Nitrogen and Phosphorus Leaching Expressed Through Simple Soil Testing

Schmanski, J. & Zimmerman, A.

Fall 2006

 

 

 

 

 

 

 

 

 

 

 

Abstract

Our group hypothesized that available nitrogen and phosphorus levels in soils within an animal pen would be higher than that outside of the pen with levels decreasing as distance increases. The experiment was carried out at the Emyn Muil Game Farm in West Bend, Wisconsin over a period of three weeks. It was found the hypothesis was not significantly supported for the phosphorus testing and not at all for the nitrogen testing with a p-value at .2285. Perhaps the nitrogen result is due to the type of nitrogen being tested in the LaMotte soil test is limited to ďavailable nitrogenĒ and is not able to be distinguished between the different nitrogen states.

 

Key words: nitrogen, phosphorus, leaching, soil

 

Introduction

Emyn Muil Game Farm is a private exotic game farm, located in West Bend, Wisconsin. West Bend is apart of the warm continental climate type, the humid temperature domain at 43.42 N latitude and 88.18 W longitude. The game farm is home to several species of animal and plant life. Sicilian donkeys, llamas, peafowl, cougar, Siberian lynx, and fox all reside on the farm. The farmís pens are surrounded by predominantly white pine trees, while other portions of the farm have mainly deciduous trees with sparse conifers, as well as a pond and also marsh lands.

Our group was interested in the leaching of the game animal waste into the soil and water supply and how this leaching would affect the nutrient levels of the surrounding soil. We did not have enough resources to test ground water so we limited our research to the nutrients in the soil. Specifically, we looked to compare the levels of phosphorus (P) and available nitrogen (N) of soils inside of animal pens, 3 meters outside of the pens, and 8 meters outside of the pens.

We expected to see the levels of P and N to be highest within the pen with a decrease as distance increased. Our hypothesis and expectations were developed based on our familiarity with farming and gardening fertilization. We know manure based fertilizers have high levels of these two nutrients. Animal waste products have the potential to leach into the ground, soil and possibly ground water supply, introducing nitrogen, phosphorus and other contaminants into the medium.

Soil contamination also has to do with geological foundations and general human awareness of pollution (Letson, et.al. 1998). The major P reserve in the earth is oceanic and N atmospheric but human wastes and animal manures add additional levels of these nutrients into the soil (Paul, 1988). Too much of either can lead to surface water pollution or ground water pollution so the balance of both is important and worth monitoring. With the increased awareness of pollution and its affects, humans have decreased N and P input into water sources and farming techniques.

The pollution of surface water is caused by runoff water from storms or excessive water flow.An example of this effect would be when the ground is hosed off and any unabsorbed nutrients flow into nearby bodies of water. Leaching is the method of ground water pollution by the filtration of nutrients, minerals, dissolved metals and other things from the top soil horizon to the lower horizons and possibly the water table. Excessive P or N leaching can be hazardous to humanís health and ecological health. The over abundance of either nutrients can lead to excessive algae growth, fish kills (Huang and Lantin,1993), and cancer in humans (Innes, 2000).

 

Methods

On October 14th & 21st, 2006 soil samples were taken from the Emyn Muil game farm which is located in the town of West Bend, in Washington County, Wisconsin. A sample of about 1 liter of soil was taken from six different sites, three at the llama pen and three at the donkey pen. A sample was collected by removing all top debris from the soil, digging 15cm deep and collecting all of the soil dug from the center of the pen. The second sample was taken 3 meters from the pen perimeter in the same protocol as the center of the pen, with the removal of ground cover and digging 15cm. The third sample was taken 8 meters from the pen enclosure with the same protocol.

Interviews were completed with the farmís owners regarding the farmís history and practices during the first visit. Each collection date had samples collected in the noon time hour. The collection sites were in the same direction at each visit, north.

After collection of the samples, tests using the LaMotte Soil Testing Kit for combination soils, model EM-code 5934 (#6) were completed. Following the manual with the testing kit, the samples were allowed to dry over night on waxed paper and then sifted in a medium sized soil sifter to give a uniform sample. As much foreign matter was removed as possible but some white pine needles remained. It was during the sifting process that a worm was found in one sample (L3).

††††††††††† The samples were labeled as stated above with the type of animal and the number of meters from pen, and the results of the soil testing were recorded. After drying, sifting and removal of debris, the testing was completed, following the instructions from the soil kit.

