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Conservation agriculture (CA) has been proposed as a viable strategy to enhance soil health and the resilience of farms to climate change, and to support the sustainability of agricultural production systems. While CA is a well-established approach, research results are lacking regarding its long-term impact on nitrogen (N) dynamics in the soil–plant system. In this study, a 20-year experiment was used to investigate the long-term effects of no-tillage in CA on soil organic carbon (SOC) and nitrogen (N) mineralization, plant N uptake, grain yields, and the grain quality of durum wheat. A CA system based on no-tillage (NT) was evaluated and compared with conventional tillage (CT) used for wheat/legumes biennial crop rotation. Results showed that soil samples from CA plots experienced significantly more N mineralization than those under CT, which was attributed to increased SOC and N. Topsoil sampled from the CA plots 20 years after the implementation of the experiment had 43% more absolute potentially mineralizable N (N0) than the CT plots, with no significant differences observed in deeper soil layers (15–30 cm and 30–45 cm). The absolute potentially mineralizable carbon (C0) in soils from the CA system was 49% and 35% higher than in soils from the CT system, at soil depths of 0–15 and 15–30 cm, respectively. Furthermore, CA resulted in higher amounts of remobilized N and higher rates of N uptake during the critical growth stages of durum wheat. The amount of N remobilized during the kernel-filling phase under CA was 59% higher than under CT. Total N uptake in wheat plants was 45% greater under CA compared to CT. The most significant differences in N uptake between the CA and CT systems were observed during two critical growth stages: late tillering to heading (1.7 times higher in CA than CT) and heading to anthesis (1.5 times higher in CA than CT). The most significant differences for N uptake were shown during the late tillering to heading stage and the heading to anthesis stage. The amount of N remobilized during the kernel filling phase under CA was 59% higher than CT. CA adoption resulted in 21% and 35% higher grain and straw yields, respectively, compared to CT. The grain and straw N yields were 21% and 51% higher, respectively, under CA than CT. Moreover, the CA system exhibited higher partial factor productivity of nitrogen fertilizer (PFP N) for both grain and straw yields. Thousand kernel weight (TKW) and hectoliter weight were also significantly higher under CA than CT. The grain protein content, wet gluten content, vitreousness, and falling number were similar between the CA and CT systems. These results highlight the benefits of long-term CA adoption to increase soil N mineralization, providing a substantial base for N uptake during the critical growth stages of durum wheat, thus leading to increased crop yield. The findings underscore the potential of CA systems in promoting sustainable agriculture and mitigating the impacts of soil degradation. [ABSTRACT FROM AUTHOR]

Sewage sludge should primarily find use in agriculture, reducing the quantity directed towards alternative disposal methods like incineration or deposition in municipal landfills. This study evaluated the agronomic value and the risk of soil and plant tissue contamination with heavy metals in sewage sludge obtained from two wastewater treatment plants (WWTP). The experiment was arranged as a 2 × 5 factorial (two sewage sludges, five sanitation treatments), involving lettuce cultivation in pots over two growing cycles. The two sewage sludges were sourced from the WWTPs of Gelfa and Viana do Castelo and underwent five sanitation and stabilization treatments (40% and 20% calcium oxide, 40% and 20% calcium hydroxide, and untreated sewage sludge). The Gelfa sewage sludge, characterized by a higher initial nitrogen (N) concentration, resulted in greater dry-matter yield (DMY) (12.4 and 8.6 g plant−1 for the first and second growing cycles, respectively) compared to that from Viana do Castelo (11.0 and 8.1 g plant−1), with N release likely being a major factor influencing crop productivity. The high N concentration and the low carbon (C)/N ratio of sewage sludge led to rapid mineralization of the organic substrate, which additionally led to a higher release of other important nutrients, such as phosphorus (P) and boron (B), making them available for plant uptake. Alkalizing treatments further stimulated sewage sludge mineralization, increasing soil pH and exchangeable calcium (Ca), thereby enhancing Ca availability for plants, and indicating a preference for use in acidic soils. Cationic micronutrients were minimally affected by the sewage sludge and their treatments. The concentrations of heavy metals in the sewage sludge, soils, and lettuce tissues were all below internationally established threshold limits. This study highlighted the high fertilizing value of these sewage sludges, supplying N, P, and B to plants, while demonstrating a low risk of environmental contamination with heavy metals. Nevertheless, the safe use of sewage sludge by farmers depends on monitoring other risks, such as toxic organic compounds, which were not evaluated in this study. [ABSTRACT FROM AUTHOR]

The use of farm dairy effluents (FDE) has become a promising alternative to increase pasture yield while reducing the environmental impact of waste accumulation into streams, but other environmental implications should be considered. The present study aimed to assess the effect of application of either raw FDE or lagoon-stored FDE compared to dissolved urea or a non-amended control on N2O emission, soil N dynamics, functional microbial activity, and the yield and N-use efficiency of a fescue pasture. The normalized N application rate of 200 kg N ha−1 was divided into four seasonal events in a greenhouse experiment. Similar fescue forage production with FDE or urea positioned FDE application to soil as an alternative disposal. The repeated application of raw effluent delivered more organic C to the soil which induced an increase in enzyme activities, a shift in the catabolic activity of the soil microbial community, and greater N mineralization potential. On the other hand, urea addition decreased the functional activity of the soil microbial community. However, N2O emissions were greater for the raw effluent, so lagoon-stored effluent is an alternative to manage FDE under these conditions, avoiding urea addition and enhancing soil metabolic activity. [ABSTRACT FROM AUTHOR]

