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CIR 1257 Bahiagrass Seed Production in Peninsular Florida1 Martin B. Adjei and Paul Mislevy2 1. This document is Circular 1257, one of a series of the Agronomy Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. First Published: October, 2000. Please visit the EDIS website at: http://edis.ifas.ufl.edu. 2. Martin Adjei, Assistant Professor, Range Cattle REC--Ona; Paul Mislevy, Professor, Range Cattle REC--Ona, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Gainesville 32611. The Institute of Food and Agricultural Sciences is an equal opportunity/affirmative action employer authorized to provide research, educational information and other services only to individuals and institutions that function without regard to race, color, sex, age, handicap, or national origin. For information on obtaining other extension publications, contact your county Cooperative Extension Service office. Florida Cooperative Extension Service/Institute of Food and Agricultural Sciences/University of Florida/Christine Taylor Waddill, Dean. Introduction Bahiagrass (Paspalum notatum) is the most widely grown warm-season perennial grass in Florida. There are approximately 2.7 million acres of bahiagrass which represent more than 70% of improved permanent pastures in Florida. Its popularity stems from the fact that it is easily established from seed in a wide range of soil fertility and drainage conditions, and is persistent under low fertility and poor grazing management. Current Production Practices Most seedsmen in Florida operate their business on a share-harvest basis. Companies provide for harvesting, hauling, cleaning, storage, and sale of seed. Actual seed production is undertaken by cattlemen to generate secondary income, especially in years when beef prices are low. Typical management of bahiagrass pasture for seed includes fertilization with N in early spring (February to March) followed by grazing until June or the first sign of inflorescence. Cattle are then withdrawn to allow inflorescence development and seed harvest. Three major problems of this production system are: (1) when pastures are more than 3-yr old they often experience reduction in seed yield; (2) Vacating pastures in June or at the first sign of inflorescence may not be the best timing for good seed yield or quality; (3) pasture fertilization in February or March, although a good practice for obtaining spring forage for grazing, does not coincide with optimum day length for seedhead production. The purpose of this publication is to indicate which cultural practices lead to improved bahiagrass seed yield and quality. Cultural Practices for Overcoming Sod-Bound Pasture When a large amount of residue is carried over from the previous season, flowering may be inhibited and, hence, seed production on bahiagrass pastures may decline. Initial studies conducted in1985 on pastures that were more than 7-yr old showed no statistical difference in seed yield between close grazing pasture from late fall to spring and burning the sod in spring (Table 1). However, seed production declined when old pasture was roller chopped because it allowed competition from re-seeding legumes such as aeschynomene and from weeds. The application of giberellic acid to a sod-bound bahiagrass pasture did not improve seed yield either. In 1986, Pensacola seed yield was depressed on all treatments, except under burning, by heavy summer (June & July) rains (11.7" in 1985 vs.
Bahiagrass Seed Production in Peninsular Florida 2 20.2" in 1986). Burning delayed seed production and provided an escape mechanism from saturated soil condition. Argentine is late flowering so seed production was not adversely affected by excessive June and July rains in 1986. Pensacola bahiagrass seed yield responded only to N application, but Argentine seed yield responded to both N and P applications (Figure 1). Soil test recommendation for that trial was 67-115-75 lb/A N-P2O5-K2O. Figure 1. Argentine Bahiagrass seed yield averaged over 1985 and 1986 as affected by N and P fertilizer application. Timing of Residue Removal, Cattle Withdrawal and Nitrogen Fertilization The research in1985 and 1986 on residue removal for seed production was done once during the spring. In order to determine the most suitable time in the growing season to remove residue and fertilize pasture, further research was conducted between 1987 and 1990. The outcome showed a difference between Pensacola and Argentine bahiagrasses regarding the best time for withdrawing cattle and applying N to pasture to initiate seed production. Pensacola bahiagrass An experiment was conducted on a 7-yr old Pensacola bahiagrass pasture in 1987 and 1988. Sections of residue from the previous year were removed at five periods: (i) dormancy in early-March, (ii) early vegetative stage in mid-April, (iii), first inflorescence visible in early-June, (iv) 2-wk after first inflorescence visible in mid-June, and (v) 4 wk after first inflorescence visible in late-June. Residue was removed by two methods burning vs. mowing to 3 inches to simulate close grazing. Immediately following each residue removal, N was applied at 0, 45 or 90 lb N/A. Plots were rested after treatment. Seed was harvested by hand when ripe which occurred between mid-July and early-September, depending on treatment. Seed Yield Pensacola seed yield was highest (300 to 700 lb/A) when residue was removed at the dormant or early-vegetative stages of maturity compared with residue removal after inflorescence appearance (Table 2). The 2-yr mean seed production across fertilizer treatments when residue was removed at the first inflorescence appearance was 150 lb/A (Table 2). Pensacola seed yield progressively declined the longer the delay of residue removal after inflorescence (Table 2) as expressed by both reductions in inflorescence density (Table 3) and seed size (Table 4). Method of residue removal (burned vs. mowed) did not affect the overall seed yield of Pensacola bahiagrass (Table 2). This means that both methods will give good seed yield if applied at the proper time. When 45 lb/A of N was applied to pasture at either the dormant or early vegetative stage, seed yield was increased by about 70% (325 vs.556 lb/A, Table 5) and inflorescence density by 60% (data not shown)) over the no fertilization treatment. Increasing the N application rate to 90 lb/A following residue removal at the dormant stage of development increased seed yield by an additional 30%. However, the 90 lb N/A application following residue removal at the vegetative stage gave no additional benefit to seed yield. Therefore, 50 to 100 lb N/A is adequate for Pensacola bahiagrass seed yield, depending on when pasture is deferred for seed production.
