This study aimed to assess the impact of different land uses on the spore density and richness of arbuscular mycorrhizal fungi (AMF) in a Red Latosol of a tropical savanna biome in Brazil (“Cerrado”). Ten soil samples and roots were obtained from a riparian forest, a pasture, an annual crop production system with no tillage, and a coffee plantation in dry and wet seasons. Spores were extracted, counted, and identified from field soils, and roots were stained to assess mycorrhizal colonization. A total of 42 AMF species were detected in all four land uses. The genus Acaulospora had the largest number of species (18), followed by Glomus (6) and Gigaspora (5). Gigaspora decipiens and Gigaspora margarita were present in all areas, regardless of the sample period. Gigaspora decipiens was the species most frequently recovered and contributed to the majority of spores in coffee plantations and riparian forest. Cetraspora pellucida was dominant in the area of no tillage and Acaulospora tuberculata in the pasture. Low species richness was detected in soils under the coffee plantation, with AMF communities dominated almost exclusively by members of Gigasporaceae. We conclude that the area under the coffee plantation caused a reduction in the richness of AMF species and promoted a dominance of a single family AMF compared with the pasture area.

Elevated soil fertility levels induced by continuous chemical fertilizer and (or) manure application may affect N loss potential and redistribution within soil-crop system. A 49-d packed soil column experiment with a factorial design of three soil fertility levels and four fertilization treatments was conducted to evaluate the effects of soil fertility and fertilization treatments on the accumulation and leaching risk of reactive N. The results showed that the 49-d cumulative leaching loss of total reactive N ranged from 176.3 to 499.0 kg N ha^-1. The cumulative leaching losses of total dissolved nitrogen (TDN) and dissolved organic nitrogen (DON) in NPK treatment were significantly higher than those in other three treatments in fertility level I and II soils. The cumulative leaching loss of NO₃^--N was significantly greater in NPK M or NPK treatment than in CK treatment in fertility level I or III soils, and it was remarkably greater in M treatment than in other three treatments in fertility level II soil. In total, 64.0% of TDN in soil leachate existed in the form of DON, and 35.1% was nitrate-N among different soil fertility and fertilization treatments. These results indicated that DON was an important component of N leaching loss and could not be neglected in sustainable development of vegetable greenhouse soil.

Exudation of low-molecular-weight organic acids (LMWOAs) from plant roots enhances phosphorus (P) acquisition from soil, either by dissolving P fixed in secondary minerals or by reducing P sorption to organo-minerals. How LMWOAs may modify P sorption in soils with contrasting pH is not well understood, much less the mechanisms involved. The effects of three common LMWOAs (oxalic, citric, and malic acids) on P sorption in calcareous, neutral, and acidic soils were studied in batch experiments, followed by sequential P fractionation to elucidate the mechanisms whereby LMWOAs alter P sorption. The sorption data of the three soils fitted better to the Freundlich equation (r² = 0.325-0.994, P < 0.05) than the Langmuir and linear equations. Oxalic, citric, and malic acids at 10 mmol kg^-1 soil decreased the Freundlich P sorption parameters K_f and n, which represent P sorption capacity and energy, due to the fact that LMWOAs reduced P sorption in NaHCO₃-Pi (soil soluble and exchangeable Pi, 23.8-30.9%) and NaOH-Pi (Fe-Pi and Al-Pi, 21.6-54.2%) fractions of the three soils. Comparing acidified P-LMWOAs solutions with the pH-adjusted P-LMWOAs solutions (pH = 7) had a minor effect on P sorption. Our results indicated that the reduction in soil P sorption was due to ligand exchange and chelation of LMWOAs with Fe and Al minerals, and the acid strength of LMWOAs had a minor effect on P sorption in calcareous, neutral, and acid soils.

Soil contamination with heavy metals is a serious concern to food production and human health. The present study was conducted to evaluate the impact of tailings from an old mining site on heavy metal contamination of soil. Using a GPS to map out different sites around the tailing dam, soil samples were taken from under grassland at the different sites, at depths of 15 cm and 1 m, using a shovel and handheld auger. The samples were prepared, acid digested, and analyzed for a multi-element suite by inductively coupled plasma atomic emission spectrometry. Results showed heavy metal concentration in the order of Cr > Zn > As > Mn > Cu > Pb > Ni > Sr > Hg. Most of the soil samples contained high concentration of As (13.46-234.6 mg kg^-1). Soil concentrations of As, Hg, Cr, and Mn also decreased with distance from the dump material. Single contamination index of each pollutant, calculated according to the South African Soil Quality Standards revealed very high and medium pollution grades for As (index = 7.39) and Cr (index = 2.16), respectively. Arsenic is a metal associated with gold ore and soil pollution by such metals can make it infertile and unsuitable for plants.

