Nitrogen Mineralization Potential Research Articles

Effect of cover crops on soil health at different landscape positions

AbstractSoil health is crucial to reaching high yields, and growing cover crops can help improve soil conditions. The goal of this study is to determine the effects of cover crops on soil health using potential respiration, potential nitrogen mineralization, and aggregates stability as indicators of soil health. The study has been conducted since 2019 at the University of Kentucky Spindletop Farm, Lexington, KY, and involves three landscape positions receiving a treatment with cereal rye, cereal rye–crimson clover mixture, and fallow soil. This study emphasized that cover crops can enhance potential respiration and microbial activity over landscape positions, with rye being more beneficial than the mixture treatment. However, cover crops were also beneficial for aggregate stability but not for potential nitrogen mineralization.

Switchgrass (Panicum virgatum L.) cultivars have similar impacts on soil carbon and nitrogen stocks and microbial function

AbstractSwitchgrass (Panicum virgatum L.) production for biofuel has the potential to produce reasonable yields on lands not suited for conventional agriculture. We assessed nine switchgrass cultivars representing lowland and upland ecotypes grown for 11 years at a site in the upper Midwest USA for belowground differences in soil carbon and nitrogen stocks, soil organic matter fractions, and standing root biomass to 1 m depth. We also compared potential nitrogen mineralization and carbon substrate use through community‐level physiological profiling in surface soils (0–10 cm depth). Average yields and standing root biomass differed among cultivars and between ecotypes, but we found no significant cultivar‐related impacts on soil carbon and nitrogen stocks, on the distribution of particulate and mineral‐associated soil organic matter fractions, nor on potential nitrogen mineralization or microbial community‐level physiological profiles. That these traits did not differ among cultivars suggests that soil carbon and nitrogen gains under switchgrass are likely to be robust with respect to cultivar differences, and to this point not much affected by breeding efforts.

In vitro anaerobic incubation: a reliable method to predict the potential of nitrogen mineralization after grassland ploughing

Description of the subject. Large amounts of nitrogen may be released after grassland ploughing, and no reliable method is available for routine laboratories to help farmers managing these cultural practices. Objectives. The objective of this study was to assess whether short-term anaerobic potentially mineralizable nitrogen (PMN) is a reliable estimator of the N amount actually mineralized in the field during the growing season after grassland ploughing. Method. PMN was determined in vitro using a 7-day anaerobic incubation on three plots of grassland that were tilled and monitored for two years. The mineral nitrogen (NO3- -N and NH4+-N) amounts were measured at different times in the three plots and used to estimate the actual in situ mineralization with the LIXIM calculation model (ISM). Results. Our results indicated that in vitro anaerobic incubation of grassland soil samples provided estimations very close to the actual data of ISM observed during the monitoring (less than 10% of relative difference). A close relationship (p = 0.0029) was found between PMN and ISM with a high correlation (R2 = 0.91). Additionally, our study revealed very high levels of nitrogen mineralization during the first and second year after grassland ploughing, even after temporary grassland of short duration (3 years). Conclusions. PMN estimated by short-term anaerobic incubation is suitable for a reliable application in grasslands of all ages. This method should be used only if the mineral N content of the soil is not too high (< 100 kg N·ha-1 in our experiment) and the mineralization depth taken in account in the calculation should be defined rigorously in each situation.

Composts of diverse green wastes improve the soil biological quality, but do not alleviate drought impact on lettuce (Lactuca sativa L.) growth

