The overuse of agrochemicals for agricultural productivity to meet the global food demand of the rapidly growing human population is a great environmental threat, particularly for aquatic ecosystems. Being associated intimately with plant health, growth, and productivity, the plant microbiome is emerging as a promising environmentally friendly and sustainable resource for agricultural productivity. For the past decades, our understanding of the interactions between plants and microorganisms and our knowledge of how to improve the plant microbiome by using microbial inoculants has increased significantly. A better understanding of the impact of the plant microbiome on mineral resources will benefit plant and soil health. In this review, we highlight the importance of microbial inoculants and their interactions with mineral fertilizers in enhancing crop productivity, as well as current challenges.

Repeated applications and combination of glyphosate-containing herbicides (GCH) with other herbicides are two weed management practices (WMP) used to compensate for GCH decreasing efficiency impacts in field crops. These practices may have serious impacts on soil functions because GCH affect soil biota and soil biological activity (SBA). Two field experiments, one with corn and one with soybean crops, were conducted during one growing season. SBA indicators, soil respiration (SR) and fluorescein diacetate (FDA) hydrolysis, were measured at two sampling times following six WMP. These WMP included one or two GCH applications (GCH alone or combined with other herbicides), applications of other herbicides only and mechanical weeding. WMP did not affect FDA neither for corn or soybean at either sampling times. In contrast, WMP affected SR in corn fields at both sampling times and SR in soybean field at the first sampling time. Repeating GCH applications and combining different herbicides led to lower SR, suggesting that these practices decreased SBA, whilst one single GCH application presented higher SR, suggesting that this practice stimulated SBA. Our study demonstrates that using GCH in combination with other herbicides or in multiple applications affects SBA in field conditions. Affecting soil functions and carbon cycle do bear serious weed management implications, and the choice of WMP should be taken into consideration to minimize their impacts on SBA for field crops sustainability.

Struvite is a phosphorus (P)-rich by-product of wastewater treatment facilities that can be recycled as a P source in agriculture. Because struvite is not water soluble, it is solubilized gradually by organic acids released by soil microorganisms and from growing plant roots when used as fertilizer. To speed up the solubilization process, struvite can be combined with biostimulants such as P-solubilizing bacteria (PSB) or earthworm casts (WC). The objective of this greenhouse study was to compare the fertilizer value of struvite, with and without PSB (Bacillus megaterium) or WC, with that of triple superphosphate in two contrasting soils (a low-P soil and a high-P soil). Oat (Avena sativa L.) was grown for 8 wk under a controlled environment, and dry matter yield at harvest, total N and total P uptake, the soil residual Mehlich-3 P, and phosphomonoesterase activity were measured. The high-P soil was unresponsive to P application, but the low-P soil was responsive. In the low-P soil, there was more Mehlich-3-extracted P when struvite was combined with PSB or WC compared with struvite alone, resulting in greater oat dry matter and more total N and more total P uptake. Combining struvite with biostimulants increased total dry matter and total P uptake by an average of 39% and 33%, respectively. We conclude that greater P release from struvite occurs when it is combined with PSB or WC, particularly in low-P soil, but this needs to be confirmed in field-scale studies.

Soil organic matter and soil particle composition play extremely important roles in soil fertility, environmental protection, and sustainable agricultural development. Visible – near-infrared reflectance (Vis–NIR) spectroscopy is a rapid, effective, and low-cost analytical method to predict soil properties. In this study, laboratory Vis–NIR spectroscopy data were used to compare the differences among partial least squares regression (PLSR), artificial neural network (ANN) and multivariate adaptive regression splines (MARSplines) based on fuzzy c-means spectral clustering and expert knowledge classification methods for soil prediction. The results showed that (1) the sand content (R² = 0.69–0.77) had the best prediction, followed by the silt (R² = 0.56–0.71) and organic matter (R² = 0.54–0.69) contents, whereas the clay content (R² = 0.29–0.65) had the poorest prediction, (2) the performance of the models followed the order of PLSR > ANN > MARSplines, and (3) the accuracies of the organic matter and sand contents were higher when applying expert knowledge classification, whereas the prediction of the clay and silt contents was better when applying spectral clustering. However, the overall accuracy of the spectral clustering method was slightly better than that of expert classification. Our findings showed that the spectral cluster-based models produced effective and interpretable prediction results for estimating soil properties. Therefore, this approach should be considered when dealing with large and heterogeneous soil samples.

