Liu, X., Burras, C. L., Kravchenko, Y. S., Duran, A., Huffman, T., Morras, H., Studdert, G., Zhang, X., Cruse, R. M. and Yuan, X. 2012. Overview of Mollisols in the world: Distribution, land use and management. Can. J. Soil Sci. 92: 383-402. Mollisols - a.k.a., Black Soils or Prairie Soils - make up about 916 million ha, which is 7% of the world's ice-free land surface. Their distribution strongly correlates with native prairie ecosystems, but is not limited to them. They are most prevalent in the mid-latitudes of North America, Eurasia, and South America. In North America, they cover 200 million ha of the United States, more than 40 million ha of Canada and 50 million ha of Mexico. Across Eurasia they cover around 450 million ha, extending from the western 148 million ha in southern Russia and 34 million ha in Ukraine to the eastern 35 million ha in northeast China. They are common to South America's Argentina and Uruguay, covering about 89 million and 13 million ha, respectively. Mollisols are often recognized as inherently productive and fertile soils. They are extensively and intensively farmed, and increasingly dedicated to cereals production, which needs significant inputs of fertilizers and tillage. Mollisols are also important soils in pasture, range and forage systems. Thus, it is not surprising that these soils are prone to soil erosion, dehumification (loss of stable aggregates and organic matter) and are suffering from anthropogenic soil acidity. Therefore, soil scientists from all of the world's Mollisols regions are concerned about the sustainability of some of current trends in land use and agricultural practices. These same scientists recommend increasing the acreage under minimum or restricted tillage, returning plant residues and adding organic amendments such as animal manure to maintain or increase soil organic matter content, and more systematic use of chemical amendments such as agricultural limestone to replenish soil calcium reserves.

Veenstra, J. J. and Burras, C. L. 2012. Effects of agriculture on the classification of Black soils in the Midwestern United States. Can. J. Soil Sci. 92: 403-411. Soil surveys are generally treated as static documents. Many soil survey users assume that pedon data generated 30 to 50 yr ago still represents today's soil, as short-term changes in soil properties are perceived to be limited to the soil surface and thus pedologically insignificant. In this study, we re-sampled and re-analyzed 82 pedons with historical descriptions and laboratory data in Iowa, United States, to evaluate changes in soil profile properties and taxonomic classification after approximately 50 yr of agricultural land use. Using historical and current data, we classified sampled pedons using Canadian Soil Taxonomy, US Soil Taxonomy and the Food and Agriculture Association World Reference Base (FAO-WRB). Our results show that soil characteristics have changed significantly enough to change the classification. In each taxonomic system, the classification of 60% or more of the sampled pedons differed from the original. Classification of 15 to 32% of the sampled pedons changed at the Order (or equivalent) level with 11 to 33% of the pedons originally classified as Black soils - Mollisols, Chernozems or Phaeozems - no longer classified as Black soils. The change in soil classification over such a short-time period challenges the validity and usefulness of treating existing soil maps as static documents as well as traditional soil classification hierarchies.

Fenton, T. E. 2012. The impact of erosion on the classification of Mollisols in Iowa. Can. J. Soil Sci. 92: 413-418. The fertile black soils in the Great Plains and Western States of the United States are dark brown Chernozems in the Canadian system of soil taxonomy and Mollisols, when a mollic epipedon is present, according to the United States soil taxonomy. Other primary criteria are organic carbon content, color, structure, and thickness of the mollic epipedon. Accelerated erosion can affect all of these properties and is especially critical for soils that have slope gradients of more than 2%. Accelerated erosion and erosion phases are recognized in field mapping based on the amount of A horizon remaining but criteria provided in the Soil Taxonomy guidelines conflict with procedures outlined in the Soil Survey Field Manual and result in a dichotomy between the classification system and field mapping practices. Soil map unit data for the five most extensive Mollisol soil series in Iowa that have multiple phases of slope and erosion were summarized and variations between the taxonomic and survey principles were identified. Eroded units comprise 26 to 77% of the total mapped area of the series studied and do not qualify as Mollisols under the taxonomic system. However, under the principle of following the genetic thread to classify soils, the taxonomic system should be modified to accommodate the eroded units that have the same genetic pathway as their uneroded counterparts. This could be accomplished by placing primary emphasis on the organic carbon content and waiving the color requirement for eroded soil map units.

