Nitrogen Mineralization Potential Research Articles

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.

Potential Nitrogen Mineralization and Its Availability in Response to Long-Term Fertilization in a Chinese Fluvo-Aquic Soil

The determination of organic nitrogen (N) mineralization is crucial for estimating N availability, quantifying exogenous inputs, and estimating associated environmental impacts. The objective of this study was to explore the effect of long-term various fertilization on soil organic N mineralization potential (NMP), which influences plant N accessibility. Treatments from a 26-year long-term field experiment with no fertilization (CK), chemical fertilizer N at 165 kg N ha−1 and P at 82.5 kg P2O5 ha−1 (NP), NP with K fertilizer at 165, 82.5, 82.5 kg ha−1 N, P2O5 and K2O (NPK), NPK at 165, 82.5, 82.5 kg ha−1 N, P2O5 and K2O with manure at 7857.14 kg ha−1 (NPKM), and NPKM at 165, 82.5, 82.5 kg ha−1 N, P2O5 and K2O with manure at 1.5× application rate (11,785.71 kg ha−1) (1.5NPKM) were examined for potentially mineralizable N by aerobic incubation at 35 °C for 30 weeks. Three pools (Pools I, II, and III) of mineralizable N were recognized. Pool I, the mineralization flush on rewetting in the first 2 weeks; Pool II, gross N mineralization between weeks 2 and 30; and Pool III, the potentially mineralizable N, predicted from the fitted curve, that did not mineralize during the incubation period. Soil microbial biomass carbon (SMBC) and N (SMBN) as well as fixed ammonium (NH4+) contents and relationship with N mineralization rate (k) were also studied. Long-term manure application yielded a significantly higher k (0.32 week−1) than other treatments (0.12–0.22 week−1) but not a significantly higher NMP. Nitrogen mineralization during the wheat and maize-growing seasons was predicted to be 8.7–26.3 (mg N kg−1 soil) and 25.9–42.1 (mg N kg−1 soil), respectively. Both labile mineralizable N pools (Pools I and II) followed the same patterns in the treatments: 1.5NPKM > NPKM > NPK > NP > CK, while the reverse was true for stable N (Pool III). The significant positive correlation between k with SMBC and SMBN (R2 = 0.93, p = 0.008 and R2 = 0.94, p = 0.006) suggested that the higher mineralization rate might be contributed by the higher soil microbial biomass in NPKM. The trends of fixed NH4+ and mineralized N were coupled. Long-term manure application significantly improved the N mineralization rate in soil. Manure application is an effective strategy to enhance soil microbial biomass and soil N availability and has the potential to reduce the dependence upon chemical N fertilization.

Soil Use Legacy as Driving Factor for Soil Erosion under Conservation Agriculture

Water erosion can cause irreversible depletions in soil quality and crop productivity. The susceptibility of the soil to erosion is affected by current and historical management practices. Historical soil management practices like ploughing or subsoil loosening may lead to irreversible degradations of soils, which in turn increases soil erosion risk. Six “Wischmeier” plots under conservation agriculture, but with different historic treatments regarding soil use and management, were evaluated. These plots were installed in 1984 in Colonia del Sacramento, Uruguay on a Vertic Argiudoll. The objective of this study was to quantify how changes in soil quality, generated by different historical soil use and management over the last 35 years, contribute to current runoff and soil erosion in a cropping system under soil conservation practices using no-till, residue retention and cover crops. Considering differences in soil legacy effects of previous land use, plots were grouped in three treatments with contrasting historic index of agricultural intensification (IAI). The IAI was developed combining the duration of land use under agricultural production and the number and intensity of tillage activity resulting in the treatments: tillage with crop-pasture rotation (TIL_CP), no-tillage under several rotations (NT_Mix) and tillage with continuous cropping (TIL_CROP) with an increasing IAI of 3.5, 7.1 and 11.8, respectively. Rainfall events, runoff water and total, fixed and volatile solids were studied from 2017 to 2019. Soil physical (bulk density, penetration resistance, infiltration rate, aggregate stability), chemical (soil organic carbon (SOC), pH, phosphorous (P-Bray)) and biological properties (particulate organic matter (POM), potentially mineralizable nitrogen (PMN)) were assessed in 2019. Yearly average runoff amounted 209, 579 and 320 mm in 2017, 2018 and 2019, respectively. Yearly average soil losses were 233, 805 and 139 kg/ha with significant differences among years. The lowest soil losses were observed in TIL_CP (231, 615 and 146 kg/ha in 2017, 2018 and 2019, respectively) with lowest IAI of 3.5. Infiltration rate was the lowest in plots with highest IAI. Soil bulk density was highest (1.3 g/cm3) in plots with high IAI. SOC and PMN were lowest in TIL_CROP (3.0% SOC and 34 mg/kg PMN), holding the highest IAI of 11.8. Conservation agriculture minimized soil erosion losses in all plots and years, and erosion was much lower than the maximum tolerable threshold of 7,000 kg/ha for this particular soil. However, in historically intensively tilled and cropped soils, soil quality showed long-term adverse effects pointing towards a reduced resilience of the agricultural system.

