Manuring and rotation effects on soil organic carbon concentration for different aggregate size fractions on two soils in northeastern Ohio, USA

Soil carbon (C) sequestration is important to the mitigation of increasing atmospheric concentration of CO₂. This study was conducted to assess soil aggregation and C concentration under different management practices. The effects of crop rotation, manure application and tillage were investigated for 0–5 and 5–10 cm depths on two silt loam soils (fine-loamy, mixed, active, mesic Aquic Fragiudalfs and fine-loamy, mixed, active, mesic Aeric Fragiadalf) in Geauga and Stark Counties, respectively, in northeastern Ohio, USA. Wet sieve analysis and gravity fractionation techniques were used to separate samples in aggregate and particle size groups, respectively. In the Stark County farms water stable aggregate (WSA) is higher in wooded (W) controls (WSA = 94.8%) than in cultivated soils with poultry manure (PM, 78.7%) and with chemical fertilizers (CF, 79.0%). Manure applications did not increase aggregation compared to unmanured soils. The C concentrations (%) within aggregates (C_agg) are higher in W than in cultivated soils (W = 5.82, PM = 2.11, CF = 1.96). Soil C (%) is enriched in the clay (W = 9.87, PM = 4.17, CF = 4.21) compared to silt (4.26, 1.04 and 0.98, respectively) and sand (0.93, 0.14 and 0.32, respectively) fractions. In the Geauga County farm, continuous corn (CC) with conventional tillage has lower WSA (83.1%) than soils with rotations (R) (93.9%), dairy manure (DM) application (93.2%) and no-till (NT) (91.1%). The C concentrations within macroaggregates (C_agg) were higher in W soils (4.84%) than in cultivated soils (ranging from 2.65 to 1.75%). The C (%) is enriched in clay (W = 8.56, CC = 4.18, R = 5.17, DM = 5.73, NT = 4.67) compared to silt (W = 2.35, CC = 0.90, R = 0.96, DM = 1.57, NT = 1.06) and sand (W = 0.44, CC = 0.33, R = 0.13, DM = 0.41, NT = 0.18). Cultivation decreased C concentration whereas reduced tillage, rotation and manure enhanced C concentration in soil.     

Soil erosion and carbon dynamics

Accelerated erosion involves preferential removal of soil organic carbon (SOC) because it is concentrated in vicinity of the soil surface and has lower density than the mineral fraction. The SOC transported by water runoff is redistributed over the landscape and deposited in depressional sites where it is buried along with the sediments. However, the fate of the SOC transported, redistributed and deposited by erosional processes is a subject of intense debate. Sedimentologists argue that SOC buried with sediments is physically protected, and that depleted in the eroded soil is replaced through biomass production. Thus, they argue that the erosion–sedimentation process leads to globally net SOC sequestration of 0.6–1.5 Gt C/year. In contrast, soil scientists argue that: (i) a large portion of the SOC transported by water runoff comprises labile fraction, (ii) breakdown of aggregation by raindrop impact and shearing force of runoff accentuates mineralization of the previously protected organic matter, and (iii) the SOC within the plow zone at the depositional sites may be subject to rapid mineralization, along with methanogenesis and denitrification under anaerobic environment. Whereas, tillage erosion may also cause burial of some SOC, increase in soil erosion and emission of CO₂ from fossil fuel combustion are net sources of atmospheric CO₂. Soil scientists argue that soil erosion may be a net source of atmospheric CO₂ with emission of 1 Gt C/year. It is thus important to understand the fate of eroded SOC by measuring and monitoring SOC pool in eroded landscape as influenced by intensity and frequency of tillage operations and cropping systems.     

