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Changes in chemical composition of warm-season perennial grasses during the growing season affect conversion of biomass to biofuels, thus influencing choice of harvest date. The objective was to quantify these changes for three candidate bioenergy grasses in the USA Gulf Coast region during two growing seasons and relate them to optimal harvest management. Grasses included two elephantgrass [Pennisetum purpureum Schum.; synonym Cenchrus purpureus (Schumach.) Morrone] entries, ‘Merkeron’ and breeding line UF1, and the energycane (Saccharum spp. hybrid) cultivar ‘L79-1002’. Quantification of cell wall constituents and mineral composition of above-ground biomass occurred monthly throughout the growing season. With the exception of hemicellulose, elephantgrass cell wall constituents (cellulose, lignin, neutral detergent fiber and acid detergent fiber) increased from early in the growing season until late summer and either remained relatively constant (UF1) or increased slightly (Merkeron) during the remainder of the season. In contrast, concentrations of energycane cell wall constituents peaked in late summer and decreased during the remainder of the growing season. Nitrogen, P, and ash concentrations decreased with increasing maturity for all grass entries, and they were much greater in leaf than in stem. Elephantgrass leaf, particularly of UF1, contributed less to total biomass harvested than energycane leaf. Likewise, the proportion of total ash harvested that was in the leaf fraction was greater for energycane than for elephantgrass when harvest occurred late in the growing season. Thus, delayed harvest until late in the season was generally a superior management strategy for elephantgass because it resulted in biomass with greater cell wall constituent concentrations, lesser leaf percentage, and lesser concentrations of N and ash, all of which may provide advantages in some conversion processes. In contrast, greater accumulation of extractives by energycane and greater lignin concentration in elephantgrasses late in the growing season may reduce efficiency of some conversion methods.

Published in Agron. J. 107:466–474 (2015) doi:10.2134/agronj14.0339 Copyright © 2015 by the American Society of Agronomy, 5585 Guilford Road, Madison, WI 53711. All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. ABSTRACT

Published in Agron. J. 106:2255–2262 (2014) doi:10.2134/agronj14.0324 Copyright © 2014 by the American Society of Agronomy, 5585 Guilford Road, Madison, WI 53711. All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. ABSTRACT

Elephantgrass (Pennisetum purpureum Schum.) and energycane (Saccharum spp. interspecific hybrid) are perennial C4 grasses with potential for use as bioenergy feedstocks. Their biomass production has been quantified, but differences in plant morphology and the relationship of morphology with biomass harvested and plant persistence are not well understood. The objective was to quantify monthly changes in morphological characteristics of elephantgrass (cv. Merkeron and breeding line UF1) and energycane (cv. L 79-1002) and relate these changes to biomass accumulation and plant responses to defoliation. All were evaluated monthly during full-season growth or when defoliated once in mid-season. Merkeron and UF1 elephantgrass generally showed similar morphological characteristics. Relative to energycane, elephantgrass had fewer tillers early in the growing season, less seasonal variation in tiller number, greater tiller mass and maximum leaf area index (LAI), and earlier spring development of LAI. Energycane showed slower leaf area development in spring, lower maximum LAI, and shorter period of increasing tiller mass and canopy height during the growing season relative to UF1. Elephantgrass had greater incidence of lodging than energycane when exposed to high wind, likely due to greater elephantgrass tiller mass. Morphological characteristics of tall-growing bioenergy grasses help to explain differences among them in biomass production and plant persistence responses to defoliation.

Harvest management practices affect productivity and persistence of grasses grown for bioenergy, but data are limited that describe their effects on the tall-growing grasses adapted to the USA Gulf Coast region. The objective was to determine harvest frequency and timing effects on biomass yield, nutrient removal, and persistence of three perennial bioenergy grasses in the southeastern USA. The experiment was conducted from 2010 through 2012. Harvest management treatments were two harvests per year (2X; July and November), one harvest per year in early November (fall), and one harvest per year after first freeze (winter). Elephantgrass (Pennisetum purpureum Schum.) cv. Merkeron and breeding line UF1 and energycane (Saccharum spp.) cv. L 79-1002 were compared. Three-year average biomass harvested was greatest for UF1 followed by Merkeron and L 79-1002 (27.8, 24.6, and 21.1 Mg ha−1year−1, respectively). Biomass harvested was not affected by harvest management in 2010 and 2011, but in 2012, the 2X treatment yielded 47 % less than winter. Biomass dry matter (DM) concentration for single harvest treatments was greater than 2X (34 vs. 25 %), but the 2X treatment removed two times more N and P in harvested biomass than fall or winter. For these grasses, fall and winter single harvest treatments were superior to 2X due to greater third year biomass yield, less nutrient removal, and harvested biomass had a greater DM concentration that may be advantageous for postharvest transport and processing.

