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Watermelons are grown at many different row widths and in-row spacings, but an ideal plant density has not been established. Experiments were conducted at one location in 1993 and at two locations in 1994 in southeastern Oklahoma. Effects of plant density and spatial arrangement on `Allsweet' and `Sangria', two standard-sized watermelons, were evaluated. Beds 0.3 m wide were formed on 0.91-, 1.83-, 2.74-, and 3.66-m centers. Various in-row spacings that ranged from 0.30 to 2.44 m were established at each row width. This resulted in various spatial arrangements of plants with densities of 1500, 3000, 6000, and 12,000 plants/ha. With 1500 and 3000 plants/ha, about one melon was harvested from each plant, and less than one melon was harvested from each plant when the density reached 12,000 plants/ha. Yield (weight/ha) increased with plant density and reached a maximum at 12,000 plants/ha. Isometric spatial arrangements did not produce greater yields than did the more-rectangular arrangement. Weight per melon decreased with increasing plant densities in two experiments, but the decrease was small relative to the increased number of melons/ha.
Poultry litter is readily available in eastern Oklahoma. Poultry litter contains most of the essential elements for plant growth, and has long been used as a fertilizer for various crops. The ratio of N-P-K is about 1-1-1. In some areas, litter has been used excessively, and buildups of certain nutrients have occurred. There are concerns that a buildup of phosphorus (P) will lead to excessive amounts of P in water systems, which will affect water quality. There are also concerns that nitrogen (N) will leach or run off into water systems and also lower the water quality. Oklahoma has enacted legislation that will control how much litter can be applied to a given field, and regulations are being set in place to monitor and control the applications of litter. Studies have been conducted at the Lane Agricultural Center in southeastern Oklahoma over the past 6 years to determine vegetable production and soil nutrient changes when different litter application strategies are followed. In general, poultry litter has produced yields of cucumbers, collards, and corn that are equal to or greater than yields of the same crops fertilized with conventional synthetic fertilizers. Buildups of certain nutrients, particularly P, are occurring. At this time, the buildups are considered beneficial. The highest rate of litter application has resulted in levels of soil P that are about half the maximum amount allowed under present legislation.
A study was conducted in southeastern Oklahoma to determine treatments or combinations of treatments that provided the best weed control and crop yield for watermelon. `Allsweet' watermelons were grown with different combinations of mechanical and chemical weed control. Treatments included naptalam, clomazone, naptalam + clomazone, bensulide, naptalam + bensulide, napropamide, trifluralin, dcpa, ethalfluralin, sethoxydim, paraquat, glyphosate, cultivation, cultivation + hoeing, cultivation + paraquat, cultivation + glyphosate, and one treatment with no weed control. Glyphosate and paraquat were applied as wipe-on when weeds were taller than watermelons. The five treatments with greatest yields were (in descending order) cultivation + hoeing, trifluralin, cultivation + paraquat, cultivation, and dcpa. The treatments with lowest yield were the control, paraquat, glyphosate, and naptalam. A visual rating (0–10, 0 is poor, 10 is ideal) was taken about 5 weeks after seeding. Treatments with a visual rating of 6 or more were trifluralin (9.4), cultivation + hoeing (9.3), napropamide (9.3), cultivation + glyphosate (7.5), cultivation + paraquat (6.8), dcpa (6.7), and cultivation (6.5). With the exception of the cultivation + hoeing, all plots were weedy at harvest time. Suppression of selected weeds by a herbicide usually allowed rapid growth of the remaining weeds.
Large amounts of poultry litter are produced in eastern Oklahoma. Nitrate leaching from stockpiled litter can contaminate water supplies. Poultry producers need additional land for disposal of litter. Poultry litter can be a good fertilizer because it usually contains 2% to 3% N, P2O5, and K2O. The ratio of N: P: K is about 1:1:1. Soils in the area often need fertilizer with about a 1:1:2 ratio for cucumber production. This study was established to determine if poultry litter alone could be used to supply all of the nutrients needed for cucumber production, and if excess nutrients would be detrimental to crop growth. Treatments consisted of two rates of raw poultry litter, two rates of composted litter, and synthetic fertilizer applied in either a single or a split application. Treatments ranged from 112, 112, and 224 kg·ha–1. The greatest yield came from the highest rate of poultry litter. Composted litter did not yield more than raw litter. Splitting the application of synthetic fertilizer did not improve yields over that of a single application of the same material.
Soils in eastern Oklahoma have low N and P levels. The poultry industry in the area produces large amounts of poultry litter. Horticultural producers could benefit from using the poultry litter as a fertilizer for various crops, but many horticultural crops require a fertilizer with a ratio of about 2:1:3 (N: P2O5: K2O). Poultry litter has an approximate ratio of 1:1:1. Poultry litter applied at a rate to supply all needed N or K will supply more P than is needed by the current crop, although low P soils can accumulate significant amounts of P before the P levels are excessive. Poultry litter at different rates and synthetic fertilizers have been applied for 3 years to a field in which cucumbers were produced. Poultry litter rates supplied N at as much as 500 kg·ha–1 and P2O5 at as much as 300 kg·ha–1. Cucumber yields were recorded, and soil tests were conducted three times a year for N, P, K, Ca, Mg, Mn, Cu, Pb, Zn, and Fe. Cucumber yields from plots fertilized with poultry litter were equal to or greater than yield from plots that received commercial fertilizer. There appears to be a trend toward increasing levels of soil P with all treatments. and decreasing levels of soil Zn with all treatments. After 3 years, there is no evidence of detrimental levels of any of the monitored elements.
