Nutritional Approach in Agriculture
Nutrition is one of the pillars of the new agronomy, without nutrients, no photosynthesis and contrary to what is described in the photosynthesis formula, it is not only water, CO2 and photons that are needed to make sugar, but also mineral salts which are essential for the good health of the plant. On this page, we will discuss the impacts that good nutrition has on the plant.
Resistance to climate change
When a plant is balanced, the harvest is guaranteed. Production of antioxidants, efficiency of water and nitrogen use, defense molecules, strengthening of cells and cuticles, nutrients play many roles in the plant to resist abiotic stresses.
CO2 capture and carbon storage
Effective photosynthesis goes hand in hand with biomass production, thus CO2 capture. This is one of the focus areas; the so-called major elements (N,P,K), magnesium and trace elements such as iron, manganese and zinc are indispensable for complete and efficient photosynthesis. If one element is lacking, the whole process slows down. A zinc deficiency limits the function of Rubisco (the major enzyme in plants that enables CO2 capture). This enzyme can represent up to 50% of the soluble proteins in a C3 plant.
Root system development
Many minerals contribute to root growth, a boron deficiency reduces cell division. Unfortunately, it is very difficult to measure this indicator but numerous laboratory studies have demonstrated the importance of minerals for a well-developed root system allowing access to more nutrients. It is a virtuous circle! Manganese and iron are essential for auxin synthesis, and potassium transports them. Auxins are plant growth hormones that regulate cell growth and root formation.
New technologies allow direct measurement of roots in the field:
Sensitivity to diseases and pests
The sensitivity of crops to diseases and pests is a crucial aspect of modern agriculture. Healthy plants are generally more resistant to fungal, bacterial and viral attacks and piercing-sucking insects. The mineral balance in the soil and plant plays a decisive role in this resistance.
When a plant lacks certain essential minerals, it may show signs of weakness, stress or nutritional imbalance. These plants are more vulnerable to fungal infections because their ability to activate natural defense mechanisms is often compromised. For example, deficiencies in minerals such as zinc or copper can weaken the plant immune system, making the plant more susceptible to fungal infections like rust or powdery mildew.
Regarding piercing-sucking pests, such as aphids or mites, a well-mineralized plant can produce defense compounds such as phenolic compounds or alkaloids. These compounds make the plant less palatable to pests and can even repel them. Moreover, a well-nourished plant can regenerate more quickly after pest attacks, thus minimizing damage. Many aphid species are attracted to leaves reflecting yellow (chlorosis) due to nitrogen or other nutrient deficiencies. Conversely, plants with excess nitrogen emit volatile compounds (e.g., acetic acid) correlated with increased pest pressure. A balanced and well-green plant is thus much less attractive.
Mineral balance in the soil also plays a major role. A mineral-poor soil can lead to nutritional deficiencies in plants, making them more susceptible to diseases.
Treating virus-infected or diseased plants
Treating plants affected by viruses or other pathogens is a major challenge. Viral infections and pathogen attacks can cause severe nutritional disorders in plants. In response to these aggressions, infected plants have increased needs for essential trace elements to produce antioxidants and defense molecules which are energetically costly.
It is important to note that treating diseased plants does not necessarily mean complete cure, as it is often difficult to completely eliminate viruses or pathogens. However, it is possible to support a plant in its fight against disease by providing the missing nutritional elements. This can help the plant activate the many metabolic reactions necessary to defend itself and recover as much as possible.
Supplying essential trace elements, such as zinc, copper, manganese and iron, can strengthen the plant's ability to synthesize antioxidants that help counteract oxidative damage caused by viral infections or pathogens. Moreover, these nutrients are involved in many vital metabolic reactions for plant health.
Varietal diversity and sensitivity to deficiencies
Plant varietal diversity plays an essential role in their sensitivity to nutritional deficiencies. Often, when selecting plants for resistance to certain diseases, it is found that they also have a better ability to extract minerals from the soil thanks to their root exudates. By actively feeding the soil microbiology, these plants gain access to essential nutrients. However, not all plant varieties or rootstocks have the same efficiency in this area. This sometimes results in marked differences in tolerance to certain deficiencies, such as iron chlorosis in some rootstocks.
On the other hand, it is important to note that some varieties or rootstocks may have weaknesses in recovering certain nutrients, as is the case with the SO4 rootstock in viticulture, which may have difficulties absorbing magnesium. This illustrates that not every plant material can excel in all areas, and variety selection must take these specificities into account.
Having a nutritional perspective is essential to prevent imbalances in crops. However, much work remains to be done in this field. Unfortunately, plant genetics research has often focused on criteria such as yields, crop preservation for transport, or disease resistance. The ability of plants to extract and efficiently use nutrients is not always a priority for seed producers as they must make compromises and adapt their seeds for very generalized soils, not for the specificities of each soil which is unique in terms of mineralogy, microbiology, depth and climatic context. When purchasing seeds, it is important to note that some even come from soilless cultures, as is the case for some vegetables and clones. This approach can be counterproductive from an agronomic point of view, as it does not consider the complex interactions between plants, soils and microbiology.
