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

Final Report for LS96-075

Project Type: Research and Education
Funds awarded in 1996: $143,529.00
Projected End Date: 12/31/2000
Matching Non-Federal Funds: $62,420.00
Region: Southern
State: U.S. Virgin Islands
Principal Investigator:
Manuel C. Palada
University of the Virgin Islands
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Project Information

Abstract:

Developing Sustainable Crop Management Systems for Improving Production of Culinary Herbs in the Virgin Islands. Culinary herbs grown in rotation with tropical legume green manure crops indicated that although there were no significant differences in fresh and dry matter yield, herbs grown in rotation with sunnhemp and hyacinth bean tended to produce higher yields than those grown with cowpea or fallow (no green manure) suggesting that without chemical fertilizers, legume green manure crops can sustain economic yield levels of culinary herbs in a crop rotation system. Organic mulches such as grass straw, wood chips and shredded paper were excellent alternative to synthetic (plastic) mulch. Additionally, organic mulch suppressed weeds, reduced irrigation water use, decreased soil surface erosion, and improved economic returns. Yield of thyme was improved by application of chicken manure, but application of either cow manure or turkey litter did not influence yield of chives, cilantro, sweet marjoram or thyme.

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.

The objectives of this project were to: (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 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; and (4) increase fertilizer and water use efficiency by using microirrigation, thereby reducing fertilizer inputs and conserving water, a scarce resource in the Virgin Islands.

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, chives, 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 chives 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 chives 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 chives grown using plastic mulch. Economic return from chives 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 chives, 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 or 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.

Project 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.

Introduction:

Culinary herbs are aromatic plants grown and marketed fresh or dry, or dried for their extractable oils (Simon, 1990). Significant quantities of dried culinary herbs are imported annually into the U.S. Estimates by the USDA Foreign Agricultural Service showed that more than $349 million of dried condiments, seasonings and flavorings and $20 million of spice oleoresins were imported into the U.S. in 1988 (USDA, 1989). In recent years, consumption of culinary herbs and spices has steadily increased in the U.S. More Americans are consuming fresh, frozen, processed and dried culinary herbs and spices than before, and this trend will continue (Simon, 1990). Factors that account for increased consumption include interest in new foods and tastes, availability of more fresh herbs, advertising promotion by food services and institutional food chains, and expanding ethnic population demanding foods and flavorings of their homeland.

Only a small percentage of the culinary herbs are domestically produced. Most of the herbs consumed in the U.S. are imported from the Mediterranean region, Africa, Latin America and the Caribbean. Although the U.S. Virgin Islands is part of the Caribbean region, domestic production of culinary herbs does not contribute significantly to exports into the U.S. mainland. Major exporting countries are Costa Rica, the Dominican Republic, Jamaica, Mexico and Trinidad. Culinary herbs are important horticultural crops in the U.S. Virgin Islands. In a 1988 survey, sales of herbs and spices constitute a major source of income for many small-scale growers in St. Thomas and St. Croix (Robles and French, 1988). In spite of their economic importance little research has been undertaken to improve field production, processing and marketing of herbs and spices. There are few research information and extension recommendation on efficient and sustainable cropping practices for growing herbs in the Virgin Islands. Some growers are already utilizing low-input management practices such as the use of organic manures and composts, however, most are still producing herbs using high inputs of chemical fertilizers and pesticides (Palada and Crossman, 1994). This management practice is neither ecologically sound nor sustainable since these inputs are not always available in a distant island. Furthermore, growers pay high costs for importing these inputs from the mainland due to added shipping costs. There is a demand from herb growers for information on recommended sustainable crop management practices, but is not met by extension service and the experiment station due to lack of research information.

Information on sustainable and improved crop management practices for culinary herb production is scanty. Documented literatures on planting methods, fertilizer application, water requirement, weed, insect and disease control are few and limited. Some of the previous studies were focused on fertilizer application, irrigation and mulching.

Herbs, like other crops take nutrients from the soil during growth and development. As the availability of nutrients becomes depleted in the soil, the grower must add the nutrients back to the soil to ensure continued growth of the present and future plantings of the crop. Information on fertilizing herbs and medicinal plants is limited and often contradictory (Cox, 1992). This is probably due to conflicting goals of producing herbs for maximum fresh and dry matter yields or growing herbs for maximum production of secondary products. Of the major nutrients required by herbs, the largest growth and yield response generally results from nitrogen application (Cox, 1992). The first increments of N added to the soil are almost always effective in increasing dry matter yields and secondary production accumulation in herbs. Further increases in N application generally do not result in large yield increase. High N fertilization may actually reduce plant growth. Such a relationship between N levels and plant response had been observed in diverse species as poppy (Laughlin, 1983), peppermint (Hornok, 1983), lovage (Galambosi and Galambosi, 1992) and rosemary (Boyle and Craker, 1991). Nitrogen also increased essential oil yield per unit dry flower weight in chamomile (Emongor and Chweya, 1992). Letchamo (1993) concluded that N application has a positive effect on chamomile yield and favors its content of active substances, but the response is dependent on genotype.