AbstractIntense soil cultivation and climate change have detrimental effects on soils. Solutions are needed to improve the biological quality and water holding capacity of agricultural soils. A greenhouse experiment was conducted to investigate the interactive effect of compost application and drought stress on a soil/plant system in order to determine the improvement of soil quality and plant growth and the alleviation of drought stress. Lettuce (Lactuca sativa L.) was grown under greenhouse conditions in a sandy soil with sufficient mineral fertilizer application to test the effect of five compost types (three made from municipal garden and park wastes with differing nutrient contents, one from municipal household waste, and one from farm plant residues) applied at 30 Mg ha−1 dry weight, with which we compared soil quality and plant growth to soil without compost application. Treatment pots were irrigated or subjected to drought conditions during the last 14 days of lettuce growth. Assays of potential N mineralization during 28 days, dehydrogenase and β‐glucosidase activities, and a phospholipid fatty acid (PLFA) analysis were performed to assess effects on soil biological quality. Gas exchange, leaf relative water content, biomass, nitrogen accumulation, and root tip growth of lettuce were measured to investigate compost and drought stress effects on lettuce physiology. All composts improved indices of soil biological quality significantly, except for fungal abundance, relative to soil without compost. The greatest increase was obtained from farm compost, which significantly increased potential nitrogen (N) mineralization and soil enzyme activities of β‐glucosidase and dehydrogenase by factors of 4, 2, and 43, respectively. Furthermore, soil with farm compost generally showed a higher abundance of soil microbial organisms compared with soil without compost, which could be related to its high cellulose and hemicellulose contents. The lowest abundance of microbial organisms was generally found in soil with garden and park waste compost with a medium nutrient content, which could be related to its low organic matter content. The beneficial effect of compost on soil biological quality did not lead to improved lettuce growth, which suggests that soil biological quality (ameliorated by compost application) is not important for a fast‐growing crop, such as lettuce, that is sufficiently fertilized. Drought stress reduced aboveground lettuce biomass, root tip growth, and the abundance of most soil microbial groups significantly, but compost in soil did not alleviate these negative effects. In conclusion, the farm compost made from grass–clover, straw, and vegetable residues is superior to garden and park waste and household waste composts in terms of beneficial effects on soil biological quality. Compost clearly improved soil biological quality, but did not influence lettuce's response to drought stress. The knowledge gained in this study is useful for producing tailor‐made compost with desired effects of improved soil biological quality.

Predicting nitrogen mineralization potential and availability of biochar-based agro-municipal solid waste co-compost using alkaline hydrolysis

Valorization of agro-municipal solid wastes into value-added nutrient-enriched slow-release organic amendments (OAs) for ameliorating soil fertility constraint has been proposed as an environmentally friendly and sustainable approach to managing challenges associated with disposal of organic wastes. However, for soils receiving OAs of complex composition, such as biochar-manure-compost (BMC), the predictive knowledge needed to synchronize amount and timing of nitrogen (N) release with plant demand, thereby minimizing environmental pollution, is still lacking. This study validated results from an alkaline hydrolysis method for estimating N mineralization potential with: (i) the standard long-term N mineralization procedure and (ii) actual N uptake from soils amended with BMCs of varied C/N ratios. The alkaline hydrolysis procedure involves direct steam-distillation of BMC-soil mixtures, requiring only 40-min for estimating N mineralization potential, whereas the standard N mineralization procedure followed 26-week laboratory incubation. For both procedures, cumulative N mineralized or hydrolyzed was fitted to the first-order exponential equation to determine the potentially mineralizable N (No) and an analogous “potentially hydrolyzable N (Nmax)” for the BMCs. Nitrogen uptake by maize was evaluated in a six-week pot experiment. The results showed that Nmax and No values differed among the BMCs, indicating differences in chemical composition, and potential mineralizabilities of the BMCs. Increasing biochar content of the BMCs decreased kinetic parameters of N mineralization compared to compost alone. Estimated Nmax values significantly correlated with No (p = 0.023) and N uptake (p = 0.005), suggesting that alkaline hydrolyzable ON can replace the long-term procedure for estimating No in BMC-amended soils, reducing experimental cost and time.

Potential Nitrogen Mineralization of Agricultural Wastes in Typic Natraqualfs: Implications for Jasmine Rice

ABSTRACT Problems of salt-affected soils can be alleviated by organic amendments, but their nitrogen (N) mineralization pattern, crucial to providing proper N synchronization with crop demand, can differently be influenced by salinity and sodicity. An incubation study was carried out objectively to investigate the mineralization and kinetic release of N in three organic wastes (OWs) – rice husk (RH), rice straw (RS), burnt rice husk (BRH) in saline-sodic (SS) and sodic (Sod) soils. The OWs were mixed into the soils and inorganic N was measured under aerobic condition (field capacity) for 28 days followed by waterlogged condition until day-112. The mineral N mineralized from all OWs was, on average, <20% of N input released into the mineral N pool with RS mineralized the highest. Mineralization occurred less in SS than in Sod soil. Nitrogen mineralization peaked at 28 days with net immobilization observed after 21-day of waterlogged condition. The mineralization rate and mineralizable N pool of these OWs had a better fit to two-pool than first-order model, showing the highest quantities in respective RS, RH and BRH and fast N pools constant rate greater in SS than in Sod soils. Net N mineralization differed among OWs, soils and incubation times. The N mineralization pattern of OWs was a function of both N sources and soil salinity. The pool and rate of mineralizable N were predicted from the initial material’s total N. The findings can lead to proper N management for jasmine rice in salt-affected soils using inorganic wastes to partially supply N.