Bahiagrass Seed Production in Peninsular Florida 3 Seed Germination Observations in the field indicated that Pensacola seed development after flowering was severely inhibited by wet soil conditions that occurred in summer. When residue removal was delayed until the first inflorescence appearance, reproductive tiller development, flowering and seed development coincided with wet summer conditions. This resulted in premature seed ripening, empty caryopses, reduced seed size, low seed yield, and poor seed quality. Consequently, average total seed germination declined from 58% for residue removal at dormancy or early vegetative stage to 17% when residue removal was delayed till the first inflorescence appearance stage of plant development. Residue removal by burning or mowing and N fertilization did not affect seed quality. For best yield and quality of Pensacola bahiagrass seed, producers in peninsular Florida should withdraw cattle from pasture after close grazing by 15 April (i.e. early-vegetative stage of plant development) and immediately fertilize with 50 lb N/A. Argentine bahiagrass A similar study was carried out in 1989 and 1990 on a 10-yr old Argentine bahiagrass pasture to determine the optimum time of the growing season to remove cattle and apply fertilizer. A set of 3 paddocks was grazed from October to February each year compared with a set that was not grazed (ungrazed). In late-February, late-March, late-April and late-May, portions of residue in both grazed and ungrazed paddocks were burned or mowed. Three rates of N (0, 90 and 180 lb/A) were applied immediately after residue removal. Inflorescence density at harvest and seed yield were measured in 1989 and 1990. Seed germination was only determined in 1989. Seed Yield Grazing from October to February or method of residue removal (burned vs. mowed) did not affect seed production or quality in 1989. However, burning in late-May increased seed yield from 70 to 130 lb/A in 1990. No inflorescences were produced in 1989 and only a few were produced in 1990 when residue was removed in late-February and forage was allowed to accumulate. Inflorescence density (data not shown) and seed yield (20 to190 lb/A) increased progressively as residue removal and N fertilization were delayed from late-February through late-April in 1989 and through late-May in 1990. In 1989, highest seed yields (125 to 190 lb/A) were obtained following residue removal in late April or late-May and 90 lb N/A, and there was no difference between burning and mowing (Table 6). In 1990, highest seed yield (130 lb/A) resulted from late-May burning and 90 lb N/A fertilization. Increasing the N application rate from 90 to 180 lb/A did not add any additional benefit to seed production, and actually reduced seed germination. Seed Germination Mean seed germination for 1989 Argentine seed lot was 71%, 73% and 58% for the 0, 90, and 180 lb N/A, respectively. Unlike Pensacola, seed germination of Argentine was not affected by method or time of residue removal, suggesting that Argentine inflorescence development is tolerant to summer water saturated soil conditions. Summary Burning and close grazing (<3") were the best pretreatments for promoting seed yield of both Pensacola and Argentine bahiagrass cultivars. Highest yield and quality of Pensacola bahiagrass seed resulted when residue was removed by burning or close grazing up to mid-April followed immediately by N fertilization. This time limit for grazing deferment on Pensacola bahiagrass could be extended for dry summer years. By contrast, Argentine seed yield was highest when residue was removed by burning or close grazing and field fertilized in late-May. Argentine seed germination remained high (75%) regardless of time of residue removal. Future trials should address interaction of N rate and duration of spring grazing on bahiagrass seed yield.
Bahiagrass Seed Production in Peninsular Florida 4 Recommendations for Bahiagrass Seed Production in Peninsular Florida PENSACOLA 1. Withdraw cattle from pasture no later than mid April. 2. Burn or mow stubble if pasture is not closely grazed (3" stubble or less). 3. Fertilize immediately with 50 lb N/A. 4. Harvest seed in July when ripe. ARGENTINE 1. Graze pasture closely ( 3" stubble or less) in April-May. 2. Withdraw cattle from pasture in late-May. 3. Immediately apply 100 lb N/A (Argentine seed yield may also respond to P) 4. Harvest seed in August when ripe. References Adjei, M.B., and P. Mislevy. 1989. Cultural and fertilizer practices for bahiagrass seed production. P. 62-63. In Proc. Beef Cattle Short Course, 18th. 3-5 May 1989. Inst. Food and Agric. Sci., Univ. of Florida, Gainesville. Adjei, M.B., P. Mislevy, and W. Chason. 1992. Seed yield of bahiagrass in response to sward management by phenology. Agron. J. 84:599-603. Adjei, M.B., P. Mislevy, and W. Chason. 2000. Timing, defoliation management, and nitrogen effects on seed yield of Argentine bahiagrass. Agron. J. 92:36-41.
