April 23, 2013

Agronomist Notes

Hello Reader

The snow is slowly melting and spring runoff has come in stages, which has reduced the erosion potential. Stubborn snowdrifts may need to be seeded around in the beginning. I’ve seen photos pop up via Twitter of fields in Saskatchewan still blanketed in 12 inches of snow. Planting dates will be later than normal and I suspect we’ll be 7 to 10 days at the earliest before planting begins, barring any new moisture.

In this issue we’ll look at planting dates and when to bring in a custom-seeding outfit to help out. Next, we’ll look at a canola seed size trial that revealed a large variance in seed size within a bag of certified canola seed. I’ve also included a canola plant density chart that uses seed weights and seeding rates to show plants per ft2. Last, we’ll look at variable rate plant growth regulators and a new approach to using them in grass seed and wheat production. We’ll finish with technical grain market news.

Have a great week.

Photo: C'mon melt! S. Larocque

The Plan B seeding strategy

Planting dates effect on yield

We’re a week away from some of the earliest planting bringing us to April 30 or May 1, best-case scenario. That’s not bad, but if we do get more precipitation or other weather delays we could be looking at a very late start. Most farms are set up to plant all their acreage within 20 days which means we could be running past the optimal planting dates for most crops. For those thinking about hiring custom seeding outfits as a Plan B I thought I’d run some numbers to help in the decision-making.

Steve’s quick math
Let’s calculate the breakeven cost of custom seeding using the Dark Brown soil zone as an example. We’ll compare the cost of custom seeding to the potential yield loss on a 4,000-acre farm seeding 2,500 ac of wheat and 1,500 ac of canola. We’ll assume the custom seeding allows us to avoid 3 days seeding past the optimal wheat window of May 14th and 3 days past the optimal canola window of May 7th. Average yields of wheat are 55 bu/ac and canola 40 bu/ac. The custom seeding outfit can plant 200 acres per day.

Custom seeding: 200 ac x 200 ac/day x $23.00/ac = $4,600/day
Canola: 200 ac/day x 40 bu/ac x $12.50 x 1% = $1,000/day
Wheat: 2,500 ac x 55 bu/ac x $7.25 bu x 1% = $797/day

In this scenario, a custom seeding contractor planting 200 acres a day would cost $4,600 while yield losses would tally just $797 to $1,000 day. In this case it doesn’t make sense to hire a custom contractor. Now, if your seeding window is pushing you past May 21st and you know you can’t finish seeding before then, custom seeding may be worth the added expense to avoid yield and grade loss from frost in September. A May 21st seeding date brings you to a September 10th harvest date, which increases the risk of frost given our average first fall frost occurs September 11th.

The key is to understand when your possible start date is and how long it will take you to put a crop in the ground. If that number is pushing you out of the optimal seeding window or into a frost risk scenario, I’d make arrangements for a custom seeder now before everyone else gets the idea and your stuck on the bottom of the list. SL

Research

Chart above: 'Best before' seeding dates for crop and soil types.

Shedding light on canola seeding weights

Canola seed sizing fundamental to vacuum planter performance

As you all know I’m a stickler for measuring kernel weights. On a typical year kernel weights can vary by 30-50% in cereals in oilseeds. In order to achieve optimal plant stand densities, the starting point is measuring thousand kernel weights. Interestingly enough, the adoption of precision vacuum planters to seed canola has shed some light on the inconsistencies in canola seed weights sold in today’s market. We know kernel weights can vary by 100% between seed lots, but so can the kernel weights within each bag of canola seed!

The adoption of precision vacuum planters has reveled a flaw in the seed weights listed on each bag of canola seed. You see, vacuum planters use 70 to 150 hole disks to meter seed inside a planter box. The holes on the disk have a specific gauge, like 1.3mm for example. Seeds that are larger allow the vacuum to pull the seed on to the hole and keep it there before the deflector knocks the seed off at the opening of the seed tube. Seeds that are smaller than the hole are sucked right through and blown out the vacuum exhaust. Seeds that are the same size as the hole get stuck inside causing it to plug. The trouble today is trying to create a disk/plate that contains holes with the right diameter to avoid blow by or plugging.

Craig Shaw at Lacombe provided the crew at Lacombe Research Station with a bag of InVigor 5440 canola seed to see how much the kernel weights vary. As you can see in the chart, the canola seed was sized with 5/64 and 6/64ths mesh screens and weighed for thousand kernel weights. The percentage of each seed weight and the resulting TKW was also measured. The TKW marked on the side of the bag of InVigor 5440 was 5.19 grams. The results showed that 68.3% of the canola seed was 5.18 grams, 7.9% weighed 3.37 grams and 23.8% weighed a whopping 6.72 grams per TKW. Based on these results, it’s no wonder we’re having trouble trying to singulate seed with vacuum planters. How do you create an accurate hole size when canola seed size varies depending on each bag, each seed lot and each variety?

To break it down further, the study found that 7.9% of the seeds were almost 2 grams smaller than the TKW marked on the bag. These seeds could have been blown out the vacuum exhaust and wasted. A likely scenario could be that the small seeds were the same size as the holes and would be the source of constant plugging. The same could be said of the 68.3% that weighed 5.18 grams. The wrong hole size could lead to serious plugging issues and makes it difficult to chose the correct hole size. Is it 1mm, 1.1mm or 1.3mm? Nobody knows at this time and as we’ve just discovered, it depends!

For those of you who run air drills, which is 98% of the market, let’s run some quick math to see what effect seed variance has on plant stand density. We’ll use a seeding rate of 5 lbs/ac and compare our findings in seed number to the TKW number on the bag of InVigor 5440.

