April 3, 2012

Agronomists Notes

Hello Reader,

It’s tool time! The liquid kit for the drill arrived last week, our 60-foot Spray Coupe arrived today, and the GreenSeeker should arrive by the end of the week. Now to find the time to put it all together before the end of April! Anyone have a couple of Superman capes we can borrow?

The ten-day forecast calls for temperatures between -5C and 6C with sunny but windy weather. Soil moisture reserves are adequate for germination but very low in our area. The snow has been gone for a while and the wind is picking up daily, which typically happens during spring. I see the ice is breaking on the Red Deer river so it won’t be long before seeding begins, I’d guess somewhere around the 20th of April.

This week we’ll discuss genetic yield potential in wheat and one of its most critical growth stages. Next, we’ll run through a quick calculation to show you how to determine product application rates wih liquid nutrients. Last, we’ll look into the variability of yield across the width of our drill and look at how some companies are measuring seeding accuracy. We’ll finish with technical grain market news.

Have a great week.

Boot stage: when wheat yield potential means the most

Have you ever wondered what the genetic yield potential of wheat is? Some would say 250 bu/ac or 300 bu/ac. In reality, the genetic yield potential of wheat is actually greater than 1,000 bu/ac. Yes that’s right, 1,000 bu/ac! Unfortunately, 90% of that yield potential is lost due to stress factors that occur during critical growth stages. Today, we’ll focus on the one growth stage in wheat where we typically lose half of our yield potential, the boot stage.

Before I begin, you’re probably wondering where I came up with 1,000 bu/ac+ yield potential. Any given wheat variety can generate between 20 and 30 florets (rows) per head with up to 6 kernels per floret (row) on average. If we know the number of heads per m2, the kernels per head and the average kernel weight, we can calculate a theoretical yield. Let’s run some numbers.

Steve’s quick math:
Plants m2 × heads/plant × kernels/head × g/tkw ÷ 100,000 = T/ha
325 × 3 × (30 florets × 6 kernels) × 45 ÷ 100,000 = 78.95 T/ha (1,174 bu/ac)

In this example, we’ve generated a yield potential 1,174 bu/ac. Not bad from my desktop. Unfortunately, when that wheat seed hits the furrow things go south. Yield loss is caused by weeds, insects, disease, seed placement, cold temperatures, hot temperatures, soil structure, drought, floods, nutrient deficiencies, low sunlight, low carbon dioxide, poor aeration and the list goes on. Today we’ll focus on the growth stage where we lose roughly 50% of our yield and it begins at the boot stage and finishes at flowering.

The boot stage in wheat is very sensitive to environmental stresses because there is so much going on physiologically. The stems are reaching maximum growth rate, leaves and heads are expanding, pollen and embryos are developing and roots are branching. All of these processes create a huge demand on the plant to supply itself with carbohydrates and nitrogen. If there is a shortage of water, yield is reduced. If temperatures climb above 18 degrees C, the plant has difficulty generating enough carbohydrates because it’s growing too fast. If the crop is too thick, it shades itself and reduces photosynthesis and subsequently the ability to produce and supply carbohydrates to the growing points. If disease is present the leaves cannot generate enough carbohydrates to support all the plant growth that is occurring during this critical time. This is why research suggests that up to 50% of the potential florets (kernels) never develop. (Kirby 1988)

Boot stage up until the end of flowering typically occurs roughly 60 days after planting or during the first two weeks of July. Unfortunately, this critical growth stage coincidences with our hottest month when rain begins to taper off. Temperatures above 18C begin to reduce pollination because the plant is growing too fast and cannot produce enough carbohydrates. Any deficiency in soil moisture at this time can have a huge impact on carbon and nitrogen availability, the two key drivers components to growth at that stage.

There are a number of strategies you can use to help improve the chances of producing viable kernels at a time when mortalities reach an astronomical 50%. We’ll focus on the nutrients that play a key role in developing viable kernels as a starting point to help you design a foliar nutrition program.

Nitrogen is the building block of amino acids and protein. Apply foliar nitrogen either through long chain urea products like N-Pact or foliar urea with rates equivalent to 5 lbs actual N/ac. (Gabala et al. 2003)
Copper improves nitrate assimilation and can be in short supply when the top six inches of soil dries out in July. Apply 0.125 lbs/ac copper at boot stage.
Magnesium is a key component in chlorophyll production which helps supply the plants with carbohydrates. Apply 1 to 2 lbs/ac of MgS04
Boron increases the pollen producing capacity of anthers and pollen grain viability. Apply foliar boron at 0.2 lbs/ac.
Calcium is critical to the movement of nitrite in plants. Apply foliar calcium at 0.2 to 0.5 lbs/ac.
The use of fulvic acids have been known to help plants assimilate nitrogen and carbohydrates more efficiently, especially during periods of stress. (Xudan 1986)

The key to generating an adequate supply of nutrients during peak demand is to load the plant during the ten days prior to the boot stage. This ensures nutrients have had enough time to absorb and translocate to the correct areas of the plant. Also, in order to achieve maximum absorption of foliar nutrients, the droplets must stay on the leaf for as long as possible. This requires applications to be done in the evening when humidity levels climb and nutrients remain in solution longer.