Forested reclamation of oil sand mines in northern Alberta often use peat salvaged from lowland organic soils as a coversoil during soil reconstruction of man-made landforms. Previous studies suggest that planted tree seedlings may be limited in part by low phosphorus (P) and potassium (K) availability in peat. Fertilization is commonly used to treat nutrient limitations on reclamation sites; however, broad spectrum applications can induce strong competition from colonizing vegetation. This study explores the ability of a targeted application of individual macronutrients to (1) reduce nutrient deficiencies in peat coversoils and improve tree growth, while (2) minimizing the colonizing competition. Liquid fertilizer was applied to 6-yr-old aspen, pine, and spruce trees in the field using five nutrient combinations: control (no fertilizer), NPK, PK, P, and K. Tree growth, foliar nutrient concentrations, vegetation cover, and environmental parameters were monitored over two growing seasons. Aspen responded the strongest to fertilization, particularly in the P treatment, whereas pine and spruce marginally responded to NPK. Competing vegetation increased in the NPK but did not respond to the P and K treatments, indicating targeted fertilization can reduce colonizing competition. Additional analyses of the soil conditions of the site suggest that other factors were potentially more limiting to the trees during the study. Targeted fertilization of forest reclamation sites at a later stand age can be an option to improve efficacy and cost savings; however, response will also depend on other site (e.g., soil pH, precipitation, and soil water content) and management (e.g., fertilizer application rate) factors.

Revealing the influences of soil salinity on soil structure and hydraulic properties contributes to understanding the mechanism of salinity restraining rehabilitation of saline sodic soil in coastal area. After being passed through a 1 mm sieve, silt loam and silty clay were irrigated with saline water to achieve different soil salinities to highlight the effect of irrigation salinity on aggregate formation from primary particles. Three irrigation events with different saline water were conducted in the same 2 mo interval in soil columns; the soil columns were subjected to natural evaporation during the interval. The soil salinity, soil structure, soil–water characteristic curve, and saturated hydraulic conductivity (K_s) results were determined after the end of the third drying subprocess. The results showed that the proportion of water-stable macroaggregates (0.25–2 mm) in the silt loam and silty clay increased as the soil salt content (SSC) increased. Under the same matric suction, the retention capacity and plant-available water capacity (PAWC) of the silt loam first increased and then decreased, with the SSC increasing to a maximum of approximately 14.5 g kg⁻¹. The retention capacity of the silty clay increased with the SSC, whereas the PAWC decreased with the SSC. The K_s of the silt loam increased with SSC. This study reveals the effects of soil salinity on aggregate formation from primary particles in wetting–drying cycles and describes the corresponding changes in hydraulic properties, which influence the rehabilitation of saline sodic soils in coastal areas.

Soil pore size distribution and pore functional characteristics are the most important for soil physical properties, water retention, and transmission. Furthermore, considerable amounts of rock fragments are present in hilly region soils. In this study, we discuss the pore size distribution and pore functional characteristics of soils as affected by rock fragments in the hilly regions of Sichuan Basin, China. The soil water characteristic curve was measured to calculate the soil total porosity and the ratio of equivalent pores in each diameter class. The results suggest that the soil total porosity decreases with increasing rock fragments size. The proportion of transmission pores increased gradually with increasing rock fragment content, whereas the fractions of storage pores and residual-bonding pores decrease gradually. Furthermore, the ratio of effective soil porosity to total porosity is higher than that of ineffective porosity to total porosity with increasing rock fragment content. In summary, increasing the rock fragment content can notably increase the proportion of soil transmission pores, thereby increasing soil aeration and water permeability. However, a high rock fragment content is not conducive to maintaining the water needed for normal plant growth.

