Influence of Harvest Management on Rhizoma Perennial Peanut Production, Nutritive Value, and Persistence on Flatwood Soils

P. Mislevy, M. J. Williams, A. S. Blount, and K. H. Quesenberry, Range Cattle REC, University of Florida, Ona 33865

Abstract

Rhizoma perennial peanut (RPP), Arachis glabrata Benth., has high nutritive value, is long lived, and drought tolerant; however, its growth and persistence on flatwood soils (spodosols) common in south Florida is thought to be poor. The objective of this study was to determine the influence of harvest management (stubble height, 1 vs 4 inches) and RPP entries [Arbrook Select (local ecotype), ‘Arbrook’ (released cultivar), PI 262839, PI 262826, ‘Florigraze’ (released cultivar), Ecoturf (PI 262840), and PI 262833] on above-ground dry biomass (DB) yield, nutritive value, root mass, and persistence on better drained spodosol soils. Harvesting RPP back to a 1-inch stubble during the initial year yielded an average of 7.8 ton/acre compared with 4.0 ton/acre DB yield at the 4-inch stubble. However, after the third and fourth harvest years, no difference (P > 0.05) was found between stubble heights or between peanut entries averaging 3.6 (2002) and 5.8 ton/acre (2003). Forage nutritive value was not affected by stubble height and varied only slightly between entries, averaging 17.2% crude protein (CP) and 69.0% in vitro organic matter digestion (IVOMD). Continuously harvesting plants at a 4-inch stubble produced 80% more root mass and improved ground cover (GC) by nearly 40%. These data indicate RPP can be successfully grown for hay production on better drained flatwood soils of the southern USA, particularly if a 4-inch stubble height is maintained at each harvest.

Introduction

Much of the initial evaluation work with RPP for forage production and as a conservation crop was done by the USDA Soil Conservation Service (now Natural Resources Conservation Service) at their Plant Materials Centers in Arcadia and Brooksville, FL. Selections ‘Arb’ (PI 118457) and ‘Arblick’ (PI 262839) trace back to this program, but their use as forage or conservation species was very limited due to problems with slow establishment and low productivity. It was not until the release of Florigraze (PI 421707) and Arbrook (PI 262817) rhizoma peanut (19,20) by the University of Florida that this species was commercially utilized. Although still slow to establish (30,35), these cultivars had much higher DB production potential than previously available material. Studies have indicated that these cultivars are adapted throughout much of the Gulf Coast region of the USA (8, 29) and have proved useful for commercial hay production (11), pasture (3,22,27,28,34), creep grazing (33), and living mulch (7). It is now estimated that about 20,000 acres (23) of these cultivars have been planted with most of this occurring on well drained soils in northern Florida and southern Georgia.

Expansion of RPP into southern Florida is hindered by lack of tolerance of available RPP cultivars to saturated soil conditions (hypoxia) that commonly occur on spodosols in this region of the state (1). Harvesting RPP to a height of 4 inches always allowed the peanut stems to extend just above the water level allowing the movement of O₂ through the stems down to the root system. Presently we do not know the exact mechanism of O₂ transport down the stem; however, we do know plants harvested at a 1-inch stubble and submerged under water will die due to hypoxia. Flooding tolerance has been one of the major criteria in recent RPP plant introduction efforts (32), but screening of newly introduced germplasm for flooding tolerance and forage production will take years. Cultivar differences and clipping management has been shown to affect flooding tolerance in alfalfa, Medicago sativa L. (4,5,24). This suggested that existing RPP cultivars or selections in the latter phases of evaluation might be managed to better tolerate flooding stress and allow expansion of RPP hay and pasture production into southern Florida. The objective of this study was to determine the effects of stubble height (1 vs 4 inches) and RPP entries [Arbrook Select, Arbrook, Florigraze, Ecoturf (PI 262840), PI 262839, PI 262826, and PI 262833] on DB yield, nutritive value, root mass, and persistence on better-drained spodosol soils.

