Soil Nitrogen Accumulation Research Articles

Organic and Inorganic Nitrogen forms as Affected by Phosphorus Additions in a Maize–Mustard Cropping System

AbstractPhosphorus (P) availability affects the accumulation and enrichment of soil nitrogen (N) forms. However, the effect of P addition on the distribution and turnover of soil N forms in the mustard–maize rotation system is unclear. A field experiment is conducted to investigate the effect of P addition on the turnover of soil N forms in a mustard–maize rotation system. The results show that after maize harvesting, the levels of ammonium N in soil with P addition are smaller compared to those without P addition. The organic N forms in soil with P addition are greater compared without P addition after mustard harvest. Moreover, the hydrolysable ammonium N and unknown hydrolysable N in soil with P addition are smaller than those without P addition after maize harvest. Structured equation model results show the intensities of hydrolysable amino acid N, hydrolysable amino sugar N, and unknown hydrolysable N transformed into ammonium N in soil with P addition are greater than those without P addition, and the intensities of these organic N forms transformed into nitrate N are weaker. The results indicate that P addition affect the accumulation and enrichment of soil N by altering the turnover of soil N forms.

AGROCHEMICAL EVALUATION OF SOILS UNDER HORTICULTURE ON THE SUITABILITY OF THEIR USAGE FOR THE MAIN AGRICULTURAL CROPS GROWING

This article reveals the results of research on the agrochemical composition of soils released from horticulture (Apple orchard) for the effectiveness of their usage in growing crops in field crop rotation. The research was conducted on Gray forest soils in the central part of Vinnytsia region in the forest-steppe of the Right Bank. The subject of research is agro-ecological indicators of soils that have been released from horticulture of varying degrees of intensity. It was found that in soils used for intensive horticulture nitrogen content of easily hydrolyzed, exchangeable potassium and humus was lower on 37.1, 23.7, 2.9 %, and mobile phosphorus, soil pH, metabolic calcium and metabolic magnesium on the contrary higher on 71.8, 12.8, 19.8 and 8.0 %, respectively, compared to the soils used for extensive horticulture. There is also a certain difference between mobile compounds of chemical metals in the soils under horticulture. The content of boron, molybdenum, cobalt and iron in the soils used for intensive horticulture was lower on 50.0, 32.8, 2.5 and 62.5 % compared to the soils of extensive horticultural lands. The concentration of sulfur was 8.0 % higher in intensive horticultural soils compared to the extensive ones. Characterizing the content of heavy metals-toxicants in soils used for intensive horticulture, it should be noted that the content of cadmium, lead, copper and mercury was higher on 4.0, 6.1, 9.5 and 6.6 %, and zinc is twice lower compared to the soils in extensive horticulture. Analysis of soils released from horticulture of varying degrees of intensity showed that the content of basic plant nutrients needs to be replenished, taking into account the growing need for basic nutrients in soils from phosphorus, potassium to nitrogen. When converting soils used for horticulture into arable land, it is necessary to take into account the measures that maximize the accumulation of soil nitrogen, in particular the cultivation of legumes. On these soils, it is not advisable to immediately grow nitrogen-loving crops, such as corn, winter wheat and sunflower, in the cultivation of which a high amount of this element is removed from the soil to form an optimal harvest. The practical significance of the results is that they will enable them to develop concrete proposals for reducing soil contamination by restoring soil fertility and improving the quality of plant material from cereals grown under exempted horticulture conditions.

Effects of Temperature and Nitrogen Application on Carbon and Nitrogen Accumulation and Bacterial Community Composition in Apple Rhizosphere Soil.

