Aims The ability to suppress soil nitrification through the release of nitrification inhibitors from plant roots is termed 'biological nitrification inhibition' (BNI). Here, we aimed at the ...quantification and characterization of the BNI function in sorghum that included inhibitor production, their chemical identity, functionality and factors regulating their release. Methods Sorghum was grown in solution culture and root exúdate was collected using aerated NH₄Cl solutions. A bioluminescence assay using recombinant Nitrosomonas europaea was employed to determine the BNI activity. Activity-guided Chromatographie fractionation was used to isolate biological nitrification inhibitors (BNIs). The chemical structure was analyzed using NMR and mass spectrometry; pH-stat systems were deployed to analyze the role of rhizosphere pH on BNIs release. Results Sorghum roots released two categories of BNIs: hydrophilic- and hydrophobic-BNIs. The release rates for hydrophilic- and hydrophobic- BNIs ranged from 10 to 25 ATUg⁻¹ root dwt. d⁻¹. Addition of hydrophilic BNIs (10 ATUg⁻¹ soil) significantly inhibited soil nitrification (40 % inhibition) during a 30-d incubation test. Two BNI compounds isolated were: sakuranetin (ED₈₀ 0.6 µM; isolated from hydrophilic-BNIs fraction) and sorgoleone (ED₈₀ 13.0 µM; isolated from hydrophobic-BNIs fraction), which inhibited Nitrosomonas by blocking AMO and HAO enzymatic pathways. The BNIs release required the presence of NH₄⁺ in the root environment and the stimulatory effect of NH₄⁺ lasted 24 h. Unlike the hydrophobic-BNIs, the release of hydrophilic-BNIs declined at a rhizosphere pH >5.0; nearly 80 % of hydrophilic-BNI release was suppressed at pH ≥7.0. The released hydrophilic-BNIs were functionally stable within a pH range of 5.0 to 9.0. Sakuranetin showed a stronger inhibitory activity (ED₅₀ 0.2 µM) than methyl 3-(4-hydroxyphenyl) propionate (MHPP) (ED₅₀ 100 µM) (isolated from hydrophilic-BNIs fraction) in the in vitro culture-bioassay, but the activity was non-functional and ineffective in the soil-assay. Conclusions There is an urgent need to identify sorghum genetic stocks with high potential to release functional-BNIs for suppressing nitrification and to improve nitrogen use efficiency in sorghum-based production systems.
Vertisols in the tropics occur in a range of climates and are used in a range of production systems. This review is a synthesis of the recent developments in pedology of vertisols achieved via ...high-resolution micro-morphology, mineralogy, and age-control data along with their geomorphologic and climatic history. This knowledge has contributed to our understanding of how the climate change-related pedogenic processes during the Holocene altered soil properties in the presence or absence of soil modifiers (Ca-zeolites and gypsum), calcium carbonate and palygorskite minerals. These state-of-the-art methods have established an organic link between pedogenic processes and bulk soil properties; the review also considers the need to modify the classification of vertisols at the subgroup level. We hope this review will fulfil the need for a handbook on vertisols to facilitate their better management for optimising their productivity in the 21st century.
► For vertisols there is no single farming system that can be universally applicable. ► This review is a synthesis of recent developments in pedology of vertisols. ► State-of-the-art information has emanated through this review. ► This review has resolved many enigmatic pedological and edaphological issues.
Nitrification in soil converts relatively immobile ammonium-nitrogen (N) to highly mobile nitrate-N (via nitrite), and this has implications for N-use efficiency by agricultural systems as well as ...for environmental quality, especially in situations where the potential for loss of soil or added N is high following nitrate formation. The literature on various physical, environmental, and chemical factors and their interactions on nitrification in soil is reviewed and discussed with examples from natural and agro-ecosystems. Among the various factors, soil matrix, water status, aeration, temperature, and pH have strong influence on nitrification. The information on factors that influence nitrification is useful when developing strategies for regulating nitrification in soils by employing chemical or biological nitrification inhibitors.
Nitrification, a microbial process, is a key component and integral part of the nitrogen (N) cycle. Soil N is in a constant state of flux, moving and changing chemical forms. During nitrification, a ...relatively immobile N-form (NH
4
+
) is converted into highly mobile nitrate-N (NO
3
−
). The nitrate formed is susceptible to losses via leaching and conversion to gaseous forms via denitrification. Often less than 30% of the applied N fertilizer is recovered in intensive agricultural systems, largely due to losses associated with and following nitrification. Nitrogen-use efficiency (NUE) is defined as the biomass produced per unit of assimilated N and is a conservative function in most biological systems. A better alternative is to define NUE as the dry matter produced per unit N applied and strive for improvements in agronomic yields through N recovery. Suppressing nitrification along with its associated N losses is potentially a key part in any strategy to improve N recovery and agronomic NUE. In many mature N-limited ecosystems, nitrification is reduced to a relatively minor flux. In such systems there is a high degree of internal N cycling with minimal loss of N. In contrast, in most high-production agricultural systems nitrification is a major process in N cycling with the resulting N losses and inefficiencies. This review presents the current state of knowledge on nitrification and associated N losses, and discusses strategies for controlling nitrification in agricultural systems. Limitations of the currently available nitrification inhibitors are highlighted. The concept of biological nitrification inhibition (BNI) is proposed for controlling nitrification in agricultural systems utilizing traits found in natural ecosystems. It is emphasized that suppression of nitrification in agricultural systems is a critical step required for improving agronomic NUE and maintaining environmental quality.