Tillage and mulching effects on physical properties of a tropical Alfisol

The mechanization of field operations like seeding, spraying and harvesting in continuous zero-tillage may lead to a severe compaction of the surface layer of coarse textured tropical soils, especially when mulch is sparse or missing. Therefore, a 2 year (1982–1984) field experiment was initiated on an Alfisol in Nigeria to study the effect of tillage, mechanization and mulch on soil structure and physical properties. Three zero-tillage treatments and a plough treatment were compared. The disk-plough and one of the no-till treatments were highly mechanized: all the field work was performed with tractors and machines, and consisted of secondary bush clearing, crop cultivation and harvest. On the other two no-till treatments, the impact of machine load was reduced, wither by hand harvesting or by performing all field operations manually. These four tillage-traffic systems were either treated with mulch or left unmulched. There were four growing seasons, with maize (Zea mays L.) as a test crop.

After 2 years of zero-tillage the bulk density (BD) and penetration resistance (PR) were significantly greater on plots with high mechanization compared with hand treated plots. Plots with hand harvest but otherwise mechanized were in between. Because of the hard-setting nature of the soil, the plougheed plots with and without mulch exhibited a dramatic change in PR and BD during the season. On no-till the infiltration transmissivity (A) was greater and BD and PR were less in the mulched compared with the unmulched treatments.

The gravel content of the topsoil was negatively correlated with BD and positively correlated with A. Geostatistical analysis revealed that within the experimental area there was a similar spatial distribution of gravel content and A after the first season. Because of the superimposing effect of gravel on BD, which cannot be accounted for by considering the gravel content per se, BD was adjusted by means of covariance analysis for evaluation of the treatment effects already mentioned.

It was concluded that mechanization of a no-till system on sandy Alfisols may only be successful in the long run if appropriate measures like mulching, crop rotation and fallow systems are applied to regenerate soil structure and to enhance macroporosity.     

Effect of Graded Levels of Surface Crop Residue Application Under Minimum Tillage on Carbon Pools and Carbon Lability Index in Sorghum (Sorghum bicolor (L.) Moench)-Cowpea (Vigna unguiculata) System in Rainfed Alfisols

A long term experiment (2005–2012) was conducted in rainfed semi-arid tropical Alfisol at Hayathnagar Research Farm of Central Research Institute for Dryland Agriculture, Hyderabad, India. The aim of this experiment was to study the long-term impacts of graded levels of surface crop residue application on carbon (C) pools, aggregate associated C, C lability index and their relationship with crop yield. The experiment was conducted in a randomized block design (RBD) with minimum tillage (MT). Experimental treatments comprised of four levels of surface application of sorghum crop residues (@ 0, 2, 4 and 6 t ha^?1). The test crops, sorghum and cowpea, were grown in rotation yearly. Based on the pooled analysis of long term data (2005–2012), the study revealed that the surface application of sorghum residue @ 6 t ha^?1 and 4 t ha^?1 recorded 21% and 16% higher sorghum grain yields, respectively over control (no residue) whereas, the corresponding increase in the cowpea yield was 50% and 60%, respectively. Besides, the concentrations of soil organic carbon (SOC), inorganic carbon (IC), total carbon (TC), particulate organic carbon (POC) in the top surface soil (upper layer, 0–5cm depth) were found significantly higher than the sub-surface soil (lower layers, 5–15 cm depth) in all the treatments. Storage of soil C was assessed in soil aggregates fractions, and it was found that the smaller size aggregate fractions (0.053mm) contained significantly (p = 0.05) higher content of SOC compared to the large sized fractions (2 mm). The amount of very labile fraction of C extracted with 12 N H₂SO₄ was significantly higher (1.04 g kg^?1) with the application of sorghum stover @ 6t ha-¹ compared to other residue level treatments, in the 0-5 cm soil layer. The Lability Index (LI) increased with the increase in the amount of residues applied and was significantly higher in the surface soils compared to subsurface soil. The results of this study will be highly relevant and of significant value from the view point of managing SOC and its different pools in soil under abiotically stressed semiarid tropical Alfisols soils.     

