Total carbon organic carbon and organic matter

Total Carbon, Organic Carbon, and Organic Matter

Soil Chemical Analysis

Statistics for Spatial Data.

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Modern Applied Statistics With S

Increases in the concentrations of greenhouse gases, carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and halocarbons in the atmosphere due to human activities are associated with global climate change. The concentration of N2O has increased by 16% since 1750. Although the atmospheric concentration of N2O is much smaller (314 ppb in 1998) than of CO2 (365 ppm), its global warming potential (cumulative radiative forcing) is 296 times that of the latter in a 100-year time horizon. Currently, it contributes about 6% of the overall global warming effect but its contribution from the agricultural sector is about 16%. Of that, almost 80% of N2O is emitted from Australian agricultural lands, originating from N fertilisers (32%), soil disturbance (38%), and animal waste (30%). Nitrous oxide is primarily produced in soil by the activities of microorganisms during nitrification, and denitrification processes. The ratio of N2O to N2 production depends on oxygen supply or water-filled pore space, decomposable organic carbon, N substrate supply, temperature, and pH and salinity. N2O production from soil is sporadic both in time and space, and therefore, it is a challenge to scale up the measurements of N2O emission from a given location and time to regional and national levels. Estimates of N2O emissions from various agricultural systems vary widely. For example, in flooded rice in the Riverina Plains, N2O emissions ranged from 0.02% to 1.4% of fertiliser N applied, whereas in irrigated sugarcane crops, 15.4% of fertiliser was lost over a 4-day period. Nitrous oxide emissions from fertilised dairy pasture soils in Victoria range from 6 to 11 kg N2O-N/ha, whereas in arable cereal cropping, N2O emissions range from <0.01% to 9.9% of N fertiliser applications. Nitrous oxide emissions from soil nitrite and nitrates resulting from residual fertiliser and legumes are rarely studied but probably exceed those from fertilisers, due to frequent wetting and drying cycles over a longer period and larger area. In ley cropping systems, significant N2O losses could occur, from the accumulation of mainly nitrate-N, following mineralisation of organic N from legume-based pastures. Extensive grazed pastures and rangelands contribute annually about 0.2 kg N/ha as N2O (93 kg/ha per year CO2-equivalent). Tropical savannas probably contribute an order of magnitude more, including that from frequent fires. Unfertilised forestry systems may emit less but the fertilised plantations emit more N2O than the extensive grazed pastures. However, currently there are limited data to quantify N2O losses in systems under ley cropping, tropical savannas, and forestry in Australia. Overall, there is a need to examine the emission factors used in estimating national N2O emissions; for example, 1.25% of fertiliser or animal-excreted N appearing as N2O (IPCC 1996). The primary consideration for mitigating N2O emissions from agricultural lands is to match the supply of mineral N (from fertiliser applications, legume-fixed N, organic matter, or manures) to its spatial and temporal needs by crops/pastures/trees. Thus, when appropriate, mineral N supply should be regulated through slow-release (urease and/or nitrification inhibitors, physical coatings, or high C/N ratio materials) or split fertiliser application. Also, N use could be maximised by balancing other nutrient supplies to plants. Moreover, non-legume cover crops could be used to take up residual mineral N following N-fertilised main crops or mineral N accumulated following legume leys. For manure management, the most effective practice is the early application and immediate incorporation of manure into soil to reduce direct N2O emissions as well as secondary emissions from deposition of ammonia volatilised from manure and urine. Current models such as DNDC and DAYCENT can be used to simulate N2O production from soil after parameterisation with the local data, and appropriate modification and verification against the measured N2O emissions under different management practices.

/pdf/nitrous-oxide-emission-from-australian-agricultural-lands-1fjm79h4e7.pdf

Nitrous oxide emission from Australian agricultural lands and mitigation options: a review

http://www.bob-mccown.com/wp-content/uploads/2012/01/ProbertEtAl1998APSIMsWaterNitrogenModules.pdf

APSIM's water and nitrogen modules and simulation of the dynamics of water and nitrogen in fallow systems

Near infrared diffuse reflectance spectrophotometry, within the wavelength range 1100 to 2500 nm, was investigated for use in the simultaneous prediction of the moisture, organic C, and total N contents of air-dried soils. An infraAlyzer 500 C (Technicon Instruments Corp.) scanning spectrophotometer was used to obtain near infrared reflectance of soils at 2-nm intervals. Calibration equations for each of the soil constituents studied were based upon selection of the best combination of three wavelengths in a multiple regression analysis. The wavelengths selected for moisture, organic C, and total N, respectively, were 1926, 1954, and 2150 nm, 1744, 1870 and 2052 nm, and 1702, 1870 and 2052 nm. The standard errors of prediction for finely ground samples (<0.25 mm) from the top layers (0-0.1, 0.1-0.2, 0.2-0.3, 0.3-0.6 m) were 0.58, 0.16, and 0.014% for moisture, organic C, and total N, respectively. The standard errors of prediction, however, were much larger for coarsely ground soils (<2 mm), soils containing low amounts of organic C (<0.3%) and total N (<0.03%), and for those with a wide range in colors. Within a narrow range in soil color and at moderate amounts of organic matter (0.3–2.5%C), the near infrared reflectance technique provides a rapid, nondestructive, and simultaneous measurement of moisture, organic C and total N in soils.

