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Project Title: Nitrogen and Plant Spacing Management for Enhancing Earliness and Concentrating Fruit Maturity of
Processing Tomatoes.
Researchers: J. Warner and T. Zhang, Agriculture and Agri-Food Canada, Harrow.
Objectives: To determine the optimum rate of nitrogen (N) fertilization and plant spacing (including both plant population densities and planting patterns) for enhancing earliness and concentrating fruit maturity of processing tomatoes.
Methodology:
Field experiments were carried out at the Greenhouse and Processing Crops Research Centre, Harrow using small plots and treatments were replicated 4 times (N management trial) or 6 times (spacing trial). Plots were harvested by hand. Leaf chlorosis/necrosis was assessed preharvest using a 0 to 5 rating with a higher rating indicating more disease. Percent fruit infected with bacterial spot and speck and severity of infection (number of spots per fruit) was also assessed at harvest.
Nitrogen management trial: Treatments consisted of 5 nitrogen rates (0, 100, 150, 200 and 250 kg of N/ha) as main plot treatments and 4 cultivars (H9230, H9492, H9553 and CC337) as subplot treatments using a split plot design. From this experiment, fruit samples were sent to Dr. Venket Rao, University of Toronto, to determine lycopene content from the different N rates and cultivars.
Spacing trial: Treatments consisted of 3 row arrangements (single row with 75cm between rows and 2 twin row systems with either 60cm or 40cm between rows) all at 1.5m centres; 2 within row plant spacings with either 40cm or 33cm between plants giving a plant population of 33,300 or 40,400 plants/ha (13,870 or 16,735 plants per acre); and 2 cultivars (H9230 and N1045) using a split split plot design.
Results:
Nitrogen management trial - fertilizer rate effects: In general, plant vigour and total yield increased as nitrogen rate increased from 0 to 250 kg N/ha. With H9230 and CC337, there was no significant difference (P<0.05) in marketable yield when nitrogen rates between 100 and 250 kg N/ha were used. With H9492 and H9553, there was no significant difference in marketable yield when nitrogen rates between 150 and 250 kg N/ha were used. With all 4 cultivars, yield was lowest when no nitrogen fertilizer was applied. With the cultivars CC337, H9492 and H9553, the green fruit yield was unacceptably high at the 250 kg N/ha rate. Based on the marketable and green fruit yields, the 150 and 200 kg N/ha rate provided the best response with CC337, H9492 and H9553. These results were similar to 1999 when the maximum yield was achieved with fertilizer applications in the 150 to 200 kg N/ha range, depending on cultivar. Fruit size, soluble solids, fruit firmness and Agtron colour were not affected by nitrogen rate.
Cultivar effects: H9553 had the greatest total and marketable yield. However, marketable yield for H9230 was similar to H9553 because of a lower quantity of green fruit for H9230 compared to H9553. Fruit size was largest for H9230 followed by H9553. Fruit size was smallest for CC337 and H9492. Soluble solids was greater for H9553 and H9492 compared to H9230 and CC337. H9492 had the firmest fruit compared to the other 3 cultivars.
Disease ratings: The late maturing cultivars, H9492 and H9553, had more bacterial speck on the fruit compared to H9230 and CC337. It is likely that the denser foliage cover with H9492 and H9553 contributed to the higher incidence of fruit speck. The foliage necrosis/chlorosis rating was lower for H9492 and H9553 compared to CC337 and H9230. This was likely because of the more vigorous growth which allowed H9492 and H9553 to keep ahead of the disease. Although there were no significant differences (P<0.05) in the amount of disease between the different nitrogen rates, there was a trend towards more speck on the fruit at the higher nitrogen rates. This is likely due to the denser foliage canopy at the higher N rates.
Spacing trial: Total and marketable yield was greater for the single row system spaced at 75 cm between rows and for the twin row system with 60 cm between rows as compared to the twin row system with 40 cm between rows. Row arrangement did not affect the amount of green fruit, fruit size or soluble solids. Changing the within row plant spacing did not significantly (P<0.05) affect yield, fruit size or soluble solids for either cultivar. There was no difference in yield between the two cultivars, however, H9230 had a larger fruit size and higher soluble solids compared to N1045.
Because of a high incidence of bacterial disease, tomato foliage and fruit was rated for disease. There was a highly significant correlation between the foliar rating and percent fruit infected or fruit disease severity index (r=0.48 & 0.38, respectively, P<0.01). Both fruit and foliar disease was greater in the twin row system spaced at 40 cm between rows compared to the other 2 row arrangements (60 and 75 cm between rows). With the single rows spaced at 75 cm between rows, within row plant spacing also affected foliar disease. A higher foliar disease rating (2.9) occurred with the 33 cm within row plant spacing compared to the 40 cm spacing (2.4). It is likely that the closer row arrangements and plant spacings which had denser foliage early in the season contributed to the presence of disease in this experiment.
The lower yield in the twin row system with 40 cm between rows in 2000 may be due to more disease rather than a competition factor between plants. This trial will be repeated another year to determine long term yield averages for the different spacings.