Potato Surface Root Proliferation

Over the past week or so, fine curly roots have proliferated just beneath soil surface (some are ringed red). However, it's not clear where these are originating. And this activity seems to be mostly above troughs in main root wave. But where main root comes closer to surface, there is little sign of it (right). Although these new roots are clearly visible through side of pot, they cannot be seen from above. i.e. they do not seem to penetrate soil surface.

PURPOSE OF ROOTS
Not sure what purpose these roots serve, but presumably they gather water from light rain showers, which hardly penetrates into soil. Should think they can also extract condensation formed overnight at soil surface from water vapour rising from below. Probably quite a lot of water to be had this way.

Had no idea potatoes were so efficient at extracting water (if that's what these roots are for). But concerned about:

• what happens if surface dries out - do roots survive and remain effective?
• what happens when roots disturbed by surface weed control - how quickly do they re-grow, if at all?
• what happens when potatoes earthed up - how quickly can they reach new surface?
• do they make mulching less effective (not so much in potatoes but in other crops)?
• implications for top dressing

WHEN SURFACE DRIES OUT
Very few commercial soils have constantly damp surfaces. Are these roots damaged by drying? Presumably not - not if their purpose is to harvest rare showers in dry soil.

WEED CONTROL
Surface hoeing could be a real problem and present much damage, at least in the short term. But most of weed control in potato drills is done by covering small weeds during 'earthing up' process. Would seem essential not to let weeds get too large to be covered this way.

MULCHING - IS IT ALWAYS EFFECTIVE?
Because mulching materials tend to be coarser than soil, it's likely these roots cannot proliferate to same extent, if at all, perhaps leaving a dry barrier between soil surface and atmosphere - one which light rain showers could not penetrate.

As already outlined, if the top couple of centimetres (inch) or so of soil surface is loosened by cultivation it forms a natural barrier (mulch) to water loss (see posts on weeding and water conservation). Therefore, all mulching really does is delay the drying process; it is probably not much more effective than the soil's own natural mulch (formed when loosened surface insulates and reduces loss due to wicking). Bearing in mind surface roots, we need to ask the question: 'Are there are circumstances where mulching might be ineffective?'

TOP DRESSING
It's always assumed feeds need working into surface. Might do more harm than good.

Any views about all of this?

Potato Laterals Not Just At Surface

Just after stating that 'potato laterals are mostly at surface' of the half litre plastic cup (see 'Why Are Potato Lateral Roots Mostly At Surface?'), more have appeared further down. These new laterals also at 'crest' of 'root wave' with little in gullies either side (this photo actually shows two roots, but seems to illustrate the point). Only this time new lateral growth is mostly upward and is more extensive. It is also comprised of only the finer roots, at the moment, though these possess root hairs, so might thicken up to be like those described last week.

THESE LATERALS NOT ON ROOT AT SURFACE
Far from being just beneath the surface, this root is nearly two thirds way down the cup. And it is unlikely that this part of the cup has been watered in the same way as the surface. This might indicate:

• perhaps potato roots grow in a wave fashion wherever they are, independent of soil water levels
• perhaps laterals at crest of roots are not responding to being near soil surface

IMPLICATIONS FOR GROWERS
It seems amazing that roots actually grow so close to the soil surface. This means that any sort of mechanical weeding is certain to damage them and impair the plant's ability to take up water.

Do Dahlia Roots Come So Close?
Dahlia feeder roots also come up to the surface. I wonder if they also come so close?

NO RESPONSE TO SYRINGE WATER
Still early days, but water applied by syringe to gully of root at top of cup does not seem to have produced a response, perhaps indicating laterals are not produced in response to moisture levels. Seems unlikely.

Potato Feeder Roots Fan Out In All Directions

These are potato feeder roots fanning out inside a half-litre (pint) pot. Two weeks ago, I cut out a 1.25mm (half inch) cube (including an eye) from a sprouting tuber and planted it in damp soil half way down the pot (green).

The roots quickly encircled the pot. But what's interesting is that the roots fanned out in all directions, up as well as down. And the upper root (red) began to level out once it got within 1.25mm of the surface.

However, as the surface dried out, it turned downwards. I then watered the pot around the stem of the freshly-emerged shoot so that it did not wet the sides but sank down the middle of the pot. As you can see, the root soon changed direction and began to follow the water downwards.

Note: This root property of also growing upwards enables us to place tomato plants (these belong to the same family as potatoes) at the bottom of a pot.