Development of Sustainable Cropping Systems for Seedless Watermelon and Fall Lettuce in Rotation with Green Manures

Final Report for LS96-077

Project Type: Research and Education
Funds awarded in 1996: $182,751.00
Projected End Date: 12/31/1999
Matching Non-Federal Funds: $92,755.00
Region: Southern
State: North Carolina
Principal Investigator:
M. R. Reddy
NCA & T State University, Natural Resources and Environmental Design
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Project Information


The goal of the project was to develop a sustainable crop rotation system for the production of seedless watermelon and fall lettuce following selected cover crops. The cover crop treatments originally were Austrian Winter Pea, Hairy Vetch, Austrian Winter Pea and rye, and Hairy Vetch and Rye, and a non-planted control. From fall of 97 Crimson Clover replaced Austrian Winter Peas. Cover crops were planted from 96-98 at seven locations in North Carolina and Virginia at experiment stations and farmer’s fields. The cover crop growth and biomass production were not significantly different under the treatments. The biomass production ranged from 3.2 to 4.8 tons per acre. In the spring of 1997-99, the cover crops were mowed down with a flail mower and left as a surface mulch to control weeds and soil erosion, and retain soil moisture. Two seedless watermelon varieties were transplanted and grown in each cover crop treatment at all of the sites. The watermelon crop was established well in North Carolina sites, and Virginia sites. Seedless watermelon yields were satisfactory in Guilford, Lenoir and Rockingham counties of North Carolina. In Guilford County, watermelon yields were the highest under Hairy Vetch Treatment (14.7 ton/acre). In Rockingham County, the treatment of Austrian Winter Pea and Rye mixture yielded 29.0 ton/acre and it was the highest among all the sites. Average yield of these three sites was 17.3 ton/acre with a standard deviation of 6 ton/acre. Average number of melons in Guilford, Lenoir and Rockingham counties was 2600 per acre, average weight was 17.3 tons/acre. A quality analysis of seedless watermelon from North Carolina sites conducted by Virginia State University revealed that the average sugar content in the watermelons from sites of Guilford and Rockingham counties was 8.17% with a standard deviation of 0.33%.

Seedless watermelon yields in Virginia ranged from 4.9 to 34.7 tons/acre. Quality analysis of Virginia melons showed meat: rind ratio 1.2 to 1.8 and it was not affected by cover crops. Also, sugar and other quality parameters were not effected by the cover crops.
Cooperating farmers of North Carolina sold all of their seedless watermelons in the local farmer’s markets. At Fletcher Crimson Clover and Rye treatment produced the highest yields (6.6 tons/acre). There was no size difference between the seedless watermelon tested. A survey was conducted by including professionals, farmers, marketeers, household individuals and others to evaluate seedless watermelons from this research and demonstration. Eighty percent of the survey participants favored the taste of seedless watermelon. Ninety-two percent of them showed their preference to buy seedless watermelons even at a higher price than seeded melons.

At the site of Guilford County, North Carolina, we monitored the nitrate leaching in watermelon plots due to cover crop mulch decomposition. The nitrate results showed that decomposition of the cover crop mulch provided enough nitrogen nutrient for the growth and development of seedless watermelon. However, there is a potential risk of nitrate leaching to deep soil or groundwater after the maturity of most of the watermelons. Pest populations were also monitored and there were no real problems with pests and diseases. However, as the cover crop mulch decomposition progressed, weeds became a problem at the middle and late stages of the watermelon growth. After the harvest of the watermelon there was not enough time for fall lettuce crop due to the timely planting of cover crops. Therefore, all the plots were tilled and planted with respective treatments of cover crops. Due to poor performance observed at some sites under the treatments of Austrian Winter Pea and the mixture of Austrian Winter Pea and rye, we replaced Austrian Winter Pea with Crimson Clover from the fall of 1997-99.

Project Objectives:

1. Facilitate production and evaluation of quality of seedless watermelon and fall lettuce in rotation with green manures for increasing farm income.

2. Explore alternative markets for the watermelons and the fall lettuce to attract better prices and income to the farmers.

3. Assess the nutrient supply, cycling, and organic matter buildup by green manure mixtures in rotation with seedless watermelon and fall lettuce.

4. Monitor the movement and fate of nitrogen and phosphorus in the soil under the production system involving green manure mixtures and rotations.


