Influence of tillage and rotation systems on distribution of organic carbon associated with particle-size fractions in Chernozemic soils of Saskatchewan, Canada

The effects of several dominant tillage and rotation systems on soil organic C content of different particle-size fractions were studied in Chernozemic soils from southwestern and east-central Saskatchewan, Canada. In an Orthic Brown Chernozem in southwestern Saskatchewan, 7 years of no-till cereal–fallow, imposed on a long-term tillage fallow–wheat rotation soil, resulted in 0.1 Mg C ha⁻¹ more organic C mass in the sand + organic matter (OM) fraction of the 0- to 5-cm layer, whereas organic C associated with coarse silt (CS), fine silt (FS), coarse clay, and fine clay of 0- to 5- and 5- to 10-cm layers was less than that of the comparable tilled cereal–fallow system. Conversion of tilled fallow–wheat rotation soil to continuous cropping had a slight effect, whereas the organic C mass in all the size fractions was significantly increased in both 0- to 5- and 5- to 10-cm layers after alfalfa was introduced on tilled fallow–wheat as perennial forage for 10 years. In an Orthic Black Chernozem in east-central Saskatchewan that was cultivated and tilled using a cereal–fallow rotation for 62 years, organic C mass decreased in sand + OM, CS, and FS of 0- to 10-cm depth. Conversion of the tilled cereal–fallow cropland soil back to seeded grassland resulted in significantly more soil organic C in sand + OM fraction after 12 years of grass seed-down. The sand + OM fraction appears to be the size fraction pool initially most sensitive to adoption of management practices that are liable to sequester carbon in the soil.     

The structure of two alluvial soils in Italy after 10 years of conventional and minimum tillage

Micro and macroporosity, pore shape and size distribution, aggregate stability, saturated hydraulic conductivity and crop yield were analysed in alluvial silty loam (Fluventic Eutrochrept) and clay soils (Vertic Eutrochrept) following long-term minimum and conventional tillage. The soil structure attributes were evaluated by characterizing porosity by means of image analysis of soil thin sections prepared from undisturbed soil samples.

The interaggregate microporosity, measured by mercury intrusion porosimetry, increased in the minimally tilled soils, with a particular increase in the storage pores (0.5–50 μm). The amount of elongated transmission pores (50–500 μm) also increased in the minimally tilled soils. The resulting soil structure was more open and more homogeneous, thus allowing better water movement, as confirmed by the greater hydraulic conductivity of the minimally tilled soils. The aggregate stability was less in the conventionally tilled soils and this resulted in a greater tendency to form surface crusts and compacted structure, compared with the minimally tilled soils. The latter tillage practice seemed to maintain, in the long-term, better soil structure conditions and, therefore, maintain favourable conditions for plant growth. In the silt loam, the crop yield did not differ significantly between the two tillage systems, while in the clay soil it decreased in the minimum tilled soil because of problems of seed bed preparation at the higher surface layer water content.     

Economics of tillage systems for spring wheat production in southwestern Saskatchewan (Canada)

The economic performance of continuous wheat (Triticum aestivum L.) and fallow-wheat rotations grown under conventional, minimum- and zero-tillage management practices on silt loam, sandy loam and heavy clay in southwestern Saskatchewan was determined during the relatively dry period of 1982–1988. The costs and returns for each rotation-tillage system were evaluated annually based on 1989–1990 price and cost conditions, and for various other plausible scenarios. Gross returns on silt loam were higher for continuous wheat (average 228 $ ha⁻¹) than for fallow-wheat systems (average 155 $ ha⁻¹). On the sandy loam, gross returns were similar for all cropping systems (average 112 $ ha⁻¹); on the heavy clay, they were higher for fallow-wheat than for continuous wheat (139 versus 119 $ ha⁻¹). Conservation tillage management increased gross returns over that obtained with conventional tillage only in years when growing season temperatures were high and precipitation was poorly distributed, or when the 21-month summerfallow period was droughty. On silt loam, gross returns were significantly lower with conservation tillage in as many as 3 of 7 years. On silt loam, net returns were highest for conventionally tilled continuous wheat when wheat prices were> 175 $ t⁻¹; at lower wheat prices, conventionally tilled fallow-wheat was the most profitable. On the other soils, minimum- and zero-tillage fallow-wheat provided the highest net returns at all wheat prices tested, with minimum tillage being slightly better at low wheat prices, but at these sites conventionally tilled fallow-wheat was not studied. The cost of production was highest for continuous wheat and for zero-tillage management. For fallow-wheat systems, conservation tillage required lower expenditures than conventional tillage for fuel, labor, machine repair and machine overheads; costs for minimum tillage averaged 9 $ ha⁻¹ and for zero tillage 15 $ ha⁻¹ lower on the silt loam. These savings were more than offset by increased herbicide costs which averaged 26 and 64 $ ha⁻¹ higher for minimum-tillage and zero-tillage systems, respectively. We concluded that producers in southwestern Saskatchean who are motivated primarily by short-term profit will find little incentive to adopt conservation tillage systems for spring wheat production, unless they are situated on soils that have already incurred severe soil loss or the soils are highly prone to further erosion losses.     