Bahiagrass Seed Production in Peninsular Florida 5 Table 1. Pensacola and Argentine bahiagrass seed production with different treatments averaged over 1985 and 1986. Pretreatment CultivarYear ChopBurnGA1 Graze yield lb/A Pensacola1985 81125102126 1986 541114450 Argentine1985 & 1986 185217154204 Source: Data from Martin Adjei and Paul Mislevy (1989) 1Gibberellic acid Table 2. Seed yield of Pensacola bahiagrass as influenced by stage of plant development at time of residue removal and method of residue removal in 1987 and 1988. Stage of Plant Development1 Method of residue removal 1987 1988 2-yr mean BurnMowBurnMowBurnMow lb/A Dormant278347561614420481 EV 522405696544609475 FIV 117235152104135170 FIV-2 549666516074 FIV-4 1647551126 Source: Data from Martin Adjei, Paul Mislevy and Wallace Chason (1992) 1Dormant (early March); EV=early vegetative (mid-April); FIV=first inflorescence visible (early June); FIV-2= 2 wk after first inflorescence visible (mid-June); FIV-4= 4 wk after first inflorescence visible (late June).
Bahiagrass Seed Production in Peninsular Florida 6 Table 3. Number of mature seedheads of Pensacola bahiagrass as influenced by stage of plant development at time of residue removal and method of residue removal in 1987 and 1988. Stage of plant development1 Method of residue removal 1987 1988 2-yr mean BurnMowBurnMowBurnMow No. of seedhead m-2 Dormant112126268232190179 EV 266191300279283235 FIV 119307206259113283 FIV-2 46929111554104 FIV-4 285027332842 Source: Data from Martin Adjei, Paul Mislevy and Wallace Chason (1992) 1Dormant (early March); EV=early vegetative (mid-April); FIV=first inflorescence visible (early June); FIV-2= 2 wk after first inflorescence visible (mid-June); FIV-4= 4 wk after first inflorescence visible (late June). Table 4. Seed weight of Pensacola bahiagrass as influenced by stage of plant development at time of residue removal and method of residue removal in 1987 and 1988. Stage of plant development1 Method of residue removal 1987 1988 2-yr mean BurnMowBurnMowBurnMow 1000-seed wt, g Dormant 1.391.471.391.481.391.48 EV 1.091.161.361.431.231.30 FIV 0.820.720.790.730.810.73 FIV-2 0.830.760.870.780.850.77 FIV-4 0.850.810.790.700.820.76 Source: Data from Martin Adjei, Paul Mislevy and Wallace Chason (1992) 1Dormant (early March); EV=early vegetative (mid-April); FIV=first inflorescence visible (early June); FIV-2= 2 wk after first inflorescence visible (mid-June); FIV-4= 4 wk after first inflorescence visible (late June).
Bahiagrass Seed Production in Peninsular Florida 7 Table 5. Seed yield of Pensacola bahiagrass as influenced by stage of plant development at time of residue removal and N fertilization rate in 1987 and 1988. Stage of plant development1 Nitrogen rate 1987 1988 2-yr mean lb/A Dormant 0 229 342 286 45 358 616 487 90 351 805 578 EV 0 338 390 364 45 529 723 626 90 526 747 637 FIV 0 118 74 96 45 185 125 155 90 225 183 204 FIV-2 0 46 27 37 45 74 82 78 90 107 68 88 FIV-4 0 20 3 12 45 32 7 20 90 45 7 26 Source: Data from Martin Adjei, Paul Mislevy and Wallace Chason (1992) 1Dormant (early March); EV=early vegetative (mid-April); FIV=first inflorescence visible (early June); FIV-2= 2 wk after first inflorescence visible (mid-June); FIV-4= 4 wk after first inflorescence visible (late June). Table 6. The effects of time and method of residue removal, and rate of N application on Argentine bahiagrass seed yield in 1989 and 1990. 1990 nitrogen rate (lb/A) Calendar month 1989 nitrogen rate 0 90 180 0 90 180 Burn Mow Burn Mow Burn Mow lb/A Late-February 0 0073848 6
Bahiagrass Seed Production in Peninsular Florida 8 Table 6. The effects of time and method of residue removal, and rate of N application on Argentine bahiagrass seed yield in 1989 and 1990. 1990 nitrogen rate (lb/A) Calendar month 1989 nitrogen rate 0 90 180 0 90 180 Burn Mow Burn Mow Burn Mow lb/A Late-March 454845402170364143 Late-April 96188146522171468936 Late-May 1091258847441326610844 Mean 63 90 70 37 22 70 38 62 32 Source: Data from Martin Adjei, Paul Mislevy and Wallace Chason (2000)