Changes of metal forms by organic amendments to Hawaii soils

Abstract

Forms of metals in soils control their availability to plants and animals and affect the environment differently. To evaluate shifts of metal forms as affected by organic amendments, a sequential extraction procedure was used to fractionate calcium (Ca), iron (Fe), magnesium (Mg), manganese (Mn), and zinc (Zn) in two Hawaii soils amended with three organic wastes. The designated forms are water‐soluble, exchangeable, sorbed, organically bound, carbonate, and residual fractions. The soils, a Mollisol (Waimanalo series) and an Ultisol (Paaloa series), were incubated at 25°C±2°C at field capacity with either chicken manure, sewage sludge, or green manure (cowpea leaves) at 0, 5, and 20 Mg#lbha^‐1 for one or five months. Organically bound metals decreased with time because of organic matter decomposition. Iron was mostly residual, but water‐soluble Fe also increased in the acid Paaloa soil. Unlike Fe, most forms of Ca and Mg were transformed to the exchangeable form in 5 months. There was no significant change of Mn forms during the 5‐month incubation. Virtually all organically bound Zn shifted to carbonate and residual forms in the neutral Mollisol (pH 6.2), but shifted to carbonate and exchangeable forms in the acid Ultisol (pH 4.5). The solubilities and exchangeabilities of the five metals in the two soils treated with sewage sludge were not significantly different from those treated with cowpea green manure or chicken manure during the 5‐month incubation. The results suggest that the additions of sewage sludge, chicken manure, or cowpea green manure to Hawaii soils at 20 Mg#lbha^‐1 do not have environmentally significant impacts in terms of Ca, Mg, Fe, Mn, and Zn. On the other hand, the amendments may decrease Ca and Mg deficiencies in highly weathered, nutrient‐poor soils such as Ultisols and Oxisols of the tropics.     

Organic amendments differ in their effect on microbial biomass and activity and on P pools in alkaline soils

Organic amendments could be used as alternative to inorganic P fertilisers, but a clear understanding of the relationship among type of P amendment, microbial activity and changes in soil P fractions is required to optimise their use. Two P-deficient soils were amended with farmyard manure (FYM), poultry litter (PL) and biogenic waste compost (BWC) at 10 g?dw?kg^?1 soil and incubated for 72 days. Soil samples were collected at days 0, 14, 28, 56 and 72 and analysed for microbial biomass C, N and P, 0.5 M NaHCO₃ extractable P and activity of dehydrogenase and alkaline phosphomonoesterase. Soil P fractions were sequentially extracted in soil samples collected at days 0 and 72. All three amendments increased cumulative CO₂ release, microbial biomass C, N and P and activity of dehydrogenase and alkaline phosphomonoesterase compared to unamended soils. The increase in microbial biomass C and N was highest with PL, whereas the greatest increase in microbial biomass P was induced with FYM. All three biomass indices showed the same temporal pattern, with the highest values on day 14 and the lowest on day 72. All amendments increased 0.5 M NaHCO₃ extractable P concentrations with the smallest increase with BWC and the greatest with FYM, although more P was added with PL than with FYM. Available P concentrations decreased over time in the amended soils. Organic amendments increased the concentration of the labile P pools (resin and NaHCO₃-P) and of NaOH-P, but had little effect on the concentrations of acid-soluble P pools and residual P except for increasing the concentration of organic P in the concentrated HCl pool. Resin P and NaHCO₃-P_i pools decreased over time whereas NaOH-P_i and all organic P pools increased. It is concluded that organic amendments can provide P to plants and can stimulate the build-up of organic P forms in soils which may provide a long-term slow-release P source for plants and soil organisms.     

Detectability of degradable organic matter in agricultural soils by thermogravimetry