Long‐term effects of cropped vs. fallow and fertilizer amendments on soil organic matter I. Organic carbon

A long‐term field experiment, conducted since 1962 in Gumpenstein (Austria) on a Dystric Cambisol, was used for the present investigation. We combined a physical fractionation procedure with the determination of natural abundance of ¹³C and FT‐IR spectroscopy to study the influence of fertilizer amendments (organic manure and mineral fertilizers) and management practices (fallow vs. cropped) on changes in organic carbon (OC) associated with different particle‐size fractions. The OC content in bulk soil decreased or was not affected by slurry+straw, PK, and NPK treatments in both fallow and cropped plots after 28 and 38 yr of treatment. However, OC in plots receiving organic manures increased depending on the quality of the organic manures applied. The ranking among the different treatments under both fallow and cropped plots was: animal manure (liquid) > animal manure (solid) > cattle slurry = slurry+straw = PK = NPK. Results showed that the two types of management practices, fallow (non‐tilled) vs. cropped (tilled) had effects on OC concentrations. Comparing the OC contribution of particle‐size fractions to the total OC amount revealed the following ranking: silt > clay > fine sand > coarse sand except in the plots receiving solid or liquid animal manure. Size fractions within treatments showed larger variations of ¹³C abundances than bulk samples between treatments. The natural abundances of ¹³C increased especially in cropped (and tilled) plots. It was shown by cluster analysis that FT‐IR spectra differentiated between the different treatments originating from different land management practices. The present study revealed that below‐ground C deposition by agricultural plants can hardly compensate the C losses due to tillage.     

Soil organic carbon and microbial communities respond to vineyard management

The farming practices in vineyards vary widely, but how does this affect vineyard soils? The main objective of this study was to evaluate the effects of vineyard management practices on soil organic matter and the soil microbial community. To this end, we investigated three adjacent vineyards in the Traisen valley, Austria, of which the soils had developed on the same parent material and under identical environmental/site conditions but were managed differently (esp. tillage, fertilizer application, cover crops) for more than 10 yrs. We found that topsoil bulk density (BD) decreased with increasing tillage intensity, while subsoil BD showed the opposite trend. Soil organic carbon (SOC) stocks in 0–50 cm depth increased from 10 kg m^?2 in an unfertilized and frequently tilled vineyard to 17 kg m^?2 in a regularly fertilized but less intensively tilled vineyard. Topsoil microbial biomass per unit SOC, estimated by the sum of microbial phospholipid fatty acids (PLFAs), followed this trend, albeit not statistically significantly. Principal component analysis of PLFA patterns revealed that the microbial communities were compositionally distinct between different management practices. The fungal PLFA marker 18:2ω6,9 was highest in the vineyard with the lowest amount of extractable Cu (by 0.01 m CaCl₂), and the bacterial‐to‐fungal biomass ratio was positively correlated with extractable Cu. Our results indicate that tillage and fertilizer application of vineyards can strongly affect vineyard soil properties such as BD and SOC stocks and that the application of Cu‐based fungicides may impair soil fungal communities.     

