The Affects of Land-use on Soil Dynamics
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The Affects of Land-use on Soil Dynamics Caleb Maney Department of Natural Resources, University of New Hampshire. Discussion and Results:. Introduction:

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Approach

The Affects of Land-use on Soil Dynamics

Caleb Maney

Department of Natural Resources, University of New Hampshire

Discussion and Results:

Introduction:

Different agricultural land uses all have a unique impact on the land. Some plants add to the nutrient value of the earth while others tend to rapidly degrade the soil. It is important to see how different agricultural uses impact the soil dynamics over a long-time period, specifically long-term monoculture.

Typically crop rotation is practiced to allow for a diversification of the soil nutrients that are used or restored by a specific species of plant. Monoculture has been shown to degrade the earth because of its use of the same soil nutrients over time eventually creating a soil that needs either fertilizer input to upkeep production or is deemed unfertile and abandoned. In this study I will be analyzing how the long-term (30 years) planting of the same crop has affected soil.

The variation in aggregate size distribution is the direct result of the different land-use. The garden plot is tilled annually resulting in the breaking up of larger aggregates. The grassland and Frasier fir soils are not overturned resulting in a larger 2mm aggregate fraction. While the old growth stand is not tilled it also does not have significant grass cover.

Average nitrogen was found to be the highest at sample sites with leaf litter input. The old growth plot had the highest values, this stand had the greatest amount of leaf-litter input and the lowest species density. Samples from the vegetable garden had the lowest value due to the uptake from plants.

Bulk density is very similar between the grassland and old growth stand. These plots were close to each other in proximity and do not have annual tillage. The vegetable garden had the highest bulk density by a significant margin. This high value can be attributed to the tillage and compaction. The lower porosity value and water content contributed to these result. Lower porosity values equate to a soil with greater density

Discussion:

The different land uses had a significant affect on the nutrient and soil dynamics. The garden was found to have lower nutrient values than any of the other soils. This is due to the uptake by plants along with the lack of an input source. The grassland was also found to have least amount of Large aggregates. This is due to the annual tilling resulting in the breaking down of aggregates. Annual tillage is the cause of the higher bulk density and lower porosity relative to the other sample sites.

The grassland and Frasier fir were found to have similar results. These two sample locations were both had a high percentage of grass cover and neither are tilled or overturned. The result of this was the same bulk density values and similar aggregate size distribution. The grassland had a lower porosity and higher water filled percentage. The lower water filled percentage in the Frasier firs is most likely the result of greater water demand. Nitrogen and Carbon were both higher in the Frasier Fir sample site. The greater percentage of these nutrients is due to the deposition of leaf litter and frequent mowing. The grassland site is hayed once to twice a year thus greatly reducing the amount of nutrient input.

The old stand was found to have the highest nutrient levels. This site had the lowest species density, no grass coverage, and a tall dense canopy. The combination of high leaf-litter input and low species density created higher values by reducing nutrient uptake while maintaining a high deposition of leaf-litter.

Objective:To determine the affect of different agricultural practices on soil dynamics.

  • Approach:

  • Samples were obtained from 4 different plots of land, each with a different land-use. The land uses that were examined were a grassland (hayed), an old growth forest, a stand of Frasier firs, and a vegetable garden.

  • Samples were collected using a 2’ODx10 cm pvc pipe

  • Samples were taken at 4 equal locations along a diagonal transect of the field.

  • Samples were then analyzed for the following data

    • Bulk Density

    • Carbon %

    • Nitrogen %

    • Porosity

    • Water filled %

    • Aggregate Size Distribution

  • Methods

    • Wet-sieve standard protocol: 2mm, 250um, 53um

    • Combustion analysis (Costech)

    • Standard Bulk Density protocol

Carbon was found to be highest for the old growth plot . Grassland and Frasier fir sample sites had similar values while the garden was found to have the lowest amount of carbon. These lower values are due to the agricultural land-use.

The garden had the lowest porosity values due to compaction and tillage. The breaking up of the soil and planting of vegetables results in a soil with greater density and less air space. This can be seen in the bulk density as well.

Site 1: Frasier Fir

Site 4: Garden

Sample Locations:

Conclusion:

There were significant variations in the soil and nutrient dynamics between plots. The tilling of soil contributed to a higher average bulk density and lower aggregation. The levels of Nitrogen and Carbon were greatest in plots that had a high rate of deposition while maintaining a low species density. There was little variation between grassland and Frasier fir sample locations, this can be attributed to the amount of similarity between the two sites.

Site 2: Grassland

Site 3: Old Growth

:Acknowledgements:Stuart Grandy, Grandy Lab,

New Hampshire agriculture experiment station, Cynthia Kallenbach

Michael Casazza, Natasha Lessard


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