Sustainable agricultural land use requires an assessment of degradable soil organic matter (SOM) because of its key function for soil fertility and plant nutrition. Such an assessment for practical land use should consider transformation processes of SOM and its sources of different origin. In this study, we combined a 120‐day incubation experiment with thermal decay dynamics of agricultural soils altered by added organic amendments. The aim was to determine the abilities and limits of thermal analysis as a rapid approach revealing differences in the degradability of SOM. The carried out experiments based on two independent sampling sets. The first sample set consisted of soil samples taken from non‐fertilized plots of three German long‐term agricultural field experiments (LTAEs), then artificially mixed with straw, farmyard manure, sheep faeces, and charcoal equal to 60 Mg ha^?1 under laboratory conditions. The second sample set based on soil samples of different treatments (e.g., crop type, fertilization, cultivation) in LTAEs at Bad Lauchstädt and Müncheberg, Germany. Before and after the incubation experiment, thermal mass losses (TML) at selected temperatures were determined by thermogravimetry indicating the degradability of organic amendments mixed in soils. The results confirmed different microbial degradability of organic amendments and SOM under laboratory conditions. Thermal decay dynamics revealed incubation‐induced changes in the artificial soil mixtures primarily at TML around 300°C in the case of applied straw and sheep faeces, whereas farmyard manure showed mainly changes in TML around 450°C. Charcoal did not show significant degradation during incubation, which was confirmed by TML. Detailed analyses of the artificial soil mixtures revealed close correlations between CO₂‐C evolution during incubation and changes in TML at 300°C with R² > 0.96. Results of the soils from LTAEs showed similar incubation‐induced changes in thermal decay dynamics for fresh plant residues and farmyard manure. We conclude that the practical assessment of SOM could be facilitated by thermal decay dynamics if modified sample preparation and evaluation algorithms are used beyond traditional peak analysis.     

Creation of Technosols to Decrease Metal Availability in Pyritic Tailings with Addition of Biochar and Marble Waste

Creation of Technosols with the use of different materials is a sustainable strategy to reclaim mine tailings and reduce metal mobility. For this purpose, a short‐term incubation experiment was designed with biochars derived from pig manure, crop residues and municipal solid waste added to tailings alone or in combination with marble waste. We aimed to assess the efficiency of the different amendments to decrease Cd, Pb and Zn availability in the Technosols and the fractions where metals were retained. Results showed that all amendments reduced metal mobility, directly related to increases in pH. Those materials with higher content of carbonates were more effective to immobilize metals (~99%). Municipal solid waste was highly effective to decrease metal mobility owing to the higher carbonate content, but addition of marble waste was needed to enhance metal immobilization with pig manure and crop residue. Decreases in Cd mobility were related to retention by the carbonate, Mn/Fe oxides and oxidizable (organic compounds) fractions. Decreases in Pb mobility were related to retention in the Mn/Fe oxides and residual fractions, while decreases in Zn mobility were related to retention in Mn/Fe oxides and oxidizable fractions. Association of Zn and Pb with the oxidizable fraction was also related to the recalcitrance of the organic compounds and so dependent on biochar type. Scanning electron microscopy coupled with energy dispersive X‐ray showed that biochar showed great affinity to interact with iron oxides, calcium sulfates and phyllosilicates. Copyright © 2017 John Wiley & Sons, Ltd.     

Release Kinetics of Some Nutrients from a Sandy Loam Soil Treated with Different Organic Amendments

ABSTRACT

An incubation study was undertaken to examine the periodic release of some macronutrients and micronutrients in a sandy loam treated with different organic amendments (farmyard manure, mushroom compost, poultry manure, vermicompost, biogas slurry, and biochar of Lantana weed) added @ 15 t ha^?1 for 120 d through entrapment of released nutrients on ion exchange resins. Among organic amendments, the highest total contents were recorded for Ca, Mg, and S in farmyard manure, for K, Fe, and Mn in mushroom compost, for P, Zn, and Cu in biogas slurry, for B in biochar. The highest average release was recorded for P, Zn, Mn, and B from poultry manure, for Cu from biogas slurry, for Fe from vermicompost, for Ca, Mg, and S from mushroom compost, and for K from farmyard manure. The kinetics of mineralization and release of these nutrients conformed well to the zero-order kinetics and also to a power function equation. The initial release amount and release rate coefficient estimated by the power function equations were correlated significantly to the general properties of organic amendments and also to the type of C species present in organic amendment. Organic amendments having relatively higher content of water soluble C or fulvic or humic acids are likely to release nutrients through an early mineralization/solubilization from soil reserve.     