Li, X. H., Han, X. Z., Li, H. B., Song, C., Yan, J. and Liang, Y. 2012. Soil chemical and biological properties affected by 21-year application of composted manure with chemical fertilizers in a Chinese Mollisol. Can. J. Soil Sci. 92: 419-428. The effects of 21-yr of application of chemical fertilizers, composted pig manure (CPM) alone, and chemical fertilizers combined with compost on soil chemical and biological properties were investigated. Soil samples (0-20cm) were collected from a long-term fertilization experiment under corn (Zea mays L.) production in 2006, prior to seeding, at the corn tasseling stage and following harvest. Fertilizer treatments were: no fertilizer (CK), nitrogen fertilizer alone (N), N phosphorus (NP), N P potassium (NPK), CPM, N CPM, N P CPM (NP CPM), and N P K CPM (NPK CPM). Long-term application of N alone resulted in a reduction of soil pH by 0.38 units and reduced the available P concentration compared with CK. An increase in soil pH was seen with CPM alone and NPK CPM. Both fertilizers sources, singly and combined, increased the total N and available N concentrations. Total P and total K concentrations were greatest with the NPK CPM treatment. All fertilizer treatments increased the soil organic carbon (SOC), light fraction organic carbon (LFOC) and microbial biomass carbon (MBC) concentrations significantly (P < 0.05) at the tasseling stage. The NPK CPM treatment showed the greatest increase in SOC (12%), LFOC (78%) and MBC (44%) concentrations, compared with CK. Soil enzyme activities (invertase, urease, acid and alkaline phosphatases) tended to be greater at tasseling than other sampling dates, with highest enzyme activities in the NPK CPM treatments. These findings suggest that a long-term application of CPM combined with NPK is an efficient strategy to maintain or increase soil quality in Mollisols for sustainable agriculture.

Kravchenko, Y., Rogovska, N., Petrenko, L., Zhang, X., Song, C. and Chen, Y. 2012. Quality and dynamics of soil organic matter in a typical Chernozem of Ukraine under different long-term tillage systems. Can. J. Soil Sci. 92: 429-438. Tillage has been reported to induce changes in soil organic matter (SOM) concentrations and quality. Conversion of plow-tillage to minimum till and no-till (NT) farming enhances the SOM pool. Enrichment of the SOM pool is essential for maintaining fertility of Chernozems, advancing food security, and improving the environment. The main objective of this study was to examine the effect of different tillage systems on the SOM concentration, its quality and dynamics including CO₂ assimilation by heterotrophic bacteria and humus characteristics - the carbon (C) concentration in humic substances and the labile soil organic C fraction (SOCL) extracted with 0.1 N NaOH - as well as the molecular masses, spectroscopic parameters and physiological effects of humic acids on germinating pea (Pisum sativum L.) seeds. Our study was conducted on a long-term experimental site on a Haplick Chernozem in the Poltava region of Ukraine over a 10-yr period from 1996 to 2006. Results indicate that conversion from conventional to reduced soil tillage systems increased SOM concentrations in 0- to 10-cm soil layer and led to the accumulation of C in fulvic acids and humins. No significant differences in SOM storage in the 0- to 100-cm layer were observed among tillage systems. However, reduced tillage systems had a higher proportion of SOCL, a lower ratio of C in humic acids/C in fulvic acids and more humic acids with molecular masses from 110 to 2000 kDa. Our study demonstrated that the quality and dynamics of SOM are closely related to soil tillage practices.

