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An ideal and efficient nitrogen (N) recommendation for precision fertilization (PF) should account for potential soil mineralizable N. This study aimed at estimating management zone (MZ) specific soil N mineralization rate (SNMR) of unamended soils. A total of 76 soil samples were collected from 21 MZs across 5 fields. An aerobic laboratory incubation was conducted under controlled conditions for two months with seven sub-sampling events. N mineralization was assessed as net increase in soil mineral N over time. Results indicated a considerable variation in mineralized soil N (9.12–41.93 mg kg−1 soil) across fields. Highest and lowest net SNMRs were 0.50 and 0.0004 mg kg−1 soil day−1, respectively. SNMRs significantly differed across MZs in three fields, while in the other two fields no significant differences were observed. In turn, 3 of 34 MZ-pairs differed (marginally) significantly (padj = 0.02–0.09) from one another, namely in MZ pairs with high variation in soil particle sizes. MZ-specific SNMRs were mostly positively correlated to pH (0.20–1.00), total N (0.12–0.99), soil mineral N (0.11–1.00) and sand (0.34–0.99), negatively correlated with clay (− 1.00 to − 0.11) and correlations with SOC were mixed (0.41 to − 0.62). This along with the support from regression analysis corroborated the existing knowledge that TN is a better predictor of mineralization than SOC. While there were only few statistically significant differences in SNMR amongst MZ per field despite mathematical differences, still incorporating MZ-specific SNMR in management decisions will be crucial in optimizing the N use efficiency in precision farming, and along with other management actions, lead to more environmentally friendly PF schemes. [ABSTRACT FROM AUTHOR]

The occurrence and spread of invasive woody species are a truly global phenomenon, but tropical regions seem to be particularly vulnerable due to high rates of soil degradation in combination with climate change, and limited resources for containment. There is increasing awareness that complete eradication programs are often not effective. The existence of many "controversial species," i.e., species with both negative and positive impacts, renders decision-making processes for management exceedingly complex. By providing a very extensive overview of the current state of knowledge on impacts and containment strategies of invasive woody species, we aim to help underpin such decisions. We discuss both negative impacts and potential benefits of invasive woody species, focusing on the two most important ones, namely animal fodder production and the positive impacts on soil functioning and soil quality. Invasive woody species can positively impact livestock production (1) indirectly by improving pasture quality because of improved soil quality and functioning, and (2) directly by supplying a high-quality protein component for animal fodder. Invasive woody species increase soil carbon sequestration and nitrogen and phosphorus availability depending on the density of the invader, its capacity to fix nitrogen, the quantity and quality of its litter, and the direct interactions between its roots and the soil microbial community. The balance between potential benefits and risks depends to a large extent on the interaction with the local environment (climate, soil, vegetation, and animals) and the socioeconomic context of each region. When an invasion process starts because there is no local predator, then management can target eradication or very strict containment. If the invasion is the result of strong disturbance of the ecosystem, then intensive but well-thought management of the invasive species would be the choice to be made, as this may help to restore the ecosystem. [ABSTRACT FROM AUTHOR]

The addition of exogenous organic matter (EOM) generally stimulates microbial activity and shapes soil structure, likely with stronger effects at a higher application dose. It is not known, however, if and how the application dose of EOM would impact its own mineralisation and that of native soil organic carbon (SOC) by such mediation of soil pore network structure. In 90-day soil incubation experiments, we compared mineralisation of ± 2 cm pieces of 13C-labelled ryegrass as EOM reference at two doses (0.5 g kg−1 vs. 5 g kg−1) and mineralisation of SOC in sandy loam and silt loam soils that were initially subjected to different degrees of disturbance, namely soil sieving at < 2 mm and < 10 mm. We found that the high EOM dose-induced mesoporosity (i.e. vol% increase of pore neck class > 300 μm class by 130% vs. unamended control) and macroporosity (i.e. EOM doses 0.5 g kg−1 and 5 g kg−1 increased the vol% of the 60–100 μm class by 80 and 120% vs. unamended control) formation in the sandy loam soil, whereas the porosity in the silt loam soil remained unaffected. The % of EOM mineralised was independent of EOM dose and therefore did not relate to the changes in soil pore network structure. However, the observed development of meso- and macropores in the sandy loam soil appeared to be associated with stronger stimulation of SOC mineralisation at increasing EOM dose (30% and 71% more SOC mineralisation at low and high dose vs. unamended control). In the silt loam soil, only the high EOM dose-stimulated SOC mineralisation vs. unamended control (28%) but soil pore network structure remained unresponsive to EOM dose. This suggests that stimulation of SOC mineralisation following EOM addition might also be in part linked to the formation of larger pores in the sandy loam soil, and that this stimulation is not always proportional to EOM dose. [ABSTRACT FROM AUTHOR]