(1) Background: Excessive use of chemical fertilizers accelerates soil acidification and increases greenhouse gas emissions. In this context, the farmland application of organic fertilizers not only reuses agricultural waste but also improves soil quality. (2) Methods: Two organic fertilizers made from chicken manure—G508 and G509—were field applied, implementing once or twice (denoted by X1 and X2, respectively) the recommended amount of nitrogen for three crops. In addition, an incubation experiment was conducted to assess the mineralization of the organic fertilizers. (3) Results: G508 did not undergo a composting process and, thus, had a higher content of nitrogen compared to G509. Therefore, although the soil properties improved under G509, the total mineral nitrogen released was lower than G508. Compared to chemical fertilizer treatment, the application of G508 and G509 increased the soil's pH value, concentrations of organic matter, available phosphorus, and exchangeable concentrations of potassium, calcium, and magnesium. In addition, the crop yield under G508X2 treatment was even higher than that under chemical fertilizer treatment. (4) Conclusions: Although G508 and G509 were both processed using chicken manure, they exhibited different nutrient-release behaviors during mineralization and also had different influences on the soil properties and growth of the three crops. [ABSTRACT FROM AUTHOR]

The partial replacement of chemical fertilizer with straw return is considered an effective method for improving the accumulation of organic matter and soil fertility, but the characteristics of soil nitrogen fixation and mineralization in a double-cropped rice paddy system are unclear. Based on a 12-year field experiment, we conducted a waterlogged incubation experiment for 49 days to determine the effect of long-term straw return combined with reducing chemical fertilizer application on the dynamic changes of mineralized soil nitrogen (N) content and mineralized N rate under the treatments, including NPK (chemical fertilizers application with straw removal), SBR (straw burned return), and SR (straw return). Results showed that, compared with SBR and NPK, SR significantly increased available nitrogen by 7.4% and 16.5%, respectively, due to the higher ammonium nitrogen and nitrate nitrogen, as well as the total carbon, available phosphorus, and slowly available potassium, suggesting that it could stock a sufficient nitrogen source. During the incubation period, the amount of N mineralization was relatively higher under SR than under SBR and NPK treatments, especially during the later mineralization time, whereas there was no difference in the N mineralization rate. In addition, SR significantly increased soil cumulative N mineralization and N mineralization potential. However, SBR significantly decreased the soil mineralizable N ratio compared with SR and NPK, which may result in a worsening of the N mineralization potential. The results indicated that long-term straw return combined with reducing chemical fertilizer application could significantly improve the N supply capacity of paddy rice field soil to better coordinate the soil N supply and immobilization. [ABSTRACT FROM AUTHOR]

The aim of the current study was to create a high quality growing medium blend that replaces 70 vol% peat with 40 vol% woody green compost and 30 vol% bark compost and organic fertilizers (i.e., blood meal and chitin), all locally sourced. A range of “woody composts”, i.e., green composts based on feedstock selection with mainly woody material from tree prunings, were produced for this purpose at green compost facilities. First, the woody composts were characterized chemically and biologically, including their microbial biomass and net N release. In comparison with regular green composts or vegetable, fruit and garden (VFG) waste composts, woody composts are more suitable for use in growing media due to their lower pH, EC and inorganic C content; however, the woody compost had a low N mineralization rate. Three types of composts supported a higher microbial biomass than wood fiber or bark compost. The additional mineral N release after 100 days for compost mixed with blood meal was tested for different VFG and green composts. A significantly higher additional net N release was measured for composts with higher initial mineral N concentrations (317 mg Nmin/L) as well as VFG composts (417 mg Nmin/L) than for green composts with a lower initial mineral N concentration (148 mg Nmin/L). In a last step, woody compost, bark compost, wood fiber, coir and peat were mixed in different ratios, resulting in six blends ranging from 100% peat-free to 100% peat. Two batches of woody compost were compared, and the blends were mixed with blood meal or chitin. A strong effect of both the organic fertilizer and the blend composition on the mineral N release was observed, with a clear link between the microbial biomass and the net N release. There was a significant negative correlation between the net change in microbial biomass and the net N release (R = −0.85), which implies that a larger increase in microbial biomass during incubation with the organic fertilizer resulted in less N mineralization. The blends containing woody compost scored better for nitrification activity, as the NH4-N concentrations were lower in these than for the blends without woody compost. For the peat blends, no effect on the microbial biomass was observed after addition of organic fertilizers; mineral N did increase, however. Woody composts have the potential to be used in high vol% in growing media blends, but the blends still need further optimization when supplemented with organic fertilizers.