Incubation Effect of Selected Organic Mulches on Various Biochemical Soil Health Indicators of Two Taro Soils Under Semi-Controlled Environment

Organic matter plays an important role in the nutrient recycling that helps improve the soil physical, chemical, and biological properties of the soil. This study looks at the characteristics of the two taro soils as affected by the application of four organic amendments used as treatments (Biochar, Mucuna, Erythrina, and grass). The effects of nutrients released from these four treatments were analyzed in the soil laboratory using various soil tests such as Labile Carbon, Fluorescein diacetate (FDA) hydrolysis activity, Potentially mineralizable nitrogen (PMN), Mineral nitrogen, Urease assay, and Phosphatase assay. The results showed that Erythrina and Mucuna are the two cover crops that significantly responded to the two soils. In terms of carbon mineralization, Mucuna and Erythrina fallow mulches had higher means compared to grass and biochar. The difference in the carbon mineralization could be attributed to the characteristics of Mucuna and Erythrina are both legume mulches which have lower C: N ratio. Therefore, they have faster rates of mineralization compared to grass and biochar fallows. However, at the highest rate of application (45 tons/ha), Mucuna was found to have faster rate of mineralization compared to Erythrina. From the other tests that were being carried out, Grass and Erythrina cover crops showed the highest levels of mean biological activity at their highest rate of application (45 tons/ha) on both soils. Mucuna and biochar covers, on the other hand, showed highest levels of mean biological activity at the lowest rate of application (15 tons/ha).

Evaluating the impact of midwestern cropping systems on soil health and soil carbon dynamics

Crop producers are becoming more interested in improving the health of their soils. The effects of cropping practices on soil health have been studied extensively, but much uncertainty remains. This study investigated the impacts of standard midwestern US agronomic practices on soil health indicators. The Soil Management Assessment Framework was used to quantify soil quality index (SQI) scores for each system. Corn–soybean (<i>Zea mays</i> L.–<i>Glycine max</i> L.) rotations received 168 kg N ha^–1 applied prior to corn. Treatments were the following: spring-applied urea ammonium nitrogen (SU168), fall-applied manure (FM) in no-till (NT) for 2 years (FM168NT2), FM with 10 years of NT and cereal rye (<i>Secale cereale</i>) cover crop (FM168NT10+R), and FM with 38 years of NT management (FM168NT38). Continuous corn (CC) treatments had FM applied annually at 224 kg N ha^–1 with eight years of stover removal (FM224CC-S) and with no stover removal (FM224CC). Soil cores were taken to a depth of 15 cm in the spring of 2017 and analyzed for total carbon (TC), total nitrogen (TN), water-stable aggregates (WSA), bulk density (BD), and potentially mineralizable nitrogen (PMN). Results showed that FM168NT38 and FM224CC had significantly greater TC and TN than other treatments. There were minimal treatment differences in total WSA &gt; 0.212 mm. No significant differences in PMN were found. Bulk density levels were significantly higher in NT treatments. The FM224CC and FM224CC-S treatments had the highest SQI scores, and FM168NT10+R had the lowest SQI score due to having higher BD and lower TC. Results suggest that the effect of cropping practices on some near-surface soil health indicators may be small and difficult to quantify. This study also demonstrated the need to adjust management to minimize compaction and maximize yield and soil health in cover-cropped systems. The study also monitored soil TC levels to a depth of 120 cm from 2007 through 2017. The rate of change in TC over time at a given depth did not differ between treatments. Total C levels did not change significantly to a depth of 15 cm. Significant increases in TC were found in all treatments except FM224CC-S at 30 to 60 cm and 90 to 120 cm depths, and in all treatments at 60 to 90 cm depth. These results suggest that C accumulation deep in the soil profile may be typical in midwestern cropping systems. Deep sampling to ≥100 cm is needed to capture the complete picture of soil C dynamics to assess soil C accumulation potential.

