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M.G. O'Connell1, G.J. O'Leary2 and D.J. Connor3

Joint Centre for Crop Improvement, 1Agriculture Victoria, MRS, Walpeup, Vic 3507, 2Agriculture Victoria, VIDA, PB 260, Horsham, Vic 3400,
Department Agriculture & Resource Management, University of Melbourne, Parkville, Vic 3052

Recent research in north-western Victoria using long-term cropping experiments questions the role of winter fallowing as a water conservation practice (1). The contribution of fallow systems to improved crop yield and stabilisation of yield fluctuations under dryland conditions is being investigated. Soil water balance of fallow and non-fallow cropping systems, involving detailed experimental field monitoring and simulation modelling will assist agronomists to offer improved management options for greater production, profitability and minimise risks to environmental degradation (e.g. dryland salinity (2), soil erosion).


The water use, of fallow and non-fallow cropping systems and the efficiency of long fallows in the Victorian Mallee is being investigated in a dryland cropping experiment at Walpeup (35o 07' S, 141o 59' E; elevation 85 m; annual rainfall 343 mm). The experiment compares fallow (field peas/fallow/wheat) and non-fallow (field peas/Indian mustard/wheat) crop rotations in a randomised block design. Each plot contains a 1.4 m deep drainage lysimeter having a surface area of 0.43 m2. Soil evaporation coefficients were measured for the sandy loam soil type (Gc 2.22) both in the field and in a glasshouse experiment.


Measurements of soil evaporation made during the vegetative growth stage of the 1994 season showed significant difference between fallowed soil and some crops, but, bare soil evaporation was not consistently different between crops. Crop growth and soil cover were poor due to drought and all soil evaporation measurements were less than 0.8 mm/day (i.e., stage 2 drying). Drying curves will be established from a glasshouse and field experiment.

Drainage below 1.5 m, measured using a neutron probe, was 17 mm under fallow and 14 mm under non-fallow rotations. However, only a number of small recharge events were recorded with the drainage lysimeter. The magnitude of each event has been <1 mm to date. We suspect the discrepancy between lysimeter data and soil water content data lie in the errors of estimates with the neutron probe method.

To establish the significance of specific agronomic practices simulation modelling is being employed, both on a site specific and regional basis. Computer models are being used to validate water balance and crop data in recharge calculations and evaluate recharge options.


1. Incerti, M., Sale, P.W.G. and O'Leary, G.J. 1993. Aust. J. Exp. Agric. 33, 885-894.

2. O'Connell, M.G., O'Leary, G.J. and Incerti, M. 1995. Agric. Water Management (in press).

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