Fertilization of Extremely Grazed and Moderately Grazed Mixed Grass Prairie With Slow Release Phosphorus and Urea

J. Volk, W.T. Barker, P. Nyren and D. Whitted


 

Table of Contents


 

Introduction

 

The 2001 growing season was the second year of a 5-year fertilization study, which is superimposed on the grazing intensity study site at the Central Grassland Research Extension Center (CGREC). In the past, most range fertilization studies in North Dakota have involved using fast release fertilizers such as ammonium nitrate and super-phosphate fertilizers. Cool–season grasses dominate Northern Great Plains Grasslands. With fast release fertilizers cool-season species are usually favored and warm-season species usually decrease in the species composition. When grazing animals harvest the forage each year they remove nitrogen and phosphorus from the system. Over the long term, productivity and species composition of the grassland can be affected. The objectives of this study are:

 

1.         To determine the changes in species composition resulting from fertilization with slow release phosphorus (P) and urea (N) on extremely grazed and moderately grazed mixed-grass prairie.

2.         To determine the production of cool-season grasses, warm-season grasses, forbs and shrubs on the slow release fertilizer treatments.

3.         To determine the seasonal uptake of phosphorus in selected forage species.

4.         To determine the soil phosphorus levels in different range sites or landscape positions on the CGREC

 

Background


Since the time of settlement we have seen deterioration in some of our rangelands. Before settlement, the abundance of large ungulates in the area was a constant supply of phosphorus for the plants and soil. When the animals died their bones deteriorated and released phosphorus into the soil. This in turn, promoted native grass growth, high forage production, and high quality soils. Over time, the depletion and deterioration of the land has allowed introduced species to increase, decreasing plant production, soil quality, and in essence has decreased livestock and wildlife production (Heady 1975).

 

Use of fertilizer on dryland ranges is a practical means of increasing forage production in certain situations. However, some range fertilization studies have shown erratic or undesirable effects. Huffine and Elder (1960) in Oklahoma found that fertilized native pastures produced two to five times more weeds (by weight) than did unfertilized pastures. On the other hand, results from a six-year study in North Dakota showed that two years of fertilization, with 90 lb of nitrogen on a heavily grazed pasture, did more to improve range condition and production than did six years without grazing (Lorenz 1970).

 

Nearly all papers on range fertilization report favorable biological results but with wide and often unpredictable variations. Substantive floristic composition changes in native grassland communities due to fertilization are well documented in the Northern Great Plains. The nature of the change generally results in a shift from an abundance of warm-season species, to just cool-season species (Goetz, Nyren et al., 1978). The most immediate and easily measured response to nitrogen fertilization has been the general increase in forage production and improvement of forage quality (Goetz, Nyren et al., 1978). A much less well understood response due to fertilization is the almost universal shift in plant species dominance from one of warm-season short grasses to cool-season mid-grasses (Goetz, Nyren et al., 1978).

Additions of phosphorus on rangeland usually favors grasses, legumes and other forbs, but nitrogen fosters the grasses and reduces the legumes (Heady 1975). In the mixed-grass prairie, fertilization alters the proportion of cool-season species and can increase undesirable weeds. Forb species for example, mainly white sage and fringed sage showed definite responses to the presence of the applied nitrogen, generally increasing with each added increment of nitrogen (Goetz 1969). In addition to the increase in density of the species, the plants showed definite tendencies toward profuse branching, which greatly increased the area of a single plant (Goetz 1969). A shift from sod-forming, warm-season short grasses to single stalked, cool-season mid-grasses has been found by most authors. Also a shift in species composition altered the seasonal growth pattern from warm-season species to cool-season species, and the nutritional value of the forage (Karn & Lorenz 1983).


Response of mixed prairie vegetation to annual applications of N and P fertilizer was studied during an eight-year period at the Northern Great Plains Research Center near Mandan, North Dakota (Lorenz 1970). Fertilizer rates of 0, 40, 80, and 160 pounds of elemental N and 0, 18, and 35 pounds of elemental P were used. Increase in dry matter production in response to N was found to be highly significant and nearly linear in nature for the 40-N and 80-N levels, but 160-N often produced no more forage than did 80-N (Lorenz 1970). Response to P was often not significant during the first three years of the study, however over the eight-year period, each increment of P produced highly significant yield increases (Lorenz 1970). Without N, response to P was small, but as N level increased, response to P increased (Lorenz 1970).