Long-term application of fused magnesium phosphate and calcium silicate change soil chemical properties, C decomposition and N mineralization in a single rice paddy field of Northeastern Japan

ABSTRACT This study investigated the long-term (31 years) effects of mineral slag fertilizer (fused magnesium phosphate [FMgP] and calcium silicate [CaSi]) application on changes in the main soil chemical properties, including pH, electrical conductivity (EC), available phosphorus (P), soil organic carbon (SOC), and total nitrogen (TN) contents in paddy soils. Soil samples were obtained from six fertilizer treatments [(1) Nitrogen, phosphorus, and potassium chemical fertilizer only (CF); (2) CF + mineral slag fertilizer (CF+); (3) CF + rice straw (RS); (4) CF + rice straw + mineral slag fertilizer (RS+); (5) CF + rice straw compost (CM); and (6) NPK + rice straw compost + mineral slag fertilizer (CM+)] at five depth soils (0–5, 5–10, 10–15, 15–20, and 20–25 cm). An anaerobic incubation experiment was performed at 30°C to determine carbon (C) decomposition and nitrogen (N) mineralization potentials at every 2-week interval (0, 2, 4, 6, and 8 weeks). The results indicated that compared to non-mineral slag additions, both EC and available P increased by 36.6–136.6% in mineral slag addition treatments. Still, only compost addition mostly influenced pH values; meanwhile, SOC and TN exhibited an increase (~23.8%) in compost addition treatments but a reduction (~12.7%) in rice straw treatments by applying mineral slag fertilizer. Mineral slag addition reduced the C decomposition potential but enhanced N mineralization potential observed by the first-order reaction kinetic models. Our study suggested that mineral slag fertilizers affected the soil organic matter and its mineralization potentials.

Reclamation of industrial waste dump using grass-legume mixture: An experimental approach to combat land degradation

The amount of solid waste generated by the industrial processes increased tremendously due to rapid industrialization. This waste contains hazardous material and unscientific disposal leads to land degradation and environmental pollution. Therefore, it must be managed carefully to reduce adverse environmental effect and restore ecosystem function. The study aims to evaluate the potential of grass (Pennisetum pedicellatum) and legume (Stylosanthes hamata) revegetation to restore the soil fertility of a steel and iron ore solid waste dump in central India. A field experiment was carried out at the reclaimed site without seeding (control), 1-year and 5-year after direct seeding of grass-legume mixture to assess the changes in soil fertility and biomass production. Soil samples (0–10 cm and 10–20 cm) were collected by laying random quadrats and analyzed for physicochemical and biological properties. Plant biomass and nitrogen (N) mineralization potential of accumulated mulch were measured along the age chronosequence. Soil fertility in terms of organic matter (SOM; 1.61%), organic carbon (SOC; 1.03%), Av. N (132.1 mg kg−1), and enzyme activity (dehydrogenase; 5.32 μg TPF g−1 h−1 and urease; 7.11 μg NH4+ g−1 h−1) at the 5-year-old revegetated site was significantly greater than that of the control site. Plant biomass (32.5–45.8 Mg ha−1) and mulch density (11.4–28.0 Mg ha−1) increased after 1- to 5-year of revegetation. Biomass C:N ratio was higher in grass while cumulative N-mineralization by legume was three times higher than in the grass. Soil moisture, SOM, microbial biomass carbon (MBC) and nitrogen (MBN), and mineralizable N increased with the mulch thickness (3–12 cm). The study concludes that direct seeding of grass-legume mixture potentially recuperates the soil fertility and increase biomass production that help ecosystem restoration. Direct seeding of the grass-legume mixture can be a promising ecological restoration tool to combat land degradation and to achieve UN sustainable development goals.

