Southwest Opener/Rotation Study: The Effect of Opener Disturbance on Weed Populations and Crop Rotations in the Dry Brown Soil

Eric Oliver¹, Bryan Nybo², Dr. Doug Derksen³, and Paul Watson³

¹Saskatchewan Soil Conservation Association, Swift Current, SK

²Wheatland Conservation Area, Swift Current, SK

³Brandon Research Centre, Brandon, MB

Introduction

Direct seeding is becoming more popular with farmers in the brown soil zone as more producers recognize the advantages of this farming system over conventional systems. Diverse rotations are also becoming more commonplace in this area as farmers seek to reduce risk, increase their potential for net returns and to improve soil quality in the process. Research has shown the benefits of a diverse rotation and low disturbance direct seeding in increased yields, seed protein content, soil organic matter, and erosion resistance. Research elsewhere has also indicated that there can be a reduction of certain annual weed populations, such as wild oats and wild millet over time. However, in the dry brown soils, this reduction of weed populations has not been as readily observed. It appears that the relatively low disturbance openers, such as spoons, sidebanders and paired row openers, are causing enough fracturing or movement of the surface soil between the rows to initiate weed growth. As a result, producers have often not observed a significant reduction of weed populations as observed in other soil zones using these openers.

Due to severe moisture limitations in the Dry Brown Soil Zone, the effect of weed pressure is magnified and will have a greater impact on yield than will occur in other soil zones. Weed control is critical for alternative crops such as oilseeds and pulses, especially in the early developmental stages. Since the margin for profit is much narrower for farmers in the dry brown soil zone due to lower potential yields, any advantage reducing the weed populations as a result of the opener will reduce input costs and make the option of including non-cereal crops more viable.

This four-year study, located at near Aneroid, Saskatchewan, is looking at the effect of four single shoot openers (angle disc, knife, spoon, and sweep), with increasing levels of soil disturbance, on four crops (durum, field peas, barley, and desi chickpeas) in a four-year, zero-till rotation. The study will evaluate the effect of soil and seedbed disturbance on weed populations and crop establishment in the Dry Brown Soil Zone. The study will also evaluate the agronomic performance of a diverse, extended rotation, with different levels of soil disturbance.

I would like to emphasize that the results indicated in this study are not specific to any manufacturer of any of the openers. The results would essentially be the same for any knife, spoon, sweep or low disturbance disc opener.

Description of Study

The four openers used in this study include an angle disc (Barton generation I disc), 0.75-inch knife, 2.25-inch spoon and a 12-inch sweep. All openers are on 9-inch row spacings. Field scale equipment was used to seed this study. The four crops (Kyle durum, Delta peas, Harrington barley, and Myles desi chickpeas) are seeded side by side with all four openers seeding each crop and the plots are replicated four times for statistical accuracy. The cropping rotation is a cereal-broadleaf rotation that will simulate a potential rotation that farmers can incorporate into their system. You may note that the rotation includes two pulses and no oilseed crops. This was done to offer a least risk, lowest input option to producers. Single shoot openers were chosen because the majority of farmers moving into direct seeding in the Brown Soil Zone begin with some type of single shoot opener.

One of the unique aspects of this study is that although the crop within each block of openers will rotate (as in a normal rotation), the pots that were seeded with a particular opener will be seeded by that opener for the entire study. This will allow any changes in weed populations over the short and long-term to be observed based on the type of opener used.

The peas and desi chickpeas were inoculated only and no fertilizer was added. 25 lbs/ac of actual nitrogen and approximately 23 lbs/ac of phosphate were applied with the seed to the barley and durum. Soil tests were taken from each plot in the fall of each year and the fertilizer requirements will be applied in the cereal crops each spring. All crops were seeded at 4 mph.

On each plot, weed population counts, crop establishment counts and yields are taken. There is a pre-seeding burnoff treatment with glyphosate and a no burnoff treatment. A no pre-seed burnoff treatment will show any effect of weed germination based solely on the level of soil disturbance each opener generates and the burnoff treatment will show any benefits of this weed control practice on the various openers and crops. Weed counts and crop establishment counts are taken on both treatments, to provide an indication of weed populations and its effect on the crop, based on the amount of soil disturbance occurring in the seeding process. Both the pre-seed burnoff treatment and the non-burnoff treatment will have in-crop herbicides applied as required. Two weed counts are taken. The first weed count is conducted just prior to spraying and the second weed count is taken about five or six weeks after the in-crop spraying treatment. Therefore, there are 128 plots in total. The weed counts involve 20-half metre square counts per plot, in which the numbers of each weed species is recorded. Yields of each crop and treatment are taken with a plot harvester.

