Earlier this year the Yield Enhancement Network (YEN) held an Ideas Lab at Stoneleigh, created to brainstorm how to push production beyond the yield plateau. CPM reports.
OSR has a yield potential of 11-13t/ha.
By Lucy de la Pasture
The concept of the Ideas Lab is to give YEN participants, sponsors and researchers an opportunity to discuss the constraints to yield in the different crops, the scope to manipulate them to enhance crop productivity and come up with practical ideas of how to do this.
Groups of growers can then monitor the effects of suggested treatments using on-farm tramline trials, explains ADAS head of crop performance, Roger Sylvester-Bradley.
He emphasises the purpose of YEN is to identify and help innovators who are producing the highest yields. The next step is to generate enough data so that researchers can dig into the reasons why they’re able to achieve such enhanced performance and then pass on this knowledge through the network.
“The biophysical yield potential of the wheat crop is 20t/ha and the focus of YEN is on bridging the technology gap so growers can get nearer to this potential,” he explains.
The yield relationship in cereal crops revolves around the capture of resources – solar energy and water – and their conversion into grain.
“We have no control over the weather that influences these resources but we can influence their capture, particularly by canopy and soil management. Conversion is much more influenced by genetics in wheat than by management practices, so resource capture is the key area we are interested in,” he explains.
“There’s scope in wheat for improving light capture (by +13%), by increasing the canopy size in early spring and by prolonging canopy survival into Aug. Such crops will also need sufficient roots to capture additional water – about +25mm for each additional week of growth. On an average soil, this means increasing root depth by 15-20cm,” he explains.
For oilseed rape the situation is different. Because yield is sink limited the initial focus must be on maximising the number of seeds set/m2, explains ADAS head of crop physiology, Dr Pete Berry.
“OSR has a yield potential of 11-13t/ha and this is more likely to be limited by water than light in terms of resource capture. But at present, the area where growers can have the biggest influence on yield is through resource conversion to dry matter and partitioning of dry matter into the seed,” he says.
“Flowering is an important period when light energy is not used efficiently due to reflection of light by flowers.
“OSR has an oil-rich seed and very few stem reserves are translocated to the seeds, with 0-10% of yield coming from stems. In contrast, in wheat up to 3t/ha of yield will be obtained from the stems,” he says.
In OSR, yield is determined by seed number, which is set in the 2-3 week period after flowering and then by seed weight. Determination of seed number takes 200-300 day degrees from when each flower loses its petals. In this period, there’s a trade-off between the number of pods formed and seeds set per pod; a target of 7-8000 pods/m2 will maximise seed number and yield, advises Pete Berry.
“To achieve this optimum pod number, a canopy with green leaf area index (GAI) of between 3 and 4 at flowering is desirable, which doesn’t look like a massive canopy when the crop comes into flower,” he notes.
The aim at this stage is to reduce light reflection by flowers, and maintain leaf area duration. Leaves have the greatest photosynthetic activity per unit area, compared with pods and stems. Then for seed filling, because of the high oil content of the seed, 45% more energy is required per g of yield than for wheat.
“When yields get up to 6-7t/ha, considerably more photosynthesis is required and more rooting is needed to depth because of an increased water requirement – at least 100mm extra compared with a 3t/ha crop,” he adds.
With more and more growers now carrying out tramline trials in their own fields, ADAS’ Dr Daniel Kindred believes it’s important they’re able to produce trustworthy results, which account for the spatial variations encountered in most field situations.
“Comparing any two tramlines is likely to produce different results and it’s important that you can be confident that any yield differences are due to the treatment and not because of other factors. Layout of the different treatments has a role to play and, if possible, differences should be applied across any spatial variation. Yield analysis using ‘Agronōmics’ can remove some of the inherent variations that occur in on-farm tramline comparisons,” he explains.
ADAS has developed an Agronōmics service to help farmers compare spatially-defined cropped areas by gathering, analysing and interpreting their data generated from precision farming technologies.
“Although not yet widely recognised, the most valuable attribute of precision farming is that they can help assess the effects of management decisions. Tramline and split field trials tend to be ignored by scientists as their lack of randomisation and statistical analysis makes them ‘unscientific’. However, the huge replication provided by yield monitors and crop sensors could provide a new way of making credible high-precision farm-scale comparisons,” he says.
Roger Sylvester-Bradley adds, “We want to get scientists so interested in the innovation that’s going on at farm level that they want to come out on farm and try to explain what’s going on. This interaction between growers and researchers doesn’t currently take place and there’s a need to raise the standard of proof for on-farm trials so farm effects are taken seriously – hence the importance of Agronōmics analysis.”
With the science now in place to provide a valid interpretation of on-farm trials, what’s the scope for growers to improve the resource capture of their crops?
Dr Charlotte White, crop physiology research scientist at ADAS Gleadthorpe, explains increasing yields means increasing water capture from the soil.
“To produce a 15t/ha crop of winter wheat requires an additional 160mm of water compared with a typical 10t/ha crop, so it’s important to understand your soil’s water-holding capacity when looking at yield potential on the farm,” she explains.