Environmental and management drivers of soil health indicators on Michigan field crop farms

Maintaining soil health is critical for sustainable field crop production. This on-farm study used participatory monitoring and employed a Bayesian linear regression model to investigate the impact of various drivers (i.e., climate, soil edaphic properties, management practices, cropping diversity, and tillage intensity) on soil health indicators. Over two years, we sampled 242 focal points in soybean fields on thirty-five farms across three regions in Michigan differing in climate, edaphic properties and management practices. Soils ranged from loam to sandy loam. Soil health indicators assessed included soil organic carbon (SOC), total soil nitrogen (TSN), permanganate oxidizable carbon (POXC), C mineralization (Cmin), potentially mineralizable nitrogen (PMN), phosphorus, calcium, soil surface and subsurface resistance, and wet aggregate stability (WAS). We observed location effects, with each of the three regions differing in their climate, soil edaphic properties, and management practices. We found that aridity and clay content are primary drivers of most soil health indicators. Specifically, crop diversity, irrespective of composition, was positively associated with Cmin and WAS. Tillage intensity was positively associated with PMN but negatively influenced POXC. Overall, we conclude that although climate and soil edaphic properties are the dominant drivers of soil health, management practices also play a critical role, especially when considering soil biological indicators.

N2O emissions in Acacia mangium stands with different ages, in Sumatra, Indonesia

We compared nitrous oxide (N2O) emissions in different-aged (1, 3, and 5 years) Acacia mangium plantations and secondary forests for two and a half years at three areas in Sumatra, Indonesia. N2O emission was high from November to March (rainy season) and low from May to November (relatively drier season). In the first year, the average ± standard deviation of annual N2O emissions in 1-year-old sites was 8.92 ± 2.29 kg ha−1 of N, which was larger than those in 3-year-old (2.58 ± 2.28 kg ha−1 of N) and 5-year-old (2.16 ± 1.12 kg ha−1 of N) sites and secondary forests (1.38 ± 0.45 kg ha−1 of N) (p < 0.001). However, there is no significant difference in N2O flux among treatments after the second year. Although nitrogen mineralization and nitrification potential did not differ among tree ages, inorganic nitrogen and NH4/NO3 ratio in 1-year-old acacia site in the first year were significantly different from those in the other aged forests and secondary forests. Results of linear mixed model suggest that water-filled pore space and nitrogen availability are key factors for N2O emission in these sites. N2O emission within 1 year after planting contributed to 41% of total emission during the 7-year rotation period. Therefore, reduction in N2O emission within 1 year after planting is important for the total emission from acacia plantation.

Microbial functions and soil nitrogen mineralisation processes in the soil of a cool temperate forest in northern Japan

There is little knowledge about microbial functional community structures and the relationships between microbial communities and nitrogen transformation processes. Here, we investigated the relationships between soil microbial communities and nitrogen mineralisation potentials in a cool temperate forest throughout the growing season. Microbial communities were assessed by quantification of the total bacterial, archaeal, and fungal gene abundances and the bacterial and archaeal amoA gene abundances, functional predictions of bacteria and fungi, and analysis of the bacterial-fungal co-occurrence network. In mid-summer, ectomycorrhizal fungal abundance was significantly higher, whereas the total bacterial abundance was significantly lower. Bacterial and archaeal amoA gene abundances were also significantly higher in mid-summer. However, regardless of the seasonal fluctuation of microbial gene abundances, the net nitrification and nitrogen mineralisation potential did not show clear seasonality. In the network analysis, the microbial community was divided into 13 modules, which were subgroups assumed to have similar niches. Furthermore, two modules that mainly consisted of microbial species of Proteobacteria and Bacteroidetes were significantly and positively correlated with the net nitrification and mineralisation potentials. Our results indicated that microbial subgroups sharing similar niches, instead of total microbial abundances and functional gene abundances, could be important factors affecting the net nitrogen mineralisation potential.

