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The effect of deep ripping and gypsum application on sodic duplex soils for pasture production

P.L. Matthew1, J.W. Sands1 , Edi R. Wijaya2, Mursahid2

1 Queensland Agricultural College, Lawes, Queensland 4343, Australia
Directorate of Technical and Vocational Education, Indonesia

Within the Lockyer Valley there is a significant area of sodic duplex soils which have a characteristically low pasture productivity. The shallow A horizon (< 0.3 m) overlying a moderately strong to rigid sodic clay B horizon limits plant rooting depth, moisture, nutrients, and at the other extreme produces waterlogging. Deep ripping hard impervious zones and gypsum applications to sodic soils are standard Methods of amelioration (1). Pasture production in the valley is under both dryland and irrigated conditions. A trial to examine the effect of deep ripping and deep ripping with gypsum on pasture yield under dryland and irrigated management practices was conducted.


Deep ripping (to a depth of 0.75 m at a spacing of 0.6 m) and deep ripping with gypsum (at a rate of 10 t ha-1 injected as a slurry into the clay) plus a control were replicated three times in two randomised complete block trials, one irrigated and one dryland. Before ripping and sowing, all plots were sprayed with glyphosate. Plots were sown with Chloris gayana (20 kg ha-1) plus Medicago sativa (5 kg ha-1) and fertilised with P (24 kg ha-1) and K (50 kg ha-1) manually. Data collected were oven dry biomass production from two harvests (at 4 and 8 months) using 1 m2 samples randomly located within the plots. After the first harvest the plots were grazed, slashed and the irrigation plots burned to remove windrows and excess vegetation. No subsequent irrigation was applied.


No significant differences in dry matter yield were detected in either trial 4 months after establishment though a response was expected due to mineralisation of N in the disturbed plots. However the error due to uneven establishment in this harvest was significant (c.v. 33T) and may have masked the results. The second harvest indicated no significant differences in the dryland trial (c.v. 17%), however in the prior irrigated trial, deep ripping (9.33 t ha-1 DM) and deep ripping plus gypsum (10.21 t ha-1 DM) significantly increased dry matter yield (P = 0.05) over the control (4.79 t ha-1 DM) though there was no difference between the ripping and ripping plus gypsum treatments.

The data indicate that there may be no response to the application of gypsum over and above ripping in the first season. Considering the high rates of application, gypsum is not a viable pasture management practice. The prospect of deep ripping improving pasture production on this sodic duplex soil is also suspect, especially under dryland conditions. Further monitoring of the site will continue, however considering the delayed return on expenditure and the possible discrepancy between pasture and animal production, it is likely that the long term economics of these practices is not viable.

1. Ellington, A. (1987). Fourth Aust. Agron. Conf. Proc., pp. 118-139.

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