By Stevan Knezevic, University of Nebraska, Lincoln
Rationale for Research and Goals
Weeds are one of the major yield limit factors in both conventional and organic crop production systems. Controlling weeds in organic farming is especially challenging and requires the use of many techniques and strategies to achieve economically acceptable weed control and crop yields.
Mechanical cultivation is a widely-used method for removing weeds between crop rows (inter-row space). However, that method leaves a strip of weeds uncontrolled within the crop row (intra-row space). Thus, the weeds that grow close to the crop row present the greatest challenge for mechanical weeding, as they directly influence crop yield. A combination of methods is therefore necessary to maintain satisfactory weed control within the entire crop row (both inter-row and intra-row space).
Propane flaming is one of the most promising alternatives for weed control in organic cropping systems. Flaming is a thermal weed control method that can kill weeds within and between crop rows using heat generated from propane burners. Propane flaming should not be a single practice for weed control, other measures are still needed in the tool box of weed management. For example, many organic farmers typically utilize at least 4-5 weeding operations per season, including a combination of multiple cultivation, harrowing, and/or hand weeding. Reducing the number of weed control operations (e.g., trips across the field) can provide significant savings to the production costs and reduce soil erosion.
Research Goal: To determine the level of weed control and crop response to flaming and cultivation conducted up to two times per season.
Materials and Methods
Field experiments were conducted in 2011, 2012, and 2013 at the University of Nebraska, Concord, Nebraska. Corn and soybean were planted in 30-inch rows with a four-row planter in 30-foot long plots.
The weed control treatments consisted of a weed-free control, which was not flamed but kept weed-free by hand weeding; a plot that was planted with crop but not weeded all season; and six weed control treatments that included: cultivation once (fourth leaf [V4] for corn and cotyledon stage[VC] for soybean), cultivation twice (V4 and sixth leaf [V6] for corn, and VC and V4 for soybean), cultivation plus flaming once (V4 for corn and VC for soybean), cultivation plus flaming twice (V4 and V6 for corn, and VC and V4 for soybean), full flaming once (V4 for corn and VC for soybean) and full flaming twice (V4 and V6 for corn, and VC and V4 for soybean).
Flaming was conducted with flame weeding equipment developed by the University of Nebraska, driven at a constant speed of 4 MPH with the ‘four-row full flamer (4-R FF)’ and the ‘four-row flamer/cultivator (4-R FC)’.
The 4-R FF had eight torches shielded with hoods to keep the heat close to the ground and targeting weeds. It uses propane at a rate of 10 gallons per acre (GPA). In the “early season setup” the hoods were kept closed while flaming during the early vegetative growth stages of crops: V4 for corn and VC for soybean. In the “late season setup” the hoods were opened to create a 4 to 6-inch gap between the two hoods, allowing the crop row to pass through the gap.
The 4-R FC was designed by retrofitting flaming torches and hoods onto a Noble Four-Row-Runner cultivator. The hoods are 12 inches wide and centered over the crop row, using a propane rate of 5GPA. Similar to the above full flamer, the hoods were kept closed while flaming at the early growth stages. During late-season flaming, the crop passed through a 4-inch opening (gap) between the two halves of the hood.
Results and Conclusions
Effect of flaming and cultivation in corn
A single cultivation at the V4 stage provided only 33% weed control in corn when plots were rated at 28 days after treatment. This is compared to 92% control with the combination of cultivation and banded flaming conducted twice (at the V4 and V6 stages). Corn cultivated once at the V4 stage had the lowest yield (130 bushels/acre), while the plots with the combination treatment of cultivation and banded flaming applied twice (V4 & V6 stages) yielded 172 bushels (Table1).
Full flaming conducted twice (V4 & V6 stages) resulted in 83% weed control and 160 bushel yields, which were statistically similar to the weed control and yields obtained from the combination treatment of cultivation and banded flaming (Table 1). There was a regrowth of grassy weeds within crop row after full flaming treatments, the reason for 83% weed control rating. There was no regrowth of broadleaf weeds.
Effect of flaming and cultivation in soybean
Soybean plots cultivated only once at the VC stage had only 30% weed control rating compared to the 83% control in the plots receiving the combination of cultivation and banded flaming twice (VC and V4 stages) (Table 2). The combination of cultivation and banded flaming applied at the VC and V4 stages provided only 83% weed control due to the regrowth of grassy species within crop row. There was no regrowth of broadleaf weeds.
There was an initial injury of soybean (data not shown), but the crop recovered well after flaming, regardless of the treatment. Full flaming conducted once at the VC stage resulted in the lowest yield (22 bushels) due to weed competition from subsequent weed flushes. The highest yields were obtained in the season-long weed-free plots (45 bushels) and the plots flamed and cultivated twice at the VC and V4 stages (42 bushels). Full flaming conducted twice at the VC and V4 stages yielded 38 bushels.
In corn, the most promising weed control methods were the combination of banded flaming with cultivation or full flaming, both conducted twice per season, which provided satisfactory weed control of 92% and 83%.
In soybean, the most promising weed control strategy was the banded flaming plus cultivation conducted twice which provided satisfactory weed control of about 83%. An additional weed control operation in soybean might be needed to obtain close to 90% level of weed control.
From a practical standpoint, these results are encouraging and need to be verified further in a larger crop production setting. Reducing the number of weed control operations to only two per season can result in a significant savings to organic crop production.
In both corn and soybean, none of the treatments provided over 95% weed control, suggesting that there is a need for more than two weed control operations per season. Some may argue that such high level weed control (>95%) may not be necessary from both economic and environmental standpoints, and the fact that most organic growers are satisfied with about 90% weed control. In order to achieve such high levels of weed control (> 95%), an innovative combination of weed control tools and timing of their use are needed. Such strategies might be highly dependant on the field-specific characteristics and cropping history. Additional studies are needed to test such a hypothesis.
Dr. Stevan Knezevic is Professor of Integrated Weed Management at the University of Nebraska.firstname.lastname@example.org.
Members of the Flame Weeding Team at University of Nebraska are: Stevan Knezevic1, Avishek Datta1, Strahinja Stepanovic1, and George Gogos2, Brian Neilson2, and Chris Bruening2.
1Haskell Agricultural Laboratory, University of Nebraska-Lincoln, Concord, NE 68728.
2Mechanical Engineering Department, University of Nebraska-Lincoln, Lincoln, NE 68588.