Effect of depth and method of primary tillage on fallow soil water and nitrate changes and wheat grain yield

Abstract

An experiment was conducted on an alluvial soil at Biloela Research Station from 1970 to 1975 to determine the effect of two depths (10 to 15 cm and 20 to 30 cm) and two methods (disc and chisel) of primary tillage on changes in soil water and nitrate-nitrogen over the fallow period and on subsequent wheat grain yield. There were no significant (P<0.05) treatment differences in available soil water levels to a depth of 1.4m at the beginning and end of the fallow period in any year. Deep (20 to 30 cm) disc primary tillage resulted in a greater increase in soil nitrate-nitrogen levels in the 0 to 40 cm layer over the fallow period than shallow (10 to 15 cm) disc or chisel primary tillage or deep (20 to 30 cm) chisel primary tillage in three of the four years of the experiment. Significant (P<0.05) increases in grain yield were obtained with deep disc primary tillage in two of the three years in which higher soil nitrate-nitrogen status occurred at planting in this treatment. The occurrence of a yield response to the higher soil nitrate-nitrogen levels in the 0 to 40 cm layer following deep disc primary tillage appeared to depend on seasonal conditions during crop growth. Grain protein content was generally similar for all treatments in any one year.