Sulfur mineralization in two soils amended with organic manures,crop residues,and green manures

The mineralization of sulfur (S) was investigated in a Vertisol and an Inceptisol amended with organic manures, green manures, and crop residues. Field‐moist soils amended with 10 g kg^—1 of organic materials were mixed with glass beads, placed in pyrex leaching tubes, leached with 0.01 M CaCl₂ to remove the mineral S and incubated at 30 °C. The leachates were collected every fortnight for 16 weeks and analyzed for SO₄‐S. The amount of S mineralized in control and in manure‐amended soils was highest in the first week and decreased steadily thereafter. The total S mineralized in amended soils varied considerably depending on the type of organic materials incorporated and soil used. The cumulative amounts of S mineralized in amended soils ranged from 6.98 mg S (kg soil)^—1 in Inceptisol amended with wheat straw to 34.38 mg S (kg soil)^—1 in Vertisol amended with farmyard manure (FYM). Expressed as a percentage of the S added to soils, the S mineralized was higher in FYM treated soils (63.5 to 67.3 %) as compared to poultry manure amended soils (60.5 to 62.3 %). Similarly the percentage of S mineralization from subabul (Leucaena leucocephala) loppings was higher (53.6 to 55.5 %) than that from gliricidia (Gliricidia sepium) loppings (50.3 to 51.1 %). Regression analysis clearly indicated the dependence of S mineralization on the C : S ratio of the organic materials added to soil. The addition of organic amendments resulted in net immobilization of S when the C : S ratio was above 290:1 in Vertisol and 349:1 in Inceptisol. The mineralizable S pool (S_o) and first‐order rate constant (k) varied considerably among the different types of organic materials added and soil. The S_o values of FYM treated soils were higher than in subabul, gliricidia, and poultry manure treated soils.     

Distribution of phosphorus in size fractions of sandy soils with different fertilization histories

A major challenge in sustainable crop management is to ensure adequate P supply for crops, while minimizing losses of P that could negatively impact water quality. The objective of the present study was to investigate the effects of long‐term applications of different levels of mineral fertilizers and farmyard manure on (1) the availability of P, (2) the relationship between soil C, N, and P, and (3) the distribution of inorganic and organic P in size fractions obtained by wet sieving. Soil samples were taken from the top 20 cm of a long‐term (29 y) fertilization trial on a sandy Cambisol near Darmstadt, SW Germany. Plant‐available P, determined with the CAL method, was little affected by fertilization treatment (p < 0.05) and was low to optimal. The concentration of inorganic and organic P extracted with a NaOH‐EDTA solution (P_NaOH‐EDTA) averaged about 350 mg (kg dry soil)^–1, with 42% being in the organic form (P_o). Manure application tended to increase soil C, N, and P_o concentrations by 8%, 9%, and 5.6%, respectively. Across all treatments, the C : N : P_o ratio was 100 : 9.5 : 2 and was not significantly affected by the fertilization treatments. Aggregate formation was weak due to the low clay and organic‐matter content of the soil, and the fractions > 53 μm consisted predominantly of sand grains. The different fertilization treatments had little effect on the distribution of size fractions and their C, N, and P contents. In the fractions > 53 μm, P_NaOH‐EDTA ranged between 200 and 300 mg kg^–1, while it reached 1260 mg kg^–1 in the fraction < 53 μm. Less than one third of P_NaOH‐EDTA was present as P_o in the fractions > 53 μm, while P_o accounted for 70% of P_NaOH‐EDTA in the smallest fraction (< 53 μm). Therefore, 16% and 28% of P_NaOH‐EDTA and P_o, respectively, were associated with the smallest fraction, even though this fraction accounted for < 5% of the soil mass. Therefore, runoff may cause higher P losses than the soil P content suggests in this sandy soil with a weak aggregate formation. Overall, the results indicate that manure and mineral fertilizer had similar effects on soil P fractions.     

Effect of Organic Residues and Their Derived Biochars on the Zinc and Copper Chemical Fractions and Some Chemical Properties of a Calcareous Soil