In subtropical regions, we have an incomplete understanding of how long-term tillage, stubble, and nitrogen (N) fertilizer management affects soil biological functioning. We examined a subtropical site managed for 50 years using varying tillage (conventional till (CT) and no-till (NT)), stubble management (stubble burning (SB) and stubble retention (SR)), and N fertilization (0 (N0), 30 (N30), and 90 (N90) kg ha−1 y−1) to assess their impact on soil microbial respiration, easily extractable glomalin-related soil protein (EEGRSP), and N mineralization. A significant three-way tillage × stubble × N fertilizer interaction was observed for soil respiration, with NT+SB+N0 treatments generally releasing the highest amounts of CO2 over the incubation period (1135 mg/kg), and NT+SR+N0 treatments releasing the lowest (528 mg/kg). In contrast, a significant stubble × N interaction was observed for both EEGRSP and N mineralization, with the highest concentrations of both EEGRSP (2.66 ± 0.86 g kg−1) and N mineralization (30.7 mg/kg) observed in SR+N90 treatments. Furthermore, N mineralization was also positively correlated with EEGRSP (R2 = 0.76, p < 0.001), indicating that EEGRSP can potentially be used as an index of soil N availability. Overall, this study has shown that SR and N fertilization have a positive impact on soil biological functioning.

Organic matter (OM) and nutrient nitrogen (N) play vital roles in the fertility and production of soil in accordance with goals of efficient environmental protection. This study aimed to show the extent to which N delivery can contribute to improving nitrogen fertilizer requirements (NFR) through comparative analysis of OM and N. Systems determining the NFR in agricultural practices have thus far been challenged to estimate the annual rate of mineralization of the soil. OM and N turnover was investigated through an available evaluation consisting of 546 representatively distributed permanent test and observation plots (TP) of the German Federal State of Saxony farms. A solid database of at least 10-year field plot card records from 2001 to 2010 was selected for the analysis. A program (BEFU) widely used in agricultural practice, along with the simplified process model CCB, were applied. For the calculation of the amount of mineral N fertilizers used, the results of three different methods for determining the NFR were compared with each other. The determination of the farmers’ demand (=actual condition of the TP) with a mean value of 132 kg N ha−1 did not show a large difference between the calculated values with 137 kg N ha−1 by the BEFU program. Based on the available results for the most important crop species cultivated in Saxony, there were clear differences in the considerations of the N delivery from the soil. The BEFU program was able to calculate an average N delivery of 17 kg N ha−1 from tabulated data, whereas with the CCB process model, 66 kg N ha−1 of mineralization was determined with a distinct higher deviation by taking into account the 10-year field histories. Using the N delivery of the TP by the CCB model, a clear reduction of the mean N fertilization level, to about 80 kg N ha−1, was therefore achieved. These differences were particularly large for TP with organic fertilization (livestock), at a relatively low N fertilization level, and for certain crop species. With a high standard deviation, the average savings potential of mineral N fertilizers was 52–57 kg N ha−1. After including the corrected values for the N mineral fertilization, a decrease in the N balances by an average of 20–25 kg N ha−1 was ultimately achieved. In particular, the heavily oversupplied plots with D and E classification decreased by approximately 50%. The results of our study demonstrate clear improvements; therefore, increased efforts should be made in the future to optimize the determination of NFR using applicable methods that consider N mineralization in agricultural practice and consultation.

Immobilisation of fertiliser nitrogen (N) by soil microorganisms can reduce N availability to crops, decreasing growth and yield. To date, few studies have focussed on the effect of different plant species on immobilisation of fertiliser N. Canola (Brassica napus) is known to influence the soil microbiome and increase mineral N in soil for future crops compared with cereals. We tested the hypothesis that canola can reduce immobilisation of fertiliser N by influencing the composition of the rhizosphere microbiome. To investigate this, we conducted a glasshouse soil column experiment comparing N fertiliser uptake between canola and wheat (Triticum aestivium) and partitioning of fertiliser N between plants and microorganisms. Plants were grown in soil to which high C:N ratio wheat residues and 15N-labelled urea fertiliser were applied. There was no difference between wheat and canola in fertiliser N uptake despite differences in fungal community composition and the carbon metabolising enzyme alpha-glucosidase in the rhizosphere. Canola obtained more soil-derived N than wheat. There was no significant difference in the rhizosphere bacterial communities present between wheat and canola and unplanted controls. Our results highlight the capacity of canola to increase mineralisation of soil N compared with wheat although the study could not describe the microbial community which facilitated this increase.

Mineralization studies are the first step in determining the usefulness of an amendment such as fertilizer, and are essential to creating guidelines for dairy waste management to help producers make informed decisions. Our goal was to assess the effects of dairy raw, composted, and digested manure amendments on C, N, and P mineralization to evaluate the feasibility of their in-farm production and use as organic fertilizers. The liquid and solid fractions of dairy effluent (LDE, SDE), dairy effluent digestate (DED), onion–cattle manure digestate and compost (OCMD, OCMC) were characterized by chemical and spectroscopic methods. Soil microcosms with LDE, SDE, DED, OCMD and OCMC and the C, N and P mineralization were determined periodically. Elemental and structural differences among amendments led to contrasting profiles of C, N, and P mineralization, and thus to differences in nutrient availability, immobilization, and CO2 emission. All processed materials were more stable than untreated waste, reducing C emissions. Digestates showed net C immobilization, and supplied the highest levels of available N, creating a relative P deficit. Instead, the compost supplied N and P via mineralization, producing a relative P excess. Future studies should aim at evaluating fertilization strategies that combine both kinds of amendments, to exploit their complimentary agronomic characteristics.