Growth and Harvest Procedures

The study plots were established on a sandy siliceous, hyperthermic typic Alaquod (Ona fine sand) in March 1999 at the Range Cattle Research and Education Center, Ona, FL. Seven rhizoma peanut entries [Arbrook Select, Arbrook, Florigraze, Ecoturf (PI 262840), PI 262839, PI 262826, and PI 262833] were planted in single rows down the center of 5- by 20-ft plots using rhizome pieces at a rate of 1,000 lb/acre. Immediately after plant emergence, N-P₂O₅-K₂O at 0-30-60 lb/acre plus elemental Cu, Zn, Fe, Mn (sulfate form) at 1.5 lb/acre, B at 0.15 lb/acre, and S at 4.5 lb/acre was applied. Fertilizer rates were determined by routine soil test analysis and recommendations by the University of Florida extension. Sixty days after planting, peanuts were treated with imazapic (Cadre) at 4 oz/acre in 30 gal H₂O. A second application of imazapic was applied in September during the initial year at the same rate, to control broadleaf weeds and annual grasses.

The field plot layout was a split plot with stubble height (1 or 4 inches) as the main plots and peanut entries as subplots. Whole plots were randomized in four complete blocks. In mid to late March of each year, plots were staged (removal of winter growth) to the proper stubble height and fertilized with 0-30-60 lb/acre N-P₂O₅-K₂O plus 1.5 lb/acre elemental Cu, Zn, Fe, Mn (sulfate form), 0.15 lb/acre B, and 4.5 lb/acre S. After staging, plots were harvested three or four times annually from 2000-2003 (Table 3). The forage removed at staging was never added to the annual yield because this was a compilation of plant material that was exposed to winter frosts, low quality, and abnormal growth during the cool season. Harvests were made each time Arbrook and Arbrook Select attained a height of 12 inches. Both the 1- and 4-inch stubble-height treatments were cut at the same time for all entries to standardize the harvest regime, resulting in similar harvests/season. We made that decision prior to the initial harvest and at that time we knew PI262833 would never attain a 12-inch height, rendering unnecessary the harvest height combination with a 12-inch trigger.

A strip of forage 19 inches by 8 ft was harvested out of the center of each plot to desired stubble height to determine DB yield. A sub-sample of the DB harvest was collected for CP and IVOMD determination for every harvest (forage nutritive value was not determined in 2003). All forage samples were dried at 140°F, ground, and analyzed for total N (9,10). Crude protein concentration was calculated as 6.25 × N. Additionally, IVOMD was determined for forage samples by the two-stage procedure of Tilley and Terry (25) as modified by Moore and Mott (18).

At the end of the fourth harvest year, root/rhizome mass was determined using a 4-inch diameter core sampler. Two core samples were extracted from each treatment and standardized at a depth of 4 inches. This means that every core was cut off at a 4-inch length to eliminate differential root length, even though 99% of the roots/rhizomes are within the surface 3 inches of soil. Core samples from each treatment were immediately washed of all soil and debris, dried at 140°F, and weighed to determine root/rhizome mass. Prior to the initial harvest (2000) and following each harvest year, percentage GC was estimated for each peanut treatment, but only data from the initial and final-year estimates were presented.

Data were analyzed using PROC GLM (SAS Institute Inc., Cary, NC) with the model statement for a split-plot experiment in a randomized complete block design. stubble height was the whole plot treatment and peanut entries the subplot treatment. Main plots were arranged in four randomized complete blocks. Dry biomass yield, CP, and IVOMD were analyzed by individual harvests. Total yearly (DB) root mass, and percentage peanut ground cover were also analyzed. Differences among entries were determined using Waller-Duncan k-ratio t-test. Differences due to stubble height were tested using least square means. When significant interactions (P ≤ 0.05) between stubble height and peanut entries were found, selection means within stubble heights were separated using Duncan’s Multiple Range Test.

Harvest Management and Rhizoma Perennial Peanut

Dry biomass yield by stubble height and by entry, CP concentration, and IVOMD are presented in Tables 1 through 4. The main effects of stubble height and RPP entry were different within years for all responses. The interaction was not different between stubble height and peanut entries for DB yield and there was only one out of 10 interactions that was different for harvest dates over three years for CP and IVOMD (August 2000 for CP and June 2002 for IVOMD), so only the main effects will be discussed.

