Search Results (24)

Intensive nitrogen (N) fertilization in greenhouse vegetable systems degrades soil structure and accelerates soil carbon (C) mineralization. Biochar application can alleviate these adverse effects by enhancing aggregate stability and mediating microbially driven nutrient cycling, yet its effects across aggregate fractions remain poorly understood. Here, we investigated how biochar (0, 20, 40 t ha⁻¹) and N interact to affect aggregate stability, C mineralization, nutrient status, and microbial properties in bulk soil and four aggregate classes (large macroaggregates: LMA, > 2000 μm; small macroaggregates: SMA, 250–2000 μm; microaggregates: MA, 53–250 μm; silt + clay: S + C, < 53 μm) in vegetable soil after a 60-day incubation. Results showed that biochar–N co-application increased mean weight diameter by 27.4–30.5% and elevated soil total organic C (TOC) in LMA by 9.11–12.0% and in MA by 8.77–20.2% relative to the N-only treatment. It also reduced β-glucosidase and oxidase activities, as well as fungal and G⁻-bacterial abundance. Biochar amendment suppressed TOC mineralization by 2.7–24.6% in bulk soil and aggregate fractions, while boosting potentially mineralizable C pools by 12.5–155.7%, and thereby increasing overall mineralization potential. Structural equation modeling revealed the size-dependent regulatory mechanisms underlying these observations. Aggregate stability directly inhibited CO₂ emissions in bulk soil and SMA, while the effects in MA and S + C fractions were mediated by shifts in nutrient stoichiometry and hydrolase activities. Our findings clarified the size-dependent mechanisms by which biochar–N co-application promoted soil C sequestration, providing a theoretical basis for the sustainable management of intensive vegetable systems. Full article

Soil amendments are widely promoted to improve turfgrass performance and soil properties in suboptimal soil; however, their effectiveness under field-managed conditions remains unclear. Two concurrent field experiments (i.e., turfgrass and soil and reduced nitrogen) were conducted from August 2022 to November 2023 in Gainesville, FL, using a randomized complete block design to evaluate organic and biological amendments under standard and reduced nitrogen (N) fertilization. In the turfgrass and soil portion, treatments included granular humic + fertilizer, liquid humic + fertilizer, biochar + fertilizer, microbial inoculant + fertilizer, compost, natural fertilizer, fertilizer, and a non-treated control. In the reduced N experiment, fertilizer rates for all amendment combinations and the natural fertilizer were applied at 50% (12.2 kg N ha⁻¹), while the full-rate fertilizer (24.4 kg N ha⁻¹) and non-treated control were included for comparison. Treatments were applied to St. Augustinegrass (Stenotaphrum secundatum (Walt.) Kuntze) and zoysiagrass (Zoysia spp. Willd.) established on a sand-based root zone. Turfgrass performance was assessed using visual quality, normalized difference vegetation index, and percent green via digital image analysis. Soil properties were evaluated using physical, chemical, and biological parameters. Treatment responses varied by amendment type and N rate. All treatments improved turfgrass performance relative to the non-treated control, with compost producing the greatest improvements in turfgrass quality and soil properties, including organic matter, pH, and plant-available P, K, and Fe. Humic substances, biochar, and microbial inoculants primarily increased potentially mineralizable N but provided limited improvements in turfgrass performance compared with fertilizer alone. Nitrogen rate was the primary determinant of turfgrass performance, with full N treatments producing the highest quality. Although reduced N treatments improved turfgrass quality relative to the control, amendment additions did not consistently enhance turfgrass performance under reduced N conditions. Full article

Nitrogen (N) management remains a primary challenge in organic grain systems, particularly in rotations where heavy N-consuming crops, such as corn and wheat, follow one another. Daikon radish (Raphanus sativus L.) is widely adopted for its ability to scavenge residual soil nitrate between cash crops; yet the subsequent availability of scavenged N to the following crop is inconsistent and often negligible. This 4-year field study (2014–2017) at the University of Minnesota Southwest Research and Outreach Center evaluated whether planting daikon radish in polyculture with berseem clover, and either annual oats or winter rye could improve N retention and timed release compared to daikon radish monoculture. Three cover crop treatments were tested across three common organic management systems: no manure with no tillage, manure with tillage, and manure plus shallow tillage incorporation before cover crop seeding. Polycultures, especially those including winter rye, produced significantly more fall biomass (up to 6435 kg ha⁻¹) than daikon radish monoculture (573–1272 kg ha⁻¹). Manure incorporation consistently increased total and daikon radish biomass, as well as the percent living cover. Despite substantial biomass differences, mid-season and fall soil inorganic N, potentially mineralizable N, permanganate-oxidizable C, and enzyme activities showed few consistent treatment effects. Corn grain yield was highest following manure with tillage incorporation but was significantly reduced after the winter rye polyculture in all years, likely due to N immobilization and delayed corn planting caused by late rye termination under wet spring conditions. Results indicate that while polycultures with winter rye maximize biomass and soil cover, they do not reliably enhance N recycling to the subsequent organic corn crop and can reduce yield. Full article