A long-term experiment (38 years) was conducted to elucidate the effects of long-term N addition on the net N mineralization in both paddy and upland soils, based on their initial soil N status, with and in connection with soil microbial biomass and N cycling extracellular enzyme activities. Two treatments without N addition CK (No fertilizer) and K (inorganic potassium fertilizer) and two treatments with N addition (inorganic nitrogen fertilizer) and NK (inorganic nitrogen and potassium fertilizer) were placed in incubation for 90 days. Results showed that the total N and soil organic carbon (SOC) contents were higher in the treatments with N application compared to the treatments without N in both paddy and upland soils. The SOC content of paddy soil was increased relative to upland soil by 56.2%, 45.7%, 61.1% and 62.2% without N (CK, K) and with N (N and NK) treatments, respectively. Site-wise, total N concentration in paddy soil was higher by 0.06, 0.10, 0.57 and 0.60 times under the CK, K, N and NK treatments, respectively, compared with upland soil. In paddy soil, soil microbial biomass nitrogen (SMBN) was higher by 39.6%, 2.77%, 29.5% and 31.4%, and microbial biomass carbon (SMBC) was higher by 11.8%, 11.9%, 10.1% and 12.3%, respectively, in CK, K, N and NK treatment, compared with upland soil. Overall, compared to upland soil, the activities of leucine-aminopeptidase (LAP) were increased by 31%, 18%, 20% and 11%, and those of N-acetyl-b-D-glucosaminidase (NAG) were increased by 70%, 21%, 13% and 18% by CK, K, N and NK treatments, respectively, in paddy soil. A significantly linear increase was found in the NO3−-N and NH4+-N concentrations during the 90 days of the incubation period in both soils. NK treatment showed the highest N mineralization potential (No) along with mineralization rate constant, k (NMR) at the end of the incubation. SMBC, SMBN, enzyme activities, NO3−-N and NH4+-N concentrations and the No showed a highly significant (p ≤ 0.05) positive correlation. We concluded that long-term N addition accelerated the net mineralization by increasing soil microbial activities under both soils.

This paper reviews the use of charcoal and wood ash in acid soils as adsorbents to improve N availability at the same time improving their soil fertility and crop productivity. Soil acidification poses a major challenge in agricultural sustainability and it is serious in highly weathered soils such as Ultisols and Oxisols which are noted for nutrient deficiency and Al and Fe ions toxicities. Understanding sorption mechanisms and isotherms is important for the improvement of soil N availability particularly inorganic N. However, understanding the sorption mechanisms in relation to charcoal and wood ash as absorbents in the literature is difficult because the soil amendments vary depending on their raw materials or sources of origin. Therefore, one of the objectives of this review is to provide recent research findings and theory development on the role of charcoal and wood ash in agriculture. Furthermore, this review focuses on how charcoal and wood ash improve N availability through physical, chemical and biological processes in mineral acidic soils. Balanced application and good understanding of the role of charcoal and wood ash as soil amendments have potential benefits to improve N availability and crop productivity.

The effects of a high biochar rate on soil carbon mineralization, when co-applied with excessive compost, have been reported in previous studies, but there is a dearth of studies focusing on soil nitrogen. In order to ascertain the positive or snegative effects of a higher biochar rate on excessive compost, compost (5 wt. %) and three slow pyrolysis (>700 °C) biochars (formosan ash (Fraxinus formosana Hayata), ash biochar; makino bamboo (Phyllostachys makino Hayata), bamboo biochar; and lead tree (Leucaena leucocephala (Lam.) de. Wit), lead tree biochar) were applied (0, 2 and 5 wt. %) to three soils (one Oxisols and two Inceptisols). Destructive sampling occurred at 1, 3, 7, 28, 56, 84, 140, 196, 294, and 400 days to monitor for changes in soil chemistry. The overall results showed that, compared to the other rates, the 5% biochar application rate significantly reduced the concentrations of inorganic N (NO3−-N + NH4+-N) in the following, decreasing order: lead tree biochar > bamboo biochar > ash biochar. The soil response in terms of ammonium and nitrate followed a similar declining trend in the three soils throughout the incubation periods, with this effect increasing in tandem with the biochar application rate. Over time, the soil NO3−-N increased, probably due to the excessive compost N mineralization; however, the levels of soil NO3−-N in the sample undergoing the 5% biochar application rate remained the lowest, to a significant degree. The soils’ original properties determined the degree of ammonium and nitrate reduction after biochar addition. To reduce soil NO3−-N pollution and increase the efficiency of compost fertilizer use, a high rate of biochar application (especially with that pyrolyzed at high temperatures (>700 °C)) to excessively compost-fertilized soils is highly recommended.