The source and form of N fertilizer can also affect growth and yield as well as the quality of secondary products in herbs. Although N is absorbed by plant roots in either ammonium or nitrate form, some species seem to prefer one form over the other while other plants have no preference. For example, sweet basil plants fertilized with ammonium N contains less linalool and eugenol oils than plants fertilizer with nitrate N (Adler et al., 1989). Ammonium form of N had similar effects on the production of essential oil in Japanese mint (Singh and Singh, 1978). In one study, ammonium N limited the production alkaloids in poppy (Costes et al., 1978), but these results could not be duplicated in a second study (Laughlin, 1983). There are few studies on comparing the effects of sources of N fertilizer on fresh and dry matter yields of herbs and spices. In a related study using various levels of ammonium nitrate in combination with P and K and micronutrients, it was found that sweet basil, sweet marjoram, pot marjoram and oregano responded favorably to 168 and 252 N kg /ha (Angell et al., 1990).

Research with varying rates of drip irrigation showed increases in growth and total yield of essential oil from herbs with increasing rates of water application (Simon, 1987). A similar study conducted one year later during a season with high rainfall showed no benefit from drip irrigation. The interaction of soil moisture and soil fertility affects the accumulation of plant products, indirectly influencing plant growth in aromatic and medicinal plants (Bernath, 1986; Franz, 1983; Penke, 1978). Experiments comparing sprinkler with drip irrigation on herbs demonstrated a more efficient water used and increased yield under drip irrigation (Collingwood et al., 1991). Integration of mulch with drip irrigation resulted in additional increase in water use efficiency and yield of basil (Palada et al., 1992; 1995). By adopting this system, herb growers can boost their income by 30 to 50 percent. Palada et al. (1993) reported that basil grown with organic mulch such as compost produced yields which were comparable or higher than synthetic (black plastic) mulch under drip irrigation. Davis (1994) found that the incidence of bacterial soft rot (Erwinia spp.) was highest in sweet and bush basil grown with wheat straw, but the disease was also high on sweet basil under black plastic mulch and bare ground. In studies with thyme, Collingwood et al. (1991) reported that yields were reduced under plots with black plastic mulch due to higher incidence of soil-borne diseases as compared with plots with no mulch.

In determining the optimum spacing and row arrangement for basil production, Davis (1993) concluded that high yields of fresh market basil can be best obtained from plants grown in double-rows with an in-row plant spacing of 15 to 23 cm, on raised bed with black polyethylene mulch and drip irrigation. These results support the study by Ricotta and Masiunas (1991) who reported that black polyethylene mulch improved yields of basil. Shalaby and Razin (1992) investigated the effects of dense cultivation and fertilization on yield of thyme and found that wider plant spacing (45 cm) promoted growth, yield and oil yield per plant. However, dense cultivation (narrow spacing of 15 cm) significantly increased yield and oil per unit area. Applied fertilizer NPK significantly increased productivity per unit area and dense population with higher levels of fertilizer application produced the maximum yield.

The effect of organic and inorganic fertilizers on yield of Japanese mint was studied by Chattopadhyay et al. (1993). They reported that herbage, essential oil yield, nutrient uptake and soil available nutrients were significantly enhanced due to application of amended compost (mint-residue amended with starter nutrients, microbial culture and soil suspension) as compared to non-amended compost, farmyard manure and inorganic fertilizer. Organic fertilized soils maintained significantly higher available nutrients throughout the crop growth period compared to inorganic fertilizer soils. Palada et al. (1994) compared the effects of organic and inorganic N fertilizers on yield of thyme and found that urea and cow manure were superior to ammonium nitrate in terms of total plant fresh yield. They concluded that urea and cow manure are best sources of N fertilizer for thyme production.

Frank et al. (1987) stated that, all herbs, spices and medicinal plants are considered minor crops with respect to the development of data for pesticide registration. Thus, today only a small number of pesticides are registered and have tolerances for use on these plants. They presented a summary of research work on development of pesticides for herbs, spices, and medicinal plants, and tolerance of some herbs species to pesticides had been established. Espaillat et al. (1992) conducted a phytotoxicity screening of four post-emergence herbicides on seven herb species and found that differences in phytotoxicity rating between herbicides, rates, and herbs were significant. Norflurazon, bentazon and dicamba showed potential for labeling on wild marjoram, lavender, winter savory, rosemary, sage and sweet marjoram.

Soil-borne fungal diseases caused by Fusarium, Verticillium, Pythium, Rhizoctonia and Sclerotia are common in mint, parsley and thyme (Schumann, 1989). Simple management techniques involving good sanitation and crop rotation can help prevent plant diseases. Crop rotations that alternate the locations of the herbs in field each year, reduce the number of disease organisms associated with any one species.

