Sulphur mineralization kinetics as influenced by soil properties

A 10-week laboratory study, using an open incubation technique, was carried out to determine net sulphur (S) mineralization potentials of soil samples obtained from some representative soils in Tuscany, Italy. The time-course of organic S mineralization in the soils was analyzed by fitting the experimental values to three kinetic models (first-order, first-order E, zero-order). The first-order model was found to be the most suitable because it provided the best fit to the experimental data and for its simplicity. Potentially mineralized S (S ₀) values ranged from a minimum of 13.6 to a maximum of 50.7 mg kg⁻¹ soil and the mineralization rate k varied from 0.111 to 0.615 week⁻¹. It was also positively related to organic C, N, and S, protease, arylsulphatase, and dehydrogenase activities. The mineralization rate did not show any significant relationship with soil properties.     

Nitrogen mineralization and CO2 and N2O emissions in a sandy soil amended with original or acidified pig slurries or with the relative fractions

The following six pig slurries obtained after acidification and/or solid/liquid separation were used in the research: original (S) and acidified (AS) pig slurry, nonacidified (LF) and acidified (ALF) pig slurry liquid fraction, and nonacidified (SF) and acidified (ASF) pig slurry solid fraction. Laboratory incubations were performed to assess the effect of the application of these slurries on N mineralization and CO₂ and N₂O emissions from a sandy soil. Acidification maintained higher NH₄ ⁺-N contents in soil particularly in the ALF-treated soil where NH₄ ⁺-N contents were two times higher than in LF-treated soil during the 55–171-day interval. At the end of the incubation (171 days), 32.9 and 24.2 mg N kg⁻¹ dry soil were mineralized in the ASF- and SF-treated soils, respectively, but no mineralization occurred in LF- and S-treated soils, although acidification decreased N immobilization in ALF- (−25.3 mg N kg⁻¹ soil) and AS- (−12.7 mg N kg⁻¹ soil) compared to LF- (−34.4 mg N kg⁻¹ soil) and S-treated (−18.6 mg N kg⁻¹ soil) soils, respectively. Most of the dissolved CO₂ was lost during the acidification process. More than 90% of the applied C in the LF-treated soil was lost during the incubation, indicating a high availability of the added organic compounds. Nitrous oxide emissions occurred only after day 12 and at a lower rate in soils treated with acidified than nonacidified slurries. However, during the first 61 days of incubation, 1,157 μg N kg⁻¹ soil was lost as N₂O in the AS-treated soil and only 937 in the S-treated soil.     

Does long-term farmyard manure fertilization affect short-term nitrogen mineralization from farmyard manure?

One of the challenges in organic farming systems is to match nitrogen (N) mineralization from organic fertilizers and crop demand for N. The mineralization rate of organic N is mainly determined by the chemical composition of the organic matter being decomposed and the activity of the soil microflora. It has been shown that long-term organic fertilization can affect soil microbial biomass (MB), the microbial community structure, and the activity of enzymes involved in the decomposition of organic matter, but whether this has an impact on short-term N mineralization from recently applied organic substances is not yet clear. Here, we sampled soils from a long-term field experiment, which had either not been fertilized, or fertilized with 30 or 60 t ha⁻¹ year⁻¹ of farmyard manure (FYM) since 1989. These soil samples were used in a 10-week pot experiment with or without addition of FYM before starting (recent fertilization). At the start and end of this experiment, soil MB, microbial basal respiration, total plant N, and mineral soil N content were measured, and a simplified N balance was calculated. Although the different treatments used in the long-term experiment induced significant differences in soil MB, as well as total soil C and N contents, the total N mineralization from FYM was not significantly affected by soil fertilization history. The amount of N released from FYM and not immobilized by soil microflora was about twice as high in the soil that had been fertilized with 60 t ha⁻¹ year⁻¹ of FYM as compared with the non-fertilized soil (p < 0.05).     