Erosional impacts on soil properties and corn yield on Alfisols in central Ohio

Accelerated soil erosion can impact upon agronomic productivity by reducing topsoil depth (TSD), decreasing plant available water capacity and creating nutrient imbalance in soil and within plant. Research information on soil‐specific cause – effect relationship is needed to develop management strategies for restoring productivity of eroded soils. Therefore, two field experiments were established on Alfisols in central Ohio to quantify erosion‐induced changes in soil properties and assess their effects on corn growth and yield. Experiment 1 involved studying the effects of past erosion on soil properties and corn yield on field runoff plots where soil was severely eroded and comparing it with that on adjacent slightly eroded soil. In addition, soil properties and corn grain yield in runoff plots were compared on side‐slopes with that on toe‐slopes or depositional sites. Experiment 2 involved relating corn growth and yield to topsoil depth on a sloping land. With recommended rates of fertilizer application, corn grain yield did not differ among erosional phases. Fertilizer application masked the adverse effects of erosion on corn yield. Corn grain yield on depositional sites was about 50 per cent more than that on side‐slope position. Corn plants on the side‐slope positions exhibited symptoms of nutrient deficiency, and the ear leaves contained significantly lower concentrations of P and Mg and higher concentrations of Mn and K than those grown on depositional sites. Corn grain yield in experiment 2 was positively correlated with the TSD. Soil in the depositional site contained significantly more sand and silt and less clay than that on the side‐slope position. There were also differences in soil properties among erosional phases. The soil organic carbon (SOC) content was 19\7 g kg⁻¹ in slightly eroded compared with 15\1 g kg⁻¹ in severely eroded sites. Aggregate stability and the mean weight diameter (MWD) were also significantly more in slightly eroded than severely eroded soils. Adverse effects of severe erosion on soil quality were related to reduction in soil water retention, and decrease in soil concentration of N and P, and increase in those of K, Ca and Mg. Severe erosion increased leaf nutrient contents of K, Mn and Fe and decreased those of Ca and Mg. Corn grain yield was positively correlated with aggregation, silt and soil N contents. It was also negatively correlated with leaf content of Fe. Copyright © 2000 John Wiley & Sons, Ltd.     

Tillage effects on physical properties of agricultural organic soils of north central Ohio

Drainage, tillage, and intensive land use lead to drastic alterations in physical characteristics of organic soils. As decomposition and soil formation progress, bulk density (ρ_b) increases and total porosity (f_t) decreases due to subsidence, shrinkage, and mineralization of soil organic matter (SOM). However, the rate of subsidence and the changes in soil properties differ among management systems. Thus, the objectives of this study were to determine the effects of different tillage practices on ρ_b and f_t of cultivated peat soils. These experiments were conducted during 2004–2005, on Histosols in north central Ohio. Soil core samples were obtained from experimental plots managed with moldboard plow (MB), no-till (NT), or left bare (B). Conversion of plow tillage to NT increased ρ_b from 0.52 to 0.57 Mg m⁻³, and decreased f_t from 0.72 to 0.70 m³ m⁻³.     

New metabolites in the degradation of alpha- and gamma-hexachlorocyclohexane (HCH): pentachlorocyclohexenes are hydroxylated to cyclohexenols and cyclohexenediols by the haloalkane dehalogenase LinB from Sphingobium indicum B90A

