Soil organic nitrogen: an overlooked but potentially significant contribution to crop nutrition

Protists are key players in the utilization of protein nitrogen in the arbuscular mycorrhizal hyphosphere

While largely depending on other microorganisms for nitrogen (N) mineralization, arbuscular mycorrhizal fungi (AMF) can transfer N from organic sources to their host plants. Here, we compared N acquisition by the AMF hyphae from chitin and protein sources and assessed the effects of microbial interactions in the hyphosphere. We employed in vitro compartmented microcosms, each containing three distinct hyphosphere compartments amended with different N sources (protein, chitin, or ammonium chloride), one of which was enriched with 15N isotope. All hyphosphere compartments were supplied with Paenibacillus bacteria, with or without the protist Polysphondylium pallidum. We measured the effect of these model microbiomes on the efficiency of 15N transfer to roots via the AMF hyphae. We found that the hyphae efficiently took up N from ammonium chloride, competing strongly with bacteria and protists. Mobilization of 15N from chitin and protein was facilitated by bacteria and protists, respectively. Notably, AMF priming significantly affected the abundance of bacteria and protists in hyphosphere compartments and promoted mineralization of protein N by protists. Subsequently, this N was transferred into roots. Our results provide the first unequivocal evidence that roots can acquire N from proteins present in the AMF hyphosphere and that protists may play a crucial role in protein N mineralization.

Going beyond improving soil health: cover plants as contaminant removers in agriculture

Agriculture faces the increasing demands of a growing global population amid simultaneous challenges to soils from climate change and human-induced contamination. Cover plants are vital in sustainable agriculture, contributing to soil health improvement, erosion prevention, and enhanced climate resilience, but their role in contaminant management is underexplored. Herein we review the utilization of cover plants for remediating contaminants such as metals, organic pollutants, nitrate, antibiotics, antimicrobial resistance genes, plastics, and salts. We explore phytoremediation strategies - including phytoextraction, phytodegradation, and phytostabilization - in cover plant management. We highlight the challenges of selecting effective cover plants and the need for biomass removal of non-biodegradable contaminants, and we advocate incorporating phytoremediation concepts into sustainable agricultural management practices beyond nutrient cycling and climate resilience.

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.

Integrating Microalgal Chlorella Biomass and Biorefinery Residues into Sustainable Agriculture and Food Production: Insights from Lettuce Cultivation

Microalgal biomass offers a promising biofertilizer option due to its nutrient-rich composition, adaptability, and environmental benefits. This study evaluated the potential of microalgal-based biofertilizers-microalgal Chlorella biomass, de-oiled microalgal biomass (DMB), and de-oiled and de-aqueous extract microalgal biomass (DAEMB)-in enhancing lettuce growth, soil nutrient dynamics, and microbial community composition. Lettuce seedlings were cultivated with these biofertilizers, and plant growth parameters, photosynthetic pigments, and nitrogen uptake were assessed. Soil incubation experiments further examined nutrient mineralization rates, while DNA sequencing analyzed shifts in rhizosphere microbial communities. Lettuce grown with these biofertilizers exhibited improved growth parameters compared to controls, with Chlorella biomass achieving a 31.89% increase in shoot length, 27.98% in root length, and a 47.33% increase in fresh weight. Chlorophyll a and total chlorophyll levels increased significantly in all treatments, with the highest concentrations observed in the Chlorella biomass treatment. Soil mineralization studies revealed that DMB and DAEMB provided a gradual nitrogen release, while Chlorella biomass exhibited a rapid nutrient supply. Microbial community analyses revealed shifts in bacterial and fungal diversity, with increased abundance of nitrogen-fixing and nutrient-cycling taxa. Notably, fungal diversity was enriched in biomass and DAEMB treatments, enhancing soil health and reducing pathogenic fungi. These findings highlight microalgal biofertilizers' potential to enhance soil fertility, plant health, and sustainable resource use in agriculture.

Tipping the plant-microbe competition for nitrogen in agricultural soils

Nitrogen (N) is the most limiting nutrient in agroecosystems, and its indiscriminate application is at the center of the environmental challenges facing agriculture. To solve this dilemma, crops' nitrogen use efficiency (NUE) needs to increase - in other words, more of the applied nitrogen needs to reach humans. Microbes are the key to cracking this problem. Microbes use nitrogen as an energy source, an electron acceptor, or incorporate it in their biomass. These activities change the form and availability of nitrogen for crops' uptake, impacting its NUE, yields and produce quality. Plants (and microbes) have, however, evolved many mechanisms to compete for soil nitrogen. Understanding and harnessing these competitive mechanisms would enable us to tip the nitrogen balance to the advantage of crops. We will review these competitive mechanisms and highlight some approaches that were applied to reduce microbial competition for N in an agricultural context.