Steve’s quick math: Based on 5 lbs/ac or 10 ac/bag

Estimated 5440: 5.19 TKW = 4,377,686 seeds per bag ÷ 43,560 ft2/acre ÷ 10 ac/bag = 10 plants ft2

True 5440: 5.18 + 3.37 + 6.72 TKW = 4,333,023 seeds per bag ÷ 43,560 ft2/ac ÷ 10 ac/bag = 9.9 plants ft2

In this example, seeding a recommended 5 lbs/ac would result in the same number of plants ft2 (10 ft2 vs 9.9 ft2) regardless of the variance in seed size. If that’s the norm for all seed lots and seed varieties, that’s good news for those seeding with air drills. The bad news for growers using vacuum planters is the high degree of variance in seed size. This experiment showed that seed size varies by 100% from 3.37 to 6.72 grams inside one bag on canola seed. Seed singulation would be impossible given these results and a method to size seed must be in place before singulation can occur.

In the end, more work needs to be done to measure the variability in seed size across seed lots and varieties. For those seeding with air drills, we need to know that we’re planting 435,600 seeds per acre not 350,000 due to an unknown variance in seed size. When it comes to vacuum planters, we need to ensure we’re seeding with a consistent seed size to improve metering, singulation and avoid plugging. Vacuum planters have tremendous potential in Western Canada. To date we have reduced seed costs by up to 50% ($35.00 ac) and have the potential to improve emergence rates, maturity and yield. Finding a way to manage seed size is key to making vacuum planters perform in Western Canada.

Canola seeding rate chart

This canola seeding rate chart is a quick reference that shows your maximum achievable plant stand density (plants ft2) based on your thousand kernel weights marked on the seed bag and your targeted seeding rate (lbs/ac).

If you have trouble seeing this chart go to: www.beyondagronomy.com

Chart Source: Herman VanGenderen, Pioneer Hi-Bred.

Variable rate plant growth regulators

Thinking outside the box

I’ve been using plant growth regulators for the last three years to try and get a handle on how they perform in our system. Our high yield wheat and barley trials sponsored by ACIDF have given us some valuable knowledge. I’m now at the point where I can see variable rate PGR’s being a better fit than flat rate given the variability in our fields. Unfortunately, there is very little data on VR PGR’s outside of cotton in the US. The only one I know using this strategy in cereals is fellow Nuffield Scholar Craige Mackenzie from Methven, New Zealand.

Craige shared some of his strategies for adjusting PGR rates across zones. He’s in the early stages but seeing some positive results to the tune of 15% increases in ryegrass seed yield and 7% increases in wheat with an overall reduction in PGR use and more even maturity. Here are some comments from Craige on his approach to VR PGR’s.

1) Farmers/agronomists need to be in the field early on to take plant stand density counts, tiller counts and conduct a mineral N test if possible to determine N availability. This will determine the need for PGR’s and will help in the decision making process to decide whether you can drive yield in those areas and keep the plants standing to intercept the full amount of light.

2) You need to take a pragmatic view of PGR’s. I use zone maps based on soil texture and elevation. I know the approximate productivity level inside each zone and which zones lodge on a regular basis. From there, the best way to predict lodging potential is to measure biomass using a GreenSeeker/ Crop sensors in the different zones right before you apply a PGR. We now use a handheld GreenSeeker to measure NDVI values in each zone by popping into the field and taking real time measurements.

3) Next, we look at NDVI readings (0.1 low to 1.0 high) and if an area has an NDVI of .7 and this is because of biomass and not nitrogen then it will get 2.8 L/ha of Moddus. An NDVI reading of 0.6 might get 1.4 L/ha and a reading of 0.5 might get 0.8 L/ha of Moddus. This would be an example of a strategy used in ryegrass seed production.

4) The best way to assess how much to apply to each zone is to look at each zone as different fields and make the decision based on that. From there, deciding how much PGR to apply in each zone becomes clearer. You can massage the rates later to make sure your applying equal to or below a standard blanket application.

6) In cereals, we would typically apply 2 L/ha of Cycocel as a blanket rate and mix in 200 ml/ha of Moddus as a top up. It makes it a bit tricky with 2 products but it still works out to be proportional to the different zones. We would also make the decision to run with Cyclocel as a blanket rate at GS 30 and then come back with a VRA of Moddus based on a GreenSeeker map. You have until GS 32 but I believe what really makes it work is to hit GS30, but you will know your situation best.

7) What makes the decisions really easy now is the handheld GreenSeeker, which allows you to measure NDVI real time in select spots inside your zones. The hand held GreenSeeker has a different camera and therefore gives you a slightly different number than the RT200 boom mounted sensors. If the readings are between 0.65 and 0.75 the numbers don’t vary much between the RT200 and hand held. Outside of that, you must use a calculation factor of 1.06 then the number will be useful for either an algorithm of just making recommendations. For example, if the hand held is reading 0.55, multiply it by 1.06 = 0.583 to bring it to an RT200 equivalent.

The end result for Craige has been a more uniform crop, an increase in yield and a reduction in PGR volume. A simple walk into the field to ground truth zones with a hand held GreenSeeker provides a simple way to assess lodging risk and allow you to adjust PGR rates accordingly. It also forces you to walk into the field to ground truth your zones which helps fine tune your observation skills. I think Craige is really on to something and I appreciate his insight’s given the minute amount of research in this area. VR PGR’s makes a lot of sense in a semi-arid climate where PGR’s allow us to push the high yielding areas even further.

Beyond Agronomy Apps

Seeding rate calculator

We just updated our seeding rate calculator which provides you with the optimal seeding rate based on target plant stand density, germination, thousand kernel weight and seedling mortality.

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