不同耕作年限对耕地土壤质地和有机碳垂直分布的影响

研究不同耕作年限新疆玛纳斯县耕地的土壤颗粒组成、不同土壤颗粒有机碳含量变化特征以及二者的相关关系。选取4种不同耕作年限耕地为研究对象,采集土层0—300cm的土壤样品,采用激光法获取土壤颗粒组成,探讨长期耕作对土壤颗粒组成以及不同土壤颗粒有机碳含量的影响。结果表明:研究区域土壤剖面颗粒组成主要以砂粒(约占21.0%~35.4%)和粉粒(约占46.0%~50.0%)为主,砂粒含量下部明显高于上部,而粉粒含量中部明显低于上部和下部;随着耕作年限增加,剖面上部(0—60cm)土壤质地由粉砂质粘壤土转变为壤土,60—100cm土层土壤质地由粉砂壤土转化为壤土,中部和下部(100—300cm)土壤质地变化较小;土壤有机碳含量随着开垦年限的增加呈现先增加后降低的趋势,增幅达到71.8%,耕作年限越长有机碳增加值趋于平缓;土壤粉粒、砂粒与有机碳含量相关性不高,而粘粒与有机碳含量呈现显著正相关关系,未耕作(Y0)、耕作20a(Y20)、耕作30a(Y30)和耕作50a(Y50)的土壤粘粒与有机碳含量的相关系数(r)范围在0.67*~0.75*,均达到显著性差异(P0.05)。耕作对土壤颗粒组成以及有机碳含量产生一定影响,科学合理的耕作能够提高土壤的固碳能力,对土壤碳循环系统起到良好的保护作用。     

Effect of Continuous Rice–Wheat Rotation on Soil Properties from Four Agro‐ecosystems of Indian Punjab

In Indian Punjab, rice–wheat is a dominant cropping system in four agro‐ecosystems, namely undulating subregion (zone 1), Piedmont alluvial plains (zone 2), central alluvial plains (zone 3), and southwestern alluvial plains (zone 4), varying in rainfall and temperature. Static and temporal variabilities in soil physical and chemical properties prevail because of alluvial parent material, management/tillage operations, and duration of rice–wheat rotation. A detailed survey was undertaken to study the long‐term effect of rice–wheat rotation on soil physical (soil separates, bulk density, modulus of rupture, saturated and unsaturated hydraulic conductivities, soil water content, and suction relations) and chemical (organic carbon, pH, electrical conductivity) properties of different textured soils (sandy clay loam, loam, clay loam, and silty clay loam) in these four zones of Punjab. Soil samples (of 0‐ to 30‐cm depth) from 45 sites were collected during 2006 and were analyzed for physical and chemical properties. The results showed that sand content and pH increased whereas silt and organic carbon decreased significantly from zones 1 to 4. Compared to other textures, significantly greater organic carbon, modulus of rupture, and pH in silty clay loam; greater bulk density in clay loam, and greater saturated hydraulic conductivity in sandy clay loam were observed. Irrespective of zone and soil texture, in the subsurface soil, there was a hard pan at 15–22.5 cm deep, which had high soil bulk density, modulus of rupture, more silt and clay contents (by 3–5%) and less organic carbon and hydraulic conductivity than the surface (0–15 cm) layer. These properties deteriorated with fineness of the soil texture and less organic carbon content. Continuous rice–wheat cropping had a deleterious effect on many soil properties. Many of these soils would benefit from the addition of organic matter, and crop yields may also be affected by the distinct hardpan that exists between 15 and 22.5 cm deep.     

A re‐evaluation of the enriched labile soil organic matter fraction

Identifying ‘functional' pools of soil organic matter and understanding their response to tillage remains elusive. We have studied the effect of tillage on the enriched labile fraction, thought to derive from microbes and having an intermediate turnover time. Four soils, each under three regimes, long‐term arable use without tillage (NT), long‐term arable under conventional tillage (CT), and native vegetation (NV), were separated into four aggregate size classes. Particle size fractions of macro‐ (250–2000 μm) and microaggregates (53–250 μm) were isolated by sonication and sieving. Subsequently, densiometric and chemical analyses were made on fine‐silt‐sized (2–20 μm) particles to isolate and identify the enriched labile fraction. Across soils, the amounts of C and N in the particle size fractions were highly variable and were strongly influenced by mineralogy, specifically by the contents of Fe and Al oxides. This evidence indicates that the fractionation procedure cannot be standardized across soils. In one soil, C associated with fine‐silt‐sized particles derived from macroaggregates was 567 g C m^?2 under NV, 541 g C m^?2 under NT, and 135 g C m^?2 under CT, whereas C associated with fine‐silt‐sized particles derived from microaggregates was 552, 1018, 1302 g C m^?2 in NV, NT and CT, respectively. These and other data indicate that carbon associated with fine‐silt‐sized particles is not significantly affected by tillage. Its location is simply shifted from macroaggregates to microaggregates with increasing tillage intensity. Natural abundance ¹³C analyses indicated that the enriched labile fraction was the oldest fraction isolated from both macro‐ and microaggregates. We conclude that the enriched labile fraction is a ‘passive' pool of soil organic matter in the soil and is not derived from microbes nor sensitive to cultivation.     

