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- Author or Editor: S. J. Locascio x
Methyl bromide (MeBr) is an important and effective soil fumigant commonly used to control weeds and soilborne pests. Because MeBr has been implicated as a contributor to the depletion of stratospheric ozone, it is scheduled for phaseout by 2005. This study examined nonchemical and chemical practices as alternatives to MeBr. Off-season flooding followed by a series of soil preplant chemical treatments [MeBr with 33% Pic; 1,3-D mixed with 17% (C-17) and 35% (C-35) Pic combined with Peb; and metam-Na combined with 1,3-D and Peb were evaluated on spring tomato (Lycopersicon esculentum Mill.) and eggplant (Solanum melongena) production in northern Florida. Pest control and tomato and eggplant yields were not significantly different between the flooded and non-flooded control plots. The most effective alternatives to MeBr were 1,3-D and Pic mixtures (C-17 and C-35) combined with Peb. Tomato and eggplant yields for these chemicals were statistically equivalent to that of MeBr. Tomato, but not eggplant, yield and nematode control were poor with metam-Na combined with 1,3-D and Peb in comparison to the other fumigant combinations. Chemical names used: 1,3-dichloropropene (1,3-D); trichloronitromethane [chloropicrin (Pic)]; S-propyl butyl(ethyl)thiocarbamate [pebulate (Peb)]; sodium N-methyldithiocarbamate (metam-sodium (metam-Na)].
Abstract
Four cultivars of cassava (Manihot esculenta Crantz), grown at 4 locations, were analyzed for root starch distribution. Starch and glucose variation among cultivars and locations indicated that both genetic and environmental factors were involved. Glucose content of all tissues sampled was less than 2%. The correlation between glucose and starch was negative in the parenchymatous and pith tissues for all cultivars except ‘HMC-2’. Location seemed to have little effect on starch concentration, which ranged from 23-33% in the central pith, 19-26% in the peel, and 34-44% in the parenchymatous tissue between the peel and the pith. The portion of the root closest (proximal) to the plant had a higher starch concentration than did the distal portion.
Modeling the growth of field-grown tomato (Lycopersicon esculentum Mill.) should assist researchers and commercial growers to outline optimal crop management strategies for specific locations and production systems. A generic crop-growth model (CROPGRO) was previously adapted to simulate the growth of fresh-market tomato under field conditions. Plant growth and development of field-grown tomato, and fruit yields, will be outlined and compared to model predictions for a number of locations in Florida, nitrogen fertilizer rates, and irrigation management practices. Possible application of the model to quantify effects of crop management on crop production will be discussed using simulated yield values for a wide range of environmental conditions.
Abstract
Maintenance of adequate available soil N for bell pepper (Capsicium annuum L.) growth is essential to high production in Florida and requires mulching, fertilizer placement, and timing of fertilizer application. Slow-release N was supplied as sulfur-coated urea, isobutylidene diurea (1BDU), or ureaformaldehyde and was compared at 3 N rates with soluble sources such as urea, ammonium nitrate, and ammonium sulfate on ‘Yolo Wonder’ pepper. In the first season, highest yields and N concentrations of tissue occurred where IBDU and urea were applied broadcast with mulch as compared with band placement. In the second season, broadcast fertilizer placement with mulch was compared with 3 split-fertilizer applications without mulch. Fruit yield was affected by a significant interaction among N sources, N rates, and mulch. Highest fruit yields were obtained with SCU and IBDU applied under mulch at 224 kg N/ha. Leaf N was higher during the season with slow-release N than with soluble N. Soil analyses data from samples taken throughout the season showed that N source and rate significantly influenced the soil available N measured as urea-N, NH4-N, and NO3-N.
Abstract
Experiments were conducted to evaluate the response of carrots (Daucus carota L.) to target plant densities of 39, 59, and 79 plants per meter of band with various row arrangements (2 band/bed with 2, 3, or 4 seeded rows/band with 3.8 to 11.4 cm between rows) on a Landerhill muck soil. Marketable and total carrot yields increased linearly with increased plant density from 24 to 85 plants per square meter. In 2 of 3 experiments, row arrangement significantly influenced yield; greatest yields were obtained when spacing between rows in a band was greater than 3.8 cm, indicating some advantage to increasing the distance between rows. Mean length and diameter of marketable roots decreased linearly with increased plant density. Length and diameter of marketable carrots were influenced by row arrangement in one of the 3 experiments. Carrots grown in rows spaced more than 3.8 cm apart were longer and had a greater diameter than did carrots grown with 3.8 cm between rows.
Abstract
Plant growth and fruit yield were enhanced by broadcast as compared with band applications of either N-P-K fertilizer or micronutrients. Plant dry wt were similar with applications of either CuSO4-5H2O at 4 and 8 lb./acre Cu or complete micronutrient frit (FTE 503) at 30 and 60 lb./acre in 2 seasons. In 1 season, fruit yields were significantly higher where CUSO4 was used. Increases in rate of either micronutrient source resulted in increased fruit yields where applications were broadcast but a decrease where banded. These responses to increased micronutrient rates were related to an increase in micronutrient efficiency with the broadcast placement and to a toxicity with the band placement.
