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A bioassay using the soil bacteria Bacillus brevisor Ensifer adhaerensfor determining plant‐available Mn in organic soils was developed. For this assay, a 1:10 soil‐agar plug was prepared in a nutrient agar plate and then overlaid with semisolid nutrient agar inoculated with either test organism. Manganese‐induced zones of growth stimulation were measured after 24‐h incubation at 27°C. There was a linear relationship between the logarithm of standard concentrations of Mn and the zone of growth stimulation. The enhanced growth was a specific response to Mn; Ca, Co, Cu, Fe, Mg, Mo, Ni, Sr, Zn, NO‐3, PO3‐4, and SO2‐4did not stimulate growth of either organism. Addition of glucose as a C and energy source or yeast extract as a source of vitamins and growth factors had no effect on growth. Six organic, six Mn‐amended organic, and 17 mineral soils were tested with this assay. This new assay clearly identified five nonamended organic soils that were Mn‐deficient as determined by the growth of spring wheat (Triticum aestivum) in a growth chamber study. There was a statistically significant correlation between the zone of growth stimulation on bioassay plates and plant relative yields, Mn concentration, and Mn uptake. The DTPA extracts of these soils did not predict this Mn deficiency. Separation of responding from nonresponding soils was achieved using the E. adhaerensbioassay. This assay allows rapid and inexpensive identification of Mn‐deficient soils.

Nine different organic and inorganic soil phosphorus fractions were obtained by a sequential extraction of samples from 168 USDA‐SCS benchmark soils, representing eight soil orders of the Soil Taxonomy. The distribution of P across the different fractions (resin, bicarbonate, hydroxide, sonification‐2nd hydroxide, acid, and acid‐peroxide digest fractions with separate organic and inorganic P determinations) and their relationships to other soil chemical properties were used to evaluate the effects of different soil development on phosphorus composition. Correlation and regression analyses of P distribution and chemical analyses confirmed the partial dependence of organic matter accumulation on available forms of P. Weathering indicators such as base saturation were related to the formation of secondary P forms. The relative proportions of available and stable as well as organic and inorganic P forms were dependent upon soil chemical properties and related to soil taxonomy. Path analysis of relationships between labile and stable P forms showed that in Mollisols much of the labile resin extractable P was derived from inorganic bicarbonate and hydroxide extractable P forms. In more weathered Ultisols, 80% of the variability in labile P was accounted for by organic P forms, suggesting that mineralization of organic P may be a major determinant of P fertility in these soils.

Changes in inorganic and organic phosphorus (P) fractions resulting from 65 years of cropping in a wheat‐wheat‐fallow rotation were studied using a sequential extraction technique. Total P content of the cultivated soil was 29% lower than that of the adjacent permanent pasture; the major loss of P (74% of total P lost) was organic P and residual P. Of the total P lost, 22% was from the extractable organic P forms, whereas 52% originated from stable P. Incubation studies were used to study seasonal P transformations during simulated fallow with and without residue incorporation and P fertilization. Nine monthly additions of cellulose (765 µg C · g−1soil) with and without P (9 µg · g−1soil) significantly altered levels of total extractable organic P and inorganic P in incubated soils. Evidence is provided for microbial activity playing a major role in redistributing P into different forms in the soil.

Organo‐mineral complexes in various size fractions from the surface horizons of two Chernozemic soils (Typic Argiboroll and Udic Haploboroll) were separated without chemical pretreatment by ultrasonic dispersion in water, followed by sieving and centrifugation. The organic carbon (C), nitrogen (N), and sulfur (S) composition in the size fractions and the degree of polycondensation of humic materials extracted by an alkaline pyrophosphate technique were compared. Fifty‐five to 58% of the organic C was in the clay fraction, with greatest absolute amounts in the coarse clay (2–0.2 µm). Carbon/nitrogen ratios narrowed as particle size decreased. The organic matter separated from the coarse‐clay and fine‐silt fractions (5–2 µm) was dominated by conventional humic acids (HA‐A), which based on their strong adsorption at 280 nm and resistance to acid hydrolysis, were considered strongly aromatic and recalcitrant in soil. In contrast, the organic matter associated with the fine clay (<0.2 µm) was largely fulvic acids (FA‐A, FA‐B) and humic acids (HA‐B) that were less aromatic than conventional humic acids and contained considerable amounts of hydrolyzable N. The fine‐ and coarse‐clay fractions (<2 µm) contained >70% of the total soil S, >80% of the HI‐reducible S, and >64% of the carbohydrate C. In relation to C and N, S was preferentially associated with the fine‐clay fractions. The C/S and N/S ratios decreased substantially from maximum values in the fine‐silt fraction (approximately 120:1 and 10:1, respectively) to minimum values in fine clay (approximately 33:1 and 4.5:1, respectively). The distinct differences between the humus of the coarse clay‐fine silt and the fine‐clay fractions indicate that size fractionation following ultrasonic dispersion in water is a promising method of isolating stable and labile forms of soil organic matter. The data also support earlier hypotheses on the nature of soil S that were based on studies of chemical separation of organic matter from complete soils.