TILTH MELLOWING

Effects of weathering action, mainly wetting and drying cycles, on the strength of the clods produced by tillage are studied. Experiments were carried out on sandy loam soils at two sites in South Australia, and on silt loam and clay soils at Wye College, England. It is found that tillage increases the amplitude of soil water content fluctuations. These bigger soil water content fluctuations resulted in a decrease in the clod strength and this in turn modified the size distribution of the clods produced by tillage in the South Australian soils. The decrease in clod strength, as measured by the drop shatter test, was followed by an increase in the proportion of the smaller aggregate size fraction produced by a second implement pass. It is suggested that, for soils in which the increase in the soil water content fluctuations after the first tillage implement pass decreases clod strength, a further implement pass should be delayed for several days. By doing this, the soil can be tilled with minimum energy and cost to produce a good seed bed.     

Carbon and net nitrogen mineralisation in two forest soils amended with different concentrations of biuret

Biuret is a known contaminant of urea fertilisers that might be useful as a slow release N fertiliser for forestry. We studied carbon (C), net nitrogen (N) mineralisation and soil microbial biomass C and N dynamics in two forest soils (a sandy loam and a silt loam) during a 16-week long incubation following application of biuret (C 23.3%, N 40.8%, O 30.0% and H 4.9%) at concentrations of 0, 2, 10, 100 and 1000 mg kg⁻¹ (oven-dried) soil to assess the potential of biuret as a slow-release N fertiliser. Lower concentrations of biuret specifically increased C mineralisation and soil microbial biomass C in the sandy loam soil, but not in the silt loam soil. A significant decrease of microbial biomass C was found in both soils at week 16 after biuret was applied at higher concentrations. C mineralisation declined with duration of incubation in both soils due to decreased C availability. Biuret at concentrations from 10 to 100 mg kg⁻¹ soil had a significantly positive priming effect on soil organic N mineralisation in both soils. The causes for the priming effects were related to the stimulation of microbial growth and activity at an early stage of the incubation and/or the death of microbes at a later stage, which was biuret-concentration-dependent. The patterns in NH₄⁺-N accumulation differed markedly between the two soils. Net N mineralisation and nitrification were much greater in the sandy loam soil than in the silt loam soil. However, the onset of net nitrification was earlier in the silt loam soil. Biuret might be a potential slow-release N source in the silt loam soil.     

Dissolved and Soil Organic Carbon after Long‐Term Conventional and No‐Tillage Sorghum Cropping

Abstract

Distribution of dissolved (DOC) and soil organic carbon (SOC) with depth may indicate soil and crop‐management effects on subsurface soil C sequestration. The objectives of this study were to investigate impacts of conventional tillage (CT), no tillage (NT), and cropping sequence on the depth distribution of DOC, SOC, and total nitrogen (N) for a silty clay loam soil after 20 years of continuous sorghum cropping. Conventional tillage consisted of disking, chiseling, ridging, and residue incorporation into soil, while residues remained on the soil surface for NT. Soil was sampled from six depth intervals ranging from 0 to 105 cm. Tillage effects on DOC and total N were primarily observed at 0–5 cm, whereas cropping sequence effects were observed to 55 cm. Soil organic carbon (C) was higher under NT than CT at 0–5 cm but higher under CT for subsurface soils. Dissolved organic C, SOC, and total N were 37, 36, and 66%, respectively, greater under NT than CT at 0–5 cm, and 171, 659, and 837% greater at 0–5 than 80–105 cm. The DOC decreased with each depth increment and averaged 18% higher under a sorghum–wheat–soybean rotation than a continuous sorghum monoculture. Both SOC and total N were higher for sorghum–wheat–soybean than continuous sorghum from 0–55 cm. Conventional tillage increased SOC and DOC in subsurface soils for intensive crop rotations, indicating that assessment of C in subsurface soils may be important for determining effects of tillage practices and crop rotations on soil C sequestration.     

