Long-Term Effects of Liming and N Fertilization on Bahiagrass Pasture

Martin B. Adjei and Jack E. Rechcigl

Revenue loss from the decline in bahiagrass forage production and cost of pasture re-establishment combined is ~$50 million yr-1 in Florida. Damage first appears as yellow patches of grass that later die and turn brown. Feeding by “Tawny” mole crickets (Scapteriscus vicinus Scudder) is the principal terminal cause but other predisposing factors are suspected to play a roleObjective This study determined the interactive effects of fertilizer and lime applications on bahiagrass yield, nutritive value and stand persistence under grazing conditions.

Materials and Methods Design: Split plot experiments on 2 separate bahiagrass pastures. Main plots: 3 randomized complete blocks of limed (to maintain a soil pH >5) vs. no- lime treatments on each pasture. Dolomitic lime applied every 2-3 yr on limed plots. Sub plots: Four annual fertilizer treatments applied to the same 15.2 x 15.2 plots from 1998 through 2003. Soil: Pomona fine sand (sandy, silicious, hyperthermic, Ultic Alaquod). Fertilizer treatments: 1) 67 kg N ha-1 (N), 2) 67-12-56 kg N-P-K ha-1 (NPK), 3) 67- 12-56kg N-P-K ha-1 plus 22 kg ha-1 of micronutrient mix (NPKM), and 4) control (no fertilizer) with N from ammonium sulfate. Micronutrient analysis: 24 g B kg-1, 24 g Cu kg-1, 114 g Fe kg-1, 60 g Mn kg-1, 0.6 g Mo kg-1, and 66 g Zn kg-1.

Plots fertilized once in March, yearly (1998-2003)

Pastures were grazed every 35 d following the initial fertilization

Forage regrowth under cage harvested every 35 d after grazing and cage moved to a new cut (7.5 cm stubble) area in plot. Forage subsamples dried, ground and analyzed for CP, IVOMD, P, K, Ca. Mg, Fe, Zn Cu and Mn.

Fertilization Grazing

Botanical composition

Forage yield

Six, 1-m2 quadrats evaluated per plot in May, yearly for % green, yellow or dead and invaded by weeds

Good plot Damaged plot

Soil Sampling Soil sampled from top to 15 cm depth (Ap horizon) and at the spodic (Bh) horizon before the experiment and at end of each season (1998-2003)

ResultsEffect of lime and fertilizer on mean annual DMY on pasture 87

0123456789

10

Dry

mat

ter

yiel

d,

t/h

a

No lime Lime

Lime treatment

N

NPK

NPKM

Cont

a a a b

a a a

b

30% better response to N with lime

0

2

4

6

8

10

12

Dry

mat

ter

yiel

d,

t/h

a

Pasture 71A

N

NPK

NPKM

Cont

Effect of fertilizer on mean annual DMY on pasture 71A

a a ab

Response to N but not lime

5-yr Mean CP

Fert.

Pasture 87 71A

N 12.9a 11.6a

NPK 12.2a 11.3a

NPKM 12.1a 11.3a

Cont. 10.7a 10.0b

CP increased with N

5-yr mean IVOMD

Fert.

Pasture 87 7iA

N 48.5ab 49.0a

NPK 49.1a 49.1a

NPKM 48.6ab 48.6a

Cont. 47.4b 47.3b

IVOMD increased with N

Dry Matter Yield

Nutritive Value Mean Tissue Minerals

0102030405060708090

100

% G

roun

d co

ver

No-lime Lime

Lime treatment

NNPKNPKMCont

pH 4.2

pH 4.3

Cont

NPKM

NPK

N

0102030405060708090

100

% g

rou

nd

co

ver

No-lime Lime

Lime treatment

N

NPK

NPKM

Cont

a

bbc

NS

N by Lime effect on Spring Vegetative Ground Cover

Damage to No-lime plots except the control on pasture 87 in spring 2003 Yellowing of No-lime plots except

the control on pasture 71A in spring 2005

Pasture 87, 5th yr Pasture 71A, 7th year

Limed strip No-lime strip

Pasture 71A, spring 2005

N

NPK

ContNPKM

Conclusions•N was key to bahiagrass pasture production.

•DMY Increase due to P & K was not cost-effective under grazing conditions.

•Repeated N fertilization without lime dropped soil pH, increased spring grass yellowing and promoted stand deterioration.

•Is problem S or Fe deficiency or Al3+ toxicity?

•Monitor soil pH every 2-4 years and lime to maintain pH of 5-6 for stand persistence.

Nutrient RangeP* (g kg-1) 1.6-2.8K* (g kg-1) 9.0-14.0Ca*(mg kg-1) 2943-5474Mg*(mg kg-1) 982-2071Zn (mg kg-1) 70-130Fe (mg kg-1) 50-70Cu (mg kg-1) 2.9-8.7Mn (mg kg-1) 33-112

* Affected (P < 0.01) by P, K or dolomite application

6-yr Mean Soil pH

Site Fertilizer No lime Limed

87

N 4.2 4.4NPK 4.3 4.5NPKM 4.3 4.6Cont 4.2 4.9

71A

N 4.3 4.8NPK 4.4 4.6NPKM 4.3 4.7Cont 4.5 4.8

Without repeated lime soil pH declined to the native state.

Soil Depth

Ap Bh

Site mg Al kg-1

87 39 196

71A 31 242

3-yr Mehlich-1 Al

Same across treatments

c c

b

a

Nitrification cause of acidity: 2NH4+ + 3O2 = 2NO2

- + 2H2O + 4H+ (Nitrosomonas)

2NO2- + O2 = 2NO3

- (Nitrobacter)