Malus sieversii grows on the slopes of the Tianshan Mountains in Xinjiang where the difference in daily temperature is significant. In recent years, the rhizosphere soil health of Malus sieversii has been severely impacted by anthropogenic disturbance and pathogenic infestation. The soil nutrient content and soil microorganism diversity are the main components of soil health. Low temperature has negative effects on soil bacterial community structure by inhibiting the accumulation of carbon and nitrogen. However, the effects of temperature and nitrogen application on soil carbon and nitrogen accumulation and the bacterial community composition in the rhizosphere soil of Malus sieversii are unclear. We set two temperature levels, i.e., low temperature (L) and room temperature (R), combined with no nitrogen (N0) and nitrogen application (N1) to explore the response of plant carbon and nitrogen uptake, rhizosphere soil carbon and nitrogen accumulation and bacterial community composition to temperature and nitrogen fertilization. At the same temperature level, plant 13C abundance (P-Atom13C), plant 15N absolute abundance (P-Con15N), soil 15N abundance (S-Atom15N) and soil urease, protease and glutaminase activities were significantly higher under nitrogen application compared with the no-nitrogen application treatment. The bacterial community diversity and richness indices of the apple rhizosphere soil in the N1 treatment were higher than those in the N0 treatment. The relative abundances of Actinobacteria, Rhodopseudomonas, and Bradyrhizobium were higher in the LN1 treatment than in the LN0 treatment. Redundancy analysis (RDA) showed that plant 13C absolute abundance (P-Con13C) and plant 15N absolute abundance (P-Con15N) were the main factors affecting the soil bacterial community composition. In summary, Nitrogen application can alleviate the effects of low temperature stress on the soil bacterial community and is of benefit for the uptakes of carbon and nitrogen in Malus sieversii plants.

Effect of different straw returning measures on resource use efficiency and spring maize yield under a plastic film mulch system

Straw returning is an effective measure for alleviating soil low organic carbon under film-mulched farmland but has not been widely adopted. A field experiment was conducted on the Loess Plateau to study the effects of different treatments on soil conditions, maize growth, yield, and nitrogen (N) accumulation and absorption to identify an appropriate straw returning measure under plastic film mulch. We investigated three straw returning measures—no straw returning with ridge–furrow plastic film mulch (RP), plow-crushed straw returning with ridge–furrow plastic film mulch (RP+S), ditch-buried straw returning with ridge–furrow plastic film mulch (RP+SD)—with two N fertilizer application rates—125 kg N·ha–1 (N125) and 175 kg N·ha–1 (N175). Combining straw returning and N application significantly improved soil hydrothermal conditions before sowing, and increased water use efficiency (WUE), N uptake efficiency (NupE), and maize yield. The RP+SD treatment had the highest aboveground biomass, root: shoot ratio, N accumulation, and NupE, and significantly increased maize yield by 13–16% at the two N fertilizer application rates, relative to RP. The RP+SD treatment had higher soil nitrate-nitrogen, total N and soil organic carbon contents, and soil water storage than the RP+S and RP treatments across both N treatments. The RP+SD–N175 treatment had the highest NupE, maize yield, and economic benefits in different treatments. In summary, ditch-buried straw returning combined with 175 kg N·ha–1 improved resource use efficiency and spring maize yield under plastic film mulch and is an effective measure for the sustainable development of film mulching systems in semi-arid areas.

A novel amended nitrification inhibitor confers an enhanced suppression role in the nitrification of ammonium in soil

PurposeNitrification inhibitor plays an important regulatory role in inhibiting the nitrification of ammonium in soils. However, most of nitrification inhibitors lack the sustainable effects in suppressing the nitrification of ammonium. In this study, a novel DMS nitrification inhibitor was prepared and tested to explore its lasting effect of nitrification suppression in black soil.Materials and methodsBoth culture experiments and field trial were performed in black soils. Three kinds of nitrification inhibitors (NIs), dicyandiamide (DCD) with low bioactivity, 3,4-dimethylpyrazole phosphate (DMPP) with high bioactivity, and a novel 3,4-dimethylpyrazole sulfate zinc (DMS) with long half-life, were applied into soils, respectively, and the abundance changes of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) were investigated; then, the accumulation changes of inorganic nitrogen, nitrogen use efficiency, and crop yields were furtherly evaluated.Results and discussionsA novel DMS nitrification inhibitor with high activity and long half-life maintained a persistent effect of nitrification suppression, and remarkably increased the accumulation of ammonium nitrogen in soil, thus improving nitrogen use efficiency and crop yields. This study implies that lowering the nitrogen loss of nitrification-triggered in soil is of great importance for improving nitrogen use efficiency.ConclusionsThis study provided an insight into the sustainable nitrification suppression of a novel DMS nitrification inhibitor under excessive application of nitrogen fertilizer in black soils. Compared with improving the activity, reasonably prolonging the validity of nitrification inhibitors in soil is a more important strategy increasing the sustainable effects of nitrification inhibition, and the survival period of nitrification inhibitors in soil should be a crucial factor improving nitrogen use efficiency.