A simplified modelling approach for quantifying tillage effects on soil carbon stocks

Soil tillage has been shown to affect long‐term changes in soil organic carbon (SOC) content in a number of field experiments. This paper presents a simplified approach for including effects of tillage in models of soil C turnover in the tilled‐soil layer. We used an existing soil organic matter (SOM) model (CN‐SIM) with standard SOC data for a homogeneous tilled layer from four long‐term field experiments with conventionally tilled (CT) and no‐till (NT) treatments. The SOM model was tested on data from long‐term (>10 years) field trials differing in climatic conditions, soil properties, residue management and crop rotations in Australia, Brazil, the USA and Switzerland. The C input for the treatments was estimated using data on crop rotation and residue management. The SOM model was applied for both CT and NT trials without recalibration, but incorporated a ‘tillage factor’ (TF) to scale all decomposition and maintenance parameters in the model. An initial value of TF = 0.57 (parameter uncertainty, PU = 0.15) for NT (with TF set to 1.0 for CT) was used on the basis of a previous study with observations of soil CO₂ respiration. The simulated and observed changes in SOC were then compared using slopes of linear regressions of SOC changes over time. Results showed that the SOM model captured observed changes in SOC content from differences in rotations, N application and crop residue management for conventional tillage. On the basis of SOC change data a mean TF of 0.48 (standard deviation, SD = 0.12) was estimated for NT. The results indicate that (i) the estimated uncertainty of tillage effects on SOC turnover may be smaller than previously thought and (ii) simple scaling of SOM model parameters may be sufficient to capture the effects of soil tillage on SOM turnover in the tilled layer. Scenario analyses showed that the average extra C input needed to compensate for soil tillage was 762 (SD = 351) kg C ha⁻¹ year⁻¹. Climatic conditions (temperature and precipitation) also affected how much extra C was needed, with substantially larger inputs being required for wetter and warmer climates.     

Soil organic carbon and nutrient content in aggregate‐size fractions of a subtropical rice soil under variable tillage

The effects of tillage on soil organic carbon (SOC) and nutrient content of soil aggregates can vary spatially and temporally, and for different soil types and cropping systems. We assessed SOC and nutrient levels within water‐stable aggregates in ridges with no tillage (RNT) and also under conventional tillage (CT) for a subtropical rice soil in order to determine relationships between tillage, cation concentrations and soil organic matter. Surface soil (0–15 cm) was fractionated into aggregate sizes (>4.76 mm, 4.76–2.00 mm, 2.00–1.00 mm, 1.00–0.25 mm, 0.25–0.053 mm, <0.053 mm) under two tillage regimes. Tillage significantly reduced the proportion of macroaggregate fractions (>2.00 mm) and thus aggregate stability was reduced by 35% compared with RNT, indicating that tillage practices led to soil structural change for this subtropical soil. The patterns in SOC, total N, exchangeable Ca²⁺, Mg²⁺ and total exchangeable bases (TEB) were similar between tillage regimes, but concentrations were significantly higher under RNT than CT. This suggests that RNT in subtropical rice soils may be a better way to enhance soil productivity and improve soil C sequestration potential than CT. The highest SOC was in the 1.00–0.25 mm fraction (35.7 and 30.4 mg/kg for RNT and CT, respectively), while the lowest SOC was in microaggregate (<0.025 mm) and silt + clay (<0.053 mm) fractions (19.5 and 15.7 mg/kg for RNT and CT, respectively). Tillage did not influence the patterns in SOC across aggregates but did change the aggregate‐size distribution, indicating that tillage affected soil fertility primarily by changing soil structure.     

Tillage effects on cassava (Manihot esculenta) production and some soil properties

Cassava is traditionally grown on tilled soils. Interest in reduced-tillage systems is increasing in the humid tropics due to erosion problems. A field study was conducted on a sandy clay loam Ultisol to compare cassava performance in three tillage systems effects on soil water and organic carbon content. Tillage treatments were: (1) ploughing, harrowing and ridging (conventional); (2) digger-made holes (minimum); (3) pushing the sharpened end of cassavs cuttigs directly into the soil (no-till). Tillage did not affect total biomass yields in the first year. In the second year, significant differences were obtained in the yield of tops but not of fresh roots. No-till and minimum tillage out-yielded the conventional system by 40% and 23%, respectively, in the yield of tops,. It was apparent that elimination of ploughing did not reduce total biomass yield. Soil moisture contents in no-till and minimum tillage were significantly higher (P = 0.05) than in the conventional-tillage system. Conv organic carbon decresed significantly (P = 0.01) over time in all tillage systems. Conventional tillage gave the highest reduction. Cassava may be grown successfully in reduced-tillage systems in Ultisols of the humid tropics.     