Zou, W., Si, B., Han, X. and Jiang, H. 2012. The effect of long-term fertilization on soil water storage and water deficit in the Black Soil Zone in northeast China. Can. J. Soil Sci. 92: 439-448. The Black Soil Zone in northeast China is one of the most important areas of agricultural production in China and plays a crucial role in food supply. However, further improvement in crop yield hinges on effective management of soil water. There is a poor understanding of how different fertilization methods affect crop water use efficiency. The objective of this study was to examine the effect of different fertilization methods on soil water storage and deficit in Black soils. A long-term experiment was conducted at the National Field Research Station of Agro-ecosystems, at Hailun County, Heilongjiang province in northeastern China from 1999 to 2008. Three fertilizer treatments including no fertilizer (CK), inorganic fertilizer (NP) and inorganic fertilizer plus organic material (NPM) were tested. The results showed that soil water storage decreased in the order CK, NP, and NPM during the growing season and the differences in soil water storage in the active root zone (0-70 cm) and below the active root zone (70-130 cm) and soil water deficit were statistically significant among the three treatments. Due to the uneven temporal distribution of rainfall and crop water uptake, soil water content was very dynamic in all three treatments: The low soil water storage and resulting soil water deficit (defined as the monthly difference between potential evapotranspiration and soil available water storage) within the 0- to 70-cm soil profile were found in both June and July. Further, soil receiving NPM was more likely to have a soil water deficit, but less likely to have excessive water. A lower risk of excess water may result in deeper root penetration and increased water use at greater depth, and thus the water deficit under the NPM treatment may not be the limiting factor for crop production. Therefore, NPM seems a viable management practice for improving crop yields in the Black Soil Zone in northeast China, possibly due to higher soil organic carbon and nutrient supply and lower probability of excess water.

Lemke, R. L., VandenBygaart, A. J., Campbell, C. A., Lafond, G. P., McConkey, B. G. and Grant, B. 2012. Long-term effects of crop rotations and fertilization on soil C and N in a thin Black Chernozem in southeastern Saskatchewan. Can. J. Soil Sci. 92: 449-461. Carbon sequestration in soil is important due to its influence on soil fertility and its impact on the greenhouse gas (GHG) phenomenon. Carbon sequestration is influenced by agronomic factors, but to what extent is still being studied. Long-term agronomic studies provide one of the best means of making such assessments. In this paper we discuss and quantify the effect of cropping frequency, fertilization, legume green manure (LGM) and hay crops in rotations, and tillage on soil organic carbon (SOC) changes in a thin Black Chernozemic fine-textured soil in southeastern Saskatchewan. This was based on a 50-yr (1958-2007) crop rotation experiment which was initiated on land that had previously been in fallow-wheat (Triticum aestivum L.) (F-W), or F-W-W receiving minimum fertilizer for the previous 50 yr. We sampled soil in 1987, 1996 (6 yr after changing from conventional tillage to no-tillage management and increasing N rates markedly) and again in 2007. The SOC (0-15 cm depth) in unfertilized F-W and F-W-W appears not to have changed from the assumed starting level, even after 20 yr of no-till, but SOC in unfertilized continuous wheat (Cont W) increased slightly [not significant (P>0.05)] in 30 yr, but increased more after 20 yr of no-till (but still not significant). No-till plus proper fertilization for 20 yr increased the SOC of F-W, F-W-W and Cont W in direct proportion to cropping frequency. The SOC in the LGM-W-W (unfertilized) system was higher than unfertilized F-W-W in 1987, but 20 yr of no-tillage had no effect, likely because grain yields and C inputs were depressed by inadequate available P. Soil organic carbon in the two aggrading systems [Cont W (N P) and F-W-W-hay(H)-H-H (unfertilized)] increased significantly (P<0.05) in the first 30 yr; however, a further 20 yr of no-tillage (and increased N in the case of the Cont W) did not increase SOC suggesting that the SOC had reached a steady-state for this soil and management system. The Campbell model effectively simulated SOC changes except for Cont W(N P), which it overestimated because the model is ineffective in simulating SOC in very fertile systems. After 50 yr, efficiency of conversion of residue C inputs to SOC was negligible for unfertilized F-W and F-W-W, was 3 to 4% for fertilized fallow-containing systems, was about 6 or 7% for Cont W, and about 11% for the unfertilized F-W-W-H-H-H systems.

