ONA REPORT

published in

THE FLORIDA CATTLEMAN AND LIVESTOCK JOURNAL


November 2015

Jiggs Bermudagrass Responses to Potassium and Phosphorus Fertilization

by Maria L. Silveira


For questions or comments regarding this publication contact: Dr. Maria Silveira, University of Florida, IFAS

While nitrogen (N) typically represents the most limiting nutrient affecting forage production in the southeastern USA, phosphorus (P) and potassium (K) are often related to long-term persistence of grass pastures and hayfields. The relatively large K removal with harvested biomass in combination with sandy-textured soils with low K-buffering capacity can lead to severe K deficiency symptoms, particularly in mechanically harvested forage production systems. To address this issue, a 3-yr field study was conducted at the UF/IFAS Range Cattle Research and Education Center, in Ona, FL to evaluate Jiggs bermudagrass responses to K and P fertilization. Treatments consisted of minimum fertilization regimens that could maintain optimum forage yield, nutritive value, and stand persistence. Potassium and P were applied in the spring (April) of 2012, 2013, and 2014 at annual levels of 0, 40, and 80 lb K2O/A and 0, 20, and 40 lb P2O5/A, respectively. Nitrogen was applied at an annual rate of 80 lb N/A. Nitrogen was applied as ammonium nitrate and P and K as super triple phosphate and potassium chloride, respectively. Soil was an Ona fine sand (sandy, siliceous, hyperthermic Typic Alaquods). Plot size was 20 x 10 ft with a 10-ft alley between plots. Initial soil pH was 5.3 and Mehlich-1 extractable P, K, and magnesium (Mg) concentrations were 23, 12, and 293 lb/A, respectively. These levels are considered to be medium for P, very low for K, and very high for Mg. Forage was harvested at 6-week intervals for a total of 4 harvest events per year to determine dry matter yield and nutritive value. Dry matter yield was determined by harvesting two 3- x 10-ft forage strips from each plot to a 3-inch stubble height using a forage harvester. The remaining herbage was harvested to the same stubble height using a sickle bar mower and removed from the plots. Forage samples were dried at 60oC for 48 hr for dry matter yield determination. Oven-dried samples were ground to pass through a 1-mm mesh screen for chemical analysis.

RESULTS

Climatological Data
Temperature patterns observed during the 3-yr study were typical for the region, with exception of below freezing temperatures that occurred in spring (March) 2013. Freezing events in this region typically occur during the months of December to February, thus the low temperatures experienced in during the spring of 2013 were atypical and resulted in negative impacts on forage production during the 2013 growing season. Annual rainfall observed during the study period was ~ 20% below the average in 2012 and 2013 (~ 43 inches in 2012 and 2013 compared to the 71-yr average of 53 inches) but approached the long-term average in 2014 (51 inches in 2014). The drought conditions experienced in the beginning of the 2013 growing season also contributed to decreased forage production during this year.

Jiggs bermudagrass responses
Jiggs bermudagrass dry matter yield increased linearly as annual K fertilization levels increased (Table 1). No effect of P fertilization on Jiggs responses was observed. Cumulative annual dry matter yield for the treatments receiving K increased ~ 26 to 377% relative to the control treatments (no K added). The largest differences between control and K-receiving treatments were observed in 2014. During this year, K fertilization increased Jiggs bermudagrass dry matter yield by as much as 377% (5357 lb/A for the treatment receiving 80 K2O/A compared to 1124 lb/A for the controls). Jiggs bermudagrass dry matter yield in 2013 was considerably lower than those reported in 2012 and 2014 due to unfavorable climatic conditions experienced during that year. Averaged Jiggs crude protein concentrations across the 3-yr study were greater in the controls compared to the treatments receiving K (Table 1). This occurred because of a dilution effect as a result of greater dry matter yield observed in the treatments receiving K.

Regardless of the K fertilization levels, Jiggs bermudagrass dry matter yield generally decreased over time during the study period. These data indicated that K levels being applied during the 3-yr study were not sufficient to sustain the same level of production. In addition, considerable stand losses and concomitant weed infestation occurred at the end of the 3-yr study, particularly in the treatments receiving no K (Table 1). Jiggs bermudagrass frequency and ground cover ranged from 50 to 54 % in the treatments receiving K compared to ~ 31 to 37% in the control treatments.

Table 1. Jiggs bermudagrass dry matter yield, frequency, ground cover, and crude protein concentration as affected by K application level.

Annual K2O application level Cumulative Dry Matter Yield Frequency1 Ground Cover1 Crude Protein2
2012
2013
2014
- - - - - - - - - - - - - - - - - - lb/A - - - - - - - - - - - - - - - - - -
- - - - - - - - - - - - % - - - - - - - - - - - -
0
4536
820
1124
37
31
15.2
40
5719
1815
3959
50
52
14.0
80
6517
2216
5357
54
54
13.7
Standard error
343
129
267
1
1
0.2
Orthogonal contrast
Linear***
Linear***
Linear***
Linear***
Linear***
Linear***

1Frequency and ground cover were measured at the end of 2014 growing season.

2Values represent the 3-yr average

*** = P ≤ 0.0001





Conclusions
Potassium fertilization resulted in greater Jiggs bermudagrass dry matter yield and decreased stand loss in the 3-yr study. Despite the positive effect of K, Jiggs bermudagrass dry matter yield observed in 2014 was significantly lower than those obtained in the first year of study and considerable stand losses and concomitant weed infestation occurred at the end of the study. Although the amounts of K exported via above-ground biomass were, in general, similar or less than those applied as fertilizer, K fertilization at the levels tested in this study were likely not sufficient to sustain the same level of production during the 3-yr study. No effect of P on Jiggs bermudagrass responses were observed. Results from this study suggested that continuous above-ground removal without proper K fertilization may result in decreased Jiggs bermudagrass performance, stand loss, and increased weed infestation. Adequate K supply is essential to sustain Jiggs bermudagrass productivity and long-term persistence.


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