Widespread use of inorganic nitrogen fertilizers, has continuously increased input costs, and been identified as a major groundwater contaminant (Hallberg, 1986; Hanlon and Hochmuth, 1992). Estimates of crop absorption of applied nitrogen from inorganic sources range from 25 to 70 percent and efficiency decreases with increased dose. Since unused nitrogen not only exceeds the economic optimum but can also be immobilized, denitrified, washed into streams or lakes, or leached from soil into underground water and the subsoils (Johnson and Wittwer, 1984; Legg and Meisinger, 1982), there has been a renewed interest in the incorporation of legumes in cropping systems as a source of nitrogen (Abdul-Baki and Teasdale, 1993 and 1994; Smith et al., 1987).

Alternatives to use of inorganic nitrogen fertilizers can be the utilization of biological nitrogen fixing properties of leguminous crops in crop rotations. Nitrogen fixed by leguminous crops can be effectively used in building and conserving soil fertility (Hoyt and Hargrove, 1986; Strivers and Shennan, 1991).

North Carolina and Virginia have a large number of small farms and limited resource growers. The small farm size and limited cash-flow of small-scale farmers, and the high cash value of many specialty crops, support the idea of producing specialty crops such as seedless watermelon and fall lettuce. This is more important now than at any other time in view of the reduced acreage in tobacco production and the great desire by many small farmers to find substitute cash crops for tobacco and maintain sustainability on the farm.

Production of seedless watermelon as specialty cash crop, with sustainable production technology, can increase farm income, diversify agriculture, and alleviate cost and environmental problems associated with the use of inorganic fertilizers. Seedless watermelons attract consumers and sell for double or triple the price of seeded watermelons.

Increasing the level of soil organic matter and reducing the use of chemical fertilizers and pesticides are important goals for sustainable agriculture. Information on green manure mixtures and cover crops and their contribution to nitrogen supply to watermelon crop is limited. A mixture of a legume and a grass species will aid in enhanced utilization of leftover nitrogen from a previous crop than just a legume alone and build up soil organic matter after incorporation. Data on nitrogen and phosphorus release during decomposition of the green manure mixtures are needed for development of prediction models. Such models will be quite useful for producers in nitrogen and phosphorus management. Crop rotations are effective cultural practices to provide control against weeds, insects, and plant diseases (Ware, 1980; Forcella and Burnside, 1993). Seedless watermelon also showed the lowest susceptibility to nematode (Meloidogyne incognita) among ten cultivars of watermelon in the study of Montalvo and Esnard (1994). Alternative markets for seedless watermelon are explored for better prices and profitability to the farmers. The expected improvement in income will strengthen the economic status of the producers.


Materials and methods:

The research and demonstration studies have been conducted at the Piedmont Complex for Agricultural Research and Extension Demonstration (PCARED) at N. C. A&T State University in Greensboro, (Guilford County) NC; The Randolph Farm (RF) of Virginia State University in Petersburg, VA; Mountain Horticultural Crops Research Station (MHCRS) of North Carolina State University, Fletcher, NC; the farms of Hilton Parker and D.L. Tuttle in North Carolina and of Dallas Graves and Emmett Lowe in Virginia. These sites represent different climates, soil types, marketing options and economic situations. Soil samples from the sites were collected prior to the initiation of the study and physical and chemical properties were determined (Table 1). The field studies were initiated fall 1996 with the planting of four cover crop treatments; Austrian Winter Peas, Hairy vetch, Austrian Winter Peas and Rye, Hairy Vetch and Rye and a non-planted control. In 1997 and 98 Austrian Winter peas was replaced by Crimson Clover due to problems with the peas. The experimental design is a randomized complete block with four replications. In late spring of 1997, the cover crops were mowed down, with a flail mower and left as surface mulch to control weeds, conserve soil moisture and reduce erosion. Transplants of a pollinator and two female parents of watermelon were transplanted in each cover crop treatment. Cover crop plots on the farmers fields (Rockingham and Lenoir counties, and Flecher site) received supplemental fertilizer whereas the A&T site(Guilford county)and Virginia sites plots didn't receive any fertilizer in cover crop treatments except the control. Supplemental irrigation was provided at the Rockingham site (Tuttle's Farm) and Fletcher site. The pests were monitored during the season, and there was no damage by the pests.

Green manure Biomass Yield

The green manures were allowed to grow till early bloom and the biomass yields under different treatments were measured and reported in tons/acre.

Seedless Watermelon Yields

At the marketable stage of the watermelons the harvesting was carried out and yields under different treatments were determined and reported in tons/acre. In 1997 most of the melons at the Fletcher site were not mature by September due to cold weather. However, the harvesting was completed and the yields measured and reported as mature and immature. During the 1998 season seedless melon yields were satisfactory at the Flecher site.

