What is the Best Time to Roll Soybeans?
Land rolling conserves soil moisture and prepares the field for harvest. Rolling helps level the field and pushes rocks into the ground, improving combine efficiency. Most producers roll immediately after planting, while some wait until the soybeans have emerged. Rolling immediately after planting provides improved seed-to-soil contact and reduces the likelihood of plant injury. Then again, it also increases the chance of soil crusting, hindering emergence. This is especially true if heavy rain occurs right after seeding. Soybean fields that are not rolled avoid this problem and can emerge more quickly. To avoid the issue of crusting some growers choose to roll their fields after beans have emerged. Over the last few years there have also been reports that early season stress from post emergent rolling may shorten internodes, stimulate early season growth and increase pod number, thereby increasing yields. OMAFRA conducted four trials in 2017 to document any yield gains or losses from post emergent rolling. Another objective of the study was to identify the best plant growth stage to roll soybeans after emergence. Two trials were no-till and two were conventionally tilled fields. The treatments applied were:
Rolling was conducted using a 30 inch diameter smooth roller filled with water weighing 450 lbs per foot of roller (Figure 1). All treatments were replicated 3 times. Soybeans were planted in 15 inch rows with a row unit planter. A small tractor with 9 inch wide tires was used to avoid driving on emerged plants with tractor tires. Rolling was conducted in the afternoon when plants are less turgid and recover more quickly from rolling.
Rolling soybeans after emergence provided a small yield gain but only when rolled at the V1 (first trifoliate) leaf stage. When rolling was delayed to the third trifoliate plant stand losses and yield reductions started to occur (see Table 1). Additional research will be necessary to determine the repeatability of the yield gain at the first trifoliate leaf stage since these gains were very small. Yields were similar in no-till and conventionally tilled fields. For those growers that choose to roll after emergence this study provides strong evidence that no yield loss is associated with rolling beans post emergent as long as it occurs at the correct plant stage. Rolling too early may cause significant stand losses. As the beans are emerging (the hook stage) they are susceptible to breaking off. Rolling should not be considered until the unifoliate stage, or even better the first trifoliate. Once beans reach the third trifoliate the stems beak off more easily, killing too many plants (see Figure 2). Rolling in the afternoon when plants are less stiff will cause less damage than rolling in the morning. Also, keep in mind that a smooth roller was used in this experiment. Using a packer is likely to cause excessive damage and should not be used for post emergent rolling.
Figure 1. Soybeans being rolled at the V1 growth stage.
Table 1. Soybean Yield Response to Land Rolling
2017, Bornholm, Lucan and Winchester, 3 replications, LSD = 1.6 (P = 0.25)
Figure 2. Rolling at the 3rd trifoliate resulted in excessive plant stand losses.
Another caution to be noted is that tilled fields sustain more damage since the small plants do not have the protective cushion corn stalk residue provides in a no-till system.
Also, some plants sustain enough damage that the main stem remains bent for the rest of the growing season (see Figure 3). This damage to the main stem did not negatively impact the yield potential of plants. Plants that were rolled twice often suffered substantial damage and did not recover so overlaps should be avoided.
Figure 3. Some plants sustain stem damage that is visible throughout the rest of the growing season.
In summary, a small yield gain was observed when soybeans were rolled at the V1 (first trifoliate) stage. The statistical confidence of this yield gain was weak so further research will be necessary to determine if this gain is repeatable. For producers that typically roll fields immediately after seeding this study provides strong evidence that no yield reductions occur if rolling must be conducted at the first or second trifoliate leaf stage due to changes in the weather.
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