Biofuel crops such as napiergrass possess traits characteristic of invasive plant species, raising concern that biofuels might escape cultivation and invade surrounding agricultural and natural areas. Napiergrass biofuel types are being developed to have reduced invasion risk, but these might be cultivated in areas where naturalized populations of this species are already present. The successful management of napiergrass biofuel plantations will therefore require techniques to monitor for escaped biofuels as distinguished from existing naturalized populations. Here we used 20 microsatellite DNA markers developed for pearl millet to genotype 16 entries of napiergrass, including naturalized populations and accessions selected for biofuel traits. Use of the markers showed a clear genetic separation between the biofuel types and naturalized entries and revealed naturalized populations undergoing genetic isolation by distance. These findings demonstrated the utility of microsatellite marker transfer in the development of an important tool for managing the invasion risk of a potential biofuel crop. Nomenclature: Napiergrass, Pennisetum purpureum Schumach.; pearl millet, Pennisetum glaucum (L.) R. Br.

Elephantgrass (Pennisetum purpureum Schum.) has demonstrated potential for use as a biomass crop, but in Florida, some naturalized types are invasive weeds in sugarcane (Saccharum sp.) fields, along roadsides, and in natural areas. It is not known whether elephantgrass introductions and breeding lines developed for biomass production (i.e., “selected”clones) differ from naturalized populations sufficiently that risk assessment and regulatory decisions should be made at the level of the clone instead of the species. The objective was to compare morphological and physiological traits of elephantgrass-naturalized populations and selected clones. Ten naturalized populations and six selected clones were evaluated in replicated trials at two field locations during 2 years. Selected clones were 8–14 % taller and had leaf blade length that was 48–87 % longer, and leaf blade width that was 61–89 % wider than naturalized clones. Selected types averaged 5.7 to 7.2 fewer tillers per plant than naturalized types, but tiller mass of selected types was 70 % greater than naturalized types. Leaf N concentration was 43 % greater for selected types and was associated with greater light-saturated leaf photosynthesis, stomatal conductance, leaf transpiration rate, and leaf dark respiration than naturalized types. Photosynthetic parameters indicated a greater maximum photosynthetic rate, leaf dark respiration, and light compensation point for selected versus naturalized clones. Clones selected for use as biomass crops differ widely in morphology and physiological response from naturalized populations, supporting a conclusion that risk assessment of elephantgrass should occur at the level of the clone rather than the species.

Carbohydrate and lignin composition of feedstock materials are major factors in determining their bioenergy potential. This study was conducted to quantify dry biomass yield and the carbohydrate and lignin composition of six potential biofuel grasses (elephantgrass, energycane, sweetcane, giant reed, giant miscanthus, and sugarcane) across three sites in Florida for plant (2009) and first ratoon (2010) crops. Dry biomass yields ranged from about 30 to 50 Mg ha−1 and were generally greatest for elephantgrass, energycane, sweetcane, and sugarcane. Accordingly, total plant carbohydrate yields (20 to 25 Mg ha−1) were comparable among sugarcane, energycane, sweetcane, and elephantgrass, but were generally less for giant reed and even less for giant miscanthus. However, the contribution of total extractable carbohydrates and total fiber carbohydrates to total plant carbohydrate yields differed among species. Sugarcane had the highest concentrations of extractable carbohydrates (219 to 356 mg g−1), followed by energycane, then sweetcane, elephantgrass, and giant reed, with giant miscanthus having the lowest. Energycane and elephantgrass tended to have significantly more fiber glucose, and elephantgrass less xylose, than other species. Variability in total lignin concentrations on a fiber basis was relatively modest (250 to 285 mg g−1) across species, but was generally highest in sweetcane and giant reed. Overall, elephantgrass and energycane were prime regional candidates for cellulosic conversion using fermentation processes due to high yields and favorable fiber characteristics, although energycane tended to have higher extractable carbohydrates.

