Oakes Irrigation Research Site
Carrington Research Extension Center * North Dakota State University
P.O. Box 531, Oakes, ND 58474-0531, Voice: (701) 742-2189, FAX: (701) 742-2700, email: rgreenla@ndsuext.nodak.edu

LIVING MULCHES INTERCROPPED IN VEGETABLES

Richard Greenland

Introduction

Materials and methods

Results summary

Table 65. Living mulch and row spacing effects on living mulch height, ground cover and end of year dry matter for living mulches intercropped in cabbage

Table 66. Effect of living mulch and row spacing on cabbage stand, height, yield and end of year dry matter

Table 67. Living mulch seeding rate effects on percent ground cover and end of year dry matter of living mulches intercropped in cabbage

Table 68. Living mulch effect on living mulch height, ground cover and end of year dry matter for living mulches intercropped in sweetcorn

Table 69. Effect of living mulch and row spacing on sweetcorn stand, height, yield and end of year dry matter

Table 70. Living mulch seeding rate effects on percent ground cover and end of year dry matter on living mulches intercropped in sweetcorn

INTRODUCTION

           In vegetable production, vegetables are planted into a fine seed bed, cultivated, and hand weeded throughout the growing season, and the plant residue is often destroyed at harvest. This leaves the soil open to erosion and reduces soil organic matter, causing deterioration of the soil. Living mulches intercropped with vegetables could help prevent soil erosion and degradation, but if not managed properly they could compete with the vegetables, causing reductions in yield and quality.

           Most of the work done with cover crops in vegetables deals with planting vegetables into an established cover crop that has been partially or totally killed. The cover crop often makes planting of the vegetable crop difficult and requires special equipment. This is especially true for small-seeded crops such as carrot. In this experiment we looked at living mulches planted at the same time or later than the vegetable crop and allowed to grow, unchecked, with the vegetable crop.

           The management of living mulches consists in the reduction of competition between the living mulch and vegetable, while at the same time increasing the dry matter production of the living mulch to as high a level as possible. When living mulches are intercropped with vegetables they can compete with the vegetable for water, soil nutrients, solar radiation and space. Proper irrigation and fertilizers should provide sufficient moisture and nutrients for both vegetable and living mulch, so competition for these elements should be minimal. Competition for solar radiation and space is a function of the size and vigor of the competing plants. A living mulch should establish well but stay small enough not to shade or crowd the vegetable during the early part of the growing season. It should be hardy enough to withstand shading by the vegetable and should grow vigorously later in the season, after the vegetable is harvested, to cover the ground to protect the soil and provide organic matter. The most critical time for competition between vegetable and living mulch is early in the season. Competition studies have shown that if the vegetable is kept weed free for the first 4 to 12 weeks, depending on the vegetable, little, if any, yield reduction occurs from weed growth after that time. We hypothesize that the living mulch would not reduce vegetable yields if it did not compete with the vegetable for the first 4 to 12 weeks, depending on the vegetable. Carrots and onions would need a longer competition-free period than cabbage or sweetcorn. Reduction of competition from the living mulch may be achieved by selecting living mulches that grow slowly or lowly, by planting the living mulch later so the vegetable has a sufficient head start before the living mulch begins to compete with it, or by reducing the planting rate of the living mulch. Planting the vegetable in narrow rows may also give the vegetable a competitive advantage. In our studies we planted selected living mulches with vegetables to see how they would compete with the vegetables when planted at the time of vegetable planting or later. In cabbage, carrot, and onion we also included two row widths to see if narrow row widths gave any competitive advantage to the vegetable. Our objective was to find the right combination of living mulch and timing of planting to protect the soil while not reducing vegetable yield or quality.