Iron (Fe) toxicity is a widespread nutrient disorder of wetland rice grown on acid sulfate soils, Ultisols, and sandy soils with a low cation exchange capacity, moderate to high acidity, and active ...Fe (easily reducible Fe) and low to moderately high in organic matter. Iron toxicity reduces rice yields by 12-100%, depending on the Fe tolerance of the genotype, intensity of Fe toxicity stress, and soil fertility status. Iron toxicity can be reduced by using Fe-tolerant rice genotypes and through soil, water, and nutrient management practices. This article critically assesses the recent literature on Fe toxicity, with emphasis on the role of other plant nutrients, in the occurrence of and tolerance to Fe toxicity in lowland rice and puts this information in perspective for future research needs. The article emphasizes the need for research to provide knowledge that would be used for increasing rice production on Fe-toxic wetlands on a sustainable basis by integration of genetic tolerance to Fe toxicity with soil, water, and nutrient management.
BackgroundAgriculture is the single largest geo-engineering initiative that humans have initiated on planet Earth, largely through the introduction of unprecedented amounts of reactive nitrogen (N) ...into ecosystems. A major portion of this reactive N applied as fertilizer leaks into the environment in massive amounts, with cascading negative effects on ecosystem health and function. Natural ecosystems utilize many of the multiple pathways in the N cycle to regulate N flow. In contrast, the massive amounts of N currently applied to agricultural systems cycle primarily through the nitrification pathway, a single inefficient route that channels much of this reactive N into the environment. This is largely due to the rapid nitrifying soil environment of present-day agricultural systems.ScopeIn this Viewpoint paper, the importance of regulating nitrification as a strategy to minimize N leakage and to improve N-use efficiency (NUE) in agricultural systems is highlighted. The ability to suppress soil nitrification by the release of nitrification inhibitors from plant roots is termed ‘biological nitrification inhibition’ (BNI), an active plant-mediated natural function that can limit the amount of N cycling via the nitrification pathway. The development of a bioassay using luminescent Nitrosomonas to quantify nitrification inhibitory activity from roots has facilitated the characterization of BNI function. Release of BNIs from roots is a tightly regulated physiological process, with extensive genetic variability found in selected crops and pasture grasses. Here, the current status of understanding of the BNI function is reviewed using Brachiaria forage grasses, wheat and sorghum to illustrate how BNI function can be utilized for achieving low-nitrifying agricultural systems. A fundamental shift towards ammonium (NH4+)-dominated agricultural systems could be achieved by using crops and pastures with high BNI capacities. When viewed from an agricultural and environmental perspective, the BNI function in plants could potentially have a large influence on biogeochemical cycling and closure of the N loop in crop–livestock systems.
► Jatropha biodiesel plant can be successfully grown to rehabilitate degraded lands. ► A 3–5-year Jatropha added to soil 1450kgCha−1year−1 and in fuel 230kgCha−1year−1. ► Added biomass each year ...recycled 85.5kg N, 7.67kg P, 43.9kg K and other nutrients. ► A 4-year plantation sequestered 2500kgCha−1 in soil and 5100kgCha−1 in biomass. ► Jatropha improved microbial activity, available nutrients and water holding in soil.
The effects of growing Jatropha in on-farm and on-station degraded lands were evaluated on carbon (C) sequestration and soil properties. Jatropha accumulated and added to soil significant amounts of C (305kgha−1year−1) from the year one itself. Overall, a 3–5-year old plantation added per year around 4000kg plant biomass equivalent to 1450kgCha−1 – 800kg C through leaves, 150kg C through pruned twigs, and 495kg C as deoiled Jatropha cake. Biodiesel C replacement in the fossil fuel was 230kgha−1. Besides adding biomass to the soil, and C replacement in fossil fuel; the standing Jatropha rendered ecosystem service by fixing 5100–6100kgha−1C as the aboveground plus belowground biomass. Carbon additions by Jatropha during 4 years increased C content in the degraded surface soil layer by 19%, resulting in about 2500kgha−1C sequestered. Huge C additions and live root activity under Jatropha increased microbial population, respiration rate and microbial biomass C and N in soil. Along with C additions, 4000kgha−1year−1 plant biomass recycled into the soil 85.5kg nitrogen, 7.67kg phosphorus, 43.9kg potassium, 5.20kg sulphur, 0.11kg boron, 0.12kg zinc and other nutrients. The C additions improved water holding capacity of the soil under Jatropha as compared with the adjacent control soil which increased by 35% at 30kPa and 21% at 1500kPa soil water potential.