The microbial-driven nitrogen cycle and its relevance for plant nutrition

Nitrogen (N) is a vital nutrient and an essential component of biological macromolecules such as nucleic acids and proteins. Microorganisms are major drivers of N-cycling processes in all ecosystems, including the soil and plant environment. The availability of N is a major growth-limiting factor for plants and it is significantly affected by the plant microbiome. Plants and microorganisms form complex interaction networks resulting in molecular signaling, nutrient exchange, and other distinct metabolic responses. In these networks, microbial partners influence growth and N use efficiency of plants either positively or negatively. Harnessing the beneficial effects of specific players within crop microbiomes is a promising strategy to counteract the emerging threats to human and planetary health due to the overuse of industrial N fertilizers. However, in addition to N-providing activities (e.g. the well-known symbiosis of legumes and Rhizobium spp.), other plant-microorganism interactions must be considered to obtain a complete picture of how microbial-driven N transformations might affect plant nutrition. For this, we review recent insights into the tight interplay between plants and N-cycling microorganisms, focusing on microbial N-transformation processes representing N sources and sinks that ultimately shape plant N acquisition.

Soil Erosion Thickness and Seasonal Variations Together Drive Soil Nitrogen Dynamics at the Early Stage of Vegetation Restoration in the Dry-Hot Valley

By changing the physicochemical and biological properties of soil, erosion profoundly affects soil nitrogen levels, but knowledge about the erosion impact on soil nitrogen (N) dynamics is still rather incomplete. We compared soil N contents at the early stage of vegetation self-restoration in response to soil erosion thickness (0, 10, 20, 30 and 40 cm), by conducting a simulated erosion experiment on sloping arable land in the dry-hot valley of Yunnan Province, southwestern China. The results showed total nitrogen (TN), ammonium nitrogen (NH4+-N) and nitrate nitrogen (NO3--N) contents reduced with increasing soil erosion thickness and decreased significantly at the soil erosion thickness of 10, 40 and 10 cm in the rainy season and 30, 10 and 10 cm in the dry season compared with 0 cm. Structural equation modeling (SEM) indicated that soil erosion thickness and seasonal variation were the important drivers of mineral nitrogen (NH4+-N and NO3--N) content. Soil erosion thickness indirectly affected mineral nitrogen through negative on TN, carbon content and Diazotrophs (nifH genes). Dry-wet season change had an effect on mineral nitrogen mediated by arbuscular mycorrhizal fungi (AMF) and nifH genes. We also found AMF had a promotion to nifH genes in eroded soil, which can be expected to benefit nitrogen fixing. Our findings highlight the importance of considering soil erosion thickness and sampling time for nitrogen dynamics, in particular, the investigation of nitrogen limitation, in the early stage of vegetation self-restoration.

Screening Cover Crops for Utilization in Irrigated Vineyards: A Greenhouse Study on Species' Nitrogen Uptake and Carbon Sequestration Potential

