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Research Report  3.2

Development of Standard Methologies:
Resident Biomass and Organic Carbon

Dr. Gary Kachanoski, Environmental Soil Services,
605 Arkell Rd., Arkell, ONT N0B 1C0
COESA Report No.:  RES/MON-002/96

Objectives & Expected Outputs
Executive Summary
Technical Abstract
 

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Objectives and Expected Outputs
Objectives: To develop and test methods of measuring resident biomass and soil carbon and to relate these measurements to other soil properties directly related to soil fitness.
Expected Outputs: 150 of 200 Ap- horizon soil samples (75 landscapes x 2 tillage systems) from the TILLAGE-2000 plots will be utilized for developing and comparing methods of soil carbon analysis. Following these analysis, attention will be given to quantifying the effects of soil management on soil carbon levels, as well as the effects of other spatial and temporal functions such as soil erosion. Extensive background documentation is available to support interpretation of the current study.
Type: Open Bid, Industry
Spending Profile: 93-94: $46.3 K,    94-95: $50.8 K,    95-96: $52.5 K,   Total: $149.6 K
Status: Available March 1996

 

Executive Summary

Organic matter is an essential component of soil. It increases the ability of the soil to provide the proper conditions to grow agricultural crops and to resist processes such as soil erosion. Soil organic matter is composed of many different components, the most important being various forms of carbon and nitrogen. The decomposition of the organic carbon and nitrogen in soil releases nutrients to growing crops. Knowledge of how this decomposition occurs will help farmers predict how much fertilizer is needed and not over apply fertilizer which may cause environmental problems. Thus, understanding the nature of soil carbon and nitrogen is very important and an area of active research. Part of that research is directed at obtaining estimates of how much soil organic carbon is presently in many of our soils and to set up permanent sampling locations so that the amounts of soil carbon can be monitored with time. This gives us an indication of the "State" of the soil resource and whether our current farming management is ensuring that the resource is sustainable.

This study used different methods to characterize the different forms of soil organic C and N, at a large number of southern Ontario sites where significant amounts of other information had already been collected. The similarities of the different methods and the influence of other soil properties such as the amount of sand content were determined. A chemical extraction method for predicting the amount of nitrogen which might be released by the biological breakdown of soil organic matter was developed. It gave very similar estimates to a long term(22 weeks) incubation method which measures the release of nitrogen during biological decomposition. The quick extractant method may be a good soil test for farmers to use in making decisions on the amount of fertilizer nitrogen to apply. In addition, the study characterized in detail the seasonal changes in soil organic C and the amount of variability within the monitoring area at any time, for 3 different fields. This allows the accuracy of the estimate of soil organic C to be determined and thus, the accuracy of any future estimates of how much change has occurred. At these sites, the amount of soil that has been lost or gained from soil erosion was the main factor in determining the amount of soil carbon present and also the amount of crop yield that was obtained. An easily measured soil erosion tracer, 137cesium, was used to determine the amount of soil loss or gain at a site and was recommended as a useful indicator for determining the "State" of the soil resource. Finally, all measurement were included in an electronic database with geographic locations so that the information can be used for future studies examining how the soil resource is changing.

TECHNICAL ABSTRACT

The objectives of this project were:

  1. to develop and test methodologies to measure resident biomass and organic soil C,

  2. to characterize forms and spatial and temporal variations of soil C sufficient to distinguish a 20% change over and above seasonal and random variations, and

  3. to relate the soil C measurements to other soil properties.

The study has two parts;

  1. method development and

  2. field characterization including spatial and temporal variations.