The prospect of culinary herb production for fresh, frozen, processed and dried products is bright and there is potential for production in the Virgin Islands to meet increasing local, regional and international demands. With tourism at the base of the modern Virgin Islands economy, local growers are developing ways to market culturally derived products that will reach and appeal to tourists and a more cosmopolitan population (Thomas and Palada, 1994). The Virgin Islands is an extremely popular tourist destination, hosting about 2 million tourists annually. It is predicted that attractively packaged, affordable local products like “bush teas” and bath herbs will appeal to many of the tourists. Other potential markets for culinary herbs are local restaurants, resort hotels and supermarkets. Expansion of herb and spice production through a greater understanding of production constraints and incorporation of appropriate sustainable management practices will economically benefit farmers, contribute to the viability of the local economy and satisfy consumer needs in the Caribbean and the U.S.

Research

Materials and methods:

Field experiments were conducted during the project period from 1996 to 2000. Experiments were established on research stations and on farmer cooperators’ farm. The field trials were grouped into four subjects addressing the above objectives.

1. Sustainable Soil Management Practices:

Two experiments were conducted to develop sustainable soil management practices for culinary herbs. The first experiment involved crop rotation of culinary herbs with green manures and the second dealt with the response of culinary herbs to application of animal manures.

1a. Crop Rotation of Culinary Herbs with Tropical Legume Green Manures

Field experiments were conducted at the University of the Virgin Islands Agricultural Experiment Station on St. Croix. The soil is Fredensborg loamy, fine carbonatic, isohyperthermic, shallow, typic calciustoll. The initial soil had an analysis of pH=7.65, organic matter=1.4%, 38 ppm N, 487 ppm K, 19 ppm P, and a CEC of 30 meq/100 g. The experimental design was randomized complete block with three replications. The green manures consisted of sunnhemp (Crotolaria juncea), cowpea (Vigna unguiculata var. Sesquepedalis), hyacinth bean (Lablab purpureus) and a natural grass/broadleaf fallow.

The green manure crops were established in June, 1996 and 1997. In each year the green manure crops were mowed in October and incorporated into the soil with disk plowing. In the natural fallow plots, the area was mowed whenever the grass/broadleaf mix reached their reproductive growth stage. The final mowing and incorporation in the natural fallow plots were performed to coincide with the green manure plots. Plant samples of green manure crops were collected for determination of dry matter and nutrient yield. Seedlings of chives, basil, parsley, sage and cilantro were transplanted in December, 1996 and 1997. Plot size for each herb species was 1.5 m x 4 m, consisting of three rows spaced 0.5 m apart. Plants were spaced 0.30 m along the row. All plots were drip-irrigated to maintain soil moisture tension at -30 kPa.

At harvest, data were collected on plant height (5 plants in center row). The same plants were sampled for data on fresh and dry weight. Plant samples were placed in an oven at 65oC and dried to constant weight for dry matter determination. Data were analyzed using the Statistical Analysis procedures (SAS, 1988). Differences among treatment means were separated using the Duncan’s Multiple Range Test.

1b. Response of Culinary Herbs to Application of Animal Manures

Separate experiments were conducted to determine the yield response of chives, cilantro, sweet marjoram and thyme to animal manures. For chives, cow manure (2%N, 1%P and 2%K) was applied at rates of 0, 10, 20 and 40 tons/ha. Cilantro, sweet marjoram and thyme were applied with turkey litter at rates equivalent to 0, 50, 100 and 150 N kg/ha. In a separate on-farm trial, thyme was fertilized with dry chicken manure at rates of 0, 5 and 10 t/ha. All trials were established using a randomized complete block design with four replications. Plots consisted of three rows 3 m long. Data were collected on plant height at first harvest, number of slips (for chives), plant fresh and dry weight. Measurements were taken from 10 plants in the middle row. The experiments using turkey litter on chives, cilantro, sweet marjoram and thyme were conducted in farmers’ field and on experiment station, while the trial on thyme applied with chicken manure was conducted on farmer’s field.

2. Sustainable Weed Management Practices Using Organic and Synthetic Mulches:

Over a four-year period, six separate experiments were conducted to evaluate the benefits of organic and synthetic mulches for culinary herbs. These trials evaluated various mulches including black fabric (weed barrier), silver-coated plastic, white-on-black plastic, grass straw, wood chips, and shredded paper on chives and parsley; black plastic, white-on-black plastic, grass straw, wood chip and weed block for basil; and grass straw, wood chips, shredded paper, and white-on-black plastic
on thyme. For comparison, a bare (no mulch) control plot was included in all experiments. The trials were conducted both in farmers’s field and on experiment station. All plots were drip irrigated to maintain a soil moisture tension of -30 kPa. Data on plant height, fresh and dry matter yields were collected at each harvest. Weed population and weed weight were determined before each weeding operation. In some trials, soil temperature was monitored at 0-5 cm, 5-10 cm and 10-15 cm depths under mulch cover.