Dry biomass. Harvesting RPP to a 1-inch stubble produced higher DB yield when compared with the 4-inch stubble height during the first two years of the study (Table 1). In 2000, DB yield for the 1-inch stubble-height harvest treatment was almost double that for the 4-inch stubble-height harvest treatment. Although stubble-height effects were present in 2001, yields were lower in 2001 compared to the previous year (decreasing 50 and 30% for the 1-inch and 4-inch stubble heights, respectively). Flooding stress was probably the reason that yields declined in 2001. In 2000, rainfall was 40% below average (13) and the plot area was never flooded. By comparison in 2001, rainfall was 21% above average, and the plots experienced extended periods of water at or above the soil surface (14). Under normal rainfall conditions, the soils at the plot site only have water at or above the soil surface for short periods of time during the summer. After a certain number of days, water logging causes hypoxia (low oxygen concentration) in soils, and plants that lack mechanisms to maintain oxygen levels under such conditions, exhibit both root and shoot growth declines (2). Justin and Armstrong (12) reported growth of Lotus corniculatus L., a forage species considered to be only intermediate in its flooding tolerance, was reduced by 50% under flooding conditions. It would be easy to understand why RPP, a drought tolerant perennial legume well adapted to light, sandy, dry soils, would exhibit similar response to flooding stress.

Table 1. Influence of stubble height on dry biomass yield of rhizoma perennial peanut over four years, 2000-2003, when averaged over peanut entries.

Stubble height (inches)	Year				Mean
	2000	2001	2002	2003	Mean
	Dry biomass yield (ton/acre)
1	7.8 a^x	3.9 a (-50%)^y	3.8 a (-3%)	5.8 a (+53%)	5.3
4	4.0 b	2.8 b (-30%)	3.5 a (+25%)	5.8 a (+66%)	4.0

^x Means within a column followed by the same letter(s) were not different at the 5% level (Waller-Duncan’s Test).

^y Values in parenthesis indicate an increase or decrease in forage yield when compared with the previous year.

In 2002 and 2003, rainfall continued to be above average [29% in 2002 and 22% in 2003 (15,16)]. During both 2002 and 2003 no yield difference was obtained between stubble heights. This may have been due to stand age; plant age has been reported to effect flooding tolerance in alfalfa plants (24,26). Rhizoma perennial peanut typically develops a large rhizome mass below the soil surface (31), which is assumed to support the plant during drought stress periods and may function similarly under flooding stress. Studies by Mislevy (17) and Nathanson (21) reported soybeans develop a massive root system near the soil surface when exposed to saturated soil conditions to help maintain O₂ level in the plant. Averaged across the four harvest years, DB yield was similar for both stubble-height treatments. Based on yield alone, no recommendation on stubble-height management can be made, but root/rhizome mass and GC estimates (see discussion below) suggest that plants clipped at the 4-inch stubble height were physiologically stronger than those clipped to the 1-inch stubble height.

The influence of RPP entry on DB yield followed a similar pattern to stubble height across the years with yield differences between entries being the most variable in the drought year of 2000 (Table 2). Dry biomass yield in 2000 ranged between a high of 8.3 ton/acre for Arbrook and Arbrook Select to a low of 3.2 ton/acre of PI 262833. During 2001, the initial year of extremely wet conditions, DB yield was less variable with only Arbrook Select and PI 262833 differing in DB yield. Dry biomass yield of all entries declined in 2001 with the greatest declines occurring for Arbrook and Arbrook Select. This was not unexpected for these two selections because Arbrook is considered to be the least flooding tolerant of the released RPP cultivars (20) and Arbrook Select is a selection out of Arbrook. However, during the third and fourth years of the study no difference was found in DB yield between entries with average DB yield in 2003 equivalent to that found in 2000 (Table 2). Three entries actually exhibited yield increases between the first and fourth year of the study [89, 54, and 26% for Ecoturf (PI 262840), PI 262833, and Florigraze, respectively], while all other entries were essentially the same or showed yield decreases.

Table 2. Influence of rhizoma perennial peanut on total biomass yield (dry basis) over four years (2000-2003), when averaged over stubble height.

