Developing Sustainable Crop Management Systems for Improving Production of Culinary Herbs in the Virgin Islands

Developing Sustainable Crop Management Systems for Improving Production of Culinary Herbs in the Virgin Islands

Summary

In the Virgin Islands, herbs are common ingredients in the local cuisine, satisfying the palates of both the visitors and residents who used them everyday. Small-scale growers in St. Croix and St. Thomas rely on sales of herbs as one major source of income. However, locally grown herbs are available only in farmers’ market and roadside stands and do not constitute a significant Virgin Islands export despite the economic importance and potential for significant income.

There is little research information on sustainable crop management practices to improve production levels, processing and marketing of herbs in the Virgin Islands. Besides, there are few extension recommendations on efficient and sustainable cropping practices for growing herbs.

Objectives
1) Develop sustainable soil management practices for culinary herb production using crop rotation with green manures, application of composts, animal manures and other organic fertilizers.
2) Evaluate sustainable weed management methods for culinary herbs using organic mulches, cover crops and biodegradable synthetic mulches.
3) Develop environmentally sound disease and pest management practices for herbs through cultural methods such as intercropping and crop rotation.
4) Increase fertilizer and water use efficiency in herb production by using microirrigation, thereby reducing fertilizer inputs and conserving water, a scarce resource in the Virgin Islands.

Approach
Over a four-year period, the project has accomplished all objectives except objective 3. Results of field experiments conducted over two cropping seasons to evaluate production of culinary herbs planted in rotation with legume green manure crops indicated that although yields were not significantly different, herbs grown in rotation with sunnhemp and hyacinth bean tended to produce higher yields than those grown without green manures. Sunnhemp and hyacinth bean produced high biomass and nutrient yield and contributed significant amount of nitrogen, phosphorus and potassium in the soil.

The benefits of organic and synthetic mulches in terms of weed control, irrigation water use and economic returns were evaluated for sweet basil, chive, cilantro, parsley and thyme over four cropping seasons both on farmer collaborators’ farm and on experiment station. Mulching materials included white on black polyethylene (plastic), black fabric weed barrier, silver plastic film, grass straw, wood chip and shredded paper. Parsley and chive grown with grass straw mulch produced significantly higher fresh yield compared to those grown under black fabric, white plastic and the control.

Weed population was significantly lower in all mulch treatments compared to bare plot. The silver plastic film was inferior to other mulching materials in that it deteriorated and lost its silver coating rendering it less effective.

Trials in farmers field showed that all mulches significantly reduced the number and biomass of weeds in basil. Basil grown with grass straw mulch produced taller plants and higher total fresh yield than all other mulches except the black fabric.

Organic mulches were also evaluated on-station for their effect on chive and thyme. Mulches included grass straw, wood chips and shredded newspaper. These treatments were compared against synthetic (white on black) plastic mulch and the control (bare). Results indicated that chives grown with grass straw and shredded paper produced higher yield and economic returns compared with chive grown using plastic mulch. Economic return from chive grown with shredded paper and grass straw mulch was on the average 5 to 12% higher than plastic mulch.

Fresh yield of thyme was highest in plots with grass straw followed by plastic mulch. All mulch treatments produced higher fresh yield than the control (bare). Weed population and biomass were highest in bare plots followed by grass straw mulch. Plastic mulch was very effective in controlling weeds, whereas, weed population and biomass in plots with wood chips and shredded paper were comparable with plastic mulch. Except for grass straw all mulch treatments resulted in reduced irrigation water use. This study indicated that organic mulch such as grass straw is also suitable for sustainable thyme production.

On-station and on-farm trials on the effect of cow manure application on yield of chive showed that application of cow manure rates of 0, 10, 20 and 40 tons/ha did not result in significant yield increase for chive, however, plant height increased with increasing manure rates. Similarly, application of turkey litter at nitrogen rates equivalent to 0, 50, 100 and 150 kg/ha did not significantly increase yield of cilantro, sweet marjoram and thyme. Small yield increases were observed with increasing rates of application. Under relatively high soil fertility levels typical of experiment station soils, application of organic manures did not result in significant yield response in culinary herbs.

The response of thyme to levels of poultry (chicken) manure was evaluated in on-farm trial in St. Thomas. Thyme was grown and applied with chicken manure at levels equivalent to 0, 5 and 10 tons/ha. Results indicated that thyme responded favorably to application of chicken manure. Fresh plant yield, total plant dry weight, leaf and stem dry weight increased with increasing levels of chicken manure. Highest thyme yield was obtained when chicken manure was applied at a rate of 10 tons/ha, while the lowest yield was obtained from plots without chicken manure. This indicates that yield of thyme can be improved by application of organic fertilizer such as chicken manure, a locally available farm resource.