Fertilizing crops with micronutrients can improve the nutrient density of food Original paper

This systematic review reported that micronutrient fertilization can increase the nutrient density of various crops. Modulating factors, limitations, and the potential to reduce rates of malnutrition were discussed.

The effect of micronutrient crop fertilization (i.e., agronomic biofortification) with one or more nutrients on crop nutrient concentrations.

Horticultural crops (e.g., leafy greens, garlic, tomatoes, peas) grown from 2012 to 2022.

This systematic review included 47 studies published from 2012 to 2022 that investigated the use of fertilizer that contained various minerals and vitamins, including zinc (12 studies), selenium (10 studies), sulfur and vitamin C (4 studies each), calcium, copper and iodine (3 studies each), iron, manganese, molybdenum and B vitamins (2 studies each), cobalt, nickel, phosphorus, potassium, magnesium, and vitamins A and K (1 study each). The growing mediums tested ranged from fields to greenhouses to soilless systems like hydroponics.

A meta-analysis including 24 studies was also conducted when the enrichment factor was reported, which was defined as the ratio of nutrient content of the fortified product compared to the control. An enrichment factor above 1 means the fortified crop contains more of the targeted nutrient.

Micronutrient fertilization has been successfully demonstrated for most studied micronutrients, including zinc, selenium, calcium, iron, and vitamins C, A, and B9 (folate). Fertilization has been shown to be successful for various horticultural crops, including leafy greens, tomato, carrots, grapes, and peas. However, most studies tested agronomic biofortification in controlled conditions (soilless, greenhouse, etc.) where it may not have the same effect as in the field or on a larger scale.

Several key aspects that can influence agronomic biofortification must be considered. Variations in soil or growth conditions, climate, crop species, agronomic practices (e.g., method and rate of application, form of fertilizer), and micronutrient sensitivity to environmental conditions and complexity of biosynthetic pathways can affect the success of biofortification practices. Moreover, the success of biofortification can depend on whether the nutrient concentrations improve in the edible portions of the plant without causing plant or human toxicity. Some studies also suggest there are potential synergistic effects when micronutrients are fortified in combination. For example, zinc may improve fortification of molybdenum and manganese.

Malnutrition, including nutrient deficiency, is a prominent issue that affects a large portion of the world’s population.^[2][3] Among the many risk factors for malnutrition, poverty is one of the strongest. Because malnutrition increases health care costs and reduces productivity, these 2 factors combine into a vicious cycle that is hard to break. There’s a reason that the United Nations’ top three sustainable development goals (SDGs) are (i) no poverty, (ii) zero hunger, and (iii) good health and well-being.^[4] Zero hunger involves an emphasis on food security, improved nutrition, and sustainable agriculture. Some researchers suggest these factors can be addressed with interdisciplinary research involving a group of “farm-to-plate” professionals (e.g., agronomists, soil scientists, food processors, and nutritionists).^[5]

One of the main questions in the space of nutritional quality of horticultural crops is whether “modern” food is actually lower in nutrients. Although some data suggest there has been a decrease in micronutrient density within the last century,^[6] which can be attributed to factors like changes in cultivars used and agronomic practices associated with the industrialization of agriculture, there are several variables that can influence the data and thus the interpretation of the result. Generally, older data were poorly controlled and do not compare very well to newer data because of either missing data and different methods of assessment. ^[7] The detection limits of older assessment methods were also quite limited compared to those of the state-of-the-art methods used today, which may contribute to apparent decreases.

Still, there is evidence to suggest that the streamlined use of high-yield varieties of certain crops (such as wheat) that channel more of their energy to carbohydrate production leave less capacity for protein and micronutrient production.^[8] This change in nutrient allocation was also correlated with increasing environmental temperatures and carbon dioxide levels resulting from anthropogenic activities. Some estimates suggest that higher carbon dioxide levels will increase the prevalence of malnutrition, particularly as it relates to iron, zinc, and protein.^[9][10]

Crop biofortification has been suggested as a relatively cost-effective and sustainable approach to tackle the burden of malnutrition and improve the nutrient density of food.^[11][12] Crop biofortification is the process of improving food crop nutrient density, whether through crossbreeding (i.e., conventional plant breeding), modern biotechnology, or agronomy (i.e., soil or leaf fertilizer application), without sacrificing any crop characteristics preferred by consumers and farmers.^[13] Thus, assuming greater nutrient density and similar (or improved) micronutrient bioavailability and retention after cooking/processing and storage, people would presumably consume and absorb more micronutrients from biofortified crops compared to nonbiofortified crops.^[14] Of the few biofortified crops that have been researched from farm to intervention, those involving iron have been shown to improve iron stores and reverse deficiency,^[15][16] and those involving vitamin A (specifically beta-carotene, a vitamin A precursor) have reduced deficiency. Interestingly, the World Health Organization doesn’t have any explicit recommendations for the use of biofortification and instead have suggested that further research is needed before any recommendations can be made.^[17]

Biofortification methods to create high-nutrient, high-yield crops

Alongside the potential benefits of crop biofortification, each method carries its own limitations related to time, specificity, acceptability, and variability.^[18] Crossbreeding — which has contributed to the high-yield, carbohydrate-rich staple crop varieties — is a lengthy process that is limited by the amount of genetic variability for micronutrients in the gene pool of each specific crop cultivar. Transgenic methods (e.g., genetically modified organisms or GMOs) are not only limited by low public acceptance and political and economic receptivity to the technology but also by concerns regarding the time required for research, development, and implementation. For example, golden rice, a transgenic form of rice that was genetically engineered to biosynthesize beta-carotene in an attempt to combat a range of eye conditions linked to vitamin A deficiency, took 8 years to develop, only to be met by unaccepting governments and problems with production yields.^[19]

Agronomic biofortification is probably the simplest form of crop biofortification, as it involves the application of fertilizers fortified with micronutrients, but results can vary broadly according to differences in mineral mobility and accumulation, soil composition, and environmental conditions. It is also the least cost effective as it requires proper regulation and management, it doesn’t guarantee improvements in nutrient concentrations of the edible plant parts, and there’s concern about environmental effects of excess fertilization.^[20]

Beyond crop biofortification there are advocates of “more natural” methods of crop micronutrient optimization, such as regenerative agriculture that includes calculated crop rotation and compost/manure use.^[21] These practices may naturally preserve or enrich soil biodiversity and crop-microbiome symbiosis.^[22] Although several successes have been demonstrated with regenerative agriculture, some key variables are still being explored (e.g., soil bacteria and fungi), as evidenced by a diversity of approaches and variables that have yet to be systematically compared and evaluated, similar to research on biofortification.

Ultimately, the solution to improving the micronutrient density of food requires collaboration among experts from a variety of fields. Once the most important strategies are identified, adequate education, regulation, and implementation are necessary to improve food nutrient density, as well as food security and the sustainability of agriculture. These methods should indirectly and partially address malnutrition, as well as the top three SDGs.^[20]

Sensory acceptance of biofortified crops tended to be high (even if there is a change in color), but the most important determinant of acceptance and adoption appeared to be availability and information on health benefits.^[1]

Iodine, vitamin A, and iron were the most important micronutrients in global public health terms.^[2]