Sulfur nutrition of winter wheat varieties with till and no‐till planting on highly weathered alfisol soils

Abstract

Winter wheat (Triticum aestivum L.) occupies large hectarage and is important in crop rotations on the highly weathered, low organic matter silt loam soils common in southern Illinois and the southern midwest United States region. Sulfur (S) is an essential element with some potential for deficiency, but it is not commonly applied to winter wheat grown on these soils. This study was conducted to determine if S nutrition is limiting winter wheat growth and grain yield. Interactive effects of topdressed fertilizer S (0 and 28 kg S/ha), tillage (disk‐till, DT and no‐till, NT), and wheat variety on plant growth, nutrient concentration, and grain yield were investigated for three crop years on two soils in southern Illinois; Cisne silt loam (fine, montmorillonitic, mesic Mollic Albaqualf), Brownstown site, and Grantsburg silt loam (fine‐silty, mixed, mesic Typic Fragiudalf), Dixon Springs site. Grain yield was unaffected by S application although flag leaf and whole plant S concentrations increased. Lack of yield response to S application was consistent each year on both soils and across all varieties and tillage systems. Equivalent yields were produced with both tillage systems at Brownstown, but slightly lower yield occurred with no‐till at Dixon Springs. Plant S concentrations and soil sulfate levels indicated sufficient S was available from sources other than fertilizer S, including extractable soil S and atmospheric deposition. Wheat variety consistently influenced plant nutrient composition and grain yield more than tillage or application of S fertilizer. If, in the future, wheat grain production, atmospheric S deposition, and extractable soil S remain at levels measured in this study, then S fertilizer applications would not be expected to increase winter wheat grain yield.     

Modelling of sinkage tests in tilled soils for mobility study

The study of the mechanical behaviour of breached surface soils allows the optimization of the running gear of the vehicles for the off-road mobility.The sinkage of the running gear causes a motion resistance which is opposed to the tractive capacity of the vehicle. In a homogeneous soil, the sinkage is predicted by the interpretation of plate sinkage tests. In order to make possible and easier the sinkage prediction of a vehicle going in a tilled soil, the article has for objective to present a method to model pressure–sinkage curve for a tilled soil with the pressure–sinkage curve of the same soil before tillage.The tilled soil is considered as two layers of the same soil whose density is lower for the upper layer than for the sub-base. The two-layered soil behaviour is modelled as the combination of the behaviour of the loose soil layer and the behaviour of the dense soil. The link between these two behaviours is a critical depth defined as the depth of the plate when the layer of soil in a critical density reaches the limit between the two layers.Sinkage tests with circular plates were carried out on four soils chosen to represent the mechanical properties of a range of soils: a sand for frictional soils, a silt for cohesive soils and a silty sand and a sandy loam for cohesive frictional soils predominant in the agricultural soils. The soils were tested in one-layered and two-layered configurations in small and large bins with well-known and controlled soil conditions.A theoretical approach allows the calculation of the critical depth with a deformation process of the soil below the plate. The critical depth depends on the density of the soil, the tillage depth, the diameter of the plate and the angle of friction of the soil.The critical depth allows the modelling of the pressure–sinkage curve for the tilled soils using the one-layered soil data. The comparison with the experimental tests in tilled soil validate the approach.     

Tillage and fertilizing effects on sandy soils. Review and selected results of long‐term experiments at Humboldt‐University Berlin

The Humboldt‐University of Berlin conducts several long‐term field trials designed to assess the effects of tillage methods, crop rotations, organic fertilization, mineral nitrogen, phosphorus, and potassium fertilizers, liming, irrigation, and weather conditions. On silty sand soils shallow ploughing resulted in a distinct accumulation of soil organic matter and phosphorus in the tilled soil layer while potassium and pH values were unaffected. On average shallow ploughing increased yields, with a tendency for higher yields in spring crops and lower yields in winter cereals. Different amounts of organic and mineral fertilizers applied over 30 years resulted in a great differentiation in soil organic matter content. In the following 32 years this variation stayed more or less unchanged, but with an overall reduction in the carbon content. In variants in which phosphate and potassic fertilizers were omitted, 16 kg ha^—1 P and 15 kg ha^—1 K per year were still being mobilized in the soil after 60 years. In treatments with mineral fertilization, the phosphorus is nearly balanced whilst only 60 % of the potassium is withdrawn from the soil. Additional organic fertilizers, given as farm yard manure, led to a nutrient surplus of 19 kg ha^—1 a^—1 P and 99 kg ha^—1 a^—1 K. Omitted liming caused an acidification of the soil to such an extent that crop production became impossible.     