Purpose: Keystone taxa play an important role in soil nutrient cycling and crop growth and can be influenced by soil tillage. We investigated the composition of keystone taxa and their relationships with soil properties under different long-term tillage practices. Methods: Four tillage treatments (i.e., CT, conventional tillage; NT, no tillage with mulch; RT, reduced tillage; and SS, subsoiling with mulch) were maintained for twenty-one years. Co-occurrence network (CoNet) was constructed to identify the keystone taxa, and redundancy analysis (RDA) was carried out to explore the relationships between keystone taxa and soil properties under the four tillage practices at two growth stages (elongation and grain filling stages) of winter wheat. Results: Compared with CT, RT had no significant effect on the microbial community and the keystone microbiome, while NT and SS remarkably altered the microbial community structure and the keystone microbiome at both growth stages. Massilia was the keystone genus under CT and RT, while Sphingomonas, Asanoa and Hoeflea were the keystone genera under NT and SS. RDA results showed that keystone genera were significantly correlated with soil organic carbon (SOC), dissolved organic carbon (DOC) and microbial biomass nitrogen (MBN) at both stages, especially at the elongation stage. Our results further revealed that the effects of NT and SS on crop growth might be related to the changes in keystone microbiome. Conclusion: Our study suggests that NT and SS may contribute to the development of sustainable agricultural production in the Chinese Loess Plateau. [ABSTRACT FROM AUTHOR]

The use of agricultural crop residues and animal manure for soil amendment is limited in most part of Ethiopia because of high competition for the uses. However, due to low SOM content in most agricultural soils, there is an urgent need for a sustainable management system of agricultural residues to replenish SOM. Vermicomposting is superior among the most efficient recycling techniques for management of available agricultural wastes. The study aimed to investigate the type of crop residues and animal manure available, determinants for their current use, quantity of residue left for composting and farmer's perception of vermicomposting in three districts of the Benishangul–Gumuz region. Farmers use the largest portion of cereal residue such as sorghum as fuel and tef straw sold at the market and/or as stall-feeding. However, legume residues were consistently preferred for use as a composting material over cereal residues. The average amount of crop residues available for composting was estimated in the range between 0.2 and 0.6 ton year−1 farmer−1, across districts. While the quantity of cow manure used for compost production significantly differs between districts and was estimated 1.7, 1.2, and 0.5 ton year−1 farmer−1 at Bambasi, Assosa, and Homosha districts, respectively. Unlike other parts of Ethiopia, the mixed farmers in the study region well recognized the benefit of animal manures and did not use them as a source of fuel. Residues were found with varying decomposition characteristics that sorghum (10.08% and 1.65%) and tef (9.16% and 1.43%) residues had higher lignin and polyphenol contents, respectively, than maize, soybean, banana, and haricot bean. In terms of their quantity and quality composition, cow and donkey manures, as well as residues of soybean, banana, and maize are the major organic resources potential for utilization in the vermicomposting process in the region. Moreover, the availability of potential organic residues at the farm level could encourage farmer's motive to adopt high-value vermicompost production. [ABSTRACT FROM AUTHOR]

