Saturday, October 20, 2018

Take care of cover crops before sowing spring cereals

December 21, 2017 by  
Filed under Crops

In recent years our knowledge of soil science, and in particular, our appreciation and actioning of that knowledge has increased massively. This knowledge helps us to understand and predict the interaction of various cover crop mixtures within our soils.

The impact of cover crops is both physical and biological and in that respect also impacts the chemical status of the soil. But it’s complicated, and what might be seen as a benefit in the long term can be a negative in the short term, says Dick Neale, Hutchinsons technical manager.

“Managing cover crops in light and medium soils is relatively straight forward with the biological interactions of one plant type with another being of most importance. In heavier soils with clay contents in excess of 30%, the management of water in the soil by the cover crop becomes the dominant factor in accessing and drilling the fields in the spring.”

Moisture movement

Growing plants, be they cover crops or cash crops, facilitates the movement of moisture in the soil by hydrostatic pressure. Plants take up nutrients in the upper soil horizons because that’s where the majority of biology is active and nutrients are cycling, so they want to keep that area moist.

“Cover crops help dry heavy soils – which they do, but, because the plants are transpiring moisture taken up by their roots, hydrostatic pressure is replacing that moisture in the rooting zone by movement of moisture from the bulk soil around and below the root zone, this creates a ‘wet’ zone immediately around the plant roots – and that’s the soil fraction we want to engage the drill with.”

Mr Neale suggests that in order to avoid this wet zone at drilling, typically in early March, the cover crop should be terminated via grazing or glyphosate some 6-8 weeks in advance of the expected drilling date.

“Nature will not tolerate imbalance and once the roots stop extracting moisture, hydrostatic pressure and gravity will re-distribute the root zone moisture back to the bulk soil around it. As the cover dies the soil surface will also be exposed to wind and sun allowing the soil surface to dry and drilling to take place in good conditions.”

Early advantage

“All things are relative, and in light soils, having that moisture near the surface in early spring is an advantage for the newly planted crop, so covers in this situation can be sprayed off just ahead of the drilling operation.”

Biology is the next consideration, he notes.

“Plants utilise allelopathic chemicals to influence other plants around them. Some plants like oats and rye species exhibit strong allelopathic effects and can be used to suppress difficult weeds like nettles, groundsel and bromes. However, these ‘benefits’ can become serious negatives when a sensitive spring cereal is sown into soils full of these natural chemicals.”

Again, the answer is allowing time for these effects to dissipate and oat or rye containing covers should be terminated eight weeks prior to a spring cereal.

“This gives sufficient time for the negative impact to decline and also allows for the stored nutrients within the cover crop to become re-available to the following crop.”

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