Fan, R., Zhang, X., Liang, A., Shi, X., Chen, X., Bao, K., Yang, X. and Jia, S. 2012. Tillage and rotation effects on crop yield and profitability on a Black soil in northeast China. Can. J. Soil Sci. 92: 463-470. To evaluate the feasibility of no-tillage (NT) practices for Black soils (Mollisols) in northeast China, knowledge of the effects of different tillage and rotation combinations on crop yield and profitability is required. An 8-yr field experiment was conducted to investigate variation of corn (Zea mays L.) and soybean (Glycine max L. Merr.) yields and economic returns under NT, moldboard plow (MP) and ridge tillage (RT) combined with continuous corn (C-C-C), corn-soybean (C-S), and corn-corn-soybean (C-C-S) rotations. Under C-S rotation, corn and soybean yields were similar to or slightly higher in NT than in MP and RT; NT corn profitability was 15.9% higher than MP, and NT soybean profitability was even higher, 62.9 and 22.4% higher than MP and RT, respectively. There were no differences in crop yield and profitability between the C-C-S and C-C-C rotations. The C-S under NT produced better yield and profitability, particularly in dry years, than the C-C-C and C-C-S rotations. Accordingly, NT combined with C-S would be a good practice to increase crop yields and profitability for the Black soils in northeast China.

Huffman, T., Coote, D. R. and Green, M. 2012. Twenty-five years of changes in soil cover on Canadian Chernozemic (Mollisol) soils, and the impact on the risk of soil degradation. Can. J. Soil Sci. 92: 471-479. Agricultural soils that are covered by vegetation or crop residue are less susceptible to degradation by wind and water erosion, organic matter depletion, structural degradation and declining fertility. In general, perennial crops, higher yields, reduced tillage and continuous cropping provide more soil cover than annual crops, lower yields, intensive tillage, residue harvesting and fallowing. This study presents a model for estimating the number of days in a year that the soil surface is protected and demonstrates its application on the Canadian prairies over the period from 1981 to 2006. Over the 25-yr study period, the average soil cover on Canadian prairie soils increased by 4.8% overall. The improvement came primarily as a result of widespread adoption of no-till and a decline in the use of summerfallow, but the gains were offset to a great deal by a shift from higher-cover crops such as wheat, oats and barley to more profitable but lower-cover crops such as canola, soybeans and potatoes. The implication of these trends is that, even though protection of prairie agricultural soils has improved over the past 25 yr, soil cover could decline dramatically over the next several decades if crop changes continue, the adoption of conservation tillage reaches a peak and residue harvesting for biofuels becomes more common.

Yang, J. Y., Huffman, T., Drury, C. F., Yang, X. M., De Jong, R. and Campbell, C. A. 2012. Estimating changes of residual soil nitrogen in Chernozemic soils in Canada. Can. J. Soil Sci. 92: 481-491. Chernozemic soils (Mollisols) account for approximately 68% of total farmland in the prairies and 54% of farmland in Canada. Although many field studies have focused on the importance of N in Chernozemic soils, few modelling studies have been conducted to examine the risk of N contamination to the environment The objective of this research was to estimate temporal and spatial changes in residual soil nitrogen (RSN) on Chernozemic soils at the 1:1 million regional scale. An annual N budget was developed for the study area for the period 1981 to 2006, using the Canadian Agricultural Nitrogen Budget (CANB v3.0) model. The difference between N inputs and outputs is considered RSN, which is defined as the inorganic N left in the soil after harvest. Average RSN levels in the sub-humid Black and Dark Gray Chernozemic soils increased from 7-9 kg N ha^-1 in 1981 to 20-23 kg N ha^-1 in 2006. Changes in RSN were much less pronounced in the arid and semi-arid Brown and Dark Brown soil zones, where average values increased from approximately 1 kg N ha^-1 to 4-7 kg N ha^-1 over 25 yr. Commercial fertilizer, manure and biological N₂ fixation were the three main sources of the increased N inputs. Drought conditions also contributed to the surplus of N in some years by reducing crop growth and thus the amount of N removed in grain and forage crops. In Chernozemic soils, more careful use of chemical fertilizer N, improved manure N management and greater use of legume-cereal rotations are recommended as methods to maintain soil fertility and reduce nitrogen loss to the environment.