Transitional grassland/forest light soils in Saskatchewan are often deficient in Cu. The high cost of micronutrient fertilizers necessitates extreme care in identifying micronutrient deficiencies and selecting effective products and methods of application. Comparison of tissue and grain or seed analysis for spring wheat (Triticum aestivumL.), canola (Brassica napusL.), and flax (Linum usitatissimumL.) vs. DTPA‐extractable soil Cu levels revealed that diagnosis of Cu deficiencies can more accurately be achieved via the latter. The critical DTPA‐extractable Cu levels were 0.40 mg Cu kg−1of soil for spring wheat and 0.35 mg Cu kg−1of soil for canola and flax. A series of field experiments comparing different forms of soil and foliar Cu fertilizers were conducted on several transitional grassland/forest soils. Copper oxide applied in the spring was generally ineffective in the year of application but alleviated Cu deficiencies in the following year. Copper‐sulfate (blue stone) and chelated products (polylignosulphonic acid) were effective in the year of application. However, the latter had no residual value at the rates of application used. This, combined with their extremely high current prices, makes them an undesirable Cu fertilizer source for the soils in the study area. Foliar Cu applications of either Cu‐sulfate or Cu‐chelate may be effective, but their performance has been erratic; hence, they should only be considered as an emergency measure for correcting of Cu deficiency.

Bromegrass (Bromus inermis) was grown under conditions of sewage effluent irrigation on undisturbed soil columns in which the 0‐ to 10‐cm layers had been treated with 10 µg Hg/g soil as 203Hg‐labeled mercuric chloride (HgCl2), phenyl mercuric acetate (PMA), and methyl mercuric chloride (MMC). Mercury concentrations in plant dry matter decreased over three successive harvests and highest values were found on MMC‐treated soils of fine texture and low organic matter content (2.0 to 0.2 µg Hg/g for first and third harvest, respectively). Exposure of the plants and soils to simulated fall conditions resulted in a small but significant increase in the Hg concentration of plant dry matter. Higher levels of Hg were found in plant stems (up to 0.88 µg Hg/g) than plant foliage (up to 0.24 µg Hg/g) at the termination of the experiment and even higher levels in the main roots (up to 42.5 µg Hg/g) and fine roots (up to 106.4 µg Hg/g) separated from the 0–10 cm soil layer. Mercury concentration of roots decreased with depth for all Hg treatments but were still 150 times greater than background levels in the MMC‐treated soils at the 40‐ to 60‐cm depth. A significant amount of all forms of applied Hg (10–32%) was lost during the experiment, presumably by volatilization. The majority of the remaining Hg in the soil was found to be strongly bound and not extractable by weak salt solutions, dilute acids, and chelates.

The adsorption of Hg by two soils, differing in chemical and physical characteristics, indicated that both organic Hg compounds (methyl mercuric chloride [MMC] and phenyl mercuric acetate [PMA]) and inorganic compounds (mercuric chloride [HgCl2]) followed the linear form of the Langmuir adsorption isotherm. The highest adsorption maxima for all Hg compounds were found for the soils which had the higher organic matter content and clay content. Adsorption maxima increased in the order MMC < PMA < HgCl2. A two‐rate effluent leaching experiment was conducted utilizing undisturbed soil cores of the same two soils and the same three Hg compounds (labeled with 203Hg) which were applied uniformly to the top 0–10 cm of each column. In contrast to the movement of other cations in the effluent and soil, even at the higher irrigation rate, none of the applied Hg was found to move below the 10‐ to 20‐cm soil layer. More MMC than HgCl2or PMA were found in the 10‐ to 20‐cm layer; however, the differences were small. The lack of movement of Hg and the high adsorption maxima was a consequence of the strong binding between Hg compounds and soil. The inability of weak chemical extractants (CaCl2, NH4OAc, DTPA, EDTA) to remove significant quantities of Hg confirmed this hyphothesis. Seven to 31% of the applied Hg was lost from the columns during the experiment presumably by volatilization.