Measurement Of Nitrate Leaching

To measure leaching of nitrate(NO3) in-situ, tensiometers and an nitrate electrode were used. The tensiometers were calibrated in laboratory prior to the installation in the field at the depths of 20,40,60,80, and 100 cm. The tensiometers also allowed the measurement of soil hydraulic head. Additional ionic strength adjuster (ISA) solution was added to a tensiometer when its liquid level dropped below the depth for the electrode to reach. Nitrate leaching under the greenmanure treatments and the control were measured during the growing season.

Statistical Techniques

Yields of greenmanure biomass and watermelon under various treatments of green manures at the experimental sites were subjected to analyses of variance using GLM and other procedures of SAS (SAS,1990). Responses from farmers and consumers were subjected to reliability analyses by SPSS (Norusis, 1993).

Research results and discussion:

Guilford, Lenoir, and Rockingham Counties (North Carolina):

Greenmanure biomass yields were not significantly different under the greenmanure treatments (Table 2) at the three sites.

Yields of seedless watermelon under different greenmanure crops were not significantly different (Table 3) in Guilford and Rockingham counties, but some differences were observed at the Lenoir site. In Guilford the watermelon yields were highest under Hairy Vetch. At Rockingham site the melon yield was highest under Austrian Winter Pea and Rye mixture.

In general the melon yields were highest under Hairy Vetch in Guilford, and lowest in Hairy Vetch and Rye treatment. In Lenoir, the melon yields were highest under Hairy Vetch and Austrian Pea and Rye treatments and lowest in Hairy Vetch and Rye. At Rockingham site highest yield of watermelon was recorded under Austrian Pea and Rye mixture and lowest in Austrian Pea. The melons were marketed at the Triad Farmer's Market and the roadside stands in Kinston area. The quality of the melons was very good and liked by the consumers.

Nitrate Leaching

Data of hydraulic heads and nitrate nitrogen concentrations observed under the different treatments were statistically analyzed. The correlation coefficients between the two parameters were not significant. However, nitrate nitrogen contents in soil solution were mostly related to (1) decomposition (nitrification) of the mulch, and (2) nutrient uptake by the growing watermelon biomass. The evolution of nitrate nitrogen contents were presented in Figure 1. In the initial stage (before 29th July) the activity of decomposition was relatively inert. As the decomposition started, a rapid accumulation of nitrate nitrogen occurred in the soil solution. This accumulation resulted in an increase of nitrate nitrogen (between 29th July and 8th August) in the entire 100cm soil profile until watermelon biomass started its rapid uptake of nitrogen. Most of the nitrate nitrogen for watermelon growth was from the top 20cm soil, some from 20-40cm depth. The watermelon rarely used nitrogen from 60cm depth and below. However, a decrease of nitrate nitrogen in soil solution below 60cm depth occurred after August 8th. This implied a tendency of nitrate nitrogen leaching. Then a steady accumulation of nitrate nitrogen in soil solution below 60cm depth was observed. After the watermelons were harvested (September 10th), decomposition of mulch was still under progress. Nitrate nitrogen in the soil profile resumed its pace of accumulation and leached to deeper soil. The content of nitrate nitrogen was 15mg/L at 100cm depth. It indicates a potential risk of nitrate leaching when crop uptake could not keep up with the release of nitrate nitrogen from mulch decomposition. It was also observed, each rainfall event caused a sudden decrease of nitrate nitrogen in soil solution at depths of 20-60cm, but did not affect nitrate concentration below 60cm depth. Typical nitrate nitrogen profiles at various phases of mulch decomposition and watermelon growth were presented in Figure 2. Curve 1 shows nitrate nitrogen content in soil solution decreased as soil depth increased at the initial stage of mulch decomposition. Curve 2 shows higher accumulation of nitrate nitrogen in the soil solutions of top layers when mulch decomposition started to release nitrate nitrogen and watermelon growth did not have a great demand for nitrogen. Curve 3 shows watermelon growth utilized most of the nitrogen from the top 20cm soil. Curve 4 shows nitrate started to build up in soil profile after watermelons were mature.

Petersburg, James City County, and King William Counties (Virginia):

Cover crop Biomass

Cover crop growth was adequate and biomass production satisfactory. However, due to problems with seed germination and transplanting equipment, the watermelon plots could not be established in the 1997 season. The situation was communicated to SARE office during midyear review. The Virginia State University decided to abandon these plots and to make fresh start during 1997-98 season. The current plans encompass conduct of these experiments for two years, as proposed originally using VSU resources.