Helmers, M. J., Zhou, X., Baker, J. L., Melvin, S. W. and Lemke, D. W. 2012. Nitrogen loss on tile-drained Mollisols as affected by nitrogen application rate under continuous corn and corn-soybean rotation systems. Can. J. Soil Sci. 92: 493-499. Nitrate-nitrogen (NO₃-N) loss from production agricultural systems through subsurface drainage networks is of local and regional concern throughout the Midwestern United States. The increased corn acreage and the practice of growing continuous corn instead of a corn-soybean rotation system due to the increasing demand for food and energy have raised questions about the environmental impacts of this shift in cropping systems. The objective of this 4-yr (1990-1993) study was to evaluate the effect of nitrogen (N) application rate (0-168 kg N ha^-1 for corn following soybean and 0-224 kg N ha^-1 for corn following corn) on NO₃-N concentration, NO₃-N losses, and crop yields in continuous corn and corn-soybean production systems on tile-drained Mollisols in north central Iowa. The results show that NO₃-N concentrations from the continuous corn system were similar to NO₃-N concentrations from the corn-soybean rotation at equivalent N application rates.When extra N fertilizer (approximately 56 kg N ha^-1) was applied to continuous corn than the corn-soybean rotation, this resulted in 14-36% greater NO₃-N concentrations in subsurface drainage from the continuous corn system. While corn yield increased as N application rate increased, corn yields at the recommended N application rates (112-168 kg N ha^-1) in the corn-soybean rotation were up to 3145 kg ha^-1 greater than corn yields at the recommended application rates (168-224 kg N ha^-1) in the continuous corn system. The corn-soybean rotation with recommended N application rates (168-224 kg N ha^-1) appeared to be beneficial environmentally and economically.

Song, F., Han, X., Zhu, X. and Herbert, S. J. 2012. Response to water stress of soil enzymes and root exudates from drought and non-drought tolerant corn hybrids at different growth stages. Can. J. Soil Sci 92: 501-507. Drought tolerant corn hybrids (Zea mays L.) are an excellent model to evaluate the effect of water stress on rhizosphere functions. The purpose of this study was to investigate the influences of water stress on soil pH, enzyme activities, and root exudates from corn. Two corn hybrids, Baidan 9 (drought tolerant) and Baidan 31 (non-drought tolerant) were grown in soil-filled pots for pH and enzyme assays and in hydroponics culture for root exudate analysis. Water stress was imposed at four growth stages: seedling, elongation, tasseling and grain-filling stages. Soil pH was lower in the rhizosphere than bulk soil, but was not affected by water deficiency. Water stress increased protease activity at the seedling stage, but reduced its activities at other stages compared to the control. A significant positive correlation was observed between pH and alkaline phosphatase activity under water stress. Compared to Baidan 31, the rhizosphere of drought-tolerant Baidan 9 had greater protease and catalase activities at all growth stages, greater alkaline phosphatase, lower acid phosphatase and greater invertase activities at elongation, tasseling and filling stages. Osmotic stress increased the organic acid concentration (malic, lactic, acetic, succinic, citric and maleic acids) in root exudates of Baidan 9 and Baidan 31; as well there was a greater fumaric acid concentration in Baidan 31 under osmotic stress than without stress. The increased soil enzyme activities and organic acids exuded from the rhizosphere of plants under water stress might contribute to drought tolerance in corn hybrids.

