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Shelterbelts and wheat production in North East Victoria

M. C. Crawford1, P. A. Noble2 and P. J. Haines1

1Agriculture Victoria, Department of Natural Resources and Environment, Rutherglen, Vic, 3685
2Catchment and Agricultural Services, Department of Natural Resources and Environment, Wodonga, Vic, 3690

Abstract

The effect of shelterbelts on crop production was studied at Dookie in north east Victoria in 1995 and 1996. Two shelterbelts, consisting of mixed native trees and shrubs, were located at right angles to each other. One was aligned north-south and the other east-west. Wheat was sown to the south east of the apex of the two shelterbelts giving protection from the north and from the west. Winds were predominantly from the west and north west during winter and more south westerly during spring. Crop growth and grain yields were measured at a range of distances from each shelterbelt. No effect of shelterbelt on grain yield was detected in either year. Possible reasons for this include variability in the density and continuity of the shelterbelt, transient waterlogging, soil variability, absence of severe wind events, lack of moisture stress, and the absence of strong drying northerly winds during grain formation.

Key words: Shelterbelts, windbreaks, wheat

In recent years, the role of trees on farms has been widely promoted. One of the reasons often put forward for the establishment of trees on cropping farms is their supposed beneficial effect on crop production through providing shelter from wind (1). However, in the Australian scientific literature, very little has been published to either support or dispute that claim (2). In 1994, the National Windbreak Program commenced scientific investigation of the effects of shelterbelts on crop and pasture production. Part of that program was conducted on a site at Dookie in north east Victoria. A brief summary of the results from 1995 and 1996 is presented in this paper.

Materials and methods

The trial was located at Dookie (36°23' S, 145°42' E, 560 mm average annual rainfall) in north east Victoria. Two shelterbelts consisting of mixed native trees and shrubs were located at right angles to each other along the west and north sides of a 22 ha paddock. One shelterbelt was aligned north-south (average height 16 m, length 240 m) and the other east-west (average height 9 m, length 400 m). The paddock was sown to wheat (cv. Katunga) in both 1995 and 1996.

Agronomic measurements were made at tree height (H) intervals along two transects: one extending south from the east-west shelterbelt and the other extending west from the north-south shelterbelt. The transects were located such that they were beyond the influence of the other shelterbelt. For presentation purposes, the distances from the shelterbelts were divided into four zones: 0-3H (competition), 3-10H (quiet), 10-16H (turbulent) and >16H (open), and the means of all observations for that zone calculated. Meteorological conditions including wind speed and direction were monitored continuously using an automatic weather station.

Results

The prevailing winds in 1995 and 1996 were mostly from the west, south west and south. In 1995, wind was predominantly from the west in May, June and July, the north in August and September and the south west in October, November and December. In 1996, it was predominantly from the south west in May, the west in September and October and the south west in November and December. No data was available for July and August, 1996. The north-south shelterbelt provided protection from wind 39 % of the time in 1995 and 43 % of the time in 1996. The east-west shelterbelt provided protection from wind 28 % of the time in 1995 and 17 % of the time in 1996. At no stage in 1995 or 1996 were wind gusts greater than 40 km/h recorded.

In both years, grain yields in the protected zone (3-10H) behind the north-south shelterbelt were similar to those in the open zone (>16H) (Table 1). The east-west shelterbelt had no effect on grain yields in 1995, but in 1996, there was a decrease in yield in the protected zone behind this shelterbelt. Lower yields in 1996 were partly due to the presence of yellow leaf spot disease which was evenly spread throughout the paddock.

Table 1: Grain yields at varying distances from shelterbelt for 1995 and 1996.

 

N-S Shelterbelt
(Protection from west winds)

E-W Shelterbelt
(Protection from north winds)

 

1995

1996

1995

1996

Distance from belt
(tree heights)

na

Mean
(t/ha)

S.E.M.b

n

Mean
(t/ha)

S.E.M.

n

Mean
(t/ha)

S.E.M.

n

Mean
(t/ha)

S.E.M.

0-3

3

4.41

0.23

6

2.23

0.16

3

4.13

0.59

6

2.19

0.27

3-10

7

4.12

0.23

14

2.48

0.19

7

4.64

0.22

12

1.62

0.15

10-16

3

4.65

0.34

8

2.62

0.14

3

4.50

0.23

8

2.13

0.26

>16

6

4.60

0.12

4

2.46

0.39

6

4.60

0.12

4

2.46

0.39

an: number of samples taken within each zone. bS.E.M.: standard error of the mean.

Discussion and conclusions

This experiment did not show any significant benefit of shelterbelts on grain yield of wheat. The effects of a living shelterbelt on crop growth are complex, with slight variations in vegetative growth being observed in early parts of the growing season (data not shown), but these differences had disappeared by harvest. The most likely reasons for this include variability in the density and continuity of the shelterbelt, transient waterlogging of the paddock during periods of 1995 and 1996, and soil variability, especially with respect to drainage. A lack of extreme wind events, absence of severe moisture stress due to adequate rainfall in both years, and the absence of drying northerly winds during grain formation may also have been partly responsible for the failure to observe any response in the crop. Further research using uniform artificial shelterbelts is being conducted to reduce confounding environmental variability that may be masking any crop response.

Acknowledgments

This project is funded by the Rural Industries Research and Development Corporation as part of the National Windbreak Program.

References

1. Grace, J. 1988. Agric., Ecosyst. and Environ. 22/23, 71-88.

2. Nuberg, I.K. 1998. Agrofor. Syst. (in press).

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