Identifying key factors controlling potential soil respiration in agricultural fields

AbstractSoil respiration is one of the main soil health indicators and is influenced by several factors in agricultural fields. Identifying key factors that control soil respiration is desirable for informed soil management decisions and for promoting and scaling up soil health. This study aimed to (i) quantify the relationships between potential soil respiration and selected soil properties, crops, and slope positions, and (ii) identify key factors controlling these relationships using a neural network model. Ninety soil samples from 0‐ to 5‐ and 5‐ to 20‐cm soil depth were collected from footslope, backslope, and summit in three fields planted with soybean (Glycine max L. Merr.), alfalfa (Medicago sativa L.), and corn (Zea mays L.). The model provided great accuracy (coefficient of determination: 0.96; root‐mean square error: 7.8; and mean absolute deviation: 3.8) and explained nearly 96% of variations in soil respiration across soil depth, crop, and slope positions. Soil depth, ammoniacal nitrogen (NH4‐N), crop types, slope position, and silt content were identified as the top five factors influencing potential soil respiration at the field level. Potential soil respiration was more sensitive to potassium, phosphorus, pH, cation exchange capacity, and mean weight diameter and less sensitive to NH4‐N, nitrate nitrogen, soil organic matter, and clay content. It increased with pH, electrical conductivity, mean weight diameter, potential nitrogen mineralization, and potassium, and it decreased with increasing silt content. Soil from 0 to 5 cm under soybean or at the summit slope position exhibited a higher respiration. Using a small dataset, this pilot study accurately predicted potential soil respiration in agricultural fields and identified key drivers controlling it. The results from this study highlight the complexity of using potential soil respiration as a standalone test for evaluating soil health. This does not diminish the usefulness of potential soil respiration as a soil health indicator to support agricultural management decisions and as a reference in future soil health studies. However, it emphasizes the importance of considering multiple factors when interpreting the significance of soil biological indicators for soil health assessments.

Soil biological indicators associated with nitrogen mineralization patterns in rice soils under long‐term integrated nutrient management

AbstractIn long‐term integrated nutrient management (INM) involving organic amendments with inorganic fertilizer application, understanding nitrogen (N) mineralization is key to assessing soil functioning. In this study, soil samples were collected following rice cropping from treatments consisting of various combinations of inorganic with organic fertilizers, including farm yard manure, wheat straw or Green Leaf Manuring, as well as 100% inorganic and a control (no fertilizer). The soil samples were incubated for 120 days at 30°C for determining N mineralization potential, and the mineralization patterns were fitted to double first‐order kinetic models to separate the potentially mineralizable nitrogen (PMN) into readily available N (PMN‐I) and resistant N (PMN‐II) fractions. The half‐lives of PMN‐I and PMN‐II ranged from 1.2 to 3.3 days and 22.4 to 63.0 days, respectively. In the organically amended soils, we observed that microbial biomass carbon (MBC) and nitrogen (MBN) increased by 43% and 41%, respectively, compared to inorganic fertilizer application alone. Moreover, the soil enzyme activity increased, revealing enhanced biological activity (dehydrogenase—31.96 μg TPF, Urease—35.69 μg urea‐N, glucosidase—57.78 μg p‐nitrophenol, fluorescein diacetate hydrolysis—45.84 μg fluorescein, N‐acetyl β‐glucosaminidase—46.47 μg p‐nitrophenol released g−1 dry soil h−1). We determined that PMN‐I was affected by the soil urease activity; whereas, PMN‐II was regulated by soil organic carbon, MBC, MBN, dehydrogenase activity and fluorescein diacetate hydrolysing capacity. These findings elucidate the soil biological indicators associated with nitrogen (N) mineralization, which can help optimize INM practice.

