Following the analysis I started in post #532 on
Teague et al, here the non-hedonistic review:
In that paper there's no comparison or "before and after" photos. Three trios of neighbouring ranches (not always, really) were selected with each ranch in every trio practising a different grazing technique: heavy continuous grazing, light continuous grazing and multi-paddock (up to 41 camps). It was assured the same technique had been used during at least 9 years previous to the beginning of the study. Some ungrazed fields were selected in the same areas for the sake of comparison.
To be brief: the study is a photograph, not a study during a certain period. Indicators have better values in rotational grazing. Among those indicators is the organic matter in the soil.
Table 6 shows soil organic matter mean values for each technique (but strangely no range is shown). The first faux pas in #532 was mixing up organic carbon with organic matter: the latter is shown in the table so soil organic carbon is 58% of that. I will stretch to the 90-100 cm layer the values for a depth of 60-90cm in order to get the soil organic carbon according to each technique:
heavy continuous grazing: 1.4% of carbon (25 kg of C/m2)
light continuous grazing: 1.79% of carbon (32 kg of C/m2)
multi-paddock: 2% of carbon (36 kg of C/m2)
graze exclosure: 2.01% of carbon (36 kg of C/m2)
What would promote jumping to the conclusion that you sequestrate in nine years 11 kg of C/m2 (12 T/ha-yr) just by changing from heavy continuous grazing to multi-paddock. It is implied that the yield is constant.
But wait a minute, where does this come from? First of all, we have overgrazed ranches and skilfully managed ranches with a range from 25 to 36 Kg of carbon / m2 in the first metre of soil. Then, why is the Soil Survey Division of the Natural Resources Conservation Service at U.S. Department of Agriculture saying otherwise? Here is the soil organic carbon map for the region (the three counties in the study are shown - click on the image for a larger version):
According to that, the soils in those countries have and average from 8 to 16 kg of carbon for square metre. Why the difference? If % of organic matter is something different than "grams of organic matter by each 100 grams of soil" as it's the standard in the trade, why there's no clarification? Maybe because the paper doesn't point to organic carbon but other indicators of soil health and proxies of productivity.
On the other hand the change from one to another point doesn't take nine years. The study says that they assured the same technique was used during at least the last nine years, and that may imply that some farmer changed from heavy to light continuous grazing -because he saw his soil going to the dogs- while the multi-paddock dudes were doing that for two generations. Who knows? No other data is provided.
On top of that, there's an explanation of the strict mechanism of selling cattle from the multi-paddocks the very moment low growing conditions or drought show. No explanation is given about what they do in the continuous-grazing ranches. Isn't the rotational grazing a technique that fosters anticipating management? Isn't it possible that the ranches using such primitive techniques as continuous grazing only sell cattle when the animals start to lose weight? The very values in tables 1 and 8 give a hint: heavy continuous and multi-paddock are shown with the same stocking rate (270 pounds of cattle per hectare) but having a huge difference in standing crop biomass (some 70% more in multi-paddock). How is this possible? Isn't being showed a heavy overgrazing for the sake of a dramatic comparison?
The important fact is how those soil analysis come to be the way they are. There's a simple reason to do continuous grazing: having less fences, less watering places and places for roundup, and less workers; less investment and less fixed expenses, in short. That makes me think that such investments rarely appear overnight, and farmers rarely have epiphanies and change their uses overnight either. Within the ranches analysed those doing multi-paddock most probably evolved along decades from a light continuous grazing into a more professional rotational grazing, and it's almost impossible that ranches doing heavy overgrazing changed overnight, got a loan and implemented rotational grazing overnight to show such spectacular improvements in a period of nine years. If that was the case, I am sure it would had been explicitly expressed in the paper.
On the other hand, the soil sampling is explained in detail, but there's a trick: they selected points far 200 m from the watering places to avoid the overgrazed and overdunged soils close to them. But in multi-padock (in some case the paddocks were just 8 hectares big) that is very far from the watering place, so there are differences. They declared they let the professional sampler to select the places to make the soil analysis, and that is good, but it puts more variability into the study.
Did I say that the ranches included slopes? In a context of overgrazing, part of the organic matter of your land is probably to end up in your neighbour's. In a context of sustainability, you are probably to get organic matter from your neighbour uphill, if he uses overgrazing.
The final reality check is comparing the induced inference of gaining 11T of carbon per hectare and year with the significantly lesser 4.68T/ha-yr of standing crop biomass in multi-paddock (table 8). Where would that carbon come from? Would it be a problem of publication? After all the counties are shown to be around 33°W and 98°N! and that is a bit above the northern lights next to Santa.
These are just a few comments about what the paper does say and doesn't really imply. The paper was never intended as a way to show how much carbon can be sequestered into soils. Doesn't surprise anybody that productivity itself -ultimately, farming is a commercial activity- is not analysed?
The paper can be compared to this:
Three families were analysed. One family earned 20k a year and spent 30k, so nine years later they are indebted 90k . Another family earned 30k a year and spent 30k so they are out of new debts. The intelligent family earned 40k a year and spent 30k so they have savings of 90k. These savings-debts of 180k in nine years are soil organic carbon. Conclusion: Waste not, want not.
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