Herbicides used included Achieve and/or Buctril M either separately or as a tank mix, depending on type of weeds. Odyssey was used on the peas and only Poast Ultra was used on the chickpeas.

Results

The environmental conditions over the first two years of this four-year study were opposite extremes in that there was a very dry year followed by a very wet year. This allowed us to observe the results under very different conditions. In 1998, although there was a total of 5.65 inches of rain during the growing season, there was no significant precipitation until June 20, which had a devastating effect on the cereal crops. The very dry soil conditions resulted in total surface disturbance with the knife, spoon and sweep. Although the angle disc caused more soil disturbance than expected, it was considerably less than the other three openers and did not fracture the soil between the seed rows. 1999 presented excellent soil moisture conditions for seeding and total growing season precipitation amounted to 14.6 inches. Surface soil disturbance was as expected, with very little with the angle disc and progressively more disturbance from the knife to sweep.

Plant Establishment

Plant establishment numbers of the crop in 1998 reflected the problems with dry soil, particularly with the cereals (Table 1). Even with on-row packing, the knife, spoon and sweep all suffered severe drying down to the seedbed. Therefore, their plant establishment numbers suffered significantly compared to the angle disc, which had superior moisture retention capability. In addition, there was not a big difference in plant establishment numbers of all crops between the burnoff and no burnoff treatments in 1998. There simply wasn't enough moisture for the weeds to have germinated in any significant numbers. As a result of the dry soil conditions, there were significant differences in plant establishment numbers between the angle disc and the other openers. With the exception of the knife on barley and durum (caused by a depth setting error at time of seeding for these two crops), the knife, spoon and sweep had between 35 and 77% less crop establishment numbers in the various crops as compared to the angle disc.

Table 1: 1998 crop establishment (plants/m²⁾.

* In 1998, an error was made in setting the depth of the knife when seeding the cereals, so these two crops were not seeded at the desired depth, resulting in exceptionally poor establishment.

With excellent moisture conditions in 1999, there was much less difference in crop establishment between the openers in the burnoff treatment (Table 2). The angle disc had on average of only between 7 and 16% higher crop establishment numbers than the three other openers for peas, barley and durum in the burnoff treatment. However, the angle disc was the only opener that had any significant difference in crop establishment between the burnoff and no burnoff treatments. This is not surprising since there is no tillage with the angle disc to cause some early weed control.

What the tables don't show is a problem that occurred with the peas on the no burnoff treatment using the angle disc in 1999. Even though the no burnoff crop establishment numbers look acceptable (Table 2), there was enough flixweed pressure to thin out the peas in patches. As a result, as the peas matured and started to brown off, they lodged in these areas. Even though the peas grown are a semi-leafless variety, there were not enough pea plants to hold themselves up. The lodging stopped abruptly at the burnoff treatment, which had good weed control and even crop establishment. This situation did not occur on any of the other openers and reinforces the importance of a pre-seeding burnoff treatment for early weed control with low disturbance disc openers.

Table 2: 1999 crop establishment (plants/m²).

* In 1999, mechanical problems caused no chickpeas to be seeded with the knife and lower than desired seeding rate for the spoon.

First Weed Count

The first weed counts are taken just prior to the in-crop herbicide treatment. In both 1998 and 1999, the dominant weeds were wild oats, buckwheat, and flixweed. In the no burnoff treatments, the flixweed had an impact on establishment in the pulse crops. Due to the very dry soil conditions in 1998, there wasn't much difference between the burnoff and no burnoff treatments or between all openers, with the exception of the spoon on chickpeas (Table 3). This was mainly due to an exceptionally heavy infestation of wild oats on the one plot. Outside of that one exception, all the weed populations were under 5 weeds/m2 on the burnoff treatment. Although the no burnoff treatment had higher initial weed populations, they were not exceptionally high either.

Table 3: First weed count showing weed density (weeds/m²) of all weeds in 1998.

With excellent moisture conditions in 1999, the weeds had no problem germinating. Table 4 indicates that on average, the angle disc initiated less weed growth in the four crops in the burnoff treatment. Although the angle disc and knife show a relatively consistent level of weed populations over the four crops, the angle disc has much lower weed populations. The spoon and sweep had much more variability in weed populations in the four crops. Table 4 also illustrates how important a burnoff is for low disturbance disc openers when there is adequate moisture available to initiate weed growth, since there is no tillage to create some weed control.