Interaction of Filth Flies and Epigeal Arthropods with Soil Nitrogen and Gas Emissions in Grazing Systems under a Legacy of Low Fertilization

During the summers of 2021 and 2022, we conducted a study in four Georgia Piedmont pastures to assess the effect of the presence of filth flies and epigeal arthropods on carbon and nitrogen emissions and soil nitrogen retention from lax rotational grazing systems under a legacy of low fertilization. Carbon dioxide (CO2), nitrous oxide (N2O), and ammonia (NH3) emissions were measured from dung on days 0, 4, 8, and 15 following depositions. Soil and manure samples were collected on days 0 and 16 and analyzed for ammonium (NH4+), nitrate (NO3−), plant-available nitrogen (PAN), and potentially mineralizable nitrogen (PMN). Manure samples were analyzed for total Kjeldahl nitrogen (TKN). The numbers of filth flies ovipositing and emerging from manure, fire ants, and epigeal arthropods around the manure were determined. Our results indicated that more than 12 ovipositing filth flies per manure pat can reduce PMN by up to 14.7 kg of nitrogen per hectare, while an increase in the biodiversity and abundance of predators may help to increase PAN and PMN in grazing systems, as well as decrease the number of emerging filth flies.

Carbon and Nitrogen Mineralization Kinetics in Soil Under Differential Nutrient Management Regimes in Inceptisols of Coastal India

ABSTRACT In intensive cropping systems, nutrient, and residue management techniques have a tendency to change the soil’s carbon (C) and nitrogen (N) cycle and, consequently, its potential for sequestration and loss. To understand the carbon and nitrogen mineralization kinetics, laboratory incubation studies were conducted with soils at variable depths from a long-term nutrient management experiment on cereal-vegetable-pulse cropping system. The experiment was laid out completely randomized design with 10 treatments replicated thrice. Long-term integrated application of inorganics with organics, biofertilizers, and amendment along with crop residues showed higher carbon and nitrogen mineralization potential and lower potential was observed in soils where crops were raised without application of any nutrient inputs (control) and uncultivated fallow. It was calculated that the potential for higher levels of carbon and nitrogen mineralization existed in the surface (0–15 cm) and subsurface (15–30 cm) layers, respectively, and was negligible in the deeper layer (30–45 cm). The mineralization rate was initially faster up to 42 days of incubation, indicating proper utilization of readily decomposable soil organic matter in the labile pools and thereafter found to slow down. Addition of lime along with the integrated use of organics and inorganics has found to raise the pH to a level that provides a suitable soil environment which affects the carbon and nitrogen mineralization kinetics resulting in buildup of total organic carbon and total nitrogen in the soils. The first-order kinetic model was the best fit in explaining the kinetic parameters of C and N mineralization. Soils under integrated nutrient management (INM) with farmyard manure (FYM) along with biofertilizers, amendment, and inorganic nutrients exhibited better carbon dynamics higher C mineralization (Cmin), potentially mineralizable C (C0), rate of C mineralization (dCmin/dt), and C mineralization quotient (qM), whereas soils applied with similar combinations with vermicompost was found effective for better nitrogen dynamics in terms of enhanced N mineralization (Nmin), potentially mineralizable N (N0), rate of N mineralization (dNmin/dt) and active N fraction over control and fallow soils. Integrated application of inorganic and organic inputs with crop residues over the years has shown beneficial impacts on soil carbon and nitrogen mineralization processes and their kinetics.

The Nitrogen Cycling Key Functional Genes and Related Microbial Bacterial Community α−Diversity Is Determined by Crop Rotation Plans in the Loess Plateau

Soil nitrogen cycling microbial communities and functional gene α−diversity indicate soil nitrogen cycling ecological functions and potentials. Crop rotation plans affect soil nitrogen fractions and these indicators. We sequenced soil samples from four crop rotation plans (fallow, winter wheat monoculture, pea-winter wheat-winter wheat-millet rotation, and corn-wheat-wheat-millet rotation) in a long-term field experiment. We examined how microbial communities and functional gene α−diversity changed with soil nitrogen fractions and how nitrogen fractions regulated them. Planting crops increased the abundance and richness of nitrogen cycling key functional genes and bacterial communities compared with fallow. The abundance and richness correlated positively with nitrogen fractions, while Shannon index did not. The abundance increased with soil total nitrogen (STN) and potential nitrogen mineralization (PNM), while Shannon index showed that nitrogen cycling key functional genes increased and then decreased with increasing STN and PON. Introducing legumes into the rotation improved the α−diversity of nitrogen cycling key functional genes. These results can guide sustainable agriculture in the Loess Plateau and clarify the relationship between nitrogen fractions and nitrogen cycling key functional genes.