Research is limited for cow-calf operations as a potential nonpoint source of P within Florida's central highlands region (CHR). The study was conducted in a bahiagrass ( Flügge) pasture. The soil is an excessively drained 'Candler' sand. In dung-designated plots, 2 kg of fresh cattle dung was deposited across the surface of a 15-cm-radius circular zone (Zone 1 [Z1]) centered within 3 × 3 m plots. In urine plots, 1 L of urine was deposited on Z1 and 1 L on Zone 2 (Z2), an area extending outward from Z1 to 30 cm from plot center. In dung and urine plots, Zone 3 (Z3) extended from Z2 to 45 cm from plot center and Zone 4 (Z4) from Z3 to 60 cm. Excreta deposition frequencies (DFs) were 0, 1, 2, and 3 times per year during 2006 and 2007. Total apparent remaining P (ARP = [fertilizer P + excreta P] - forage P removal) for Z1 of dung plots was 21, 447, 905, and 1249 kg ha for DF0, DF1, DF2, and DF3, respectively. In 2008, soil was incrementally sampled to a depth of 120 cm in all zones. Urine deposition did not increase soil P. Soil P levels and the degree of P saturation percentages increased with DF but only in the upper 10 cm of topsoil beneath Z1 of dung plots. Our results suggest that the risk of dung P reaching groundwater is low due to a considerable P retention capacity within the rooting zone of the Candler soil.

Forage dry matter harvested (DMH) and nutritive value (NV) are affected by livestock excreta. Efforts to model nutrient cycling in grazed grasslands would benefit from increased understanding of the duration and spatial pattern of excreta effects on grassland patches. These responses were measured on ‘Pensacola’ bahiagrass ( Paspalum notatum Flugge) swards treated with two excreta types (dung and urine) from two excreta source pastures (Average and High management intensities based on N fertilizer and stocking rates) applied at four frequencies (0, 1, 2, 3 per year) during 2 yr. Forage DMH under dung pats decreased, but DMH surrounding the pat was not affected by application frequency. Suppression of DMH by dung was ≥112 d and extent of suppression increased as application frequency increased. In contrast, DMH under urine increased linearly (2950 to 6250 kg ha -1 for the Average management intensity and 3480 to 6450 kg ha -1 for the High management intensity) as application frequency increased and effects were observed 15 cm beyond the deposit’s edge. Forage NV was not affected by dung, but it increased with increasing urine application frequency and for distances up to 30 cm from the edge of the urine deposit. Urine increased DMH for ≥84 d and increased crude protein for ≥28 d following a single urine application and ≥84 d after multiple applications. Data show that duration and spatial patterns of forage response to dung and urine differ, but effects of both can be long lived and are increased by multiple deposits to a patch.R. Whtie-Leech, Natural Resource Conservaton Si ervcie, Clinton, NC, 28328; K. Liu, Dep. Grassland Science, China Agricultural University, Haidian District, Beijing 100193, China; L.E. Sollenberger, and K.R. Woodard, Agronomy Dep., University of Florida, Gainesville, FL 32611-0500; S.M. Interrante, The Noble Foundation, 2510 Sam Noble Parkway, Ardmore, OK 73401. Received 3 July 2012. *Corresponding author (kesiliu@gmail.com).

Livestock excreta deposition in grazed grassland is nonuniform and concentrated around shade, water, and supplement feeding locations. The consequences of repeated dung or urine deposition to grassland patches have not been well quantified in terms of effects on forage dry matter harvested (DMH), forage nutritive value, and nutrient recovery. These responses were measured on ‘pensacola’ bahiagrass (Paspalum notatum Flugge) swards treated with two excreta types (dung and urine) from two excreta source pastures (the Average and High management intensities based on N fertilizer and stocking rates) applied at four frequencies (0, 1