Carbon and nitrogen mineralization dynamics in different soils of the tropics amended with legume residues and contrasting soil moisture contents

Seasonal drought in tropical agroecosystems may affect C and N mineralization of organic residues. To understand this effect, C and N mineralization dynamics in three tropical soils (Af, An₁, and An₂) amended with haricot bean (HB; Phaseolus vulgaris L.) and pigeon pea (PP; Cajanus cajan L.) residues (each at 5 mg g⁻¹ dry soil) at two contrasting soil moisture contents (pF2.5 and pF3.9) were investigated under laboratory incubation for 100–135 days. The legume residues markedly enhanced the net cumulative CO₂–C flux and its rate throughout the incubation period. The cumulative CO₂–C fluxes and their rates were lower at pF3.9 than at pF2.5 with control soils and also relatively lower with HB-treated than PP-treated soil samples. After 100 days of incubation, 32–42% of the amended C of residues was recovered as CO₂–C. In one of the three soils (An₁), the results revealed that the decomposition of the recalcitrant fraction was more inhibited by drought stress than easily degradable fraction, suggesting further studies of moisture stress and litter quality interactions. Significantly (p < 0.05) greater NH₄⁺–N and NO₃⁻–N were produced with PP-treated (C/N ratio, 20.4) than HB-treated (C/N ratio, 40.6) soil samples. Greater net N mineralization or lower immobilization was displayed at pF2.5 than at pF3.9 with all soil samples. Strikingly, N was immobilized equivocally in both NH₄⁺–N and NO₃⁻–N forms, challenging the paradigm that ammonium is the preferred N source for microorganisms. The results strongly exhibited altered C/N stoichiometry due to drought stress substantially affecting the active microbial functional groups, fungi being dominant over bacteria. Interestingly, the results showed that legume residues can be potential fertilizer sources for nutrient-depleted tropical soils. In addition, application of plant residue can help to counter the N loss caused by leaching. It can also synchronize crop N uptake and N release from soil by utilizing microbes as an ephemeral nutrient pool during the early crop growth period.     

Predicting plant sulfur deficiency in soils: results from Ohio

We developed a model for plant available sulfur (S) in Ohio soils to predict potential crop plant S deficiency. The model includes inputs of plant available S due to atmospheric deposition and mineralization of soil organic S and output due to leaching. A leaching index was computed using data on annual precipitation; soil pH and clay content that influence sulfate adsorption; and pore water velocity based upon percent sand, silt, and clay. There are five categories of S status ranging from highly deficient to highly sufficient, and the categories are defined based on whether the crop S requirement was 15 or 30kg S ha⁻¹ year⁻¹. The final database derived from the model includes 1,473 soil samples representing 443 of the 475 soil series in Ohio. For a crop requiring 15kg S ha⁻¹ year⁻¹, most soils (68.6%) were classified as variably deficient, which implies that the response to S fertilization will be variable but often positive depending on specific crop conditions. For a crop requiring 30kg S ha⁻¹ year⁻¹, 43.2% of soils were classified as variably deficient, but 49.7% were classified as moderately or highly deficient, implying that a response to S fertilization will usually or always occur. The model predicts crop S status for a single state in the USA, but with proper inputs, it should be applicable to other areas.     

Effects of long-term mineral fertilization on microbial biomass,microbial activity,and the presence of <Emphasis Type="Italic">r</Emphasis>- and <Emphasis Type="Italic">K</Emphasis>-strategists in soil

Long-term effects of mineral fertilization on microbial biomass C (MBC), basal respiration (R _B), substrate-induced respiration (R _S), β-glucosidase activity, and the r–K-growth strategy of soil microflora were investigated using a field trial on grassland established in 1969. The experimental plots were fertilized at three rates of mineral N (0, 80, and 160 kg ha⁻¹ year⁻¹) with 32 kg P ha⁻¹ year⁻¹ and 100 kg K ha⁻¹ year⁻¹. No fertilizer was applied on the control plots (C). The application of a mineral fertilizer led to lower values of the MBC and R _B, probably as a result of fast mineralization of available substrate after an input of the mineral fertilizer. The application of mineral N decreased the content of C extracted by 0.5 M K₂SO₄ (C _ex). A positive correlation was found between pH and the proportion of active microflora (R _S/MBC). The specific growth rate (μ) of soil heterotrophs was higher in the fertilized than in unfertilized soils, suggesting the stimulation of r-strategists, probably as the result of the presence of available P and rhizodepositions. The cessation of fertilization with 320 kg N ha⁻¹ year⁻¹ (NF) in 1989 also stimulated r-strategists compared to C soil, probably as the result of the higher content of available P in the NF soil than in the C soil.     

