THE EFFECT OF ROTATIONAL BREAKS FROM CONTINUOUS SUGARCANE ON SOIL PHYSICAL PROPERTIES

This paper reports on the effect of various breaks from continuous sugarcane on soil physical properties as part of the sugar yield decline joint venture. Field trials were conducted at Tully, Bundaberg, and in the Burdekin valley to examine the impact of various types of breaks from continual sugarcane on soil physical properties. The breaks consisted of a pasture, a break crop and a bare fallow, and were designed to generate differences in soil conditions before planting back to sugarcane. Soil physical properties were assessed during the breaks as well as at the end of the break period, to quantify both the rate and extent of change in soil properties. Soil bulk density decreased with the frequency of soil disturbance, the amount of root activity and increased in the area trafficked by tractors, harvesters and haulouts. However, soil bulk density is not necessarily a good indicator of soil hydraulic properties, with pastures, although having high bulk density also, containing large numbers of macro pores resulting high hydraulic conductivity. Compacted inter-rows in continuous cane, and to a lesser extent alternate crops, resulted in very low hydraulic conductivity. Crop and bare fallow treatments were less able to infiltrate incident rainfall, unless surface cover was present, due to lower aggregate stabilities and a greater tendency to develop surface crusts. Lowest infiltration capacity was generally in the continuous cane treatments - due primarily to the high proportion of the ground surface area that was compacted. Breaks also resulted in small but significant increases in soil water holding capacity, relative to continuous cane. Data presented in this study show that sugarcane culture can provide relatively good soil physical conditions (at least in the crop rows), provided wheel traffic and resultant compaction can be avoided in future farming systems.