Simultaneous Determination of Moisture, Organic Carbon, and Total Nitrogen by Near Infrared Reflectance Spectrophotometry

The roles of microbial biomass (MBC) and substrate supply as well as their interaction with clay content in determining soil respiration rate were studied using a range of soils with contrasting properties. Total organic C (TOC), water-soluble organic carbon, 0.5 M K2SO4-extractable organic C and 33.3 mM KMnO4-oxidisable organic carbon were determined as C availability indices. For air-dried soils, these indices showed close relationship with flush of CO2 production following rewetting of the soils. In comparison, MBC determined with the chloroform fumigation–extraction technique had relatively weaker correlation with soil respiration rate. After 7 d pre-incubation, soil respiration was still closely correlated with the C availability indices in the pre-incubated soils, but poorly correlated with MBC determined with three different techniques—chloroform fumigation extraction, substrate-induced respiration, and chloroform fumigation–incubation methods. Results of multiple regression analyses, together with the above observations, suggested that soil respiration under favourable temperature and moisture conditions was principally determined by substrate supply rather than by the pool size of MBC. The specific respiratory activity of microorganisms (CO2-C/MBC) following rewetting of air-dried soils or after 7 d pre-incubation was positively correlated with substrate availability, but negatively correlated with microbial pool size. Clay content had no significant effect on CO2 production rate, relative C mineralization rate (CO2-C/TOC) and specific respiratory activity of MBC during the first week incubation of rewetted dry soils. However, significant protective effect of clay on C mineralization was shown for the pre-incubated soils. These results suggested that the protective effect of clay on soil organic matter decomposition became significant as the substrate supply and microbial demand approached to an equilibrium state. Thereafter, soil respiration would be dependent on the replenishment of the labile substrate from the bulk organic C pool.

Relationships of soil respiration to microbial biomass, substrate availability and clay content

The kinetics of organic C loss were studied in six southern Queensland soils subjected to different periods (0-70 years) of cultivation and cereal cropping. The equation: Ct = Ce + (C0 - Ce)exp(- kt), where C0, Ce and C, are organic C contents initially, at equilibrium and at time k respectively, and k is the rate of loss of organic C from soil, was employed in the study. The parameter k was calculated both for %C (kc) and for weight of organic C/volume of soil (k,), determined by correcting for differences in sampling depth due to changes in bulk density upon cultivation. Mean annual rainfall largely determined both C, and Ce, presumably by influencing the amount of dry matter produced. Values of kc and kw varied greatly among the soils studied. For the 0-0.1 m depth, kw was 0.065, 0.080, 0.180, 0.259, 0.069 and 1.224 year-1 respectively for Waco (black earth - initially grassland), Langland-Logie (grey brown and red clays - brigalow), Cecilvale (grey, brown and red clays - poplar box), Billa Billa (grey, brown and red clays - belah), Thallon (grey, brown and red clays - coolibah) and Riverview (red earths - silver-leaved ironbark). The k values were significantly correlated with organic Chrease activity ratio (r = 0.99***) and reciprocal of clay content (r = 0.97**) of the virgin soils. In stepwise multiple regression analysis, aggregation index (for kc values) or exchangeable sodium percentage (for kw) and organic C/urease activity ratio of soils were significantly associated with the overall rate of loss of organic C. It was inferred, therefore, that the relative inaccessibility and protection of organic matter against microbial and enzymic attack resulted in reduced organic C loss. Losses of organic C from the deeper layers (0-0.2 m, 0-0.3 m) were observed in Waco, Langlands-Logie, Cecilvale and Riverview soils, although generally rate of loss decreased with depth.

Long-term trends in fertility of soils under continuous cultivation and cereal cropping in southern queensland. ii* Total organic carbon and its rate of loss from the soil profile

Ram C. Dalal

Papers

Nitrous oxide emission from Australian agricultural lands and mitigation options: a review

APSIM's water and nitrogen modules and simulation of the dynamics of water and nitrogen in fallow systems

Simultaneous Determination of Moisture, Organic Carbon, and Total Nitrogen by Near Infrared Reflectance Spectrophotometry

Relationships of soil respiration to microbial biomass, substrate availability and clay content

Long-term trends in fertility of soils under continuous cultivation and cereal cropping in southern queensland. ii* Total organic carbon and its rate of loss from the soil profile