Cover crops did not improve soil health but hydroclimatology may guide decisions preventing cash crop yield loss

IntroductionCover crop (CC) is an essential tool to improve or maintain soil health, potentially improving cash crop productivity. Several recent reports of cash crop yield reduction following cover cropping necessitated this research to guide efficient CC decisions in the season before corn (Zea mays) or soybean (Glycine max) is to be grown.MethodsTherefore, we designed this multi-year, multi-location study to include the farmers who plant CC following the harvest of a small grain crop, majorly wheat (Triticum aestivum) or oats (Avena sativa), and then grow corn or soybean cash crop in the subsequent season. We also selected the farmers who used a fall CC mix that was winter-terminated, to avoid further complexities. The major objective of this study was to document soil health changes and cash crop yields following CC in eight selected locations around SD for three consecutive CC seasons between 2017-2020. Experimental plots were laid out at the farmer-cooperators’ CC fields, where no cover (NC) ‘control’ was tested against CC in a randomized complete block design (RCBD). Soil samples were analyzed for selected soil health indicators (SHIs): potentially mineralizable nitrogen (PMN), permanganate oxidizable carbon (POXC), soil respiration (SR), soil microbial biomass (SMB), soil nitrate-nitrogen, soil organic matter (SOM), and other basic soil properties (pH, electrical conductivity, etc.); crop and residue biomass were calculated, and cash crop economic yields were measured. Results and discussionNo statistically significant (p&amp;lt;0.05) advantage was found for SHIs or cash crop yields under CC plots compared to NC plots as these fields had healthy soils (long-term no-till was practiced, high SOM levels &amp;gt;30 g kg-1). These findings directed us to investigate hydroclimatological parameters and climatological indices such as accumulated precipitation, standardized precipitation index (SPI), and standardized precipitation-evapotranspiration index (SPEI) for their impact on CC’s influence on cash crop yields. ConclusionOur analyses indicated that hydroclimatology, especially SPEI for the month before CC planting can be used as a tool to guide successful CC decisions, reducing the risk of cash crop yield loss. Further investigations with SPI and SPEI, along with other climatological parameters are needed to explore and design better CC management tools.

Understanding the cadmium passivation and nitrogen mineralization of aminated lignin in soil

Aminated lignin (AL) was prepared and first applied to remediation of cadmium (Cd) pollution in soil. Meanwhile, the nitrogen mineralization characteristics of AL in soil and its effect on soil physicochemical properties were elucidated by soil incubation experiment. The results showed that the Cd availability was dramatically lowered in soil by adding the AL. The DTPA-extractable Cd content of AL treatments was considerably reduced by 40.7–71.4 %. The soil pH (5.77–7.01) and absolute value of zeta potential (30.7–34.7 mV) enhanced simultaneously as the AL additions increased. The content of soil organic matter (SOM) (99.0–264.0 %) and total nitrogen (95.9–301.3 %) were gradually enhanced due to high C (63.31 %) and N (9.69 %) content in AL. Moreover, AL significantly elevated the content of mineral nitrogen (77.2–142.4 %) and available nitrogen (95.5–301.7 %). The first-order kinetic equation of soil nitrogen mineralization revealed that AL greatly enhanced nitrogen mineralization potential (84.7–143.9 %) and reduced environmental pollution by lowering the loss of soil inorganic nitrogen. AL could effectively reduce the availability of Cd through direct (self-adsorption) and indirect effects (improvement of soil pH, SOM and reduction of soil zeta potential), thereby achieving passivation of Cd in soil. In short, this work will develop a novel approach and technical support for soil heavy metal remediation, which is of great significance for improving the sustainable development of agricultural production.

Mechanisms Driving the Distribution and Activity of Mineralization and Nitrification in the Reservoir Riparian Zone.