Peanut entry	Year				Mean	Change (%)^z
	2000	2001	2002	2003	Mean	Change (%)^z
	Dry biomass yield (ton/acre)
Arbrook Select	8.3 a^x	3.8 a	2.6 a	4.4 a	4.8	-47
Arbrook	8.3 a	3.5 ab	2.8 a	4.9 a	4.9	-41
PI 262839	6.3 b	3.3 ab	3.4 a	5.9 a	4.7	-5
PI 262826	6.2 bc	3.3 ab	4.5 a	5.8 a	4.9	-6
Florigraze	5.4 c	3.5 ab	3.6 a	6.8 a	4.8	+26
Ecoturf (PI 262840)	4.1 d	3.2 ab	4.0 a	7.7 a	4.7	+89
PI 262833	3.2 e	2.8 b	4.4 a	5.0 a	3.9	+54
Mean	6.0 A^y	3.3 B	3.6 B	5.8 A	—	—

^x Means within a column followed by the same letter(s) were not different at the 5% level (Waller-Duncan’s Test).

^y Means within a row followed by the same upper case letter were not different at the 5% level (Waller-Duncan’s Test).

^z Percentage change was calculated as the difference in dry biomass yield between year 2000 and 2003.

Forage nutritive value. Crude protein concentration, averaged over three years of nutritive analysis, was 17.2% for all entries, but there were differences in CP concentration between peanut entries for all sampling dates (Table 3). Generally, Ecoturf (PI 262840) and PI 262833, had higher CP concentration compared to the other entries. On average, CP concentration for Ecoturf and PI 262833 was 19.2 and 18.9%, respectively. These higher protein levels may reflect higher leaf-to-stem ratios although this was not determined. Observations during harvest indicate Arbrook and Arbrook Select were taller, contained fewer leaves and were more stemmy than the other entries. Since harvest dates were based on canopy height of Arbrook and Arbrook Select, lower leaf-to-stem ratios would also explain why Arbrook Select and Arbrook consistently had lower CP than all other entries averaging 15.0 and 14.8%, respectively (Table 3).

Table 3. Influence of rhizoma peanut entry on crude protein (CP) concentration at selected harvest dates during 2000, 2001, and 2002, when averaged over stubble height.

Year	Peanut entry	CP (%)
Year	Peanut entry	May	June	July	August	October	Mean
2000	Arbrook Select	17.2 bc^x	18.9 c	—^y	13.4^z	17.0 c	16.6
	Arbrook	15.8 c	17.6 c	—	14.8	17.1 c	16.3
	PI 262839	18.3 ab	20.8 b	—	19.0	21.5 a	19.9
	PI 262826	19.9 a	22.5 a	—	17.5	20.0 b	20.0
	Florigraze	18.7 ab	22.3 ab	—	17.0	19.6 b	19.4
	Ecoturf (PI 262840)	18.7 ab	22.8 a	—	20.8	21.8 a	21.0
	PI 262833	17.7 b	21.6 ab	—	18.7	20.7 ab	19.7
	Avg	18.0	20.9	—	17.3	19.7
2001	Arbrook Select	16.9 e	—	15.7 d	—	12.3 b	15.0
	Arbrook	17.8 de	—	16.5 d	—	11.4 b	15.2
	PI 262839	20.5 c	—	20.8 b	—	12.6 b	18.0
	PI 262826	21.0 bc	—	19.5 c	—	12.6 b	17.7
	Florigraze	18.5 d	—	18.8 c	—	12.3 b	16.5
	Ecoturf (PI 262840)	21.6 b	—	22.1 a	—	14.5 a	19.4
	PI 262833	22.9 a	—	21.6 ab	—	14.9 a	19.8
	Avg	19.9	—	19.3	—	12.9
2002	Arbrook Select	—	14.6 d	11.0 d	—	11.4 d	12.3
	Arbrook	—	14.7 d	10.5 d	—	12.1 cd	12.4
	PI 262839	—	17.6 b	13.9 bc	—	13.6 bc	15.0
	PI 262826	—	17.6 b	14.9 ab	—	14.9 b	15.8
	Florigraze	—	16.3 c	13.2 c	—	12.6 cd	14.0
	Ecoturf (PI 262840)	—	19.3 a	16.2 a	—	15.4 b	17.0
	PI 262833	—	17.6 b	15.4 a	—	17.7 a	16.9
	Avg	—	16.8	13.6	—	13.9

^x Means within a column for each year followed by the same letter(s) were not different at the 5% level (Waller-Duncan’s Test).