Soil health assessment after 40 years of conservation and conventional tillage management in Southeastern Coastal Plain soils

AbstractConservation tillage (CST) and cover crops are important components of soil health management. In the present study, we applied two independent soil health assessment approaches to evaluate the impacts of 40‐yr CST and additional 4‐yr cover cropping on a range of soil health indicators and the overall soil health in typical southeastern Coastal Plain soils. Soils were collected at 0–15 cm and analyzed for physical, chemical, and biological indicators. The Soil Management Assessment Framework (SMAF) and Cornell's Comprehensive Assessment of Soil Health (CASH) were used to calculate soil health indices. When compared to conventional tillage, 40‐yr CST increased active carbon (C) from 301 to 420 mg kg–1 and organic nitrogen (N) mineralization potentials from 0.78 to 0.91 mg kg–1 d–1, but it reduced soil electrical conductivity from 133 to 101 μs cm–1. No difference in soil aggregate stability, total C, extractable phosphorous and potassium, microbial biomass C, respiration, and glucosidase activities were observed between the two tillage treatments. Cover cropping had no impacts on any measured variables, except that it increased soil total N. Regardless of tillage and cover cropping, both the SMAF and CASH scoring functions suggested no changes in overall soil health. Soil organic C (SOC) was the only indicator positively correlated with both the SMAF and CASH indices, indicating its importance in maintaining the health of the tested soils. Moreover, CASH index recommended improving soil structure and SOC as the management priority to maintain or improve the overall soil health. Increasing organic inputs along with CST is seemingly the optimal management option.

Assessing the impact of soil aggregate size on mineralization of nitrogen in different soils, China

Soil aggregates play a critical role to support the development of soil nitrogen (N) pools, but the underlying mechanism by which soil aggregate size impacts N mineralization remains unclear. The objective of this study was to determine the effect of aggregate size in soil N mineralization through cultivation experiments of different type soils. The topsoil samples of ten typical profiles in different regions of China were collected, and a series of laboratory column incubation experiments were conducted to quantify the relationship between the distribution of soil aggregate size and the concentration and mass of mineral N (i.e., NH4-N and NO3-N) under N fertilizer addition. The results indicated that the weight of aggregate with different sizes was less affected by the intensity of fertilization, which was mainly influenced by the soil types. In most soils, the weight of soil aggregates of 1–0.5 mm accounted for the largest proportion of aggregates in the five categories (i.e., 5–2 mm, 2–1 mm, 1–0.5 mm, 0.5–0.25 mm, and < 0.25 mm). Moreover, the intermediate aggregates (1–0.5 mm and 0.5–0.25 mm) were detected to have the highest mineral N concentration and mass, and they were also demonstrated to be significantly (P < 0.05) correlated to the potential nitrogen mineralization (PNM) rates in most soils. Subsequently, the obtained PNM indices were classified into three levels: i.e., >65% (highly responsive), 45%–65% (moderately responsive), and < 45% (lowly responsive), and we proposed the preliminary strategies on fertilizer types, agricultural intensity, and crop selection for different soils. The outcome of this study provides new insights into the relationship between soil aggregate sizes and N mineralization abilities and will help in developing guidelines for fertilizer management.

Spatial and Temporal Distribution of Soil Microbial Properties in Two Shrub Intercrop Systems of the Sahel