Biomass yield and tissue mineral composition can affect total energy yield potential, conversion efficiencies and environmental impacts, but relatively few data are available for sweet sorghum [Sorghum bicolor (L.) Moench] grown in the southeastern USA. Therefore, a study was conducted at two locations in North and Central Florida on marginal sand soils comparing the effects of planting date (PD) on dry biomass yield and mineral composition of leaf, stem, and grain heads for ‘M-81E’ and ‘Dale’ sweet sorghum cultivars. Overall tissue mineral concentrations were relatively low for sweet sorghum, attributable to low K and Ca concentrations. Ash and mineral concentrations were generally greater for Dale, especially for the early PD. Leaf and grain heads were greater in mineral concentrations compared to stems. Dry biomass yield averaged 19.4 Mg ha−1 and was greater for M-81E and the early PD. Stems accounted for 73% of the total biomass compared to leaves (13%) across all treatments. Total N, P, and K removals averaged 136, 27.6, and 81.4 kg ha−1, respectively. Overall, leaves removed 30, 23, and 19% of total N, P, and K compared to 34, 34, and 61% by stem, respectively. Considering lower biomass but greater mineral concentrations in leaf and grain heads compared to stems, returning leaf residues and possibly grain heads to the soil have the potential to offset nutrient and energy inputs needed on these marginal soils and enhance the sustainability of sweet sorghum cropping systems.

Published in Agron. J. 103:1827–1833 (2011) Posted online 29 Sept 2011 doi:10.2134/agronj2011.0176 Copyright © 2011 by the American Society of Agronomy, 5585 Guilford Road, Madison, WI 53711. All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. S is a unique C4 grass in that it is capable of high biomass, grain, and sugar yields (Rooney et al., 2007; Zhao et al., 2009). Thus, it has received considerable attention in recent years for use as a biofuel crop (Amaducci et al., 2004; Goff et al., 2010). Sweet sorghum, in particular, offers potential advantages over other candidate biofuel crops because it stores readily fermentable sugars in the stalk that can be converted to liquid fuels and bio-based products with current technologies. It is also an annual crop that can be integrated into existing crop rotations, and it is readily established from seed. Moreover, it does not have to compete directly with food or feed. Despite these potentially attractive features, relatively little is known about the production of sweet sorghum for bioenergy use in the southeastern United States, as it has traditionally been grown on limited acreage primarily for syrup production in the transition area of Kentucky and Tennessee. Thus, there is a need for a better understanding of the yield potential of currently available, commercial sweet sorghum cultivars, especially with regard to ratoon crop yields for sweet sorghum production at low latitudes in the United States. Sweet sorghum biomass yields have been variable within and across studies due to cultivar, environment and management practices. Wortmann et al. (2010) reported dry stalk yields from 8 to 48 Mg ha–1 across a range of N fertilization rates, three cultivars, and multiple plant populations in Nebraska. Soileau and Bradford (1985) reported dry biomass yields ranging from 6 to 18 Mg ha–1 across a range of fertilization and liming treatments in northern Alabama. Similarly, Tamang et al. (2011) reported total dry matter yields of 9 to 18 Mg ha–1 for ‘Della’ and M-81E sweet sorghum cultivars across a range of N fertilization rates in the Southern High Plains. Miller and Ottman (2010) reported no effect of irrigation frequencies on M-81E sweet sorghum dry matter yields, which ranged from 20 to 31 Mg ha–1 in the southwestern United States. Although sweet sorghum biomass yield data are abundant for some growing regions, estimation of commercial-scale ethanol yields from sweet sorghum is complicated by not always knowing the fraction of total soluble solids (brix) that are fermentable sugars and the sugar recovery efficiency during milling. Miller and Ottman (2010) measured juice sugars directly with high performance liquid chromatography (HPLC) and reported an average ethanol yield of 2726 L ha–1. When total stalk nonstructural sugars were measured directly (i.e., not expressed juice), estimated ethanol yields for M-81E sweet sorghum ranged from 3533 to 5414 L ha–1 (Zhao et al., 2009). Tamang et al. (2011) estimated ethanol yields of 1968 to 2700 L ha–1 from measured brix values for a single crop of two sweet sorghum cultivars over 2 yr without irrigation in Nebraska. These studies indicated that sweet sorghum ethanol yields from a single crop may be comparable to maize (Wortmann et al., 2010). Moreover, sweet sorghum has been shown to use less water and N than maize for similar ethanol yields (Keeney and DeLuca, 1992; Geng et al., 1989). Although sorghum is better adapted to the southeastern USA than maize (Zea mays L.), use of sweet sorghum as a ABSTRACT Sweet sorghum [Sorghum bicolor (L.) Moench] is a potential bioenergy crop that is capable of high biomass and sugar yields, but production for biofuel in the Southeast is not well understood. The present study examined the effects of planting date (three dates from mid-March to mid-June) on primary and ratoon crop fresh biomass, brix, and estimated sugar yield of three sweet sorghum cultivars (‘Dale’, ‘Topper 76-6’, and ‘M-81E’) grown at three sites from North (29°24¢ N) to South Florida (26°40¢ N). Across all treatments, primary crop fresh biomass, brix and estimated sugar yields were 70 Mg ha–1, 148 g kg–1, and 5.69 Mg ha–1, respectively. Primary crop yields were greatest for the two earliest planting dates (mid-March to mid-May), and for our southernmost site. The yield potential for ratoon crops was in general only about half as much as the primary crop across all years, sites, and cultivars for the earliest planting date. An exception, however, was ratoon crop yields at the southernmost site, which were in some cases equal to or greater than primary crop yields. Low primary crop brix values were found for all cultivars on the muck soils in South Florida compared to the other two sites, and for M-81E compared to Dale and Topper 76-6. These low brix values were correlated with greater fresh biomass production. Further research is needed on planting dates for optimizing primary and ratoon crop yields along with varietal development with improved ratoon crop yields.