Crops nitrogen supply through the in situ mineralization of soil organic matter is a critical process for plant nutrition. However, accurately estimating the contribution of mineralization remains challenging. The complexity of biological, chemical, and physical processes in the soil, influenced by environmental conditions, makes it difficult to precisely quantify the amount of nitrogen available for crops. In this study, we created a database by collecting results from 121 mineralization monitoring experiments carried out between 2015 and 2021 on different experimental plots across Wallonia, Southern Belgium, and assessed the efficiency of predictive mineralization methods. The most impactful analytical parameters on in situ mineralization (ISM), determined using LIXIM program, appeared to be potentially mineralizable nitrogen (PMN) (r = 0.79). PMN, estimated by anaerobic soil incubation, also allowed the effective consideration of the after-effects of grassland termination and manure inputs. A multiple linear regression (MLR) combining PMN, POxC, pH, TOC:N, and TOC:clay significantly improved the prediction of soil nitrogen mineralization available for crops, achieving r = 0.87 (vs. r = 0.58 for the current method), while reducing dispersion by 41% (RMSE 56.35 → 33.13 kg N·ha⁻¹). The use of a more flexible Bootstrap Forest model (BFM) further enhanced performance, reaching r = 0.92 and a 50.8% reduction in dispersion compared to the current method (RMSE 56.35 → 27.76 kg N·ha⁻¹), i.e., about 16% lower RMSE than the MLR. Those models provided practical and efficient tools to better manage nitrogen resources in temperate agricultural systems. Full article

Agroforestry systems are sustainable farming practices with multiple benefits like enhanced biodiversity, soil nutrient cycling, soil physical properties, and carbon sequestration. Investigating these multiple beneficial effects of agroforestry systems compared to monoculture cropping systems under diverse pedo-climatic zones and crop-tree combinations is required to gather robust field evidence for agroforestry performance. Hence, the objective was to investigate the beneficial effects of agroforestry systems on soil properties and crop yields in a combined food and energy production (CFE) agroforestry system compared to the conventional winter wheat (CWW) production system in Denmark. The field methods consisted of soil and crop cut sampling, soil moisture measurement, earthworm abundance count in CFE compared to the CWW fields, and climate data for 2023. The study demonstrated that an agroforestry system viz CFEmean and natural forest (NF) had a lower bulk density viz. 1.48 and 1.01 g cm⁻³, respectively compared to CWW (1.74 g cm⁻³) with intensive use of fertilizers and chemicals. CFEmean and NF had higher soil organic matter, total nitrogen %, available potassium (K), potentially mineralizable nitrogen, soil moisture retention, and earthworm count under drought conditions compared to CWW. The study demonstrated that alley cropped winter wheat (CFE WW) recorded similar grain yields and significantly higher straw and aboveground biomass accumulation compared to CWW with intensive use of chemical and fertilizer inputs. The biomass belt (BB) effects on alley crop yield varied with the distance with negative effects on grain, straw, and aboveground biomass yields in CFE WW at the nearest points from the BB, and yields increased gradually in the alley fields further away from the BB with maximum grain yields at 62.83 m away from the BB. The study provided a robust field evidence on the beneficial effects of agroforestry on soil properties and crop and biomass yields compared to CWW for informed decision-making by land managers for the adoption of agroforestry practice. Full article

