April 24, 2012

Agronomists Notes

Hello Reader,

It’s April 23rd and the countryside will be crawling with air drills soon. Ground temperatures have warmed up, hovering between 5 and 10C which is above average and should lead to some rapid emergence. Weed emergence is just starting with the recent warm weather and showers last week which is ideal for pre-seed spray timing.

This week’s newsletter will be brief as most of you are in the field or supporting those who are. We’ll look at some post-seed herbicide strategies in cereals and peas, seeding direction, and canola timing. We’ll also do a little quick math on liming before finishing with technical market news.

Have a great week.

Steve’s quick tips

Ground temperatures are warm, so if you plan on applying a post seed herbicide application, be sure to get in there quickly. Shallow seeded (<1") wheat or barley could begin emerging within 7 days.
The forecast calls for heavy rain on Thursday, April 26th. Avoid applying residual herbicides like PrePass post seeding as there is a risk of florasulam washing into in the furrow and potentially stunting crops.
Germination and emergence should be rapid given the lower residue levels and warmer soil temperatures. If you're comfortable with it, you can reduce your seedling mortality rates by 5% given current conditions. For example, the seeding rate for wheat on a cool soil would be 30 plants ft2 × 35 grams ÷ 94% germ - 15% mortality ÷ 10.4 = 128 lbs/ac. The calculation for wheat on a warm soil would be 30 plants ft2 × 35 grams ÷ 94% germ - 10% mortality ÷ 10.4 = 120 lbs/ac
Don't expect a long residual period with products like Express Pro and Pre-Pass like we've experienced in previous years. Warm soil temperatures with adequate moisture speed the breakdown of residual herbicides.
If you plan on heavy harrowing this spring, be sure it’s not recreational. A sure-fire way to stimulate weed growth is to tickle them with iron prior to seeding. I've seen a 3ac patch of wild oats turn into a 150 acre patch with one spring heavy harrow. SL

Soil temperature and germination

The soil temperature has been relatively warm in our area with the last few days above 20C really ramping things up. The germination chart here shows that soil temperatures are in the ideal range for all crops to germinate quickly.
Keep this in mind when you’re planning a post herbicide application or planting. Seeding peas and malt barley back to back may have you in a bind at harvest when they mature at the same time. Good luck out there! SL

Source: Alberta Agriculture

Post-seed herbicide strategies

Are you wondering if spraying after seeding might be a better fit on some of your fields? Post-seed herbicide options can be effective but there are a few things to consider.

Openers with high soil disturbance, seeding speed and moisture influence soil throw. You may cover emerged weeds with soil which can lead to herbicide misses and strips across the field.
Rainfall shortly after application can wash residual products like PrePass into the furrow and stunt wheat or barley. Watch the forecast closely and try to avoid sandy land and low organic matter soils which are more prone to leaching.
Express Pro is not supported in a post-seed application but if it is used, there is a leaching risk if it rains heavily after application.
If you miss the post-seed window in cereals and the crop begins to emerge you can follow up with Express SG + surfactant at the 1 leaf stage.
With peas you can apply Heat and CleanStart prior to ground crack. Heat is registered in a post-seed application but CleanStart is not at this time. SL

Can I seed canola next week?

If you plan on seeding canola next week, here is what I suggest. First, understand that seeding canola as shallow as we do with soil temperatures between 5 and 10 degrees will trigger some emergence within seven days. If you look at the chart, 50% of the plants will emerge within 5 days when average soil temps are 16 degrees and 16 days if soil temperatures average 4 degrees. We're somewhere in between that so you can expect 50% emergence within 7 to 10 days.

