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Rotational benefits of alternative crops can be affected by their sowing time

D.P. Heenan and G.M. Murray

NSW Agriculture, Agricultural Research Institute, Wagga Wagga NSW 2650

Over the past decade alternative crops such as the grain legumes and canola have been widely accepted as profitable cash crops and as a means of improving yields of following cereal crops. The optimum time for sowing these crops can vary between species. Also, the possible time for sowing can vary markedly from one season to the next as a result of the unreliable autumn breaks in southern Australia. This unpredictable weather causes variable sowing times that may influence yields of the crops and benefits to the subsequent wheat crop. A field experiment has examined the influence of sowing time on these factors.

Methods

Lupins (Lupinis angustifolius), field pea (Pisum sativum), canola (Brassica campestris), linseed (Linum usitatissimum), lentils (Lens culinaris), and barley (Hordeum vulgare), were sown at three times in 1989, 21 April, 19 May and 23 June, on a red earth at Wagga Wagga. After harvest, stubble of all plots was incorporated. Wheat was sown on 21 May 1990 with 20 kg P/ ha on all plots. Plots following canola and linseed also received 30 kg N/ha as urea.

Results and discussion

In the first sowing of 1989, cut worm (Agrotis infusa), damaged lupins, canola, linseed and lentils while diseases damaged field peas (Ascochyta pisi), lentils (clover stunt virus), canola (blackleg, Phoma lingam) and barley scald (Rhyncosporium secalis). Grain yields, except for lupins, were highest for the second sowing date. Wheat yields after the non cereal crops were significantly higher (P<0.01) than after barley (Table 1).

Table 1. Yields of wheat sown on 21 May 1990 following six alternative crops sown at different times in 1989.

Delaying the sowing date of lupins, field peas and linseed reduced subsequent wheat yields by 7.8%, 6.8% and 5.4%. However, late sowing of barley, canola and lentils increased yields by 33.8%, 4.7% and 2.5%. The interaction between sowing date and crop species was significant (P<0.05). Grain protein was higher following grain legumes but was reduced by delayed sowing of both lupins and field peas. Grain protein was increased with late sowing of canola, linseed, barley and lentils, with a significant interaction (P<0.01) between sowing time and species. Effects on wheat yield and grain protein were related to effects on soil nitrogen and disease. Soil mineral nitrogen was higher after grain legumes and was reduced by later sowing of lupins and field peas. The diseases take all (Gaeumannomyces graminis var. tricici) and eyespot (Tapesia yallundae) were at very low levels in wheat after all the non-cereal crops. Incidence of these diseases was greatest after early sown barley but after the late sown barley it was similar to that after the non-cereal crops.

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