 

Methods

 

Two sites of 148 ft by 197 ft were chosen, one being in an extremely grazed pasture and the other in a moderately grazed pasture. Within each site, four repetitions of 69 ft by 49 ft were laid out and seven different treatments were placed within each repetition. Each treatment size is 9.8 ft by 49.2 ft. There is a 16.4 ft alley way between each repetition and a 21 ft buffer from the outside. In the year 2000 the fertilizer rates applied were 24 and 48 lbs/acre P applied May 1st; 24 and 48 lbs/acre P applied June 20th; and 33 and 66 lbs/acre N applied June 20th. The fertilizers used are slow release Polyon fertilizers provided by Pursell Technologies Inc. Over the course of the summer four clipping sets were taken of five plant species to determine the uptake of phosphorous. The five species clipped were western wheatgrass (Agropyron smithii), green needlegrass (Stipa viridula), Kentucky bluegrass (Poa pratensis), smooth brome (Bromus inermis), and buckbrush (Symphoricarpos occidentalis). These samples were dried at 150 degrees Fahrenheit then ground through a 1 mm screen in a Wiley Mill and are now being tested for phosphorous content in the NDSU Animal and Range Sciences Nutrition Lab. Also a separate clipping was performed to establish production on each of the treatments. This was done by clipping three samples on each treatment and separation of these samples into warm-season grasses, cool-season grasses, forbs, shrubs, litter and standing dead plant material. These samples were dried at 150 degrees Fahrenheit for 48 hours and then weighed. An average of the three samples per treatment was calculated and an average of each treatment on all four repetitions of each grazing intensity was taken.

 

Results

 

Production data were taken in the summers of 2000 and 2001. The results are listed in Table 1. In the extremely grazed pasture, cool-season grasses increased from 2000 to 2001 except in the control plot (treatment 1) where they decreased. Warm-season grasses increased from 2000 to 2001 in treatments 3, 4, and 5 but decreased in treatments 1, 2, 6, and 7. Forbs increased from 2000 to 2001 in treatments 1, 2, 4, and 7 but decreased in treatments 3, 5, and 6. Shrubs increased from 2000 to 2001 in treatments 4, 5, 6, and 7 but decreased in treatments 1, 2 and 3 (Table 1).

 

In the moderately grazed pasture, cool-season grasses increased from 2000 to 2001 in treatments 1, 4, 5, and 6 but decreased in treatment 2, 3, and 7. Warm-season grasses increased from 2000 to 2001 in treatments 3, 6, and 7, decreased in treatments 1, 2, and 4, and stayed the same in treatment 5. Forbs increased from 2000 to 2001 in treatments 1, and 3 but decreased in all other treatments. Shrubs increased from 2000 to 2001 in treatment 2 but decreased in the other treatments (Table 1).

 


Table 1. Aboveground Production for 2000 & 2001 in Lbs/acre.

Treatment

Treatment

 Number

Date

Extremely grazed

Moderately Grazed

Cool

Season

Grass

Warm

Season

Grass

Forbs

Shrub

Cool

Season

Grass

Warm

Season

Grass

Forbs

Shrub

Control

 

1

2000

2035.8

48.9

641.3

60.2

2174.1

36.7

676.3

367.1

2001

1924.3

7.7

686.4

36.0

2656.2

0.0

973.4

191.8

48# P May 1

  

2

2000

1205.4

68.2

562.9

91.2

3166.6

2.0

918.2

69.7

2001

1943.7

13.6

766.6

9.1

2520.2

0.0

828.7

189.7

48# P June 20

 

3

2000

1082.2

24.2

530.5

102.3

2671.2

1.3

748.9

499.5

2001

1973.1

57.2

473.4

70.1

2131.9

192.6

774.0

263.9

33# N June 20

 

4

2000

1215.2

44.2

633.0

54.5

2601.7

160.8

897.1

487.3

2001

1540.3

133.4

921.9

80.3

2877.8

1.8

620.8

255.1

66# N June 20

 

5

2000

1366.4

57.8

727.0

51.5

2211.2

0.0

905.3

454.8

2001

2319.1

82.0

640.4

75.1

3291.2

0.0

441.1

315.9

24# P May 1

 

