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)

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

 
From the photos above we would expect that the 150 K will again out-yield the Nil K and add to the extra grain production gained.

 

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.

 
 
Luigi Moreschi
By Luigi Moreschi
- Northern Agronomist
Luigi is from a family farm at Lake King and has always had a passion for agriculture. 

He is a highly respected agronomist for CSBP and has been based at Dongara for nearly 20 years.

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