► The manuscript presents the results from long-term hydrological studies on two major soils of semi-arid tropics (SATs). ► Usefulness of such studies in identifying appropriate soil and water ...management strategies/practices is demonstrated. ► Results suggest that the Alfisols and Vertisols in the SAT have very contrasting hydrological behavior. ► Implications of the findings for improving the performance of hydrological models on Alfisols and Vertisols are discussed. ► Large semi-arid areas in Asia and Africa can benefit from the results of the study.
Understanding of the hydrological behavior of soils is a prerequisite for developing appropriate soil and water management practices. Such information for Alfisols and Vertisols, the two major soils in the semi-arid tropics (SATs), is scanty especially from a long-term perspective. In this paper, we describe and discuss results from long-term (from 1976 to 2010) hydrological studies conducted on small agricultural watersheds on Vertisols and Alfisols at the ICRISAT Center, Patancheru, India. The hydrological behavior of soils are characterized in terms of runoff volume, peak runoff rate, number of runoff events, soil loss, sediment concentration and deep drainage loss under different rainfall, crop cover and soil moisture conditions to aid in developing effective soil and water management practices. We also provide details on the effects of annual and monthly rainfall on the hydrological behavior of these soils in different rainfall regions. The results show that Alfisols and Vertisols in the SATs have very contrasting hydrological behavior. Several findings emerging from our studies, are rather unexpected. For example, the sandy Alfisols with higher saturated hydrological conductivity generated higher runoff compared to the clayey Vertisols with extremely low saturated hydraulic conductivity. The undesirable early season runoff from Alfisols is higher than from Vertisols. The contribution of 1–2 big storms to annual runoff and soil loss was high on both soils. The contrasting hydrological behavior of these two soils is due to differences in soil characteristics such as crusting, sealing and low structural stability in Alfisols; and the presence of cracks during the early season and formation of micro-cracks during rainless periods in Vertisols. The results suggest that the information from the long-term hydrological studies is useful for determining appropriate soil and water management practices and strategies in different rainfall regions.
Background and aims Nitrification and denitrification are the two most important processes that contribute to greenhouse gas emission and inefficient use of nitrogen. Suppressing soil nitrification ...through the release of nitrification inhibitors from roots is a plant function, and termed "Biological Nitrification Inhibition (BNI)". We report here the role and contribution of sorgoleone release to sorghum-BNI function. Methods Three sorghum genotypes (Hybridsorgo, IS41245 and GDLP 34-5-5-3) were evaluated for their capacity to release sorgoleone, which has BNI-activity, in hydroponic and soil culture. Sorgoleone released was measured using HPLC; BNI-activity was determined using a luminescent recombinant Nitrosomonas europaea assay. Results Sorgoleone production and BNI-activity release by roots are closely associated (1 µg of sorgoleone is equivalent to 1 ATU activity in assay). Purified sorgoleone inhibited Nitrosomonas activity and suppressed soil nitrification. Sorghum genotypes release varying quantity of sorgoleone; GDLP 34-5-5-3 and Hybridsorgo showed higher capacity for both sorgoleone release and BNI-activity than did IS41245. In soil culture, GDLP 34-5-5-3 released higher quantity of sorgoleone into the rhizosphere, which had higher BNI-activity, and suppressed soil nitrification to a greater extent than did by IS41245. Conclusions These results demonstrate genetic differences for sorgoleone release and its functional link with BNI-capacity; there is potential for genetic improvement of sorghum BNI-capacity and deployment of this in low-nitrifying sorghum production systems.
▶ Ample variability for Fe, Zn, Ca, protein contents and agronomic traits. ▶ Identified promising accessions for high Fe, Zn, Ca and protein and grain yield. ▶ Identified diverse grain ...nutrient-specific accessions to study inheritance. ▶ Contrasting accessions to map nutrient traits. ▶ Diverse accessions to breed broad based nutrient-rich high yielding cultivars.
Finger millet is a promising source of micronutrients and protein besides energy and can contribute to the alleviation of iron (Fe), zinc (Zn) and protein malnutrition affecting women and preschool children in African and south-east Asian countries. The most cost effective approach for mitigating micronutrient and protein malnutrition is to introduce staple crop cultivars selected and/or bred for Fe, Zn and protein dense grain. Breeding finger millet for enhanced grain nutrients is still in its infancy. Analysis, detection and exploitation of the existing variability among the germplasm accessions are the initial steps in breeding micronutrient and protein-dense finger millet cultivars. Evaluation of finger millet core collection for grain nutrients and agronomic traits revealed a substantial genetic variability for grain Fe, Zn, calcium (Ca) and protein contents. The accessions rich in nutrient contents were identified and their agronomic diversity assessed. The accessions rich in Zn content have significantly higher grain yield potential than those rich in Fe and protein content. Grain nutrient-specific accessions and those contrasting for nutrient contents were identified for use in the strategic research and cultivar development in finger millet.
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