^y Empty column indicates plants were not harvested on that date.

^z Entry means interacted with stubble height.

Average IVOMD for the RPP selections for the three years was 69.0%, but differences in IVOMD between peanut entries existed for most sampling dates within years (Table 4). Plant introduction 262833 (70.9%, three year average) was higher in IVOMD than Arbrook Select (66.7%, three year average) and Arbrook (66.9%, three year average) for most dates with the other entries falling in between these extremes. The exception to this was the October 2001 sampling date, which showed no difference between entries and had a 66.7% average IVOMD concentration for all entries. These IVOMD values are considered very good for tropical forage legumes and are similar to those presented by Williams et al. (34) and Valencia et al. (27) from grazing studies with RPP.

Table 4. Influence of rhizoma peanut entry on in vitro organic matter digestion (IVOMD) at selected harvest dates during 2000, 2001, and 2002, when averaged over stubble height.

Year	Peanut entry	IVOMD (%)
Year	Peanut entry	May	June	July	August	October	Mean
2000	Arbrook Select	66.6 b^x	64.0 c	—^y	65.6 d	69.3 de	66.4
	Arbrook	65.8 b	65.2 c	—	65.5 d	68.4 e	66.2
	PI 262839	71.7 a	67.2 b	—	69.2 b	70.9 c	69.8
	PI 262826	69.3 a	67.6 b	—	67.8 c	70.2 cd	68.7
	Florigraze	71.7 a	70.1 a	—	68.8 bc	72.3 ab	70.7
	Ecoturf (PI 262840)	71.9 a	69.5 a	—	71.7 a	71.4 bc	71.1
	PI 262833	71.8 a	70.1 a	—	71.7 a	73.4 a	71.8
	Avg	69.8	67.7	—	68.6	70.8
2001	Arbrook Select	70.3 b	—	70.5 b-d	—	66.9 a	69.2
	Arbrook	70.4 b	—	69.6 de	—	67.0 a	69.0
	PI 262839	71.7 b	—	69.8 c-e	—	65.6 a	69.0
	PI 262826	70.1 b	—	69.2 e	—	65.9 a	68.4
	Florigraze	71.7 b	—	71.5 b	—	68.3 a	70.5
	Ecoturf (PI 262840)	73.8 a	—	70.7 bc	—	65.7 a	70.0
	PI 262833	74.0 a	—	73.5 a	—	67.4 a	71.6
	Avg	71.7	—	70.7	—	66.7
2002	Arbrook Select	—	63.2^z	68.7 b	—	61.7 c	64.5
	Arbrook	—	63.3	68.8 b	—	64.6 bc	65.6
	PI 262839	—	65.2	68.4 b	—	65.6 ab	66.4
	PI 262826	—	63.7	68.5 b	—	65.1 b	65.8
	Florigraze	—	65.4	70.0 ab	—	68.5 a	68.0
	Ecoturf (PI 262840)	—	67.4	68.1b	—	66.4 ab	67.3
	PI 262833	—	67.6	71.9 a	—	68.3 a	69.3
	Avg	—	65.1	69.2	—	65.7

^x Means within a column for each year followed by the same letter(s) were not different at the 5% level (Waller-Duncan’s Test).

^y Empty column indicates plants were not harvested on that date.

^z Entry means interacted with stubble height.

In contrast to entry differences, stubble height did not affect CP or IVOMD concentration. Averaged across all peanut entries forage CP concentration and IVOMD were similar for both the 1-inch (16.8 and 69.0%) and 4-inch (17.6 and 68.2%) stubble, respectively. Apparently, there was not enough difference in the basal three inches of the RPP plants to affect overall CP or IVOMD concentration.