The use of black soldier fly frass fertilizer (BSFFF) is being promoted globally. However, information on nitrogen (N) fertilizer equivalence (NFE) value and synchrony of N mineralization for crop production remains largely unknown. Comparative studies between BSFFF and commercial organic fertilizer (SAFI) were undertaken under field conditions to determine synchrony of N release for maize uptake. The BSFFF, SAFI, and urea fertilizers were applied at the rates of 0, 30, 60, and 100 kg N ha−1. The yield data from urea treated plots were used to determine the NFE of both organic inputs. Results showed that maize from BSFFF treated plots had higher N uptake than that from SAFI treated plots. High N immobilization was observed throughout the active growth stages of maize grown in soil amended with BSFFF, whereas soil treated with SAFI achieved net N release at the silking stage. Up to three times higher negative N fluxes were observed in SAFI amended soils as compared with BSFFF treated plots at the tasseling stage. The BSFFF applied at 30 and 60 kg N ha−1 achieved significantly higher NFE than all SAFI treatments. Our findings revealed that BSFFF is a promising and sustainable alternative to SAFI or urea for enhanced maize production.

Optimal manure management can maximize agronomic benefits and minimize environmental impacts. Field experiments were conducted in the Pacific Northwest (Vancouver, Canada) to determine how chicken and horse manures that were fall-applied to meet nitrogen crop demand affect soil ammonium (NH4+) and nitrate (NO3−), apparent net mineralization (ANM) and nitrification (ANN), crop biomass and nutrient concentration, and fluxes of nitrous oxide (N2O), carbon dioxide (CO2), and methane (CH4). Relative to horse manure, chicken manure increased soil NH4+ by 60-fold, ANM by 2-fold, and ANN by 4-fold. Emissions of N2O (+600%) and CO2 (+45%) were greater and growing season CO2 emissions (−40%) were lower after application of chicken than horse manure. Productivity of cover crop (+30%), legume cover crop (−25%), and squash cash crop (+20%) were affected by chicken relative to horse manure. Overall, fall-applied chicken manure increased yields, N availability, and environmental impacts relative to horse manure.

Native grasslands in the Great Plains of North America have mostly disappeared in the past century due to agricultural expansion. A grazing study was established on Paleustolls and Argiustolls supporting a remnant, but historically grazed tallgrass prairie in central Oklahoma. Stocking method of beef cattle was differentiated into continuous and rotational treatments (10 sub-paddocks) in 2009 and these treatments continued until present. Soil was sampled in 2009 and 2012 at depths of 0–6, 6–12, 12–20, and 20–30 cm and in 2017 at depths of 0–15 and 15–30 cm. Total, particulate, microbial biomass, and mineralizable C and N fractions were highly stratified with depth, having 2–10 times greater concentration at a depth of 0–6 cm as that at 20–30 cm. Strong associations existed among most of these soil organic C and N fractions, given the large range that resulted from sampling at multiple depths. No discernable differences in soil organic C and N fractions occurred due to stocking method at any sampling time or depth. Evidence for biological nitrification inhibition suggested a mechanism for conservation of available N with less opportunity for loss. In addition, strong association of available N with biologically active C indicated slow, but sustained release of N that was strongly coupled to C cycling. We conclude that stocking method had a neutral effect on conservation of already high antecedent conditions of soil organic C and N fractions during the first 8 years of differentially imposed management.

About 1% of New Zealand farmland is managed organically. Nitrogen is the nutrient most likely to limit organic crop production. A potential solution is incorporation of compost to supply N. About 726,000 t of municipal garden and kitchen wastes are sent to landfills annually. Composting offers a means of reducing the impact of landfill wastes on the wider environment. Organically certified compost (N content typically 2% to 2.5%) is available from some municipal composting plants. To be effectively used on organic farms, the rate of N release (mineralization) must be known. Laboratory incubations were conducted to quantify mineralization of compost N under controlled (temperature and moisture) conditions. Nitrogen availability and crop yields from a one-off application of compost (25–100 t·ha−1) were also assessed in two field trials (using cereal and forage crops). The results suggested that a relatively small part (13%–23%) of compost N was used by the crops in 3–4 years. Much of this was mineral N present at the time of application. Mineralization rates in the laboratory and field studies were much lower than expected from published work or compost C:N ratio (considered an important indicator of N mineralization potential of composts).