6

2000

1192.8

163

521.8

29.6

2736.0

3.0

532.0

573.1

2001

1972.5

23.5

443.5

74.5

3127.0

18.4

439.7

247.9

24# P June 20

 

7

2000

1085.6

203.7

593

28.2

2512.3

0.0

1008.1

281.3

2001

2740.7

0.0

649.8

174.3

1934.8

180.4

554.3

67.8


Phosphorus Concentrations in the Moderately Grazed Pasture

 

Phosphorus levels on the moderately grazed pasture in the summer of 2000 showed that levels were erratic (Table 2). More often than not P levels were marginal or deficient with the exception of the first clipping in June where all species met the requirements of a 1200 lb lactating cow. The nitrogen treatments applied June 20th showed a deficiency for all species except buckbrush in the last two clipping dates. The control plot was also highly deficient except for the June clipping date where all species met the requirements.

 

The 48 lb P applied on May 1st showed the best results for meeting the needs of a 1200 lb lactating cow across the four clipping dates with the exception of Kentucky bluegrass which was deficient in the July and August clippings, and green needlegrass was deficient in the July clipping.

 

The 48 lb P applied June 20th did not respond as well. Kentucky bluegrass, smooth brome, and buckbrush met the requirements in the July clipping but for the August and September clippings buckbrush and western wheatgrass met the requirement, and in the September clipping green needlegrass also met the requirement.

 

The 24 lb P applied May 1st showed Kentucky bluegrass was deficient in the last three clippings along with smooth brome in the June clipping and smooth brome and green needlegrass in the July clipping. The 24 lb P applied June 20th showed similar results with the exception of green needlegrass which was deficient in the July clipping and western wheatgrass in the August clipping.

 


Table 2. Percent Phosphorus Concentrations for the Year 2000 for Moderately Grazed Pastures by Species and Clipping Dates

 

Treatments

 

Date of

Clip

Species

Control

48# P

May 1

48# P

June 20

33# N

June 20

66# N

June 20

24# P

May 1

24# P

June 20

Minimum Required

June 7

Kentucky bluegrass

0.23

0.25

-

-

-

0.26

-

0.19

 

smooth brome

0.28

0.28

-

-

-

0.25

-

0.19

 

green needlegrass

-

-

-

-

-

-

-

0.19

 

buckbrush

0.31

0.30

-

-

-

0.27

-

0.19

 

western wheatgrass

0.28

0.31

-

-

-

0.30

-

0.19

July 7

Kentucky bluegrass

0.17

0.17

0.20

0.17

0.16

0.15

0.14

0.18

 

smooth brome

0.16

0.22

0.19

0.17

0.16

0.17

0.17

0.18

 

green needlegrass

0.16

0.18

0.17

0.23

0.17

0.23

0.18

0.18

 

buckbrush

0.2

0.25

0.21

0.19

0.18

0.21

0.19

0.18

 

western wheatgrass

0.18

0.24

0.18

0.18

0.19

0.20

0.22

0.18

Aug. 7

Kentucky bluegrass

0.13

0.17

0.15

0.12

0.14

0.14

0.13

0.17

 

smooth brome

0.16

-

0.16

0.19

0.13

0.15

0.17

0.17

 

green needlegrass

0.14

0.30

0.14

0.16

0.15

0.16

0.14

0.17

 

buckbrush

0.18

0.21

0.21

0.18

0.18

0.21

0.20

0.17

 

western wheatgrass

0.14

0.21

0.18

0.17

0.15

0.18

0.17

0.17

Sept. 7

Kentucky bluegrass

0.13

0.15

0.13

0.12

0.12

0.14

0.12

0.14

 

smooth brome

0.12

0.16

0.14

0.12

0.13

0.17

0.15

0.14

 

green needlegrass

0.13

0.19

0.15

0.13

0.14

0.15

0.17

0.14

 

buckbrush

0.18

0.21

0.20

0.16

0.16

0.19

0.20

0.14

 

western wheatgrass

0.16

0.22

0.17

0.13

0.14

0.17

0.16

0.14

Bold values indicate marginal to deficient for a 1200 lb lactating cow


Phosphorus Concentrations in the Extremely Grazed Pasture

 

The phosphorous concentrations in the extremely grazed pasture were better than those found on the moderately grazed pasture (Table 3). Overall, most of the deficiencies were in the July clipping and only Kentucky bluegrass, and western wheatgrass were deficient in the June clipping on the control plot. The control treatment had the most deficiencies. All species were deficient in the July clipping and only buckbrush met the requirements in the August clipping. In the September clipping smooth brome and buckbrush met the minimum requirements.