Root/rhizome mass and ground cover. Harvesting above-ground biomass to a 4-inch stubble over a 4-year period resulted in higher root/rhizome mass (0.88 oz/12.6 inch²) compared with the 1-inch stubble (0.49 oz/12.6 inch²) (Table 5). The higher root/rhizome mass produced from the 4-inch stubble may be the result of more photosynthetic material remaining at the base of the plant following harvest and may be an indication of better physiological condition. Generally, harvesting RPP at the 1-inch stubble removes all photosynthetic material, thus forcing the plant to develop new shoots at the soil surface or from rhizomes below the soil surface at the expense of carbohydrate reserves (6). This in turn could be one reason why the shorter stubble supported less root/rhizome mass. No difference was found in root/rhizome mass between peanut entries within each stubble height (Table 5).

Table 5. Influence of peanut entry and stubble height on
root mass (dry basis) following 4 years of clipping.

Peanut entry	Stubble height (inches)
	1	4
	Root mass (oz/12.6 inch²)
Arbrook Select	0.39 a^x	0.63 a
Arbrook	0.53 a	0.78 a
PI 262839	0.42 a	0.85 a
PI 262826	0.60 a	0.99 a
Florigraze	0.35 a	0.81 a
Ecoturf (PI 262840)	0.60 a	1.27 a
PI 262833	0.67 a	0.74 a
Avg	0.49	0.88^y

^x Means within a column followed by the same letter(s)
were not different at the 5% level (Duncan’s Test).

^y Difference due to stubble height averaged over peanut
entries was significant at the 5% level.

Stubble height also affected percentage GC of RPP. Continuous harvesting all peanut entries over a 4-year period back to a 4-inch stubble produced on average 91% GC compared with the 66% GC for the 1-inch stubble (Table 6). All peanut entries responded in a similar manner to stubble-height treatments, and although this decline varied numerically, there was no difference between entries and no entry by stubble-height interaction. Of the entries in the study, PI 262833 appeared to be more tolerant to the close clipping averaging 96% GC at the 1-inch stubble and 100% GC at the 4-inch stubble. On the other hand, the tall entries, Arbrook Select and Arbrook, numerically had the lowest GC, averaging 40 and 61%, respectively, at the 1-inch stubble and 78 and 75% GC, respectively, at the 4-inch stubble. For this reason, neither Arbrook Select nor Arbrook can be recommended even for the better drained flatwood soils of peninsular Florida.

Table 6. Rhizoma peanut ground cover (%) as influenced by stubble height
during initial harvest year (2000) and after four years of harvests (2003).

Year	Peanut entry	stubble height (inches)
Year	Peanut entry	1	4
2000	Arbrook Select	100	100
	Arbrook	100	100
	PI 262839	100	100
	PI 262826	100	100
	Florigraze	100	100
	Ecoturf (PI 262840)	100	100
	PI 262833	100	100
	Avg	100	100
2003	Arbrook Select	40 a^x	78 a
	Arbrook	61 a	75 a
	PI 262839	64 a	95 a
	PI 262826	75 a	98 a
	Florigraze	49 a	90 a
	Ecoturf (PI 262840)	76 a	100 a
	PI 262833	96 a	100 a
	Avg	66	91^y

^x Means within a column followed by the same letter were not different
at the 5% level (Duncan’s Multiple Range Test).

^y Difference due to stubble height averaged over peanut entries was
significant at the 5% level.

Conclusion

Clipping RPP to a 1-inch stubble height almost doubled DB yield compared to the 4-inch stubble height during the first harvest year, but this yield increase was not observed as the stand aged. By year three and four there was no difference in yield between stubble-height treatments. Arbrook Select and Arbrook produced the highest DB yield during the drought year of 2000, averaging 8.3 ton/acre, which was 65% greater than the average of all other peanut entries. But by the third year, there was no difference in yield between entries suggesting, that in all but the driest years, Arbrook Select and Arbrook will not be able to express their genetic potential on spodosols.

Stubble-height treatments also did not affect forage nutritive value. Forage nutritive value did vary due to entry on some harvest dates, but differences were minor. On average, forage nutritive value was excellent averaging 17.2% CP and 69.0% IVOMD over three years.

