Organic farmers build soil life by adding compost and other organic materials, diversifying crop rotation, growing cover crops, using legumes to provide nitrogen (N), and integrating crops and livestock. Soils rich in organic matter retain more air and water and produce higher yields than soils with low organic matter content. They also provide a constant release of nutrients to plants, inhibit erosion, and harbor a robust population of beneficial microorganisms. Soil health is the foundation of organic agriculture systems.
Fertile soil provides essential nutrients to plants and, at the same time, supports a diverse and active biotic community that helps soil resist environmental degradation. Organic producers face unique challenges in managing soil productivity. The current guidelines on nutrient management for organic farmers are fairly general in nature. Organic farmers rely on intuition and observation, advice from sellers, conventional soil testing and their own experience to make decisions about the quantity and types of soil amendments they should apply.
As a result, there is enormous variability both in the amounts of nutrients that are applied and in the resulting state of soil fertility in organically managed farms. Organic farmers seek to build soil or improve its inherent fertility through the use of crop rotations, animal and green manures, and cover crops. Crop rotation and tillage practices should provide adequate seedbed and pest control while minimizing erosion. Nutrient reserves are maintained through the use of natural (non-synthetic) substances and approved synthetic substances that are on the National List of Allowed and Prohibited Substances.
This list includes some synthetic inputs approved for fertility, such as elemental sulfur, aquatic plant extracts, and liquid fish products. Many substances on the National List have restrictions or annotations on their use, source, or rate of application. Organic farmers are advised to consult their certifying agent before purchasing or applying any synthetic input. See Can I use this input on my organic farm? for more information.
In addition, organic producers must document their soil management practices in their organic agriculture system plan as part of their certification, and keep a record of all inputs purchased and applied. The subjects ate a conventional or organic diet with identical amounts of the same foods for 22 days, and then changed diets and repeated the process. Similarly, a global meta-analysis of organic agriculture systems revealed that the combination of conservation tillage, cover crops and organic amendments greatly improved soil health by increasing soil organic matter and microbial biomass (Crystal-Ornelas et al. Diverging study designs and the possibility that confounding factors can blur differences help fuel discussions about the supposed health benefits of organically grown foods.
However, the most striking and relevant result for human health from previous studies is that significantly more phytochemicals are constantly found in organic foods, a result that is normally overlooked, since they are not considered nutrients despite their known connections to human health. Since crop varieties grown for conventional agricultural systems produce low yields when grown in soils poor in organic matter without synthetic fertilizers, reproduction for optimal performance in agricultural systems that promote soil health presents significant opportunities to improve both nutrient density and yield. And since agricultural practices affect the levels of several phytochemicals in crops, the interpretation of whether agricultural practices affect the nutritional quality of foods seems to depend on how nutrients are defined. These findings establish contradictory narratives about the possible differences between organic and conventional foods.
The yields of zinc and wheat available to plants in the soil did not differ between conventional and organic farms, but organic wheat averaged 20% more zinc content. It should be noted that zinc levels were traced with colonization by mycorrhizal fungi, which conventional agricultural practices reduced. Fruit quality, antioxidant capacity and flavonoid content of organically and conventionally grown blueberries. Most of the studies reviewed found significant differences in the composition of the soil community, and organic agriculture practices increased soil abundance and life activity (Lori et al.
Nutritional and sensory characteristics of “early potato” cultivars in organic and conventional cultivation systems. To assess the effects of agricultural practices on nutrient density, soil health adds a much-needed dimension: the supply of micronutrients and phytochemicals that promote human health. While the first research on the effects of conventional agriculture on nutritional quality focused on improving dietary protein intake, researchers discovered the possible adverse influences of nitrogen fertilizers and other now-conventional agricultural practices on vitamin content and mineral density long before the microbial roots of those connections were understood (Montgomery and Biklé, 2011). The conventional distinction and standard definitions of what constitutes a nutrient are not adequate to fully assess the dietary impact of agricultural practices on human health.