A soil sulfur test for pastures and crops

Abstract

Soil testing for S has generally been unsuccessful when using extractants that remove only sulfate from the soil.An assessment of a range of extractants to predict S status was undertaken on soil samples taken from 18 field trials in northern N.S.W. The extractants were water, 0 . 0 1 M monocalcium phosphate (MCP) and 0 . 5 M NaHC03, 0.25 M KC1 heated for 3 h at 100, 80, 40, or 25°C. The highest correlation between soil S test level and % maximum yield was found in the 40°C KC1 extractant (r2 = 0.73). This compares with an r2 value of 0.47 for the widely used MCP extractant.A study using a soil from a pot experiment where rice was grown showed that the KC1 extract removed more S from the H1 reducible (ester sulfate) fraction than did MCP. This S fraction is believed to be important in supplying S to plants.A comparison of the specific radioactivity of soil extractants and rice plants confirmed that the KC1 40°C extract removes S from similar soil pools as do plants. The procedure is recommended for wider evaluation.

Moderate sodium has positive effects on shoots but not roots of salt-tolerant barley grown in a potassium-deficient sandy soil

“…Laboratory analysis showed that the surface soil was loamy sand and contained 1 mg NO 3 -N and 1 mg NH 4 -N/kg (Searle 1984), 2 mg P and 15 mg K/kg (Colwell 1963), 2 mg S/kg (Blair et al 1991), and 13 g organic C/kg (Walkley and Black 1934) Basal nutrients were evenly mixed in the soil of each pot. Six seeds were sown per pot, and 10 days later the seedlings were thinned to two uniform plants.…”

Whole-farm management of soil nutrients drives productive grazing systems: the Cicerone farmlet experiment confirms earlier research

“…The soil P and S levels were measured using the Colwell P method (Colwell 1963) and the KCl-40 S test (Blair et al 1991).…”

“…Both of these soil tests give an estimate of the level of available P and S to pasture systems and have been calibrated for the Northern Tablelands and critical concentrations determined (Holford and Crocker 1988;Blair et al 1991). The maintenance applications of farmlets B and C were set such that they were likely to still be responsive to P and S applications, while farmlet A was designed to achieve >90% of potential pasture production in the region.…”

“…The maintenance applications of farmlets B and C were set such that they were likely to still be responsive to P and S applications, while farmlet A was designed to achieve >90% of potential pasture production in the region. The target soil P and S levels of farmlet A (higher input) were 60 and 10 mg/kg, respectively [~50% higher than critical response levels suggested by Colwell (1963) and Blair et al (1991)]. For farmlets B and C the target P and S levels were set at 20 and 6.5 mg/kg, respectively.…”

“…The soils of the Northern Tablelands of New South Wales (NSW), Australia, were nutrient poor when grazing enterprises began in 1832; this constrained production through to the 1930s when applications of single superphosphate (SSP) with white clover (Trifolium repens) commenced, leading to dramatic increases in productivity (Robinson and Lazenby 1976). This is highlighted in data presented by the Commonwealth Scientific and Industrial Research Organisation (CSIRO) and NSW Agriculture (CSIRO 1964) and a more recent review indicating that at least 70% of soils in the southern portion of the Northern Tablelands were moderately or severely deficient in phosphorus (P) and/or sulfur (S) (Edwards and Duncan 2002) based on critical values of 30 mg/kg for P (Colwell 1963) and 6-8 mg/kg for S (Blair et al 1991).…”