Organic Matter In Soil Boosts Garden Yields


March 7, 2018

Just how much can adding organic matter to soil affect your harvest? About 22% more food to pick on average, according to a recent study. Not the standard scientific study, mind you. This research team at West Virginia University went about this discovery properly. They knew that a long-term study meant more than just a year or two when it comes to learning what happens over time. That’s important because building soil isn’t quickly achieved.

Nature works wonders when left to her own devices. It’s never an instant thing and usually a team effort from start to finish. So, wisely, this organic farming study at WVU started in 1999 when researchers created 32 – 16’x24′ growing plots measuring to study what happens over time when you add organic matter to the soil every year.

organic matterSixteen plots had high organic inputs and the other half got very little. In fact, those low input plots got treatment similar to conventional farm fields. Which means they only added an annual cover crop of rye and vetch for organic matter to the soil. Then they applied chemical fertilizer to make up soil fertility loss to crops. But the high input plots got treated with 10 tons per acre of dairy manure. The fall applications for both groups of plots also had mixed species hay mulch added every other year.

At the beginning of this organic matter in soil study in 1999, they took measurements of existing organic matter in the top 6″ of soil in each plot. All the plots had 4.4% soil organic matter profiles. Over the years they planted green beans, lettuce, green peppers, tomatoes, and zucchini on a 4-year rotation schedule.

Five years into the study, the high input plots contained 6.4% organic matter in the soil. The low input conventional plots had only increased to 5.2%. Ten years later, those low input plots weren’t much better with 5.4% organic matter content. Yet, the organic plots that also had dairy manure treatments measured out at a whopping 8.7% organic matter.

As the authors of the paper published in the April issue of the scientific journal Hort Technology (vol. 27) stated – dairy manure added to green manure and hay mulch incorporation delivers significant economic returns. Low input plots had much lower yields. Peppers had the highest yield increase from all that extra organic matter in soil at 25% more fruits. Zucchini and green beans weren’t far behind at 24% bigger harvests. Tomatoes, however, didn’t increase as significantly at 9% more yield. But this plant has a particular set of needs. If one thing is off, yield and fruit quality will drop.

Milking cow manure is rich in calcium, which no doubt assisted the tomatoes despite the fact that the soil showed low phosphorus and potassium levels. A bit surprising given all that organic matter in soil addition over the years. There are both soil type and environmental factors that may contribute to that result, but it’s hard to say if they discussed that in the full report. Only the summary has free access.

organic matter

Dairy manure is also important here because it comes from lactating animals. Both biodynamic farming and a special preparation that allows growing plants in the desert insist that it is stronger than the manure from other animals. If you read Evan Folds Archea and the Origin of Earth article in the last issue of Garden Culture, you will learn more about manure elixir. The reason I mention it here is that dairy manure is likely your wisest choice in brown manure for building organic matter in your soil.

Check the label on the bagged compost with manure you buy. If it’s bargain-priced, the bag probably contains unidentified cow manure, steer manure, chicken or poultry manure… anything but dairy manure. Plain old NPK isn’t everything plants need to excel. Balanced fertility also includes micronutrients, enzymes, carbs, and more. So you might want to consider spending a little more on manure that contains dairy manure.

As this study shows you, not all organic matter is equal. If you really needed ‘accredited’ proof that the effort of working animal manures and other organic matter in soil was worth it – here it is. And it’s published in a leading science journal.

Images courtesy of Local Food Initiative, Futurilla, and USDA (respectively).



Contributing Writer at Garden Culture Magazine
The garden played a starring role from spring through fall in the house Amber was raised in. She has decades of experience growing plants from seeds and cuttings in the plot and pots.

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