Recovery rate of organic c in organic matter fractions of Grantsburg soils

Abstract

Walkley‐Black method is a simple and rapid method for organic carbon analysis. Because of incomplete oxidation of organic carbon (C), the recovery of organic C is low with this method. Assuming the 77% recovery of organic C with Walkley‐Black method, the results are corrected with a correction factor of 1.30. The objective of this study is to determine the soil organic C recovery rate and appropriate correction factor for Walkley‐Black (wet combustion) method for tilled soils in southern Illinois. Soil samples were collected in 1995 and 1996 from a trial established in southern Illinois on a moderately well drained, Grantsburg (fine‐silty, mixed, mesic Oxyaquic Fragiudalf) soil. Organic C contents with the Leco analyzer (dry combustion) were significantly higher as compared to the Walkley‐Black method in different tillage systems (no‐till, chisel plow and moldboard plow), soil organic matter fractions (whole soil and mineral fraction) and soil depths (0–5 and 5–15 cm). The recovery percentage of organic C was lower than the assumed percentage with the Walkley‐Black method. No significant differences in organic C recovery percentage were found due to differences in tillage systems and depths, whereas the recovery percentage was lower in mineral fraction as compared to the whole soil. The lower organic C recovery percentage was due to the more stable organic C compounds in the mineral fraction. On the basis of these findings, correction factors of 1.35 and 1.41 are proposed for whole soil and mineral organic C analysis with Walkley‐Black method, respectively for tilled Grantsburg and other similar soils in southern Illinois.     

Tillage Effects on Particulate and Mineral‐Associated Organic Matter in Two Tropical Brazilian Soils

Abstract

Two Ferralsols (350 and 600 g kg^?1 clay) from the Brazilian Cerrado Region were evaluated for long‐term effects (5 and 8 years) of no tillage on carbon (C) stocks in particulate (>53 µm) and mineral‐associated (<53 µm) soil organic matter (SOM) fractions. Carbon stocks in particulate SOM increased under no tillage compared with conventional tillage, and the rate was higher in the clayey soil (0.62 Mg C ha^?1 yr^?1) than in the sandy clay loam soil (0.31 Mg C ha^?1 yr^?1). In contrast, the mineral‐associated SOM in the top soil layer (0–20 cm) was not affected by tillage system. Sequestration of atmospheric C in tropical no‐tillage soils seems to be due to accumulation of C in labile SOM fractions, with highest rates in clayey soils probably due to physical protection.     

Tillage and amendment effects on soil carbon and nitrogen mineralization and phosphorus release

The influence of tillage and nutrient amendment management on nutrient cycling processes in soil have substantial implications for environmentally sound practices regarding their use. The effects of 2 years of tillage and soil amendment regimes on the concentrations of soil organic matter variables (carbon (C), nitrogen (N) and phosphorus (P)) and C and N mineralization and P release were determined for a Dothan fine-sandy loam soil in southeastern Alabama. Tillage systems investigated were strip (or conservation) and conventional tillage with various soil nutrient amendments that included no amendment, mineral fertilizer, and poultry waste (broiler litter). Surface soil (0–10 cm depth increment) organic matter variables were determined for all tillage/amendment combinations. Carbon and N mineralization and P release were determined on surface soils for each field treatment combination in a long-term laboratory incubation. Soil organic P concentration was 60% greater in soils that had been conventionally tilled, as compared with strip-tilled, both prior to and following laboratory incubation. Carbon and N mineralization results reflected the effects of prior tillage amendment regime, where soils maintained under strip-till/broiler litter mineralized the greatest amount of C and N. Determination of relative N mineralization indicated that strip tillage had promoted a more readily mineralizable pool of N (6.1%) than with conventional till (4.2%); broiler litter amendments had a larger labile N fraction (6.7%) than was found in soils receiving either mineral fertilizer (4.1%) or no amendment (4.7%). Tillage also affected P release measured during the incubation study, where approximately 20% more inorganic P was released from strip-tilled soils than from those maintained under conventional tillage. Greater P release was observed for amended soils as compared with soils where no amendment was applied. Results from this study indicate that relatively short-term tillage and amendment management can significantly impact C, N, and P transformations and transfers within soil organic matter of a southeastern US soil.