Microwave technology for weed management

Author: Graham Brodie | Date: 01 Mar 2016

Take home message

Microwave heating, using a suitable device to project the microwave energy onto plants and the soil, can:

  1. Kill weeds and their seeds in the field, without limitations of wind or moisture;
  2. Kill dormant seeds in the soil;
  3. Significantly reduce bacterial numbers in the top layer of the soil; however these populations recover to become significantly higher than their initial values within a month of treatment;
  4. Not significantly affect fungi or protozoa in the soil; and
  5. Significantly increase grain yields in a number of crops, including canola and wheat.

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Herbicide resistance is becoming an important problem in Australia no-till farming systems. Many weed species have developed multiple resistance to different herbicide groups. Several strategies have been suggested to address this issue, including tillage, flaming, and steam treatment. Many of these strategies are not compatible with no-till strategies.

A sustained research programme has demonstrated that microwave heating, using a suitable device to project the microwave energy onto plants and the soil, can kill weed plants and their seeds. Microwave treatment is not affected by incumbent weather conditions such as wind or rain.

The following species have been tested with good success: Ryegrasses – annual and perennial; barnyard grass; barley grass; bellyache bush; brome grass; clover; feathertop Rhodes grass; fleabane; hemlock; mimosa pigra; parthinium; rubber vine; wild oats; and wild radish. The microwave energy density required to kill plants varies according to the species.

Microwave treatment significantly reduces bacterial numbers in the top layer of the soil; however their numbers rebound to a significantly higher population after one month (Table 1). Microwave treatment has no measurable effect on fungi or protozoa in the soil.

Microwave soil treatment also significantly increases the yield and maturation rate of subsequent crops grown in the treated soil (Table 2).

Table 1. Effect of microwave treatment and soil depth on total viable bacteria

Soil depth (cm)

Time from
microwave
treatment (days)

Estimated microwave treatment
(J cm-2)

0

150

300

600

0

1

6.20d

5.57d

4.73d

1.78d

31

18.90c

38.48a

38.25a

19.67c

5

1

3.78d

4.71d

4.23d

1.18d

31

18.73c

24.28bc

29.95b

28.22b

10

1

4.06d

2.93d

3.87d

1.74d

31

16.93c

26.13bc

28.90b

18.00c

LSD (P = 0.05)

7.30

Note: entries with different superscripts are significantly different from one another

Table 2. Response of subsequent crops to growing in microwave treated soil

Microwave treatment
(J cm-2)

0

Hand weeded

168

384

576

LSD
(P = 0.05)

Change from control

Canola pod yield
(g pot-1)

0.27a

0.56a

0.36a

1.25b

1.95c

0.55

550 %

Days to flowering -
canola

71.4a

67.6ab

70.2a

63.2b

61b

7.1

14.6%

Wheat grain yield
(g pot-1)

0.66a

0.67a

0.68a

0.75a

1.25b

0.30

90 %

Rice grain yield
(g pot-1)

40.00a

41.3a

43.25a

59.00ab

64.00b

18.90

60 %

Tomato dry shoot yield
(g pot-1)

4.13a

4.25a

6.05a

14.44b

14.46b

3.10

250 %

Note: entries with different superscripts are significantly different from one another

In conclusion, microwave treatment kills weeds and their seeds in the top layer of soil. Microwave treatment reduces bacterial populations in the top layers of soil, but has no effect of fungi or protozoa. Bacterial numbers recover within one month of treatment. Microwave soil treatment also enhances crop growth and yield.

Acknowledgements

The research undertaken as part of this project is made possible by the significant contributions of growers through both trial cooperation and the support of the GRDC, the author would like to thank them for their continued support.

Contact details

Graham Brodie
The University of Melbourne
Dookie Campus, Nalinga Rd., Dookie, Victoria, 3647
Ph: 03 5833 9273
Fx: 03 5833 9201
Email: grahamb@unimelb.edu.au