CONSERVATION TILLAGE PROVIDES BONUS CROPS
B.J. Radford and A.J. Key
Queensland Department of Primary Industries, PO Box 201, Biloela, Qld 4715

We examined the effects of four tillage practices with and without applied fertiliser on seven successive grain crops (4 wheat, 1 sorghum and 2 maize) on an alluvial soil in a semi-arid sub-tropical environment in central Queensland.

MATERIALS AND METHODS

We investigated four fallow management practices (in 4 replications of 72x22 m plots): TT (traditional tillage by disc plough/scarifier/cultivator), SM (stubble mulch tillage by chisel plough/blade plough/rod weeder), RT (reduced tillage) and ZT (zero tillage). Fertilised subplots (18x22 m) received a total of 375 kg N/ha, 60 kg S/ha and 7 sprays of 1% ZnSO₄.7H₂O.

RESULTS

The three conservation tillage treatments (SM, RT and ZT) stored more soil water and produced more grain than TT when fertiliser was applied (Table 1). ZT outyielded TT by 1.13 t/ha/year or 7.9 t/ha during the seven years. This represents 3.7 bonus crops in seven years (based on the mean yield of the TT treatment). SM, RT and ZT also gave higher net profits than TT (Table 1).

Table 1. Effect of four tillage practices with applied fertiliser (N, S and Zn) on mean annual soil water storage, grain yield and gross margins during seven years.

Tillage practice	Available soil water, 0-1.6 m (mm)	Grain yield at 12% moisture content (kg/ha)	Gross margin (A$/ha)
TT SM RT ZT	119 166 189 187	2.16 2.99 3.04 3.29	224 370 357 379
l.s.d., P=0.05	25	0.30	56

DISCUSSION

These results are in stark contrast to the statement of Uren (4) that minimum tillage systems throughout the world have resulted in very little change in yield irrespective of climate, soil type, crop and fertiliser practice. Large, positive yield responses to conservation tillage have also been obtained elsewhere in central Queensland when soil fertility has been adequate (1, 2). Further information on this experiment is available (3).

REFERENCES

1. Asghar, M., Lack, D.W., Cowie, B.A. and Parker, J.C. 1993. Proc. 7th Aust. Agronomy Conf., Adelaide. pp. 300-303.
2. Lawrence, P.A., Radford, B.J., Thomas, G.A., Sinclair, D.P. and Key, A.J. 1994. Soil and Tillage Res. 28, 347-364.
3. Radford, B.J., Key, A.J., Robertson, L.N. and Thomas, G.A. 1995. Aust. J. Exp. Agric. 35, 223-232.
4. Uren, N. 1991. Agric. Sci. 4, 45-48.