The natural N isotope composition of soil organic matter associated with organo‐mineral particle size fractions of two cultivated and two native grassland soils was studied. In the native soils, N associated with the coarsest (sand size) fraction showed a low enrichment (+7 per mil 15N enrichment) typical for recent plant materials. A similarly low enrichment was observed in the silt‐sized fractions (+9 δa15N) whereas clays had a higher 15N abundance (>12 δa15N), characteristic of residual material from microbially‐mediated N mineralization. Cultivation initially resulted in the incorporation of a large pulse of low‐enrichment plant material that could be detected in the sand and coarse silt fractions, as well as in the fine clays that contain a large portion of the soil's microbial products. The 15N abundance of fine‐silt and coarse‐clay‐associated N appeared relatively unchanged even after prolonged cultivation of 60 yr. Increases in the 15N abundance of the sand and silt fractions were attributed to reduced inputs of plant residues under cultivation. A large drop in the 15N abundance of the fine‐clay‐sized materials indicated a major change in the nature of microbial N transformations.

Losses of carbon, nitrogen, and phosphorus from soil particle‐size fractions during cultivation were examined and their implications on the nutrient‐supplying potential of soils is discussed. Particle‐size fractions were obtained by ultrasonic dispersion in water from three north American grassland soils (Cryoborolls) of different textures. Soils that had been cultivated under small grain‐fallow rotations for between 4 and 90 years were compared with similar soils under native prairie. Four years of cultivation of a Blaine Lake silt loam resulted in an extensive depletion of organic matter associated with particles > 50 µm (43% of the initial C lost). This was considered a result of physical disintegration which led to accumulation of these materials in finer particle‐size fractions. With continued cultivation this accumulated material was slowly transformed within the system, accompanied by net losses of 34% C and 29% N from the total soil over 60 years. Reductions in organic P content amounted to 20% and were accompanied by slight increases in inorganic P content. Fine clay (< 0.2 µm) associated organic matter was rapidly depleted during the first 60 years but showed little change thereafter, reaching a new equilibrium level at approximately one‐half its original C content. Losses of fine silt (5 to 2 µm) and coarse clay (2 to 0.2 µm) associated organic materials were substantially less, and the proportion of total soil organic matter in these forms increased with time of cultivation. The relative abundance of these biologically resistant, more humified materials in cultivated soils indicated that the remaining organic matter may have a reduced capability for supplying nutrients by mineralization. The continuing, slow mineralization of these more resistant organic matter fractions of the Blaine Lake soil after 90 years of cultivation suggests that organic matter losses may not level off further in the near future. In addition, losses of organic matter from the B horizon were evident after 60 and 90 years. Organic matter losses during 65 years cultivation of a coarser sandy loam soil showed a similar distribution and magnitude across size fractions, while a heavy clay soil was characterized by a greater stability of the silt and clay associated organic matter, which lost only 10% C during 70 years of cultivation.

The role of S in humus formation and transformation was hypothesized on the basis of C/N/S ratio and percent HI‐reducible S determinations on organic fractions obtained from soil Ap horizons by a 0.1MNaOH − 0.1MNa4P2O7(pH 13.0) extraction‐separation technique. Differences in C/N/S ratios of the conventional humic acid (HA‐A) fractions were greater (from 113:10.6:1 to 270:23.3:1) than those of the total soil organic matter (61:6.5:1 to 112:9.7:1) in soils along an environmental gradient delineated by semiarid Chernozemic Brown to sumhumid Luvisolic Gray soils. This fraction (HA‐A) is thought to represent the end product of the humification process. Differences in C/N/S ratios of conventional fulvic acid (FA‐A), clay associated humic acid (HA‐B) and <2 µm humin were smaller than for HA‐A along the gradient. On the basis of C/N/S ratios and the average percentage of HI‐reducible S in each fraction, e.g. HA‐A, 26%; HA‐B, 44%; FA‐A, 82%; and <2 µm humin, 52%; it was postulated that FA‐A, HA‐B, and <2 µm humin contained the majority of potentially labile S.

