Nutrient Content of Agricultural Soil:
Fertilized verses Unfertilized
Bliss Feaster
&
Lisa V Michel
10/30/03
Instructor: Rebecca Burton
Ecology Independent Research Project
Abstract
In this experiment it was tested whether or not fertilized soil contained a higher nutrient content when compared to unfertilized soil. It was found that phosphorous and sulfate levels were higher in fertilized soils and the content of nitrite nitrogen was equal in fertilized and unfertilized soils.
Keywords: Fertilizer, organic farms, nutrients
Introduction
One
of the key elements involved with high levels of crop productivity is
fertile
soil, which “provides essential nutrients for crop plant growth,
supports a
diverse and active biotic community, exhibits a typical soil structure
and
allows for an undisturbed decomposition” (Mader et al. 2002). Within the state of
The
soil composition varies across different farms and crops; these
differences can
include type of farming, type and amount of fertilizer used,
the type of crop grown and even the influences of past crop rotations. Within the state of
Many of the provided inferences for these findings dealt with the influences of crop rotation, type of soil present, evidence of crop disease and the overall biological differences involved within each of these types of farming (Olesen et al. 2000). Not only is soil fertility an area of interest, but also the number and diversity of species that are present when the organic and conventional crops are compared. In relation to previous research, there have also been conclusive findings showing a larger amount of species within organic plots as compared to the conventional plots (Mader et al. 2002).
This experiment was designed to discover whether nutrient content differed between organic and fertilized agricultural soils. It was hypothesized that fertilized soils would have and overall higher nutrient content. If fertilized agricultural soils contain a higher nutrient content, then the hypothesis will be supported. If unfertilized soils contained a higher nutrient content, then the hypothesis will be falsified.
Soil Sampling Methods
Two
sites were chosen to obtain samples based on the crop type and the
method of
fertilization. Both sites were located
within Wood County Wisconsin. The
address of the first site was 5174
When sampling the soil, sealed plastic bags were used to collect and store the samples. At each sample site, 10 samples of approximately 30 grams each were collected. Upon returning to the lab, the samples were placed in individual glass bottles and dried in a Lab-LineÒ Imperial III radiant heat oven. They were allowed to dry for one hour at 144oC. Once the samples were dried they were capped off using corks and set aside for three days until the testing was performed.
Soil
Testing Methods
All soil testing methods were performed using a LaMotte soil testing kit as well as the Model STH Series Combination Soil Outfit Instruction Manual for testing procedures. The numbers following the equipment is the stock number from the LaMotte kit.
Soil Preparation
In order to conduct nutrient content testing on the soil samples, a soil extraction procedure was performed to set the soil in liquid form. For each of the 20 samples an extraction tube (0704) was filled to the 14 mL line with Universal Extraction Solution (5173). A plastic soil measure (0819) was used to add two level measures of the soil sample. The tube was then capped and shook by hand for one minute. A plastic funnel (0459) and piece of filter paper (0465) were used to filter the liquid soil suspension into a separate extraction tube. The filtered extract in the second extraction tube was then used to perform the tests for soil nutrients.
Nitrite Nitrogen Test
Five drops of the soil extract was added to a large depression on a spot plate (0159) using a transfer pipet (0364). To the depression, one drop of Nitrite Nitrogen Test Reagent #1 (5151) and one drop of Nitrite Nitrogen Test Reagent #2 (5152) was added. The mixture was then stirred using a stirring rod. Three drops of Nitrite Nitrate Test Reagent #3 (5153) was added to the depression and stirred once again using a stirring rod. The mixture was then allowed to sit for one minute. The color of the mixture was then read by matching the color of the sample to a color standard on the Nitrite Nitrogen Color Chart (1310). The units were read in parts per million (ppm).
Phosphorous Test
A transfer pipet (0364) was used to fill a “Phosphorous B” tube (0244) to the mark with the soil extract. Six drops of Phosphorous Test Reagent #2 (5156) was added and then the tube was capped and shook by hand. Next, one Phosphorous Reagent #3 Tablet (5157) was added to the tube. Again the tube was capped and shook by hand until the tablet dissolved. The color of the sample was then immediately compared to the Phosphorous Color Chart (1312). The test results were read in pounds per acre and the converted into parts per million.
Sulfate Test
A transfer pipet (0364) was used to transfer five drops of the soil extract to a flat bottom turbidity vial (0242). One drop of Sulfate Test Solution (5171) was added to the vial and swirled gently to mix. The turbidity of the sample was compared to the turbidity standards of the Sulfate Chart (1314). The test results were then read in parts per million.