This study examines the potential of 23 plant species, comprising 10 legumes, 9 grasses, and 4 forbs, as cover crops to enhance carbon (C) sequestration and soil nitrogen (N) in vineyards. After a 120-day evaluation period, cover crop biomass was incorporated into the soil, and grapevine seedlings were planted in its place. Among the established cover crops, the C input potential ranged from 0.267 to 1.69 Mg ha-1, and the N input potential ranged from 12.3 to 114 kg ha-1. Legume species exhibited up to threefold greater shoot dry weight (SDW) compared to grass species. Ladino white clover, Dutch white clover, and Clover blend were superior in SDW, total dry weight (TDW), total C content, and total N content. Legumes exhibited slightly higher root dry weight (RDW) than grasses, with the exception of Fall rye leading at 15 g pot-1, followed by Ladino white clover and Dutch white clover at an average of 12 g pot-1. Legumes, particularly clover blend and Alsike clover, displayed high shoot N concentration at an average of 2.95%. Root N concentration in Legumes (Fabaceae) were significantly higher at 1.82% compared to other plant families at 0.89%, while their root C/N ratio was lower at 18.3, contrasting with others at 27.7, resulting in a faster turnover. Biomass production exhibited a negative relationship (R2 = 0.51) with soil residual NO3-. Fall rye, Winfred brassica, and buckwheat had the highest N utilization efficiency (NUtE) values (ava. 121 g g-1). Alsike clover, Ladino white clover, and clover blend showed the highest N uptake efficiency (NUpE) values (ava. 75%). The Readily Available N (RAN) Reliance Index (RANRI) is introduced as a novel indicator for quantifying the extent to which a plant relies on RAN for its total N requirement. The RANRI value represents the percentage of the plant's total N sourced from RAN, ranging from 11% for legumes to 86% for grasses. This implies a substantial influx of nitrogen through a pathway independent of RAN in legumes. Grape shoot N concentration positively correlated with soil NO3- (R2 = 0.31) and cover crop C/N ratio (R2 = 0.17) but negatively correlated with cover crop TDW (R2 = 0.31). This study highlights legume plants as more effective in C and N assimilation during establishment but cautions about potential soil mineral N depletion before reaching their full biological N fixation capacity.

Peculiarity of the early metabolomic response in tomato after urea, ammonium or nitrate supply

Nitrogen (N) is the nutrient most applied in agriculture as fertilizer (as nitrate, Nit; ammonium, A; and/or urea, U, forms) and its availability strongly constrains the crop growth and yield. To investigate the early response (24 h) of N-deficient tomato plants to these three N forms, a physiological and molecular study was performed. In comparison to N-deficient plants, significant changes in the transcriptional, metabolomic and ionomic profiles were observed. As a probable consequence of N mobility in plants, a wide metabolic modulation occurred in old leaves rather than in young leaves. The metabolic profile of U and A-treated plants was more similar than Nit-treated plant profile, which in turn presented the lowest metabolic modulation with respect to N-deficient condition. Urea and A forms induced some changes at the biosynthesis of secondary metabolites, amino acids and phytohormones. Interestingly, a specific up-regulation by U and down-regulation by A of carbon synthesis occurred in roots. Along with the gene expression, data suggest that the specific N form influences the activation of metabolic pathways for its assimilation (cytosolic GS/AS and/or plastidial GS/GOGAT cycle). Urea induced an up-concentration of Cu and Mn in leaves and Zn in whole plant. This study highlights a metabolic reprogramming depending on the N form applied, and it also provide evidence of a direct relationship between urea nutrition and Zn concentration. The understanding of the metabolic pathways activated by the different N forms represents a milestone in improving the efficiency of urea fertilization in crops.

Formation of reactive intermediates in paddy water from different temperature zones for the promotion of abiotic ammonification

The paddy field is a hot area of biogeochemical process. The paddy water has a large capacity in photo-generation of reactive intermediates (RIs) due to abundant photosensitive dissolved organic matter (DOM), which is influenced by the spatial heterogeneity of paddy soils but rarely been explored. Our work presents the first investigation of the role of soil properties on photochemistry in paddy water. Soil organic matter (SOM), determined by the temperature, was the dominant factor for the photo-generation of RIs in paddy water of main rice producing areas. The RI concentrations generated with abundant SOM from cool regions are 0.05-8.71 times higher than those for the warm regions in China. The humic-like substance and aromatic-like compounds of DOM plays an essential role in RIs generation, which is abundant in paddy soils rich in SOM from Chinese cool regions. In addition, RIs can efficiently accelerate the photo-ammonification of urea and free amino acids by 15.2 %-164 %, leading to 0.13-0.17 mmol/L/d photo-produced ammonium after fertilization, which is preferentially absorbed by rice. The findings of this study will extend our knowledge of the geochemistry of global paddy field ecosystem. The potential role of RIs in nitrogen cycle should be highlighted in the agroecosystem.

