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BOOK EXCERPT July 2018 WINES&VINES 51 Although fertilizers can quickly boost crop yields on degraded land, the increase in re- turns on rich, fertile soil is marginal at best. And as it is, only about half the nitrogen ap- plied as fertilizer gets taken up by crops. The part that isn't does not stick around, causing problems off the farm. Most chemical fertilizers readily leach into groundwater because they are soluble by design. Add a lot in the fall and by spring much of it can end up in a river, reservoir, or water well. Law of return Soon after Haber and Bosch uncorked the ni- trogen genie, an observant English agronomist began to question the new agricultural gospel. Based on years of work developing large-scale composting methods for commercial planta- tions in India, Sir Albert Howard proposed his Law of Return in the 1930s to explain why returning organic matter to the fields was es- sential to soil health, healthy crops, and boun- tiful harvests. At a time when there was little knowledge of how nutrients reached plants, Howard thought that mycorrhizal fungi played a big role. In his experience, well-made compost boosted growth of mycorrhizal fungi. And fields with abundant mycorrhizae consistently produced abundant healthy crops. This led Howard to see fungi as nature's recyclers. He suspected that mycorrhizal fungi fed on decay- ing organic matter and served as root exten- sions that provided essential nutrients to plants. In Howard's view, chemical fertilizers could not replace soil organic matter, because adding a few elements could never provide all the mineral nutrients and substances in soil that fungi rounded up and delivered to plants. While Howard grasped the general pattern, he could not really explain why fungi helped nourish plants. To agronomists, Howard's talk of altruistic fungal magic seemed just that. Still, he was sure that the agrochemical band- wagon was speeding down a dead-end street. "There is a growing conviction that the increase in plant and animal diseases is some- how connected with the use of artificials. In the old days of mixed farming, the spraying machine was unknown, the toll taken by trou- bles like foot-and-mouth disease was insignifi- cant compared with what it is now. The clue to all these differences—the mycorrihizal as- sociation—has been there all the time. It was not realized because the experiment stations have . . . [thought] only of soil nutrients and have forgotten to look at the way the plant and the soil come into gear." (An Agricultural Testa- ment, A. Howard, 1940, London, Oxford Uni- versity, p. 158.) Howard's lack of an explanation for exactly how fungi and other microbes helped plants undermined the scientific community's interest in his challenge to conventional wisdom. Be- sides, the clear evidence of the near-miracu- lous effects of fertilizers in reviving flagging crop yields on degraded fields spoke for itself. In short order, Howard's ideas were eclipsed by the Green Revolution's fertilizer-intensive approach to boosting crop yields. Life of the soil Another influential agricultural myth is an innocent half-truth I learned in college — that chemistry and physics govern soil fertility. In particular, I was taught that a soil's fertility lay in its cation exchange capacity — its ca- pacity to hold positively charged ions, essen- tial nutrients like potassium (K + ) and calcium (Ca 2+ ), loosely enough for soil water to take them up. This is not wrong, there's just more to the story. When farmers send samples off to a com- mercial lab to find out what is in their soil, it is with an eye toward what they need to add to boost plant growth. But the standard soil chemistry tests only measure the soluble frac- tion of what is in the soil, the stuff that water percolating through the soil can readily pick up and hand off to plants. c u lt i vat o r s o f c o m f o r t 1 5 % o f f c o d e : w v 0 7 @ r e d b a c k b o o t s . c o m S U P P O R T I N G W I N E G R O W E R S A N D V I N T N E R S T H R O U G H T H E G R A P E V I N E F O R o v e r 2 0 Y E A R S . c u lt i vat o r s o f c o m f o r t 1 5 % o f f c o d e : w v 0 7 @ r e d b a c k b o o t s . c o m S U P P O R T I N G W I N E G R O W E R S A N D V I N T N E R S T H R O U G H T H E G R A P E V I N E F O R o v e r 2 0 Y E A R S .