The aim of the current study was to create a high quality growing medium blend that replaces 70 vol% peat with 40 vol% woody green compost and 30 vol% bark compost and organic fertilizers (i.e., blood meal and chitin), all locally sourced. A range of "woody composts", i.e., green composts based on feedstock selection with mainly woody material from tree prunings, were produced for this purpose at green compost facilities. First, the woody composts were characterized chemically and biologically, including their microbial biomass and net N release. In comparison with regular green composts or vegetable, fruit and garden (VFG) waste composts, woody composts are more suitable for use in growing media due to their lower pH, EC and inorganic C content; however, the woody compost had a low N mineralization rate. Three types of composts supported a higher microbial biomass than wood fiber or bark compost. The additional mineral N release after 100 days for compost mixed with blood meal was tested for different VFG and green composts. A significantly higher additional net N release was measured for composts with higher initial mineral N concentrations (317 mg Nmin/L) as well as VFG composts (417 mg Nmin/L) than for green composts with a lower initial mineral N concentration (148 mg Nmin/L). In a last step, woody compost, bark compost, wood fiber, coir and peat were mixed in different ratios, resulting in six blends ranging from 100% peat-free to 100% peat. Two batches of woody compost were compared, and the blends were mixed with blood meal or chitin. A strong effect of both the organic fertilizer and the blend composition on the mineral N release was observed, with a clear link between the microbial biomass and the net N release. There was a significant negative correlation between the net change in microbial biomass and the net N release (R = −0.85), which implies that a larger increase in microbial biomass during incubation with the organic fertilizer resulted in less N mineralization. The blends containing woody compost scored better for nitrification activity, as the NH4-N concentrations were lower in these than for the blends without woody compost. For the peat blends, no effect on the microbial biomass was observed after addition of organic fertilizers; mineral N did increase, however. Woody composts have the potential to be used in high vol% in growing media blends, but the blends still need further optimization when supplemented with organic fertilizers. [ABSTRACT FROM AUTHOR]

In subtropical regions, we have an incomplete understanding of how long-term tillage, stubble, and nitrogen (N) fertilizer management affects soil biological functioning. We examined a subtropical site managed for 50 years using varying tillage (conventional till (CT) and no-till (NT)), stubble management (stubble burning (SB) and stubble retention (SR)), and N fertilization (0 (N0), 30 (N30), and 90 (N90) kg ha−1 y−1) to assess their impact on soil microbial respiration, easily extractable glomalin-related soil protein (EEGRSP), and N mineralization. A significant three-way tillage × stubble × N fertilizer interaction was observed for soil respiration, with NT+SB+N0 treatments generally releasing the highest amounts of CO2 over the incubation period (1135 mg/kg), and NT+SR+N0 treatments releasing the lowest (528 mg/kg). In contrast, a significant stubble × N interaction was observed for both EEGRSP and N mineralization, with the highest concentrations of both EEGRSP (2.66 ± 0.86 g kg−1) and N mineralization (30.7 mg/kg) observed in SR+N90 treatments. Furthermore, N mineralization was also positively correlated with EEGRSP (R2 = 0.76, p < 0.001), indicating that EEGRSP can potentially be used as an index of soil N availability. Overall, this study has shown that SR and N fertilization have a positive impact on soil biological functioning. [ABSTRACT FROM AUTHOR]

Mineralization studies are the first step in determining the usefulness of an amendment such as fertilizer, and are essential to creating guidelines for dairy waste management to help producers make informed decisions. Our goal was to assess the effects of dairy raw, composted, and digested manure amendments on C, N, and P mineralization to evaluate the feasibility of their in-farm production and use as organic fertilizers. The liquid and solid fractions of dairy effluent (LDE, SDE), dairy effluent digestate (DED), onion–cattle manure digestate and compost (OCMD, OCMC) were characterized by chemical and spectroscopic methods. Soil microcosms with LDE, SDE, DED, OCMD and OCMC and the C, N and P mineralization were determined periodically. Elemental and structural differences among amendments led to contrasting profiles of C, N, and P mineralization, and thus to differences in nutrient availability, immobilization, and CO2 emission. All processed materials were more stable than untreated waste, reducing C emissions. Digestates showed net C immobilization, and supplied the highest levels of available N, creating a relative P deficit. Instead, the compost supplied N and P via mineralization, producing a relative P excess. Future studies should aim at evaluating fertilization strategies that combine both kinds of amendments, to exploit their complimentary agronomic characteristics. [ABSTRACT FROM AUTHOR]

Immobilisation of fertiliser nitrogen (N) by soil microorganisms can reduce N availability to crops, decreasing growth and yield. To date, few studies have focussed on the effect of different plant species on immobilisation of fertiliser N. Canola (Brassica napus) is known to influence the soil microbiome and increase mineral N in soil for future crops compared with cereals. We tested the hypothesis that canola can reduce immobilisation of fertiliser N by influencing the composition of the rhizosphere microbiome. To investigate this, we conducted a glasshouse soil column experiment comparing N fertiliser uptake between canola and wheat (Triticum aestivium) and partitioning of fertiliser N between plants and microorganisms. Plants were grown in soil to which high C:N ratio wheat residues and 15N-labelled urea fertiliser were applied. There was no difference between wheat and canola in fertiliser N uptake despite differences in fungal community composition and the carbon metabolising enzyme alpha-glucosidase in the rhizosphere. Canola obtained more soil-derived N than wheat. There was no significant difference in the rhizosphere bacterial communities present between wheat and canola and unplanted controls. Our results highlight the capacity of canola to increase mineralisation of soil N compared with wheat although the study could not describe the microbial community which facilitated this increase. [ABSTRACT FROM AUTHOR]

