Jennifer
Collins
Plant
and Soil Science Department
Evaluating Agricultural Phosphorus in Various
Sustainable Cropping Systems
Introduction
Phosphorus is a macronutrient that is essential for
plant growth. Phosphorus aids in seed production,
enhances root growth, energy storage and transfer. Phosphorus is often applied to agricultural
land to increase crop production or as an effort to balance the depletion of
soil P caused by removal of harvested biomass.
Crop production, however, is not the only sector of agriculture that
uses P. Animal agriculture often supplements P into the diets to improve animal
performance. Animal waste generally has
a high concentration of P due to feed concentrations and inorganic inputs. Consequently, livestock feedlots and cattle
grazing can introduce substantial amounts of P-rich manure to the
environment. Concern has developed
regarding animal agriculture and its effect on the environment because when
phosphorus is lost from fields it can impair surface water quality. This is becoming a key issue in the Southern
High Plains with the increasing amount of animal agriculture. Since most phosphorus adheres to soil
particles, factors that affect soil erosion are critical to phosphorus
movement. The P index is a tool that
accounts for this. It assesses the
potential for phosphorus to move from agricultural fields to surface
water. It uses an integrated approach
that considers soil and landscape features as well as soil conservation and P
management practices in individual fields.
Overall Objective
The overall objective is to evaluate changes
in soil P concentrations in integrated crop and livestock production systems.
Specific
Objectives
- Evaluate Phosphorus
differences among integrated crop and livestock production systems
- Evaluate the potential
for off-site movement
- Expand P index
knowledge with the use of field tests and site erosion characteristics
Materials and
Methods
Sites and cages were established in the
paddocks. Soil samples were collected at
these sites in 1997, 2002 and 2003.
Three soil cores were collected per sampling site location to a depth of
2 ft. The three soil cores were divided
into 0-6”, 6-12”, 12-18”, and 18-24” sections and combined for each depth. Available P was determined by the Olsen
bicarbonate extraction method.
Additional soil samples have been taken in the established cages to
evaluate the difference in an area that has never been affected by cattle in
comparison to the other sites within those paddocks. These data are being
analyzed.
To determine the potential for
off-site movement, the RUSLE2 program is being applied. This program will
enable us to gather valuable information more specific to the site and
incorporate it into the P index equation.
Results
Results to date are summarized in the following tables and figure.
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Table
1.1. Preliminary Statistical Summary of the Effects Of Source by Year on the
Concentration of P in Soils |
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Source |
May-97 |
May-02 |
Jan-03 |
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Rotation |
No |
Yes |
No |
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Depth |
Yes |
Yes |
Yes |
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Rep |
No |
No |
No |
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Rot*Depth |
No |
Yes |
Yes |
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Table
1.2. Preliminary Statistical Summary of the Effects of Source by Year on the
Concentration of P in Soils |
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Source |
0-6" |
6-12" |
12-18" |
18-24" |
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Rotation |
No |
Yes |
Yes |
No |
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Date |
Yes |
Yes |
Yes |
Yes |
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Rep |
No |
No |
No |
No |
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Rot*Date |
No |
No |
Yes |
No |
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Table
1.3. Preliminary Statistical Summary of the Effects of Source by Rotation on the
Concentration of P in Soils |
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Source |
Continuous Ctn. |
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Rye/Ctn/Wht |
Wht/F/Rye |
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Depth |
No |
Yes |
Yes |
Yes |
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Date |
Yes |
Yes |
Yes |
Yes |
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Rep |
No |
No |
No |
No |
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Depth*Date |
No |
No |
Yes |
Yes |
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* Yes
indicates a significant difference at the 5% level indicated by their p
values |
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Figure 1. Concentrations of phosphorus as influenced by rotation, time, and depth of
sampling.