Impact of mineral fertilizers on winter wheat quality using No-Till technology

The paper presents the study of the influence of ammophos, potassium magnesia and ammonium nitrate on the content of protein, gluten and grain unit of winter wheat using No-Till technology in the edaphoclimatic conditions of the southern zone of Rostov Region. It was shown that the application of mineral fertilizers to the surface soil layer during winter wheat cultivation using No-Till technology improves the grain quality. The highest grain quality parameters (protein content – 13.4% and gluten content – 25.3%, grain unit – 780.0 g/l) were obtained when ammophos and potassium magnesia were jointly added prior to sowing at a depth of 10 cm with double dressing of ammonium nitrate in the tillering and booting phases. High direct dependence of protein content in winter wheat grain on the accumulation of nitrate nitrogen in soil in the booting phase was revealed in all test layers: 0–10 (r = 0.85), 10–20 (r = 0.72), 0–30 cm (r = 0.76). The gluten content in the grain and its grain unit significantly depended on the mobility of phosphorus in the surface soil layer – 0–10 cm (r = 0.66 and 0.52, respectively). Along with the quality improvement of winter wheat grain, the rational use of mineral fertilizers in the No-Till system increases its yield. There is a direct positive relationship between grain protein content and winter wheat yield (r = 0.93).

Limited irrigation and fertilization in sand-layered soil increases nitrogen use efficiency and economic benefits under film mulched ridge-furrow irrigation in arid areas

Hetao Irrigation District (HID) in the upper Yellow River Basin of China is vulnerable due to the scarcity of water resources and environmental pollution caused by nutrient leaching. Appropriate irrigation and fertilization management are essential for improving crop productivity and developing sustainable agriculture in the HID. A two-year field experiment investigated the effects of irrigation and fertilization regimes on soil water, nitrogen accumulation and distribution in the soil profile and plant organs, nitrogen use efficiency, and economic benefits of spring maize (Zea mays L.) under film mulched ridge–furrow system. Three irrigation levels—I1 (high, 400 mm), I2 (medium, 300 mm), and I3 (low, 200 mm)—and two fertilization levels—F1 (high, 300 kg N ha−1) and F2 (low, 150 kg N ha−1) were designed. Mean soil NO3−-N contents did not significantly differ between I2 and I3 and were significantly higher than I1. I1F1 and I1F2 remarkably increased soil NO3−-N accumulation in the 80 − 100 cm soil layer at harvest. High irrigation increased the risk of N leaching into the deep soil layer. I2F2 increased plant nitrogen accumulation and promoted nitrogen transport to grains, improved nitrogen harvest index, and internal use efficiency. Under 400 or 300 mm irrigation amount, soil moisture and plant growth had little difference. Grain yields among I1F1, I1F2, I2F1, and I2F2 did not significantly differ in 2017 and 2018. In the relatively poor rainfall year (2017), I2F2 had 13.1%, 211.8%, and 294.1% higher net income than I2F1, I3F1, and I3F2, respectively, but 24.5% and 33.0% lower net income than I1F1 and I1F2, respectively. In 2018 with normal rainfall, I2F2 had 38.5%, 4.8%, 29.5%, 114.3%, and 96.2% higher net income than I1F1, I1F2, I2F1, I3F1, and I3F2, respectively. Therefore, the film mulched ridge–furrow irrigation system with 300 mm irrigation and 150 kg N ha−1 fertilization is a promising approach for reducing water supply and nitrogen leaching, and obtaining acceptable grain yield and economic benefits for spring maize production in the upper Yellow River Basin of China.

