The effect of timing of annual ryegrass (Lolium rigidum)
emergence on the uptake and utilisation of N by wheat was investigated in a
field trial on a duplex soil at Katanning, Western Australia, and in a
glasshouse study in which 15N-fertiliser was applied.
Three treatments were used to investigate the effect of timing of annual
ryegrass emergence on the uptake and utilisation of N by wheat: simultaneous
sowing of wheat and annual ryegrass, sowing of annual ryegrass 1 week before
wheat, and sowing of the annual ryegrass 1 week after wheat. A control
treatment, consisting of wheat sown alone, was also included. Plant densities
during the field trial were 105 and 140 plants/m2
for wheat and annual ryegrass, respectively, whereas in the glasshouse they
were 105 plants/m2 for wheat and 155
plants/m2 for annual ryegrass. Fertiliser-N was
applied at seeding of wheat at 50 kg N/ha in the field trial and 60 kg
N/ha in the glasshouse.
The introduction of annual ryegrass into the wheat system reduced the
production of biomass and the grain yield of wheat. The earlier the annual
ryegrass was introduced into the system, the greater the reduction in the
biomass and grain yield of wheat. Poor tillering and slow rates of growth were
accountable for the reduction in biomass, whilst the reduction in wheat grain
yield was caused by the reductions in ear number, kernels per ear, and kernel
size. Grain N content and hence grain protein was also reduced by the
introduction of annual ryegrass into the wheat system. Irrespective of the
timing of introduction of annual ryegrass, the low N uptake of wheat resulted
from a reduction in the uptake of both soil and fertiliser-N. This indicates
that annual ryegrass competed with wheat not only for the fertiliser-N that
was applied at seeding of wheat, but also for mineralised soil N. The
competition for N reduced the total recoveries of fertiliser-N in the wheat
plant. Total recoveries of fertiliser-N in the wheat plant suggest that
59% of the fertiliser-N was not taken up by wheat when annual ryegrass
was sown 1 week earlier than wheat or at the same time as wheat, whereas only
32% was not taken up by the wheat when annual ryegrass was sown 1 week
later than wheat. More competitive wheat genotypes would be those with better
efficiency in the uptake of N and its utilisation in maintaining yield and
grain protein under infestations of annual ryegrass.
GW10, a Member of P450 Subfamily Regulates Grain Size and Grain Number in Rice