For the 1997-98 crop season, the five cover crop treatments (Hairy Vetch (HV), Crimson Clover (CC), HV+RYE, CC+RYE, and a bare ground control) were planted as a RCBD with four replications (20 main plots). The field plot design is set to accommodate planting of watermelon varieties (two females and one male) in each of the 20 main plots. These experiments were planted on September 19, September 23, and September 24, 1997, respectively at Petersburg, King William County, and James City County (Virginia). The Austrian Winter Pea (AWP) was replaced with Crimson Clover due to lack of winter hardiness in currently available AWP cultivars. The growth of cover crops is satisfactory.

In the 1998-99 season the cover crops were established at Petersburg and Prince George County in Virginia. The watermelon seedlings were transplanted in the third week of May 1999.

The seedless watermelon yields are presented in Table 4. At Petersburg and James City County locations, the four cover crops treatments had significantly higher (P = 0.05) number of fruits, per acre, fruit yield and fruit sizes compared to control. The fruit yields and numbers at King Williams county were similar to the other Virginia sites, however, the fruit size was different.

Watermelon Quality Analysis

Virginia State University conducted the watermelon quality analysis on the melons supplied by A& T and Rockingham sites. The data on whole melon weight, sugar and moisture content of meat and rind after storage at 7 C for 14 days is presented in table 4.

Fletcher Site (N.C.):

Yields Of Watermelon

During the 1997 season the melon crop was not satisfactory. However, 1998 crop was satisfactory and the yields are presented in Table 7.

All total season yields factors, for both seedless and seeded melons, were significantly higher for the cover crop treatments than for bareground. For the entire study, there was only one significant interaction. It occurred for the number of seedless melons produced over the entire season. The interaction appears to be the result of the unusually low number of melons produced by A&C 2532 grown on hairy vetch + rye.

It is quite clear from the 1998 data that cover crops were extremely beneficial to the production of watermelon, both seedless and seeded, in Fletcher. As was the objective of the test, we attempted to provide for most of the crop nitrogen needs with cover crops. Except for a very small amount of fertilizer added early in the growing season (25lbs N/A and a nominal amount with a foliar feed), this was accomplished. I don't know how these yields compare to the other test sites. I do know they are low compared to seedless watermelon yields from trials in the Kinston, NC area. Due to environmental factors, however, watermelon yields in western NC are not expected to be more than the state average without use of some practices which will warm the soil and increase early season growth.

Participation Summary

Educational & Outreach Activities

Participation Summary:

Education/outreach description:
Education and Outreach

Other farmers, community groups and extension specialists participated in field demonstrations of cover crops and seedless watermelon production. Consumer preference of seedless watermelon was evaluated by taste panels and found favorable. Test marketing of melons was conducted at Triad Farmers' Market, Winn Dixie and U Crop supermarkets and road side stands. Papers were presented on the production of seedless watermelons at the Sustainable Agriculture Conference in Flat Rock, N.C., High Point, N.C. and Clemson, S.C. American Society of Agronomy Annual Meetings, and Research Symposium of 1890 Land Grant Colleges & Universities. A video is in production on the sustainable cropping system for distribution to farmers and extension specialists.

Project Outcomes

Project outcomes:

The cooperating farmers in North Carolina and Virginia are quite satisfied with the production of seedless watermelons. One of the cooperating farmer is interested in expanding the production to increase his farm income. Some of the extension agents familiar with the study are interested to promote the production of seedless watermelon among their farmers in some counties.


In North Carolina, when seedless watermelons were on the market, 88 participants were contacted to conduct a survey to evaluate the quality and acceptance of the seedless watermelons by the consumers. Forty-nine percent were professionals, forty-four percent were farmers, household individuals, marketeers and others, six percent were cooperative extension agents. Majority of the participants were urban and rural families with 3 to 5 dwellers in their homes. Forty-eight percent of the survey participant had tasted or purchased seedless watermelon before while 52% of them had not or had no knowledge of seedless watermelon.

The survey showed that 80% of the participants enjoyed the flavor and taste of seedless watermelon and rated the flavor “Good” or “Excellent”. Fifty-eight percent of them admitted that they were willing to purchase seedless watermelons from sustainable agricultural systems even at a higher price than seeded watermelons. Consequently, 92% of them showed their preference to buy seedless watermelons when both seedless and seeded watermelons were available.


Areas needing additional study


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Hanlon, E. A., and G. J. Hochmuth. 1992. Recent changes in phosphorus and potassium fertilizer recommendation for tomato, pepper, muskmelon, watermelon, and snapbean in Florida. Commun. Soil Sci. Plant Anal. 23:2651-2665.

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Stivers, L. J., and C. Shennan. 1991. Meeting the nitrogen needs of processing tomatoes through cover cropping. J. Prod. Agric. 4:330-335.

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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.