The Sahel is an ecologically vulnerable region where increasing populations with a concurrent increase in agricultural intensity has degraded soils. Agroforestry offers an approach to remediate these landscapes. A largely unrecognized agroforestry resource in the Sahel are the native shrubs, Piliostigma reticulatum, and Guiera senegalensis that to varying degrees already coexist with row crops. These shrubs improve soil quality, redistribute water from the deep soil to the surface (hydraulic lift), and can improve crop growth. However, little information is available on whether these shrubs affect spatial and temporal dynamics of microbial communities. Therefore, the objective of this study was to determine microbial composition and activity in the wet and dry seasons of soil in the: shrub rhizosphere (RhizS), inter-root zone (IntrS), and outside the influence of shrub soil (OutS) for both G. senegalensis and P. reticulatum in Senegal. A 3 × 2 factorial field experiment was imposed at two locations (490 and 700 mm annual rainfall with G. senegalensis and P. reticulatum, respectively), that had the soil sampling treatments of three locations (RhizS, IntrS, and OutS) and two seasons (wet and dry). Soils were analyzed for: microbial diversity (DGGE with bacterial 16S or fungal 28S rRNA gene sequences phospholipids fatty acid, PLFA); enzyme activities; microbial biomass carbon (MBC); and nitrogen (N) mineralization potential. For the DGGE profiling, the bacterial community responded more to the rhizosphere effect, whereas, the fungal community was more sensitive to season. PLFA, MBC, enzyme activities and inorganic N were significantly higher in both seasons for the RhizS. The presence of shrubs maintained rhizosphere microbial communities and activity during the dry season. This represents a paradigm shift for semi-arid environments where logically it would be expected to have no microbial activity in the extended dry season. In contrast this study has shown this is not the case that rather the presence of shrub roots maintained the microbial community in the dry season most likely due to hydraulic lift and root exudates. This has implications when these shrubs are in cropped fields in that decomposition and mineralization of nutrients can proceed in the dry season. Thus, enabling accumulation of plant available nutrients during the dry season for uptake by crops in the rainy season.

Soil biological response to multi-species cover crops in the Northern Great Plains

Farmers in semi-arid regions are experimenting with cover crop mixtures as partial summer fallow replacement, with the goal of increasing soil biological activity. We compared extracellular enzyme activity, microbial biomass, potentially mineralizable nitrogen (PMN) and mycorrhizal colonization levels after growing cover crops comprised of one or four functional groups. We asked whether cover crops can alter those soil processes and components relative to fallow during the cash crop growing season, and whether a cover crop mixture (CCM) will have a greater impact than a single-species legume green manure (LGM) after one and two rotations with wheat. Cover crops were planted at two sites in Montana April 2012 and May 2014, and at two additional sites in May 2013, and April 2015, terminated at each site approximately 60 days after seeding. Wheat was the cash crop for the following growing season. Cover crop treatments included a fallow control, a sole pea LGM, and a FULL mix consisting of eight species, with two species of each of four functional groups. Four additional treatments of single functional groups were compared following the second rotation of cover crops. The geometric mean of soil enzyme activity increased after cover crops relative to fallow (1.1–1.3 fold) at two sites after the first rotation, and by 1.1–1.4 fold after the second rotation at three sites. At the fourth site, the geometric mean of the FULL mix was greater than LGM or fallow by 1.4 and 1.5 fold. The response of individual enzymes was less consistent. Microbial biomass and PMN increased after LGM and/or FULL at three of eight site-years, by 1.2–1.7 for microbial biomass and 1.6–2.1 for PMN. Mycorrhizal colonization of wheat increased in at least one cover crop treatment relative to fallow at four of six site-years, and decreased in cover crops relative to fallow at one site. There were no differences in soil biological traits measured among single-functional-group treatments. Soil biological parameters were correlated with cover crop biomass in 7 of 16 comparisons at two sites after one rotation. After two rotations, 5 of 8 soil parameters were correlated with cover crop biomass at one site, with no correlations for the remaining sites. Precipitation declined 30–50 % from the first rotations at those three sites. Positive effects of cover crops on soil biological parameters in semi-arid systems may be measurable only when environmental conditions do not limit growth.

Fertilization enhances mineralization of soil carbon and nitrogen pools by regulating the bacterial community and biomass