Municipal biosolids (MBS) represents an alternative source of nutrients for the production of bioenergy crops like elephantgrass (Pennisetum purpureum Schum.). Two experiments were conducted during 2 yr in Florida to evaluate the effect of soil incorporation vs. surface application of MBS on: (i) elephantgrass dry matter (DM) yield, tissue N and P concentration and removal, and soil C and P (Exp. 1); and (ii) organic N mineralization and DM decomposition rates of MBS measured in the field using a litter bag incubation technique (Exp. 2). In Exp. 1, three treatments supplied 350 kg total N ha -1 yr -1 from surface-applied municipal biosolids (MBS-SA), soil-incorporated municipal biosolids (MBS-INC), and surface-applied ammonium nitrate (NH 4 NO 3 ). A fourth treatment provided 700 kg total N ha -1 yr -1 from MBS-SA (double rate of municipal biosolids, 2x-MBS). In Exp. 2, MBS was field incubated in litter bags placed on the soil surface or at a 5-cm soil depth. Elephantgrass DM yield, and N and P removal were greater for MBS-INC than MBS-SA. Dry matter yield for MBS-INC was not different than for NH 4 NO 3 fertilizer (22.5 vs. 24.3 Mg ha -1 ). Removal of N and P increased 39 and 10 kg ha -1 yr -1 , respectively, for MBS-INC and MBS-SA. Total organic N mineralized was greater for MBS-INC (386 g kg -1 ) than MBS-SA (308 g kg -1 ). Incorporation of MBS increases elephantgrass DM yield and nutrient removal compared to surface application and allows MBS to replace a greater proportion of inorganic N fertilizer.

The Lower Suwannee River Basin (LSRB) in northern Florida is environmentally sensitive. This study evaluated two surface-applied N sources for ‘Tifton 85’ bermudagrass (Cynodon spp.) hay production and associated risk of nitrate contamination of groundwater. The study was conducted at two locations in the LSRB where soils are deep, sandy Entisols. During a 2.5-yr period, bermudagrass received sole N source ammonium nitrate (AN), applied at 42, 84, 126, and 168 kg N ha −1 per growth interval, or sole N source broiler (chicken, Gallus gallus domesticus) litter (BL), applied at 84 and 126 kg N ha −1 . Plots were arranged using a randomized block design with three or four replications depending on the location. Suction-cup lysimeters were installed at a 1.4-m soil depth to monitor nitrate movement from the primary rooting zone. For AN, dry matter yield and crude protein (CP) concentration increased with an increase in N level, while forage P declined and in vitro digestible organic matter increased. Forage yield with BL was 64, 48, and 67% of yield with AN applied at common levels in 1998, 1999, and 2000, respectively. Forage CP was mostly less for BL than for AN, but forage P was greater for BL. A potential risk to groundwater quality due to nitrate leaching below the primary rooting zone was observed only with AN applied at 168 kg N ha −1 . Probable ammonia emissions from surface-applied BL, however, likely resulted in poorer bermudagrass production and could impact nearby surface waters.