Cultivation has substantially reduced the organic matter contents of many prairie soils. This study attempts to quantify the losses of C, N, and P from three prairie soils of different textures during cultivation. For this purpose cultivated and adjacent uncultivated soils (2 Cryoborolls and 1 Cryorthent) were sampled and their C, N, and P contents as well as their bulk densities and horizon depths were compared. Reductions of about 35% in the C concentration were observed in clay and silt loam soils after 60 to 70 years of cultivation. At the same time reductions in N concentrations were greatly influenced by the presence or absence of legume [alfalfa, (Medicago sativaL.)] crops grown in the fields and losses varied between 18 and 34%. Phosphorus concentrations were reduced by 12% and all P losses were accounted for by the organic fraction. During a similar period of cultivation a lighter textured sandy loam had experienced greater reductions in C, N, and P concentrations of 46, 46, and 29%, respectively. In this soil P was lost from both the organic and inorganic fractions. Prolonged cultivation of 90 years did not result in a decrease in the rates of losses of C, N, and P on the silt loam soil. Conversion of concentration data to area based total C, N, and P budgets resulted in a decrease in the differences seen between cultivated and uncultivated soils. This was caused by an increase of soil bulk densities under cultivation and by an increase in the standard deviations of the data due to variability of horizon depths in cultivated fields.

One‐time heavy application of P on certain soils can provide sufficient available P to sustain crop production over a period of several years, but may cause Zn nutritional problem for crops. A field study was conducted to determine the effect of applied Zn on wheat (Triticum aestivumL.) grown on residual P plots and identify the mechanism of P ✕ Zn interaction. This study was conducted in 1984 in a continuous wheat system on a clayey, mixed, frigid Typic Hyploboroll soil that had received 0, 80, and 160 kg P ha−1in 1979. Three experiments were carried out using a split plot randomized complete block design with three levels of P as main plots and rates of soilapplied Zn‐sulfate (0, 5, 10, and 20 kg Zn ha−1) or Zn‐chelate (0, 0.5, 1.0, and 2.0 kg Zn ha−1) or foliar‐applied Zn‐chelate (0 and 0.35 kg Zn ha−1) as subplots. A one‐time application of 80 or 160 kg P ha−1increased wheat yield significantly. In the presence of P, application of Zn resulted in significant increase in grain yield and Zn uptake into grain. Applied P increased soil P levels and tissue P concentration, but resulted in a significant decrease of tissue Zn levels. DTPA (diethylenetriaminepentaacetic acid)–extractable soil Zn levels in the non–Zn‐amended treatment were independent of P application rate. Plant roots in high P treatments contained significantly lower levels of vesicular‐arbuscular mycorrhizal (VAM) infection than the control. Further, a close relationship was observed between Zn levels in the aboveground plant parts and VAM infection.

Large differences in organic matter contents of a Udic Haploboroll soil were observed in the A horizons of adjacent cultivated (for 65 years) and permanent pasture sites. Relatively lower net losses of S (38%) comared to C (44%) and N (49%) and narrower C/N/S ratios indicated that S is more resistant to mineralization during cultivation processes than C and N. Organic S concentrations were lower in all 6 fractions obtained from a 0.1MNaOH‐0.1MNa4P2O7(pH 13.0) extraction separation but differences were noted in absolute amounts and relative proportions of C, N and S lost from specific fractions. Three fractions, conventional humic acid (HA‐A), clay associated humic acid (HA‐B) and humin (<2 µm), accounted for 80% of the total S difference. In contrast, the fulvic acid (FA‐A) fraction which had narrower C/N/S ratios, contained more HI‐reducible S and was thought to be more labile than other fractions, only contributed 14% of the total S loss. It was postulated that the breakdown and oxidation of HA‐A, HA‐B and humin <2‐µm fractions during mineralization would liberate low molecular weight S compounds which would temporarily accumulate in FA‐A fractions thereby accounting for a small net decrease in total S and a high percentage of HI‐reducible S in this fraction in the cultivated soil.