Yan, Y., He, H., Zhang, X., Chen, Y., Xie, H., Bai, Z., Zhu, P., Ren, J. and Wang, L. 2012. Long-term fertilization effects on carbon and nitrogen in particle-size fractions of a Chinese Mollisol. Can. J. Soil Sci. 92: 509-519. The response of soil organic matter (SOM) dynamics to long-term fertilization may be deduced from changes in the accumulation and distribution of different soil organic carbon (SOC) and nitrogen (N) pools. The SOC and N in particle-size fractions were therefore measured to assess the influences of pig manure and synthetic fertilizer application on the characteristics of these pools. A long-term fertilization experiment, established in 1979 in the Mollisol area (Gongzhuling, China) was used for this study. Composite soil samples (0-20cm) were collected in 2005 from 12 treatment plots that had received annual applications of pig manure, synthetic fertilizers or combinations of both. Soils were fractionated into fine clay (<0.2 µm), coarse clay (0.2-2 µm), silt (2-50 µm), fine sand (50-250 µm) and coarse sand (250-2000 µm) and then SOC and N contents in each particle-size fraction were measured. Although most of the SOC and N were associated with clay and silt fractions, the large proportion of silt in the soil mass played a key role in the retention of SOC and N. The application of pig manure alone increased accumulation of SOC and N in each particle-size fraction, but preferential enrichment was found in the coarse sand fraction. This indicates that pig manure is efficient in restoring SOM in the temperate Chinese Mollisol under a tilled maize (Zea mays L.) monocropping system and having a long frozen period in winter. The application of synthetic fertilizers had no clear effect on SOC and N accumulation or their distribution in particle-size fractions. However, the combined application of pig manure and synthetic fertilizers enhanced the accumulation of SOC and N in all particle-size fractions, and led to a shift of SOC and N from fine to coarse particles. We extended the hierarchy model for SOC protection to consider a shift in SOC accumulation from fine to coarse particles, depending on the initial SOC content of the specific soil. The findings reveal a clear positive interaction between pig manure and synthetic fertilizers that may improve the quantity of SOM in the temperate Chinese Mollisol.

Zhou, K., Liu, X., Zhang, X., Sui, Y., Herbert, S. J. and Xia, Y. 2012. Corn root growth and nutrient accumulation improved by five years of repeated cattle manure addition to eroded Chinese Mollisols. Can. J. Soil Sci. 92: 521-527. The use of fertilizers with additional cattle manure application on eroded soil has been reported to improve cereal yields. Limited research exists on the long-term effect of cattle manure on root growth and nutrient uptake by corn (Zea mays L.) grown on eroded soils. A field experiment was established in Hailun city, Northeast China to determine the impact of long-term cattle manure addition on corn production in eroded Mollisols. There were five levels of simulated-erosion, which removed 0, 5, 10, 20, 30 cm of topsoil. Two soil amendments were: (1) chemical fertilizer at the rate normally used by farmers in the region and (2) chemical fertilizer plus 15 000 kg ha^-1 (dry weight basis) of cattle manure. Root growth (length, surface area and dry weight) was assessed at the three-leaf stage. Nitrogen (N), phosphorus (P) and potassium (K) uptake and accumulation by corn were evaluated at the three-leaf stage and at harvest. Compared with chemical fertilizer alone, 5 yr of repeated cattle manure addition significantly increased root surface area by 18-35%, and root dry weight by 45-129% in soil with simulated-erosion. The improvement of root growth by manure application was mainly correlated with the changes in larger size aggregate. N content increased by 12-59%, P by 31-129%, and K by 297-494% in corn at the three-leaf stage, and the same trend was found at harvest. Long-term cattle manure addition increased corn yield by 7% in soils with 5 cm topsoil removal, and gave similar yields in soils with 10 and 20 cm topsoil removal as non-eroded plots receiving chemical fertilizer only. Our results suggest that the increased corn yield in manure-amended soils was related to greater N, P and K accumulation due to larger root surface area and biomass. Addition of cattle manure with chemical fertilizer would be a practical and effective approach to restore soil productivity and improve corn yields in eroded Chinese Mollisols.