Degradability of organic matter (OM) in soil depends on its spatial location in the soil matrix. A recent breakthrough in 3D-localization of OM combined dual-energy X-ray CT-scanning with OsO4 staining of OM. The necessity for synchrotron-based µCT and the use of highly toxic OsO4 severely limit applications in soil biological experiments. Here, we evaluated the potential of alternative staining agents (silver nitrate, phosphomolybdenic acid (PMA), lead nitrate, lead acetate) to selectively enhance X-ray attenuation and contrast of OM in CT volumes of soils containing specific mineral soil particle fractions, obtained via lab-based X-ray µCT. In comparison with OsO4, administration of Ag+ and Pb2+ resulted in insufficient contrast enhancement of OM versus fine silt (< 20 µm) or clay (< 2 µm) mineral particles. The perfusion procedure used in this work induced changes in soil structure. In contrast, PMA staining resulted in a selective increase of OM's attenuation contrast, which was comparable to OsO4. However, OM discrimination from other soil phases remained a challenge. Further development of segmentation algorithms accounting for grey value patterns and shape of stained particulate OM may enable its automated identification. If successful in undisturbed soils, PMA staining may form an alternative to OsO4 in non-synchrotron based POM detection. [ABSTRACT FROM AUTHOR]

The nitrogen status of most Zambian soils is inherently low. Nitrogen-fixing trees such as Faidherbia albida (F. albida) could have the potential to restore soil fertility. We conducted a study to examine the role of mature F. albida trees on the soil microbial communities and overall N fertility status in Zambia. Soil samples were collected under and outside the canopies of F. albida trees in representative fields from two sites namely; Chongwe (loamy sand) and Monze (sandy loam). To assess the long term canopy effects; total N, mineral N and soil organic carbon (Corg) content were directly measured from soils collected under and outside the canopy. Short term litter effects were assessed by subtracting concentrations of biochemical properties of non-amended controls from amended soils with F. albida litter during an 8 week incubation experiment. We also determined N mineralization rates, microbial community structure—Phospholipid fatty acids, microbial biomass carbon, and labile organic carbon (Corg[K2SO4]) during incubation. For the long term canopy effect, average N mineralization rate, Corg, total N and mineral N content of non-amended soils under the canopy were (all significant at p < 0.05) greater than soils outside the canopy on both sites. In the short term, amending soils with litter significantly increased N mineralization rates by an average of 0.52 mg N kg−1 soil day−1 on soil from Monze. Microbial biomass carbon measured after 4 weeks of incubation was on average significantly higher on amended soils by 193 and 334 mg C kg−1 soil compared with non-amended soils in Chongwe and Monze soils, respectively. After 6 weeks of incubation, the concentration of all selected biomarkers for major microbial groups concentrations in non-amended soils were significantly higher (all p < 0.05) under the canopy than outside in Monze soil. Using principal component analysis, we found that the segregation of the samples under and outside the canopy by the first principal component (PC1) could be attributed to a proportional increase in abundances of all microbial groups. Uniform loadings on PC1 indicated that no single microbial group dominated the microbial community. The second principal component separated samples based on incubation time and location. It was mainly loaded with G-positive bacteria, and partly with G-negative bacteria, indicating that microbial composition was dominated by these bacterial groups probably at the beginning of the incubation on Monze soils. Our results show that the improvement of soil fertility status by F. albida could be attributed to a combination of both long term modifications of the soil biological and chemical properties under the canopy as well as short term litter fall addition. [ABSTRACT FROM AUTHOR]

