RYEGRASS FORAGE YIELD AND QUALITY RESPONSE TO SULFUR AND NITROGEN-FERTILIZER ON COASTAL-PLAIN SOIL

Sulfur (S) deficiency has been reported in some upland soils of the so uthern United States and S application has improved forage quality on the low-S soils. A field experiment was conducted for three years to d etermine ryegrass (Lolium multiflorum L.) dry matter yield and forage quality response to S fertilization. Frilled elemental S was applied e ach year at two rates (0 and 45 kg S/ha) in combinations with three ra tes of nitrogen (N) (168, 224, and 280 kg/ha). Wet depositions of S in rain were monitored over the seasons. Sulfur fertilization generally did not increase seasonal dry matter yield and plant uptake of S. Nitr ogen application generally increased dry matter yield and protein cont ent during the season. Averaged over the three-year period, however, f orage yield and S uptake increased from 7.7 to 10.5 Mg/ha and 13.9 to 18.8 kg/ha, respectively, as N fertilization increased from the lowest to highest treatment rates. Forage dry matter for each harvest ranged from 0.6 to 2.2 Mg/ha, while S, protein, in vitro dry matter digestib ility (IVDMD), and N/S ratio tended to decline seasonally from 2.5 to 1.8, 266 to 142, and 795 to 716 g/kg, and 17.8 to 11.9, respectively. Sulfur input from rainfall was small with a three-year average of 5.8 kg/ha (+/-0.64 SE). In some locations of the southern United States, S may not be limiting even when applying high rates of N to high-yieldi ng forages which annually remove large quantities of S. Because of the lack of yield response from S application and low inputs of S from we t deposition, S from sources other than rainfall may have been conside rable.