Wet soils can prevent growers from transplanting tomatoes at the ideal size and age. Experiments were conducted to determine the length of time that transplants can be held before yield is reduced Also, different techniques for holding and hardening plants were compared. Seven ages of `Sunny' tomato plants (4, 5, 6, 7, 8, 9, 10 weeks old at transplanting) were either grown normally, grown with limited water, or grown with limited fertilizer. Plants were grown in trays containing 128 cells, with each cell approximately 3.2 by 3.2 by 11 cm. Water was applied for 3 minutes either once a day or twice a day. Fertilizer (20-20-20) was applied either once a week or once during the entire seedling production period. Transplants were later planted in the field. The experiment was conducted in 1990, 1991, and 1993. The yield response to transplant age was quadratic, with maximum yield occurring with 6, 7, and 8 week old transplants. In general, the greatest yield occurred when water was withheld, and the lowest yield occurred when fertilizer was withheld from the transplants
Watermelon is the major fresh-market vegetable grown in Oklahoma, but growers have few labeled herbicides from which to choose. Grower surveys in Oklahoma have identified weed control as the major production problem facing watermelon producers. In 1995 and 1996, various mechanical and chemical weed control strategies have been explored. `Allsweet' watermelons were grown with various combinations of labeled and unlabeled herbicides, as well as mechanical control treatments. Treatments included bensulide, clomazone, DCPA, ethalfluralin, glyphosate, halosulfuron, napropamide, naptalam, paraquat, pendimethalin sethoxydim, and trifluralin. Certain chemicals were used in combination. Paraquat and glyphosate were used as wipe-on materials. Glyphosate and paraquat could not be applied until weeds were taller than the watermelon foliage, causing serious weed competition. In general, superior results were obtained from hand-weeded plots, trifluralin, and DCPA. Halosulfuron gave superior control of broadleaf weeds, but had a negligible effect on grasses. Napropamide gave good control of grasses and broadleaf weeds other than solanaceous weeds. No chemical, when used alone, gave satisfactory control throughout the growing season. Early cultivation, followed by chemical application at layby, appears to be one of the better treatments.
Watermelon growers are advised to grow melons in a given field no more than 1 year out of 4. Bermudagrass pastures are abundant in the southern U.S., but ranchers are reluctant to destroy a pasture for 1 year and plant it with melons if they must then re-establish a sod. A project was designed to develop a system for growing watermelon in a permanent pasture with only a minimal amount of tillage, and without destroying the established forages in the pasture. The approach is to compare and evaluate several techniques for growing watermelons in strip-tilled areas within a permanent pasture. These techniques include cultivation, plastic mulches, and herbicides applied to 2-m strips separated by untilled bermudagrass. Research was done in 1996 at two university research centers in Oklahoma and Texas. The treatments with greatest watermelon yields, in decreasing order, were black polyethylene mulch, hand-weeded control, photodegradable mulch, biodegradable mulch, cultivation plus sethoxydim, sethoxydim alone, cultivation alone, and the weedy check. At harvest, 63% of the area in the cultivation alone treatment, 40% of the area in the plastic mulch treatment, and 1% of the area in the sethoxydim treatment were covered with a regrowth of bermudagrass. Forage was also collected from row areas of plots. Forage amounts, in decreasing order, were from cultivation alone, weedy check, sethoxydim alone, photodegradable mulch, polyethylene mulch, biodegradable mulch, cultivation plus sethoxydim, and the clean control.
Factors of crop management such as irrigation, cultivation, cultivar selection, and control of insect pests and plant diseases play important roles in watermelon production. To gain a better understanding of how intensity of crop management affects yield, we conducted a comparative study contrasting high and low intensity management in 1997, 1999, and 2000. High-intensity management (HM) included the use of trickle irrigation, black plastic mulch, insecticides, and fungicides, not used under low-intensity management (LM). We examined the effects of management intensity on watermelon productivity, the variation in such effects among watermelon cultivars, and the mediating effect of survival of watermelon plants, abundance of insect pests, and incidence of anthracnose (% leaves with anthracnose lesions). The results indicated that HM produced 100% greater marketable fruit yield per area and marketable fraction of total fruit than LM in 2 out of 3 years. The effect of management intensity on plant survival was related to this effect on yield in 1 out of 2 years, and contributed to the latter by increasing weight and number of marketable fruit per plant under HM. We detected no significant effect of abundance of insect pests and incidence of anthracnose on yield. There was variation in the effect of management intensity on yield among watermelon cultivars in 1 out of 3 years. The triploid `Gem Dandy' showed great differences in yield between HM and LM in 2 years, producing on average 28.9 Mg·ha-1 of marketable fruit yield under HM compared to 14.0 Mg·ha-1 under LM. `Gem Dandy' also produced 100% higher yield of marketable fruit per area, per plant, and marketable fraction of total fruit than the open-pollinated diploid `Allsweet' or the diploid hybrid `Sangria.' Each year during the 3-year study, all three cultivars had a similar density of insect pests, incidence of anthracnose, and plant survival after transplant and at harvest. This study provided information on the collective impact of multiple aspects of watermelon management on yield.