Nitrogen Release from Biosolids Applied to Sandy Soil Amended with Lime

Most bahiagrass pastures in Florida are nutrient deficient; however, ranchers have been reducing fertilizer application due to the low cattle prices. Pelletized biosolids applied to bahiagrass pastures on an acid sandy soil increased forage yield and quality linearly with rates up to 17.6 Mg/ha and between 50 to 80% of the N was made available within the first year of application. Soil pH may have a pronounced effect on mineralization from biosolids, though. The objective ofthis laboratory study was to investigate the effects ofvariable soil pH attained by liming of an acid sandy soil. on the mineralization ofN from pelletized biosolids. Biosolids at the rate of'D, 1.-.1,2.2.4.4.8.8 and 17.6 Mg/ha and calcitic limestone at the rate ofO, 2.2, 4.4, and 8.8 MgIha were added to a myakka fine sand. Soil pH values were determined bi-weekly after the addition of lime and biosolids The N mineralization process at the various lime/pH levels was assessed by a Ilion-leached incubation system. Soil samples were removed bi-weekly and extracted with water for the determination ofNH4 and NOJ • The soil pi I values varied from 5.5 to 6.7 with increasing lime application rates. Increasing biosolids resulted in slight decreases in ssoil pH within each lime level. Ammonium was the predominant form ofN within the first two weeks of incubation; however. as time progresses. NOJ predominated. Nitrogen mineralization stabilized at 10 weeks and was reduced by the highest lime rate.