Thomas, who owns a 3,000-acre mixed dryland and irrigation farm near Magrath, Alta., asked me to visit his operation in early June. He wanted help identifying the weeds in three barley fields as well as advice on a herbicide package that would best fit his farm. He also mentioned the plants in one of the barley fields were growing more slowly than the others.
After scouting the barley fields for weeds and offering herbicide recommendations, I felt we also needed to address the growth and development issues identified in one of the fields.
When compared with the other two, the plants in the third field were visibly stressed. For example, the affected plants were slow growing and far behind those in the other fields in development. These stunted plants were much smaller and paler in colour when compared to those in the other two fields, which contained healthy, normal plants.
Furthermore, the plants’ oldest leaves were red to purple in colour, which probably occurred as soon as the crop emerged. The leaves also had purple margins and the plants’ stems and stalks had reddish-purple streaks from the soil surface to the first two leaves. This discolouration was noticed when the crop was entering the four-leaf stage.
Additionally, Thomas and I discovered the affected plants’ roots were smaller, thinner and had fewer root hairs when compared with those taken from the other fields. The ground cover in the affected field was also less than that of the other fields.
Prior to seeding, all three fields were sprayed with a tank mix of Group 9 and Group 2 herbicides for the pre-seed burndown application. Then, the three barley fields were planted the same day; however, the two fields with healthy plants were seeded on winter wheat stubble, whereas the field in question was seeded on canola stubble.
“Could some sort of herbicide residue be causing the plant discolouration and slow growth in this field?” Thomas asked. “Because all three fields were treated the same way.”
Not only were we going to look at the field’s history, but we would be examining fertilizer records, soil test results, evidence of environmental or disease stressors, and anything else we could think of that might be causing the symptoms in the field.
Since barley was planted under both dryland and irrigated conditions, we could immediately rule out excessive or inadequate moisture stress as the cause of the symptoms.
We started reviewing Thomas’ records, such as the affected field’s crop and herbicide histories as well as the crop yields pulled off it. Based on 2016 yields and soil test results from 2017, we calculated fertilizer removal rates for comparison with soil test levels and recommendations. We also examined fertilizer records and soil tests to determine if fertilizer amounts, timing and application methods were correct.
Nothing from these records could account for the damage to the barley plants. Furthermore, the same fertilizer blend was used on all three fields, and no visual sign of fertilizer injury was evident.
Thomas thought the plants’ symptoms may be related to herbicide injury either due to application issues or chemical residue. However, the symptoms present were not typical of herbicide injury. Thomas’ herbicide application records for the previous canola crop and this year’s barley crop also didn’t support herbicide injury as the cause of plant damage.
We examined the plants’ roots for seedling diseases or early seeding stress, but aside from being smaller and thinner than those of the healthy plants, the roots looked normal. The seed planted in all three fields was also from the same source. The plants from two of the three fields emerged normally and were growing well, eliminating the seed as the symptoms’ cause.
Additionally, there was no difference between the fields with respect to seeding operations. Seeding depth was one and a half inches, on average, across all three fields.
When we checked the crop for pest pressure, there was no significant presence of insects, insect feeding or damage. In terms of straw management, more straw was present on the fields seeded into winter wheat stubble, however it hadn’t caused any seedbed issues that spring.
As far as I was concerned, we’d eliminated any doubts I had about the cause of plant injury in this field. With swift action, we could also prevent yield damage.
Crop Advisor’s Solution: Watch for phosphate deficiency on canola stubble
The only difference between the fields was two were seeded on winter wheat stubble and had healthy plants, while the other, injured, field was seeded on canola stubble. This fact also supports the diagnosis of phosphate deficiency.
For example, canola doesn’t form a mycorrhizal symbiotic association between soil fungi and plant roots. Because arbuscular mycorrhizal (AM) fungi don’t colonize canola roots, populations of AM fungi decline for future crops.
With less AM fungi present in the soil, phosphate is not broken down to a useable form as readily as a crop needs in its early growth stages. Root development is limited and access to phosphate fertilizer banded away from the root zone is not available in those critical early growth stages.
Because the previous crop was canola, thus depleting AM fungi in the soil, and the phosphate fertilizer was applied in a mid-row band and not with the seed that spring, the barley plants couldn’t access phosphate in the early stages of development when needed, due to the lack of phosphate readily available in the soil.
Knowing this, Thomas will make the equipment changes necessary to apply fertilizer with the seed rather than in the mid-row band. Applying a starter blend of phosphate with the seed will promote good emergence while alleviating any crop stress at that time.
Phosphate is important for plant emergence and early root development. Good crop emergence and early above- and below-ground growth will provide the best chance for Thomas to obtain his yield goals.
Because Thomas also uses liquid fertilizer, he could spray the crop with a blend including phosphate early in the spring at emergence through the pivot for irrigation (fertigation) or foliar-applied.
When Thomas incorporated liquid fertilizer applications to the barley field seeded on canola stubble, the plants responded well and showed no effects of the slow growth and phosphate deficiency exhibited early on. Because the problem was diagnosed early and treated promptly and correctly, the yield from that field was the same as the other two seeded on winter wheat stubble.
The areas of the three barley fields under irrigation yielded about 110 bushels per acre and made malt grade, while the dryland corners of the pivot fields yielded around 50 bu/ac, but did not make malt grade due to the dry conditions.
Knowing that seeding into canola stubble can present challenges with respect to available phosphate in the spring, scouting early (i.e. at emergence) can prevent nutrient problems like this. Once symptoms are identified, quick action can be taken to feed the crop the nutrients it needs to start growing normally.
Early-season scouting for agronomic issues is vital at emergence so that any challenges to crop development can be overcome quickly to minimize effects on yield. Furthermore, continued scouting once corrective measures have been taken is important to determine if the crop is responding. Don’t assume the treatment has rectified the problem without follow-up scouting.
Bruce MacKinnon, B.Sc., CCA, works for Richardson Pioneer Ltd. in Magrath, Alta.