Combining and concentrating nanocelluloses for cryogels with remarkable strength and wet resilience

Cellulose cryogels are promising eco-friendly materials that exhibit low density, high porosity, and renewability. However, the applications of these materials are limited by their lower mechanical and water resistance compared to petrochemical-based lightweight materials. In this work, nanocelluloses were functionalized with cationic and anionic groups, and these nanomaterials were combined to obtain strong and water-resilient cryogels. To prepare the cryogels, anionic and cationic micro- and nanofibrils (CNFs) were produced at three different sizes and combined in various weight ratios, forming electrostatic complexes. The complex phase was concentrated by centrifugation and freeze-dried. Porous and open cellular structures were assembled in all compositions tested (porosity >90 %). Compressive testing revealed that the most resistant cryogels (1.7 MPa) were obtained with equivalent amounts of negatively and positively charged CNFs with lengths between 100 and 1200 nm. The strength at this condition was achieved as CNF electrostatic complexes assembled in thick cells, as observed by synchrotron X-ray tomography. In addition to mechanical strength, electrostatic complexation provided remarkable structural stability in water for the CNF cryogels, without compromising their biodegradability. This route by electrostatic complexation is a practical strategy to combine and concentrate nanocelluloses to tailor biodegradable lightweight materials with high strength and wet stability.

Nitrogen Sources Reprogram Carbon and Nitrogen Metabolism to Promote Andrographolide Biosynthesis in Andrographis paniculata (Burm.f.) Nees Seedlings

Carbon (C) and nitrogen (N) metabolisms participate in N source-regulated secondary metabolism in medicinal plants, but the specific mechanisms involved remain to be investigated. By using nitrate (NN), ammonium (AN), urea (UN), and glycine (GN), respectively, as sole N sources, we found that N sources remarkably affected the contents of diterpenoid lactone components along with C and N metabolisms reprograming in Andrographis paniculata, as compared to NN, the other three N sources raised the levels of 14-deoxyandrographolide, andrographolide, dehydroandrographolide (except UN), and neoandrographolide (except AN) with a prominent accumulation of farnesyl pyrophosphate (FPP). These N sources also raised the photosynthetic rate and the levels of fructose and/or sucrose but reduced the activities of phosphofructokinase (PFK), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), phosphoenolpyruvate carboxylase (PEPC) and pyruvate dehydrogenase (PDH). Conversely, phosphoenolpyruvate carboxykinase (PEPCK) and malate enzyme (ME) activities were upregulated. Simultaneously, citrate, cis-aconitate and isocitrate levels declined, and N assimilation was inhibited. These results indicated that AN, UN and GN reduced the metabolic flow of carbohydrates from glycolysis into the TCA cycle and downstream N assimilation. Furthermore, they enhanced arginine and GABA metabolism, which increased C replenishment of the TCA cycle, and increased ethylene and salicylic acid (SA) levels. Thus, we proposed that the N sources reprogrammed C and N metabolism, attenuating the competition of N assimilation for C, and promoting the synthesis and accumulation of andrographolide through plant hormone signaling. To obtain a higher production of andrographolide in A. paniculata, AN fertilizer is recommended in its N management.

Enhancing soil health and nutrient availability for Carrizo citrange (X Citroncirus sp.) through bokashi and biochar amendments: An exploration into indoor sustainable soil ecosystem management

This study investigated the efficacy of organic soil amendments: bokashi (Bok), biochar (BC), and their combination (Bok_BC) in promoting soil health, nutrient availability, and growth of Carrizo citrange (X Citroncirus sp. Rutaceae, Parentage Citrus sinensis × Poncirus trifoliata) under indoor greenhouse settings. Results indicate significant alterations in soil parameters like total carbon (C), total nitrogen (N), and C:N ratio due to Bok, BC, and Bok_BC treatments. BC treatments boosted total C, while Bok increased total N, compared to controls. A note-worthy 25 % average decrease in C:N ratio was observed with Bok and Bok_BC, nearing the optimal 24:1 C:N for microbial growth. This highlights the potential of waste by-products in balancing nutrient release to benefit soil health and plant development. Analysis of nitrite (NO2-), nitrate (NO3-), and ammonium (NH4-N) levels revealed a dynamic relationship between soil treatments and time. Bok and Bok_BC amendments combined with both fertilizer doses [700 and 1400 Electrical Conductivity, EC] showed an initial NH4-N spike (averaging 1513 and 1288 μg N/g dry, respectively), outperforming control soils (average 503 μg N/g dry). Other key elements like phosphorus, potassium, calcium, and chlorine also experienced initial surges in Bok and Bok_BC soils before declining, suggesting a gradual nutrient release. The concentration of potentially toxic elements remained mostly stable or inconclusive, warranting further exploration. Bok, BC, and Bok_BC treatments considerably influenced germination rate and plant growth. The germination rate averaged 24.2 %, 23 %, and 22.5 % for Bok, BC, and Bok_BC, compared to the 15.9 % control. Plant height increased with Bok, BC, and Bok_BC to 18.4 cm, 18.7 cm, and 16.4 cm, respectively, from the 14.8 cm control. The results remained consistent across fertilizer doses, emphasizing the soil amendments' role in bolstering soil and plant health. In summary, the research underscores the potential of carbon-based amendments like bokashi and biochar in enhancing soil health, reducing reliance on synthetic fertilizers, and fostering sustainable soil ecosystems. The insights are pivotal for advancing sustainable agriculture in indoor greenhouse settings for nursery plant production.