Organic matter (OM) and nutrient nitrogen (N) play vital roles in the fertility and production of soil in accordance with goals of efficient environmental protection. This study aimed to show the extent to which N delivery can contribute to improving nitrogen fertilizer requirements (NFR) through comparative analysis of OM and N. Systems determining the NFR in agricultural practices have thus far been challenged to estimate the annual rate of mineralization of the soil. OM and N turnover was investigated through an available evaluation consisting of 546 representatively distributed permanent test and observation plots (TP) of the German Federal State of Saxony farms. A solid database of at least 10-year field plot card records from 2001 to 2010 was selected for the analysis. A program (BEFU) widely used in agricultural practice, along with the simplified process model CCB, were applied. For the calculation of the amount of mineral N fertilizers used, the results of three different methods for determining the NFR were compared with each other. The determination of the farmers' demand (=actual condition of the TP) with a mean value of 132 kg N ha−1 did not show a large difference between the calculated values with 137 kg N ha−1 by the BEFU program. Based on the available results for the most important crop species cultivated in Saxony, there were clear differences in the considerations of the N delivery from the soil. The BEFU program was able to calculate an average N delivery of 17 kg N ha−1 from tabulated data, whereas with the CCB process model, 66 kg N ha−1 of mineralization was determined with a distinct higher deviation by taking into account the 10-year field histories. Using the N delivery of the TP by the CCB model, a clear reduction of the mean N fertilization level, to about 80 kg N ha−1, was therefore achieved. These differences were particularly large for TP with organic fertilization (livestock), at a relatively low N fertilization level, and for certain crop species. With a high standard deviation, the average savings potential of mineral N fertilizers was 52–57 kg N ha−1. After including the corrected values for the N mineral fertilization, a decrease in the N balances by an average of 20–25 kg N ha−1 was ultimately achieved. In particular, the heavily oversupplied plots with D and E classification decreased by approximately 50%. The results of our study demonstrate clear improvements; therefore, increased efforts should be made in the future to optimize the determination of NFR using applicable methods that consider N mineralization in agricultural practice and consultation. [ABSTRACT FROM AUTHOR]

A long-term experiment (38 years) was conducted to elucidate the effects of long-term N addition on the net N mineralization in both paddy and upland soils, based on their initial soil N status, with and in connection with soil microbial biomass and N cycling extracellular enzyme activities. Two treatments without N addition CK (No fertilizer) and K (inorganic potassium fertilizer) and two treatments with N addition (inorganic nitrogen fertilizer) and NK (inorganic nitrogen and potassium fertilizer) were placed in incubation for 90 days. Results showed that the total N and soil organic carbon (SOC) contents were higher in the treatments with N application compared to the treatments without N in both paddy and upland soils. The SOC content of paddy soil was increased relative to upland soil by 56.2%, 45.7%, 61.1% and 62.2% without N (CK, K) and with N (N and NK) treatments, respectively. Site-wise, total N concentration in paddy soil was higher by 0.06, 0.10, 0.57 and 0.60 times under the CK, K, N and NK treatments, respectively, compared with upland soil. In paddy soil, soil microbial biomass nitrogen (SMBN) was higher by 39.6%, 2.77%, 29.5% and 31.4%, and microbial biomass carbon (SMBC) was higher by 11.8%, 11.9%, 10.1% and 12.3%, respectively, in CK, K, N and NK treatment, compared with upland soil. Overall, compared to upland soil, the activities of leucine-aminopeptidase (LAP) were increased by 31%, 18%, 20% and 11%, and those of N-acetyl-b-D-glucosaminidase (NAG) were increased by 70%, 21%, 13% and 18% by CK, K, N and NK treatments, respectively, in paddy soil. A significantly linear increase was found in the NO3−-N and NH4+-N concentrations during the 90 days of the incubation period in both soils. NK treatment showed the highest N mineralization potential (No) along with mineralization rate constant, k (NMR) at the end of the incubation. SMBC, SMBN, enzyme activities, NO3−-N and NH4+-N concentrations and the No showed a highly significant (p ≤ 0.05) positive correlation. We concluded that long-term N addition accelerated the net mineralization by increasing soil microbial activities under both soils. [ABSTRACT FROM AUTHOR]

This paper reviews the use of charcoal and wood ash in acid soils as adsorbents to improve N availability at the same time improving their soil fertility and crop productivity. Soil acidification poses a major challenge in agricultural sustainability and it is serious in highly weathered soils such as Ultisols and Oxisols which are noted for nutrient deficiency and Al and Fe ions toxicities. Understanding sorption mechanisms and isotherms is important for the improvement of soil N availability particularly inorganic N. However, understanding the sorption mechanisms in relation to charcoal and wood ash as absorbents in the literature is difficult because the soil amendments vary depending on their raw materials or sources of origin. Therefore, one of the objectives of this review is to provide recent research findings and theory development on the role of charcoal and wood ash in agriculture. Furthermore, this review focuses on how charcoal and wood ash improve N availability through physical, chemical and biological processes in mineral acidic soils. Balanced application and good understanding of the role of charcoal and wood ash as soil amendments have potential benefits to improve N availability and crop productivity. [ABSTRACT FROM AUTHOR]

