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Research Report  2.7

Crop Rotations and Cover Crop Effects on Erosion Control,
Tomato Yields and Soil Properties in Southwestern Ontario.

R. W. Johnston,
Soil Science and Horticultural Soil Management,
Ridgetown College of Agricultural Technology,
Ridgetown, ONT, N0P 2C0
COESA Report No.:   RES/FARM-007/97

Objectives & Expected Outputs
Executive Summary

View / Download Report  [869 KB pdf]


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Objectives and Expected Outputs
Objectives: To better evaluate the effects of rotations on soil structure, evaluate and measure drainage differences, evaluate differences in moisture holding capacity, and any further improvements in tomato yields. It is also proposed to further evaluate changes in weed, insect and disease control.
Expected Outputs: The first four years of research have shown increased tomato yields by 36-40 t/ha in favour of rotated vs monoculture, tomato quality was improved, water ponding reduced on the soil on rotated plots and increased earthworm activity stimulated in rotated plots.

The effects of rotation and cover crops in place at two locations near Dresden and Leamington could not be fully assessed in such a short time frame. The longer time for evaluation will provide a more reliable recommendation for farmers on proper rotation and cover crop management.
Type: Contribution Agreement, OMAFRA
Spending Profile: 94-95: $50.0 K,     95-96: $50.0 K,    96-97: $50.0 K,    Total: $150.0 K
Status: Available March 1998


Executive Summary

Vegetable production in southwestern Ontario is a high value industry that is primarily based on coarse textured soils under very intensive culture conditions. The tomato crop alone is valued in excess of fifty million dollars per year. The industry is mainly concentrated in this area due to the longer warmer growing season which permits the production of long season high value crops. Competition, mechanization and a limited land resource have resulted in the development of extremely intensive cropping systems.

Mechanization necessary for competitive vegetable production has promoted practices on these fragile soils which reduce soil organic matter, structure, aeration, moisture penetration and storage. Any motivation in crop rotation is economic and not soil related. Scientific documentation on the production of processing tomatoes and its effect on land productivity is not widely available in the literature. In Ontario only one small research project on processing tomato rotations was carried out in the early fifties near Smithfield.

In April of 1989, a large project was initiated by Ridgetown College at two locations near Leamington and Dresden on sandy loam sites to research methods of improving soil conditions on intensively farmed soils and to improve the sustainability of processing tomato yields. To accomplish this objective nine short term crop rotations (1 - 3 years) were set up at Leamington and eight rotations (1 - 4 years) at Dresden. All crops were grown each year to increase data collected. These rotations included high residue crops such as rye, winter wheat and corn as well as forage legumes, red clover, and alfalfa which are historically soil improving crops. Four rates of nitrogen were included ( 0, 45, 90, 135 kg/ha of N) to study carry over nitrogen from legumes. Rates were increased to 0, 60, 120, and 180 kg/ha N at Leamington in 1994 - 1996. Rotation effect was greater at Dresden than Leamington.

Crop rotations, applied nitrogen, and crop residue had a very dramatic effect on tomato yields at both locations giving the following results:

  1. Continuous tomatoes yielded the lowest of any rotation each year at both locations all seven years of the trial.

  2. Marketable processing tomato yields were increased at Leamington and Dresden by 18.0% and 23.5% respectively when grown in rotation compared to continuous culture.

  3. When the best four crop rotations are selected at each location (7 year average) marketable tomato yields were increased by 22.5% and 33.9% over continuous tomato culture.

  4. The best four crop rotations (highest tomato yields) at Leamington were alfalfa-tomatoes (AT), cucumbers-green beans-tomatoes (CuGBT), winter wheat under seeded to red clover-tomatoes (Wus-T) and winter wheat-soybeans-tomatoes (WST). Dresden had three similar best rotations with the winter wheat-red clover-tomatoes replacing the winter wheat under seeded-tomato rotation.

  5. Tomato plug plants growing in the best four rotations at each location had 24.8% and 37.8% more early growth six weeks after planting respectively compared to continuous culture.

  6. Tomato plants retained more leaves and were greener at harvest in rotation than continuous tomatoes or the next lowest yielding rotations; soybean-tomatoes and winter wheat-soybeans-corn-tomatoes.

  7. The greener plants however gave slightly improved (lower) Agtron readings indicating better colour. Rotated tomatoes were approximately 2 points lower in Agtron readings, however, this did not increase monetary value.

  8. Green tomato yields were increased by crop rotation (probably a nitrogen effect) but the proportion of the total yield remained relatively the same as continuous tomatoes.

  9. Marketable tomatoes at Leamington had slightly higher soluble solids of 0.2% to 0.5% and slightly higher total solids when grown in rotation. Although this is not a value added component to producers, it certainly is to processors and is part of grower-processor contracts in the United States.

  10. Nitrogen fertilizer had a very dramatic effect on growth and yield of tomatoes particularly at Leamington. Marketable tomato yield was increased up to the highest rate of nitrogen at Leamington. The difference between 120 kg/ha and 180 kg/ha was not significant but was present 6 years out of 8 and is a profitable response.