Soil nitrogen regulates symbiotic nitrogen fixation in a legume shrub but does not accumulate under it

AbstractLegumes in dryland ecosystems face the challenge of maintaining energetically costly symbiosis with N2‐fixing rhizobia, in a water‐ and nutrient‐limited environment. Controlled experiments showed a strong reduction in symbiotic N2fixation in response to elevated levels of nitrogen availability, but this regulation of N2fixation was not found in dryland field settings. Here, we ask whether regulation of N2fixation occurs in the field and what are the possible consequences for dryland soil nitrogen. We measured plant investment in root nodules and rates of bacterial activity, in seedlings and adults of a common N2‐fixing shrub,Calicotome villosa,in five field sites naturally varying in soil nitrogen and phosphorus availabilities. Additionally, we measured nitrogen concentrations and availabilities in the soil underC.villosaand a reference non‐fixing shrub. Biomass investment in root nodules was significantly reduced in response to elevated levels of soil nitrate in adult shrubs, but no such effect was found for seedlings. Soil nitrogen concentration underC.villosashrubs was low compared to the soil under a non‐fixing reference shrub. We provide evidence that symbiotic N2‐fixing plants in drylands tightly regulate their investment in symbiotic N2fixation, therefore controlling nitrogen inputs into the soil. These findings challenge the long‐held notion that the growth of N2‐fixing plants necessarily leads to the accumulation of soil nitrogen in their surroundings over time.

Conservative agriculture facilitates soil carbon, nitrogen accumulation, and aggregate stabilization under periodic flooding regimes

Aggregates play crucial roles in protecting soil carbon (C) and nitrogen (N) loss since aggregates could mediate the effect of environmental factors on the C and N accumulation. As ecotone habitats, reservoir riparian zones undergo disturbances from both land use and dam-regulated flooding, which could pose threats to aggregate stability. Yet, we know little about the effects of the flooding intensity and land use on the dynamics of soil C and N, as well as the mediating role of soil aggregates. In this study, along a flooding gradient, firstly we examined the effects of seven land-use types (corn, rice paddy, and vegetable lands; Chinese fir, willow, and mulberry restored lands; and grassland) on soil C and N accumulation; secondly, we identified the size distribution and stability of aggregates in mediating the effect of riparian land uses under periodic flooding regimes. We found that the C and N concentrations in soil aggregate fractions were all significantly impacted by land-use types, and aggregate-size distribution showed tight links with both land-use types and C and N contents. Conservative farmlands contained a higher proportion of macro-aggregates which stores significantly higher C and N concentrations than micro-aggregates. Notably, higher aggregate stability was also found in conservative farmland. We concluded that, in the riparian ecotone, conservative farming promotes C and N accumulation via stabilizing aggregate fractions, and suggested the conservative practices could be acceptable for soil conservation considering the scarcity of land resources in the ambient mountainous regions.

Symbiotic and Free‐Living N2 Fixation in Subtropical Pueraria lobata Communities of Southwest China

AbstractBiological N2 fixation plays crucial roles in determining the pattern and pace of ecological succession and carbon sequestration. Nevertheless, the rates and controls of symbiotic (SNF) and free‐living (FNF) N2 fixation have rarely been investigated simultaneously. Here we measured SNF and soil FNF rates for eight early succession ecosystems dominated by kudzu (Pueraria lobata (Willd.) Ohwi) in a subtropical region of China in growing and nongrowing seasons. N2 fixation rates were measured using acetylene reduction assay against a 15N2 uptake method. Both SNF and soil FNF rates were significantly higher in the growing season than in the nongrowing season. The two forms of N2 fixation contributed equally to total N2 fixation rate across the eight sites with soil FNF being higher than SNF in half of the sites. Total N2 fixation rates ranged from 7.12 to 61.93 kg N ha−1 yr−1 with an average of 22.93 ± 6.52 kg N ha−1 yr−1. N2 fixation contributed significantly to soil nitrogen and carbon accumulation. Both SNF and FNF were significantly related to soil moisture. Additionally, SNF and soil FNF were strongly correlated with phosphorus availability and vanadium/iron availability, respectively, most likely implying that SNF was limited by phosphorus and soil FNF was limited by vanadium or iron. Our findings suggest that SNF and soil FNF may be limited by different sets of nutrients within an ecosystem.