Mineralization and denitrification in upland, nearly saturated and flooded subtropical soil II. Effect of organic manures varying in N content and C:N ratio

 Nitrogen and carbon mineralization of cattle manure (N=6 g kg^–1; C:N=35), pressmud (N=17.4 g kg^–1; C:N=22), green manure (N=26.8 g kg^–1; C:N=14) and poultry manure (N=19.5 g kg^–1; C:N=12) and their influence on gaseous N losses via denitrification (using the acetylene inhibition technique) in a semiarid subtropical soil (Typic Ustochrepts) were investigated in a growth chamber simulating upland, nearly saturated, and flooded conditions. Mineralization of N started quickly in all manures, except pressmud where immobilization of soil mineral N was observed for an initial 4 days. Accumulation of mineral N in upland soil plus denitrified N revealed that mineralization of cattle manure-, pressmud-, poultry manure- and green manure-N over 16 days was 12, 20, 29 and 44%, respectively, and was inversely related to C:N ratio (R ²=0.703, P=0.05) and directly to N content of organic manure (R ²=0.964, P=0.01). Manure-C mineralized over 16 days ranged from 6% to 50% in different manures added to soil under different moisture regimes and was, in general, inversely related to initial C:N ratio of manure (R ²=0.690, P=0.05). Cumulative denitrification losses over 16 days in control soils (without manure) under upland, nearly saturated, and flooded conditions were 5, 23, and 24 mg N kg^–1, respectively. Incorporation of manures enhanced denitrification losses by 60-82% in upland, 52–163% in nearly saturated, and 26–107% in flooded soil conditions over a 16-day period, demonstrating that mineralized N and C from added manures could result in 2- to 3-fold higher rate of denitrification. Cumulative denitrification losses were maximal with green manure, followed by poultry manure, pressmud and cattle manure showing an increase in denitrification with increasing N content and decreasing C:N ratio of manure. Manure-amended nearly saturated soils supported 14–35% greater denitrification than flooded soils due to greater mineralization and supply of C.     

Glufosinate and ammonium sulfate inhibit atrazine degradation in adapted soils

The co-application of glufosinate with nitrogen fertilizers may alter atrazine cometabolism, thereby extending the herbicide’s residual weed control in adapted soils. The objective of this study was to assess the effects of glufosinate, ammonium sulfate, and the combination of glufosinate and ammonium sulfate on atrazine mineralization in a Dundee silt loam exhibiting enhanced atrazine degradation. Application of glufosinate at rates of 10 to 40 mg kg⁻¹ soil extended the lag phase 1 to 2 days and reduced the maximum degradation rate by 15% to 30%. However, cumulative atrazine mineralization averaged 85% 21 days after treatment and was independent of treatment. Maximum daily rates of atrazine mineralization were reduced from 41% to 55% by application of 1 to 8 g kg⁻¹ of ammonium sulfate. Similarly, cumulative atrazine mineralization was inversely correlated with ammonium sulfate rates ranging from 1.0 to 8 g kg⁻¹ soil. Under the conditions of this laboratory study, atrazine degradation was relatively insensitive to exogenous mineral nitrogen, in that 8 g (NH₄)₂SO₄ per kilogram soil repressed but did not completely inhibit atrazine mineralization. Moreover, an additive effect on reducing atrazine mineralization was observed when glufosinate was co-applied with ammonium sulfate. In addition, ammonium fertilization alters the partitioning of ¹⁴C-atrazine metabolite accumulation and nonextractable residues, indicating that ammonium represses cleavage of the triazine ring. Consequently, results indicate that the co-application of glufosinate with N may increase atrazine persistence under field conditions thereby extending atrazine residual weed control in adapted soils.     

Effects of cow manure and sewage sludge on the activity and kinetics of <Emphasis Type="SmallCaps">l</Emphasis>-glutaminase in soil

A study was conducted to investigate the effects of cow manure and sewage sludge application on the activity and kinetics of soil l-glutaminase. Soil samples were collected from a farm experiment in which 0, 25, and 100 Mg ha⁻¹ of either cow manure or sewage sludge had been applied annually for 4 consecutive years to a clay loam soil (Typic Haplargid). A chemical fertilizer treatment had also been applied. Results indicated that the effects of chemical fertilizer and the solid waste application on pH in the 18 surface soil (0–15 cm) samples were not significant. The organic C content, however, was affected significantly by the different treatments, being the greatest in soils treated with 100 Mg ha⁻¹ cow manure, and the least in the control treatment. l-Glutaminase activity was generally greater in solid-waste applied soils and was significantly correlated (r = 0.939, P < 0.001) with organic C content of soils. The values of l-glutaminase maximum velocity (Vmax) ranged from 331 to 1,389 mg NH₄ ⁺–N kg⁻¹ 2 h⁻¹. Values of the Michaelis constant (K _m) ranged from 35.1 to 71.7 mM. Organic C content of the soils were significantly correlated with V _max (r = 0.919, P < 0.001) and K _m (r = 0.763, P < 0.001) values. These results demonstrate the considerable influence that solid waste application has on this enzymatic reaction involved in N mineralization in soil.     

