Canola

Chris Gazey from Agriculture WA harvested 4 trials that had been limed in 1991, 1994 and 2 in 1996. Aglime of Australia harvested 2 trials limed in 1985* and 1995*. Each trial had received varying rates of limesand, from 0 to 5t/ha and initial pH levels ranged from mid to high 4’s.  The highest rate of limesand (between 2 and 5t/ha) produced the greatest yield increase in 5 of the 6 trials.

All responses were highly profitable with canola prices around $350/t and yield increases were around 0.1 to 0.4t/ha. Extra profits from applying Aglime would be in the order of $35 to $140 per ha.

Applying Aglime to paddocks cropped to canola leads to large profits as each lime application lasts many years (see results above for 1985 limed site) . On the other hand, growing canola on acid soils without liming can result in significant reductions in profit.

These results confirm that WA farmers should adopt the practice now common in Victoria and New South Wales where farmers apply lime in the year canola is sown to gain immediate return on their investment. In many cases the cost of liming is recovered by the yield response in the first canola crop.

Effect with different limes

In one of Chris Gazey’s trials, (1996a), dolomite and G lime (commonly called burnt lime) were compared with limesand. (Figure 2). To compensate for the lower neutralising value of the dolomite (67%), adjustments were made to the rates applied.  Both G lime and limesand were applied around 1 and 2 t/ha while dolomite rates were 50% higher – 1.5 and 3.0 t/ha.

The results clearly show that limesand was the superior liming material with dolomite being much less effective even when applied at higher rates. In fact, 1t/ha of limesand gave a higher canola yield than 3t/ha of dolomite. In addition, the 1t/ha rate of limesand gave the same yield response as 2t/ha of G lime.

Monitor for best results

Increased soil pH after liming makes most nutrients more available but trace elements (especially zinc and manganese) tend to become less available. It is very important that plant analyses are undertaken every few years to check that nutrients are sufficient for maximum crop yields, particularly after liming.