Both parts of the study make use of extensive information already collected as part of the Provincial Tillage-2000 project. In Part 1, a total of 150 Ap horizon soil samples were selected from the Tillage-2000 benchmark monitoring locations (ie. 75 soil landscapes x 2 tillage systems = 150 samples ). The samples cover a wide range in soil texture/type (Brookston Clay-loam to Fox sand) and have detailed back-up information already available. Analysis carried out on these samples as part of this project include; Light Fraction C and N (150 samples), Macro-organic C and N (150 samples), total C and N (150 samples), potentially mineralizable C (100 samples), and total mineral N (150 samples). In addition, a subset of 20 Ap horizon soil samples were selected which cover a range in soil textures (sand to clay-loam) , landscape position (severely eroded, depositional), and total organic C. These samples were used for detailed chemical analysis using 13C-NMR and a new hot CaCl2 chemical extraction procedure. These detailed analyses are being completed by Dr. E. Gregorich, CLBRR, Agric. Canada (Ottawa), and Dr. M. Goss (Univ. of Guelph).

In Part 2, two T2000 sites covering three textural groups were chosen for field sampling. The sites are the Lobb farm (Huron Co.), which has a sand to sandy loam textured catena sequence and a silty clay-loam to clay-loam catena sequence, and the Pottruff farm (Brant Co.), which has a loam catena sequence. Each catena sequence has three benchmark monitoring locations; upper (eroded), middle (transitional), lower (depositional). Sampling was by soil horizons with the objective of obtaining a measure of the solum specific mass (ie the amount of C and N per unit land area from the surface to the depth of the pedogenic B/C interface). A monitoring area ( 15 m by 15 m ) was established at each benchmark with 15 subsampling points of reference. At each sampling time, an undisturbed soil core (3.175 cm diam.) was taken in the immediate area surrounding each of the 15 subsample grid points. The cores were sliced according to A and B horizon. Sampling times were set to characterize major crop growth stages (planting/spring, sidedress/emergence, full canopy, harvest/fall ). A separate measurement of soil bulk density and thickness was obtained for each of the subsamples. Each of the subsamples were combined to get a single bulk sample representing the benchmark. Chemical analysis were completed on the composite samples. For one sampling each year, the individual grid samples were separately dried, weighed and analyzed for chemical properties to get an idea of the spatial covariance between chemical composition and solum thickness, and the inherent spatial variability. The above ground crop biomass at time of harvest was also sampled as well as surface crop residue amounts. All plant and surface residues samples were analyzed for Total C and N. Soil samples were analyzed for total C, inorganic C, organic C, total N, macro-organic matter C and N, and microbial biomass C and N.

In Part 1, statistical analysis indicated many of the C and N measurements were correlated to each other. Soil sand content was significantly correlated to many variables. The Light Fraction and Macro-organic fractions are measuring different components of the soil organic C and have different C/N ratios. The Macro-organic fraction had the highest correlation to potentially mineralizable C and N. A new hot CaCl2 chemical extraction procedure was very highly correlated (r=0.98 ) to potentially mineralizable N, suggesting it might be an excellent new soil N test. It may also be a good extractant for raw manure to estimate mineralizable N. The measurements of all of the C and N fractions have been entered into a digital database which contains all of the other T2000 measurements. The database has been submitted along with this report.

In Part 2, the spatial and temporal variations of soil C and N were characterized and included in a digital database. Total solum C was measured with an accuracy of at least 16% at all benchmarks. The sampling procedure was accurate enough to measure seasonal changes and active deposition was measured at 2 out of the 3 lower slope positions. Variability of the Macro-organic fraction was higher than for total C, and microbial biomass measurements had the highest variability. All measurements of C had to have a correction for inorganic C because of high carbonates particularly in eroded benchmarks. Measurements of C by Loss on Ignition (LOI) at 500 C did not correlate well to organic C calculated from total C corrected for inorganic C. Thus, LOI should not be used for monitoring purposes to track the state of the soil resource. The major influence on soil C amounts was the amount of soil mass at a benchmark from the surface to the depth of the solum. Sampling by solum depth also allows a mass balance of soil C to be calculated. Measurement of a soil erosion tracer (137cesium) at the benchmarks indicated that soil loss could explain the landscape differences in soil C, which was also reflected in current crop yields and above ground plant biomass C production. Thus, 137cesium may be a good agri-environmental indicator for the state of the soil resource.

 


 

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