Weed Management in Organic Sweet Corn and Edamame Soybean
Introduction
| Organic growers need reliable weed management techniques. Organic standards prohibit the use of synthetic herbicides, but allow a range of tools (physical controls), and at least one natural herbicide (chemical control), as elements of an integrated organic weed management program. These are usually used in combination with cultural controls, such as crop rotation and cover cropping. |
Corn Gluten Meal Corn
gluten meal, sold as a herbicide for organic growers,
was
one of the materials used for weed management in this field-scale
study. Click here to
see results of our complementary studies evaluating its
effectiveness. |
The success of a particular weed management technique may depend on other elements of the organic system. Primary tillage, for example, affects not just soil structure and quality, but also the distribution of weed seeds through the soil profile. Spading machines, used throughout Europe, are becoming popular among US organic growers as a replacement for the moldboard plow and roto-tiller. By thrusting blades in and out of soil, they incorporate cover crop residues and loosen soil without inverting the plow layer.
In 2004 we established replicated research plots to test the effectiveness of six organic weed management strategies used over multiple growing seasons in combination with either conventional tillage or spading. Our main crop were sweet corn (Zea mays L.) and edamame, a type of soybean (Glycine max [L.] Merr.) that is boiled and eaten green as a vegetable.
Objectives
-
Compare the abilities of three cultivation methods, two flame weeding methods, and a natural herbicide to control weeds in organic vegetable row crops.
-
Compare the effects of conventional tillage and spader tillage on weed control in organic vegetable production, and test for interactions between the effectiveness of primary tillage and weed management techniques.
Methods
Three replicate blocks of twelve plots (5 x 10 m) were established using a randomized complete block design on land in transition to organic production at the Kentucky State University Research Farm (Fig. 1). Each treatment was a unique combination of one of two primary tillage tactics (Table 1) and one of six organic weed management strategies (Table 2).
Figure 1. Experiment site, 2005.
| Treatment | Description | Frequency | Picture |
| 1. Conventional (moldboard plow + roto-tiller) | Moldboard plow inverts soil and roto-tiller breaks clods. | Single pass with each implement |  |
| 2. Conservation (spading machine) | Spading machine loosens soil without inverting. | Double pass |  |
| Treatment | Description | Frequency | Picture |
| 1. Control | Hand hoeing | Weekly (weather permitting) |  |
| 2. Rolling cultivator | Tined wheels disturb soil between rows and throw it into rows | Weekly (weather permitting) between crop emergence and row closure |  |
| 3. Spring-tine weeder | Tines comb soil between rows |  |
|
| 4. Flame weeder | Propane torches heat weeds between rows, rupturing cells |  |
|
| 5. Stale seedbed | Full coverage with propane torches | Once, before crop emergence |  |
| 6. Corn gluten meal | Soil amendment with a herbicidal byproduct of corn processing | Single treatment (100 g/m2) at crop emergence |  |
The main crop alternated between sweet corn (2004 and 2006) and edamame soybean (2005 and 2007), with winter cover crops of rye and vetch. Each plot contained six crop rows, spaced 90 cm apart.
Data collection
- Crop yield - At harvest, the marketable portion of each crop is collected from two one-meter-square quadrats spanning the two center rows of each plot.
- Weed pressure - After harvest all weeds are removed from the harvest quadrats, then identified, counted, dried, and weighed.
- Soil quality - Soil samples are taken from each plot three times in the growing season, and analyzed for nutrient content, organic matter content, enzyme activity, labile carbon content, and weed seed content.