The effects of a high biochar rate on soil carbon mineralization, when co-applied with excessive compost, have been reported in previous studies, but there is a dearth of studies focusing on soil nitrogen. In order to ascertain the positive or snegative effects of a higher biochar rate on excessive compost, compost (5 wt. %) and three slow pyrolysis (>700 °C) biochars (formosan ash (Fraxinus formosana Hayata), ash biochar; makino bamboo (Phyllostachys makino Hayata), bamboo biochar; and lead tree (Leucaena leucocephala (Lam.) de. Wit), lead tree biochar) were applied (0, 2 and 5 wt. %) to three soils (one Oxisols and two Inceptisols). Destructive sampling occurred at 1, 3, 7, 28, 56, 84, 140, 196, 294, and 400 days to monitor for changes in soil chemistry. The overall results showed that, compared to the other rates, the 5% biochar application rate significantly reduced the concentrations of inorganic N ( NO 3 − - N + NH 4 + - N ) in the following, decreasing order: lead tree biochar > bamboo biochar > ash biochar. The soil response in terms of ammonium and nitrate followed a similar declining trend in the three soils throughout the incubation periods, with this effect increasing in tandem with the biochar application rate. Over time, the soil NO 3 − - N increased, probably due to the excessive compost N mineralization; however, the levels of soil NO 3 − - N in the sample undergoing the 5% biochar application rate remained the lowest, to a significant degree. The soils' original properties determined the degree of ammonium and nitrate reduction after biochar addition. To reduce soil NO 3 − - N pollution and increase the efficiency of compost fertilizer use, a high rate of biochar application (especially with that pyrolyzed at high temperatures (>700 °C)) to excessively compost-fertilized soils is highly recommended. [ABSTRACT FROM AUTHOR]

The use of black soldier fly frass fertilizer (BSFFF) is being promoted globally. However, information on nitrogen (N) fertilizer equivalence (NFE) value and synchrony of N mineralization for crop production remains largely unknown. Comparative studies between BSFFF and commercial organic fertilizer (SAFI) were undertaken under field conditions to determine synchrony of N release for maize uptake. The BSFFF, SAFI, and urea fertilizers were applied at the rates of 0, 30, 60, and 100 kg N ha−1. The yield data from urea treated plots were used to determine the NFE of both organic inputs. Results showed that maize from BSFFF treated plots had higher N uptake than that from SAFI treated plots. High N immobilization was observed throughout the active growth stages of maize grown in soil amended with BSFFF, whereas soil treated with SAFI achieved net N release at the silking stage. Up to three times higher negative N fluxes were observed in SAFI amended soils as compared with BSFFF treated plots at the tasseling stage. The BSFFF applied at 30 and 60 kg N ha−1 achieved significantly higher NFE than all SAFI treatments. Our findings revealed that BSFFF is a promising and sustainable alternative to SAFI or urea for enhanced maize production. [ABSTRACT FROM AUTHOR]

Optimal manure management can maximize agronomic benefits and minimize environmental impacts. Field experiments were conducted in the Pacific Northwest (Vancouver, Canada) to determine how chicken and horse manures that were fall-applied to meet nitrogen crop demand affect soil ammonium (NH4+) and nitrate (NO3−), apparent net mineralization (ANM) and nitrification (ANN), crop biomass and nutrient concentration, and fluxes of nitrous oxide (N2O), carbon dioxide (CO2), and methane (CH4). Relative to horse manure, chicken manure increased soil NH4+ by 60-fold, ANM by 2-fold, and ANN by 4-fold. Emissions of N2O (+600%) and CO2 (+45%) were greater and growing season CO2 emissions (−40%) were lower after application of chicken than horse manure. Productivity of cover crop (+30%), legume cover crop (−25%), and squash cash crop (+20%) were affected by chicken relative to horse manure. Overall, fall-applied chicken manure increased yields, N availability, and environmental impacts relative to horse manure. [ABSTRACT FROM AUTHOR]

Native grasslands in the Great Plains of North America have mostly disappeared in the past century due to agricultural expansion. A grazing study was established on Paleustolls and Argiustolls supporting a remnant, but historically grazed tallgrass prairie in central Oklahoma. Stocking method of beef cattle was differentiated into continuous and rotational treatments (10 sub-paddocks) in 2009 and these treatments continued until present. Soil was sampled in 2009 and 2012 at depths of 0–6, 6–12, 12–20, and 20–30 cm and in 2017 at depths of 0–15 and 15–30 cm. Total, particulate, microbial biomass, and mineralizable C and N fractions were highly stratified with depth, having 2–10 times greater concentration at a depth of 0–6 cm as that at 20–30 cm. Strong associations existed among most of these soil organic C and N fractions, given the large range that resulted from sampling at multiple depths. No discernable differences in soil organic C and N fractions occurred due to stocking method at any sampling time or depth. Evidence for biological nitrification inhibition suggested a mechanism for conservation of available N with less opportunity for loss. In addition, strong association of available N with biologically active C indicated slow, but sustained release of N that was strongly coupled to C cycling. We conclude that stocking method had a neutral effect on conservation of already high antecedent conditions of soil organic C and N fractions during the first 8 years of differentially imposed management. [ABSTRACT FROM AUTHOR]