Crop Yields at Dahlen

The table below shows the mean yields for each of the 14 years when crops were harvested. In all but one year, N (2005) and P (2008) treatments resulted in significant yield responses. There were interactions between N and P in over half the years, but this tended to be because of no response to N when P was not applied rather
than a synergy of responses at higher rates. The timing of N application resulted in significant effects on yield in 5 of the years, but this effect was weak in the more recent years of the experiment.

N and P interaction does occur – at the higher N rates, Colwell P is less that at the lower N rates – probably because there is less P offtake at the lower/lowest N rates. In terms of yield interaction, for wheat in only one of three years there were significant interactions – the nature of that interaction was that there was little N response when there was no P applied (not unexpected).

Timing of N is a less important aspect than many would suggest – for the non-legumes, there were only 3 of 11 years where splitting was significantly different to up-front – in 1996 for barley (upfront better) and in 2010 with canola ( split better). For all the others there were no significant differences – there were differences in lentils with splitting but that is not that important really – as no N was applied in those years and this is a residual effect

Table Mean site yields (t/ha) and the level of significance of the yield response to N, P, fertilizer timing (T) and
the interaction of N and P.

Year

1996

‘97

‘98

‘99

‘00

‘01

‘03

‘04

‘05

‘07

‘08

‘09

‘10

Crop

Barl

Cpea

Cano

Whea

Barl

Lent

Whea

Barl

Lent

Whea

Barl

Cpea

Cano

Site Mean Yield (t/ha)

3.26

1.62

1.32

1.84

3.05

0.90

3.69

1.00

1.03

2.25

1.10

0.51

2.54

N

***

***

***

***

***

***

***

***

ns

**

***

***

***

P

***

***

***

***

***

***

***

***

***

**

ns

***

***

T

***

ns

***

ns

***

ns

ns

ns

**

ns

ns

ns

*

N*P

***

ns

***

ns

***

***

***

***

ns

ns

***

ns

ns