ABSTRACT

Addition of more resistant organic materials, such as biochars, to soils not only enhances soil C sequestration but also can also benefit soil fertility. The aim of this study was to investigate the effect of two organic materials (sheep manure and vermicompost) and their biochars produced at two pyrolysis temperatures (300 and 500°C) applied at 5% (w/w) on the chemical fractions of Zn and Cu and some chemical characteristics of an unpolluted, light textured calcareous soil. Addition of the raw organic materials and their-derived biochars significantly enhanced plant available K, P, and Zn but significantly decreased plant available Cu in the soil. Sheep manure biochar produced at 300°C was most effective at increasing plant available P (13-fold) and K (1.9 fold) likely due to formation of more soluble forms of P and K compared to raw material or biochar produced at higher temperature (500°C). Whereas, raw vermicompost and sheep manure were most effective at enhancing plant available Zn, by increasing water soluble and exchangeable Zn fraction likely due to organic complexation. All amendments, especially biochars produced at 300°C reduced water soluble and exchangeable Cu mainly attributed to increased soil P availability. The results of this study showed that in the short-term, addition of the low-temperature biochars was best for enhancing soil P and K availability, but concomitantly reduced Cu availability the most, whereas, addition of the raw organic materials was better for enhancing Zn availability compared to the biochars.     

Fractionation of copper and cadmium and their binding with soil organic matter in a contaminated soil amended with organic materials

Purpose  

The contamination of agricultural soils by heavy metals is a worldwide problem. Organic amendments can be used for the immobilization and binding of heavy metal ions in soils by complexation, adsorption, and precipitation. A field trial was carried out to evaluate the influence of some low-cost organic materials such as rice straw (RS), green manure (GM), and pig manure (PM) on the distribution of Cu and Cd and the retention of these metals by organic matter fractions in heavy metal-polluted soils.     

Phosphorus characterization of manure composts and combined organic fertilizers by a sequential‐fractionation method

Characterization of the forms of phosphorus (P) in organic soil amendments was conducted by sequential P fractionation. More than 60% of total P was inorganic P (P_i). The major P_i forms in the cattle‐manure composts were NaHCO₃‐ and HCl‐extractable P fractions. HCl‐extractable P_i was the predominant P form and a considerable proportion of the total P was present in the HCl‐extractable organic P fraction in the poultry manure composts and combined organic fertilizers.     

Influence of fertilization and organic amendments on organic‐carbon fractions in Heilu soil on the loess plateau of China

The influence of fertilization on organic‐carbon fractions separated by density and particle size in Heilu soil (Calcic Kastanozems, FAO) was investigated in a 20‐year (1979–1999) long‐term experiment on the Loess Plateau of China. Compared to an unfertilized treatment, N application alone did not increase total organic carbon (TOC) and its fractions of density and particle size. However, the treatment of N + P fertilization significantly increased salty‐solution–soluble organic carbon (SSOC), microbial biomass C (MB‐C), and organic C associated with fine silt. When manure was applied alone and in combination with N and P fertilizer, the light fraction of organic C (LFOC), SSOC, and MB‐C were increased significantly, and the TOC was as high as that of a native Heilu soil. Organic C associated with different particle‐size fractions was also increased significantly, and the allocation of C among the fractions was altered: the proportions of C in sand (>50 μm), coarse‐silt (20–50 μm), and fine‐clay (<0.2 μm) fractions were increased whereas fine‐silt (2–20 μm) and coarse‐clay (0.2–2 μm) fractions were decreased. It is concluded that N fertilizer alone is not capable of restoring organic‐matter content in the Heilu soils of the Loess Plateau and that C‐containing material like manure and straw is necessary to produce significant increase in soil organic carbon in these soils.     

Effects of Organic Amendments on Soil Physical Attributes and Aggregate-Associated Phosphorus Under Long-Term Rice-Wheat Cropping

The quantification of phosphorus(P) in bulk soil and P distribution in different size fractions of water-stable aggregates(WSAs)are important for assessing potential P loss through runoff. We evaluated available and total P distribution within WSAs of a sitty clay to clay soil in a long-term fertility experiment of a rice-wheat cropping system in India. Surface soil samples were collected from seven plots amended with NPK fertilizers in combination with or without organic amendments, farmyard manure(FYM), green manure(GM), and paddy straw(PS). The plot with no NPK fertilizers or organic amendments was set as a control. The soil samples were separated by wet sieving into four soil aggregate size fractions: large macroaggregates( 2.0 mm), small macroaggregates(0.25–2.0 mm), fine microaggregates(0.05–0.25 mm), and a silt + clay-sized fraction( 0.05 mm). Structural indices were higher in the soil receiving organic amendments than in the soil receiving inorganic fertilizer alone. Organically amended soil had a higher proportion of stable macroaggregates than the control and the soil receiving inorganic fertilizer alone, which were rich in microaggregates. Total and available P contents within WSAs were inversely related to the aggregate size, irrespective of treatment. The distribution of available and total P in the soil aggregate size fraction was as follows: silt + clay-size fraction small macroaggregates fine microaggregates large macroaggregates. Within a size class, aggregate-associated available and total P contents in the organically amended soil were in the following order: FYM PS ≥ GM. The available P content of the microaggregates( 0.25 mm) was 8-to 10-times higher than that of the macroaggregates( 0.25 mm), and the total P content of the microaggregates was 4-to 5-times higher than that of the macroaggregates. Cultivation without organic amendments resulted in more microaggregates that could be checked by the application of organic amendments such as FYM and GM, which increased the proportion of water-stable macroaggregates by consolidating microaggregates into macroaggregates.     

