Craig H. Canaday, Jim E. Wyatt, and Don D. Tyler

The effects of different nitrogen and potash fertilizers on diseases, growth, and yield of no-till and conventional tillage staked tomatoes were evaluated in a factorial experiment that included eight different tillage-nitrogen-potash combinations. The no-till system led to earlier flowering, greater plant loss, more severe early blight, and lower yields than the conventional tillage system. The significantly higher yields with conventional tillage were due in large part to increases in the number of marketable extra-large tomatoes.

West Tennessee silt loam soils are some of the most highly erosive soils in the United States. No-till production of West Tennessee row crops has increased significantly in recent years as growers have learned the advantages of this production system and as UT researchers have developed the management techniques needed for successful no-till production of cotton, corn, and soybeans. Advantages include decreased soil erosion, improved soil structure, increased water infiltration, and more timely access to fields for applying pest management sprays or for conducting planting and harvesting operations. Some of these advantages, e.g. improved soil structure and water infiltration, are not fully realized until no-till production systems have been continuously used for several years.

Most research on no-till production of vegetable crops has not been of a continuous nature. Fields are tilled in the fall to plant a winter cover crop, such as wheat or hairy vetch. The cover crop is killed the following spring with herbicides, then vegetable crops are planted using no-till production techniques. At the end of the growing season, however, the field is again tilled and seeded with another winter cover crop. This research seeks to evaluated the effects of continuous no-till production on diseases, growth, and yield of staked tomato. Effects of other management decisions, such as fertilizer choice, are incorporated into a study conducted at the University of Tennessee West Tennessee Experiment Station in Jackson.

Site description. The soil in the test field was a Calloway-Henry silt loam complex, 0-2% slope with 1% O.M., high soil test levels of available P, and moderate to high soil test levels of available K. The soil contained over 1280 lb Ca/acre, over 64 lb Mg/acre, and ca. 3 lb Zn/acre. Soil pH ranged from 5.8 to 6.9 (fall 1999 soil tests). Pelletized Dolomitic Limestone with a Tennessee Relative Neutralizing Value (RNV) of 98.2 was hand-broadcast Feb 4, 2000, as needed over each 5 x 50 ft. plot at rates recommended by the fall ‘99 soil tests.

Experimental design. The 2000 test was a factorial experiment with three factors: (1) tillage (no-till vs conventional tillage), (2) nitrogen source (ammonium nitrate vs calcium nitrate), and (3) potash source (muriate vs sulfate). Each of the eight possible combinations of these factors was replicated four times in a randomized complete block design.

Tillage. The no-till plots had not been tilled since the fall of 1996 when they were seeded with Kentucky 31 tall fescue, while conventional tillage plots were tilled annually. In the 2000 test, a 'middle-buster' was used to simulate the use of a chisel plow in the latter plots. On March 23, the middle-buster with a single center shank was pulled down the middle of each conventional tillage plot, cutting a furrow 6 - 8 in. deep and 45 ft. long. The center shank was then removed and the remaining two shanks mounted on the toolbar 32 inches apart (16 in. on either side of the former center shank). The middle-buster was then pulled thru the plots a second time with this new configuration, creating a ridge down the center of the plot and cutting two new furrows 5-6 inches deep on either side of the ridge. Hand rakes were used to pull soil tossed outside the conventional tillage plots by the second pass with the ‘middle-buster’ back into the plots (i.e., off the undisturbed grass beside the plots). A small disk was run over the plots (twice) to cut-up large soil clods and to reduce the height of the ridge. After all operations were complete, the plots appeared as a tilled strip, 6 ˝ ft. wide, with a low ridge, 2 - 3 in. high, down the center of the each plot.

Fertilizers. The first application of nitrogen to both no-till and conventional tillage plots was on Apr 6, three weeks before setting transplants, at 15 lb N/acre as a broadcast strip down the center of each plot. Nitrogen was applied seven additional times to both conventional and no-till plots at 6 -10 day intervals as sidedressings at 15 lb N/acre per application. All plots were fertilized twice with potash at 30 lb K₂O/acre per application, once one month before setting transplants and again as a sidedressing one month after transplanting.

Cultural practices. Herbicides, supplemented with occasional mowing or hand-hoeing, were used for weed control. Roundup-Ultra at 1.5 quart/acre (a 2.0% solution) was applied to no-till plots on March 14 in a 30-inch-wide band. Roundup-Ultra at 1.5 quart/acre was applied to both no-till plots (as a 30-inch band) and conventional tillage plots (as a 42-inch-wide band) on April 13. A third application of Roundup-Ultra (a 2.0% solution) was applied as above to both conventional and no-till plots in the morning of April 27 to kill emerging yellow nutsedge and an infestation of Bermuda grass.