Influence of prokaryotic microorganisms on initial soil formation along a glacier forefield on King George Island, maritime Antarctica

Compared to the 1970s, the edge of the Ecology Glacier on King George Island, maritime Antarctica, is positioned more than 500 m inwards, exposing a large area of new terrain to soil-forming processes and periglacial climate for more than 40 years. To gain information on the state of soil formation and its interplay with microbial activity, three hyperskeletic Cryosols (vegetation cover of 0–80%) deglaciated after 1979 in the foreland of the Ecology Glacier and a Cambic Cryosol (vegetation cover of 100%) distal to the lateral moraine deglaciated before 1956 were investigated by combining soil chemical and microbiological methods. In the upper part of all soils, a decrease in soil pH was observed, but only the Cambic Cryosol showed a clear direction of pedogenic and weathering processes, such as initial silicate weathering indicated by a decreasing Chemical Index of Alteration with depth. Differences in the development of these initial soils could be related to different microbial community compositions and vegetation coverage, despite the short distance among them. We observed—decreasing with depth—the highest bacterial abundances and microbial diversity at vegetated sites. Multiple clusters of abundant amplicon sequence variants were found depending on the site-specific characteristics as well as a distinct shift in the microbial community structure towards more similar communities at soil depths > 10 cm. In the foreland of the Ecology Glacier, the main soil-forming processes on a decadal timescale are acidification and accumulation of soil organic carbon and nitrogen, accompanied by changes in microbial abundances, microbial community compositions, and plant coverage, whereas quantifiable silicate weathering and the formation of pedogenic oxides occur on a centennial to a millennial timescale after deglaciation.

Effects of tillage and fertility on soil nitrogen balance and greenhouse gas emissions of wheat-maize rotation system in Central Henan Province, China.

Energy saving, emission reduction, and efficiency improvement are important directions for agricultural development in Central Henan Province, the main grain production area in the Huang-huai-hai Plain. Based on the tillage and fertilization positioning experiment in 2010, we investigated the effects of three tillage methods (deep tillage, shallow tillage, and no-tillage) and two fertilization methods (nitrogen fertilizer and nitrogen fertilizer+organic fertilizer) on soil nitrogen balance and greenhouse gas emissions from 2018 to 2019. The results showed that soil nitrogen accumulation increased with organic fertilizer addition. During wheat and maize maturation, soil total nitrogen accumulation in the 0-60 cm layer was the highest under the treatment of shallow tillage+organic fertilizer, being 8058.53 and 8299 kg N·hm-2, respectively, being 3.2%-27.4% and 4.3%-7.2% higher than other treatments. The treatment with organic fertilizer addition resulted in nitrogen surplus. The shallow tillage+organic fertilizer treatment led to the highest nitrogen surplus (13.57 kg N·hm-2), which was 9.52 and 0.18 kg N·hm-2 higher than deep tillage+organic fertilizer and no tillage+organic fertilizer treatments. Nitrate leaching was the main way of nitrogen losses, accounting for 73.4%-76.9% of the total losses. The amount of nitrate leaching was the highest in deep tillage+organic fertilizer treatment (48.37 kg N·hm-2), being 18.9%-35.1% higher than other treatments. Results of greenhouse gases emission during 2018-2019 showed that global warming potential was the highest under the treatment of deep tillage+organic fertilizer, which was 33070 kg N·hm-2, being 6.6%-26.8% higher than other treatments. The treatment of organic fertilizer addition increased the emission of N2O and CO2 and reduced the absorption of CH4. The annual grain yield was highest under the treatment of deep tillage+organic fertilizer, which was 5.0%-17.1% higher than other treatments. The crop harvest index was the highest under the treatment of shallow tillage+organic fertilizer. The recommended cropping mode in Central Henan Pro-vince is shallow tillage+organic fertilizer, which could ensure crop yields, maintain soil nitrogen balance, and reduce greenhouse gas emissions.

Coastal reclamation alters soil microbial communities following different land use patterns in the Eastern coastal zone of China

