The earth at work be­neath our feet

Feed the soil not the plants, says study

Weekend Argus (Saturday Edition) - - FRONT PAGE -

THE gar­dener has a long, touchy-feely re­la­tion­ship with the soil. As ev­ery good cul­ti­va­tor knows, you as­sess the earth by hold­ing it. Is it dark and crumbly, is there an earth­worm or bee­tle in there, is it moist, and when you smell it, are you get­ting that pleas­ant earthy aroma?

All these signs are re­as­sur­ing, and have been through the ages, but they are mere in­di­ca­tors of some­thing much greater and in­fin­itely mysterious: a hid­den uni­verse be­neath our feet.

This cos­mos is only now re­veal­ing it­self as a re­sult of sci­en­tific dis­cov­er­ies based on bet­ter mi­cro­scopic imag­ing and DNA anal­y­sis.

There is much still to learn, but it boils down to this: Plants nur­ture a whole world of crea­tures in the soil that in re­turn feed and pro­tect the plants, in­clud­ing and es­pe­cially trees. It is a sub­ter­ranean com­mu­nity that in­cludes worms, in­sects, mites, other arthro­pods you’ve never heard of, amoe­bas, and fel­low pro­to­zoa. The dom­i­nant or­gan­isms are bac­te­ria and fungi. All these play­ers work to­gether, some­times by eat­ing one an­other.

The aware­ness of this bio­sphere should change the way gar­den­ers think about cul­ti­vat­ing plants and heighten ev­ery­one’s un­der­stand­ing of the natural world. In other words, don’t ever call it “dirt” again.

The sheer vi­tal­ity of it is mind-bend­ing: A tea­spoon of good loam may con­tain a bil­lion bac­te­ria, yards of fun­gal strands, sev­eral thou­sand pro­to­zoas and a few dozen ne­ma­todes, ac­cord­ing to Jeff Lowen­fels, co-au­thor of Team­ing With Mi­crobes.

This is, ba­si­cally, how it works: Plants man­u­fac­ture car­bo­hy­drates through pho­to­syn­the­sis, but not just for them­selves. They re­lease some of their car­bon sug­ars into the soil, which causes the bac­te­ria and fungi to show up to feed. The bac­te­ria crowd around the root zone, and the fungi form vast net­works of in­ter­lock­ing strands that of­ten link one plant to an­other. The bac­te­ria con­vert ni­tro­gen and other nu­tri­ents into forms the plants can use, of­ten by get­ting de­voured by other mi­crobes.

The fun­gal strands, the mycelium, ef­fec­tively in­crease the root mass of its host plant by as much as a thou­sand times and trans­port a bevy of good­ies to the host plants, in­clud­ing phos­pho­rus, cop­per, cal­cium and zinc. There is also ev­i­dence that trees use this net­work to send signals to one an­other if, say, leaf-eat­ing pests have ar­rived.

In his Ted Talk, my­col­o­gist Paul Stamets re­ferred to mycelium as “Earth’s natural In­ter­net”.

Although some plant (and human) dis­eases are caused by soil-borne fungi and bac­te­ria, most of these mi­crobes are ben­e­fi­cial and keep the bad ones in check. The or­gan­isms as­sist in other ways, by in­creas­ing the size of soil par­ti­cles, which im­proves the abil­ity of the soil to hold wa­ter and air.

Even in the mid­dle of a city, the sub­ter­ranean world is thriv­ing.

Sci­en­tists took al­most 600 soil sam­ples from across New York’s Cen­tral Park and dis­cov­ered a sur­pris­ing di­ver­sity and rich­ness. They iden­ti­fied more than 120 000 types of bac­te­ria and more than 40 000 species of fungi, pro­to­zoa and arthro­pods.

Among the un­ex­pected find­ings: The mi­cro­bial species were the same, more or less, as those found in parts of the world with dra­mat­i­cally dif­fer­ent flora and cli­mates from New York’s, in­clud­ing Antarc­tic cold deserts, trop­i­cal forests and grass­lands.