The stability of soil organic matter is a key predictor of changes in management practices due to the progressive decomposition of organic compounds. However, the dynamics of soil compounds and to what extent the composition of microbes controls the process are still unclear. Black soils from Northeast China without fertilizer (CK), soil treated with chemical fertilizer (NPK), NPK plus maize straw (NPKS), and NPK plus cattle manure (NPKM) were collected and separated into the labile fraction (macroaggregates > 150 μm) and the recalcitrant fraction (microaggregates 150 μm) for a 14-day incubation. The net carbon (C) and net nitrogen (N) mineralization potentials of the labile fraction were 15.87–26.11 and 0.74–1.48 mg kg−1 soil day−1, respectively, which were between 1.4 and 2.3 times higher than those of the recalcitrant fraction. Compared with CK, NPKS and NPKM significantly increased C and N mineralization in the labile fraction but not in the recalcitrant fraction. Boosting regression tree analysis suggested that total nitrogen (TN), microbial biomass nitrogen (MBN), and bacterial abundance accounted for 48.9%, 31.7%, and 14.0% of the total net C mineralization, respectively. Additionally, soil organic carbon (SOC), microbial biomass carbon (MBC), and bacterial abundance accounted for 39.4%, 37.3%, and 22.1% of the total net N mineralization, respectively. Path analysis showed that TN, MBN, and Brevundimonas positively influenced soil net C mineralization. SOC and MBC positively affected soil net N mineralization, whereas unclassified Comamonadaceae had a negative impact. The mineralization of soil C and N was affected by the inputs of external inorganic nutrients and organic materials and was attributed to the bacterial community, in which Brevundimonas positively responded and contributed to mineralization, while unclassified Comamonadaceae responded negatively.

Pre-incubation Soil Handling Can Influence Comparability of Potentially Mineralizable Nitrogen Results

ABSTRACT Potentially mineralizable nitrogen (PMN) is a widely used indicator of a soil’s organic nitrogen (N) availability, and is often measured by incubation. While it is known that the handling of soil prior to incubation (i.e., pretreatment) may affect N mineralization during the incubation, the effect of pretreatments on the relationships in PMN between samples has not been fully evaluated. The objectives of this study were to determine the effects of refrigeration, freezing, air-drying, and soil grinding on PMN derived from a 7-day anaerobic incubation across soils of contrasting textures (silt loam and sand) and cropping histories (mixed rotation, continuous corn at varying N rates, and rotationally grazed pasture), and to assess the comparability of results across pretreatments. Analysis of variance was used to compare the individual and interaction effects of pretreatment and soil, and linear regression was performed to compare the effects of different pretreatments relative to one another. All pretreatments had distinct effects on mineralized N. While the relationships between soils remained consistent across pretreatments, a soil-by-pretreatment interaction effect was detected, driven by differences in field-moist versus air-dried pretreatments. These findings suggest that while relationships between soils may reasonably be compared across studies utilizing differing PMN soil pretreatments, standardization or calibration of soil handling methods is needed for applications such as routine soil testing, in which consistent and comparable values are required.

Ağaçlandırma Çalışmaları Üzerinden Geçen Zamanın Toprak Özellikleri ve Azot Mineralizasyonu Üzerindeki Etkilerinin Belirlenmesi (Giresun-Şebinkarahisar Örneği)

Aim of study: In this study, it is aimed to reveal the effects of time on some soil properties and nitrogen mineralization potential in scotch pine afforestation areas.&#x0D; Material and methods: The study was carried out in the afforestation areas in Şebinkarahisar Forest Management Directorate. Soil samples were taken from two depth levels (0-15 cm and 15-30 cm Soil samples were taken from afforestation areas (afforested 1, 5 and 20 years ago) and adjacent unforested(control) areas. Some physical and chemical analyzes as well as nitrogen mineralization measurements were done in the soil samples.&#x0D; Main results: It was determined that the period after afforestation has a statistically significant effect on the change of soil properties. Thus, while the sand and C / N ratio decreased with afforestation, clay, bulk density and pH increased. The difference in the effect of the time passed over planting times in terms of net mineralization data in nitrogen mineralization was found to be statistically insignificant. Equal incubation conditions prevented the difference in planting time.&#x0D; Highlights: With the study, changes in soil properties have been revealed through afforestation studies in areas that are sensitive to erosion and the necessity of improving potantial erosion sites has emerged.