Coastal reclamation seriously disturbs coastal wetland ecosystems, while its influences on soil microbial communities remain unclear. In this study, we examined the impacts of coastal reclamation on soil microbial communities based on phospholipid fatty acids (PLFA) analysis following the conversion of Phragmites australis wetlands to different land use types. Coastal reclamation enhanced total soil microbial biomass and various species (i.e., gram-positive bacterial, actinomycete, saturated straight-chain, and branched PLFA) following the conversion of P. australis wetland to aquaculture pond, wheat, and oilseed rape fields. In contrast, it greatly decreased total soil microbial biomass and various species following the conversion of P. australis wetland to town construction land. Coastal reclamation reduced fungal:bacterial PLFA, monounsaturated:branched PLFA ratios, whereas increasing gram-positive:gram-negative PLFA ratio following the conversion of P. australis wetland to other land use types. Our study suggested that coastal reclamation shifted soil microbial communities by altering microbial biomass and community composition. These changes were driven primarily by variations in soil nutrient substrates and physiochemical properties. Changes in soil microbial communities following coastal reclamation impacted the decomposition and accumulation of soil carbon and nitrogen, with potential modification of carbon and nitrogen sinks in the ecosystems, with potential feedbacks in response to climate change.

Impacts of Critical Periods of Weed Control (CPWC) on Nitrogen Utilization and Grain Yield in Aerobic Rice Cultivation

The cultivation of aerobic rice appears to be a potential option while mitigating threats of looming water scarcity for sustainable rice production. Although, severe prevalence of multi-flush weed pressure inhibiting nitrogen utilization for optimum grain yield becomes the crux of the problem for up-scaling this technology. Thus, the hypothesis of the study was that critical period of weed control (CPWC) governs nitrogen accumulation in aerobic soil—plant continuum, which appears to be the major determinant of ultimate grain yield in aerobic rice cultivation. With this view, the field studies were successively conducted in two locations at Panthnagar, Uttar Pradesh during 2015 and at Cuttack, Odisha during 2016 in India. Nitrogen utilization was estimated with varying magnitude of critical period of weed prevalence at 15 days interval since sowing till 75 days of crop growth. Results recorded significantly higher nitrogen uptakes of 106.6 and 106.0 kg ha−1 while maintaining near weed-free situations during initial 75 days of crop growth at Panthnagar and Cuttack respectively, which were however comparable with similar situations maintained also at 60 and 45 days of crop growth in respective location. Consequently, stands at these situations produced comparable grain yield of 5.56 and 5.25 t ha−1, 5.40 and 5.00 t ha−1, and 5.15 and 4.70 t ha−1 at corresponding locations, which were significantly higher than those corresponding weedy stands producing 1.35 and 0.90 t ha−1, 1.48 and 1.10 t ha−1, and 2.86 and 2.45 t ha−1 grain yields in respective locations. Thus, higher nitrogen gains of 0.42 and 0.06%, and 0.31 and 0.03% were attributed to initial 75 and 60 days weed-free stands respectively at Panthnagar and Cuttack. While, nitrogen losses were maximum of 24.99 and 25.69%, and 24.26 and 24.85% at corresponding weedy crop stands; although, initial 15 day’s weedy crop stands or initial 45 days weed-free stands recorded the lowest nitrogen losses of 0.64 and 1.35%, and 1.51 and 2.16%, instead. Therefore, the study contributed above novel information explaining the dynamic correlation of nitrogen balance with prevalence and also magnitude of CPWC where N uptake culminated at 45 days weed-free situation ensuring optimum aerobic rice productivity.

Depth Profile of Soil Carbon and Nitrogen Accumulation over Two Decades in a Prairie Restoration Experiment

Prairies converted from agriculture are known to accumulate carbon (C) and nitrogen (N) and are an important contribution to terrestrial C sequestration. However, estimates of decadal accumulation rates of C and N and their vertical distribution in the soil profile are highly variable among studies, in part due to the lack of repeated inventories of soil C and N stocks over long time periods. We determined the depth profile of soil C and N accumulation and bulk density following the transition from agriculture to planted prairie. Using 13 contiguous plantings with similar land-use histories, planted sequentially from 1995 to 2007, we sampled soil C, N, and bulk density three times over the course of two decades (2000, 2010, and 2019), combining a chronosequence approach with repeated inventories through time. In the top 20 cm of the profile, we found consistent accumulation of C and N, corresponding to 58% (0–10 cm) and 29% (10–20 cm) increases in soil C concentrations and 3.18% (0–10 cm) and 2.7% (10–20 cm) increases in soil N concentration over 19 years. In contrast, we found no change in C or N concentrations at 20–65 cm depth. A chronosequence approach did not detect C or N accumulation in any single sample year. Rather, initial soil C and N content appeared to be the best predictor of final concentrations. Our results suggest that the majority of C and N accumulation is occurring in the top portion of the profile and that restored prairies continue to sequester C two decades after initial planting.