Role of Soil Microbiota Enzymes in Soil Health and Activity Changes Depending on Climate Change and the Type of Soil Ecosystem

The extracellular enzymes secreted by soil microorganisms play a pivotal role in the decomposition of organic matter and the global cycles of carbon (C), phosphorus (P), and nitrogen (N), also serving as indicators of soil health and fertility. Current research is extensively analyzing these microbial populations and enzyme activities in diverse soil ecosystems and climatic regions, such as forests, grasslands, tropics, arctic regions and deserts. Climate change, global warming, and intensive agriculture are altering soil enzyme activities. Yet, few reviews have thoroughly explored the key enzymes required for soil fertility and the effects of abiotic factors on their functionality. A comprehensive review is thus essential to better understand the role of soil microbial enzymes in C, P, and N cycles, and their response to climate changes, soil ecosystems, organic farming, and fertilization. Studies indicate that the soil temperature, moisture, water content, pH, substrate availability, and average annual temperature and precipitation significantly impact enzyme activities. Additionally, climate change has shown ambiguous effects on these activities, causing both reductions and enhancements in enzyme catalytic functions.

Organic matter stability and lability in terrestrial and aquatic ecosystems: A chemical and microbial perspective

Terrestrial and aquatic ecosystems have specific carbon fingerprints and sequestration potential, due to the intrinsic properties of the organic matter (OM), mineral content, environmental conditions, and microbial community composition and functions. A small variation in the OM pool can imbalance the carbon dynamics that ultimately affect the climate and functionality of each ecosystem, at regional and global scales. Here, we review the factors that continuously contribute to carbon stability and lability, with particular attention to the OM formation and nature, as well as the microbial activities that drive OM aggregation, degradation and eventually greenhouse gas emissions. We identified that in both aquatic and terrestrial ecosystems, microbial attributes (i.e., carbon metabolism, carbon use efficiency, necromass, enzymatic activities) play a pivotal role in transforming the carbon stock and yet they are far from being completely characterised and not often included in carbon estimations. Therefore, future research must focus on the integration of microbial components into carbon mapping and models, as well as on translating molecular-scaled studies into practical approaches. These strategies will improve carbon management and restoration across ecosystems and contribute to overcome current climate challenges.

Root phenotypes for improved nitrogen capture

Background

Suboptimal nitrogen availability is a primary constraint for crop production in low-input agroecosystems, while nitrogen fertilization is a primary contributor to the energy, economic, and environmental costs of crop production in high-input agroecosystems. In this article we consider avenues to develop crops with improved nitrogen capture and reduced requirement for nitrogen fertilizer.

Scope

Intraspecific variation for an array of root phenotypes has been associated with improved nitrogen capture in cereal crops, including architectural phenotypes that colocalize root foraging with nitrogen availability in the soil; anatomical phenotypes that reduce the metabolic costs of soil exploration, improve penetration of hard soil, and exploit the rhizosphere; subcellular phenotypes that reduce the nitrogen requirement of plant tissue; molecular phenotypes exhibiting optimized nitrate uptake kinetics; and rhizosphere phenotypes that optimize associations with the rhizosphere microbiome. For each of these topics we provide examples of root phenotypes which merit attention as potential selection targets for crop improvement. Several cross-cutting issues are addressed including the importance of soil hydrology and impedance, phenotypic plasticity, integrated phenotypes, in silico modeling, and breeding strategies using high throughput phenotyping for co-optimization of multiple phenes.

Conclusions

Substantial phenotypic variation exists in crop germplasm for an array of root phenotypes that improve nitrogen capture. Although this topic merits greater research attention than it currently receives, we have adequate understanding and tools to develop crops with improved nitrogen capture. Root phenotypes are underutilized yet attractive breeding targets for the development of the nitrogen efficient crops urgently needed in global agriculture.

