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Direct drilling of soybean varieties in coastal N.S.W.

P.J. Desborough

Agricultural Research Station, Grafton, N.S.W. 2460

The extensive, hill-lands on the North Coast of New South Wales are low in fertility and have traditionally been utilised for low-intensity beef cattle grazing. In the past decade there has been a rapid increase in cropping activity on these native/naturalised grass pastures, using soybeans and winter cereals. One major limitation to further crop expansion in this gently to steeply undulating country is the serious risk of extensive soil erosion after cultivation.

Direct drilling of soybeans is now widespread in U.S.A. and Brazil. The advantages of reduced erosion, greater timeliness of operations and lower fuel consumption are obvious benefits to future cropping in this area. However, before direct drilling can be recommended it is desirable that we know what effects adoption will have on soybean yield and variety selection.

Five soybean varieties were compared at Grafton when direct drilled into a low-fertility, podzolic soil supporting unimproved grass, inactivated with glyphosate. The trial was sown on 4 January, 1979 after topdressing with superphosphate (500 kg ha-1) and potassium sulphate (75 kg ha-1).

TABLE I. Yield and mature plant height of five soybean varieties direct drilled at Grafton in 1979.

Variety

Yield
t ha-1

Height
cm

Bossier

4.27

65

P24

3.84

61

Davis

3.83

64

Fitzroy

3.77

99

Bragg

3.24

50

SE+

0.178

2.7

Effective pasture control, good plant establishment (final plant counts of 28-29 m2) and adequate soil moisture led to high yields in all varieties, but with Bragg yielding significantly less (p<0.05) than the other four. With the exception of Fitzroy, plant height was slightly less than optimum.

Another trial was sown on an adjacent area on the same day into conventionally cultivated soil and with the same fertilizer inputs as above. Whilst the two trials cannot be compared statistically, under cultivation Bragg and Bossier yielded 3822 and 3466 kg ha-1 respectively and were 53 and 61 cm tall at maturity. This suggests an interaction between variety and cropping system.

These results indicate that, firstly, it is possible to grow high-yielding soybean crops with direct drilling, and secondly, it may be necessary to select varieties adapted specifically to each system.

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