Although we generally understand the advantages of crop rotations, sometimes it’s useful to remind ourselves what they are and to dig a little deeper.
While it’s true that you don’t have to rotate crops if you don’t your risk of crop failure will increase, as will your use of fertiliser to replace nutrients and chemicals to control sunflower pests and diseases.
This article will look at some of the benefits and reasons why crop rotations make sense and will focus on the implications for sunflowers.
What is crop rotation?
A crop rotation is a cropping system in which two or more crops are grown in a fixed sequence.
This means moving your crops around every season so that no crop is grown on the same field two years running.
Of course there will always be exceptions and we all cut corners from time to time for various practical reasons. But generally speaking the greater number of crops in a rotation, the longer the gap, and the greater the benefit of that rotation.
Pest and disease control
Growing the same plant on the same ground year after year, provides a continuous food supply or habitat for soil-borne pests and diseases.
This can lead to the steady accumulation of the pest or disease as their population or inoculum increases year on year.
Eventually this can reach a level that causes significant economic damage to your crop.
By rotating crops with other plant families you essentially deny the pest or disease a food supply, which then interrupts their lifecycle and limits their population from building up.
Extensive rotations will help reduce pest and disease pressure.
The control of sunflower cutworms, phomopsis, sclerotinia, and rust can all benefit from suitable rotations.
Continuous planting with one crop will favour weeds that suit that lifecycle, germinating when the crop is planted and maturing at or before harvest so seeds are returned to the soil.
Employing a suitable crop rotation helps control weeds in two ways.
Different crops with different lifecycles, particularly mixing spring and winter crops, helps break the lifecycle of weeds and reduces the return of seeds to the soil weed bank.
Crops from different plant families allow for different herbicide groups and modes of action to be used, making weed control easier and more effective. For example, graminicides are generally more effective in a broad leaved crop than in a cereal and vice versa.
An additional benefit of a crop rotation that allows herbicides with different modes of action to be used, is helping to reduce the incidence of weed herbicide resistance.
The overuse of chemicals from one herbicide group eventually selects for plants that can survive herbicide treatment, resistant plants will multiply until they dominate the population.
Today, weeds have evolved resistance to 23 of the 26 known herbicide sites of action and to 167 different herbicides in more than 100 weed species around the world.
Interestingly, the inherent resistance plants have to herbicides has been put to good use with the development of enhanced crop tolerance technology as used in Nuseed hybrid sunflower varieties.
Enhanced crop tolerance technology such as Nuseed’s Clearfield®, Clearfield Plus® and Express®, allows growers to achieve more effective weed control in their sunflower crops, making sunflower an ideal crop to include in rotations to assist in reducing the weed seed bank.
Nutrients and water
Different crops use soil nutrients and water in different ways, some crops are hungrier than others, some crops return nutrients back to the soil, and some crops make for better organic matter.
By mixing up a rotation with crops from different plant families, with different soil nutrient and soil moisture demands and with different root types and rooting depths, you can optimise your nutrient budget, fertiliser requirements, moisture demands and help improve your soil structure all at the same time.
Sunflowers have a particularly deep tap root, which develops rapidly and penetrates downward to as much as 1.8 metres below the soil surface, allowing the plant to access moisture and nutrients beyond the reach of most annual field crops. This is one of the reasons why sunflowers are able to tolerate dry conditions and generally have a low requirement for additional fertiliser.
That deep tap root also does an excellent job at opening up the soil structure and rectifying any compaction problems.
Oilseed rape and some bean crops also have a good tap root although not as deep as sunflowers.
Legumes are good for fixing atmospheric nitrogen and making it available to the following crop, and the fiberous root systems of cereals are good at mopping up fertiliser left behind by row crops.
There is a lot written about rotations, what works well, what doesn’t, how long each crop requires a break, and what will happen if you don’t follow that advice.
You can research the detail of any proposed rotation but it’s worth keeping in mind a few simple guiding principles.
More plant families in a rotation is generally better.
Naturally this has to be balanced with economic viability, location, soil type, climate etc. but the greater the range of crops you grow the better it is for crop and soil health. Multi species cover crops are a particularly exciting development here.
The longer the break between a crop the better.
There’s plenty of research that will stipulate how many years you should leave between growing any particular crop, with dire warnings that failure to follow this advice will lead to crop death. Basically the longer the gap the better, but this needs to be balanced with real world decisions. Three to four years is generally sufficient for most crops but if you need to occaisionally reduce this for practical reasons then it shouldn’t be too much of an issue.
Don’t go chasing markets.
The economics of farming are such that if a particular crop achieves high prices one year, chances are the following year will see more of that crop grown, leading to lower prices. When formulating a rotation, ignore seasonal variations in prices and focus on what suits your business, soils, climate, logistics and so on. Consider the profitability of the rotation over the whole cycle, rather than just one crop or one season.
Don’t be afraid to experiment.
Try growing a new crop to you or a different variety of hybrid. If you’re unsure, start small to see how you get on, if nothing else it helps keep things interesting for you and might improve your profitability.