• Nutrients and plants working together
• Optimum roots deliver most nitrogen
• Focus should be on untreated yields
Managing soils to maximise the synergy between nutrients, soil micro-organisms and the crop itself is key to getting the most out of high yielding varieties, say experts.
Understanding vital interactions taking place below ground can help growers make better use of nitrogen, avoid excessive greenhouse gas emissions and keep soil in good heart for future crops, says independent soil specialist Neil Fuller.
“Get the soil working in your favour and there’s a wealth of benefits to tap in to,” Mr Fuller told visitors to an Open Day at KWS trials site at Fowlmere, Cambridgeshire.
“Building up organic matter will ensure everything is held together well and there is an abundance of nutrients, but at any one time there is a symbiosis of activity going on that helps feed the plant and contributes to a healthy, high-yielding crop.
“The top layer of soil is particularly important and the rhizosphere directly around the roots is where much of the action takes place. Around 75% of mineral nutrients for a crop come from the top 10cm of soil where thicker roots prevalent help maximise nutrient uptake.
“It’s the activity of microbes around these roots that actually encourages the plant to release amino acid exudates into the rhizosphere which feed the soil biota and in turn make Nitrogen and phosphate available to the plant.”
Such activity is essential for nutrient transfer, explains Mr Fuller.
“Phosphate will take 30 years to shift unaided through the topsoil while nitrate takes just 10 days to move through the top 10cm of soil and for ammonia it’s around 90 days.
“The role of this soil biota is key in making best use of nitrogen but better timing of applications can also result is less nitrogen being needed before yields are reduced.
“One of the largest contributors to an arable crop’s carbon footprint is the amount of applied nitrogen that does not get picked up by the plant and instead is converted into the powerful greenhouse gas nitrous oxide.”
Poorly timed applications or those taking place in unfavourable conditions can add to the problem significantly as can poor cultivations and compacted soil structures, added Mr Fuller.
“Soil compaction or poorly incorporated organic matter, such as straw, can lead to dense anaerobic layers. Subsequently, nitrogen sitting in cold wet soil can turn to nitrous oxide, which has the potential to be lost from the soil at the rate of 5kg/ha/year.
“While this loss might not be noticed agronomically, it has the greenhouse gas equivalent of 1.5 t/ha of carbon dioxide entering the atmosphere every year which is highly significant.”
Although roots near the surface boost nitrogen utilisation efficiency, they also pump carbon into the soil to promote biological activity. “The carbon balance in the soil helps regulate nitrogen uptake and this is strongly related to how carbon cycles through the crop.
“A high-yielding crop has a substantial daily CO2 requirement which, if it were to take this solely from the atmosphere, it would need the equivalent of a 20m column of air per day to meet.
“In good soils, CO2 concentrations are much higher than in the air and it is likely this is where most of the carbon is taken from by a high-yielding crop and again soil biology is key to this.”
High untreated yields
KWS technical specialist Olivia Potter says the ability of a variety to produce an abundance of shallow roots is likely to be a key factor in how effectively it is able to take up nutrients and deliver high performance.
“It’s highly likely that the plants that have the highest Nitrogen Use Efficiency (NUE) and have the greatest level of in-built resilience are the ones which also have the most appropriately adapted root systems.
“High yield potential is a proven indicator of how well plants use nutrients, so a good starting point for selecting varieties able to make the best use of soil resources is to start with high untreated yield.
“High untreated yield is usually an indication of plant resilience and resistance to abiotic stresses so it’s no surprise that varieties like KWS Extase and KWS Palladium with 90% plus untreated yields on the latest RL also have strong agronomic traits.”
Looking to the future, KWS breeders believes their new Group 4 hard wheat KWS Dawsum has many of the features required to deliver optimum performance in a variety of soils and production systems.
“It’s a good blueprint for the type of variety we believe is needed for a more sustainable future and a great example of our SPP (Sowing for Peak Performance) initiative in action,” says Ms Potter.
“For a start, it has high outright yield at 104% of control indicating it uses available Nitrogen very efficiently but it also has a high untreated yield at 92% – just 1% behind the highest performer in this respect KWS Extase at 93%.
“This is underpinned by resistance scores of 9 for yellow rust, 8 for mildew and 7 for brown rust with robust genetics ensuring it delivers its full potential regardless of soil type, drilling slot and whether it’s a first or second wheat. Short stiff straw further adds to its resilience.”