APPLICATION OF VETIVER GRASS IN SOIL EROSION AND SEDIMENT CONTROL ON THE DARLING DOWNS

(C. KNOWLES-JACKSON)

Early Experience

Flooding is a regular occurrence on the floodplains of the Darling Downs. Under the natural conditions of tree and grass cover, flood waters were spread out over the floodplains and caused little damage. When these areas opened up for cropping, most of the natural vegetation was removed, roads and fences were constructed and crops were grown in square or rectangular paddocks. These changes resulted in the diversion and concentration of floodwater into fast moving flows that caused crop damage and Soil erosion, and seriously affected the productivity of this valuable area.

To reduce the damage caused by floods, management practices have been developed to keep the water spread out and slow moving as occurred naturally.

Strip Cropping

Hector Tod a landholder in the Linthorpe creek area of the Darling Downs pioneered the use of strip cropping in Australia.

Strip Cropping is a soil conservation technique employed by dryland, floodplain farmers of the Darling Downs and north - western slopes of New South Wales. The floodplain refers to low gradient land (maximum slope 1%) which is subject to periodic, major overland flows. Strip cropping involves farming the land in strips of equal width, where the strips are positioned perpendicular to the water flow.

The management of the strips is governed by the farmer's crop rotation policy. A three-strip rotation implies that three years are required for the complete cycle. The rotation would be repeated throughout the length of the strip cropping sequence. Therefore if a farm was partitioned into sixty (60) strips, the three-strip combination would be repeated twenty (20) times.

The success of strip cropping significantly depends upon the crop rotation system (Marshall. 1988). The crop rotation provides agronomic advantages such as reduction in disease and insect problems, better use of soil moisture and improved soil nitrogen through the inclusion of legumes. In terms of soil erosion, the sequence of crops and crop stubbles is essential for strip cropping to be an effective soil conservation technique.

The principle aim of strip cropping is to protect the fallow land which must occur in a dry land crop rotation. The strip cropping arrangement forces the flood waters laterally thereby reducing the depth and velocity of flow (Smith et al, 1991). The flow is further resisted by the crops and fallow conditions, which act to prevent erosive velocities occurring in the bare or unprotected strips. Each strip would retard the flow in a different manner: the overall effect being a reduced velocity of flow over the unprotected strips. (Dryland farmers often refer to strip cropping as a "free irrigation" -prior to strip cropping flood flows were concentrated and tended to rapidly runoff the land, whereas flows throughout strip cropping are spread and slower, thus allowing more infiltration opportunity time).

Shortcoming's of Strip cropping

One of the main shortcomings of strip cropping is that during drought crops cannot be grown to protect the floodplains from overland flooding. During prolonged periods of drought as experienced in extensive areas of Eastern Australia in the 1990's large areas of the floodplains had no residual cover from previous crops, or any growing crops, hence extensive areas were exposed to potential serious erosion.

Use of Vetiver Grass on the Floodplains

The drought and the increasing occurrence of dryland cotton in the farming system has exposed the floodplains to increased erosion.

Vetiver Grass is now being grown on the floodplains of the Darling Downs in an effort to provide protection in erosion sensitive areas.

Vetiver grass is being grown in associations with existing strip cropping layouts so that the beneficial characteristics of the two systems can compliment each other.

Vetiver grass with its deep rooting and fast growing properties will quickly form an effective vegetative barrier that will impede the rate of flow of the floodwaters. Unlike the annual crops, Vetiver with its deep rooting characteristics will be able to withstand the effects of drought more effectively.

The use of Vetiver grass in the concentrated flow areas is also proving to be a valuable tool in aiding the siltation and stabilisation of those areas. Mechanical structures have not proved to be successful on the black soil plains of the Darling Downs. Where mechanical structures have been built on these heavy black clay soils they have generally failed. These structures have been costly to build, to maintain and the resultant damage has been extensive when they have failed. Vetiver grass is proving to be cheep and effective.

It is hoped that Vetiver grass will prove to be one more tool available in the fight against soil erosion.

STRIP CROPPING WITH VETIVER GRASS

A LANDHOLDER PERSPECTIVE

(Mark HenseI, Prairie View, Jondaryan)

INTRODUCTION

� aim of a land holder - to leave the land in better condition than when we started
� protection of soil essential
� management of water prudent
� slow water - reduces soil movement
� spread the water - greater area for moisture infiltration
� 15-20% increase in yield can double profit - 50% of profit from overland flow 'irrigation

POINTS

1. Farm history
a) purchased in '30's
b) originally grassland, dairy farm
c) cultivation commenced with growing oats and wheat in large square paddocks
d) farm suffered sheet and gully erosion in major floods
e) flood water following heavy rain in uplands once took a week to reach Prairie View
- now flood peak arrives in about 8 hours

2. Need for Vetiver grass
a) need to control erosion at all times, even in drought conditions when no
crops can be grown. more run off in drought time due to depleated ground cover
b) good strong hedge will slow and spread water and give better water infiltration
c) small benefit from wind protection

3. Management
a) water newly planted grass
b) burn, slash after risk of severe frost has past, excess height unnecessary.
if left to grow unchecked the centre of row will die due to lack of sun light
c) apply fertiliser
d) replant gaps in row

4. Disadvantages
a) loss of yield up to 2m from hedge in adjacent crops
b) harbor for mice
c) sensitivity to roundup - minimum tillage - spraying of crops and fallow
d) wash outs in weak spots
e) weeds in potting mix
f) labor intensive to establish

5. Advantages of Monto Vetiver
a) Low risk of becoming a weed - no viable seed
- no stolons
- no rhysomec
- can be killed with glyphosate
b) Drought tolerant when established
c) Regenerates after frost (-1 2*c)
d) Regenerates after fire

6. FUTURE MANAGEMENT
a) need to develop direct planter to save on labour, speed up planting operation
b) widen strips
c) keeping hedges clashed may reduce erosion problems where water breaks through
d) keep hedges to a height of less than SOOmm may reduce yield loss caused by shading
e) need to produce something from the hedge - essential oil - sale of planting material

CONCLUSION
There is no universal solution to the management of flood water and soil erosion. Vetiver grass is a useful management tool.