The importance of modeling dependencies of spatial variability of soil water content on soil matric potential grows due to the proliferation of ensemble modeling, data assimilations, and other soil water modeling applications. The objective of this work was to investigate conversions between cumulative distribution functions of water contents at different matric potentials. In total, 80 samples were taken in the nodes of the grid to measure soil water retention using sand and sand–kaolin capillarimeters at absolute values of soil matric potential of 0.001, 0.003, 0.010, 0.020, and 0.050 MPa, and with the water vapor desorption method at 3, 21, 39, 82, and 142 MPa. The probabilities of distributions of both non-transformed and log-transformed soil water contents being normal appeared to be larger than 0.05 in most cases. Using the probit function to represent the observed variability allowed us to match cumulative probability distributions at different soil water potentials. Slopes of dependencies of probits on non-transformed and log-transformed water contents had one-parametric linear dependencies on the logarithms of the absolute value of soil matric potential in capillary and adsorptive potential ranges.

Development of Anthroposols for land reclamation requires consideration of a variety of factors to support plant establishment and growth. Water limitation is a key challenge when using mine waste as a growth medium, and these materials also have poor structure and lack organic matter and nutrients. These greenhouse experiments assessed effectiveness of treatments composed of hydrogel and organic amendments to increase plant establishment and growth under water-limited conditions in mine waste materials (crushed rock, lakebed sediment, and processed kimberlite) from a diamond mine in northern Canada. Amendments were hydrogel, peat, sewage, and soil, mixed with waste materials (substrates) at four application rates, and seeded with slender wheat grass (Elymus trachycaulus). One experiment assessed germination response with limited watering during germination, and the other experiment assessed growth response with adequate water during germination followed by restricted water. Substrate had the greatest effect on germination, with processed kimberlite and crushed rock being most successful, at least 10% higher than lakebed sediment. Sewage amendment resulted in the largest plants (mean 0.22 g in lakebed sediment, 0.40 g in crushed rock and processed kimberlite, 0.05 g no amendment); sewage had a limited effect on germination. Highest organic amendment application generally improved plant response. Hydrogel did not improve plant growth, although it increased germination up to 63% in processed kimberlite. Type of mine waste, amendment, and rate of application impacted germination and plant growth and can be altered to build a suitable Anthroposol for reclamation.

Combined paper mill biosolids (PB) are a well-known fertilizing source of nitrogen (N) and phosphorus (P). Many jurisdictions have established default values for estimating their agronomic N and P contribution, but nutrient release can vary with their chemical properties, and this has been little studied. The objective of this incubation study was to compare four PB of different sources along with a de-inking paper sludge (DPS) for their N and P release in three contrasting soils under controlled conditions (25 °C, 60% water-filled pore space). Treatments consisted of PB or DPS at 50 Mg fresh mass ha⁻¹, PB at 30 Mg fresh mass ha⁻¹ plus inorganic N to supply 100 kg available N ha⁻¹, inorganic NP fertilizer, and an unfertilized control. Measurements of NO₃ + NH₄-N were made after 3 d and 1, 2, 3, 4, 6, 8, 12, and 16 wk of incubation. Mehlich-3 P was measured after 2 and 16 wk of incubation. Nitrogen mineralization generally declined a few days after PB addition and then gradually and constantly increased. The P mineralization of PB also increased with time. By the end of incubation, net N and P release averaged 30% (7%–49%) and 75% (16%–116%) of the NP fertilizer, respectively. The intensity of release, however, varied with material characteristics and soil type. Mineral N addition to the 30 Mg PB ha⁻¹ promoted N release to a level comparable to NP fertilizer. Soil N immobilization occurred with the DPS application. Current default N value used for PB in Quebec and Ontario is appropriate but not P.