Soil organic matter, comprising ~58% soil organic carbon (SOC), is attributed with increased water holding capacity in the surface horizon of agricultural soil. This paper addresses the role of SOC as a component of a common functional unit in soil from analysis within a single field and over multiple fields. Soil data measured on the fields during the SMAPVEX12 satellite prelaunch algorithm development campaign exhibited high correlation among SOC, field-mean soil water content (SWC), bulk density, and soil texture. The analysis extended over a wide range of soil texture and wetness in the top 5 cm of soil over 50 agricultural fields covering ~400 km² of southern Manitoba. Data collected over a much smaller area from Ontario silt loam soils at the Elora Research Centre demonstrated a similar correlation between SOC and SWC in intensive field sampling. This intercorrelation of SOC and SWC is examined with partial least-squares regression, principal component analysis, and geostatistical semivariograms. A model is proposed to interpret the feedback process between SOC and SWC to explain the persistent correlation. Further work to substantiate the strengths and limits of the relationship between SOC and SWC may be beneficial for estimating SWC for remote sensing, agriculture, hydrology, and ecosystem function.

The objective of this study was to characterize the organic matter (OM) in density-size fractions of soil samples from a commercial organic farm using diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. The soil samples were separated by density fractionation with a sodium iodide (Nal) solution (1.6 g cm^-3) into free particulate OM (fPOM), occluded particulate OM (oPOM), heavy particulate OM (hPOM), and mineral-associated OM (MAOM) fractions. The OM characterization by DRIFT spectroscopy was the difference in spectra obtained before and after sodium hypochlorite (NaClO) oxidation. However, the infrared absorption bands derived from the soil mineral matrix interfered with the detection of the absorption bands of polysaccharides. An increase in the amount of organic C under organic management was observed for all the density-size fractions, but the functional group composition of the NaClO-oxidizable OM differed among the fractions. The NaClO-oxidizable OM in the fPOM fraction was characterized by a high lignin content, whereas the oPOM fraction had high amounts of aliphatic compounds and lignin. The hPOM fraction contained less lignin and more proteinous materials, and the MAOM fraction was rich in proteinous materials. This study demonstrates that DRIFT spectroscopy combined with NaClO oxidation is a powerful tool for characterizing the relatively unstable OM in soils.

Several models predict soil pore space indices (the relative gas diffusion coefficient, D_s/D_o and the pore tortuosity, t), but information is lacking on which models predicted indices better relate to soil processes. We compared pore space indices′ predictive models based on air-filled porosity (f_a) alone vs. models using air-filled porosity and total pore space (Φ) (f_a Φ). We also assessed the relationships between these indices and CO₂ and N₂O. The study was conducted from 2011 to 2014 on a silt loam soil at Lincoln University. Soil samples were collected at 0-10 and 10-20 cm depth and oven dried at 105 °C for 72 h. After drying, f_a and Φ were calculated and later used in models for predicting D_s/D_o and t. CO₂ and N₂O were measured with a Shimadzu gas chromatograph (GC) and a photoacoustic gas analyzer (PSA). Results showed that D_s/D_o predicted using f_a alone (Marshall and Buckingham) was higher as compared with values predicted with models based on f_a Φ (Sallam et al., Millington, and Jin and Jury) (P < 0.001). However, values of t predicted with models based on f_a alone were lowest (P < 0.001). CO₂ and N₂O measured with GC better related with D_s/D_o and t.

Soil scientists who interact with K-12 students or teachers may benefit from knowing what the provincial curricula say, what a typical classroom teacher knows, and what resources, programs, and opportunities are available regarding soil education. Many provinces have a soil science unit at the Grade 2-4 level in their curriculum. In all provincial curricula, soil science concepts are found in units on living things, plants, and ecosystems, from Grades 1-12. Even in Kindergarten, hands-on soil programs effectively address many skills and attitudes' expectations in the provincial curricula. What is the use of having soil science in the curriculum, however, if the teachers responsible for student learning do not understand the key concepts? Preliminary results using a 25-item soil questionnaire show that incoming preservice teachers do have some initial understanding of soil, scoring 50% on a pretest application, when a random score would be 25%. After engaging in several hours of hands-on learning, followed by a wait time of several months, they then scored at 68%, thus gaining one third of what was lacking in their understanding. This may encourage those involved with soil education outreach to teachers. Resources for teaching hands-on soil science to elementary students will be noted, including an integrated science-language method called “Soil Science through Stories”. At the secondary level, we have the national “Soil 4 Youth” program, which integrates soil science into school programs across Canada and is supported by the Canadian Society for Soil Science. New STEM (science, technology, engineering, and mathematics) approaches to education also offer opportunities for innovative teaching of soil science to Canadian students.