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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.

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.