Boron supplying power, boron adsorption capacity and productivity of some acidic soils from the Central Tablelands of New South Wales

Abstract

The reliability of the hot-water soluble boron (HWSB) content of a soil as a measure of total boron available to plants during intensive cropping, and its relationship with the boron-supplying power (BSP) of the soil, as affected by the soil's parent material, was studied in a glasshouse trial. Fifteen surface soils (0- 15 cm) from six parent materials from the Central Tablelands of New South Wales were used. In each pot of soil, three crops were planted in succession: sunflower (Helianthus annuus cv. Hysun 3 I), subterranean clover (Trifolium subterraneum cv. Woogenellup), and maize (Zea mays cv. XL45). Lime and borax were applied in a 2x2 factorial combination. Crop responses to these applications, their relationship with soil BSP and HWSB content, and soil boron adsorption capacity (BAC) when borax was added were also investigated. In soils not treated with borax or lime, the following were significantly correlated (r > 0.51): crop yield, crop uptake of boron, HWSB content before cropping, and BSP. However, BSP was not correlated with the amount of HWSB lost from the soil during cropping. In sandstone, granitic and quartz-rich fine sedimentary soils, the amount of boron taken up by the crops was not significantly different from the amount of HWSB removed from the soil. Therefore, their BSP (0, 74 and 145 g B/ha respectively) was not significantly greater than zero and thus their HWSB content simply and reliably measures their boron status. From crop responses in granitic and quartz-rich fine sedimentary soils (HWSB content 0.26 and 0.30 �g B/g of air dried soil, respectively) it was shown that these soils require boron supplementation whenever their HWSB content is less than about 0.34 �g B/g air dried soil, particularly if they are cropped intensively or heavily limed. The BSP of tuff, basaltic and alluvial soils (388, 407 and 620 g B/ha) was significantly greater than zero. Therefore, these soils have boron reserves not measured by the HWSB method and their HWSB content does not reliably measure boron available for crops. All soils adsorbed boron when borax was applied. The BAC did not differ significantly between the six soil types. The overall effect of lime was to significantly increase dry matter yield. Boron uptake by the crops, and soil BSP and BAC were not significantly affected by liming.