rate (Dra) by 4.1–29.0% and 2.6–64.4%, respectively, and decreased the dry weight (DW) of the clogging substance by 14.0–64.6% and 15.0–75%, respectively, in the two planting seasons, compared with that of the non-magnetization treatment. The composition of the main clogging substances was estimated using X-rays; the results showed that quartz, silicate, and carbonate were the dominant substances that induced emitter clogging. Magnetization treatment can reduce the content of clogging substances and is thus a possible mechanism to alleviate clogging. Our study demonstrated that water magnetization treatment is an effective, chemical-free treatment method with great potential for clogging control in drip fertigation systems.

Hydrological regulation of nitrate sources, transformation and transport pathway in a karstic river

A comprehensive understanding of nitrate dynamics in rivers is vital for nitrogen management, especially for the karst zone with high leaching of nitrate producing potential risk to environmental quality. However, identification of the source-transformation-pathway of nitrate is limited in the karst rivers. Thus, a suit of hydrogeochemical parameters, including δ15N-NO3−, δ18O-NO3−, δ13C-DIC, δ18O-H2O, soil-related parameters (DOC) and geogenic ions (Mg2+, DIC), were used to identify nitrate sources and dynamics in the Wujiang River, a typical karstic river as a tributary of Changjiang River. The combined use of a conceptual model of normalized NO3− and DOC, and other hydrogeochemical parameters (δ13C-DIC, Mg2+, DIC) suggested that most nitrates were transported through the soil/epikarst pathway in the wet season, whereas >70 % of nitrates were transported through groundwater pathway in the dry season for Wujiang River. Nitrification and mixing were the dominant processes, meanwhile ∼31 % of nitrate was denitrified in the wet season in this study. The reanalysis of δ15N-NO3− and δ18O-NO3− values for reported karstic rivers in China and worldwide also revealed the predominant nitrification and denitrification in karst regions. The Bayesian model indicated that chemical fertilizer (CF, 42 %) and soil organic nitrogen (SON, 32 %) contributed the most in the wet season, while ∼60 % of nitrate originated from SON (31 %) and manure and sewage wastes (M&S, 30 %) in the dry season in the Wujiang River. The sustained contribution of non-point sources from nitrification through the soil/epikarst pathway might be related to the widespread porosities in the karst rivers. Thus, measures to reduce nitrogen leaching and improve fertilizer use efficiency should be considered, like water and soil conservation, slow-release fertilizer and nitrification inhibitors. Additionally, a suit of hydrogeochemical indicators proves to be helpful for identification of source, transformation and transport pathway of nitrate in the karst basin.

The theoretical potential for tailored fertilizer application. The case of maize in Sub-Saharan Africa

Adjusting crop nutrient rates to local differences in soil fertility and yield potential is considered a promising way of improving fertilizer use efficiency in smallholder agriculture. Despite its obvious appeal, the benefits of this approach have not been evaluated empirically. In the absence of appropriate data, the theoretical potential of nutrient tailoring needs to be evaluated, and suitable models exist to do this. Such analysis may provide a benchmark for expectations of success and would form a valuable starting point for reflection and debate on the limitations of current data, models, and assumptions. This study presents a theoretical ex-ante assessment of the short-term economic benefits of fertilizer adjustments to differences in nutrient and water constraints, under the assumption that these are the only determinants of nutrient response. Combining two calibrations of a mathematical production function with digital maps of predicted nutrient and water availability, economically optimum macro-nutrient rates and resulting maize yields were calculated across a theoretical representation of soils across Sub-Saharan Africa. Consistent economic benefits from fertilizer application were predicted, raising theoretical yields from 19 to as much as 61 or 88% of water limited levels depending on the model used. Under the magnitude of soil fertility variation considered here, matching nutrient rates to indigenous levels was predicted to result in marginal added benefits at best, particularly at higher, more profitable, investment levels. Strong spatial heterogeneity in water limitation translated into more pronounced effects of rate adjustments to water limited yields, raising average predicted profit by up to 127 USD/ha compared to a fixed-rate recommendation. This suggests that tailoring to different yield levels can offer non-trivial benefits if good estimates of yield potential are available. Adding realistic levels of uncertainty around soil fertility and use efficiency parameters reduced predicted gain from tailoring and suggested that acquiring sufficient experimental data for improved nutrient recommendations, both general and specific, may be challenging. The implications and limitations of these theoretical results and potential improvements in validation, predictions and outcomes are discussed.

EgNRT2.3 and EgNAR2 expression are controlled by nitrogen deprivation and encode proteins that function as a two-component nitrate uptake system in oil palm

Oil palm (Elaeis guineensis Jacq.) is an important crop for oil and biodiesel production. Oil palm plantations require extensive fertilizer additions to achieve a high yield. Fertilizer application decisions and management for oil palm farming rely on leaf tissue and soil nutrient analyses with little information available to describe the key players for nutrient uptake. A molecular understanding of how nutrients, especially nitrogen (N), are taken up in oil palm is very important to improve fertilizer use and formulation practice in oil palm plantations. In this work, two nitrate uptake genes in oil palm, EgNRT2.3 and EgNAR2, were cloned and characterized. Spatial expression analysis showed high expression of these two genes was mainly found in un-lignified young roots. Interestingly, EgNRT2.3 and EgNAR2 were up-regulated by N deprivation, but their expression pattern depended on the form of N source. Promoter analysis of these two genes confirmed the presence of regulatory elements that support these expression patterns. The Xenopus oocyte assay showed that EgNRT2.3 and EgNAR2 had to act together to take up nitrate. The results suggest that EgNRT2.3 and EgNAR2 act as a two-component nitrate uptake system in oil palm.