All experiments except one site at Wongan Hills were responsive to different rates of N, but the effect of DMPP on grain yield was limited, and there were no significant differences in grain yields when fertiliser N was applied as conventional or ENTEC urea in most studies (Fig.
1] as ENTEC ureayielded significantly more thanNappliedasconventional urea (2975 [+ or -] 254 vs 2609 [+ or -] 196 kg grain [ha.
However, at both Merredin sites, both Wongan Hills sites and at the Cunderdin site, there was no effect of ENTEC urea on grain protein concentrations (Table 2).
There were no differences in grain N recovery (kg N in grain per hectare) in any experiment as a result of the use of ENTEC urea (Table 2).
The first aim of the present study was to determine whether the use of DMPP (applied as ENTEC urea) was able to slow the effects of nitrification in a range of soil types and environments and under both glasshouse and field conditions.
In contrast, there was limited evidence of differences in soil (0-10 cm) mineral N concentrations throughout the growing season when N was applied as urea or ENTEC urea in any of the six field experiments (Fig.
2017) and thus may have suppressed the inhibitory effects of the DMPP in the ENTEC fertiliser.
The final hypothesis investigated in the present study proposed that the use of ENTEC urea would alter crop performance (grain yield, grain protein content and grain N recovery per hectare), although it was recognised that this could be greatly influenced by soil type and environment.
The obvious question arising from this is why did grain yield responses to ENTEC urea occur at only these two sites and not at the other four locations or in the glasshouse (Figs 4,7)?
Further studies will be required to determine whether ENTEC urea would be of most benefit on these soil types.
2) Although yield responses to ENTEC urea were only observed on soils containing a heavy clay pan, there were two sites at the Wongan Hills location (within 1 km of each other and on similar soil types) and only one of them responded to ENTEC urea (Fig.
There was no evidence of improved grain N recovery or grain protein content as a result of the use of ENTEC urea compared with urea alone (Table 2).