High-yielding biomass crops remove signifi cant quantities of soil nutrients, and nutrient replacement using inorganic fertilizers may not be sustainable. Municipal biosolids (MBS) are an alternative nutrient source. Organic N is the primary N form in MBS, and patterns of N mineralization can determine the eff ectiveness of MBS as an N source. Th e objectives of this experiment were to: (i) determine the eff ect of season of application on organic N mineralization rate and dry matter (DM) decomposition of Class A MBS measured in the fi eld with litter bags and (ii) compare N mineralization measured using a fi eld-based technique with that predicted from the DECOMPOSITION model. Treatments were season of MBS application (spring and summer) during 2 yr. Organic N mineralization measured using litter bags followed the same pattern and arrived at a similar endpoint as predicted by the DECOMPOSITION model in three of four seasons. Lower spring temperatures and rainfall were associated with lower rates of N mineralization and DM decomposition during the 50 d following spring vs. summer application of MBS. When MBS were applied in summer, organic N mineralization leveled off approximately 50 d aft er application compared with 150 to 250 d following spring application. Seasonal weather conditions and N mineralization patterns should be considered when determining whether to apply MBS as the source of N, the timing of MBS application, and if single or split applications are best.

High-yielding bioenergy crops remove large quantities of soil nutrients. Nutrients must be replenished in a manner that mini-mizes production costs and negative environmental impact. Class A municipal biosolids (MBS) were evaluated as an alternative nutrient source to inorganic fertilizer for ‘Merkeron’ and Chinese Cross elephantgrasses ( Pennisetum purpureum Schum.) in a 2-yr fi eld experiment in Florida. Elephantgrass plots received 0, 33, 67, or 100% of total N applied (350 kg ha –1 yr –1 ) from MBS, with the remainder from NH 4 NO 3 . Dry matter (DM) yield, tissue N and P concentrations and removal, and soil C and P concentrations were assessed. Elephantgrass yield decreased linearly from 24.2 to 20.1 (Merkeron) and 24.3 to 16.9 Mg ha –1 (Chinese Cross) as the percentage of N supplied by MBS increased from 0 to 100. Nitrogen removal decreased from 208 to 127 kg ha –1 yr –1 over the same range of N from MBS. Phosphorus removal ranged from 28 to 43 kg ha –1 yr –1 , but the eff ect of N source was not consistent. Th ere was no eff ect of percentage of N from MBS treatment on soil responses including water-extract-able (WEP), Mehlich-1, or total P, nor was there an eff ect on total C concentration in the Ap horizon. Replacing 33% of N from inorganic fertilizer with N from MBS reduced elephantgrass biomass production 0 to 11%, so there is potential benefi t to includ-ing MBS in a fertilization program for bioenergy crops, even in situations where MBS are limited to P-based application rates.

In northern Florida, year-round forage systems are used in dairy effluent sprayfields to reduce nitrate leaching. Our purpose was to quantify forage N removal and monitor nitrate N (NO - 3 -N) concentration below the rooting zone for two perennial, sod-based, triple-cropping systems over four 12-mo cycles (1996-2000). The soil is an excessively drained Kershaw sand (thermic, uncoated Typic Quartzipsamment). Effluent N rates were 500, 690, and 910 kg ha -1 per cycle. Differences in N removal between a corn (Zea mays L.)-bermuda-grass (Cynodon spp.)-rye (Secale cereale L.) system (CBR) and corn-perennial peanut (Arachis glabrata Benth.)-rye system (CPR) were primarily related to the performance of the perennial forages. Nitrogen removal of corn (125-170 kg ha -1 ) and rye (62-90 kg ha -1 ) was relatively stable between systems and among cycles. The greatest N removal was measured for CBR in the first cycle (408 kg ha -1 ), with the bermudagrass removing an average of 191 kg N ha -1 . In later cycles, N removal for bermudagrass declined because dry matter (DM) yield declined. Yield and N removal of perennial peanut increased over the four cycles. Nitrate N concentrations below the rooting zone were lower for CBR than CPR in the first two cycles, but differences were inconsistent in the latter two. The CBR system maintained low NO - 3 -N leaching in the first cycle when the bermudagrass was the most productive; however, it was not a sustainable system for long-term prevention of NO - 3 -N leaching due to declining bermudagrass yield in subsequent cycles. For CPR, effluent N rates ≥ 500 kg ha -1 yr -1 have the potential to negatively affect ground water quality.

