From the report «The Take-Half, Leave-Half Fallacy«, from John Kempf, published at ACRES USA.
Mr. Kempf argues that the widely accepted soil building grazing guideline “take half, leave half” is based on a misunderstanding of how different plants allocate sugars and build soil carbon. Many USA producers report that despite decades of rotational grazing, their soil organic matter has stagnated or declined, prompting the author to examine how grasses, forbs, and legumes partition carbohydrates at key growth stages. He explains that grasses store most of their surplus energy in root biomass rather than in root exudates, which means they regrow quickly after a 50% graze but contribute relatively little to long‑term soil carbon unless grazed down to the ground.
Research cited in the article shows that only a small fraction of carbon in aboveground biomass remains stable in soil, whereas more than 90% of carbon released as root exudates persists long‑term as humic substances with decades‑long half‑lives. Because grasses devote only about 5% of their sugars to exudates, they are poor builders of stable soil carbon. Forbs, by contrast, allocate roughly 35% of their sugars to exudates and maintain strong symbioses with soil microbes, making them far more effective at generating long‑term soil organic matter.
The author notes that consistent “take half, leave half” grazing favours grasses because their large root reserves allow rapid regrowth, while forbs—storing less energy in roots—are outcompeted and decline over time. This shift reduces soil carbon formation and diminishes plant diversity. To counter this, he recommends periodically grazing grasses very intensively, down to the ground, to temporarily weaken their root systems and allow forbs to reestablish. Although this practice may reduce forage yield in the first year, producers commonly observe higher meat production per acre in subsequent years due to the greater nutrient density of forb‑rich pastures.
The author situates these insights within the context of native ecosystems, where forbs vastly outnumber grasses and contribute to high species diversity and robust soil microbial communities. Historical accounts of bison grazing—removing grasses down to the dirt—are presented as evidence that natural grazing regimes did not follow the “take half, leave half” rule. The author concludes that reintroducing periodic heavy grazing can restore forb populations, enhance soil carbon sequestration, and improve long‑term pasture productivity.