Contribution of organic amendments to soil organic matter detected by thermogravimetry

Sustainable soil management requires reliable and accurate monitoring of changes in soil organic matter (SOM). However, despite the development of improved analytical techniques during the last decades, there are still limits in the detection of small changes in soil organic carbon content and SOM composition. This study focused on the detection of such changes under laboratory conditions by adding different organic amendments to soils. The model experiments consisted of artificially mixing soil samples from non‐fertilized plots of three German long‐term agricultural experiments in Bad Lauchstädt (silty loam), Grossbeeren (silty sand), and Müncheberg (loamy sand) with straw, farmyard manure, sheep faeces, and charcoal in quantities from 3 to 180 t ha^?1 each. In these mixtures we determined the organic carbon contents by elemental analysis and by thermal mass losses (TML) determined by thermogravimetry. The results confirmed the higher reliability of elemental analysis compared to TML for organic carbon content determination. The sensitivity of both methods was not sufficient to detect the changes in organic carbon content caused by small quantities of organic amendments (3 t ha^?1 or 0.1–0.4 g C kg^?1 soil). In the case of elemental analysis, the detectability of changes in carbon content increased with quantities of added amendments, but the method could not distinguish different types of organic amendments. On the contrary, the based on analysis of degradation temperatures, the TML allowed this discrimination together with their quantitative analysis. For example, added charcoal was not visible in TML from 320 to 330°C, which is used for carbon content determination. However, increasing quantities of charcoal were reflected in a higher TML around 520°C. Furthermore, differences between measured (with TML_110–550) and predicted mass loss on ignition using both organic carbon (with TML₃₃₀) and clay contents (with TML₁₄₀) were confirmed as a suitable indicator for detection of organic amendments in different types of soils. We conclude that thermogravimetry enables the sensitive detection of organic fertilizers and organic amendments in soils under arable land use.     

Soil enzyme activities,microbial community composition and function after 47 years of continuous green manuring

Green manuring practices can influence soil microbial community composition and function and there is a need to investigate the influence compared with other types of organic amendment. This study reports long-term effects of green manure amendments on soil microbial properties, based on a field experiment started in 1956. In the experiment, various organic amendments, including green manure, have been applied at a rate of 4 t C ha⁻¹ every second year. Phospholipid fatty acid analysis (PLFA) indicated that the biomass of bacteria, fungi and total microbial biomass, but not arbuscular mycorrhizal (AM) fungi, generally increased due to green manuring compared with soils receiving no organic amendments. Some differences in abundance of different microbial groups were also found compared with other organic amendments (farmyard manure and sawdust) such as a higher fungal biomass and consequently a higher fungal/bacterial ratio compared with amendment with farmyard manure. The microbial community composition (PLFA profile) in the green manure treatment differed from the other treatments, but there was no effect on microbial substrate-utilization potential, determined using the Biolog EcoPlate. Protease and arylsulphatase activities in the green manure treatment were comparable to a mineral fertilized treatment receiving no additional C, whereas acid phosphatase activity increased. It can be concluded that green manuring had a beneficial impact on soil microbial properties, but differed in some aspects to other organic amendments which might be attributed to differences in quality of the amendments.     