Table 4: First weed count showing weed density (weeds/m²) of all weeds in 1999.

Second Weed Count

The second weed count was taken approximately 5 or 6 weeks after the in-crop spray treatments. Each plot was evaluated as to whether the weed population warranted a herbicide treatment. Unfortunately in 1998, no significant precipitation occurred until after the in-crop spray treatment. As a result, the effect of the herbicide treatment for weed control was minimal that year. The majority of the weeds germinated after the in-crop spraying treatment. However, there was still a trend that the angle disc produced fewer weeds than the other three openers.

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Table 5: Second weed count showing weed density (weeds/m²) of all weeds in 1998.

Due to the depth setting error, extremely poor crop establishment resulted in no crop competition in the durum and as a result, very high weed population occurred.

As noted earlier, there was some mechanical problems during the seeding of the chickpeas that resulted in losing the knife opener results for 1999 and some of the chickpea plots seeded with the spoon had the same problem. This resulted in the chickpea plots seeded with the spoon having a less than desirable seeding rate. However, the overall trend of lower weed populations in the angle disc plots still occurred as compared to the remaining openers in the burnoff treatment (Table 6). It does make sense that the openers causing fewer weeds to grow initially, the weed density after the in-crop herbicide treatment should also be lower, compared to those openers causing higher initial weed densities. I would like to emphasize that the in-crop herbicide treatment was excellent and although some of the weed numbers may seem somewhat high, the majority of the weeds in all the crops were no taller than two or three inches. The combination of in-crop spraying, crop canopy, and crop competition resulted in excellent weed control.

Table 6: Second weed count showing weed density (weeds/m²) of all weeds in 1999.

* Caused by mechanical problems.

Yields

Yields were taken with a plot harvester over the entire length of each plot.

Chickpeas:

Although 1998 was generally dry, the angle disc produced a significantly higher yield than other three openers in the burnoff treatment (Table 7). The knife, spoon and sweep all have very similar yields. This trend is the same in the no-burnoff treatment. This similar yield between the burnoff and no-burnoff treatments is likely due to the very dry conditions, resulting in very few weeds being emerged at the time of the pre-seeding burnoff (Table 3). Therefore, there is little difference in yield between the burnoff and no-burnoff treatments. Although we are missing the 1999 knife data for the chickpeas and the spoon had lower than desired crop establishment due to mechanical problems during seeding, the trend remains similar to 1998 with respect to chickpea yields in the burnoff treatment (Table 8).

Peas:

The pea yields for all the openers in 1998 were not significantly different (Table 7). This perhaps surprising lack of difference, is likely related to the fact that the peas were advanced far enough before the weeds began to emerge. As a result, there was little adverse effect of the weeds on the pea yields in 1998. Peas, although not a great weed competitor, are better competitors than chickpeas. Therefore, there is a different yield response in peas than in chickpeas in 1998.

With the excellent moisture conditions in 1999, there was significant weed populations emerging early on. Due to the angle disc having a lower weed density than the other openers, the trend in 1999 was that the angle disc had a higher yield over the other three openers (Table 8). There was little difference between the pea yields of the knife, spoon and sweep in 1999. The angle disc suffered a significant reduction in yield in the no-burnoff treatment as compared to the other openers, reinforcing the importance of the pre-seeding burnoff.

Barley:

In 1998, the barley yields were severely affected by the drought conditions at time of seeding (Table 7). Very low yields occurred with all openers. However, the angle disc did have significantly higher yields than the knife and spoon. Although the angle disc produced a little higher yield than the sweep, statistically, there was no significant difference between them. Once again, due to the incorrect depth setting of the knife, it resulted in very poor emergence and as a consequence, yielded very poorly as well. For 1999, there was little difference between the yields of all openers (Table 8). Although the angle disc does appear to be slightly higher, it is not likely a significant difference. This lack of significant difference in yields is likely a result of a combination of good in-crop weed control and a competitive crop like barley, which develops a canopy quite quickly.

Durum:

Durum yields in 1998 were significantly different between all the openers, with the angle disc having the highest yield, then the sweep, then spoon, and then the knife (Table 7). As with the barley, the incorrect setting of the seeding depth of the knife resulted in very poor emergence and yield in 1998. All the 1998 yields in all openers reflected the effect of the drought conditions that year. For 1999, there is very little difference between the yield of the various openers (Table 8). The reasons for the lack of significant difference in yield between the openers in durum would be the same as the barley.