Unfortunately, what I can’t tell you today is which nutrients will respond most in your soil, in your climate with your management background. I do suggest you look at these nutrients to try and load the plant prior to its peak demand. The boot stage and up until flowering is one of the most critical times in a plants life where kernels are generated. We often get 24 to 32 kernels per head on average. The genetic yield potential of wheat is to develop between 120 to 180 kernels per head. The boot stage is where kernel numbers are set, and it doesn’t take Steve’s quick math to tell you we’re a long way from 180 kernels per head. SL

If you want a highly technical but great read on wheat development visit here.

Pictured above: Wheat plant at boot stage.

Calculating application rates inside foliar products

We often talk about liquid nutrition rates in lbs/ac in Western Canada. This can often lead to confusion or misunderstanding of what rates to apply to generate the targeted amount of nutrients. I thought I would show you a brief lesson on how to calculate an application rate using liquid nutrients.

When calculating liquid nutrient rates you need three things: 1) the guaranteed analysis, 2) the net weight in lb/gallon, and 3) the targeted nutrient rate.

I’ll use the label shown above to help calculate the amount of product we need to apply 0.5 lbs/ac of Calcium using a product that contains 8% Calcium.

Standard
Step 1: Equation: Net Weight lbs/US gallon × Guaranteed Analysis = lbs of nutrient/gallon
10.6 lb/gallon × 0.8 lbs Ca/lb = 0.848 lbs/gallon

Step 2: Gallons of Ca/acre
0.5 lb Ca/acre ÷ 0.848 lbs Ca/gallon = 0.589 gal/acre.

I’ll use the label shown above to help calculate the amount of product we need to apply 227 g/ac of Calcium using a product that contains 8% Calcium.

Metric
Step 1: Net Weight kg/litre × 1000 g/kg × Guaranteed Analysis = grams of calcium per litre
1.27 kg/litre × 1000 × 8% = 101.6 g Ca/litre

Step 2: Required grams of Ca/ac ÷ g Ca/litre = litres/ac
227 grams/ac ÷ 101.6 = 2.23 litres/ac

The easiest method to calculate nutrient application is to use the metric equation. If you need to convert grams into pounds or vice versa just remember there are 454 grams in one pound. It sounds simple, but calculating nutrient rates is an important step that is often missed because people simply don’t know how and rely on the manufacturer to suggest application rates. Now you’ll know how much you need to put on and how to calculate what each nutrient is costing you. SL

Pictured above: Liquid nutrient analysis.

Measuring yield distribution across each row

Row by row seed distribution and performance

I was reading through an e-newsletter sent out by Precision Planters from Tremont, Illinois. They were advertising their bolt on vacuum planter metering system that kept track of seeding performance row by row. For example, their 20/20 SeedSense monitor keeps track of plant population, % seed singulation, % skips, down force of each opener and ground contact. This technology allows you to achieve optimum plant densities by monitoring the seeding performance of each row. If our goal is to achieve optimum plant densities then how do we know our drill is placing seed uniformly on each row? Also, what is the yield difference between each row and how much does it vary?

To answer that question I’ve included a performance chart that documents the yield on each row across our drill. We hand threshed and weighed one meter of row on each of the 28 runs across our drill. We were originally trying to assess the yield difference on the rows beside the tram lines. You can easily see the variance in yield across each row in the chart. Barley yield in bu/ac is on the left axis while each row number is marked on the bottom axis. We’ve got a high of 179 bu/ac with a low of 71 bu/ac and a field average of 106 bu/ac net. (The 179 bu/ac was recorded in the row beside the un-seeded tram line that has two seed tubes running to it.)

The average yield of this drill width was recorded at 135 bu/ac with a variance of 74 bu/ac below the average and 44 bu/ac above the average. There were 16 rows that fell below the 135 bu/ac average. If seed distribution within the row was the problem and we could fix it, we could increase our average yield by 10% if we brought those 13 rows rows up to the average. The only way to know is to begin measuring and unfortunately, we haven’t gotten there yet.

So what is causing the yield variance across our drill? How do other drills compare? If we had the Precision Planting technology like the 20/20 SeedSense, perhaps we could monitor how seed is distributed within each row to draw some conclusions. In my opinion, if we truly want to optimize plant stand densities in the future we have to change our thinking to manage each foot of row versus each acre. That’s the kind of precision ag I desire for the future. SL

Precision Planters 20/20 SeedSense

Pictured above: Yield by row across our 30-ft drill. Source: S. Larocque