Physics and Chemistry Focus Can Boost Soil Biology

Restructure soils before attempting no-tillage

Dick Neale, technical manager at agronomy group Hutchinsons, urged attendees to dig deep and examine field soil profiles before assessing what actions may be needed to progress a move to reduced/no-till crop establishment.

“Inspect soils between October and March, when proper assessment of moisture can be made. After that, they won’t change greatly until harvest. If you’re currently deep-tilling, restructuring soils will take time, with results usually visible after three years. What you should achieve by gradually reducing movement depth is relatively dry soil that resists compaction and can carry machine weight without leaving significant wheelings. Over time a brown biological organic matter topsoil layer should build up in the upper profile to reach-depending on soil type and use of the right practices in the right conditions – some 350-625mm (14-25in) depth. This will crack and fissure naturally in drier periods, aiding drainage while offering resilience against both high rainfall and drought. Soil that caps instead is usually deficient in surface organic matter – before addressing surface drainage issues by subsoiling, loosening where there may be no issue, consider using natural solutions such as cover crops and compost, and leaving longer stubble, especially if taking off straw.

“Addressing issues often isn’t about spending more money, but about using existing investment more wisely, and improvement measures can often be cheap to achieve.

“Most arable fields host near surface-dwelling endogeic worms, horizontal burrow borers that help aggregate soil, aiding structure and pulling in organic matter from the surface. A well-structured soil will also encourage deep-boring anecic worms to take this material deeper, by as much as two metres, aiding drainage and oxygenation at depth, allowing roots to exploit their channels. Good residue management is key to managing this interlinked process, and within three years results tend to become apparent. Healthy soil will contain about 30 deep-working anecic worms/sq m, cycling nutrients and organic matter and helping boost yields.”

Acknowledging that many of those who have tried cover crops have had widely differing experiences, Mr Neale nevertheless suggested there is proven value in having growing roots in soil for as much of the year as possible.

“If you’ve not found the right mix for your situation and/or not been given sound advice on managing it correctly, bad experiences can happen. But there’s a definite value to keeping roots in the soil as much as possible, and a few guidelines worth following. Cover crops need establishing right behind the combine, especially on heavy soils, to make the most of maximum day length and convert sun energy into food for soil biology via root exudates. They don’t need to produce high, bulky growth, and while, above the surface, surface destruction is best by mid-November to ensure they aren’t encouraging slugs by trapping too much moisture, the roots should ideally be left intact.”

Correct pH

Mr Neale also underlined the importance of correct pH, and its influence over almost every other aspect of soil health.

“It impacts biology, structure and nutrient flow. A lab test is only an indicator. Ensure that, if you’re getting pH 6-6.5 lab results, they are checked with a field test, as contamination by a tiny amount of chalk in a sample can neutralise acidity.

“Placing fertiliser – especially phosphate – can help here. Between pH 8.0 and 8.5, its availability starts to narrow as it begins to associate itself with calcium, while deficiencies of iron, manganese, copper, boron and zinc can also manifest themselves. Equally, soils with a low CEC cannot store positively-charged cations, and there’s no point trying to build a potassium index as there is nothing to retain it.”

Asked about the possibility of incorporating root crops into a reduced tillage system, Mr Neale pointed out that some sugar beet growers were already using strip tillage for beet crops.

“It’s only the drill that requires fine tillage, not the crop. The newer double disc drills can work well in these circumstances, following a strip cultivator.

“Potatoes are obviously a different story, and don’t fit well, but as rotation gaps between them are long, the soil should hold up better when the crop is being established, and recover quicker after harvest. And trials have shown the value of moving the minimum of soil to keep it together and prevent formation of greens. Better-structured soil won’t fall apart when rain hits it.”