Phenylalanine-mediated changes in the soil bacterial community promote nitrogen cycling and plant growth

Soil amino acids (AAs) are the most active components of soil N, which can be mineralized or absorbed by bacteria as N and C sources. We hypothesized that exogenous AAs could regulate the bacterial community and affect soil N cycling, and the effect sizes could vary depending on individual AAs. Here, we applied feather (keratin)-based compost rich in AAs to Poncirus trifoliata (L.) to evaluate the regulation of bacterial community by AAs; furthermore, we applied six individual AAs to test their effects. The compost significantly increased soil hydrolysable AA content, ammonia monooxygenase gene abundance, and plant growth and changed bacterial community structure. Redundancy analysis revealed that the effects of AAs on the bacterial community composition were greater than those of soil chemical properties, and phenylalanine (Phe) was the most effective among thirteen individual AAs. When applied individually, Phe caused the greatest increase in N cycling-related enzyme activity and plant growth and most significantly altered the bacterial community structure among the six exogenous AAs. Notably, Phe significantly increased the relative abundances of Burkholderia-Caballeronia-Paraburkholderia, Azospirillum, Cupriavidus, and Achromobacter, whose abundances were significantly positively correlated with plant biomass, and significantly reduced the relative abundances of Arachidicoccus, Pseudopedobacter, Sphingobacterium, and Paenibacillus, whose abundances were significantly negatively correlated with plant biomass. We demonstrate that soil AAs strongly shape the bacterial community. Particularly, Phe enhances N cycling and plant growth by increasing the potentially beneficial bacterial taxa and inhibiting the potentially harmful bacterial taxa, which needs further validation.

Fertilizer source and application method influence sugarcane production and nutritional status

INTRODUCTION

The contrasting weather conditions throughout the sugarcane harvest period in south-central Brazil (April to November) influence fertilization management in sugarcane ratoon.

METHODS

Through field studies carried out over two cropping seasons, we aimed to compare the performance of sugarcane at sites harvested in the early and late periods of the harvest season as a function of fertilizer sources associated with application methods. The design used in each site was a randomized block in a 2 x 3 factorial scheme; the first factor consisted of fertilizer sources (solid and liquid), and the second factor consisted of application methods (above the straw, under the straw, and incorporated into the middle of the sugarcane row).

RESULTS

The fertilizer source and application method interacted at the site harvested in the early period of the sugarcane harvest season. Overall, the highest sugarcane stalk and sugar yields at this site were obtained with the incorporated application applying liquid fertilizer and under straw applying solid fertilizer, with increments of up to 33%. For the site harvested in the late period of the sugarcane harvest season, the liquid fertilizer promoted a 25% higher sugarcane stalk yield compared to the solid fertilizer in the crop season with low rainfall in the spring, while in the crop season with normal rainfall, there were no differences between treatments.

DISCUSSION

This demonstrates the importance of defining fertilization management in sugarcane as a function of harvest time, thereby promoting greater sustainability in the production system.

Vertical migration of nutrients and water-soluble organic matter in the soil profile under pre-sowing seed treatment with plant growth promoting rhizobacteria

Studies conducted in a stationary lysimeter experiment in the conditions of the washing water regime have shown that the use of PGPR for pre-sowing seed inoculation of agricultural crops reduces vertical migration of biogenic nutrients and water-soluble organic matter down the soil profile. The effect of seed inoculation with PGPR on the reduction of nutrient losses was not specific to the type of rhizobacteria and was similar for crops grown on different mineral fertilizers backgrounds (spring barley and winter rye seeds were inoculated with the nitrogen-fixing bacteria—Azospirillum brasilense 410 and A. brasilense 18-2, respectively, while maize seeds were inoculated with the phosphate-mobilizing Paenibacillus polymyxa KB). Seed inoculation has decreased nitrogen leaching down the soil profile by 4–9 kg/ha, phosphorus compounds—by 0.5–3.0 kg/ha, potassium—by 0.6–3.0 kg/ha, calcium—by 6–42 kg/ha, magnesium—by 3.0–6.0 kg/ha, water-soluble organic matter—by 0.8–8.0 kg/ha, subject to crop and norms of mineral fertilizers. Maize seeds inoculated with phosphorous-mobilizing P. polymyxa KB under crop cultivation on the cattle manure background did not affect the intensity of nutrient migration. On the other hand, the combination of green manure (narrow-leaved lupine as an intermediate crop) with pre-sowing seed inoculation had significantly reduced nutrient losses beyond the root zone soil layer. It is concluded that the use of PGPR in crop production on mineral and green manure backgrounds contributes to the preservation of soil fertility by limiting biogenic nutrients and water-soluble organic matter leaching with the water drainage down the soil profile. Pre-sowing seed inoculation had no significant effect on the vertical migration of nutrients in the soil on the background of cattle manure, due to the highly competitive environment created with the introduction of microorganisms from organic fertilizer, preventing the establishment of close interactions between PGPR and plants.