Table 7: Crop yields in bu/ac for 1998.

Table 8: Crop yields in bu/ac for 1999.

Comments

In 1998, there was a very noticeable difference between the angle disc and the other openers. Observations after seeding in 1998 showed little soil disturbance with the angle disc, but severe surface disturbance with all three of the other openers. Even the knife fractured the whole soil surface between the seed rows. This resulted in weeds being initiated between the rows as well as in the rows, with the knife, spoon and sweep. The soil also dried down to the seedbed almost immediately in the cereal crops with these three same openers. The angle disc, due to its low disturbance characteristics, conserved considerably more soil moisture than the other three openers. In addition, it tended to have noticeably fewer weeds as well.

The wet 1999 season showed a distinct trend of lower weed populations with the low disturbance angle disc and the other openers in this study. In addition, initial weed growth showed classic differences between the angle disc and knife as compared to the higher soil disturbance openers of the spoon and sweep. Initial weed growth in the angle disc and knife were essentially just in the seed row, whereas the spoon and sweep had weeds growing not only in the seed rows, but between them as well.

Other differences noted during the past two years of this study was in the case of the peas and chickpeas, they were slightly ahead in development as compared to these same crops seeded with the other three openers. Flowering was earlier and the plants tended to be taller when seeded with the angle disc. The peas showed the most differences in plant height with an average of 3-4 inches taller than the knife, spoon or sweep in chickpeas and 4-6 inches in peas.

Summary

Although we are only half way through this study, some early trends are emerging. The angle disc has an advantage during dry years in conserving soil moisture, results in higher crop establishment, and generally has in less weed problems. During wet years, like 1999, moisture conservation is not an issue and crop establishments are essentially the same, no matter what opener you use. However, there was an increased yield advantage with the angle disc on the pulses in the wet year, which is likely attributed to less weed pressure associated with the angle disc. Pulses are poor competitors, so any weed pressure can have an effect on yield. The cereals, being much more competitive, did not show a significant yield difference between any of the openers in this study during a wet year.

The burnoff appears to be a critical agronomic practice when using the angle disc, or any low disturbance disc opener, since there is no weed control through tillage. We will need to evaluate the effectiveness of the burnoff treatment for the other three openers at the end of the four-year study. It is still too early to determine the differences between the knife, spoon and sweep. The sweep has performed better than I expected, but it should be noted that the crops being used in this study are all coarse grains. If oilseeds were in the study, the sweep may not perform as well, due to problems associated with seeding shallow with sweeps. The knife has not performed as well as expected so far, but the full four years of this study will be needed before more certain performances can be determined.

At this point in the study, the trend is that very low disturbance disc openers can provide some advantages over the other single shoot openers used in this study for the Dry Brown and Brown Soils in wet and dry years. Their low soil disturbance has shown to conserve available soil moisture, reduce weed populations and thereby increase yields. These are short-term results and it is interesting that we are able to see weed reductions in the short-term with the angle disc. It would be worthwhile to see how these openers perform over the long-term, such as 7-10 years. In addition to the aforementioned advantages, low disturbance direct seeding disc openers also leave the soil surface quite smooth, which makes spraying operations in particular, much easier on equipment and the operator. It is also possible that in some years, it may not be necessary for an in-crop herbicide application or only spot spraying may be required if using a low disturbance disc opener in this soil zone. It should be stressed that like any opener, low disturbance disc openers are not suited for every situation or soil zone. The results from this study are reflective of the conditions in the Dry Brown Soil Zone.

Acknowledgements

I would gratefully like to acknowledge the following groups for their funding of this project in 1998. They include Saskatchewan Agriculture and Food, Saskatchewan Soil Conservation Association, Southwest Regional Agriculture Council, and District #4 ADD Board. Funding for this project from 1999-2001 is provided by the Canada-Saskatchewan Agri-Food Innovation Fund. I wish to recognize the work conducted by Dr. Doug Derksen and Paul Watson from Brandon Research Centre for their advice and work on statistical analysis. In addition, I would like to thank Wheatland Conservation Area and Saskatchewan Soil Conservation Association for their work on this study. Acknowledgement is also extended to Allan Oliver (the cooperator), and Jim Pratt, Pat Gerwing, and Trevor Lennox from Saskatchewan Agriculture and Food for their assistance on this project. Also, thanks to Bourgault Industries for the use of their air drill and cart for the 1998 field season.