The test was planted in the afternoon of April 27 with ‘Mountain Fresh’ tomatoes (18 six-week-old transplants/row) using a modified mechanical transplanter. Plants were suckered once. Plots were irrigated as needed to avoid moisture stress and to help dissolve sidedressed fertilizers using a drip irrigation system consisting of 0.5 gallon/hr emitters spaced every two feet along side tomato rows. Plants were tied to stakes using a modified ‘Florida weave’.

Sencor 75 DF at 0.67 lb/acre was applied as a directed spray on May 30 to 15-inch-wide bands on each side of no-till rows and to 45-inch-wide bands on each side of conventional tillage rows. Poast at 1.5 pint/acre was applied on June 8 as a directed spray to 15-inch-wide bands on each side of tomato rows.

Fungicides were applied five times using a hydraulic sprayer: four applications of Quadris 2.08 SC at 5.8 - 6.0 fl oz/acre/application (on May 15, May 29, June 22, and August 8) plus one application of Bravo WeatherStik at 1.0 quart/acre (on July 17). Insecticides were applied five times: SpinTor 2SC at 5.8-6.0 oz/A on May 29, June 2, July 17, and August 8 and Asana XL at 7.0 fl oz/acre on June 22. All fungicide and insecticide sprays were applied at 300 psi using a hydraulic sprayer equipped with two to three ceramic, hollow-cone drop nozzles on each side of rows.

Tomatoes were picked 2-3 times/week from June 23 through August 1 at the 'breaker-stage' of maturity (12 harvests). A final (13th) harvest of all green tomatoes of marketable size remaining on plants was made on August 3. Harvested tomatoes of marketable quality were graded by size into four categories: small (7 x 7 boxes), medium (6 x 7 boxes), large (5 x 6 boxes), and extra-large (4 x 5 boxes). Yields (boxes/acre) in the following tables area based on 3600 plants/acre. Small tomatoes were considered unmarketable and are not included in yield tables. All disease, growth, and yield data were subjected to analysis of variance (ANOVA) for a factorial experiment with a randomized complete block (RCB) design.

Three tomato diseases were observed on the West Tennessee Experiment Station during the spring and early summer of 2000. An outbreak of Sclerotinia stem rot (white mold) appeared in early May and eventually killed many plants. Disease losses were significantly greater on no-till than on conventional tillage plots (Table 2). Tomato spotted wilt virus appeared in late May and killed or stunted an occasional plant. In mid-August, severe defoliation was occurring in many plots. Most of this defoliation was due to early blight, some to drought stress, and some to plant death due to southern blight. Early blight was more severe on no-till than on conventional tillage plots. Use of calcium nitrate instead of ammonium nitrate made a minor, though significant, decrease in defoliation (Table 2).

None of the factors studied in the 2000 test appeared to affect plant height (Table 1). Flowering was slightly advanced in no-till plots on May 11 compared to conventional tillage (Table 1). The earlier senescence of leaves and flowers in these plots may have contributed to the plant losses to Sclerotinia sclerotiorum by providing infection sites.

Marketable yields were significantly higher with conventional tillage than with no-till (Table 3). This was largely due to significant increases in the number of extra-large tomatoes. The yield advantage with conventional tillage appeared early and continued throughout the season (Table 4). None of the other factors in the 2000 test led to significant differences in marketable yields.

The 2000 test was the first year in the study in which significant disease losses were noted early in the growing season. The yield advantage of conventional tillage over the no-till system may be due in part to these disease problems. Plot yields, however, were divided by the number of healthy plants in plots on August 1 to determine the average yield per plant.

These plant-adjusted yields were then multiplied by 3600 plants per acre to determine plot yields for data analyses and tables. Clearly, some additional factor(s) other than stand losses contributed to the lower yields with the no-till system. Additional tests and analysis of supplementary soil structure data may help resolve this question in the coming years.

Table 1. Effects and interactions of tillage method, nitrogen source, and potash source on plant height and flowering of staked tomato, Jackson, TN, 2000.

Table 2. Effects and interactions of tillage method, nitrogen source, and potash source on plant stand, early blight ratings, and disease losses of staked tomato, Jackson, TN, 2000.

Table 3. Effects and interactions of tillage method, nitrogen source, and potash source on marketable yields of staked tomato, Jun 23 - Aug 3 (13 harvests), Jackson, TN, 2000.

Table 4. Effects of tillage method on marketable yields of staked tomato, Jackson, TN, 2000 - by harvest period.