Effects of Direct Drilling on the Phosphorus Uptake and Fertilizer Requirements of Wheat

Abstract

The effect of direct drilling on the phosphorus (P) relations of ~vheatw as examined in seven field experiments over three years. Compared with conventional cultivation of the soil, direct drilling concentrated available phosphorus nearer the soil surface and resulted in higher strength and lower root length in surface soil (0-10 cm). Tissue-P concentration and dry weight of young plants (< 10 weeks) were consistently lower after direct drilling. It appeared therefore that direct drilling limited the uptake of soil phosphorus. An unknown factor also reduced plant dry weight per unit of P taken up in some experiments, whilst high rates of P fertilizer generally failed to give equal P concentration or dry weight in early growth. It is suggested that the young plants were unable to exploit fully the banded fertilizer because of insufficient adaptation of roots to the concentrated source of P and that this effect is a greater disadvantage for a direct-drilled crop. Direct drilling gave lower grain yields in four experiments when no fertilizer was applied, but where rates of P fertilizer were high, the two tillage treatments produced equal'pields. In these four experiments direct-drilled crops needed more fertilizer to attain 90% of the maximum yield. Crops in cultivated soil had the higher dry weight at anthesis and therefore the higher potential yield at equal rates of P fertilizer (in two years), but they failed to realize their potential at high rates of fertilizer because their greater vegetative growth led to increased water stress after flowering.