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Ontario fields below ideal potassium level for soybeans

May 14, 2013, Ontario – Up to 20 per cent of Ontario fields are below ideal levels of potassium for soybeans, according to the OMAFRA Field Crop Report released May 8.

The report, courtesy of the Ontario Soil and Crop Improvement Association, also recaps planting updates for canola, cereals and forages in Ontario.

Planting is 30 per cent complete in southern growing areas and nicely started in northern districts. Begin checking emerged canola every two to three days for flea beetles. Striped flea beetles are becoming more common every year. They are tougher, emerge earlier from overwintering sites than the black crucifer type, feed more aggressively and are more tolerant of seed treatments. Flea beetles prefer warm sunny weather, and high populations can overwhelm a canola field, reducing stand population and causing uneven growth. If conditions are wet and cool, look for feeding damage on the undersides of leaves or for girdling of the stem. If populations are high in slow growing canola, you may not be able to rely solely the seed treatment to provide control. Threshold for control is 25 per cent leaf feeding.

Rye for forage is advancing rapidly, with early planted fields approaching flag leaf stage. Highest protein is achieved at flag leaf, but yields are much higher at later stages. Winter wheat has entered the rapid growth stage with stem elongation underway. Temperatures have been ideal for cereal growth: no high temperatures or warm nights to increase lodging concerns. Nitrogen applications are complete. Advanced wheat is at second node, perfect timing for the first fungicide application: most wheat is at first node. Disease levels remain low. Annual weeds have germinated and herbicide applications are underway, far too late for control of dandelion or winter annual weeds. Manganese and sulphur deficiency are evident on fields with a history of the respective nutrient deficiency. Correct these shortfalls immediately to avoid significant yield loss. Spring cereal plantings are winding up, with quick emergence and excellent stands. Frost seeded cereals have a huge jump this spring, already at the three- to four-leaf stage as other spring cereals just emerge. 

More than 70 per cent of the provincial corn crop has been planted. The crop left to plant is on heavier land that is just now reaching planting condition. Ontario farmers are now equipped to plant 15 per cent of the corn crop per day. There has been a bit of a fertilizer supply issue, or really a logistical issue in getting fertilizer delivered to farms since so much activity has occurred in such a short time span. Farmers are encouraged to plant the crop to achieve optimal planting dates and field conditions, and not delay waiting on fertilizer application but ensuring at least 34 kg/ha (30 lbs/ac) of nitrogen (N) goes down with the planter. Conditions for the crop planting have been near optimal. The earliest planted corn on light textured soils has emerged. With weather conditions to date, expect corn to emerge in seven to eight days. Pre-emergent herbicide application is in full swing. With the rapid emergence of corn watch staging and product labels carefully. Pre-emergent herbicides require moisture to be effective. If rain is not received within five to seven days after application, a shallow cultivation is recommended to activate the herbicides and kill the first flush of very small whitish/green weeds. Most pre-emergent herbicides will not control emerged weeds, especially grasses, even when the weeds are still essentially invisible.  

Alfalfa winterkill is particularly severe in the Ottawa Valley and New Liskeard. There are many options, depending on the calendar date, urgency for short term feed, and forage yield and nutrient quality requirements. Forage supplies are extremely tight, and acreage needs to be increased to rebuild inventories. The best option is to replace the winterkilled stand by seeding a new forage stand in a new field in the crop rotation. Corn can follow the winterkilled alfalfa to take advantage of the 123 kg/ha (110 lb/ac) N credit and the rotational benefit of 10 to 15 per cent corn yield increase. A direct seeding can be done, or use a companion crop such as cereals or cereal-pea mixtures. Do not reseed alfalfa into a winterkilled alfalfa stand, unless it was seeded the preceding spring. Autotoxicity reduces the germination and growth of new alfalfa plants for the life of the stand. Nitrogen application can increase yield and protein in good grass stands.

Pasture growth has progressed well over the past week with warm temperatures. Growth over the next couple of weeks will be rapid; this first rotation is when you get your pastures set for the remainder of the season. Do not over graze, leaving three to four inches of grass behind will allow for rapid re-growth and the development of a strong stand. Assess your pasture now to determine if an annual crop will be needed for mid- or late- summer grazing. Sorghum-sudan, brassicas, cereals, annual rye grass or corn are crops to consider.

Soybean planting has started in much of the province. Soil conditions have been excellent in dryer areas and soil temperatures have been ideal. Some growers have finished planting both corn and soybeans. When temperatures are warm soybeans can emerge in less than one week. Glyphosate burndowns should be applied five to seven days before planting to ensure adequate translocation into perennial weeds. If annual weeds are the target, a three-day pre-plant interval is adequate. It’s estimated that up to 20 per cent of Ontario fields are below ideal levels of potassium (K) for soybeans. Applying K before planting is an acceptable practice for fields with low soil test levels. Any field with less than 100 ppm K in soil test results may suffer significant yield losses, especially in dry years. A 50 bu/ac crop removes about 70 lbs/acre of potassium.

May 15, 2013  By OMAFRA/Ontario Soil and Crop Improvement Association


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