2a. Influence of Mulch Type on Weed Control and Yield of Parsley and Chives

Experiments were conducted on demonstration plots of the V.I. Department of Agriculture, St. Croix and in farmer’s field to determine the effectiveness of various mulches in controlling weeds and their influence on marketable yield of parsley and chives. The soil at the V.I. Department of Agriculture is a Hogenborg fine, smectitic, isohyperthermic, sodic, haplustert. The experiment was established using a randomized complete block design with four replications. The treatments consisted of white on black polyethylene mulch, black fabric weed barrier, silver plastic film, grass mulch (hay) and a non-mulch treatment. Each treatment plot was 1.2 m x 3.6 m, consisting of three rows 0.4 m apart. Seedlings of parsley were transplanted on December 13, 1996 at a spacing of 0.3 m within rows. All plots were drip-irrigated to maintain a soil moisture tension of -30 kPa. Weed samples were taken from each plot prior to weeding. The fresh weight of the weed biomass was recorded and the samples were oven-dried for determination of dry matter. Fertilizer was applied to all treatments at the rate of 100 N, 50 P and 50 K in kg/ha. Cow manure was used to provide 50% of the N. Urea, triple superphosphate and sulphate of potash were applied to complete the required amounts of nutrients. The grass mulch treatment was applied on December 20, 1996. The data collected at each harvest were plant height and fresh weight. The harvested samples were then placed in an oven and dried to a constant weight. The parsley was harvested three times at intervals of approximately 30 days beginning on January 27, 1997.

Similar mulch treatments and procedures were followed at the experiment conducted in farmer’s field using chives. The trial was planted on December, 1996 and harvested on March, 27, 1997.

2b. Influence of Mulch Type on Weed Control and Yield of Sweet Basil

Sweet basil was grown in farmer’s field under various mulching materials including grass straw, black fabric (weed barrier), black plastic (weed block), white-on-black plastic and wood chips. A bare (control) plot was also established for comparison. Plants were grown at row spacing of 30 cm and plant spacing of 39 cm. The trials used a randomized complete block design with three replications. Drip irrigation was maintain at soil moisture tension of -30 kPa. At each harvest, data were collected on plant height, plant, leaf and stem fresh and dry weights and weed population.

2c. Evaluation of Organic Mulches for Chive Production

Field experiments were conducted at two locations during the 1999 cropping season. The Agricultural Experiment Station, University of the Virgin Islands on St. Croix (Lat. 17o42’N, Long. 64o48’W) where the soil is Fredensborg, loamy, fine carbonatic, isohyperthermic, shallow calciustolls (Lugo Lopez et al., 1998). The other site was at the Virgin Islands Department of Agriculture adjacent to the experiment station. The soil is a Hogensborg, fine smectitic, isohyperthermic, sodic, haplustert (Lugo-Lopez, 1998). Average rainfall in both locations is 1015 mm per year with pan evaporation of 2000 mm. The field trial at the experiment station was planted on May 24, 1999 and harvested on September 22. The second trial was planted immediately on September 22 and was harvested on December 21. Planting date for the VI Department Agriculture (VIDA) trial was May 6, 1999 and harvested on July 23, 1999. Chives were grown in organic mulches including grass straw, shredded paper and wood chips. These treatments were compared with synthetic mulch (white on black plastic) and the control (bare). All treatments included the application of microirrigation. Components of the drip irrigation system included a 15 mm polyhose as submains (Hardie Irrigation, El Cajon, CA) and laterals made of 15 mm New Hardie tape with laser drilled orifices spaced at 20 cm apart.

The experiment was established using a randomized complete block design with four replications. Each treatment plot was 1.23 m x 3.6 m, consisting of three rows 0.41 m apart. Plants were spaced 0.30 m within rows. All plots were irrigated to maintain soil moisture at -30 kPa. Tensiometers (Irrometer, Riverside, CA) were installed to monitor water use by taking weekly readings for each treatment. All plots were applied with dehydrated cow manure (2-1-2) at the rate of 8 kg/plot or 18 t/ha). Chive tillers (slips) of about 15 cm were transplanted on the dates previously mentioned at both locations. All mulching materials were applied at planting or one day after planting except for the grass straw mulch which was installed two weeks after planting. Weed samples were taken from each plot prior to hand weeding. Number and weed fresh weight were recorded and samples were oven dried for dry matter determination. Soil temperature was measured at 0-5, 5-10 and 10-15 cm depth at weekly intervals using a Reotemp soil thermometer. At harvest data were collected on chive plant height, number of tillers (slips) and fresh yield. Total water use was determined by subtracting the initial flow meter reading from the final reading at the termination of the trial. Data were also collected on labor (man hours) for all operations and costs of inputs. Using fresh yield and cost data, an economic analysis was performed to compare the costs and returns from each mulching material.

