Soil Saneters:

I am seeking some common ground and understanding on an issue which seems to be of extreme importance to many organic farmers and consultants but given little attention by academic scientists - that is soil cation balancing and the importance of calcium (Ca) in soil structure.

Time and again, when speaking with organic farmers and the consultants who serve them, I find the importance of cation balancing and soil Ca come to the center of the conversation. In lay terms, the basic idea is that inadequate exchangeable Ca results in poor soil structure, characterized by "tightness" because the amount of pore space for air is less than optimal. Consequently, root health is compromised and nutrient availability and uptake reduced. A general rule often given is that the ratio of Ca to magnesium (Mg) should be about 5-7 to 1. If it is less - you need to add Ca.

As the research manager of a long-term study/comparison of organic, low-input, and conventional farming systems at the Univ. of California at Davis, I am sometimes criticized by these folks for giving inadequate attention to this issue. In this study, all of the farming systems are managed according to "best farmer management" strategies - which are determined by a group of academic and Extension researchers, Extension farm advisors, and farmers. Admittedly, we have not made or altered any management practices in this study based on soil Ca:Mg ratios. Consequently, some organic farmers and consultants argue that the organic system in this study is being shortchanged because we have not given the soil Ca:Mg ratio proper attention.

When I ask where I can get more information on this matter I am usually referred to William Albrecht and his Papers. He published a number of studies during the 1920-1940s in the J. Amer. Soc. Agron. but I have found that his name now seems to be reserved for the pages of Acres USA (not to diminish Acres USA). My point is that I find no recognition or ackowledgement of him or his work in basic or advanced textbooks on soil science and fertility management or among research scientists - even among those who are doing research on organic and low-input agriculture. It seems that Albrecht is to many in the organic movement what Stinner is to the Biodynamic movement. I see some people adhere to his "Papers" with almost religious conviction.

Getting back to my problem: The Ca:Mg ratios of the soils at this study site are nowhere near 5-7:1. In fact, they are less than 1:1. The Ca:Mg ratio in the organic system in this study is significantly (statistically) higher than that of the conventional system due to the Ca in the composted and aged manures that have been added over the years, but in absolute terms the difference is still quite small. There is a clear difference, however, in water infiltration rates between the organic and conventional systems. Rates are much greater in the organic system (which we presume is due largely to the higher soil organic matter levels in this system). Therefore, if any of the farming systems in this study is in need of management to remedy a soil structural problem it would be the conventional system. And, indeed, the group has discussed applying gypsum to improve infiltration rates in the conventional system.

However, the claims go beyond simply improving soil structure to enhance root growth and plant health. I am also told that the nitrogen (N)-use efficiency of the organic system would improve and that disease severity would decline with an increase the Ca:Mg ratio. The latter doesn't particularly interest me right now because diseases have not been a serious yield-limiting factor in any of the farming systems. But, the potential to improve N management in the organic system does. As many studies comparing organic to conventional systems have found, the release of mineral N from organic amendments and soil organic matter and uptake by the crop are not always predictable. Hence, we generally apply considerably more N to 'nitrophilic' crops in the organic system to compensate for unpredictable N mineralization and make up for that taken up by soil microbes or weeds. But losses from the organic system (due to leaching, denitrification, and volatilization) are not any greater in the organic compared to the conventional system. Therefore I do not see how the addition of Ca would reduce the amount of N which needs to be added - even over a long term.

Ouestions:

Are Albrecht's views accepted by "mainstream" soil scientists or are his ideas considered fringe? Do any university laboratories adhere to any of his concepts? Can anyone direct me to studies on Ca:Mg ratios and cation balancing (I have found very few)? Also, do any growers on the list have personal experiences with using soil Ca:Mg ratios in fertility or disease management ?

Thanks in advance,

Sean

M. Sean Clark
Research Manager
Sustainable Agriculture Farming Systems Project
Department of Agronomy and Range Science
University of California
Davis, CA 95616
msclark@ucdavis.edu
TEL:(916) 752-2023
FAX:(916) 752-4361