Wang, E., Cruse, R. M., Chen, X. and Daigh, A. 2012. Effects of moisture condition and freeze/thaw cycles on surface soil aggregate size distribution and stability. Can. J. Soil Sci. 92: 529-536. Freeze/thaw cycles can affect soil aggregate stability, which in turn impacts wind and water erosion. The objectives of this laboratory study were: (1) to determine the effect of variable freeze/thaw cycles and soil water conditions on aggregate size distribution and stability; and (2) to evaluate differences in aggregate size distribution and stability between disturbed soil and undisturbed soil cores as affected by freeze/thaw cycles and soil water conditions. Surface soil was collected before freezing in late fall of 2009. Aggregates isolated from disturbed soil or intact soil cores were subjected to a factorial combination of 3 gravimetric water content treatments: 0.15 m³ m^-3, 0.23 m³ m^-3 or 0.30 m³ m^-3, and 3 freeze/thaw treatments: 0, 3, or 9 cycles. A freeze/thaw cycle involved soil freezing at -10^°C for 24 h, followed by thawing at 5^°C for 24 h. Most aggregate size classes were affected significantly (P<0.05) by freeze/thaw cycles except for wet-sieved aggregates >5 mm. Dry-sieved aggregates were relatively more sensitive to the freeze/thaw treatment than wet-sieved aggregates. The mean weight diameter (MWD) of dry-sieved aggregates was significantly (P<0.05) greater at 0.30 m³ m^-3 than 0.15 m³ m^-3 water content, but the opposite trend was observed for MWD of wet aggregates and aggregate stability. There was a significant (P<0.05) response of the MWD in dry-sieved aggregates to the interactive freeze/thaw×water content effect that differed for aggregates obtained from disturbed soil and those in the undisturbed soil core, but not for the MWD of wet-sieved aggregates and aggregate stability.

Song, C., Zhang, X., Liu, X. and Chen, Y. 2012. Effect of soil temperature and moisture on soil test P with different extractants. Can. J. Soil Sci. 92: 537-542. Temperature and moisture are important factors affecting adsorption, transformation and the availability of soil phosphorus (P) to plants. The different temperatures and moisture contents at which soil is sampled might affect the results of soil test P (STP). In order to evaluate the effect of the temperature and moisture, as well as the fertilization level, on the results of soil test P, an incubation study involving three soil temperatures (5, 10, and 20°C), and three soil moisture contents (50, 70, 90% of field water-holding capacity) was conducted with Chinese Mollisols collected from four fertilization treatments in a long-term experiment in northeast China. Four soil P test methods, Mehlich 3, Morgan, Olsen and Bray 1 were used to determine STP after a 42-d incubation. The effect of temperature and moisture on STP varied among soil P tests. Averaged across the four fertilization treatments, the temperature had significant impact on STP, while the responses varied among soil P test methods. Mehlich 3, Morgan and Bray 1 STP decreased and Olsen STP increased with increase in temperature. Effect of soil moisture was only significant for Mehlich 3 P and Olsen P. Soil temperature had greater impact on STP than soil moisture content. The responses of the Olsen method to temperature differed from the other three methods tested. The interaction between soil temperature and soil moisture on soil test P was only significant for Mehlich 3 P. Fertilization level does not affect the STP in as a clear pattern as the temperature and moisture varied for all four methods. Consistent soil sampling conditions, especially the soil temperature, appear to be the first step to achieve a reliable STP for any soil P test.

Mi, L., Wang, G., Jin, J., Sui, Y., Liu, J. and Liu, X. 2012. Comparison of microbial community structures in four Black soils along a climatic gradient in northeast China. Can. J. Soil Sci. 92: 543-549. Surveys of microorganisms across climatic gradients provide important information about their biodiversity and spatial distribution, which is linked to fundamental ecological functions. The present study investigated the bacterial communities, including total and culturable communities, and fungal communities in Black soils collected from Lishu (lat. 43°20'N, long. 124°28'E), Dehui (lat. 44°12'N, long. 125°33'E), Hailun (lat. 47°26'N, long. 126°38'E) and Beian (lat. 48°17'N, long. 127°15'E) in northeast China. Bacterial and fungal communities were evaluated by polymerase chain reaction (PCR)-denaturing gradient gel electrophoresis (DGGE) banding patterns of partial 16S rDNA and fungal rDNA internal transcribed spacer regions (ITS), respectively. Bacterial and fungal diversity, based on the number of DGGE bands, were similar among the locations, but cluster analysis of banding patterns showed distinct microbial communities along the climatic gradient. A closer relationship was found among soil bacterial (total and culturable) and fungal communities in neighboring locations than those at greater distance, which suggested that the spatial distribution of microbial community existed in the Black Soil Zone. Comparison of DGGE profiles among the four locations showed that the changes of fungal community and culturable bacterial community were greater than that of bacterial community, suggesting that fungal community and culturable bacterial community are more suitable to study microbial biogeographic distribution in Black soils.