Data Analysis Methods
Once all the test results were in (Table 2), averages were calculated for each of the sample types and nutrients (Table 3). These averages were then used to create a bar graph of the nutrient averages (Figure 1). A paired T-test was performed for each of the nutrients to see if there was a significant difference between the nutrients in the fertilized and unfertilized soil samples (Table 4).
Data
Table 1: Site Agricultural Information
|
Site Information |
Site 1: Fertilized |
Site 2: Unfertilized |
|
Address |
5174 |
|
|
Size |
4 Hectares |
16 Hectares |
|
Years used for agriculture |
63 years |
21 years |
|
Fertilization Type |
Dairy Cow Manure |
None |
|
Crop Type |
Current: Hay Prior: Oats, corn and hay |
Current: Hay Prior: Wheat, alfalfa, hay and clover |
The following data was collected from the nutrient content tests.
Table 2: Collected Data
|
Sample |
Nitrite Nitrogen |
Phosphorous |
Sulfate |
|
Fertilized 1 |
1 ppm |
100 ppm |
50 ppm |
|
Fertilized 2 |
1 ppm |
75 ppm |
100 ppm |
|
Fertilized 3 |
1 ppm |
75 ppm |
100 ppm |
|
Fertilized 4 |
1 ppm |
75 ppm |
100 ppm |
|
Fertilized 5 |
1 ppm |
75 ppm |
100 ppm |
|
Fertilized 6 |
1 ppm |
75 ppm |
100 ppm |
|
Fertilized 7 |
1 ppm |
75 ppm |
50 ppm |
|
Fertilized 8 |
1 ppm |
75 ppm |
100 ppm |
|
Fertilized 9 |
1 ppm |
75 ppm |
100 ppm |
|
Fertilized 10 |
1 ppm |
50 ppm |
50 ppm |
|
Unfertilized 1 |
1 ppm |
50 ppm |
50 ppm |
|
Unfertilized 2 |
1 ppm |
50 ppm |
50 ppm |
|
Unfertilized 3 |
1 ppm |
50 ppm |
50 ppm |
|
Unfertilized 4 |
1 ppm |
50 ppm |
100 ppm |
|
Unfertilized 5 |
1 ppm |
50 ppm |
50 ppm |
|
Unfertilized 6 |
1 ppm |
50 ppm |
50 ppm |
|
Unfertilized 7 |
1 ppm |
34.5 ppm |
50 ppm |
|
Unfertilized 8 |
1 ppm |
50 ppm |
50 ppm |
|
Unfertilized 9 |
1 ppm |
75 ppm |
50 pm |
|
Unfertilized 10 |
1 ppm |
50 ppm |
50 ppm |
Table 3: Nutrient Averages
|
Sample |
Nitrite Nitrogen |
Phosphorous |
Sulfate |
|
Fertilized |
1 |
76.1 |
85 |
|
Unfertilized |
1 |
51.25 |
55 |
The calculated averages were used to create a bar graph.
Figure 1: Nutrient Averages
T-tests were performed for each of the nutrients to show if the differences were significant or not.
Table 4: T-tests
|
|
Nitrite Nitrogen |
Phosphorous |
Sulfate |
|
T-Test |
N/A |
.001415 |
.005121 |
Results
From the data it was shown that there is a significant difference between the amount phosphorous and sulfate in the two soil types. This is due to the P-valued, derived from the T-test, being less than 0.05. It was shown that there is a higher content of these two nutrients in the fertilized soil samples. There was no difference found in the nitrite nitrogen content of the soils.
Discussion
The differences in nutrient content between the fertilized and unfertilized soils may be due to several different factors. This first of these factors is the type of crop grown. This factor did not have an affect on the phosphorous and sulfate levels but may have explained the similarity in nitrite nitrogen content. In prior studies it has been found that organic or unfertilized soils contain 34 to 51% lower nutrient input of phosphorous. This idea may account for the phosphorous levels being lower in the unfertilized samples since there is less phosphorus to begin with. The difference in sulfate levels may be due to the type of bedrock that the soil is located on and not the fertilization of the soil. Sulfates as well as phosphorous are derived from the bedrock. If the original bedrock contains less of these nutrients, the soil will also contain less.
If this experiment were to be revisited, a great sampling would increase the statistical validity of the results. Different types of nutrient could be tested to show a greater difference in nutrient content based on the fertilization of the soil. Another area to look into would be farms that use chemical fertilizers and compare them to farms that use other types of fertilizers.
Literature Cited:
Mader, P., Fliebbach, A., Dubois, D., Gunst, L., Fried, P., Niggli, U. 2002. Soil Fertility and Biodiversity in Organic Farming. Science 296: p 1694-1698.
Olesen, J., Askegaard, M., Rasmussen,