Common questions for wet and unharvested acres

May 3, 2017 - Issue 6

CCC agronomists are getting three common questions with regard to wet fields and unharvested. They are:

1. What if I plant canola on canola acres that are still not harvested?

Farmers who didn’t get the cash return they expected from unharvested canola 2016 fields are wondering about the economics of planting those same fields back to canola in 2017.

The first challenge will be what to do with the crop still out there. What is the state of it? Can it still be combined? If not combined, then what? Alberta Agriculture has a helpful factsheet to help answer these questions.

After that, volunteer canola could be a priority issue. Wait for the first flush to germinate and use a pre-seed burnoff. (Note: Do not spray crop yet to be harvested IF you have any plans to harvest it for food or feed. It will have excessive herbicide residues.)

Once residue from the previous crop is chopped and spread and volunteers are dealt with, here are the rotation considerations:

Canola on canola presents short- and long-term risks for yield and disease in particular. There will likely be an agronomic disadvantage to changing your typical rotation plans in response to this unusual situation. Unharvested canola is still a canola crop, and carries with it the same disease and insect risks as any other canola-on-canola planting.

If a farmer, knowing the costs and added risks, choosing to seed canola on canola, then plan for a three- or four-year break from canola afterward and include these management steps:

–Rotate to a different HT system to provide in-crop volunteer management.
–Fertilize as usual, or close to usual based on yield outlook. While nutrients from last year’s crop are still on the field in the seed (if unharvested) and residue, they will not all be immediately available as plant break-down tends to release nutrients slowly.
–Set lower yield expectations. Rotation studies suggest a 10-20% yield loss for canola on canola compared to canola on wheat.
–Watch closely for signs of disease. Clubroot and blackleg are known to be higher risk in tight — especially back to back — rotations.

Many growers have already adopted a rotation plan that maximizes their canola acres. That same decision making process should still be applied in 2017 to maintain a workable and efficient crop rotation plan for 2018 and beyond. Canola on canola is tough to manage normally, but with this year it will be even more difficult with the high amount of volunteers and challenges for residue management and timing of operations.

2. What can we expect for seed mortality in excessively wet soils?

In cool wet soils, mortality rates should be higher — given that cool soils slow germination and emergence, which increases the exposure to seed and seedling pathogens that cause rots and blights. Saturated soils also increase mortality.

But as cool, wet soils turn to warm, moist soils, conditions become optimal for very low mortality (high survival) rates.

For improved return on the seed investment, waiting for these conditions would be preferable — as long as seeding occurs by mid to late May.

Considerations:

—Fertilizer catch up. With minimal fall fertilizer applied due to the late harvest, farmers in systems that usually rely on fall applications will have to find new application alternatives this spring. Seed-placed nitrogen can damage seeds, and although moisture does reduce the risk from small amounts for seed-placed N, note that other factors are already putting stress on the seed and seedlings. Ideally, apply only phosphate in the seed row and at rates no higher than 20 or so lb./ac. of phosphate. Seed-placed phosphate will be particularly helpful in cool soils.
—More seed. In high-mortality situations, seeding rates will need to be increased to meet the target stand. (Use the Target Plant Density Calculator at canolacalculator.ca to work through risk factors that influence target recommendations.) Once the economic cut off for seeding rates is reached (each farmer will have a different tolerance for seed investment per acre, but adding one or two lb./ac. is probably the most one would accept), use other tactics to improve seed survival or plan to manage the thin stand closely all year to protect the surviving plants from weed competition and insects.
—Target stand. If seeding into a field with no residue uniformity issues, seeded early enough that maturity in fall is not a concern, weed pressure is light and under control AND no history of recurring flea beetle pressure, then 4-6 plants per square foot is a good economic target density. In fields with less than these ideal conditions, target density can be bumped to 6-8 plants. Larger seed could improve emergence in stressful conditions, but probably estimate only about 10%.
—Seeding options. If wet conditions persist to the end of May, broadcast seeding becomes an option to consider. But keep in mind that if weather warms, conditions could improve quickly and be better than average by mid to late May. Seeding into cool, wet soil can aggravate poor soil seedbed tilth in vulnerable soils like Gray Wooded and Solonetzic, so delay seeding if you can. Reduced packing pressure in this situation is important.

3. What to do about ruts?

Canola Watch dealt with this topic in an earlier article. But a twist is what to do about ruts in fields that are still very wet. The answer: You have to wait. Otherwise you risk making more ruts and compacting the soil.

Waiting for rut remediation could mean late seeding – in which case you may want to have seed of early-maturity varieties or from alternative shorter-season crops on hand.

Canola Watch