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



Results


Moderately Grazed Trial

Total production on the moderately grazed trial resulted in no treatment effects over the four years (Table 3). A year effect resulted in 2002 being significantly lower than 2000, 2001, and 2003. Cool season grasses, warm season grasses, forbs, and shrubs had similar treatment effects although year effects were prominent in each plant class. Phosphorus, being a limiting factor in plant growth, and the second most important nutrient behind nitrogen, should be a concern late in the grazing season in regards to the plants being able to meet the minimum cattle requirements of phosphorus. During the grazing season the control was deficient of phosphorus 37% of the time (Table 2). The 33 lb N/ac was deficient 44% of the time and 66 lb N/ac was deficient 49% of the time, versus the May 1 applications of 24 lb P/ac being deficient 12% and 48 lb P/ac 2% of the time. The June 20 applications of 24 lb P/ac were deficient 11% and 48 lb P/ac 9% of the time. It appears that the higher lbs/ac applied is more beneficial than the earlier date applied. This is opposite what was found on the extremely grazed trial where the earlier application seemed more beneficial than the higher pounds applied. Overall, the moderately grazed trial and the extremely grazed trial were similar in percent time phosphorus deficient from 2000 to 2002. The moderately grazed trial resulted in a phosphorus deficiency on the nitrogen treatments 47% of the grazing season. The phosphorus treatments were deficient 9%, of the season and the control was deficient 37% of the grazing season. The extremely grazed trial resulted in a phosphorus deficiency on the nitrogen treatments 37% of the grazing season. Phosphorus treatments were deficient 12% of the season and the control was deficient 42% of the grazing season. Forbs on the moderately grazed fertilization exclosure had a year effect with 2001 and 2002 having significantly lower forb diversity than 2000. A treatment effect was also observed with 33 lbs N/ac having higher forb diversity than 24 lbs P/ac June 20, 66 lbs N/ac June 20, control, and 48 lbs P/ac May 1 (Figure 2).

 

 
Table 2. Slow release fertilizer treatment application rates and percent time (from June-September) that plants did not meet the minimum phosphorus requirements of a 1,200 lb lactating cow with respect to fertilizer treatments on the extremely grazed and moderately grazed exclosures, Central Grasslands Research Extension Center, Streeter.

 

Fertilizer Type Date Applied Rate Applied Extremely Grazed Moderately Grazed
      Percent time P deficient
Control None None 42% 37%
Phosphorus May 1 24 lb/ac 11% 12%
Phosphorus May 1 48 lb/ac 7% 2%
Phosphorus June 20 24 lb/ac 16% 11%
Phosphorus June 20 48 lb/ac 13% 9%
Urea June 20 33 lb/ac 31% 44%
Urea June 20 66 lb/ac 42% 49%


 

 

 

Table 3. Above ground production (lb/ac) for fertilizer treatments on moderately grazed mixed grass prairie at Central Grasslands Research Extension Center, Streeter.

 

Fertilizer Treatment

  Year Control May 1

24 lb

P/ac

May 1

48 lb

P/ac

June 20

24 lb

P/ac

June 20

48 lb

P/ac

June 20

33 lb

N/ac

June 20

66 lb

N/ac

Cool-season

grass

2000y 2174abcd 2736abcd 3166bcd 2512abcd 2671abcd 2034abc 1936abc
2001y 2656abcd 3127bcd 2520abcd 2740abcd 2131abcd 2877abcd 3291cd
2002x 1787ab 1868ab 1717a 2036abc 1931abc 1985abc 2198abcd
2003y 2447abcd 2535abcd 2522abcd 2292abcd 2337abcd 2932abcd 3435d
Warm-season

grass

2000 36 3 1 0 1 160 64
2001 0 18 0 0 192 1 0
2002 31 2 1 0 20 2 3
2003 0 0 61 62 65 0 0
Forb 2000z 676ab 532ab 918abc 1008abc 748abc 1421bc 1169abc
2001y 973abc 439a 828abc 649ab 773abc 620ab 441a
2002x 533ab 263a 325a 306a 364a 529ab 271a
2003z 1040abc 773abc 1656a 1220abc 797abc 656ab 539ab
Shrub 2000z 367 573 69 281 541 449 390
2001xy 191 247 189 174 263 255 315
2002x 88 218 111 92 226 187 269
2003xy 265 263 166 411 279 246 224
Total 2000y 3254 3844 4156 3801 3962 4066 3561
  2001y 3821 3833 3538 3564 3362 3755 4048
  2002x 2441 2352 2154 2434 2542 2705 2741
  2003y 3753 3572 4407 3986 3479 3835 4199
1Means in a plant class followed by a different letter differ (P<0.05).

2 Means in the year column in each plant class followed by a letter differ (P<0.05).




 


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