Study on soil physical and chemical properties and carbon and nitrogen sequestration of grassland under different utilization modes

This research investigated the effects of natural grassland and artificial grassland degradation on soil physical and chemical properties, in particular the change in carbon and nitrogen contents and carbon sequestration. Representative areas of natural grassland, grazed artificial grassland and mown artificial grassland in Ar Horqin Banner, Inner Mongolia, were selected for study. Parameters measured in the study area were soil moisture content, soil bulk density, soil microbial content and soil nutrient levels. Growth status of the study sites was also evaluated using the NDVI value and in general the ranking for growth status under the different utilization modes was: mown artificial grassland>grazed artificial grassland>natural grassland. Soil water content in the 0-20 cm depth ranked: grazed artificial grassland>mown artificial grassland>natural grassland, and the differences were significant (P mown artificial grassland>natural grassland. The soil microorganism nitrogen content of the grazed artificial grassland for the 0-10 cm depth was (28.45±8.30) mg•kg-1, which was significantly higher than values in the natural grassland and mown artificial grassland (P grazed artificial grassland>mown artificial grassland, and soil carbon and nitrogen storage of natural grassland and grazed artificial grassland for the 10-30 cm depth were significantly higher than that of mown artificial grassland (P<0.05). The performance characteristic of grazed artificial grassland was soil carbon and nitrogen accumulation, while that of mown artificial grassland was carbon and nitrogen loss. In addition, with increase in soil depth, the carbon and nitrogen storage of natural grassland and mown artificial grassland show a decreasing trend. Thus it can be seen that the establishment of artificial grassland and human intervention such as seeding and irrigation will effectively improve soil quality and grassland growth status, but to a certain extent there may be a negative effect on soil carbon and nitrogen sequestration potential.

Influence of Soybean (Glycine max. L) Sowing Methods and Seed Rate on Nitrogen Accumulation in Soil

The soybean (Glycine max L.) is a crop with a high demand for nitrogen (N). The root nodules that form in soybeans can fix atmospheric N effectively. To quantify available N in the soil a field experiment was conducted at Regional Sugarcane and Rice Research Station, Rudrur to evaluate the impact of varying sowing methods and seed rates on yield of soybean and available N in soil after harvest of crop. Planting methods and seed rates significantly influenced seed yield and available nitrogen in the soil. Broad Bed Furrow (BBF) method with seed rate 50 kg ha-1 recorded significantly higher number of pods per plant (105) and mean seed yield of 1891 kg ha-1 over flatbed with 50 kg seed rate ha-1 (1757 kg ha-1) respectively. Broad Bed and Furrow method of planting recorded a significantly higher live root nodules and available nitrogen in soil with 50 kg seed rate ha-1. Seed rate of 75 kg/ha recorded highest available N in soil on broad bed and furrow method. Broad Bed Furrow (BBF) method with seed rate 50 kg ha-1 recorded highest net returns (₹ 53,233 ha-1) and highest B:C ratio (2.72) over flat bed of planting.

Soil nutrient variation impacted by ecological restoration in the different lithological karst area, Shibing, China

To carry out differentiated ecological restoration activities and formulate appropriate environmental conservation strategies for karst regions with different underlying bedrocks, it is essential to investigate the impact of ecological restoration and lithological differences on soil nutrients. The Karst world heritage site in Shibing, Guizhou province, China was selected as the study site. Here, we determined pH and nutrient differences in soil profiles of dolomite and limestone areas with ecological restoration activities. The results showed that (1) the main controlling factors of the topsoil were different from those of the core and bottom soils. (2) The topsoil was more sensitive to ecological restoration. Soil organic carbon, total nitrogen, and available nitrogen contents in the topsoil samples from the post-agricultural succession areas were significantly higher than those in the cultivated areas (P < 0.05), and were at 2.04–3.99, 1.62–4.07, and 1.52–3.18 -fold, respectively. (3) The core and bottom soils were mainly affected by the differentiated dissolution between the dolomite and limestone areas. The available nitrogen in the core and bottom soils were significantly lower in the dolomite area than in the limestone area (P < 0.05), and were 76.5% and 40.8% lower, respectively. Total phosphorus, available phosphorus and pH in the bottom soil were significantly higher in the dolomite area than in the limestone area (P < 0.05), and were 1.12, 1.86, and 2.63-fold, respectively. (4) Shrub recovery played a major role in the rapid accumulation of soil carbon and nitrogen in the dolomite area. Consequently, shrub development is very critical in the early stages of ecological restoration of dolomite areas following agricultural abandonment.

