Nitrogen Removal and Nitrate Leaching for Forage Systems Receiving Dairy Effluent
2002
Woodard, Kenneth R. | French, Edwin C. | Sweat, Lewin A. | Graetz, Donald A. | Sollenberger, Lynn E. | Macoon, Bisoondat | Portier, Kenneth M. | Wade, Brett L. | Rymph, Stuart J. | Prine, Gordon M. | Van Horn, Harold H.
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 (NO⁻ ₃–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 NO⁻ ₃–N leaching. For CSR, NO⁻ ₃–N levels in soil water (1.5 m below surface) increased steeply during the period between the harvest of one forage and canopy closure of the next. Overall, the BR system was better than CSR at removing N from the soil and maintaining low NO⁻ ₃–N concentrations below the rooting zone.
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