The riparian zone ecosystems have greater energy flow and elemental cycling than adjacent terrestrial and aquatic ecosystems. Mineralization and nitrification are important initiating processes in the nitrogen cycle, but their distribution and activity under different environmental conditions in the riparian zone and the driving mechanisms are still not clear. We investigated the effects of environmental and microbial factors on mineralization and nitrification activities by analyzing the community of alkaline (apr) and neutral (npr) metallopeptidase, ammonia-oxidizing archaea (AOA), and bacteria (AOB) in soils and sediments under different land-use types in the riparian zone of Miyun Reservoir, as well as measuring potential nitrogen mineralization and ammonia oxidation rates (AOR). The results showed that the mineralization and nitrification activities of soils were greater than those of sediments. AOA and AOB dominate the ammonia oxidation activity of soil and sediment, respectively. NH4+ content was a key factor influencing the ecological niche differentiation between AOA and AOB. The high carbon and nitrogen content of the woodland significantly increased mineralization and nitrification activity. Microbial communities were significantly clustered in the woodland. The land-use type, not the flooding condition, determined the distribution of microbial community structure. The diversity of npr was significantly correlated with potential N mineralization rates, while the transcript abundance of AOA was significantly correlated with ammonia oxidation rates. Our study suggests that environmental changes regulate the distribution and activity of mineralization and nitrification processes in the reservoir riparian zone by affecting the transcript abundance, diversity and community structure of the microbial functional genes.

The contrasted impacts of grasshoppers on soil microbial activities in function of primary production and herbivore diet

Herbivory can have contrasted impacts on soil microbes and nutrient cycling, which has stimulated the development of conceptual frameworks exploring the links between below- and aboveground processes. The “productivity model” predicts that herbivores stimulate microbial activities and accelerate nutrient mineralization in productive ecosystems, while they have an opposite effect in less productive ecosystems. In parallel, the “diet model” predicts that herbivores feeding on conservative plants accelerate nutrient cycling while those feeding on exploitative plants decelerate nutrient cycling, due to changes in litter inputs. Since these two frameworks can lead to conflicting predictions in some cases, experimental evidence combining herbivore diet and plant productivity is required. During two consecutive years, we conducted an experiment controlling the presence of three grasshopper species consuming either grasses, forbs or both in twelve natural and managed alpine grasslands with contrasted productivities. In order to assess the effects of herbivory on soil microbes, we measured their extracellular enzymatic activities, biomass and potential nitrogen mineralization (PNM). Soil and vegetation were also characterized to test how much they modulated the effects of herbivory on microbes. Contrary to the predictions of the diet model, the effects of herbivory on microbial characteristics did not depend on the herbivores diet, but were influenced by primary production, though in a way that differed from the productivity model. The most productive sites were constituted by exploitative plant species which depleted N resources in the soil, and by microbes producing relatively few extracellular enzymes, leading to a lower PNM. Herbivory increased microbial biomass and decreased the production of extracellular enzymes in those sites, possibly through the stimulation of root exudates produced by exploitative species. The least productive sites were characterized by conservative plants, high soil C content, and by microbes having a resource acquisition strategy (more extracellular enzymes, higher PNM). Herbivory decreased microbial biomass and increased the production of extracellular enzymes in those sites. This pattern can be explained by the loss of carbon associated with insect respiration, which increases the resource requirements of microbes and by a lower production of root exudates by conservative species. Therefore, the effects of two years of herbivory on soil microbes were at odds with the productivity model, which focuses instead on longer term effects corresponding to herbivory-induced changes in plant species composition. This highlights the multidimensional feature of the impacts of herbivory on ecosystem functioning, both in space and time.