Florida dairies need year-round forage systems that prevent loss of N to ground water from waste effluent sprayfields. Our purpose was to quantify forage N removal and monitor nitrate N (NO3(-)-N) concentrations in soil water below the rooting zone for two forage systems during four 12-mo cycles (1996-2000). Soil in the sprayfield is an excessively drained Kershaw sand (thermic, uncoated Typic Quartzipsamment). Over four cycles, average loading rates of effluent N were 500, 690, and 910 kg ha(-1) per cycle. Nitrogen removed by the bermudagrass (Cynodon spp.)-rye (Secale cereale L.) system (BR) during the first three cycles was 465 kg ha(-1) per cycle for the low loading rate, 528 kg ha(-1) for the medium rate, and 585 kg ha(-1) for the high. For the corn (Zea mays L.)-forage sorghum [Sorghum bicolor (L.) Moench]-rye system (CSR), N removals were 320 kg ha(-1) per cycle for the low rate, 327 kg ha(-1) for the medium, and 378 kg ha(-1) for the high. The higher N removals for BR were attributed to higher N concentration in bermudagrass (18.1-24.2 g kg(-1)) than in corn and forage sorghum (10.3-14.7 g kg(-1)). Dry matter yield declined in the fourth cycle for bermudagrass but N removal continued to be higher for BR than CSR. The BR system was much more effective at preventing NO3(-)-N leaching. For CSR, NO3(-)-N levels in soil water (1.5 m below surface) increased steeply during the period between the harvest of one forage and canopy dosure of the next. Overall, the BR system was better than CSR at removing N from the soil and maintaining low NO3(-)-N concentrations below the rooting zone.

The utilization of dairy waste effluent provides nutrients and water for crop growth and allows producers to comply with regulations governing on-farm recycling of nutrients. Dry matter (DM) yield and nutritive value were measured for forages from five year-round cropping systems at effluent N rates of 450, 675, and 900 kg ha -1 yr -1 during 4 yr on a Kershaw fine sand (coated, thermic Typic Quartzipsamments) in northern Florida. Cropping systems were rye (Secale cereale L.) grown in tandem with either bermudagrass (Cynodon spp.), corn (Zea mays L.)-bermudagrass (CBR), corn-forage sorghum [Sorghum bicolor (L.) Moench; CSR], rhizoma peanut (Arachis glabrata Benth.; PR), or corn-rhizoma peanut (CPR). Annual yields increased with N level in Years 1 and 2, but not during Years 3 and 4. Yields were similar among BR, CBR, and CSR (25.9 Mg ha -1 ) in Year 1. In Year 2, BR (31.2 Mg ha -1 ) had the greatest yield followed by CBR and CSR (avg. 25.5 Mg ha -1 ). In Years 3 and 4, yields of BR (21.1 Mg ha -1 ) and CBR (20.7 Mg ha -1 ) declined while yield of CSR remained constant. Systems CPR and PR yielded less during the 4 yr (17.6 Mg ha -1 ). In vitro digestibility of BR (580 g kg -1 ) was lower than for the other systems (mean of 653 g kg -1 ). Cropping system had a major impact on forage yield and nutritive value, but N rates above 450 kg ha -1 had relatively little effect on these responses.

This paper contains results of four research projects conducted over a five-year period (1986–1990), to evaluate high yielding perennial bunchgrasses as a renewable energy source. In peninsular Florida, tall bunchgrasses including elephantgrass (Pennisetum purpureum Schum.) and energycane (Saccharum spp.), have produced far greater annual dry biomass (DB) yields than forage and sweet sorghums (Sorghum bicolor (L.) Moench). In the colder locations in Florida's panhandle and at Auburn, Alabama, adapted elephantgrass and energycane genotypes produced comparable-to-much larger DB yields than the annual sorghums. A long near-linear period of DB accumulation, lasting 140 to 196 days, was responsible for the high yielding ability of the perennial bunchgrasses. However, the daily rate of DB accumulation of the bunchgrasses and the efficiency by which incoming solar energy was converted to chemical energy in plant biomass, were not unlike those of other C-4 grasses during active growth. The biomass of elephantgrass and energycane can be stored easily by ensiling because harvested herbage (before ensiling) has a low buffering capacity. Propagation quality of elephantgrass stems can be improved by applying high rates of fertilization to nursery plants.