K. S, Vadivel R, T. K. D, Raj R, Pooniya V, Babu S, Rathore SS, L. M, Tiwari G. Nitrogen use efficiency-a key to enhance crop productivity under a changing climate

Nitrogen (N) is an essential element required for the growth and development of all plants. On a global scale, N is agriculture's most widely used fertilizer nutrient. Studies have shown that crops use only 50% of the applied N effectively, while the rest is lost through various pathways to the surrounding environment. Furthermore, lost N negatively impacts the farmer's return on investment and pollutes the water, soil, and air. Therefore, enhancing nitrogen use efficiency (NUE) is critical in crop improvement programs and agronomic management systems. The major processes responsible for low N use are the volatilization, surface runoff, leaching, and denitrification of N. Improving NUE through agronomic management practices and high-throughput technologies would reduce the need for intensive N application and minimize the negative impact of N on the environment. The harmonization of agronomic, genetic, and biotechnological tools will improve the efficiency of N assimilation in crops and align agricultural systems with global needs to protect environmental functions and resources. Therefore, this review summarizes the literature on nitrogen loss, factors affecting NUE, and agronomic and genetic approaches for improving NUE in various crops and proposes a pathway to bring together agronomic and environmental needs.

Recent trends in nitrogen cycle and eco-efficient nitrogen management strategies in aerobic rice system

Rice (Oryza sativa L.) is considered as a staple food for more than half of the global population, and sustaining productivity under a scarcity of resources is challenging to meet the future food demands of the inflating global population. The aerobic rice system can be considered as a transformational replacement for traditional rice, but the widespread adaptation of this innovative approach has been challenged due to higher losses of nitrogen (N) and reduced N-use efficiency (NUE). For normal growth and developmental processes in crop plants, N is required in higher amounts. N is a mineral nutrient and an important constituent of amino acids, nucleic acids, and many photosynthetic metabolites, and hence is essential for normal plant growth and metabolism. Excessive application of N fertilizers improves aerobic rice growth and yield, but compromises economic and environmental sustainability. Irregular and uncontrolled use of N fertilizers have elevated several environmental issues linked to higher N losses in the form of nitrous oxide (N2O), ammonia (NH3), and nitrate (NO3 -), thereby threatening environmental sustainability due to higher warming potential, ozone depletion capacities, and abilities to eutrophicate the water resources. Hence, enhancing NUE in aerobic rice has become an urgent need for the development of a sustainable production system. This article was designed to investigate the major challenge of low NUE and evaluate recent advances in pathways of the N cycle under the aerobic rice system, and thereby suggest the agronomic management approaches to improve NUE. The major objective of this review is about optimizing the application of N inputs while sustaining rice productivity and ensuring environmental safety. This review elaborates that different soil conditions significantly shift the N dynamics via changes in major pathways of the N cycle and comprehensively reviews the facts why N losses are high under the aerobic rice system, which factors hinder in attaining high NUE, and how it can become an eco-efficient production system through agronomic managements. Moreover, it explores the interactive mechanisms of how proper management of N cycle pathways can be accomplished via optimized N fertilizer amendments. Meanwhile, this study suggests several agricultural and agronomic approaches, such as site-specific N management, integrated nutrient management (INM), and incorporation of N fertilizers with enhanced use efficiency that may interactively improve the NUE and thereby plant N uptake in the aerobic rice system. Additionally, resource conservation practices, such as plant residue management, green manuring, improved genetic breeding, and precision farming, are essential to enhance NUE. Deep insights into the recent advances in the pathways of the N cycle under the aerobic rice system necessarily suggest the incorporation of the suggested agronomic adjustments to reduce N losses and enhance NUE while sustaining rice productivity and environmental safety. Future research on N dynamics is encouraged under the aerobic rice system focusing on the interactive evaluation of shifts among activities and diversity in microbial communities, NUE, and plant demands while applying N management measures, which is necessary for its widespread adaptation in face of the projected climate change and scarcity of resources.