In severely deficit soil, lentil (Lens culinaris Medic) crop requires micronutrients for increased production. Micronutrient management is, therefore, very important for lentil productivity but mostly ignored. This study was carried out from 2014–2015 to 2016–2017 to understand the effects of zinc (Zn), boron (B), and molybdenum (Mo) on lentil productivity, nodulation, and nutrient uptake and how these elements improve soil micronutrient fertility. The experiment was laid out in randomized complete block design, and the treatments were replicated thrice. Different combinations of Zn, Mo, and B were contrasted with no application of micronutrients. The treatments were Zn alone (Zn), B alone (B), Mo alone (Mo), Zn combined with B (ZnB), Zn with Mo (ZnMo), B with Mo (BMo), and Zn combined with B and Mo (ZnBMo). Doses of Zn, B, and Mo were 3, 2, and 1 kg ha⁻¹, respectively. In this trial, the highest average seed yield (1807 kg ha⁻¹) and yield increment (44%) was obtained in ZnBMo combined application with macronutrients. Single, dual, and combined application of Zn, B, and Mo had significant effects on yield parameters and yield of lentil (P < 0.05). The highest nutrient uptake, maximum nodulation (63.5 plant⁻¹), and the highest protein content (26.6%) in seed were recorded from the treatment receiving all three micronutrients. The increased lentil yield might be associated with increased nodulation and nutrient uptake by the crop under micronutrient-applied treatments. The results suggest that combination of Zn, B, and Mo could be applied for increased lentil production in micronutrient deficit soils.

Fertilization can cause obvious shifts in nitrate-reducing community composition in agricultural ecosystems; however, little is known about the behaviors and functional characters of isolated nitrate reducers adapted to a specific environment. In this study, 849 nitrate-reducing bacteria were isolated from various fertilization treatments in a long-term paddy field experiment; the isolates were further characterized in functions with both culture-dependent and independent methodologies. The results showed that CK (no fertilizer) treatment had four genera with even relative abundance, whereas the other three treatments had their own predominant genera with Chromobacterium in nitrogen (N) fertilizer, Serratia in NPK (nitrogen, phosphorus, and potassium fertilizer) and Enterobacter in NPKC treatment (NPK plus rice straw). The isolates of Serratia and Enterobacter grew faster and produced significantly more nitrites than those of Chromobacterium and Burkholderia in the normal growth medium, suggesting that the dominant isolates from nutrient-rich environment, such as NPK and NPKC treatments, are better adapted to high nutritional conditions. On the contrary, the strains of Chromobacterium and Burkholderia possessed stronger nitrite production ability in comparison with the isolates of Serratia and Enterobacter in the diluted growth medium, indicating that the selected isolates from CK and N treatments have the capability to develop under nutrient-limiting conditions. Our results indicated that the behaviors and functions of nitrate reducers appears to be important in adapting to their dwelling habitats.

Accurate determination of evapotranspiration (ET) has tremendous potential in guiding irrigation and improving the efficiency of water resources utilization in the North China Plain. Eddy covariance (EC) method is currently a popular method for determining field-scale ET. However, due to varying foot print and unclosed energy balance, the applicability of EC in different regions needs to be tested and corrected. In present work, we compared the ET of the winter wheat – summer maize rotation cropland measured by the EC method with the ET measured by large-scale lysimeters on different time scales. The degree of energy balance closure of EC measurements in this region is 78%. After adjusted by using Bowen ratio forced closure method, the ET monitored by EC is comparable with those monitored by large-scale lysimeters. The results also indicated that the consistency of the observed ET by the EC and lysimeters got better with an increasing time scale, especially for the multi-year average ET values with a relative deviation of less than 1%. The short-time events such as irrigation and precipitation and the mismatch of the varying footprint area of the EC and the small fixed source area of the lysimeter should be responsible for the discrepancy of ET in two methods on daily scale. However, the factors of crop biomass, total available water, and local climate condition exert more effects on the observed ET on large time scale. Overall, the EC technique is responsible for ET measurement of winter wheat – summer maize rotation cropland of the North China Plain.