           A preliminary study was conducted from October 2003 to March 2004 at the Facultad de Ciencias Agrarias near Balcarce, Argentina. White clover, red clover, common vetch, strawberry clover, and/or barley were planted in cabbage, carrot, sweet corn, and potato. The red clover formed a dense, tall cover. The white clover also formed a dense cover, but it wasn’t as tall. Common vetch grew very tall but did not create a dense cover until later in the season. Strawberry clover did not establish well and we decided it was not adapted for living mulch use. Barley established much quicker than the other living mulches. It was killed with a herbicide when about 6 inches tall. Previous research had shown that this was about the right time to kill the barley to keep it from competing with carrot and direct- seeded cabbage. It may not compete with transplanted cabbage and potato until it is taller. The red and white clovers that were planted early competed with the carrot and reduced yield, but did not reduce transplanted cabbage or sweetcorn yield. These clovers planted at a later date seemed to have about the right coverage for carrots, but too little for cabbage and sweetcorn.

           A study was established at the Oakes Irrigation Research Site in the spring of 2004. Lessons learned from the Argentina study, such as selection and timing of planting of living mulches, were implemented in this study. We studied living mulches in cabbage, sweetcorn, onions, carrots, and potato, but only the results of the cabbage and sweetcorn will be presented in this report. Adjustments of time of living mulch seeding and species used as living mulches will need to be made as more information is acquired through these experiments.

MATERIALS AND METHODS

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RESULTS

Cabbage study: The hairy vetch that was planted early (four days after transplanting cabbage) grew too vigorously and severely reduced cabbage yield, number of heads, and head size. The red clover planted early also slightly reduced cabbage yield and head size. The white clover planted late had trouble getting established. Hairy vetch and red clover planted late or white clover planted early did not reduce cabbage yield and established a good ground cover by the end of the season. None of the treatments increased total end of season dry matter. The narrow rows had higher head numbers and yield than the wide rows, however, this may have been due to better planting patterns in the narrow rows. We tried to keep the number of plants/acre in both row widths the same, but the planter wheels turned slower while planting the narrow rows and the workers were able to place the plants in the transplanter better than in the wide rows, resulting in a better stand in the narrow rows. Hairy vetch grew faster, taller, covered the ground better, and produced more dry matter than the other living mulches. Red clover was second best in all those areas and white clover was last. Narrow row cabbage reduced living mulch height, ground cover, and end of year dry matter. Planting the living mulch at a higher seeding rate did not usually increase percent ground cover or end of season dry matter.

Sweetcorn study: None of the living mulch treatments affected sweetcorn yield, height, etc. Hairy vetch planted early or late and red clover planted early increased total (sweetcorn plus living mulch) end of season dry matter. The living mulches planted early grew taller, provided better ground cover, and had more end of year dry matter than living mulches planted late. The higher seeding rate increased ground cover for the late planted living mulches but not for the early planted living mulches.

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Table 65. Living mulch and row spacing effects on living mulch height, ground cover and end of year dry matter for living mulches intercropped in cabbage in 2004.

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Table 66. Effect of living mulch and row spacing on cabbage stand, height, yield and end of year dry matter in 2004.

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Table 67. Living mulch seeding rate effects on percent ground cover and end of year dry matter of living mulches intercropped in cabbage in 2004.

¹Seeding rates (in lbs/acre) were as follows: white clover: high - 1.8, low - 1.1; red clover: high - 4.0, low - 2.0;

   hairy vetch: high - 19, low - 10.

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Table 68. Living mulch effect on living mulch height, ground cover and end of year dry matter for living mulches intercropped in sweetcorn in 2004.

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Table 69. Effect of living mulch and row spacing on sweetcorn stand, height, yield and end of year dry matter in 2004.

¹Rating from 0 to 10 with 0 = no plants and 10 = perfect stand.

²Values in this column followed by the same letter are not significantly different at the 0.05 level. There were no statistically

   significant differences between values in any other column.

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Table 70. Living mulch seeding rate effects on percent ground cover and end of year dry matter on living mulches intercropped in sweetcorn in 2004.

¹Seeding rates (in lbs/acre) were as follows: white clover: high - 1.3, low - 0.7; red clover: high - 3.7, low - 2.0;

  hairy vetch: high - 13.2, low - 6.6.

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