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Feed your plants for human health
Human health depends on food quality. Food quality, in turn, depends on plant nutrition. In particular, plant nutrition determines the contents of protein, vitamins and minerals.
Nitrogen
All proteins contain nitrogen (N). So, within limits, extra N fertiliser will increase protein content. However, the primary consequence of higher N is higher yield, as chlorophyll, which produces sugars, has a high N content. More N means more chlorophyll means more sugars and starch. So the protein increase is less than the yield increase.
But too much N can, of course, lead to problems. Management tools (such as computer programs) that allow you to balance quantities, timing, form and placement of N (and other) fertilisers can optimise both yield and quality while minimising adverse effects such as wastage and runoff. For example, it might be possible to apply controlled-release fertilisers or foliar sprays to increase yield or protein content while reducing losses.
Minerals
It should not be a surprise that most of the nutrients that are essential for humans are also essential for plants. Increasing the uptake of minerals by crops will (again, within limits) increase the contents of those minerals in the food that we eat. So fertilising to improve plant yields also improves nutritional quality. Plants won’t take up more than they need, but “need” can be determined by the availability of other minerals – as we’ve discussed before in relation to Liebig’s Law of the Minimum. If any nutrients are lacking, increasing their availability to the plant will automatically increase the plant’s uptake of other nutrients. This fact highlights the importance of identifying both the availability of nutrients in the soil and the actual uptake by the crop, for which soil and plant tissue testing is the only reliable way to know.
Eat your greens
Fruits and vegetables are essential components of a healthy diet. Much of the world’s population relies on plants for most, if not all, of their diet. So well nourished fruits and vegetables (in addition to cereals and other grains) provide the bulk of most people’s vitamin intake.
N fertilisation can increase the content of chemicals called carotenoids (which the body turns into vitamin A), although it can also decrease the content of vitamin C (which relies on balanced uptake of other nutrients). Foliar sprays of potassium plus sulphur can improve the sweetness of several fruits in addition to their contents of several vitamins. The nutritional content and eating quality of bananas also benefit from potassium.
Test and test again
When you are developing your fertiliser programs, keep in mind that in benefiting your crop, you are also benefiting the people who will eat it.
For maximum nutrient content, a comprehensive fertiliser program is essential. This can work only with attention to testing of both soil and plant tissues.
Further reading
Bruulsema T. 2011. Plant nutrition, food quality, and human health. Plant Nutrition Today. International Plant Nutrition Institute, Norcross, GA, USA.
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