3. Sustainable Disease and Pest Management Practices:

3a. Insect Pests and Diseases Associated with Culinary Herbs

Using ongoing trials on green manure rotation and mulching materials, insect pests and diseases were to be monitored and recorded. However, this activity was not successfully implemented due to lack of participation from collaborator.

3b. Control of Leaf Miners on Basil Using Organic Sprays

Basil was grown in replicated plots and sprayed with rotenone at various frequencies to control leaf miners. Spray frequencies consisted of 0x, 1x and 2x per week at rates of one and four teaspoons per gallon. This trial was damaged by hurricane Marilyn after two harvest samples were collected.

4. Microirrigation for Efficient Water and Fertilizer Use:

Under this objective irrigation water use of chives and thyme grown with and without mulch under drip irrigation were monitored and compared. Data for basil, cilantro and parsley are not reported.

Research results and discussion:

1. Sustainable Soil Management Practices:

1a. Crop Rotation of Culinary Herbs with Tropical Legume Green Manures

Biomass and Nutrient Yield of Green Manure Crops. Significant differences were observed in dry matter yield of green manure crops in both years. As shown in Table 1, sunnhemp was superior to hyacinth bean and cowpea, producing 10.97 and 13.12 t./ha in 1996 and 1997, respectively. Hyacinth bean produced significantly higher dry matter yield than cowpea in 1997. Sunnhemp produced a dry matter yield which was 50 to 75% higher than hyacinth bean and cowpea (Table 1). Both sunnhemp and hyacinth bean look promising as green manure crops in the Virgin Islands.

Data on Table 2 show the nutrient content and contribution of green manure crops in 1997. In terms of nitrogen, sunnhemp produced significantly higher N yield (457 kg./ha) than cowpea and hyacinth bean. The N yield of hyacinth bean was also significantly higher than cowpea. Sunnhemp and hyacinth bean also produced higher P and K than cowpea. Highest calcium was obtained from hyacinth bean. No significant differences were observed for magnesium yield among the green manure crops (Table 3), but sunnhemp and hyacinth bean had a higher Mg yield than cowpea. The data suggest that sunnhemp and hyacinth bean may contribute significant amount of major nutrients for soil fertility improvement.

Green Manure Effect on Chives. The green manure treatments did not significantly influence plant height, fresh and dry matter yield (Table 3). However, data showed that in both years, fresh yield was highest for chives grown after hyacinth bean (1807 and 2786 g./m2, respectively). Chives grown after fallow (no green manure) produced the lowest fresh and dry matter yield, except in 1998 where chives grown after cowpea produced the lowest fresh yield (Table 3). It appears that green manures have potential for improving yield of chives.

Green Manure Effect on Sweet Basil. In 1997 no significant differences were obtained for plant height, fresh and dry matter yield of sweet basil as influenced by green manures (Table 4). However, basil grown after cowpea produced higher fresh yield than the other treatments. Hyacinth bean produced the lowest fresh and dry basil yield. In 1998, significant differences in plant height was observed among green manure treatments. Tallest plants were observed when basil was grown after sunnhemp, however, this height was not significant compared with basil after fallow. Basil grown after hyacinth bean and sunnhemp produced the highest fresh and dry matter yield. This indicates that these green manure crops may have beneficial long term effects on basil production.

Green Manure Effect on Parsley. Two types of parsley were planted in the trial. In 1997, an upright stem parsley was used while a curled leaf parsley was planted in 1998. Data shown in Table 4 indicate that plant height was not affected by green manure treatments in both types of parsley. Significant differences in fresh yield was only obtained in 1997 (Table 5). Highest yield (1803 g./m2) was produced when parsley was planted after sunnhemp, while the lowest yield (1124 g./m2) was obtained from cowpea rotation. No significant differences were observed in dry matter yield in 1997. In 1998, both fresh and dry matter yield of parsley were not affected by green manure rotation, however, all green manure crops resulted in higher fresh and dry matter yield of curled leaf parsley (Table 5). The data would suggest that parsley can benefit from green manure rotation.

Green Manure Effect on Purple Basil. There was no significant effect by green manure rotation on plant height, fresh and dry matter yield of purple basil on both years (Table 6). However, sunnhemp rotation consistently resulted in higher fresh and dry matter yield than other rotation treatments. Purple basil planted after sunnhemp produced the highest fresh yield of 1065 and 1701 g./m2 in 1997 and 1998, respectively. Lowest yield was obtained from hyacinth bean rotation (Table 6). The data indicate that purple basil may benefit from sunnhemp rotation.