There was a strong as­so­ci­a­tion be­tween the di­verse or­gan­isms in each sam­ple. “Un­rav­el­ling these re­la­tion­ships will be crit­i­cal to build­ing a more in­te­grated un­der­stand­ing of be­low-ground ecol­ogy,” the re­searchers wrote in a pa­per pub­lished by the jour­nal for the Bri­tish Royal So­ci­ety. “Our work high­lights that most of the di­ver­sity found in soil re­mains un­de­scribed.”

Enough is known, how­ever, to cre­ate a 21st cen­tury sub­set of farm­ing known as re­gen­er­a­tive agri­cul­ture. The farm­ers have dis­cov­ered that if you fos­ter this bio­sphere, you don’t need ex­pen­sive fer­til­iz­ers be­cause the mi­crobes re­pay the plants with nu­tri­ents. They also, for ob­vi­ous rea­sons, avoid pes­ti­cides that would kill this soil life.

The farm­ers do as lit­tle soil dig­ging as pos­si­ble be­cause tra­di­tional tillage de­stroys the fun­gal net­works and the de­sir­able soil struc­ture. Cover crops keep the soil life happy be­tween grow­ing sea­sons.

Ad­vo­cates of this low­im­pact farm­ing say it can re­store soil car­bon lost by the his­toric con­ver­sion of for­est and prairie to farm­land and help to mit­i­gate green­house gases. In the 1990s, Sara F. Wright, an agri­cul­tural re­search ser­vice sci­en­tist in Beltsville, Mary­land, dis­cov­ered a sticky coat­ing to fun­gal threads named glo­ma­lin that, it turns out, is a ma­jor reser­voir for car­bon.

Lowen­fels says it’s also time for gar­den­ers to adopt prac­tices that nur­ture the soil bio­sphere. To say he thinks deeply about this sub­ter­ranean world is an un­der­state­ment. In ad­di­tion to Team­ing With Mi­crobes, he has writ­ten Team­ing With Nu­tri­ents. His lat­est ti­tle is Team­ing With Fungi, which dwells on the type of fungi that di­rectly as­so­ciate with plant roots. They are known as my­c­or­rhizal fungi, and he’s a big fan of adding them to his plants when they are in­stalled, ei­ther as a spray or in pow­dered form avail­able from the gar­den cen­tre. “It works. My tomato plants are big­ger than the con­trol, they’ve got more fruit on them, the plants are so healthy,” he said. “My car­rots are un­be­liev­able this year.”

Some gar­den­ers turn to com­post tea to build soil mi­crobes. This is made by aer­at­ing sug­ars, com­post and hu­mic acids in non-chlo­ri­nated wa­ter and then spray­ing the brew on plants and soil. Oth­ers are not con­vinced that this is needed, though ev­ery­one agrees that the way to fos­ter the soil food web is to top­dress grow­ing beds and lawns with or­ganic mat­ter such as shred­ded leaves or fin­ished com­post.

James Nardi, a bi­ol­o­gist at the Univer­sity of Illi­nois in Ur­bana, of­fers this ad­vice: “Work with your fel­low non­hu­man gar­den­ers. I never use syn­thetic fer­til­iz­ers, and I never use pes­ti­cides.” Nardi’s 2007 book, Life in the Soil, re­mains an ex­cel­lent in­tro­duc­tion to the sub­ject.

In au­tumn, he mixes horse ma­nure with fallen leaves, shreds the mix­ture and ap­plies it as a mulch to his grow­ing beds. “In the spring, I have this lovely, spongy soil,” he said. Lowen­fels shreds au­tumn leaves on his lawn and lets the bio­sphere use them over the win­ter.

The or­ganic gar­dener’s mantra has never seemed more ap­pro­pri­ate. Feed the soil, not the plant. – Washington Post

PICTURE: DAVID RITCHIE

The or­ganic gar­dener’s mantra has never seemed more ap­pro­pri­ate. Sci­en­tists have found a plan­e­tary in­ter­net of non-human gar­den­ers.

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