Microbial biomass and C mineralization in agricultural soils as affected by atrazine addition

This study examines the effects of atrazine on both microbial biomass C and C mineralization dynamics in two contrasting agricultural soils (organic C, texture, and atrazine application history) located at Galicia (NW Spain). Atrazine was added to soils, a Humic Cambisol (H) and a Gleyic Cambisol (G), at a recommended agronomic dose and C mineralization (CO₂ evolved), and microbial biomass measurements were made in non-treated and atrazine-treated samples at different time intervals during a 12-week aerobic incubation. The cumulative curves of CO₂–C evolved over time fit the simple first-order kinetic model [Ct = Co (1 − e ^−kt )], whose kinetic parameters were quantified. Differences in these parameters were observed between the two soils studied; the G soil, with a higher content in organic matter and microbial biomass C and lower atrazine application history, exhibited higher values of the total C mineralization and the potentially mineralizable labile C pool than those for the H soil. The addition of atrazine modified the kinetic parameters and increased notably the C mineralized; by the end of the incubation the cumulative CO₂–C values were 33–41% higher than those in the corresponding non-added soils. In contrast, a variable effect or even no effect was observed on the soil microbial biomass following atrazine addition. The data clearly showed that atrazine application at normal agricultural rates may have important implications in the C cycling of these two contrasting acid soils.     

How increasing availabilities of carbon and nitrogen affect atrazine behaviour in soils

 The effect of increasing amounts of glucose and mineral N on the behaviour of atrazine was studied in two soils. One had been exposed to atrazine under field conditions (adapted soil), the other had not (non-adapted soil), resulting, respectively, in an accelerated degradation of atrazine in the adapted soil and in a slow degradation of the herbicide in the non-adapted soil. The dissipation of ¹⁴C-atrazine via degradation and formation of non-extractable "bound" residues was followed during laboratory incubations in soils supplemented or not with increasing amounts of glucose and mineral N. In both soils, glucose added at rates of up to 16 g C kg^–1 soil did not modify atrazine mineralization but increased the formation of bound residues; this was probably due to the retention of atrazine by the growing microbial biomass. Atrazine dealkylation was enhanced when a large amount of glucose was added. In both soils, the addition of the largest dose of mineral N (2.5 g N kg^–1 soil) decreased atrazine mineralization. The simultaneous addition of glucose and mineral N enhanced their effects. When the largest doses of mineral N and glucose were added, atrazine mineralization stopped in both soils, and the proportion of bound residues increased. Glucose and mineral N additions influenced atrazine mineralization to a greater extent in the adapted soil than in the non-adapted one, as revealed by ANOVA, although glucose addition had a greater effect than N. The competition for space and nutrients between atrazine-degrading microorganisms and the total heterotrophic microflora probably contributed to the decrease in atrazine mineralization. Received: 9 June 1998     

Gross nitrogen mineralization and nitrification rates and their relationships to enzyme activities and the soil microbial biomass in soils treated with dairy shed effluent and ammonium fertilizer at different water potentials