Sui, Y.-y., Jiao, X.-g., Liu, X.-b., Zhang, X.-y. and Ding, G.-w. 2012. Water-stable aggregates and their organic carbon distribution after five years of chemical fertilizer and manure treatments on eroded farmland of Chinese Mollisols. Can. J. Soil Sci. 92: 551-557. Water-stable aggregates are the foundation for both water and fertility conservation and nutrient release in the soil. We investigated the effects of 5 yr of different fertilizer treatments (chemical fertilizer and fertilizer manure) on water-stable aggregates and their organic carbon distribution patterns within five different simulated erosion levels (removal of 0, 5, 10, 20, and 30 cm of topsoil) in an eroded Black soil of northeast China. Water-stable aggregates greater than 0.25 mm in size and aggregate-associated-carbon (AAC) contents in the aggregates were greater in the soils with fertilizer manure application than those with chemical fertilizers alone. Both water-stable aggregates and AAC contents declined (P<0.05) gradually as soil removal depth increased. The decline in aggregates larger than 1 mm with increased erosion depth was greater in the fertilizer-only application than that in the fertilizer manure application. The minimum value was found in the case of 30 cm topsoil removal under the fertilizer-only application. Significant correlations (P<0.05) between water-stable aggregates greater than 1 mm and soil organic carbon (SOC) were observed in the soil with fertilizer manure application. A significant positive correlation was observed between SOC and all different aggregate classes with both chemical fertilizer and fertilizer manure applications. AAC within large aggregates and SOC contents were significantly higher in the fertilizer manure treatment than in the fertilizer-only treatment. The study shows that water-stable aggregates (>1 mm) can be used as an indicator in evaluating the influence of carbon transformation on soil quality. The increases in SOC by cattle manure application to eroded Black soil might be responsible for the larger size aggregate formation.

Jiang, X., Wang, E., Chen, X., Xia, X. and Shi, C. 2012. Field study on macropore flow in typical Black soils of northeast China. Can. J. Soil Sci. 92: 559-566. Macropores are important preferential pathways for the transport of water and contaminants in soil. A series of hood infiltration experiments were conducted using dye tracers (Brilliant Blue FCF) at pressure heads of -5.0 cm, -3.0 cm, and -1.0 cm at a conventional tilled site on Keshan Farm, northeast China. The study objective was to combine the test method of dye tracing with a hood infiltrometer to analyze soil subjected to conventional tillage methods. Dye staining patterns and macroporous networks were analyzed by excavation, mapping, photography, and image analysis. Results showed that macropore flow began very near the soil surface under three pressures heads of -5.0 cm, -3.0 cm and -1.0 cm, and that a pressure head of -1.0 cm resulted in more lateral flow. Soil deeper than 40.0 cm was less disturbed, which resulted in good continuity. At pressure heads of -5.0, -3.0 and -1.0 cm, the dye staining technique resulted in maximum stained depths of 74.3, 60.7 and 64.7 cm, respectively, with maximum stained widths of 41.6, 41.5 and 47.9 cm, respectively (at depths from 14.0 to 28.0 cm). Soil under a pressure head of -1.0 cm had the highest initial and steady infiltration rates of 13.0 and 4.1 mm min^-1, respectively. Soil under a pressure head of -5.0 cm showed the most connectivity. To distinguish the macropores from the interaction area of macropore flow and the soil matrix surrounding the macropores, the stained area was separated into different classes based on dye color.

Zhao, Y., Wang, E., Cruse, R. M. and Chen, X. 2012. Characterization of seasonal freeze-thaw and potential impacts on soil erosion in northeast China. Can. J. Soil Sci. 92: 567-571. Freeze-thaw cycles are regarded as a critical factor inducing and accelerating gully erosion in the Black soil region (Chernozem) of northeast China. The major objective of this study was to identify the effect of seasonal freeze-thaw processes on soil structure relevant to soil erosion. Perched water due to an argillic horizon brings about higher water potential in the top soil, which lowers the soil shear strength and increases the risk of soil erosion by rainfall and surface flow; and the argillic horizon, with a higher clay content, is more vulnerable to freeze-thaw processes, which break or weaken the structure of the argillic horizon, increasing its vulnerability to gully erosion.