Green Manure Effect on Cilantro. The effect of green manure rotation on cilantro plant height, fresh and dry matter yield was not significant (Table 7). However, it was apparent that both hyacinth bean and sunnhemp have positive effects on fresh and dry matter yield of cilantro. Yields from this rotation were higher compared to cowpea and fallow rotations. Cilantro planted after hyacinth bean and sunnhemp produced 20-50% more fresh yield than cowpea and fallow rotation. (Table 7). Hyacinth bean and sunnhemp are therefore promising green manures for cilantro production.

Green Manure Effect on Sage. Sage grown after sunnhemp produced significantly higher yield than the other rotation treatments (Table 8). Both fresh plant and dry matter yields of sage following sunnhemp were superior to cowpea, hyacinth bean and fallow rotations. Sunnhemp increased sage fresh yield by 50-60% and dry yield by 39-54% (Table 8). Sunnhemp therefore is the best green manure crop for rotation with sage.

This study has shown that green manures grown in rotation with culinary herbs have the potential of improving yields. Sunnhemp and hyacinth bean are green manure crops that showed positive benefits on basil, cilantro and sage. Chives and parsley did not significantly benefit from green manures as indicated by almost similar plant fresh and dry matter yield. However, there was a consistent increase in yield when hyacinth bean and sunnhemp were grown in rotation with chives and parsley. The significant effect of sunnhemp and hyacinth bean on yield of culinary years can be attributed to their greater biomass production and nutrient contribution compared to cowpea and fallow rotations. Additional research is needed to determine the long term effect of green manures on soil fertility and crop yields.

1b. Response of Culinary Herbs to Application of Animal Manures

Chive Response to Cow Manure. Plant height, number of slips and fresh yield of chives were not significantly increased by application of cow manure at rates of 0, 10, 20 and 40 t.ha-1 (Table 9). However, there was a tendency for plant height and number of slips to increase with increasing levels of cow manure.

Response of Cilantro, Sweet Marjoram and Thyme to Turkey Litter. Application of turkey litter at rates equivalent to 0, 50, 100 and 150 kg N/ha did not significantly influence the yield of cilantro, sweet marjoram and thyme (Table 10). However, for sweet marjoram there was a tendency for yield to increase with N application up to 150 kg/ha. For cilantro and thyme maximum yield was attained with turkey litter application equivalent to 100 kg/ha.

The absence of significant response to animal manures can be attributed to the relatively high soil organic matter content and residual nutrient levels in the VI Department of Agriculture plots where the trials were conducted.

Effect of Chicken Manure on Yield of Thyme. The response of thyme to application of chicken manure under farmer’s field conditions was significant (Table 11). Thyme plant fresh weight, dry weight, leaf and stem dry weight were significantly increased with application of 10 t/ha. At this application rate, fresh and dry weight of plants, leaves and stems were significantly higher than 0 and 5.0 t/ha application rate. It appears that chicken manure is favorable for thyme.

2. Sustainable Weed Management Practices Using Organic and Synthetic Mulches:

2a. Influence of Mulch Type on Weed Control and Yield of Parsley and Chives

Parsley. Parsley plant height was significantly affected by application of mulches. Plants in the straw mulch were consistently taller than other mulch treatments. Data on Table 12 show that for the first harvest, plants in grass straw mulch produced significantly taller plants than both the white and silver plastic mulches. At the second harvest, plants from grass straw mulch plot were significantly taller than plants under black fabric (weed barrier) mulch. The mean plant height for the three harvests showed that plants grown under straw mulch were significantly taller than plants from all other mulch treatments, except for the control. The significant differences in plant height observed for the first two harvests did not result in any significant yield differences, even though the grass straw mulch and bare soil (control) had higher fresh and dry matter yields than other treatments. Significant differences in yield were observed during the third harvest (Table 12). Parsley grown with grass straw mulch produced a significantly higher fresh (811 g./m2) and dry (141 g./m2) compared to parsley grown under black fabric (weed barrier) and white plastic mulch.

Weed population was significantly higher in bare soil (no mulch) treatment than all mulched plots (Table 13). Fresh and dry weed biomass (weight) were almost similar for all mulch treatments, but significantly lower than the control (bare soil). The plots were weeded on a regular basis which prevented weeds from getting big enough to accumulate any appreciable biomass. The weed population data give an indication of potential weeds that would be encountered if plots were not weeded as often as they were in this trial. Problems were encountered regarding the use of the silver mulch. A combination of rainfall and high temperature caused the mulch to lose its silver coating on a large percentage. This caused light penetration through the transparent areas of the mulch and contributed to a high weed population under the plastic mulch. The mulch also started to deteriorate before the trial was terminated. A root knot nematode problem also developed during the latter stages of the trial. The loss of plants caused by this pest ranged from 40% (silver mulch) to 17% in the straw and bare soil (no mulch) treatments. This higher nematode infestation in the synthetic mulch would probably indicate that these mulches create a micro-environment that is ideal for the development of nematodes.