  11. 120 kg/ha of nitrogen increased tomato yields 36% over no nitrogen in Leamington. This increase was greater in non legume rotations. At Dresden, 90 kg/ha of nitrogen increased tomato yields 25.0% over no nitrogen. The use of forage legumes lowered nitrogen response at both locations as might be expected; however, tomatoes responded to the first increment of nitrogen (60 kg at Leamington, 45 kg at Dresden) and occasionally to 120 kg at Leamington. This response is probably due to the very early requirement of available nitrogen for early plant growth.

  12. Fertilizer nitrogen increased the yield of green tomatoes but this was not large.

  13. Nitrogen also reduced Agtron readings over no nitrogen giving increased red colour.

  14. Nitrogen increased soluble solids significantly at Leamington but gave a slight non significant increase at Dresden.

  15. Nitrogen soil tests conducted in early May indicated some buildup of nitrogen in rotations, particularly those containing legumes. Nitrogen was concentrated in the 0-30 cm depth at both locations.

  16. A nitrogen soil test used for corn in Ontario did not prove feasible to accurately indicate tomato crop nitrogen requirements.

  17. Tomato plug plants can be grown in high crop residue situations with beneficial results provided a coulter is used to cut through trash ahead of the furrow opener. This crop residue totally reduced the need for replanting due to windblown sand particles.

  18. It would appear from this research that tomatoes were stunted following planting into high grain corn residue. This occurred all years and lasted through to harvest with lower yields at Dresden.

  19. Crop rotation did have a desirable effect on soil physical and chemical properties. Of the rotations sampled, crop rotation had a small non significant effect on percent wet aggregate stability over continuous culture of tomatoes. Visual observation would indicate a wider difference. Seedbeds were much easier to prepare following crop rotation.

  20. Soil organic matter was increased at both locations as well as organic carbon (not significantly) by crop residues.

  21. Crop rotation caused a significant reduction in soil bulk density compared to continuous culture.

  22. Limited data indicated the four best yielding rotations increased microbial biomass carbon significantly over continuous culture at both locations.

  23. Soil moisture holding capacity was increased slightly at Dresden but not at Leamington by rotations.

  24. Limited data indicated the rainfall infiltration rate was increased substantially by crop rotation at Leamington.

  25. Data taken with a handheld penetrometer revealed a solid layer at the 18 cm depth at Leamington and the depth for maximum pressure required to penetrate was considerably deeper for forages, red clover and alfalfa. Alfalfa roots were measured to a depth of 90 cm after one year.

  26. Weed escapes from herbicides used in tomatoes were substantially less following a rye cover crop used in the continuous tomatoes and the cucumber-green bean-tomatoes rotations at both locations. Grass weed escapes were prevalent in tomato plots following red clover and alfalfa, (winter wheat-red clover-tomatoes and alfalfa-tomatoes rotations) at both locations.

  27. Parasitic nematodes (root lesion and root knot) did not appear to build up under continuous tomato culture at both locations. These nematodes increased in numbers substantially after red clover and in some cases soybeans. This fact did not appear to affect yields as those plots containing red clover were some of the highest yielding rotations.

A complete economic analysis cannot be reported as yields were not taken on all crops because of severe budget constraints from 1992 to 1996. Crop rotation had very dramatic effects on soil condition, tomato growth, yield and quality, however, with the high value per tonne of tomatoes ($90.00) economics in favour of rotation are not easily obtained. All vegetable crops are destructive of soil structure because of the low crop residue and intensive cultivation. Although economics are of utmost importance, the long term productivity of these soils are also important.

A companion trial was conducted at the two locations to study continuous tomatoes and ten cover crops from 1990 to 1992. From these trials, rye, ryegrass, hairy vetch, Austrian winter peas and oilseed radish were chosen to be included in a second cover crop trial in 1993 to 1995 where cover crops were planted in three crop rotations, continuous tomatoes (CT), winter wheat-tomatoes (WT), and green beans-sweet corn-tomatoes GBSCT) and at Dresden green beans-peas-tomatoes GBPT after each crop and on fall prepared beds. The previous trial was terminated because of the development of extremely poor soil conditions. The continuous tomato comparison was maintained on a reduced scale.

The results of the second trial were as follows:

  1. Crop rotation increased marketable tomato yields over continuous culture.

  2. Fall beds yielded 2 to 5 t/ha more than spring beds at Leamington only.

  3. Common rye was the cheapest most easily managed effective cover crop.

  4. Ryegrass was not only a very vigorous cover crop but also became a very persistent weed after two years of planting.

  5. It was very difficult to get good stands of hairy vetch, Austrian winter peas and oilseed radish following tomatoes. (The seeding date is too late).

  6. Every trial ran with cover crops (5 years) has shown that a cover crop grown from late August to early May has been beneficial to tomato yields. This effect is not statistically significant but is always there in the range of 2 to 8 t/ha depending on the year and soil conditions. The cover crop is worth $150 to $675/ha in terms of increased tomato production.

The results of these trials indicate for best tomato yield and quality tomatoes could be grown every other year where a forage legume is utilized or once in three years where a high crop residue non legume such as winter wheat is planted. Under no circumstances should the crop residue be sold in the early stages of setting up the rotation. For sustainable field processing tomato and vegetable crop yields, the use of rotation crops with high crop residue is essential. A rye cover crop is also very beneficial for organic matter, soil structure and soil erosion control in intensive vegetable crop production.

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