One of the proposed alternative chemicals for methyl bromide is 1,3-D. The most common forms of 1,3-D products are cis- or trans-isomers of 1,3-D with the fungicidal agent, chloropicrin, containing such mixtures as 65% 1,3-D and 35% chloropicrin (C-35). Soil fumigants are commonly applied under a polyethylene film in Florida raised bed vegetable production. Much of the research regarding cropping system effects of alternative fumigants to methyl bromide has focused primarily on plant growth parameters, with little regard to the atmospheric fate of these chemicals. The objective of this research was to determine both the atmospheric emission of 1,3-D under different plastic film treatments and to evaluate effects of application rates of 1,3-D and C-35 on plant pests, growth, and yield of Sunex 9602 summer squash (Cucurbita pepo L.). Results showed that use of a high barrier polyethylene film (or virtually impermeable film - VIF) greatly reduced fumigant emission compared to ground cover with conventional polyethylene films or uncovered soil. Summer squash seedling survival was a severe problem in several of the 1,3-D alone treatments where no fungicidal agent was added, whereas C-35 resulted in excellent disease control at both full and one-half of the recommended application rates for this chemical. Both 1,3-D and C-35 provided good plant stands and higher yields when applied at their recommended application rates. However, all squash yields were lower than typical squash production levels due to late planting and early winter frost kill. Chemical names used: 1,3-dichloropropene (1,3-D); trichloronitropropene (chloropicrin).
Tomato (Lycopersicon esculentum Mill.) was grown to evaluate various chemicals as possible alternatives to methyl bromide as a soil fumigant. Due to pest pressures from weeds, nematodes, and soil fungi, the use of a broad-spectrum fumigant is essential for economical tomato production. Methyl bromide (MBr) is the fumigant of choice for most growers using polyethylene mulch culture. In 1991, MBr was identified to be in a group of chemicals allegedly responsible for depletion of the stratospheric ozone layer. The U.S. Environmental Protection Agency (EPA) has since called for a phaseout of MBr by the year 2001. At several locations in Florida, alternative soil fumigants were evaluated including 98% MBr-2% chloropicrin (Pic) at 450 kg·ha–1, 67% MBr 33% –Pic (392 kg·ha–1), Pic (390 kg·ha–1), 1,3-dichloropropene + 17% Pic (1,3-D+C17) at 327 L·ha–1, and metham sodium (935 L·ha–1). Metham sodium was also applied by drip irrigation as well as enzone (1870 L·ha–1). Dazomet (448 kg·ha–1) was surface applied and incorporated. Pebulate (4.5 kg·ha–1) was incorporated with some treatments. Pic and 1,3-D+C17 treatments provided control of nematodes and soil fungi. With the addition of pebulate, some nutsedge control also was obtained. Tomato fruit yields with 1,3-D+C17 + pebulate and with Pic + pebulate ranged from 86% to 100% of that obtained with MBr treatments. Pest control and crop production were lower with the other treatments than with the above combinations and with MBr. These studies indicate that no one pesticide can provide the broad spectrum control provided by MBr.
Tomato (Lycopersicon esculentum Mill.) was grown with polyethylene mulch at five locations during a total of nine seasons to evaluate the effects of K source and K rate on fruit yield and leaf K concentration with drip and subsurface irrigation. K sources evaluated were KCl, K2SO4, and KNO3, and K rates varied from 0 to 400 kg·ha-1. Preplant soil K concentrations by Mehlich-1 extraction on the sandy soils and loamy sands used in the study varied from 12 mg·kg-1 (very low) to 60 mg·kg-1 (medium). In seven of the eight studies, K source did not significantly influence fruit yield or leaf K concentration. In the other study with subsurface irrigation at Bradenton in Spring 1992, marketable yields were significantly higher with KNO3 than with KCl as the K source. Tomato fruit yield responded to the application of K in all studies. At Gainesville, Quincy, and Live Oak, with drip irrigation on soils testing low to medium in K, maximum yields were produced with 75 to 150 kg·ha-1 K where the K was broadcast preplant. These rates were 25% to 30% higher than those predicted by soil test. At Bradenton and West Palm Beach on soils testing low to very low in K, where all or part of the K was applied in double bands on the bed shoulder with subsurface irrigation, yield responses were obtained to 225 to 300 kg·ha-1 K. These rates exceeded the maximum recommended K rate of 150 kg·ha-1. Tomato leaf tissue K concentrations increased linearly with increased rates of K application, but were not influenced by K source. These data suggest that the recommendation for K on soils testing low in K be increased from 150 to 210 kg·ha-1 and that this increase should suffice for tomatoes grown with either drip or subsurface irrigation.
Nitrate concentrations in the springs and rivers in northern Florida have been increasing, and several state agencies are interested in implementing nitrogen management programs on farms to reduce N entering the groundwater. Watermelon was grown in the first season of a six-season project under various cultural and fertilization programs to investigate the relationship of N management with N leaching. Treatments were a factorial arrangement of two cultural systems (polyethylene mulch with drip-irrigated beds and unmulched, overhead irrigated beds) and three N fertilization programs [N at the extension-recommended rate, N at the commercial-watermelon-producer rate (1.5 times recommended), or N at the recommended rate with 50% of N from poultry manure]. Nitrate in the soil beneath the watermelon crop was monitored at the 2-m depth with porous-crop suction lysimeters and soil sampling. Yields were greater with the mulch/drip irrigation system compared with the unmulched/sprinkler cultural system; however, fertilization program had no effect on yield. Nitrate-N concentrations in the soil solution at the 2-m depth with all fertilizer treatments were only slightly elevated (3 to 5 mg·L-1) above that in the unfertilized soil (< 1.0 mg·L-1) early in the season when no rain fell. Later in the season, soil solution nitrate-N concentrations at the 2-m depth increased to >50 mg·L -1 with the unmulched treatment and with the greater fertilization rate. Polyethylene mulch, drip irrigation, and recommended N rate combined to maintain groundwater nitrate-N concentration below 10 mg·L-1 for most of the production season and only slightly above 10 mg·L-1 during the summer off-season when rainfall was frequent.