EFFECT OF ZERO AND ZONAL TILLAGE ON CANE GROWTH AND YIELD ON A HEAVY CRACKING CLAY SOIL IN THE HERBERT VALLEY

AN EXPERIMENT involving permanent 1.8 m beds, different tillage treatments and dual cane rows planted with a DDO planter fitted with twin opposed press wheels was established on heavy cracking clay soil in the Herbert to evaluate the effect of varying amounts of tillage on cane growth and yield. Four main tillage treatments were included: zerotillage, zonal tillage (only tilling the crop growth zone and not the interrows) after the wet season, zonal tillage before the wet season, and zonal tillage both before and after the wet season. These tillage treatments were split between two sugarcane varieties, Q208A and KQ228A. Shoot emergence was highest with zero-tillage and poorest with tillage before and after the wet season. There was a trend for zonal tillage before the wet season to have fewer shoots than zonal tillage after the wet season. The early growth advantage with zero-tillage over the three zonal tilled treatments was associated with lower maximum and higher minimum soil temperatures with zero-tillage during the period of crop establishment. Shoot/stalk number differences were maintained through to harvest at 16 months of age, resulting in zero-tillage having a significantly higher yield than the treatment which was zonal tilled both before and after the wet season. The poor result for double zonal tillage was most likely due to damage caused to soil structure by tillage with a rotary hoe on the heavy clay soil, and the consequent adverse effect this had on plantavailable soil water. There were significant differences between the two varieties in stalk number, stalk weight, cane yield, ccs and sugar yield. Stalk weight and ccs was significantly higher for KQ228A but stalk number, cane yield and sugar yield was significantly higher for Q208A. Although specific data were not collected there was no indication of enhanced stool tipping with zero-tillage, and in fact observations indicated that plots tilled before and after the wet season displayed more stool tipping. It may be that with zero-tillage on a heavy cracking clay soil, natural soil repair from the adverse effects of compaction is enhanced when tillage is withheld.