Soil fertilization with fertilizers derived from renewable sources is a topic of great interest in terms of the sustainable management of organic waste. To optimize the management of nitrogen supplied to the soil with digestates, it is necessary to deepen knowledge on the process of mineralization of organic nitrogen over time. In this research, a laboratory incubation system was utilized to study the impact of various digestate sources on nitrogen mineralization processes in soils and nitrogen mineralization kinetics. Six types of digestates of different origins and composition were administered to soil and the soil samples were placed under controlled conditions. The release of N was determined by measuring ammonium-N and nitrate-N concentrations in leachates during a 12-week period of incubation. The nonlinear regression technique was used to fit the cumulative leaching of total N to the Stanford and Smith first-order kinetic model during the incubation period. The results showed that the differences between digestates, nitrogen and organic carbon concentration, and C/N ratio influenced both ammonification and nitrification processes in the soil and the nitrogen mineralization kinetics. The processing of the statistical data highlighted that the potentially mineralizable nitrogen (MPN) followed first-order kinetics. Full article

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. Full article

Organic vegetable producers in Georgia, USA, utilize a range of amendments to supply nitrogen (N) for crop production. However, differences in soil type, fertilizers and environmental conditions can result in variability in N mineralization rates among commonly utilized organic fertilizers in the region. In this study, the effects of temperature on N mineralization from three commercial organic fertilizers [feather meal (FM), pelleted poultry litter (PPL) and a mixed organic fertilizer (MIX)] in two soil types from Georgia, USA (Cecil sandy clay loam and Tifton loamy sand) were evaluated for 120 d. Net N mineralization (Net N_min) varied with soil type, fertilizer and temperature. After 120 d, Net N_min from the FM fertilizer ranged between 41% and 77% of total organic N applied, the MIX fertilizer ranged between 26% and 59% and the PPL fertilizer ranged between 0% and 22% across all soil types and temperatures. Incubation at higher temperatures (20 °C and 30 °C) impacted Net N_min of FM fertilizer in the Tifton series soil. Temperature and soil type had a relatively minor impact on the potentially mineralizable N of the PPL and MIX fertilizers after 120 d of incubation; however, both factors impacted the rate of fertilizer release shortly after application, which could impact the synchronicity of N availability and plant uptake. Temperature-related differences in the mineralization of organic fertilizers may not be large enough to influence a grower’s decisions regarding N fertilizer inputs for vegetable crop production in the two soils. However, organic fertilizer source will likely play a significant role in N availability during the cropping season. Full article

Management-intensive Grazing (MiG) has been proposed to sustainably intensify agroecosystems through careful management of livestock rotations on pastureland. However, there is little research on the soil health impacts of transitioning from irrigated cropland to irrigated MiG pasture with continuous livestock rotation. We analyzed ten soil health indicators using the Soil Management Assessment Framework (SMAF) to identify changes in nutrient status and soil physical, biological, and chemical health five to six years after converting irrigated cropland to irrigated pastureland under MiG. Significant improvements in biological soil health indicators and significant degradation in bulk density, a physical soil health indicator, were observed. Removal of tillage and increased organic matter inputs may have led to increases in β-glucosidase, microbial biomass carbon, and potentially mineralizable nitrogen, all of which are biological indicators of soil health. Conversely, trampling by grazing cattle has led to increased bulk density and, thus, a reduction in soil physical health. Nutrient status was relatively stable, with combined manure and fertilizer inputs leading to stabilized plant-available phosphorous (P) and increased potassium (K) soil concentrations. Although mixed effects on soil health were present, overall soil health did increase, and the MiG system appeared to have greater overall soil health as compared to results generated four to five years earlier. When utilizing MiG in irrigated pastures, balancing the deleterious effects of soil compaction with grazing needs to be considered to maintain long-term soil health. Full article

Seagrass beds are considered to be substantial sinks of “blue carbon”. However, differentiation in the carbon sink capacities of seagrass beds in different regions with distinct nutrient conditions remains unclear. In this study, sediment carbon stocks, seagrass biomass, and microbial community structures and potential functions of seagrass beds in eutrophic seawater adjacent to Hainan Island and oligotrophic seawater around the Xisha Islands were compared. Our results showed that sediment mineralizable organic carbon and dry bulk density were substantially higher on Hainan Island than on the Xisha Islands (t-test, p < 0.05), while sediment carbon stocks and the total organic carbon were comparable between the two regions (p > 0.05). Similarly, seagrass biomass was much higher on Hainan Island (p < 0.05). Sediment carbon stocks positively correlated with sediment nitrogen and negatively correlated to sediment pH and grain size (p < 0.05). Bacterial diversities were similar in the two regions, while fungi were more diverse on Hainan Island (p < 0.05). Proteobacteria, Desulfobacterota, Ascomycota and Basidiomycota could account for degrading organic carbon on Hainan Island. Proteobacteria and Bacteroidota may contribute primarily to carbon loss in the seagrass beds of the Xisha Islands. This study strengthens our understanding of the effects of human activities on carbon sequestration in seagrass bed ecosystems. Full article