Chives. All types of mulch were effective in controlling weeds (Table 14). Differences in weed count, fresh and dry weight of weeds between mulched plots and the bare soil (control) were significant, indicating that mulches are very effective in reducing weed growth. Significant differences were also observed in plant height and fresh yield of chives (Table 15). Chives grown under grass straw mulch are taller and have higher yield than those growth with other mulches. All mulching materials maintained integrity except for the silver film. Deterioration of the silver plastic film was observed similar to that in the parsley trial. This indicates that towards the end of the trial its effectiveness in controlling weeds may be reduced.

2b. Influence of Mulch Type on Weed Control and Yield of Sweet Basil

Basil plants grown in plots with grass straw mulch were significantly taller than plants grown with other mulch types (Table16). Plant fresh weight of basil under grass straw mulch was superior to other treatments and significantly higher than plants with no mulch (Table 16). Leaf fresh yield of basil with grass straw mulch was also significantly greater than other mulch types except the weed block. Differences in dry weight of plants and leaf were also significant among mulch types with grass straw showing the highest dry weight (Table 17).

All types of mulch significantly reduced the number and biomass of weeds compared with the no-mulch (bare) treatment (Table 18). Among mulch types, wood chips was the most effective in controlling weeds in terms of number and biomass. Grass straw mulch was as effective in controlling weeds as synthetic mulches.

This study has shown that organic mulches such as grass straw and wood chips were similarly effective in controlling weeds as synthetic mulches. Mulching with organic mulches, therefore, has the potential of increasing marketable yield of basil.

2c. Evaluation of Organic Mulches for Chive Production

Plant Height and Number of Slips. No significant differences in plant height (data not shown) were observed at either UVI Ag. Experiment Station (UVI) or the Virgin Islands Dept. of Agriculture (VIDA). The number of tillers differed significantly at both locations (Table 19). At UVI, chives grown in plots without mulch (bare) produced a higher number of tillers than all mulch treatments except paper and straw mulches. At the VIDA, chives grown in plastic mulch was superior in the number of slips to shredded paper mulch (Table 19). The higher number of slips in bare plots compared to mulched plots would indicate that mulching may have a restrictive or inhibitory effect on the development of slips in chives. The effect is more apparent in wood chip, plastic and shredded paper and less in grass straw mulch. The higher number of tillers at UVI compared to VIDA may be attributed to a longer growing season at UVI.

Chive Fresh and Dry Matter Yield. At UVI, chives grown with bare (no mulch), shredded paper and straw mulch produced the highest yields but there were no significant differences (Table 20). At the VIDA, all mulch treatments produced higher yield than bare plots (Table 20). However, plastic and wood chip mulch were superior to bare plots. The higher yield of chives in bare plots at UVI is associated with higher number of slips compared to all treatments with mulch. The data from the VIDA indicate that organic mulches have almost similar effect with synthetic mulch in terms of fresh yield. Differences in fresh yield were not significant among mulch treatments. Crossman and Palada (1998) reported that yield of fresh and dried chives grown with grass straw mulch was significantly higher than yields obtained from white plastic mulch and bare plots. They suggested that straw mulch may provide a more suitable environment for the growth of chives compared to synthetic plastic mulch. At UVI significantly more dried biomass of chives was obtained from plots without mulch than with straw mulch (Table 21). At VIDA the plastic mulch plots was superior to both the straw and no-mulch treatments for production of dried chives.

Weed Dry Weight. Lowest weed dry weight was observed in plastic mulch at most sampling dates (data not shown). At both locations, all mulched plots resulted in lower weed population and biomass yield compared to bare (no mulch) plots (Fig. 1). Between the three organic mulch, weed biomass was greater in grass straw mulch than in shredded paper or wood chip mulch. The higher weed growth in grass straw mulch can be attributed to weed seeds present or mixed with grass straw during cutting and baling of hay. This result is consistent with previous studies (Davis, 1994; Palada, et al., 1999) where there was a high incidence of weed growth in straw mulch when applied in basil.

Soil Temperature. Plots under organic mulch had lower soil temperature than synthetic (plastic) mulch and bare plots (data not shown). At UVI, measurements indicated that mean soil temperature in plots with organic mulch (grass straw, shredded paper and wood chips) were several oC lower than synthetic mulch and bare plots. This result is consistent with those reported by Palada, et al., (1999) where the use of organic mulches particularly grass straw modified soil temperature in basil. This effect is important in the tropics where soil temperature can rapidly increase and inhibit early seedling growth and establishment.