Effects of polymer materials on the transformation and utilization of soil nitrogen and yield of wheat under drip irrigation

AbstractNitrogen management is the key to improve crop yield. Polymer materials are widely used as water‐retaining agents in agriculture, but little is known about how polymer materials affect the transformation and utilization of soil nitrogen. This study focused on the effects of three polymer materials (humic acid extracted from cottonseed meal, H; modified polymer prepared by using polyacrylamide as main raw material, P; and composite polymer material composed of humic acid and modified polymer, HP) on the characteristics of soil and plant nitrogen accumulation in soils with/without plants under drip irrigation. The results showed that polymer materials increased the nitrogen accumulation and dry weight of leaf, spike axis + husk and grain, but decreased those of stem. Among them, the H treatment had the highest nitrogen uptake (34.5 kg·hm−2) after flowering stage, and the P treatment had the highest nitrogen transport (21.1% higher than no polymer materials, CK). Moreover, the wheat yields for the H and P treatments significantly increased by 19.7% and 12.6%, respectively. Polymer materials had an inhibitory effect on nitrogen fractions (soil total nitrogen (TN) and microbial biomass nitrogen (MBN) at the early stage of the culture, but there were significant improvements at the flowering and mature stages. The effects of polymer materials on the storage of TN and its fractions were different. Among them, the storages of soil TN, nitrate‐nitrogen (SNO3‐‐N), and ammonium‐nitrogen (SNH4+‐N) for the H treatment were increased, but the SNO3‐‐N in soil with plants was decreased by 1,317 kg·hm−2 compared with that in soil without plants, and the decrease was the largest among the decreases caused by the three polymer materials; the soil SNO3‐‐N for the P treatment was increased, but also the decrease in the SNO3‐‐N was smaller than that for the H treatment; the SNO3‐‐N for the HP treatment was increased, but the SNH4+‐N was decreased. Redundancy analysis showed that humic acid and modified polymer materials mainly increased soil MBN, NH4+‐N, and nitrogen accumulation of plant organs except for stem, which finally increases wheat yield.

Soil nitrogen accumulation, denitrification potential, and carbon source tracing in bioretention basins

Bioretention basins are one of the most commonly used green stormwater features, with the potential to accumulate significant levels of nitrogen (N) in their soil and to permanently remove it through denitrification. Many studies have investigated the N removal potential of bioretention basins through the assessment of inflow and outflow concentrations. However, their long-term N removal through soil accumulation and denitrification potential is less known. This study investigated the temporal variation of total N (TN) accumulation and denitrification potential in soils of 25 bioretention basins within a 13-year soil chronosequence, in a subtropical climate in Australia. The denitrification potential of a subset of seven bioretention basins was investigated in accompaniment with nutrient and soil characteristics. Additionally, stable isotopes (δ13C and δ15N) were used to assess temporal changes in the soil composition as well as to identify the sources of carbon (C) into these basins. Over 13 years of operation, TN accumulated faster in the top 5 cm of soil than deeper soils. Soil TN density was highest in the top 5 cm with an average of 1.4 kg N m−3, which was about two times higher than deeper soils. Site age and soil texture were the best predictors of soil TN density and denitrification (1 to 9.7 mg N m−2 h−1). The isotope values were variable among basins. Low δ15N values in young basins (-1.02‰) suggested fixation as the main source of N, while older basins had higher δ15N, indicating higher denitrification. Bioretention plants were the primary source of soil C; although the occurrence of soil amendment also contributed to the C pool. To improve the performance of these bioretention basins, we recommend increasing vegetation at initial years after construction, and enhancing more frequent anaerobic conditions in the high soil profile. These two conditions can improve denitrification potential, and thus the performance of these basins for improving water quality.