On farm management of Vetiver grass hedgerows.

Dick Grimshaw to The Vetiver Network International (TVNI) group

 
 I want to start a discussion on vetiver hedge management and would welcome comments on the following note that I have prepared.
"With the increasing potential of multipurpose uses of vetiver grass hedgerow (VGH) by farmers it is important to give some thought as to how the hedges are managed - basically planting design, maintenance and harvesting. The primary purpose of VGH is for soil and water conservation, secondary uses include pest control, forage, thatch, handicrafts, waste water clean up, biomass and more.
The basic (primary) design. Hedges should be aligned on an “average” contour.
Optimum within line planting distance to obtain optimum hedge density in two years should be 15 cm.
The lateral distance between VGH will vary with slope, the optimum distance for erosion control is at 2 meter Vertical Interval. Some examples: 1% slope 104 meters apart; 5% slope 23 meters; 10% 11 meters; 25% 4 meters. Often farmers on steeper slopes will start with hedgerows further apart, and then later as experience builds up they add more hedgerows between existing ones if needed. Whereas on flatter slopes the farmer may have more hedges than actually needed as in the case when used for marker lines (ridges)
On very small fields/farms/gardens planting a vetiver hedge all around the boundary of the area will provide adequate protection as well as demarcating the field boundary.
VGH management. Hedgerows can grow to maximum height (often 2 meters), but are often cut for various purposes during the year. It is recommended that the minimum cutting height is 20 - 30 cm. A 20 - 30 cm high hedge will be dense, stiff and will withstand rainfall runoff. Attached image can be considered a “perfect” hedge
When to Cut?
Most farmers cut the hedges to harvest the leaves for various purposes. Depending on the rate of leaf growth vetiver can be cut and harvested at frequencies of three weeks or more. If the leaf is for forage frequent cutting assures optimum leaf nutrient values. For handicrafts long green leaf is best. Mature leaves work well for other uses such as thatch, mulch, and less nutritious forage. If cutting only once a year it is best to cut just prior to the rainy season.
Managing Hedges as habitat for crop insect predators and for “dead end trap” plant purposes.
With the new knowledge of using vetiver as a habitat that shelters huge numbers of beneficials that parasitize or predate on crop insects such as stem borer eggs and larva, and as a “dead end” trap plant to control stem borer in maize, sorghum and rice, additional considerations need to be taken into account including:
(1) From the time of crop seedling emergence, and then for at least 8 weeks, vetiver should be in good flush - in other words fast and lush leaf growth. This period coincides with the rainy season or in some cases when crops may be irrigated
(2) The maximum spacing for hedgerows should be 60 meters (coincides with spacing for a 2% slope) because a stem borer moth will fly 30 meters to look for its preferred vetiver habitat. These 60 meter apart hedgerows (key rows) should not be cut in total. Hedgerows in between could be managed differently, but if managed in the same way as the key hedgerows will provide improved optimum insect attractant efficiency and increased insect habitat.
(3) In China it has been found that if VGH are not needed for soil conservation purposes a vetiver plant every 5 meters within a line of vetiver is all that is required to attract the stem borer moth, so it would be possible to cut the vetiver within the 60 meter key hedgerows ending up with a hedgerow looking like a castle crenelated battlement! The same would be true for maize and sorghum protection.
(4) There are many other very useful insects residing in the vetiver hedgerows. The vetiver provides benefits for beneficial insects in 2 ways: structure (cover to hide in, and protection against wind etc.) and food (leaf exudates and dew condensation early in the morning). We need these insects during the crop season -- out of season, cutting no lower than 30 cm, should still provide the necessary habitat for insects. Since generally farmers do not cut all their hedgerows at one time, insects can move from cut to uncut hedges and thus maintain their population."