Technical hexachlorocyclohexane (HCH) and lindane are obsolete pesticides whose former production and use led to widespread contaminations posing serious and lasting health and environmental risks. Out of nine possible stereoisomers, alpha-, beta-, gamma-, and delta-HCH are usually present at contaminated sites, and research for a better understanding of their biodegradation has become essential for the development of appropriate remediation technologies. Because haloalkane dehalogenase LinB was recently found responsible for the hydroxylation of beta-HCH, delta-HCH, and delta-pentachlorocyclohexene (delta-PCCH), we decided to examine whether beta- and gamma-PCCH, which can be formed by LinA from alpha- and gamma-HCH, respectively, were also converted by LinB. Incubation of such substrates with Escherichia coli BL21 expressing functional LinB originating from Sphingobium indicum B90A showed that both beta-PCCH and gamma-PCCH were direct substrates of LinB. Furthermore, we identified the main metabolites as 3,4,5,6-tetrachloro-2-cyclohexene-1-ols and 2,5,6-trichloro-2-cyclohexene-1,4-diols by nuclear magnetic resonance spectroscopy and gas chromatography-mass spectrometry. In contrast to alpha-HCH, gamma-HCH was not a substrate for LinB. On the basis of our data, we propose a modified gamma-HCH degradation pathway in which gamma-PCCH is converted to 2,5-cyclohexadiene-1,4-diol via 3,4,5,6-tetrachloro-2-cyclohexene-1-ol and 2,5,6-trichloro-2-cyclohexene-1,4-diol.     

Empirical relationships for soil organic carbon transport from agricultural watersheds in Ohio

Improved quantification is needed for long‐term soil organic carbon (SOC) transport in runoff at watershed scales. Coshocton wheel samplers were used to collect runoff samples from no‐till and chisel‐till watersheds in corn (Zea mays) and soybean (Glycine max) rotations over 13 years. Samples were analyzed for SOC, N, P, K, and soil losses. The SOC losses, ranging from 0 to 357 kg ha⁻¹ event⁻¹, were correlated (r² = 0·80–0·94) in power law relationships with N, P, K, soil loss, and runoff. Two events occurring in corn when soybean and cover crop residue were present in no‐till had combined SOC transport of 460 kg ha⁻¹, nearly double the no‐till losses of a previous 11‐year period and 20 times higher than chisel‐till in the same events. Infrequent, extreme transport events that are not well characterized empirically, particularly in no‐till, can strongly influence hydrologic C transport from agriculture watersheds. Copyright © 2007 John Wiley & Sons, Ltd.     

Fodder production and soil health with conjunctive use of saline and good quality water in ustipsamments of a semi‐arid region

Food and fodder shortage in arid and semi‐arid regions force farmers to use marginal quality water for meeting the water requirement of crops which result in low quality, reduced production and an adverse impact on soil properties. A field study on loamy‐sand (Hyperthermic Typic Ustipsamments) saline soil was conducted during 1999–2001 at Central Institute for Research on Buffaloes, Hisar. This involved assessment of effects of conjunctive use of saline water, EC = 4·6–7·4 dSm⁻¹, SAR = 14–22 ((mmol⁻¹)^½ with good quality water on five fodder crop rotations: oat‐sorghum (Avena sativa‐–Sorghum bicolor), rye grass–sorghum (Loleum rigidum—Sorghum bicolor), Egyptian clover—sorghum (Trifoleum alexandrinum—Sorghum bicolor), Persian clover—sorghum (Trifoleum resupinatum—Sorghum bicolor) and Indian clover–sorghum (Melilotus indica—Sorghum bicolor) and certain soil properties associated with it. Leguminous winter fodder crops were more sensitive to poor quality water use. Reductions in fodder yield with use of saline water alone throughout season were 85, 68, 54, 42, 36 and 26 per cent in Indian clover, Egyptian clover, Persian clover, oat, rye grass and sorghum respectively as compared to good quality water. Leguminous fodder crops produced protein rich (12–14 per cent) and low fibre (18–20 per cent) fodder as compared to poor quality grassy fodder under good quality water irrigation but their quality deteriorated when saline water was used. These leguminous crops accumulated proportionately higher Na⁺ (1·58 per cent) resulting in adverse impact on their growth as compared to grassy fodder crops. Higher soil salinity (12·2 dSm⁻¹), SAR = 20 (mmol⁻¹)^½ was recorded with saline water irrigation; and slight adverse impact was noticed on infiltration rate and contents of water dispersible clay. Alternate cyclic use of canal and saline water could be an option for fodder production under such conditions. Copyright © 2006 John Wiley & Sons, Ltd.