Lime improves emergence of canola on an acidic, hardsetting soil

Abstract

Much of the agricultural lime applied in southern New South Wales, Australia, is applied to crops of canola (Brassica napus L.), but little is documented on the response of canola to lime. The few documented responses in grain yield of canola to lime application have been ascribed to decreased toxicities of aluminium and manganese. However, there is evidence that lime can have a structural effect on soil. A field experiment was limed in 1982 (0–5 t/ha) and was relimed in 1996 (0–5 t/ha) to give factorial combinations of 5 rates of 'old' (1982) and 6 rates of 'new' (1996) lime. When sown to canola in 1999 there was an increase in density of canola (from 17 to 60 plants/m²) and grain yield (from 1200 to 2700 kg/ha) associated with increasing rates of lime application. The emergence of canola was increased by 15% for each 1 unit increase in soil pH_Ca.

Two subsequent pot experiments, conducted on cores taken from a subset of field plots with different liming histories, showed that lime application increased emergence of canola by about 9% for each 1 unit increase in soil pH_Ca. In addition, 2 contrasting watering treatments (gentle spraying and rapid flooding) were applied to the pots to either avoid or accentuate any soil structural breakdown. Flooding gave lower emergence compared with spraying (19 and 31%, respectively). Soil strength measurements (penetration resistance and shear strength) conducted on the surface soil (0–1 cm depth) during the second glasshouse experiment showed that lime application and gentle watering (spraying rather than flooding) resulted in lower soil strength. The soil strength measurements were related to emergence of canola. It is proposed that soil structural stability was the major contributor to these observed emergence differences. This is the first evidence in New South Wales of lime affecting plant performance via its influence on soil structure.