Economic Returns. Growing organic chives offers good economic opportunity for herb farmers in the Virgin Islands. Although the cost of production is high due to high labor and input costs, a grower can make a decent profit from one-sixteenth (1/16) acre or 0.06 ha. Table 22 shows the economic comparison of alternative mulch for chive production in the Virgin Islands based on 0.06 ha plot. The economic analysis used the mean yield data from two locations. Economic comparison shows that the average net economic return above mulch cost was highest ($5482) from plots with shredded paper mulch followed by plots with grass straw mulch ($5167). The use of plastic and wood chip mulch resulted in lower net returns compared to bare (no mulch plot). The use of organic mulch (shredded paper and grass straw) provided 2 to 10% more returns compared to bare plots and 5 to 12% more returns over plastic mulch. Grass straw is locally available and biodegradable. When fully decomposed it contributes organic matter to the soil. It also provides soil cover reducing soil erosion during heavy rainfall. Therefore, it does not only improve yield and economic returns, but also conserve and protect soil resources and the environment.

This study has shown that organic mulches such as shredded paper and grass straw offer good alternative to synthetic (plastic) mulches for chive production. Chives grown with grass straw and shredded paper produced higher yield and economic returns compared with chives grown using plastic mulch. Economic return from chives grown with shredded paper and grass straw mulch was on the average 5 to 12% higher than plastic mulch. To improve production and income, herb growers should consider using organic mulch and realize other benefits including weed control and soil conservation.

3. Sustainable Disease and Pest Management Practices:

3a. Insect Pests and Diseases Associated with Culinary Herbs

Using ongoing trials on green manure rotation and mulching materials, insect pests and diseases were to be monitored and recorded. However, this activity was not successfully implemented due to lack of participation from collaborator.

3b. Control of Leaf Miners on Basil Using Organic Sprays

Basil was grown in replicated plots and sprayed with rotenone at various frequencies to control leaf miners. Spray frequencies consisted of 0x, 1x and 2x per week at rates of one and four teaspoons per gallon. This trial was damaged by hurricane Marilyn after two harvest samples were collected. Yield data from two harvests did not show significant differences between treatments.

4. Microirrigation for Efficient Water and Fertilizer Use:

Under this objective irrigation water use was only monitored on chives and thyme grown with and without mulch under drip irrigation. Total water use was compared between mulch treatments.

Chive Irrigation Water Use. At UVI, total irrigation water use was lowest in plots with plastic mulch (Fig. 2). Irrigation water use in plots with straw and paper mulch was slightly higher than bare plots. At VIDA, plots with paper mulched used the lowest irrigation water. Irrigation water use from plots with plastic, straw and wood chips was almost similar with bare plots. Overall, mulching did not reduce water use in this study and results are not consistent with previous studies. Technical problems with the drip irrigation system were sometimes experienced due to loose connections of fittings and unattended excessive leakage in the drip lines which result in erratic flow meter reading.

Thyme Irrigation Water Use. Except for grass straw, all mulches resulted in reduced irrigation water use of thyme (Fig. 3).Thyme grown under white plastic mulch used the lowest (385 cu.m./ha) irrigation water. This is equivalent to 44% of the total water use in bare (control) plots. The use of wood chip and shredded paper mulch resulted in 12 and 19% reduction in irrigation water use, respectively (Fig. 4). The high irrigation water use in grass straw mulch is consistent with that obtained in chive mulch study at UVI.

Participation Summary

Educational & Outreach Activities

Participation Summary

Education/outreach description:
Education and Outreach

The project has conducted two farmers’ field days, one in St. Croix and one in St. Thomas. Farmers in St. Croix visited the green manure crop rotation trials as well as trials in farmers’ fields. In St. Thomas, herb growers had the chance to view the plots planted to spring onion (chives) and basil conducted by two project cooperators. A total of 20 growers participated in these activities.

Two evening workshops were held in St. Croix and St. Thomas. During the workshops farmer cooperators presented and discussed the results of their on-farm trials with the workshop participants. The result of on-station trials were also presented by project investigators and collaborators. The discussion focused on agronomic yield, but questions were raised about the economic returns and benefits from various treatments using organic practices. These questions were not well addressed due to lack of economic analysis for agronomic data during that time when the project was in progressed.

In addition to field days and workshops, project participants also presented seminars, attended scientific conferences and presented posters and technical papers. Posters were also presented during the Virgin Islands Agriculture and Food Fair both in St. Croix and St. Thomas. All in all a total audience of more than 1000 was reached through this program.

Project Outcomes

Project outcomes:

Based on the results from studies conducted over the four-year project period, the use of green manures in rotation with culinary herbs demonstrates their potential for improving yield of culinary herbs without the need for fertilizer application. In nutrient-poor soils, animal manures are good alternatives to chemical (commercial) fertilizers and will have an economic impact for small scale herb growers in the Virgin Islands. Promising results from the use of organic mulches will have a greater impact on weed control thereby reducing labor input mainly by hand weeding. These are the potential contributions the project has demonstrated so far. The project has demonstrated the benefits of using sustainable crop management practices for culinary herb production such as utilization of local resources for management of soil fertility, reducing crop-weed competition and decreasing irrigation water use. Further research is needed in pest management addressing major insect pests and diseases of culinary herbs.

Recommendations:

Areas needing additional study

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Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.