Does soil organic matter matter for crop productivity?

The review article, “Does Soil Organic Matter Matter for Crop Productivity?” was carried out by Ahamed Fazal Sultanbawa in The Open Agriculture Journal.

A new narrative review challenges one of the most widely held assumptions in agriculture that high soil organic matter is essential for strong crop yields and presents evidence from long-term field trials and modern soilless farming to argue that soil organic matter plays a largely indirect and conditional role in crop productivity, rather than the central, indispensable one it is so often assigned.

If you want to publish your article please visit : https://bit.ly/4de0DRi

The Assumption Under Examination

Soil organic matter (SOM) is the material derived from the decomposition of plant, animal, and microbial matter in the soil, and it is widely used by scientists, farmers, and policymakers as the single most important indicator of soil health and productive capacity. The premise is intuitive, richer, darker soil supports better crops. This view underpins a great deal of agricultural extension advice, the promotion of composting, no-till farming, and the sale of organic amendments and humic acid products. But does the evidence actually support it? The author of this review, Ahamed Fazal Sultanbawa, CEO of CropQuest Pty Ltd in Brisbane, Australia, sets out to test this assumption critically by drawing on long-term field experiment data, peer reviewed research on specific SOM components, and a direct comparison with crop production systems that contain no soil at all.

What the Evidence Actually Shows

The review opens with a example that anchors the entire argument: the Magruder Plots at Oklahoma State University, a wheat trial that has run continuously since 1892. Despite over 130 years of continuous wheat production with no fertiliser added, and despite soil organic matter declining from 4% to just 1%, the control plot has continued to produce wheat yields above one tonne per hectare. A similar SOM decline with stable productivity was observed in Oregon State University’s Columbia Basin wheat trial, established in 1931. These long-term datasets suggest that, at least above a very low threshold, reducing SOM does not directly cause proportional yield losses. The review then examines specific components of SOM that are often poorly discussed in mainstream agronomy. Soil waxes the hydrophobic compounds that accumulate from the breakdown of plant cuticles are one such component. Rather than improving soil, the buildup of these waxes, especially from Eucalyptus, Acacia, and grass species common in Australia and similar climates, can make soils water-repellent, reduce infiltration, and impair biological activity. This has practical implications for widely promoted practices such as mulching with bark or leaf matter and adding organic crop residues under no-till systems. On humic acids and commercial humate products, the review is similarly sceptical, noting that these products require much higher application rates than claimed to achieve meaningful changes in soil cation exchange capacity, and that rates above 0.1 grams per kilogram of soil can actually cause soil dispersion and increase susceptibility to erosion rather than improving structure. The review does acknowledge genuine benefits of SOM: it supports beneficial soil microorganisms including nitrogen-fixing bacteria, phosphorus-solubilising fungi, and arbuscular mycorrhizal fungi that contribute meaningfully to crop nutrition; it improves aggregate stability in soils rich in binding polysaccharides; and it offers some improvement in water-holding capacity, particularly in sandy soils, though the relationship is non-linear and levels off at higher SOM concentrations. For nutrient supply, the review raises a practical concern that is often overlooked: the rate at which SOM releases nutrients through decomposition does not always align with the stages of crop growth when those nutrients are most needed, making SOM a poor substitute for a managed fertiliser programme in commercial agriculture. The review’s sharpest counterargument to SOM’s claimed centrality comes from soilless production data. Advanced greenhouse tomato production achieves over 600 tonnes per hectare per year, and some systems exceed 1,000 tonnes figures that are five times or more than the best soil-based yields anywhere. Aeroponic systems have produced 53% more bell peppers, 35% more cherry tomatoes, and 50% more squash than field-grown equivalents. These systems operate with no SOM equivalent in their nutrient solutions, yet consistently outperform soil-based production. While the review acknowledges that energy costs are substantially higher in soilless systems one study found hydroponically grown lettuce required 82 times more energy than conventionally grown lettuce the productivity advantage is real and provides an objective benchmark against which the claimed importance of SOM can be assessed.

A More Measured Conclusion and Practical Takeaways

The review concludes that SOM does matter, but not in the categorical way that its promotion often implies. Its role is primarily indirect: supporting the physical structure that gives soil stability against wind and water erosion, maintaining the conditions in which beneficial microorganisms can thrive, and contributing to nutrient cycling over time. The evidence from long-term trials supports a saturating, non-linear relationship between SOM and crop yields, with the relationship most pronounced between 1% and 4% SOM and with diminishing returns above that range. Below approximately 0.5% SOM, soil physical structure begins to fail in ways that can reduce productivity and accelerate erosion, suggesting that a minimum threshold matters more for land stability than for direct crop nutrition. The practical message for growers and advisors is that programmes built primarily around raising SOM through expensive organic amendments or humic acid products are unlikely to deliver proportional yield benefits, and that a managed nutrition programme independent of SOM contribution is a more reliable strategy for commercial crop productivity. For soil-based agriculture’s long-term sustainability, however, maintaining adequate SOM levels remains important, not because the soil organic matter itself drives yields directly, but because the broader ecosystem processes it supports microbial activity, structural stability, and water movement underpin the conditions that make productive farming possible. The research was led by corresponding author Ahamed Fazal Sultanbawa, CEO, CropQuest Pty Ltd, Brisbane, Australia.

Read the published article here: https://bit.ly/4jnVaw2

Article title: Does Soil Organic Matter Matter for Crop Productivity?

DOI: 10.2174/0118743315502617260909110930
http://dx.doi.org/10.2174/0118743315502617260909110930