In the 48 lb P applied May 1st treatment only buckbrush in the July clipping did not meet the requirements. This treatment and the 24 lb P applied May 1st treatment had the least number of deficient species. In the 24 lb P applied May 1st only smooth brome was deficient in the July clipping.

 

The 33 lb N applied June 20th and 66 lb N applied June 20th treatments were virtually identical with all species except green needlegrass being deficient in the July clipping. In the August clipping Kentucky bluegrass was deficient in both treatments and western wheatgrass was deficient in the August and September clipping in the 66 lb N treatment.

 

The 48 lb P applied June 20th looked similar to the N treatments in that all species except green needlegrass were deficient in the July clipping. Western wheatgrass was the only deficient species in the September clipping.

 

In the 24 lb P applied June 20th treatment, the only species not deficient was green needlegrass in the July clipping. In the August clipping smooth brome was deficient and western wheatgrass was deficient in the September clipping. Overall the control plot was the most deficient throughout the sampling periods with 14 out of 19 samples below the minimum requirement.

 

The 48 lb P applied May 1st and the 24 lb P applied May 1st were the best with only one deficient sample. Other results such as plant available phosphorus, basal covers, densities, and species changes will be reported in the January CGREC meeting.

 
 

Table 3. Percent Phosphorus Concentrations for the Year 2000 for Extremely Grazed Pastures by Species and Clipping Date.

 

 

 

Treatments

 

Date of

Clip

Species

Control

48# P

May 1

48# P

June 20

33# N

June 20

66# N

June 20

24# P

May 1

24# P

June 20

Minimum Required

June 7

Kentucky bluegrass

0.16

0.23

-

-

-

0.31

-

0.19

 

smooth brome

0.22

0.27

-

-

-

0.26

-

0.19

 

green needlegrass

-

-

-

-

-

-

-

0.19

 

buckbrush

0.25

0.25

-

-

-

0.25

-

0.19

 

western wheatgrass

0.07

0.26

-

-

-

0.28

-

0.19

July 7

Kentucky bluegrass

0.16

0.19

0.17

0.16

0.15

0.19

0.14

0.18

 

smooth brome

0.17

0.21

0.16

0.16

0.16

0.17

0.13

0.18

 

green needlegrass

0.15

0.23

0.25

0.20

0.25

0.19

0.19

0.18

 

buckbrush

0.18

0.17

0.17

0.16

0.17

0.20

0.17

0.18

 

western wheatgrass

0.18

0.21

0.18

0.18

0.16

0.19

0.18

0.18

Aug. 7

Kentucky bluegrass

0.14

0.24

0.22

0.16

0.16

0.18

0.20

0.17

 

smooth brome

0.16

0.20

0.19

0.19

0.18

0.18

0.16

0.17

 

green needlegrass

0.17

0.23

0.20

0.24

0.24

0.30

0.24

0.17

 

buckbrush

0.19

0.25

0.23

0.18

0.21

0.21

0.22

0.17

 

western wheatgrass

0.13

0.19

0.20

0.26

0.17

0.21

0.25

0.17

Sept. 7

Kentucky bluegrass

0.12

0.16

0.19

0.15

0.15

0.18

0.15

0.14

 

smooth brome

0.16

0.17

0.19

0.16

0.17

0.20

0.16

0.14

 

green needlegrass

0.14

0.18

0.19

0.18

0.17

0.20

0.16

0.14

 

buckbrush

0.16

0.18

0.21

0.18

0.18

0.21

0.20

0.14

 

western wheatgrass

0.13

0.21

0.06

0.16

0.14

0.15

0.14

0.14

Bold values indicate marginal to deficient for a 1200 lb lactating cow

 

 

J. Volk is graduate student, W.T. Barker is professor, D.Whitted is research specialist, NDSU Animal and Range Sciences Department, Fargo, ND; P. Nyren is director, NDSU Central Grasslands Research Extension Center, Streeter, ND.



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