Accumulation of plant nutrients and changes in soil properties of sandy soils under fertilized pasture in southeastern South-Australia .II. Total sulfur and nitrogen, organic carbon and pH

Abstract

The accumulation of total sulfur in sand over clay soils growing improved pastures was measured in three areas of the south-east of South Australia. Accumulation rates in the top 10 cm of soil ranged from 4.6 to 6.3 kg ha-1 yr-1 and in the 10-30 cm layer from 1.3 to 3.7 kg ha-1 yr-1. Assuming all of this sulfur came from applied single superphosphate, the recoveries of applied sulfur in the sand layer were 42, 63 and 57% for the Hundreds of Coles, Willalooka and Senior respectively. Using a 'balance sheet' approach, the calculated annual maintenance superphosphate rates, that will supply sufficient sulfur, ranged from 110 to 250 kg ha-1. Total soil nitrogen accumulation rates were 55, 48 and 37 kg ha-1 yr-1 for the Hundreds of Coles, Willalooka and Senior respectively. The enhanced nitrogen accretion in Coles was attributed to improved legume production resulting from both increased superphosphate dressings and higher average annual rainfall in that area. Organic carbon levels were highly correlated with pasture age, with increases in the top 10 cm of soil ranging from 0.022% to 0.034% per year. Soil pH was highly correlated with pasture age, with decreases as large as 0.036 units per year in the top 10 cm and 0.025 units per year in the 10-30 cm layer measured in the Hundred of Willalooka.