If it was April 25th and I was planning on seeding canola, I would look at the long term temperature forecast and identify any hard frost events (-3 C) or cold fronts moving in. If the frost or cold front coincided with the 50% emergence mark, then I would hold off seeding for a few days. For example, it's April 25th, soil temperatures are 8 degrees Celsius and it looks like I will see 50% emergence within 10 days. The forecast is for a cold front with lows of -5 C on May 5th and 6th. I would hold off seeding canola until April 30 and target emergence dates thereafter. SL

For a great chart on long term temperature forecasts go to the Weather Network

Pictured above: Predicting seedling emergence on soil temperatures and growing degree days. Source: Canola Council of Canada

Grid sampling reveals major variability in soil pH

I’ve had a chance to review the results of our 5-acre grid sampling on roughly 5,000 acres inside my client base and own farm. What continues to pop up is the high degree in variability with soil pH. As we know, nutrient availability is highly dependent on pH and the grid sampling has revealed some red flags on many fields.

For example, the map you see here is a 425 acre field with pockets of high pH in the NW and east with low pH throughout the center of this field. Low pH can lead to sulphur tie up from elevated aluminum levels as well as a reduction in magnesium, phosphate, copper and boron availability. On this particular field we had sulphur deficiencies in canola show up in 2011 in those low pH areas.

The option I'm looking at for our trouble fields is variable rate lime. The response of wheat, barley, canola and peas can definitely be variable but certainly worth looking at on a small scale to start. I’ve drawn on the experience of a few local agronomists who have used lime and wood ash to reclaim pH’s below 5 and they’ve all experienced a profitable outcome that has lasted a number of years, even after 1 tonne/ac of wood ash.

If you have a field that is not performing and you suspect it may be low pH, it may be a good idea to sample it intensively through grid sampling or a Veris to map out pH. The cost to produce pH maps can be anywhere from $4.00 to $7.50 an acre and can be done anytime between spring and fall.

I can purchase lime from Rogers Sugar for the cost of the trucking, which is the most expensive part. It works out to $22.00 a tonne plus application at $4.00 per tonne. I will be doing tests this fall of 1, 2, 3 and 4 tonnes an acre to see how our soils and crops respond. With the pH map we’ve produced, we can choose a VR application or select the problem areas of the field to treat first.

Let’s run some numbers of the return on investment necessary to lime this field with variable rate.

Lime cost + application: $26.00 per tonne applied at 1.5 tonne/ac
VR Map: $2.50/acre
5 ac grid sampling (macros and pH, EC): $5.00/acre
Acres under 5.5 pH: 120 acres
Total cost: ($2.50 ac + $5.00 ac) + ($26.00 x 120 ac) = $3187.50 + $3120.00
Total cost per acre: $14.84/ac

In this example using variable rate lime, we would need a $14.84 return to break even or a $29.68/ac return to generate a 2:1 ROI. To break it down further we would need an 8 bu/ac increase in wheat inside the 120 acres to break even. In a highly acid soil you may see a return in the first year but more than likely it will be a few years to generate a profitable ROI. Some producers in our area with pHs below 5 have seen consistent yield increases of 3 to 5 bushels on wheat after a wood ash or lime application.

As fields become more acidic over time from direct seeding and applying ammonium based fertilizer, I can see variable rate liming making a lot of sense in the future. If you have fields that just don’t seem to perform as well as others or certain areas that don’t perform well, perhaps you should take a look at intensive pH sampling. You never know what you’ll find. SL

Update and correction on Authority

Regarding the application of Authority (sulfentrazone) prior to seeding peas

Re-cropping restriction: Farmers have experienced no crop injury planting canola 12 months after application unless it’s been a drought year. Nufarm is currently working on reducing the restriction for canola to 12 months after application.
Pros and Cons: Authority is excellent on controlling kochia, even at the lowest rate. As well, Authority controls Russian thistle at the low rate of 88ml/ac as well as cleavers (including group 2 resistant) and chickweed at higher rate of 118ml/acre. Unfortunately volunteer canola control is not great. (The rating of control is >85% control.)
Residual properties: Authority applied at the 32ac/jug rate will provide 60 days of control of kochia and 50 days for wild buckwheat. Kerrie Harvie, NuFarm