Numerous biological and chemical methods have been proposed over the years for estimating the nitrogen (N) mineralization capacity of soils; however, none of them has found general use in soil fertility testing. The efficacy of a recently proposed alkaline hydrolysis method for assessing N availability in soils compared with the standard long-term incubation technique for determining potentially available N was evaluated. The nitrogen mineralization of 12 surface soils incubated under aerobic conditions at 25 °C for 26 weeks was determined. Field-moist soils were direct-steam distilled with 1 M KOH or 1 M NaOH; the NH₃ released was trapped in boric acid, and its concentration was determined successively every 5 min for 40 min. The cumulative N mineralized or hydrolyzed was fitted to the first-order exponential equation to determine the potentially mineralizable N (N_o) and an analogous “potentially hydrolyzable N (N_max)” for the soils. The flush of CO₂ (fCO₂) following the rewetting and incubation of air-dried soils under aerobic conditions for 3 days was also determined. The results showed that the N_max values differed considerably among the soils, indicating differences in the chemical nature and reactivity of the organic N content of the soils, and were significantly correlated with N_o and fCO₂ values. The estimated N_max and N_o values ranged from 105 to 371 mg N kg⁻¹ and 121 to 292 mg kg⁻¹, respectively. Based on the simple and inexpensive nature of the alkaline hydrolysis procedure, the reduction in the incubation time required to obtain N_o (months to minutes), and the strong association between N_max and N_o, we concluded that N_max is a good predictor of the biologically discrete and quantifiable labile pool of mineralizable soil organic N (ON), and the use of the alkaline hydrolyzable ON as a predictor of N_o merits consideration for routine use in soil testing laboratories for estimating the N-supplying capacity of soils. Full article

Agriculture can play a primary role in the context of nutrients recovery by promoting the use of organic fertilizers (OFs). In order to use them efficiently, it is necessary to predict the nitrogen (N) bioavailability, which is a challenging matter due to the different physical-chemical characteristics of commercially available OFs. This study aims to evaluate hot-water extractable N as a rapid and cheap chemical indicator of bioavailable N. The trial was conducted on nine animal-based OFs obtained from different raw materials and treatment processes. They were fully characterized and the bioavailable N was determined by a 7-week soil incubation experiment. The results showed that hot-water extractable N underestimated bioavailable N in the case of leather meal based OFs; however, a significant linear regression fitting was achieved (R² = 0.53). The C:N ratio was also assessed, which showed a negative correlation (−0.87) and a better linear regression fitting (R² = 0.76) with the bioavailable N, but manifested some limitations in the prediction of leather meal based products. This experiment showed that both hot-water extractable N and C:N ratio can provide useful information for farmers in managing this class of OFs. Full article

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. Full article

In recent years, pasture production changed from conventional tilled single pastures to minimum tilled mixed pastures in the Tsitsikamma region, South Africa. However, storage of soil organic matter (SOM) under minimum tilled mixed pastures is not yet quantified. This study evaluated SOM indices in the upper 60 cm soil of six-year-old mixed pastures in the Upper (UT) and Lower (LT) Tsitsikamma regions. Soil samples were collected at 0–15, 15–30, 30–45, and 45–60 cm soil layers of five farms (F1, F2, F3, F4, and F5) treated with different rates of fertilizer (NPK) alone and in combination with dairy effluent (DE) and/or poultry manure (PM). Results of this study indicated that there were no significant differences in bulk density, total nitrogen (N), and rate of potentially mineralizable N (PMN) between farms in the UT region. In the LT region, NPK, DE, and PM combinations improved soil C accumulation relative to the soil application of NPK. Higher C/N ratios in the LT region suggested adequate C for microbial energy and maintenance. Integrating manure into minimum tilled pasture mixtures as a replacement for synthetic fertilizers seems to be a feasible option to promote SOM storage, but remains only feasible by applying site-specific management strategies. Full article

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. Full article