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 Wisconsin, there are approximately 15.9 million acres of crop land which are used primarily for agriculture (Wisconsin Farm Bureau Federation 2002).  This crop land is often a focus for intense research and development for new methods of soil improvement and conservation.  In fact, Wisconsin was the first state within the nation to establish a county soil conservation project (Wisconsin Farm Bureau Federation 2002). 

 

            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 Wisconsin there are two drastically different farming techniques that are utilized; these include organic and fertilized farming.  Previous studies focused on soil differences between these two farming types have shown conclusive findings displaying organic soils as possessing a higher pH level with a lower amount of dissolved nutrients (Mader et al. 2002).

 

            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 County D, Vesper, WI 54489 and spanned four hectares.  The second site was located at 10451 Griffith Avenue, Wisconsin Rapids, WI 54494.  This site consisted of sixteen hectares.  Site one has been utilized for agriculture for 63 consecutive years and site two had been used for agriculture for 21 consecutive years.  In the past 63 years, site one has rotated crops of corn, hay and oats on a regular basis.  In the past year site one grew hay.  Site two was most recently used to grow hay but the twenty years prior the land was used to propagate hay, wheat, alfalfa and clover.   Site one used dairy cow fertilizer and site two used no fertilizer, just water.  Due to the type of fertilizers used, site one was designated as the fertilized farm and site two was designated as the unfertilized farm.  A summary of the site information can be found in table 1.

            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 County D

Vesper, WI  54489

10451 Griffith Avenue

Wisconsin Rapids, WI  54494

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.

 fig 1

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, I. 2002. Design of Organic Farming Crop-Rotation Experiment. Soil and Plant Science 50: p 13-21.

 

Wisconsin Farm Bureau Federation. 2003. Fun Facts About Wisconsin Agriculture. Retrieved from http://www. wisagclassroom.org. 8 October 2003.