Evaluation of Alkaline Hydrolyzable Organic Nitrogen as an Index of Nitrogen Mineralization Potential of Some Coastal Savannah Soils of Ghana

Numerous biological and chemical methods have been proposed over the years for estimating the nitrogen (N) mineralization capacity of soils; however, none of them has found general use in soil fertility testing. The efficacy of a recently proposed alkaline hydrolysis method for assessing N availability in soils compared with the standard long-term incubation technique for determining potentially available N was evaluated. The nitrogen mineralization of 12 surface soils incubated under aerobic conditions at 25 °C for 26 weeks was determined. Field-moist soils were direct-steam distilled with 1 M KOH or 1 M NaOH; the NH3 released was trapped in boric acid, and its concentration was determined successively every 5 min for 40 min. The cumulative N mineralized or hydrolyzed was fitted to the first-order exponential equation to determine the potentially mineralizable N (No) and an analogous “potentially hydrolyzable N (Nmax)” for the soils. The flush of CO2 (fCO2) following the rewetting and incubation of air-dried soils under aerobic conditions for 3 days was also determined. The results showed that the Nmax values differed considerably among the soils, indicating differences in the chemical nature and reactivity of the organic N content of the soils, and were significantly correlated with No and fCO2 values. The estimated Nmax and No values ranged from 105 to 371 mg N kg−1 and 121 to 292 mg kg−1, respectively. Based on the simple and inexpensive nature of the alkaline hydrolysis procedure, the reduction in the incubation time required to obtain No (months to minutes), and the strong association between Nmax and No, we concluded that Nmax is a good predictor of the biologically discrete and quantifiable labile pool of mineralizable soil organic N (ON), and the use of the alkaline hydrolyzable ON as a predictor of No merits consideration for routine use in soil testing laboratories for estimating the N-supplying capacity of soils.

Reduced tillage and rotational diversity improve soil health in Missouri

AbstractThe Missouri Soil and Water Conservation Program was initiated by the Department of Natural Resources (DNR) to address challenges related to soil and water degradation by examining soil health under real‐world management practices. Soil health data from 5,300 field sites enrolled in a DNR cost‐share program were analyzed for the effects of tillage intensity [no‐till (NT), reduced tillage (RT), and intensive tillage (IT)] and crop rotational diversity (monoculture, two‐crops, and three or more crops in rotation) within and across six regions in the state. Soil health indicators included soil organic carbon (SOC), active carbon, potentially mineralizable nitrogen (PMN), and aggregate stability. At the state level, SOC, active carbon, and PMN were 14.4, 14.0, and 17.5% greater under NT, and 10.2, 11.0, and 11.2% greater under RT, respectively, compared with IT. Aggregate stability was greater under NT (33.8%) and RT (30.4%) relative to IT (28.0%). Across the state, diversified rotations with three or more crops exhibited 6.1 and 7.9% greater SOC, 6.5 and 7.9% greater active carbon, and 10.7 and 11.6% greater PMN relative to two‐crop rotations or monocultures, respectively. Aggregate stability was significantly greater under diversified rotations (35.5%) relative to two‐crop rotations (30.6%) and monoculture (30.8%). This study highlights the value of on‐farm datasets from real crop production systems and illustrates the potential to increase soil health with adoption of conservation tillage and extended crop rotations in Missouri.

Combined livestock grazing-exclusion and global warming decreases nitrogen mineralization by changing soil microbial community in a Tibetan alpine meadow

Alpine meadows play a key role in maintaining biodiversity, soil nutrient retention, and herders’ livelihoods in mountain regions. Livestock grazing-exclusion is common in grassland management to protect and promote the sustainable use of alpine meadows. However, there are few studies evaluating the effects of traditional light grazing practices in alpine regions and grazing-exclusion impacts on soil nutrient, especially under conditions of climate warming. In this study, we conducted a five-year grazing-exclusion and warming manipulation experiment to examine the effects of grazing-exclusion on soil nitrogen fractions, microbial communities, and enzyme activities under climate warming. Treatments consisted of light-intensity grazing, grazing-exclusion, and combined grazing-exclusion and warming. Our results showed that grazing-exclusion significantly decreased potential nitrogen mineralization at a 0–5 cm depth and at altitudes of 3850 m, 4000 m, 4150 m, and 4250 m. Combined grazing-exclusion and warming also significantly decreased potential nitrogen mineralization at a 0–5 cm depth and at relatively higher altitudes of 4000 m, 4150 m, and 4250 m. Grazing-exclusion, combined grazing-exclusion and warming all shifted microbial communities from bacteria toward fungi. Grazing-exclusion significantly decreased the relative abundances of phylum Chloroflexi (bacteria) and phylum Ascomycota (fungi), while combined grazing-exclusion and warming significantly increased the relative abundances of phylum Basidiomycota (fungi). The relative abundances of phylum Ascomycota (fungi) demonstrated a positive relationship with potential nitrogen mineralization, but the relative abundances of phylum Basidiomycota (fungi) had a negative relationship with potential nitrogen mineralization. The activities of dehydrogenase and protease in grazing-exclusion and combined grazing-exclusion and warming meadows were lower than those in grazed meadows. Our results demonstrated that in the context of climate change and global warming, grazing-exclusion is unsuitable as a tool for the sustainable management of alpine meadows from soil nitrogen mineralization and fractions point of view. Of concern, climate warming could potentially amplify the adverse effects of grazing-exclusion and causes depletion of soil nutrients in the alpine meadow. This research suggests that a light-intensity grazing (0.5 yak ha−1 year−1) is beneficial to increase soil enzyme activity and N mineralization in alpine meadows. Our results provide substantial evidence and a useful baseline and guidance for the sustainable grazing management of alpine meadows as environments change due to climate warming in the future.

