Biostasy

The Theory of Biorhexistasy describes climatic conditions necessary for periods of soil formation (pedogenesis) separated by periods of soil erosion. Proposed by pedologist H. Erhart in 1951, the theory defines two climatic phases: biostasy and rhexistasy.

If I recall, H. Erhart figured this out while on the Congo river contemplating a low sediment load in a high rainfall, potentially highly erosive setting. Impressive. There is a soil science truism that clean water is hungry water, and can't wash across or through the land without taking some with. From a soil scientist's perspective, water is soil in highly dilute form. (So is air.)

Reading between the lines, I don't think Erhart had a research budget much beyond travel expenses. He simply deduced from what he knew of tropical weathering that the river had to be laden with dissolved minerals, calcium especially, washed from the soil by percolating rain water. Groundbreaking as that was in its own right, he didn't stop there. Using induction, he reasoned that when similar conditions dominated it ages past, rivers would have delivered abundant calcium to ancient seas subsequently (at the close of the age, perhaps) yielding vast limestone deposits. He saw these ages as lush, moist, and warm with accelerated chemical weathering accompanied by the formation of deep soils. Biostasy. Between periods of biostasy, he envisioned conditions dominated instead by physical weathering: severe fluctuations in temperature and moisture, sparse vegetation, shallow exposed soils, rivers choked with sediments, but with low solute content. This insight informs interpreting endokarstic sediments(Yves Quinif) in Europe where stalacite formation is observed to be greatest, and with least sediment, during interglacial periods due to higher dissolved calcium content, and less soil erosion.

Simply as a mental exercise, consider a scenario where atmospheric carbon dioxide hits 1200 ppm 200 years from now. In the context of biorhexistasy, what is going to dominate? biostasy, rhexistasy or will it be something well outside H. Erhart's elegant construct? Considering that the Congo and the sediment laden Nile coexist in the same age, it is certainly conceivable that biorhexistasy will continue to play out differently based on location, with neither dominating. But the undeniable effect of higher carbon dioxide is higher chemical weathering. So maybe rhexistasy during the transition, followed by biostasy.

(Recycled from nscss.org)

Soil Management - 9 Crop Specific Guidelines

Searching on the term "soil husbandry", I came across this rather concise web presentation on environment-sensitive farming. It covers a wide variety of crops, cropping systems and soil types, so I am sure most will find something in here that is new. For me it was tramlines. Enjoy!

Garden Char Processing

I've added some photos to Flickr on how I currently prepare my charcoal for add ing to garden soil. This is in support of the Biochar for Gardeners FAQ.

I am lightly soaking (shallow soak, lots of turning to keep surfaces moist) my charcoal to precondition it for a crush-and-chop reduction and then screening. To soak, I add soluble mineral fertilizer and fish emulsion. Once in the soil, these will stimulate biologic conditioning and will help prevent stalled plant growth due to induced N deficiency, a concern with direct use of fresh char in the garden.

Also, regarding the mineral fertilizer, I have it in the back of my mind that adding ammonium sulphate (a common ingredient in off-the-shelf soluble fertilizer formulations) to the soak water will boost water penetration. I am thinking this might help because ammonium sulphate is used hold farm chemicals on waxy plant surfaces (like thistle), and because saltier water generally tends to penetrate further and faster into problem soils. I am encouraged to think that ammonium sulphate helps to overcome fresh charcoal's water repellency, even if only to a slight degree.

Soil pH and Plant Nutrients

Doug Edmeades gives out sound advice on pH.

It used to be believed (going back to the early days of soil science) that the ‘ideal’ soil was neutral: neither acid nor alkaline it had a pH of 7.0. This early belief still prevails especially in Charlatanville. However, with the benefit of much subsequent research our view of the ideal soil pH has changed.

First, it is now known that different plants have different tolerance to acidity. Restricting the discussion to pasture species, browntop is very tolerant to acidity which is one reason why it thrives in undeveloped soils. Ryegrasses are more sensitive and like a higher pH. Clovers are more sensitive again and, of the legumes, lucerne is very fussy. Our pastoral agriculture is focussed on growing clover-ryegrass and the optimal pH is 5.8-6.0 – this is the pH at which pasture production and especially clover production is optimised. In contrast, a straight lucerne stand requires a pH of about 6.5.

Liming pastoral soils above pH 6.0 is not recommended for several reasons. First, there is no benefit in terms of production and it can have detrimental effects on both pasture production and animal health. As the soil pH increases the availability of soil molybdenum (Mo) increases and thus the pasture Mo content increases. This can, in some cases, induce copper deficiency in animals. Also, increasing the soil pH above 6.0 reduces the concentration of soil zinc (Zn) and manganese (Mn) concentrations. This can result in induced Zn and Mn deficiency. Liming soils, contrary to popular belief, is not always beneficial!

He also works up a sensible New Zealander's criticism of liming to "fix" the Ca:Mg:K ratio.

Lime is typically calcium carbonate. For us in New Zealand the active ingredient in lime is the carbonate not the calcium (Ca). Our soils fortunately are rich in Ca – indeed often awash with Ca – a result of their origin (from the sea) and youthfulness (not very weathered).

Given that the benefits of liming are related to the change in soil pH then it should be obvious that the only useful guide and hence measurement for the requirement of lime is the soil pH. This is the adopted science-based approach used in New Zealand.