Simulation of net N immobilisation and mineralisation in substrate-amended soils by the NCSOIL computer model

 The capability of the NCSOIL computer model to simulate the effects of residue fractions on mineralisation-immobilisation turnover was evaluated. Heterogeneous organic substrates were represented in the model by three Van Soest pools, decomposing at different rates. Dried and ground wheat straw, sunflower stalks, wheat stubble and sheep manure (5.22 g kg^–1 soil) were respectively added to a Chromic Calcixerert and aerobically incubated for 224 days at 22±2  °C and 75% field capacity. The CO₂ evolution rates peaked shortly after the C amendments were added, with the highest rate in the sunflower- stalk-amended soils. The addition of organic substrates induced rapid N immobilisation. Net mineralisation was detected earliest in the sunflower-stalk treatment (day 14), while soils with the other amendments showed no net N mineralisation until day 52. The NCSOIL model was calibrated for this soil with CO₂ and inorganic N data from the control soil, yielding a χ² value of 0.011. The overestimation by the model of the C mineralisation data in the case of C-amended soils clearly showed that the concept of three Van Soest pools, decomposing independently at a specific rate constant, is not valid. A retardation factor, that was related to the lignin content of the decomposing material, was introduced into the model. After its introduction the model satisfactorily simulated the C mineralisation rates. However, for all plant residues, N mineralisation was underestimated towards the end of the incubation period. In the case of the soil amended with sheep manure, there was a large discrepancy between simulated and experimental N mineralisation-immobilisation kinetics, suggesting a different allocation of N in animal manure to N-containing fractions compared to that of plant residues. The results indicated that a N fractionation procedure for organic residues should be tested and incorporated into the model. Received: 9 January 1998     

Permanent–soil monitoring sites for documentation of soil‐fertility development after changing from conventional to organic farming

For monitoring soil fertility after changing farm management from highly conventional to organic farming on the newly established research farm of Kassel University, two permanent–soil monitoring sites were installed in 1999. Representative locations for installing the permanent–soil monitoring sites were selected using geographical information systems (GIS), based on available data from geology, topography, soil taxation, land use, and intensive auger‐borehole records and analysis with a very high spatial resolution of data. The soils are represented by a Luvisol derived from loess and a Vertisol developed from claystone. The soil properties of the two monitoring sites measured immediately after changing to organic farming showed high contents of extractable nutrients as a result of the former intensive fertilization practice during conventional farm management. The microbial soil properties of the two monitoring sites were in the medium range of regional soils. A first evaluation of the development of soil properties was done after 5 y of monitoring. The soil organic‐matter content increased slightly after grass‐clover and after application of farmyard manure. The amounts of K and P decreased clearly at the loess site without application of farmyard manure. At the clay site, the unique application of farmyard manure led to increasing contents of extractable K and P in the top soil. The variation of soil properties increased clearly after perennial crops like grass‐clover and in years after application of farmyard manure.     

Retention of copper by a calcareous soil and its textural fractions: influence of amendment with two agroindustrial residues

Metal availability in soils is strongly related with sorption processes and the possible association of the metal ions with a particular particle-size fraction. Therefore, studies of metal retention by a soil will be aided if retention by different size fractions is also studied. Sorption of copper on a calcareous soil and its textural fractions was studied in batch assays. The soil was amended over 3 years with two agroindustrial residues, a composted olive mill sludge and vinasse. Sorption of Cu on the calcareous soil was very large (110 mmol kg⁻¹) and was enhanced by both amendments. Metal retention by the clay fraction of the unamended soil was less than that of the whole soil, but increased dramatically after amendment with olive mill sludge. This was caused by the larger calcite content in this fraction as well as the increase in organic matter content. The amount of Cu sorbed was very large in the silt fraction, again because of the carbonate content of this fraction (300–460 g kg⁻¹). Copper sorption decreased dramatically after removal of carbonate. Copper retention tended to be enhanced by organic amendments. This was particularly evident in the silt fraction, as a consequence of the organic matter accumulation in this fraction.
Copper sorption on the calcareous soil and its silt fractions (unamended and amended) was irreversible. By contrast, desorption was measurable from all the carbonate-free samples (both whole soil and textural fractions), although in all cases a large hysteresis was observed. We conclude that carbonate was the main component responsible for the lack of reversibility.     