Evaluation of nitrogen mineralization under various irrigation water qualities and nitrogen application rates for mulched drip irrigation in an arid region

AbstractUnderstanding the interactive effects of irrigation water quality and fertilization on nitrogen mineralization (Nmin) and accurately predicting Nmin are of great importance for the secure and efficient utilization of brackish water in arid regions. A pot experiment was conducted to determine the Nmin under different drip irrigation water salinities and nitrogen application rates and to modify the nitrogen mineralization potential (N0) and mineralization rate constants (k) of the first‐order kinetic equation of Nmin. An in situ field experiment was conducted to validate the modified equation. The results showed that the amounts of Nmin for water salinities of 1.27, 3.03, and 4.90 g L−1 were 58.9, 76.1, and 45.4 kg ha−1, respectively. Nmin was stimulated when the soil salinities were lower than 6.6, 6.1 and 3.9 g kg−1 for nitrogen application rates of 255, 315 and 375 kg ha−1, respectively. Nitrogen application significantly reduced Nmin. When the nitrogen application rate increased to 375 kg ha−1, the net Nmin rate remained lower, and the effects of salinity on Nmin were attenuated. The Nmin model with modified N0 and k values was developed considering the impacts of soil organic nitrogen, nitrogen application rate, and soil salinity. Model testing indicated that the modified model provided an acceptable estimation of Nmin under field conditions. It will be helpful for developing rational fertilization strategies of drip irrigation with brackish water in arid regions.

Agricultural management affects active carbon and nitrogen mineralisation potential in soils

AbstractBackgroundSoil organic matter (SOM) is important for soil fertility and climate change mitigation. Agricultural management can improve soil fertility and contribute to climate change mitigation by stabilising carbon in soils. This calls for cost‐effective parameters to assess the influence of management practices on SOM contents.AimsThe current study aimed at understanding how sensitively the parameters active carbon (AC) and nitrogen mineralisation potential (NMP) react to different agricultural management practices compared to total organic carbon (TOC) and total nitrogen (Nt). We aimed to gain a better understanding of SOM processes, mainly regarding depth distribution and seasonality of SOM dynamics using AC and NMP.MethodsWe looked mainly at four parameters, namely permanganate oxidisable carbon (AC), nitrogen minerlaisation potential (NMP), total organic carbon (TOC) and total nitrogen (Nt). Data were obtained in five long‐term field experiments (LTEs) testing four management practices: (1) tillage, (2) compost application, (3) crop residue management, and (4) mineral fertilization.ResultsAC was specifically sensitive in detecting the effect of tillage treatment at different soil depths. NMP differentiated between all different tillage treatments in the upper soil layer, it showed the temporal dynamics between the years in the compost LTE, and it was identified as an early detection property in the crop residue LTE. Both AC and NMP detected short‐term fluctuations better than TOC and Nt over the course of two years in the crop residue LTE.ConclusionWe suggest that AC and NMP are two valuable soil biochemical parameters providing more detailed information on C and N dynamics regarding depth distribution and seasonal dynamics and react more sensitively to different agricultural management practices compared to TOC and Nt. They should be integrated in monitoring agricultural long‐term experiments (LTEs) and in field analyses conducted by farmers. However, when evaluating results towards long‐term carbon storage, their sensitivity toward annual fluctuations should be taken into account.