 Gross N mineralization and nitrification rates and their relationships to microbial biomass C and N and enzyme (protease, deaminase and urease) activities were determined in soils treated with dairy shed effluent (DSE) or NH₄ ⁺ fertilizer (NH₄Cl) at a rate equivalent to 200 kg N ha^–1 at three water potentials (0, –10 and –80 kPa) at 20  °C using a closed incubation technique. After 8, 16, 30, 45, 60 and 90 days of incubation, sub-samples of soil were removed to determine gross N mineralization and nitrification rates, enzyme activities, microbial biomass C and N, and NH₄ ⁺ and NO₃ ^– concentrations. The addition of DSE to the soil resulted in significantly higher gross N mineralization rates (7.0–1.7 μg N g^–1 soil day^–1) than in the control (3.8–1.2 μg N g^–1 soil day^–1), particularly during the first 16 days of incubation. This increase in gross mineralization rate occurred because of the presence of readily mineralizable organic substrates with low C : N ratios, and stimulated soil microbial and enzymatic activities by the organic C and nutrients in the DSE. The addition of NH₄Cl did not increase the gross N mineralization rate, probably because of the lack of readily available organic C and/or a possible adverse effect of the high NH₄ ⁺ concentration on microbial activity. However, nitrification rates were highest in the NH₄Cl-treated soil, followed by DSE-treated soil and then the control. Soil microbial biomass, protease, deaminase and urease activities were significantly increased immediately after the addition of DSE and then declined gradually with time. The increased soil microbial biomass was probably due to the increased available C substrate and nutrients stimulating soil microbial growth, and this in turn resulted in higher enzyme activities. NH₄Cl had a minimal impact on the soil microbial biomass and enzyme activities, possibly because of the lack of readily available C substrates. The optimum soil water potential for gross N mineralization and nitrification rates, microbial and enzyme activities was –10 kPa compared with –80 kPa and 0 kPa. Gross N mineralization rates were positively correlated with soil microbial biomass N and protease and urease activities in the DSE-treated soil, but no such correlations were found in the NH₄Cl-treated soil. The enzyme activities were also positively correlated with each other and with soil microbial biomass C and N. The forms of N and the different water potentials had a significant effect on the correlation coefficients. Stepwise regression analysis showed that protease was the variable that most frequently accounted for the variations of gross N mineralization rate when included in the equation, and has the potential to be used as one of the predictors for N mineralization. Received: 10 March 1998     

Recovery of fertilizer nitrogen from continuous corn soils under contrasting tillage management

Tillage systems influence soil properties and may influence the availability of applied and mineralized soil N. This laboratory study (20°C) compared N cycling in two soils, a Wooster (fine, loamy Typic Fragiudalf) and a Hoytville (fine, illitic Mollic Epiaqualf) under continuous corn (Zea mays) production since at least 1963 with no-tillage (NT), minimum (CT) and plow tillage (PT) management. Fertilizer was added at the rate of 100 mg ¹⁵N kg^–1–1 soil as 99.9% ¹⁵N as NH₄Cl or Ca(NO₃)₂ and the soils were incubated in leaching columns for 1 week at 34 kPa before being leached periodically with 0.05 M CaCl₂ for 26 weeks. As expected, the majority of the ¹⁵NO₃^– additions were removed from both soils with the first leaching. The majority of applied ¹⁵NH₄⁺ additions were recovered as ¹⁵NO₃^– by week 5, with the NT soils demonstrating faster nitrification rates compared with soils under other tillage practices. For the remaining 22 weeks, only low levels of ¹⁵NO₃^– were leached from the soils regardless of tillage management. In the coarser textured Wooster soils (150 g clay kg^–1), mineralization of native soil N in the fertilized soils was related to the total N content (r² 0.99) and amino acid N (r² 0.99), but N mineralization in the finer textured Hoytville (400 g clay kg^–1) was constant across tillage treatments and not significantly related to soil total N or amino acid N content. The release of native soil N was enhanced by NH₄⁺ or NO₃^– addition compared to the values released by the unfertilized control and exceeded possible pool substitution. The results question the use of incubation N mineralization tests conducted with unfertilized soils as a means for predicting soil N availability for crop N needs.     

Short-term carbon mineralization in saline–sodic soils

Previous studies have shown that carbon (C) mineralization in saline or sodic soils is affected by various factors including organic C content, salt concentration and water content in saline soils and soil structure in sodic soils, but there is little information about which soil properties control carbon dioxide (CO₂) emission from saline-sodic soils. In this study, eight field-collected saline–sodic soils, varying in electrical conductivity (EC_e, a measure of salinity, ranging from 3 to 262 dS m⁻¹) and sodium adsorption ratio (SAR_e, a measure of sodicity, ranging from 11 to 62), were left unamended or amended with mature wheat or vetch residues (2% w/w). Carbon dioxide release was measured over 42 days at constant temperature and soil water content. Cumulative respiration expressed per gram SOC increased in the following order: unamended soil<soil amended with wheat residues (C/N ratio 122)<soil with vetch residue (C/N ratio 18). Cumulative respiration was significantly (p < 0.05) negatively correlated with EC_e but not with SAR_e. Our results show that the response to EC_e and SAR_e of the microbial community activated by addition of organic C does not differ from that of the less active microbial community in unamended soils and that salinity is the main influential factor for C mineralization in saline–sodic soils.     