Long-term management impacts on soil C, N and physical fertility: Part I: Broadbalk experiment

For many centuries manure application to the soil has been common practice. Organic amendments and fertiliser applications can increase crop yields and soil organic matter (SOM). However, the long-term impacts on soil physical fertility are often neglected. This study was carried out on the Broadbalk Wheat Experiment at Rothamsted, UK, established in 1843 on an Aquic/Typic Paleudalf soil. Application of farmyard manure (FYM), N fertiliser and wheat straw on total organic C (C_T), labile C (C_L) and non-labile C (C_NL), total N (N_T), mean weight diameter (MWD) and unsaturated hydraulic conductivity (K_unsat) were studied on wheat (Triticum aestivum) and adjacent woodland and pasture areas. Manure additions, N fertiliser and straw incorporation increased all C fractions, particularly the C_L fraction. The addition of 35 t ha⁻¹ year⁻¹ of FYM increased C_T to 2.5 times that of the control (no fertiliser) treatment and C_L to 5 times that of the control. With highest N application and straw returned, C_T increased by 1.3 times and C_L by 1.5 times that of the control treatment. There were linear relationships between rate of N fertiliser applied and all C fractions, with the rate of increase almost double with straw than straw removed. Manure application improved MWD, as did high N fertiliser additions with straw returned. Application of N fertiliser only increased MWD and K_unsat (at 10 mm tension) if straw was returned, while the addition of manure resulted in decreased K_unsat. The highest K_unsat rate was on the high N fertiliser, straw returned treatments. The uncropped areas all had high soil structural stability. Similar relationships occurred between all C fractions and N_T and MWD for the high C soils, but relationships were much stronger with C_L than the other C fractions in the low C soils. These results showed that soils with low C concentration are more reliant on C_L for structural stability.     

Phosphorus forms and enzymatic hydrolyzability of organic phosphorus in soils after 30 years of organic and conventional farming

Lower P‐input levels in organic than conventional farming can decrease soil total and available P, which can potentially be resupplied from soil organic P. We studied the effect of 30 y of conventional and organic farming on soil P forms, focussing especially on organic P. Soil samples (0–20 cm) were taken in a field experiment with a nonfertilized control, two organic systems receiving P inputs as animal manure, and two conventional systems receiving only mineral P or mineral P and manure. Soils were analyzed for total, inorganic, organic, and microbial P, by sequential P fractionation and by enzyme additions to alkaline soil extracts. Samples taken prior to starting the experiment were also analyzed. Average annual P balances ranged from –20 to +5 kg ha^–1. For systems with a negative balance, labile and moderately labile inorganic P fractions decreased, while organic and stable inorganic P fractions were hardly affected. Similar quantities and proportions of organic P extracted with NaOH‐EDTA were hydrolyzed in all soils after addition of an acid phosphatase, a nuclease, and a phytase, and enzyme‐stable organic P was also similar among soils. Thus, neither sequential fractionation nor enzyme addition to alkaline soil extracts showed an effect of the type of applied P (manure vs. mineral) on organic P, suggesting that organic P from manure has largely been mineralized. Thus far, we have no indication that the greater microbial activity of the organic systems resulted in a use of stable P forms.     

Effect of organic manure on organic phosphorus fractions in two paddy soils

We investigated the transformation of the organic P fractions from organic manure in two paddy soils (Ultisol, Entisol) and the influence of organic manure or cellulose on organic P under anaerobic conditions. The results obtained from the P fractionation experiment indicated that during the incubation labile and moderately labile organic P fractions increased in the Ultisol and decreased in the Entisol, which might be related to the difference in the organic matter content of both soils. Immediately after the application of organic manure, a large part of labile and moderately labile organic P supplied with the manure was transformed into moderately resistant organic P, possibly Ca- or Mg-inositol P were transformed into Fe-inositol P. During anaerobic incubation, the labile forms of organic P in the soils treated with organic manure were increased along with the incubation period in the first 4 weeks. The change in the moderately labile fraction was dramatic. It increased sharply in the first 2 weeks, then decreased, which was more pronounced in the soils treated with pig faeces. The moderately resistant fraction decreased during the whole incubation period. This indicated that under anaerobic conditions, the moderately resistant fraction can be transformed into labile and moderately labile organic P fractions, perhaps as Fe³⁺-inositol P is reduced to Fe⁺²-inositol P. Cellulose as an organic substrate had an increasing effect on organic P, especially when it was combined with inorganic P. Therefore, it is suggested that the application of inorganic P fertilizer combined with organic manure may be an effective way of protecting inorganic P against intensive sorption in soils.