Potential N mineralization and availability to maize in black soils in response to soil fertility improvement in Northeast China

Understanding the soil nitrogen (N) mineralization potential (N0) and crop N availability during the growing season is essential for improving nitrogen use efficiency (NUE) and preventing over-fertilization, which lead to negative environmental impacts. Five black soils with different levels of fertility were selected in Northeast China. The N0 and kinetics of these soils were estimated through laboratory experiments at different incubation temperatures (15, 25, and 35 °C). N mineralization dynamics were simulated using field soil temperature according to the incubation results. Moreover, the N uptake dynamics of maize were simulated according to the literature. Compared with the very low-fertility soils, the cumulative mineralized nitrogen increased under all incubation temperatures (15, 25, and 35 °C), by 48–136%, 8–61%, and 24–59%, respectively, in the medium- and high-fertility soils. The highest N0 values (96.90, 115.31, and 121.33 mg/kg at the three different temperatures) were recorded in the very high-fertility soils. The soil N mineralization dynamics and N uptake of maize in the growing season were highly consistent over time, although the soil N supply could not meet the maize growth requirements. The higher the soil fertility, the lower the N fertilizer requirement. Different fertilizer strategies were developed based on the cumulative mineralized N, N uptake by maize, and NUE in soils with different fertility levels. We suggested a reduction of 50–65 kg N/ha in N fertilizer in the two highest fertility soils. This study provided basic data to reduce chemical N fertilizer to improve NUE and reduce negative environmental impacts.

Soil‐nitrogen, potentially mineralizable‐nitrogen, and field condition information marginally improves corn nitrogen management

AbstractAnaerobic potentially mineralizable nitrogen (PMN) combined with preplant nitrate test (PPNT) or pre‐sidedress nitrate test (PSNT) may improve corn (Zea mays L.) N management. Forty‐nine corn N response studies were conducted across the U.S. Midwest to evaluate the capacity of PPNT and PSNT to predict grain yield, N uptake, and economic optimal N rate (EONR) when adjusted by soil sampling depth, soil texture, temperature, PMN, and initial NH4–N from PMN analysis. Pre‐plant soil samples were obtained for PPNT (0‐ to 30‐, 30‐ to 60‐, 60‐ to 90‐cm depths) and PMN (0‐ to 30‐cm depth) before corn planting and N fertilization. In‐season soil samples were obtained at the V5 corn development stage for PSNT (0‐ to 30‐, 30‐ to 60‐cm depths) at 0 kg N ha−1 at‐planting rate and for PMN when 0 and 180 kg N ha−1 was applied at planting. Grain yield, N uptake, and EONR were best predicted when separating soils by texture or sites by annual growing degree‐days and including PMN and initial NH4–N with either NO3–N test. Using PSNT (mean R2 = .30)‐instead of PPNT (mean R2 = .19)‐based models normally increased predictability of corn agronomic variables by a mean of 11%. Including PMN and initial NH4–N with PPNT or PSNT only marginally improved predictability of grain yield, N uptake, and EONR (R2 increase ≤ .33; mean R2 = .35). Therefore, including PMN with PPNT or PSNT is not suggested as a tool to improve N fertilizer management in the U.S. Midwest.

Alkaline Hydrolyzable Organic Nitrogen as an Index of Nitrogen Mineralization in Soils: Relationship with Activities of Arylamidase and Amidohydrolases

ABSTRACT This study investigated the relationship between a recently proposed alkaline hydrolysis method for estimating the chemical index of nitrogen (N) mineralization potential of soils and the activities of arylamidase and four amidohydrolases involved in hydrolysis of organic N (ON) in soils. Nitrogen mineralization was studied in 13 soils from uncultivated fields in Iowa, USA, by direct steam distillation of 1 g field-most soil treated with 1 M KOH or 1 M NaOH. The distillate was collected in boric acids, which was changed every 5 min for a total of 40 min. The NH4 +-N in the distillate was determined by titration with 0.005 M H2SO4. The cumulative amounts of N hydrolyzed were fitted to the first-order exponential equation to determine the “potentially hydrolyzable N (Nmax )” for the soils. The activities of arylamidase, L-asparaginase, L-glutaminase, amidase, and L-aspartase were assayed at their optimal pH values. Results showed that estimated Nmax values were strongly correlated with the activities of arylamidase and amidohydrolases. The activities of arylamidase and the amidohydrolases were significantly correlated, indicating that the activities of the two groups of enzymes are coupled in mineralization of ON in soils. Based on the specificity of enzyme reactions and the strong relationship between estimated Nmax values and the activities of arylamidase and amidohydrolases, we concluded that similar amide-N bonds were susceptible to enzymatic and alkaline hydrolysis, and that alkaline hydrolyzable ON can be used as an index of N mineralization in soils.