††††††††††† Because numerical values were not able to be obtained from the soil testing kit, values were assigned. High concentration would receive a numerical value of 4 and trace amounts would receive a value of 1. This would allow the use of a T-test to obtain the

p-value and identify if our results were statistically significant or not.

 

 

†† Results

††††††††††† Our hypothesis was not supported. The nitrogen testing had no significant difference, showing mostly trace available N for all samples for the Donkey pen as well as the Llama Pen (Table 1 & 2). The phosphorus results were more interesting and supported our hypothesis (Figure 1), especially in the llama pens.

 

Sample Description

Nitrogen Reading

Phosphorus Reading

Within Pen

Trace 1

High 4

Within Pen

Trace 1

High 4

3 Meters from Pen

Trace 1

High 4

3 Meters from Pen

Trace1

High 4

8 Meters from Pen

Trace 1

Low 2

8 Meters from Pen

Trace 1

Low 2

Table 1: Levels of Phosphorus and Nitrogen in Soil Sample No.2 Donkey Pen

 

Sample Description

Nitrogen Reading

Phosphorus Reading

Within Pen

Trace 1

Medium 3

Within Pen

Trace 1

Medium 3

3 Meters from Pen

Trace 1

Low 2

3 Meters from Pen

Low 2

Low 2

8 Meters from Pen

Trace 1

Trace 1

8 Meters from Pen

Trace 1

Low 2

Table 2: Levels of Phosphorus and Nitrogen in Soil Sample No. 2 Llama Pen

Text Box: Assigned Nitrogen Levels

 

Figure 1: Phosphorus Levels for Donkey and Llama Pens

 

The assignment of numerical values for the high, medium, low and trace levels of nitrogen and phosphorus lead to difficulty in graphing the results. The p-value of 0.2285 was obtained using a 2 tailed type 3 T-test based on the phosphorus levels and the nitrogen values were not used in any statistical manor, as there was basically no variance (Table 1 & 2).Neither the llama or donkey pen provided results that were statistically significant.

 

Discussion

In interviewing the farm owners we discovered that in the construction of the pens a mix of sand and clay was added to the area in order to protect the animalís hooves. Also, the pens were raked free of feces on a weekly basis but the perimeters of the pens were undisturbed.

We were somewhat surprised that the N levels did not follow our hypothesis. However in post-research, we were reminded of the different oxidation states of the nitrogen atom. The changes between different states are regulated by microorganisms in the soil (Paul, 1988). The original soil manipulation, the weekly raking and dependence of microbes for nitrogen to change states are all variables that could have affected why the test results were not as significant as we expected.

It is unknown if the owners of the farm repeatedly add the sand/clay mixture to the pens. The mix of sand and clay would eventually layer out with the lighter sand staying atop and the heavier clay sinking downward. The raking of the pens would assist in continual mixing of the pen soil as well as removal of feces. These manipulations would affect the native soilsí and microbesí interactions with nitrogen.

The addition of sand/clay to the pen soil would change the top soil, making leaching within the sandy topsoil occur at a faster rate. The weekly raking of the pens could affect the results by changing the microorganismsí chance to shift the states of the nitrogen. These different states of N relate to the available N that was measured in the simple LaMotte soil test. This could also affect the ability for the nitrogen to leach into the soil by the removal of the nitrogen source. Or perhaps this affected our results by not allowing the excrement an opportunity to fully decompose into the soil.

In repeating this experiment it would be ideal to have an animal enclosure without the additional sand/clay mix. This would allow for the native soil to express the leaching of both N and P without the potential accelerator of sand. Perhaps a comparison of a pen with weekly raking and non- weekly raking would be helpful in identifying first how much the weekly raking affects the leaching. Then compare those results to the 3m and 8m readings. Also, rather than simply digging the 1L soil, it would be suggested to take a soil core sample from each of the sample sites, which would allow us to test more than just the top soil.

If able, testing of surrounding water supplies would be beneficial. Investigating the leaching of the nutrients in the animal excrement and if it is contaminating the water table. It is known animal waste products are capable of leaching into the soil and even the ground water supply which could introduce additional nitrogen, phosphorus and other contaminants into the area this could significantly affect the surrounding marsh areas (Letson, 1998).

 

 

 

 

 

 

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