“Root density is a critical factor with 1cm of root/cm3 of soil required to capture most available water and nitrogen. It’s something that has changed in modern crops,” she notes.
“In the 1970s and 1980s, cereal crops generally had root densities above the critical level. In today’s crops, rooting appears to be reduced and far more crops have less than the critical root density required for efficient use of water and nutrients. We don’t know whether this is caused by the genetics of new varieties or other factors such as greater soil compaction.”
So how do you get roots deeper? Charlotte White explains that there is no simple answer, many factors are involved.
“Strong soils limit root growth and yield and soils get stronger as you go down through the soil profile. But a soil also gets stronger as it dries so it’s harder for roots to penetrate. In the top 60cm of soil only 30-40% of roots are found in biopores and cracks. But below 60cm, 85-100% of roots exploit these pre-formed channels and adopt these as ‘motorways for growth’,” she explains.
It’s logical to assume that deep rooting in one crop will help the next crop’s roots to follow – cover and companion crops are often planted with this objective in mind.
“It’s important to question whether the deep rooting crop has had enough time to get roots to depth if it’s being sown in the autumn before a spring crop is then planted.”
Roger Sylvester-Bradley points out that maximum rooting depths worldwide average at about 2m but to produce high-yielding crops, a maximum rooting depth of 3m is often desirable.
“That means if you’re farming on a shallow soil, such as Cotswold brash, then you have a natural cap on yield potential,” he comments.
Senior ADAS soil scientist, Dr Anne Bhogal, adds that soil management to encourage deep rooting is all about soil structure. At a sub-soil level, cracks and pores are formed by repeated wetting and drying cycles and by earthworms. Drainage and control of trafficking are very important, but organic matter content of the topsoil can also help.
“It’s possible to build resilience to compaction or erosion by increasing the activity of ‘biological engineers’. This will help maintain porosity, aeration and connectivity with the subsoil,” she explains.
So how do you achieve this? The answer is fundamentally in organic matter management, she answers.
“Organic matter carries a negative charge so causes aggregation of particles in the soil. It also provides a food source for soil biology, which not only recycle nutrients but also help with soil aggregation, providing the ‘glue’ which sticks particles together.
“Organic matter also acts as a natural ‘sponge’ in the soil that increases its available water-holding capacity,” she adds.
And the best way to improve organic matter content is to apply it, she advises, although any measurable impact will take several years to become apparent. Different organic materials can also have very different effects.
“Organic matter retention from green compost or biosolid cake is ten times greater than from wheat straw. But even with typical dressings of these materials (20-30t/ha), the organic matter already present in the soil will only increase by a small fraction, say one hundredth.
“An FYM application supplying 250kg/ha N, contributes approx. 1300kg/ha in organic matter and, if applied for a number of years, can lead to an increased soil water-holding capacity of 5%,” she explains.
Earthworm activity provides a reliable indication of a soil’s biological health. Dr Jackie Stroud has a NERC-funded soil security fellowship at Rothamsted and her research is focused on making crops more productive by improving soil fertility.
As an integral part of her ‘Ploughing on Regardless?’ project, she spends a great deal of time hunting for earthworms. A significant aspect of soil heath is a functioning population of soil ecosystem engineers, earthworms, she explains.
“There are typically seven species of earthworms found in arable fields. Epigeic earthworms are poor burrowers so dwell in surface litter. Endogeic earthworms inhabit the topsoil and form horizontal burrows, with Allobophora chlorotica and A. caliginosa often being the most common endogeic species found in arable soils.
“Anecic earthworms, such as Lumbricus terrestris, are the UK’s largest earthworms and most sensitive to soil management. They’re surface feeding and play a crucial role in forming deep, vertical burrows – to 2m depth – where they live.
“They anchor their tails in the burrow while foraging for food on the surface and pull food to a feed store or ‘midden’ at the burrow entrance,” she explains.
“Anecic earthworm populations have often collapsed under conventional agricultural land management practices, linked to intensive tillage, poor organic matter management and agrochemical applications,” she says.
“For growers converting to minimum tillage regimes, an abundance of ‘nature’s ploughs’ is likely to be critical to the long-term success of such management regimes. A healthy soil with plenty of earthworms, indicating good biological activity, is capable of producing yield increases of as much as 25%,” she points out.
But how can you assess how many deep-burrowing earthworms you have?
“It’s easy to go out into fields and assess anecic earthworm numbers. Get out and go midden hunting,” she enthuses.
“Spring and autumn are the best times to go out worm hunting. Each midden represents the presence of one L. terrestris, with midden counts higher than 30/m2 indicating an abundant population.”
Using midden counting can be a useful tool to evaluate soil management techniques because when soils become over-worked, anecic earthworm populations and their associated middens become locally extinct, she advises.
“This is because intense soil disturbance brings anecic earthworms to the surface, where they’re gobbled up by greedy seagulls and surface food is buried, thus their populations decline. Changing soil management practices by moving towards zero tillage may help to regenerate soil health,” she concludes.