Nutrient dynamics in wetland ecosystems are largely controlled by soil moisture content. Therefore, the influence of soil moisture content on N mineralization should be explicitly taken into account in hydro-ecological models. The aim of this research was to establish relationships between N mineralization and soil moisture content in loamy to silty textured soils of floodplain wetlands in central Belgium. Large undisturbed soil cores were taken, incubated for 3 months under various moisture contents, and zero order and first order N mineralization rates were calculated. We used the percentage water-filled pore space (WFPS) as an expression of soil moisture because it is a better index for aeration dependent biological processes than volumetric moisture content or water retention. The relationship between the N mineralization rate and %WFPS was described by a Gaussian model. The optimum WFPS for N mineralization ranged between 57% and 78%, with a mean of 65% - 6% WFPS. Expected annual net N mineralization rates at field temperature (9.7°C) and at optimal moisture content varied between 30 and 186 kg N ha-1 (0-15 cm depth) year-1, with a mean of 110 ± 42 kg N ha-1 (0-15 cm) year-1. The mean N turnover rate amounted to 2.3 ± 1.1 g N 100 g-1 N year-1. Multiple linear regressions between N mineralization and general soil parameters showed that soil structure has an overriding impact on N mineralization in wetland ecosystems. [ABSTRACT FROM AUTHOR]

Unusually high SOC levels have been reported for sandy cropland soils in North-Western Europe. A potential link with their general heathland land-use history was investigated by comparing two soil pairs of relict heathland and cultivated former heathland in the Belgian sandy region. A sequential chemical fractionation yielded similar sizes in corresponding SOM fractions between the heathland and cropland soils (i.e. NaOCl resistant: 12.3–15.0 g C kg−1 and NaOCl + HF resistant: 2.6–5.3 g C kg−1). Higher amounts of clay sized N in the cropland plots can be attributed to N additions from mineral fertilizers and animal manure. Temperature resolved Pyrolysis Field Ionization Mass Spectroscopy analysis showed that the composition of both relict heathland and cultivated soils was surprisingly similar, in spite of over 60 years of intense cropland management. The mass spectra of SOM in both heathland-cropland soil pairs investigated was dominated by signals from lipids, alkylaromatics and sterols. The accumulation of this SOM rich in aliphatics was logically linked to the high input of lipids, long-chain aliphatics and sterols from heathland vegetation and the low soil pH and microbial activity. Based on the relatively high OC surface loadings of HF-extractable OM (13–44 mg C m−2 Fe and 1.2–2.3 mg C m−2 clay), direct organo-mineral bonds between OM and Fe-oxides or clay minerals seem to be only partly involved as a stabilization mechanism in these soils. The distinct bimodal shape of the thermograms indicates that OM-crosslinking could furthermore contribute substantially to SOM stabilization in these soils. This study therefore corroborates the previously proposed view that lipids may be bound in networks of alkylaromatics, the structural building blocks of OM macromolecules. We hypothesize that such binding is able to explain the measured retention of these OM components, even under several decades of cropland management. [ABSTRACT FROM AUTHOR]

A loamy sand was incubated with and without addition of carrot leaves at six different water contents ranging from 6% to 20% (g 100 g–1 dry soil) and N mineralization was monitored during 98 days. We calculated zero- and first-order rates for mineralization in the unamended soil and first-order rates for N mineralization in the residue-amended soil. Although N mineralization was strongly affected by soil moisture, rates were still important at 6% water content (corresponding to permanent wilting point), particularly in the residue-amended soil. Soil water content was recalculated as soil water tension and as percent water-filled pore space (%WFPS) and a parabolic, a logistic and a Gaussian-type function were fitted to the relation between N mineralization rates and water content, %WFPS or pF. Water potential was a less suitable parameter than either %WFPS or water content to describe the soil water influence on N mineralization, because N mineralization rates were extremely sensitive to changes in the water potential in the range of pF values between 1.5 and 2.5. In the residue-amended soil the Gaussian model yielded an optimum %WFPS of 56% for N mineralization, which is slightly lower than optimum values cited in literature. N mineralization in the unamended soil was more influenced by soil water than N mineralization from fresh crop residues. This could be explained by less water limitation of the microbial population decomposing the residues, due to the water content of the residues. The effect of the water contained in the residues was most pronounced in the lowest water content treatments. The water retention curves of both undisturbed and repacked soil were determined and suggested that extrapolation of results obtained during laboratory incubations, using disturbed soil, to field conditions will be difficult unless soil bulk density effects are accounted for, as is the case with the use of %WFPS. [ABSTRACT FROM AUTHOR]