Winter cereal production on the Darling Downs - an 11 year study of fallowing practices

A long term field experiment to compare 4 methods of fallowing for annual winter cereal production on a Darling Downs Vertisol was started in 1968 on the Hermitage Research Station near Warwick, Queensland. Fallowing systems being investigated are (i) tined tillage with stubble burnt (TcSb); (ii) tined tillage with stubble retained (TcSr); (iii) zero tillage with stubble burnt (TzSb); and (iv) zero tillage with stubble retained (TzSr); each at 3 rates of nitrogen (N) fertiliser application. This paper reports the effect of these treatments on fallow water accumulation, fallow N mineralisation, crop growth and yield, for the period 1968-79. Average values for available soil water in the 0-150 cm zone at sowing were 195 mm for TcSb, 212 mm for TcSr, 225 mm for TzSb and 252 mm for TzSr, and for storage efficiency (percentage of fallow rainfall stored) were 18, 20, 25 and 27% respectively. The relatively greater water storage efficiency of Tz treatments occurred mainly in fallow seasons when initial storage was low. Nitrogen mineralisation during fallows averaged 61 kg/ha and was depressed in some years by Sr. Carryover of available N in excess of crop requirements was shown at the higher rate of N fertilisation. Grain yields averaged over 12 crops were similar for the 4 fallowing systems. The lack of grain yield response to the improved water storage under TzSr was probably caused by yellow spot disease (Pyrenophora tritici-repentis) and root lesion nematode (Pratylenchus thornei), which were most prevalent under this treatment in wheat crops. Poor early growth of barley under TzSr limited its water use and grain yield potential, however, the cause of the poor early growth of barley is not known. A reduction in grain yield of 232 kg/ha associated with Sr was overcome with the addition of 23 kg N/ha as urea.