Regardless of entry, stubble-height harvest treatments did affect both root/rhizome mass and percentage GC. Root mass was generally about 80% higher for the 4-inch stubble-height harvest treatment compared to the 1-inch stubble-height treatment. This may be partly responsible for the 38% better RPP GC for the 4-inch stubble-height treatment when compared with the 1-inch stubble-height treatment after 4 yr of harvests. Although this reduction in GC did not affect DB yield, it does raise the concern that in future years DB yield might be affected or weed issues might develop with this stubble height. For this reason, we recommend that RPP hay producers on Florida spodosols maintain a 4-inch stubble height.

Literature Cited

1. Aiken, G. E., Pitman, W. D., Chambliss, C. G., and Portier, K. M. 1991. Responses of yearling steers to different stocking rates on a subtropical grass-legume pasture. J. Anim. Sci. 69:3348-3356.

2. Barrett-Lennard, E. G. 2003. The interaction between waterlogging and salinity in higher okabts: Causes, consequences and implications. Plant Soil 253:25-54.

3. Bennett, L. L., Hammond, A. C., Williams, M. J., Kunkle, W. E., Johnson, D. D., Preston, R. L., and Miller, M. F. 1995. Performance, carcass yield and carcass quality characteristics of steers finished on rhizoma peanut (Arachis glabrata) - tropical grass pasture. J. Anim. Sci. 73:1881-1887.

4. Barta, A. L. 1988. Response of field grown alfalfa to root waterlogging and shoot removal. I. Plant injury and carbohydrate and mineral content of roots. Agron. J. 80:889-892.

5. Cameron, D. G. 1973. Lucerne in wet soils: The effect of stage of regrowth, cultivar, air temperature, and root temperature. Aust. Agric. Res. 24:851-861.

6. Davis, D. K., McGraw, R. L., Beuselinck, P. R., and Roberts, C. A. 1995. Total nonstructural carbohydrate accumulation in roots of annual Lespedeza. Agron. J. 87:89-92.

7. French, E. C., and Prine, G. M. 1998. Perennial peanut: An alternative forage of growing importance. Coop. Ext Ser. Bull. SS-AGR-39. Univ. of Florida, Gainesville, FL.

8. French, E. C., Prine, G. M. Prine, Ocumpaugh, W. R., and Rice, R. W. 1994. Regional experience with forage Arachis in the United States. pp. 169-186. In: P.C. Kerridge and B. Hardy (ed.). Biology and Agronomy of Forage Arachis. Centro Internat. Agric. Trop. (CIAT), Cali, Columbia.

9. Gallaher, R. N., Weldon, O. C., and Futral, J. G. 1975. An aluminum block digester for plant and soil analyses. Soil Sci. Soc. Am. Proc. 39:803-806.

10. Hambleton, L. G. 1977. Semi automated method for simultaneous determination of phosphorus, calcium, and crude protein in animal feeds. J. Assoc. Off. Anal. Chem. 60:845-854.

11. Hammond, A. C., Padgett, L. J., Williams, M. J., and Kunkle, W. E. 1992. Relative feeding value of rhizoma perennial peanut hay as a supplement to bahiagrass hay for wintering cows and heifers. Prof. Anim. Sci. 8:48-54.

12. Justin, S. H. F. W., and Armstrong, W. 1987. The anatomical characteristics of roots and plant response to soil flooding. New Phytol. 106:465-495.

13. Kalmbacher, R. S. 2001. Climatological Report 2000. Range Cattle Res. and Educ. Center., Res. Rep. RC-2001-1. Univ. of Florida, Gainesville, FL.

14. Kalmbacher, R. S. 2002. Climatological Report 2001. Range Cattle Res. and Educ. Center., Res. Rep. RC-2002-1. Univ. of Florida, Gainesville, FL.

15. Kalmbacher, R. S. 2003. Climatological Report 2002. Range Cattle Res. and Educ. Center., Res. Rep. RC-2003-1. Univ. of Florida, Gainesville, FL.

16. Kalmbacher, R. S. 2004. Climatological Report 2003. Range Cattle Res. and Educ. Center., Res. Rep. RC-2004-1. Univ. of Florida, Gainesville, FL.

