EFFECT OF ROW COVERS AND BLACK PLASTIC MULCH ON THE YIELD OF DETERMINATE TOMATOES|
Dragan ŽNIDARČIČ, Stanislav TRDAN and Jože OSVALD
Agronomy Department, Biotechnical faculty, University of Ljubljana, Jamnikarjeva 101, 1000 Ljubljana, Slovenia. (contact e-mail: firstname.lastname@example.org)
The tomato is one of the most commonly grown fresh market vegetables in Slovenia. But in general this vegetable are more difficult to grow during in last few years because of higher insect populations, climatic conditions are more favourable to diseases, and failure to set fruit because of high temperatures prior to flowering. The lower yield might be partly due to the incomparable cultural practice.
The numerous experiments have reported the benefits of row covers and black plastic mulch in several fruiting crops, but research is limited on response of tomatoes. The combinations of two soil treatments (black plastic mulch, no mulch) by two crop cover levels (polypropylene fibril cover material, no cover) were tested in 2002 and 2003, in order to verify the possibility of improving yield.
Material and methods
The 2002 and 2003 study was located in the Experimental Station of the Biotechnical Faculty in Ljubljana. 'Hector' determinate tomato (Lycopersicon esculentum Mill.), was seeded and kept under greenhouse conditions (15-20 oC; 60-80% relative humidity). The seedlings were irrigated every day and fertilizer solution, 15-11-29 (1 g l-1) was supplied weekly. One week before transplanting, the starter fertilizer (45N-45P2O-45K2O kg ha-1) was incorporated into the soil. The seedlings, at the six-leaf stage, were transplanted to experimental plots in mid to late April. Spacing was maintained at 50 cm between rows and 40 cm between plants with 12 plants/row. Plants were set in 15 cm high by 100 cm wide beds. All beds were uniformly irrigated using a drip system. Additional fertilizer was added through the drip system during the growing season. Peters 20:20:20 and CaNO3 were applied during the experiment via the drip irrigation system to provide a total of 120 mg l-1 N, 80 mg l-1 P2O5 and 120 mg l-1 K2O per week.
The experimental design was a randomized complete block with treatments arranged factorially and replicated four times. The experimental unit consisted of three rows with eight plants in each row. In the experiment black plastic mulch (BPM) was combined factorially with a row cover treatment to give four treatments namely: bare soil (BS), black plastic mulch, BPM with RC (polypropylene row cover) and BS with RC. Black plastic mulch was laid by a mulch applicator to the appropriate treatments. The polypropylene row covers was supported on plastic rods, shaped in the form of an U with the ends pressed into the soil, and spaced 2 m apart along the bed. The dimensions of the cover tunnels were 1 m wide and 60 cm high. Approximately 30 days after transplanting the covers were removed. Other routine cultural operations were the same to all the treatments attended regularly.
Tomato fruits, which were handpicked at the pink to full-ripe stage, were selected randomly from each treatment in the centre rows only. Harvesting was carried out on a weekly basis until fruit set was observed.
Data were collected on total yield and marketable yields. All yield data from the sampling area was converted to a per-hectare basis. Results were analysed using a two-way analyses of variance. Statistical differences were determined using Duncan's multiple rang test at P = 0.05.
Results and discussion
In 2002, yield of all tomato growing practises were generally low. This yield reduction was attributed to the unusually wet weather conditions during growing season. Tomato production in the wet rainy season was not remunerative because tomato were characterised by a high incidence of pests and diseases, low fruit set and poor fruit quality. The cumulative total fruit yield per unit area, with the exception of marketable yield, was significantly enhanced by the use of BPM + RC. The total weight yield in BPM + RC extrapolated to 15.93 tonnes per hectare, while the other growing methods produced the equivalent between 11.65 and 12.49 tonnes per hectare. When marketable tomato yields were compared from the various growing methods, it should be noted, however, that the use of row covers significantly increased marketable yield per unit area. Tomatoes grown in BPM + RC and the BS + RC produced higher yields (6.72 and 7.21 t ha-1, respectively) than those grown in BS and the BPM (4.27 and 4.36 t ha-1, respectively).
In 2003, all growing practises compared to the control (BS), were significant better total and marketable yield. As in other studies, fruits produced on bare soil were more stressed and misshappened than fruits produced on black plastic mulch and under row covers. Both BS + RC and BPM increased total and marketable yield compared to the control. But when the total or marketable yields were compared between BS + RC and BPM, these two cultural practices resulted in almost similar yields. Data suggest that BPM + RC generally favoured tomato yield more than other growing practises. The total (31.01 t ha-1) and marketable (28.72 t ha-1) yield in BPM + RC were significant the best. In agreement with other studies on other crops, this dramatic increase in tomato yield where BPM and RC were used together, is partially due to an increase in air and soil temperatures around the plant-growing environment.
Figure 1: Effects of various growing methods on average total (marketable + cull) and marketable fruit yield of tomato. Means followed by the same small (capital) letter are no significant difference between the total (marketable) yield, level of significance 5%.
In two production season, the different management strategies implemented in the four production systems resulted in significant differences in yield and quality of tomatoes. Under Slovene ecological conditions, black plastic mulches and row cowers used alone or in combination offer the grower a management tool which can increase yield and quality. These growing methods demonstrated the ability to produce the highest yield of tomatoes per hectare. In plants grown with no row cover, the presence of plastic mulch resulted in higher plant yield relative to plants grown in bare soil.
More information is needed about different synthetic mulching materials and/or colours for use in the production of tomatoes. The future use of plastic mulches will be influenced by the advantages to be gained over the use of red and metalized silver coloured mulch.
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