Assessing spatial variability of selected soil properties in Upper Kabete Campus coffee farm, University of Nairobi, Kenya

This study aimed to evaluate spatial variability of selected soil parameters as a smart agricultural technology guide to precise fertilizer application. A farm designated as Field 3 which is under Arabica coffee within a bigger Soil Mapping Unit (SMU) was selected for a more detailed soil observation at a scale of 1:5000. Soil samples were taken at depths of 0–15 and 15–30 cm across 20 sample locations in grids and selected properties analysed in the laboratory. Kriging interpolation method was used to estimate the accuracy of interpolation through cross-validation of the top soil parameters. In 0 to 15 and 15–30 cm depth, soil reaction, percentage organic carbon and percent nitrogen showed low variability of 5.1% and 5.8%, 10.4% and 12.7%, 14.5% and 17.6% respectively. Phosphorus was deficient in both depths and showed moderate variability of 36.2% and 42.3% in 0–15 and 15–30 cm respectively. Calcium and Magnesium ranged from sufficient to rich and showed moderate and low variability in top and bottom depths, respectively. All micronutrients were sufficient in the soil. The soils were classified as Mollic Nitisols. Results showed that soil parameters varied spatially within the field therefore, there is need for variable input application depending on the levels of these elements and purchasing of fertilizer blends that are suitable for nutrient deficiencies. Precision agriculture is highly recommended in the field to capitalize on soil heterogeneity.

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There is need for variable agricultural input application in farms.

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Field spatial variability is a panacea to economically sound soil management.

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Precision agriculture is recommended for profits and environmental protection.

Physiological Characteristics and Transcriptomic Dissection in Two Root Segments with Contrasting Net Fluxes of Ammonium and Nitrate of Poplar Under Low Nitrogen Availability

To investigate physiological and transcriptomic regulation mechanisms underlying the distinct net fluxes of NH4+ and NO3- in different root segments of Populus species under low nitrogen (N) conditions, we used saplings of Populus × canescens supplied with either 500 (normal N) or 50 (low N) μM NH4NO3. The net fluxes of NH4+ and NO3-, the concentrations of NH4+, amino acids and organic acids and the enzymatic activities of nitrite reductase (NiR) and glutamine synthetase (GS) in root segment II (SII, 35-70 mm to the apex) were lower than those in root segment I (SI, 0-35 mm to the apex). The net NH4+ influxes and the concentrations of organic acids were elevated, whereas the concentrations of NH4+ and NO3- and the activities of NiR and GS were reduced in SI and SII in response to low N. A number of genes were significantly differentially expressed in SII vs SI and in both segments grown under low vs normal N conditions, and these genes were mainly involved in the transport of NH4+ and NO3-, N metabolism and adenosine triphosphate synthesis. Moreover, the hub gene coexpression networks were dissected and correlated with N physiological processes in SI and SII under normal and low N conditions. These results suggest that the hub gene coexpression networks play pivotal roles in regulating N uptake and assimilation, amino acid metabolism and the levels of organic acids from the tricarboxylic acid cycle in the two root segments of poplars in acclimation to low N availability.

Nitrogen Use Efficiency Definitions of Today and Tomorrow

Crop production has a large impact on the nitrogen (N) cycle, with consequences to climate, environment, and public health. Designing better N management will require indicators that accurately reflect the complexities of N cycling and provide biological meaning. Nitrogen use efficiency (NUE) is an established metric used to benchmark N management. There are numerous approaches to calculate NUE, but it is difficult to find an authoritative resource that collates the various NUE indices and systematically identifies their assets and shortcomings. Furthermore, there is reason to question the usefulness of many traditional NUE formulations, and to consider factors to improve the conceptualization of NUE for future use. As a resource for agricultural researchers and students, here we present a comprehensive list of NUE indices and discuss their functions, strengths, and limitations. We also suggest several factors-which are currently ignored in traditional NUE indices-that will improve the conceptualization of NUE, such as: accounting for a wider range of soil N forms, considering how plants mediate their response to the soil N status, including the below-ground/root N pools, capturing the synchrony between available N and plant N demand, blending agronomic performance with ecosystem functioning, and affirming the biological meaning of NUE.