17. Mislevy, P., Blount, A. R., Martin, F. G., and Scully, B. T. 2005. Soybean and clay cowpea grown for forage production in the subtropics. Online. Crop Management doi:10.1094/CM-2005-0926-01-RS.

18. Moore, J. E., and Mott, G. O. 1974. Recovery of residual organic matter from in vitro digestion of forages. J. Dairy Sci. 57:1258-1259.

19. Prine, G. M., Dunavin, L. S., Moore, J. E., and Roush, R. D. 1981. "Florigraze’ rhizoma peanut: a perennial forage legume. Coop. Ext Ser. Bull. S-275. Univ. of Florida, Gainesville, FL.

20. Prine, G. M., Dunavin, L. S., Glennon, R. J., and Roush, R. D. 1986. "Arbrook’ rhizoma peanut: a perennial forage legume. Coop. Ext Ser. Bull. S-332. Univ. of Florida, Gainesville, FL.

21. Nathanson, K., Lawn, R. J., De Jabrun, P. L. M., and Byth, D. E. 1984. Growth, nodulation and nitrogen accumulation by soybean in saturated soil culture. Field Crops Res. 8:73-92.

22. Ortega-S., J. A., Sollenberger, L. E., Quesenberry, K. H., Cornell, J. A., and Jones, C. S. 1992. Productivity and persistence of rhizoma peanut pastures under different grazing managements. Agron. J. 84:799-804.

23. Quesenberry, K. H. 1999. Value of UF/IFAS forage legume cultivars to Florida livestock production. Soil Crop Sci. Soc. Florida Proc. 58:23-27.

24. Rai, S. D., Miller, D. A., and Hittle, C. N. 1971. Response of alfalfa varieties to different water table depths at various stages of growth. Agron. J. 63:331-332.

25. Tilley, J. A., and Terry, R. A. 1963. A two-stage technique of the in vitro digestion of forage crops. J. Br. Grassl. Soc. 18:104-111.

26. Teutsch, C. D., and Sulc, R. M. 1997. Influence of seedling growth stage on flooding injury in alfalfa. Agron. J. 89:970-975.

27. Valencia, E., Williams, M. J., Chase, C. C., Jr., Sollenberger, L. E., Hammond, A. C., Kalmbacher, R. S., and Kunkle, W. E. 2001. Pasture management effects on diet composition and cattle performance on continuously stocked rhizoma peanut-mixed grass swards. J. Anim. Sci. 79:2456-2464.

28. Valencia, E., Williams, M. J., Sollenbeger, L. E., and Kalmbacher, R. S. 1999. Management effects on botanical composition of rhizoma perennial peanut-mixed grass associations. Agron. J. 91:431-438.

29. Venuto, B. C., Elkins, W., and Redfearn, D. 2000. Soil fertility effects on growth and nutrient uptake of rhizoma peanut. J. Plant Nutr. 23:231-241.

30. Williams, M. J. 1993. Planting date and preplant tillage effects on emergence and survival of rhizoma perennial peanut. Crop Sci. 33:132-136.

31. Williams, M. J. 1994. Reproductive-resource allocation in rhizoma peanut. Crop Sci. 34:477-482.

32. Williams, M. J. 2005. Germplasm collection with NPGS, a regional perspective. Online. Breeders workgroup, Proc. of the S. Pasture and Forage Crop Improvement Conf., Philadelphia, MS, May 11-13, 2005. Oklahoma State Univ., Stillwater, OK.

33. Williams, M. J., Chase, C. C., Jr., and Hammond, A. C. 2004. Performance of cows and their calves creep-grazed on rhizoma perennial peanut. Agron. J. 96:671-676.

34. Williams, M. J., Hammond, A. C., Kunkle, W. E., and Spreen, T. H. 1991. Stocker performance on continuously grazed mixed grass-rhizoma peanut and bahiagrass pastures. J. Prod. Agric. 4:19-24.

35. Williams, M. J., Kelly-Begazo, C. A., Stanley, R. L., Quesenberry, K. H., and Prine, G. M. 1997. Establishment of rhizoma peanut: Interaction of cultivar, planting data, and location on emergence and groundcover. Agron. J. 89:981-987.