FOLIAR SPRAY EXPERIMENTS IDENTIFY NO BORON DEFICIENCY BUT MOLYBDENUM AND MANGANESE DEFICIENCY FOR CANOLA GRAIN PRODUCTION ON ACIDIFIED SANDY GRAVEL SOILS IN SOUTHWESTERN AUSTRALIA

Abstract

Since the early 1990s canola (oilseed rape, Brassica napus L.) has become a major crop species grown on the predominantly sandy soils of southwestern Australia. Numerous studies have been undertaken to determine the fertilizer requirements of the crop in the region. This paper reports results of a field experiment conducted at three sites on typical acidified (pH [Ca] ∼4.6) sandy gravel soils to identify if molybdenum (Mo), manganese (Mn) or boron (B) were deficient for canola grain production. Different levels of each element, separately or as mixtures, were applied as foliar sprays at mid-flowering. Maximum grain yield responses of ∼11–20% to applied Mo, as sodium molybdate (39% Mo), were obtained when 40 g Mo/ha was applied. Maximum grain yield responses of ∼13–28% to applied Mn were achieved by applying 1000 g ha⁻¹ Mn, as manganese sulfate (24% Mn). A mixture of 40 g Mo ha⁻¹ and 1000 g Mn ha⁻¹ increased grain yields by ∼15–38%. Boron, applied as borax (11% B), sprayed individually or in combination with Mo or/and Mn, had no effect on grain yields. None of the foliar spray treatments had any effect on oil concentration in canola grain. The sprays did not cause any visible damage to foliage. Soil acidification has been shown to induce Mo deficiency for cereal crops in the region and both soil acidification and induced Mo deficiency are alleviated by applying sufficient lime to raise pH of top 10 cm soil to 5.5 or greater, and this strategy should also apply to canola. Further research is required to determine the fertilizer Mn requirements for canola grain production in the region.

Keywords:

• boron
• Brassica napus L.
• manganese
• molybdenum
• oil concentration
• oilseed rape
• protein

ACKNOWLEDGMENTS

Funds were provided by the Government of Western Australia and the Grains Research and Development Corporation (GRDC). Technical assistance was provided by Frank O’Donnell and the Great Southern Agricultural Research Institute, Katanning. Chemical analyses of soil and plant samples were conducted by the Chemistry Centre (WA).