Influence of soil compaction on carbon and nitrogen mineralization of soil organic matter and crop residues

 We studied the influence of soil compaction in a loamy sand soil on C and N mineralization and nitrification of soil organic matter and added crop residues. Samples of unamended soil, and soil amended with leek residues, at six bulk densities ranging from 1.2 to 1.6 Mg m^–3 and 75% field capacity, were incubated. In the unamended soil, bulk density within the range studied did not influence any measure of microbial activity significantly. A small (but insignificant) decrease in nitrification rate at the highest bulk density was the only evidence for possible effects of compaction on microbial activity. In the amended soil the amounts of mineralized N at the end of the incubation were equal at all bulk densities, but first-order N mineralization rates tended to increase with increasing compaction, although the increase was not significant. Nitrification in the amended soils was more affected by compaction, and NO₃ ^–-N contents after 3 weeks of incubation at bulk densities of 1.5 and 1.6 Mg m^–3 were significantly lower (by about 8% and 16% of total added N, respectively), than those of the less compacted treatments. The C mineralization rate was strongly depressed at a bulk density of 1.6 Mg m^–3, compared with the other treatments. The depression of C mineralization in compacted soils can lead to higher organic matter accumulation. Since N mineralization was not affected by compaction (within the range used here) the accumulated organic matter would have had higher C : N ratios than in the uncompacted soils, and hence would have been of a lower quality. In general, increasing soil compaction in this soil, starting at a bulk density of 1.5 Mg m^–3, will affect some microbially driven processes. Received: 10 June 1999     

Mineralization of organic sulfur and its importance as a reservoir of plant-available sulfur in upland soils of north China

 An open incubation technique was used to measure S mineralization in a range of upland soils of north China. Six mineralization patterns were examined, and a soil S-exhaustion experiment with ryegrass (Lolium multiflorum L.) was conducted to investigate the availability of various organic S pools to plants. For all of the 12 soils tested, the release of S as SO₄ ^2– was curvilinear with time, and during a 28-week incubation at 30  °C the amount of S mineralized ranged from 14.0 mg S kg^–1 soil to 37.4 mg S kg^–1 soil. A first-order model and Gompertz model appeared to best describe S mineralization. Examination of the soils after incubation revealed the bulk of the mineralized S was mainly derived from the C-bonded S pool, while the majority of mineralized S under soil S exhaustion by ryegrass was derived from the HI-reducible S pool. Received: 9 July 1998     

Gross nitrogen mineralization-, immobilization-, and nitrification rates as a function of soil C/N ratio and microbial activity

A laboratory experiment was designed to challenge the idea that the C/N ratio of forest soils may control gross N immobilization, mineralization, and nitrification rates. Soils were collected from three deciduous forests sites varying in C/N ratio between 15 and 27. They were air-dried and rewetted to induce a burst of microbial activity. The N transformation rates were calculated from an isotope dilution and enrichment procedure, in which ¹⁵NH₄Cl or Na¹⁵NO₃ was repeatedly added to the soils during 7 days of incubation. The experiments suggested that differences in gross nitrogen immobilization and mineralization rates between the soils were more related to the respiration rate and ATP content than to the C/N ratio. Peaks of respiration and ATP content were followed by high rates of mineralization and immobilization, with 1-2 days of delay. The gross immobilization of NH₄⁺ was dependent on the gross mineralization and one to two orders of magnitude larger than the gross NO₃⁻ immobilization. The gross nitrification rates were negatively related to the ATP content and the C/N ratio and greatly exceeding the net nitrification rates. Taken together, the observations suggest that leaching of nitrate from forest soils may be largely dependent on the density and activity of the microbial community.     

Biochemical composition and kinetics of C and N mineralization of animal wastes: a typological approach