Elephantgrass (Pennisetum purpureum Schum.) was evaluated in the colder subtropics of Florida as a potential forage source for ruminants. Our objective was to determine if this thick-stemmed bunch-grass could be stored as a silage. A dwarf (Mott') and two tall (PI 300086 and Merkeron') elephantgrass were harvested one, two, and three times per season and ensiled (direct-cut) during 1986 and 1987. Dry matter (DM) recoveries for all silages ranged from 861 to 984 g kg −1 of DM ensiled (...)

Elephantgrass (Pennisetum purpureum Schum.) is known throughout much of the wet tropics for its prolific growth and usage as a forage for ruminants. In a 3-yr study conducted on a well-drained, infertile soil (loamy, siliceous, hyperthermic, Grossarenic Paleudult) and under subtropical conditions near Gainesville, FL, the response of this forage to three harvest frequency regimes was measured. Genotypes evaluated were four tall elephantgrasses (PI 300086, Merkeron', N-43, and N-51), a dwarf elephantgrass (Mott), and a semi-dwarf Pennisetum glaucum (L.) R. Br. × P. purpureum Schum. hybrid (Selection 3) (...)

There is concern that P from dairy effluent sprayfields will leach into groundwater beneath Suwannee River basins in northern Florida. Our purpose was to describe the effects of dairy effluent irrigation on the movement of soil P and other nutrients within the upper soil profile of a sprayfield over three 12-mo cycles (April 1998-March 2001). Effluent P rates of 70, 110, and 165 kg ha(-1) cycle(-1) were applied to forages that were grown year-round. The soil is a deep, excessively drained sand (thermic, uncoated Typic Quartzipsamment). Mean P concentration in soil water below the rooting zone (152-cm depth) was < or = 0.1 mg L(-1) during 11 3-mo periods. Mehlich-1-extractable (M1) P, Al, and Ca in the topsoil increased over time but did not change in subsoil depths of 25 to 51, 51 to 71, 71 to 97, and 97 to 122 cm. Topsoil Ca increased as effluent rate increased. High Ca levels were found in dairy effluent (avg.: 305 mg L(-1)) and supplemental irrigation water (avg.: 145 mg L(-1)) which likely played a role in retaining P in the topsoil. An effect of effluent rate on P and Al concentrations in the topsoil was not detected, probably due to large and variable quantities present at project initiation. The P retention capacity (i.e., Al plus Fe) increased in the topsoil because Al increased. Dairy effluent contained Al (avg.: 31 mg L(-1)). Phosphorus saturation ratio (PSR) increased over time in the topsoil but not in subsoil layers. Regardless of effluent rate, the P retention capacity and PSR of subsoil, which contained 119 to 229 mg kg(-1) of Al, should be taken into account when assessing the risk of P moving below the rooting zone of most forage crops.

In northern Florida, forages are grown in dairy effluent sprayfields to recover excess P. Our purpose was to evaluate five year-round forage systems for their capacity to remove P from a dairy sprayfield. The soil is a Kershaw sand (thermic, uncoated Typic Quartzipsamment). Systems included bermudagrass (Cynodon spp.)-rye (Secale cereale L.) (BR), perennial peanut (Arachis glabrata Benth.)-rye (PR), corn (Zea mays L.)-forage sorghum [Sorghum bicolor (L.) Moench]-rye (CSR), corn-bermudagrass-rye (CBR), and corn-perennial peanut-rye (CPR). Forages were grown for five 12-mo cycles. Effluent P rates were 80, 120, and 165 kg ha-1 cycle-1. The 5-cycle P removal was 67 kg ha-1 cycle-1 for BR, 54 kg ha-1 for CBR, 52 kg for CSR, 45 kg for PR, and 43 for CPR. Removal of P by winter rye was low. There were differences in system rankings among cycles primarily due to changes in the performance of perennial forages. In the first two cycles, BR had the greatest P removal (91 kg ha-1 cycle-1) due to high bermudagrass yield and P concentration. In the first cycle, P removal was lowest for PR (36 kg ha-1) because perennial peanut was slow to establish. In later cycles, P removal for BR declined because bermudagrass yield and P concentration declined. It increased for PR because peanut yield increased. The yield of corn in CBR, CPR, and CSR was consistently high but P concentration was modest (avg. 2.2 g kg-1). Sorghum produced moderate but stable yield and had low P levels (avg. 1.8 g kg-1). Effluent rate marginally affected the performance of most grasses. For P recovery in dairy sprayfields in northern Florida, the best warm-season forage would likely be a high yielding, persistent bermudagrass.