Sunflower yields vary between fields and within fields, and it’s up to the grower and agronomists to try and understand the causes of these differences and, where possible, eliminate the causes.
Today, as we are overwhelmed with increasingly complex monitoring and intelligent farming systems, sometimes it’s good to get back to basics.
This article is about reminding ourselves of some of those basic principles of agronomy to help improve the profitability and performance of our sunflower crops.
Good agronomy starts with the previous crop
To be more accurate, it starts with all the crops previously grown in that field, to a greater or lesser extent, they will all have had an impact on soil condition, soil structure, soil fertility, pest and diseases, when you can plant, how you can plant and so on.
As the crop manager / farmer, you will be aware of this and will have built up a picture of the land under your management.
While it’s understandable that our time is often focused on operations, getting out and about and walking your fields, kicking the soil around and digging holes really helps to gain a useful insight of your land.
A spade is an essential piece of equipment for any agronomist, along with a soil thermometer, pH meter, sharp knife and a soil penetrometer (but these can be expensive, a meat skewer or similar can still give you a “feel” for compaction issues).
If you see problems in a crop, go and investigate, dig holes and look at the soil profile; considering a significant and important part of the plant is underground, it’s not unsurprising that many of the above ground issues can be traced to what’s going on below ground.
Whether you plough and cultivate, just disc or direct drill, there are some basic principles to consider.
Selecting the right seed is high on the list when thinking about improving yield and oil quality.
If you start with seed that has a low genetic potential to yield then it really doesn’t matter what you do to the crop, the inherent ability to yield isn’t going to be there.
Getting performance out of a crop requires putting performance in and hybrid sunflowers will perform well in no-till, minimum or conventional-tillage systems
High-quality hybrids seed, with herbicide tolerance technologies such as Clearfield® Cleafield®Plus and Express® trait, is a very good starting point.
Hybrid seeds are produced when plant breeders cross two different varieties, the off-spring exhibit hybrid vigour, grow strong, are more vigorous than either parent and will produce more yield.
Vigour can be thought of as plants that will continue to perform under increasingly difficult conditions as illustrated by this chart.
Nuseed produces a range of high-quality confectionary hybrid sunflowers and, oil hybrids sunflowers, both high oleic and linoleic varieties, with herbicide tolerance technologies.
Optimum plant populations
It is important to achieve the correct plant density (plant population) to obtain the optimum yield and there are two parts to achieving the correct number of plants in a field.
- Selecting the optimum plant population
If the plants are widely spaced, then not all the land is covered by leaves and not all light available for photosynthesis is intercepted.
If plant density is increased to allow all the sunlight to be intercepted than a positive yield increase will occur.
As the space between the individual plant’s decreases, then neighbouring plants begin to interfere with each other (known as intraspecific competition) and the yield from individual plant decreases, although the overall crop yield will increase.
This is because, even though each plant is not fulfilling its full potential, the crop is making more efficient use of the limiting factors for growth and is particularly true with respect to the efficiency of utilisation of sunlight and the ability of the crop canopy to capture more light at higher plant populations.
However, as the population increases the yield response will start to diminish until a plateau is reached when no further yield response to plant population can be achieved.
In biological terms, the optimum plant population is at the point where the plateau starts, in practice the optimum is lower than this when seed costs are taken into account.
Finding the optimum plant population is difficult, fortunately, Nuseed varieties are supplied with recommended plants per hectare.
- Achieving the desired population at planting.
Generally, but not always, sunflowers are precision planted. To achieve the desired plant population requires the seed to be placed at the correct distance apart, otherwise known as in-row spacing.
There are several ways to calculate the in-row spacing but the easiest is to calculate the length of one-hectare row and divide the target plant population into it.
- The length of one-hectare row is one hectare expressed as 10,000m2, divided by the width of one row.
- For example, 10,000m ÷ 75m = 13,333m.
- The length of one-hectare row, in this case, is 13,333m.
- Then divide the length of one-hectare row by the target plant population.
- For example, 13,333m ÷ 60,000 = 0.22m or 22cm.
This means that if you set up your planter to place seeds 22cm apart on 75cm row widths you will achieve a plant population of 60,000 seeds per hectare.
Setting up the planter
There are many different types of machines used to plant sunflowers so it wouldn’t be possible to go through each one in this article, but there are a few common issues to keep in mind.
- Once you have set up one row to give the desired planting rate and depth, make sure you adjust all rows to the same setting, this will give a uniform result across the width of the machine.
- Don’t plant too deep or too shallow; too deep and emergence may be delayed, too shallow and they may not absorb enough moisture or may be damaged by residual herbicides.
- Don’t plant too fast, one of the biggest causes of uneven establishment is planting too fast as seeds fall off or are not collected by the planting mechanism.
- Fill all the seed hoppers uniformly so that you can spot any unit not working correctly, they should all be emptying at a uniform rate.
- Check the planter from time to time and recalibrate when changing seed varieties or batches.
- Lower tyre pressures to reduce soil compaction particularly to rows adjacent to wheelings.
Feeding the crop
Arguably the second largest influence on yield and oil quality after seed genetics is nutrition, and there are several issues to keep in mind when planning fertiliser applications.
- Testing soil to determine the availability of phosphorous and potassium is useful in targeting applications.
- The previous crop, soil type and the expected yield will need to be considered when determining the application rate of nitrogen.
- Nitrogen is taken up in large quantities and is essential for many plant processes.
- A nitrogen deficiency will limit crop yield.
- An excess of nitrogen can reduce oil content and affect oil quality, including a reduction in protein and oleic acid.
- Sunflower seed is sensitive to fertiliser so aim to limit the amount placed in close contact to the seed at planting.
Maintaining green leaf area
Pest and diseases
Yield depends on effective light interception by the crop canopy and pests and foliar diseases can reduce yield by reducing the canopy’s photosynthetic ability.
As leaves die from the effect of disease, they shrink and start to curl up and much of the sunlight energy passes right through the canopy and is wasted.
This reduces the rate of yield accumulation and may shorten the yield-forming period.
Leaf-eating pests also reduce the leaf area to the same effect but also leave the plant susceptible to secondary infection.
Maintaining green leaf during the yield forming period is important and well-timed sprays help maintain the green leaf area, particularly the upper leaves, until seed formation and filling ends.
Regular crop monitoring to identify pest and diseases, coupled with an understanding of how to measure the problem and understanding of thresholds allows growers to make informed decisions about control measures.
Managing Crop Growth
The principles of practical agronomy and successful farming is all about getting the basics right, understand what it is you are trying to achieve, set targets, assess the progress, adjust inputs, then monitor and learn from the process.