Forty-seven different animal wastes were characterized using chemical and organic matter fractionation methods (water extraction and Van Soest method) and 224-day incubation studies to assess their decomposition in soil. Simple correlation and multiple factor analysis were performed to establish relationships between the composition of these wastes and C and N mineralization. Carbon and N contents ranged from 101 to 469 mg C kg⁻¹ dry matter (d.m.) and from 4 to 39 mg N kg⁻¹ d.m. Soluble C and N represented less than 9% of organic C and 1.5% of total N at 20°C, respectively. The C fractions soluble at 100°C or in neutral detergent were larger and represented 14 and 32% of the organic C, respectively. The hemicellulose-like (HEM) and cellulose-like (CEL) fractions contained about 16.5 and 6% of the organic N, respectively. The C distribution in the lignin-like (LIG) and CEL fractions was comparable, but the former contained more N. Carbon mineralization varied from 5 to 62% of the organic C added during the 224-day incubation; 70% of the wastes induced net N mineralization at the end of incubation (from 3 to 51% of organic N). Other wastes induced net soil inorganic N immobilization, from −1 to −31% of the organic N added. Most highly significant correlations were established between the C mineralization and the C present in the water-soluble fraction at 20°C, and the HEM and LIG fractions. Relationships between N mineralization and biochemical characteristics were weak, except with the soluble Van Soest fraction, and highly significant correlations were observed between N mineralization rates calculated at 224 days of incubation and the organic N content or C/N ratio of wastes. Finally, an objective hierarchical classification based on composition criteria and C and N mineralization led to the definition of six different classes of wastes. It permitted differentiation between four composted wastes and intrinsically different wastes (i.e., cattle manures, pig manures, and poultry manures) which could not be objectively regrouped. It also placed some very different types of waste (solid phase from pig slurry separation, pig manures, and composted pig mixtures) in the same class.     

Soil chemical and microbiological properties in hay production systems: residual effects of contrasting N fertilization of swine lagoon effluent versus ammonium nitrate

This study characterized soil chemical and microbiological properties in hay production systems that received from 0 to 600 kg plant-available N (PAN) ha⁻¹ year⁻¹ from either swine lagoon effluent (SLE) or ammonium nitrate (AN) from 1999 to 2001. The forage systems contained plots planted with bermudagrass (Cynodon dactylon L.) or endophyte-free tall fescue (Festuca arundinaceae Schreb.). In March 2004, the plots were sampled for measurements of a suite of soil chemical and microbiological properties. Nitrogen fertilization rates were significantly correlated with soil pH and K₂SO₄-extractable soil C but not with total soil C, soil C/N ratio, electrical conductivity, or Mehlich-3-extractable nutrients. Soil supplied with SLE had significantly lower Mehlich-3-extractable nutrients than the soil supplied with AN. Two indicators of soil N-supplying capacity (potentially mineralizable N and amino sugar N) varied with plant species and the type of N fertilizer. However, they generally peaked at an application rate of 200 or 400 kg PAN ha⁻¹ year⁻¹. Soil microbial biomass C also peaked at an application rate of 200 or 400 kg PAN ha⁻¹ year⁻¹. Nitrification potential was significantly higher in soil supplied with AN than in the unfertilized control but was similar between SLE-fertilized and unfertilized soils. Our results indicated that an application rate as high as 600 kg PAN ha⁻¹ year⁻¹ did not benefit soil microbial biomass, microbial activity, and N transformation processes in these forage systems.     

Leaching of soil organic carbon and nitrogen in sandy soils after cultivating grass-clover swards

Several studies have focused on the formation and losses of dissolved organic matter in forest systems, whereas a limited number have dealt with this aspect in agricultural soils. The purpose of this study was to estimate the leaching of dissolved organic carbon (DOC) and nitrogen (DON), with focus on the period after cultivating grass-clover swards. Grass-clovers were ploughed in the spring prior to sowing cereals followed by either catch crops or bare soil. The concentrations of DOC and DON decreased with soil depth and ranged at 90-cm soil depth between 7 and 21 mg C L⁻¹ and between 1 and 3 mg N L⁻¹, respectively, in a sandy loam soil, and between 16 and 63 mg C L⁻¹ and between 1 and 10 mg N L⁻¹, respectively, in a coarse sandy soil. The resulting DOC/DON ratios were in the range between 2 and 42, with higher values in the coarse sandy soil than in the sandy loam soil. The total percolation was 218 mm in the sandy loam soil and 596–645 mm in the coarse sandy soil, which resulted in an annual leaching of 22–40 kg DOC ha⁻¹ year⁻¹ and 3–4 kg DON ha⁻¹ year⁻¹ in the sandy loam soil, and 174–310 kg DOC ha⁻¹ year⁻¹ and 10–31 kg DON ha⁻¹ year⁻¹ in the coarse sandy soil. It was shown that higher amounts of DOC were lost by leaching under the catch crops than from bare soil, that losses of DON were higher from bare soil than from soils with catch crops and that DON contributed significantly to the total N loss. Thus, DON needs to be taken into account in N-balance calculations.