So what about all this base saturation ratio argument? In the 1930s there were two competing theories about plant nutrition. One said that the ratio of the nutrients Ca, Mg, K and Na was important. These were measured as the proportion of the soil cation exchange capacity (CEC) – the ability of a soil to store these nutrients called cations. Thus your hear some say that the Ca saturation of a soil is 50% meaning that 50% of the CEC was occupied by Ca. The other theory was that plants did not care what the ratio of nutrients were – the plant was fine providing the minimum amount of each nutrient was present. This is called the Sufficiency Theory distinguishing it from the Ratio Theory.

After almost 80 years of research the jury is definitely in. The Ratio Theory is not consistent with observations and hence is now set aside. Indeed we now know that using the Ratio Theory as a basis for fertiliser recommendations can be and often is misleading. For example the Base Saturation Ratios of Ca in most New Zealand soils would suggest they are Ca deficient. The fact is they are not and Ca deficiency has never been recorded in New Zealand.

There are other problems with the Ratio Theory. It applies to only 3 nutrients (Ca, Mg and K – appreciating that Na is not required for plant growth (except on some crops such as sugar beet).

What about all the other 13 plant nutrients? Also we now know that soils have variable charge – this realization has occurred within my 30-year career. The consequence is that the CEC depends on the pH at which it is measured. The old method still used by the quack brigade measures the CEC at surprise, surprise the “ideal” soil pH of 7.0. This inflates the CEC thus reducing the base saturation ratios, especially for Ca. By sticking to this now disproved methodology the quacks can be certain that the soil test results will say the Ca base saturation ratio is low therefore apply my product because it contains Ca.

My region's soils are similarly well supplied with calcium. My agricultural consultancy mentors taught me to be skeptical of the Ca:Mg:K approach to evaluating soil nutrient status. In my region it was used to justify expensive formulations of foliar applied applied calcium, or to justify adding expensive soluble calcium to the irrigation water on soils with a good supply of calcium. Normally on high value crops in good years when adding extra nutrients for insurance has legs. Charlatans is not too strong a word. Back in the 1980's these folks would use A&L Laboratories, well established, amny offices, with an excellent professional reputation, and which reported Ca:Mg:K in a ratios friendly format. I'll bet this is still the case. You can't beat something like that for conferring legitimacy, can you?

The originator of the ratios approach, soil scientist William Albrecht was a brilliant observer of nature with a considerable body of work which still gets a lot of play. The basic premise of Albrecht's 1938 Loss of Soil Organic Matter and Its Restoration is solid: it takes a ready supply of soil calcium and nitrogen to build soil organic matter. His concepts continue to be stretched beyond to the breaking point both by well meaning folks exchanging advice on organic farming methods, as well as in efforts to sell product to the unsuspecting. Yet we don't read much in the way of criticism of the ratios approach. It is excellent of Doug Edmeades to voice his concern.

No Miracles

Charcoal cannot replace the need for adding mineral nutrients.

I am an unabashed charcoal enthusiast. Used properly, adding charcoal to soil improves biomass production and soil health. Sometimes dramatically when soil productivity is low. Certainly part of the effect is increased nitrogen use efficiency: less N lost to nitrification and leaching. Charcoal also tends to be associated with higher post harvest soil levels of P and K for reasons that are not entirely clear. Perhaps this effect also is due to increased efficiency.

Most TP enthusiasts, myself included, are convinced that the most mysterious effects from adding charcoal relate to soil biology, more than they relate to direct physical and chemical effects, although those realms play important roles also. And, in keeping with my previous post, it seems clear to me that increased energy efficiency is a critical bit here. Plants and microbes are growing more biomass with less effort for reasons that can't be entirely explained by traditional nutrient-based perspectives. Yes, the charcoal adds potassium, yes it raises soil pH, yes it increases soil water and nutrient holding capacity. But the results speak to more, much more.

The behavior of charcoal amended soil seems to defy the limits of the soil-biology system understood by traditional science. However, it would be entirely foolish to think that simple soil nutritional requirements are not still in play. Nutrient deficiencies limit living systems. Charcoal may promote efficiencies that help stretch the budget in regards to those limits, but in the end, the most limiting nutrient before adding charcoal is probably still going to be the most limiting nutrient after adding charcoal.

What got me thinking about this was consulting soil scientist Doug Edmeades’ posts on soil organic matter. The first, Carbon farming: take-off or rip-off, explored how carbon sequestration efforts can cut both ways. The second, Soil Organic Matter Matters, hits on the most-limiting-nutrient.

Pasture plants need 16 nutrients. Without all 16 the clover will disappear, the pasture will be N deficient, the quality grasses will fail, pasture production would collapse followed by a need to cut back the stocking rate and, given sufficient years, a farm would be back to native pastures and bush. In the process soil carbon levels would decline.

Collapsed pasture production is no idle threat. We know that the collapse of legumes in pasture systems in Europe and in the eastern US helped motivate the expansion of the western US. Against that historical backdrop, Benjamin Franklin famously demonstrated sulfur deficiency when he added gypsum to alfalfa to form the words "This has been plastered". Doug Edmeades mentions this because soil carbon sequestration enthusiasts seem to have temporarily lost track of these limits. The same caution applies to charcoal.

There is great potential for increasing productivity through judicious use of charcoal. However, TP enthusiasts must not lose sight of the fact that charcoal cannot replace the need for adding mineral nutrients.