EFFECTS OF AMMONIUM-SULFATE APPLICATION ON THE RHIZOSPHERE, FINE-ROOTAND NEEDLE CHEMISTRY IN A PICEA-ABIES (L) KARST STAND

Rhizosphere, fine-root and needle chemistry were investigated in a 28 year old Norway spruce stand in SW Sweden. The uptake and allocation p attern of plant nutrients and aluminium in control plots (C) and plots repeatedly treated with ammonium sulphate (NS) were compared. Treatme nts started in 1988. Current year needles, one-year-old needles and cy lindrical core samples of the LFH-Iayer and the mineral soil layers we re sampled in 1988, 1989 and 1990. Compared to the control plots, pH d ecreased significantly in the rhizosphere soil in the NS plots in 1989 and 1990 while the SO4-S concentration increased significantly. Alumi nium concentration in the rhizosphere soil was generally higher in the NS plots in all soil layers, except at 0-10 cm depths, both in 1989 a nd 1990. Calcium, Mg and K concentrations also increased after treatme nt with ammonium sulphate. Ammonium ions may have replaced these eleme nts in the soil organic matter. The NS treatment significantly reduced Mg concentrations in fine roots in all layers in 1990. A similar tren d was found in the needles. Ca concentrations in fine roots were signi ficantly lower in the NS plots in the LFH layer in 1990 and the same p attern was found in the current needles. The N and S concentrations of both fine roots and needles were significantly higher in the NS plots . It was suggested that NS treatment resulted in displacement of Mg, C a and K from exchange sites in the LFH layer leading to leaching of th ese cations to the mineral soil. Further application of ammonium sulph ate may damage the fine roots and consequently adversely affect the wa ter and nutrient uptake of root systems.