Differences in soil water retention (SWR) characteristics between soil types and the factors driving those differences provide important information for land management, particularly in regions such as the Colombian Andes, which have limited water-storage infrastructure and where soils provide plant-available water and other ecosystem services. The objective of this study was to explore relationships between SWR and physical, chemical, and mineralogical properties of Andisols and Inceptisols through a case study of two watersheds in the Colombian Andes. This study identified a complex relationship between total carbon (TC), short-range order (SRO) minerals, and SWR. Both soil types had high SWR, with volumetric water content at permanent wilting point between 39% and 53%. Principal component analysis showed association of SWR with TC, SRO minerals, and % clay in both soil types. The Andisols of this study were coarse textured, allophanic (rich in allophane and imogolite — up to 17% in the B horizon), and with up to 15% TC in the A horizon. In contrast, the Inceptisols were fine textured (>30% clay) and higher in ferrihydrite than the Andisols. The formation of organo-metallic complexes was observed in A horizons; however, TC was lower under pasture than forest in both soil types. The addition of organic matter to soils with SRO minerals, such as the soils of this study, may foster the formation of organo-metallic complexes, stabilize soil C, and enhance SWR. Consequently, both study sites may benefit from management practices that increase soil organic matter.

Due to widespread adoption of no-till management and use of glyphosate-resistant transgenic crops, glyphosate is the most widely used herbicide worldwide. However, its effect on soil microbial communities is inconsistent. We studied the effects of glyphosate, tillage, and crop rotation on the diversity and composition of soil bacterial communities in wheat (Triticum turgidum var. durum Desf.) rhizosphere after 6 and 7 yr of glyphosate applications. In a 2 × 2 × 2 factorial design, there were two crop rotation treatments: continuous wheat (W–W) and wheat in rotation with field pea (Pisum sativum L.) (P–W); two tillage treatments: minimum tillage (MT) and no-till (NT); and two glyphosate treatments: no application or pre-seeding application at the recommended rate. None of the treatments affected wheat rhizobacterial α-diversity or the relative abundances of most bacterial groups. The most abundant phyla were Proteobacteria (25.1% relative abundance), Actinobacteria (21.7%), Acidobacteria (8.7%), Bacteroidetes (5.9%), Firmicutes (1.4%), Armatimonadetes (1.3%), and Verrucomicrobia (1.2%). Glyphosate reduced the relative abundance of Alphaproteobacteria in W–W rotation but increased it in P–W rotation, and it reduced the relative abundance of Opitutus spp. The W–W rotation had greater relative abundances of the classes Bacilli (Firmicutes) and Gammaproteobacteria, and genera Bacillus and Opitutus (Verrucomicrobia), than the P–W rotation. Compared with MT, NT increased the relative abundance of the phylum candidate division WPS-1, but it reduced that of Phenylobacterium spp. in W–W rotation. These treatment effects probably had implications for soil functioning, including nutrient cycling and biological disease/pest control.

A total of 344 soil cores were taken in annually cropped fields of Alberta, Saskatchewan, Manitoba, and Ontario from 2011 to 2013 in areas where the field shapes, or obstacles within fields, required the driving pattern of farm operations to overlap. Soil nitrate-N concentrations in overlapping areas were 60% greater, soil Olsen-P concentrations were 23% greater, and pH was 0.5 units greater at 0–15 cm depth compared with non-overlapping areas, suggesting smaller nutrient use efficiency and potential for greater nutrient loss.

Conservation tillage and crop residues should increase the soluble organic carbon and nitrate concentration in agricultural soil, which increases the denitrification potential. Basal denitrification (72 h laboratory incubation) was 2.1–2.7 times higher in a sandy loam soil under 15 yr of conservation tillage than conventional tillage and 1.8–2.0 times higher with high-residue (additional input 8.6–9.4 Mg dry matter·ha⁻¹·yr⁻¹) than low-residue inputs. Adding glucose and nitrate increased the soil denitrification potential 3- to 14-fold. Denitrification was limited by carbon availability, even in soil with 15 yr of conservation tillage and high-residue inputs.