In 2017 CSBP decided to set up a trial site at Strawberry, halfway between Dongara and Mingenew on Christmas tree sand looking at potassium fertiliser strategies for a lupin-wheat rotation.
One of the questions often posed by growers who have deeper sands that are very low for soil K to depth, what would happen if I targeted this area with a one off dump of potassium fertiliser?
To try and answer this question with some numbers, one of the treatments included in the trial was a one off application of 300 kg/ha of Muriate of Potash (150 kg/ha K) in year 1, followed by no further applications of K over the life of the trial (5 years). In 2020 we are now at year 4 of the trial.
Starting Soil Test (March 2017)
|
Depth |
pH |
Colwell P |
PBI |
Colwell K |
|
0-10 cm |
6.3 |
12 |
8 |
10 |
|
10-20 cm |
6.5 |
10 |
8 |
6 |
|
20-30 cm |
5.3 |
9 |
7 |
4 |
|
30-30 cm |
4.8 |
13 |
7 |
3 |
|
40-50 cm |
4.7 |
14 |
8 |
3 |
Good soil pH, good soil P to depth, but horrible soil K levels, despite the grower using some K in his previous crops of wheat and lupins.
Rainfall
|
Year |
Jan |
Feb |
Mar |
Apr |
May |
Jun |
Jul |
Aug |
Sep |
Oct |
Nov |
Dec |
|
2017 |
48 |
38 |
25 |
0 |
18 |
9 |
49 |
73 |
59 |
6 |
4 |
14 |
|
2018 |
34 |
0 |
3 |
0 |
41 |
48 |
106 |
89 |
11 |
17 |
2 |
5 |
|
2019 |
0 |
0 |
0 |
4 |
6 |
168 |
52 |
50 |
5 |
13 |
1 |
1 |
|
2020 |
0 |
65 |
3 |
5 |
30 |
49 |
46 |
104 |
16 |
NA |
NA |
NA |
All four years were below average rainfall. The 300 kg/ha MOP was not applied until April 2017, thereby missing the summer rain of that year. In 2019 between 7 June and 7 July the site received over 200mm of rain.
Soil Test K sampled April 2018
Change in soil test K levels measured the year after application of the 300 kg/ha MOP. (Average of 3 reps)
|
K Applied in 2017 |
Depth |
Colwell K |
|
Nil K |
0-10 cm |
< 15 |
|
10-20 cm |
< 15 |
|
|
20-30 cm |
< 15 |
|
|
300 kg/ha MOP |
0-10 cm |
47 |
|
10-20 cm |
24 |
|
|
20-30 cm |
18 |
Photos
Taken 6 October 2020 comparing the Nil K treatment in year 4 (LHS), and the 300 kg/ha MOP (4th year after application) in year 4 (RHS)
.png?sfvrsn=aa1e6b3e_0 "Potassium on lupins Nil v 150 K (2)")
Plant Test
On August 10 all plots were sampled for analysis of tissue K levels. Crop was at early podding.
Tissue K levels for theses 2 treatments were:
Nil – 0.58%
300 kg/ha MOP – 1.02%
The MOP applied in year 1 is still having a noticeable affect on the crop tissue K levels in year 4.
Yield Response
Cumulative yield response (2017-2019) to K fertiliser applied in year 1 (t/ha)
|
Treatment |
YEAR |
Total Grain Produced |
Extra Grain produced |
||
|
2017 (wheat) |
2018 (lupins) |
2019 (wheat) |
|||
|
Nil K |
0.62 |
1.12 |
0.56 |
2.30 |
- |
|
150 K in 2017 |
1.43 |
2.45 |
0.99 |
4.87 |
2.57 |
Comments
This trial shows that the substantial rate of K applied in 2017 is still having an effect on the crop in 2020. The rainfall over the past 4 years has been below average which would limit the potential for leaching, but if this is to become the new weather norm, then maybe larger applications of K in specific areas of paddocks to break the back of the deficiency maybe feasible.
This site in 2019 did have a major leaching event with over 8 inches of rain falling in a month in the early part of the season, but the lupins are still responding to the K fertiliser in 2020.