Hidden deficiencies
Hidden deficiencies or "hidden hunger" in English constitute an insidious problem in plant nutrition. Most of the time, plants do not immediately show the classic visual signs of deficiency, such as chlorosis (loss of green color) or changes in leaf color. If the deficiency is visible to the naked eye, it is already an advanced deficiency which significantly impacts crop growth and yields. The stage before deficiency is the deficiency stage (not visible to the naked eye).
Preventing deficiencies is crucial, because once symptoms are visible, it is often difficult to fully restore the plant and recover yield losses. Early detection of deficiencies is therefore essential to maintain crop health and optimize yields. For this, there are advanced diagnostic methods to detect deficiencies well before they become visible to the naked eye. Sap analysis of the plant is one such method. It allows to measure nutrient concentrations in the plant in real time, thus providing valuable insight into its nutritional status. By regularly monitoring sap composition, farmers can identify nutritional imbalances at an early stage.
Preventing deficiencies is often more effective than treating them once established. This can be achieved by adjusting fertilization according to the specific needs of the crop and using sustainable agricultural practices to maintain soil health. Nutritional balance is essential for healthy plant growth, and balanced fertilization programs are key to achieving this.
Other analyses are also very interesting:
- Dry matter analysis has a very robust reference framework, providing an overview of nutrients accumulated in the leaves.
- Twig analysis, widely used in arboriculture, allows to determine reserves available for crop start-up and to plan a nutritional program even before leaf appearance.
Adjusting fertilization plans and reducing inputs
Precise adjustment of the fertilization plan is a crucial approach to ensure optimal yields and preserve the environment. It is difficult to determine the exact amount of fertilizer needed for a crop, as this cannot be done by eye. Despite progress in fertilization calculations in France, it is essential to ask the crops themselves.
Traditional calculation methods, such as balance method to determine nitrogen inputs, are useful but do not always take into account the real needs of the crops. Monitoring crop nutrition through soil analyses and sap analyses allows understanding if calculations were accurate and if nutrient inputs were appropriate. Nowadays, it is preferable to apply slightly less nitrogen at first and correct if necessary rather than applying too much. Precision fertilization, based on the real needs of the crops, is essential to improve Economic profitability and minimize environmental impacts.
It is important to emphasize that every kilogram of fertilizer unnecessarily applied has an economic and environmental cost. This can negatively affect its carbon footprint unless these inputs are fully valorized by the crop. It is therefore important to find the right balance between providing essential nutrients to plants and avoiding over-fertilization. The simplest and most accurate method today is to perform a "Haney Test" before crop establishment and monitor it through sap analyses to check balances and make corrections if necessary.
Taste and nutritional richness of productions
The taste and nutritional richness of agricultural products are intimately linked to fertilization management and crop nutrition. Agricultural practices aimed at optimizing nutrition can significantly impact the taste and nutritional quality of harvested products.
Nutritional balance for better taste quality
The balance of nutrients in the soil and plant can influence the flavor and taste quality of agricultural products. Deficiencies or excesses of certain minerals can alter the taste of fruits, vegetables and other products. For example, a potassium deficiency can affect the sweetness of fruits, while a calcium deficiency can cause texture problems. By closely monitoring crop nutrition, farmers can adjust nutrient inputs to obtain products with better taste quality. This is partly what gives the terroir effect, as some soils being better suited to certain plant genetics will reveal the flavors of fruits and vegetables.
Impact on nutritional richness
Essential nutrients absorbed by plants from the soil are also essential for human nutrition. Adequate nutrition levels can increase the content of nutrients such as vitamins, minerals and proteins. Any mineral deficiency will inevitably be reflected in the productions.
Prevention of nutritional deficiencies in consumers
Adequate plant nutrition can also help prevent nutritional deficiencies in consumers. By providing agricultural products richer in essential nutrients, it helps people maintain a balanced diet. This can have a significant impact on public health by reducing rates of micronutrient deficiencies. For information, 2 billion people suffer from zinc deficiency, mostly in developing countries. It is also estimated that 10 to 20% of the world population is deficient in magnesium.
Valorization of local production
When agricultural products show superior taste and nutritional quality, this can boost the local economy. Farmers have the opportunity to promote their products as high quality, which can lead to increased sales in local and regional markets.
There are companies that perform mineral content analyses. For example, Symbiotik Agroecologie offers analyses on 30 elements for less than 50 euros.
Protein autonomy for livestock farmers
Nutrients are essential for protein synthesis and DNA stability.’ They are like the "growth partners" of plants, ensuring they stay healthy and develop properly. Very often we observe higher CP' (Crude Protein) contents when adequate nutrition is implemented.
Magnesium, molybdenum, boron, cobalt and sulfur are all essential for protein production in legumes by facilitating atmospheric nitrogen fixation, a key process in protein synthesis. A deficiency in any of these elements can compromise legumes’ ability to produce proteins. They are therefore crucial elements for the nutritional value of these crops. Healthy legumes will enable livestock farmers to achieve protein autonomy.
Improvement of biological activity
Plant roots secrete organic compounds called root exudates. Plant nutrition impacts the production of these root exudates, particularly through nutrient availability, and on the activation of soil microbiology. Plants adjust the composition of their exudates according to their nutritional needs, thus attracting different beneficial soil microorganisms.
This interaction between plants, root exudates and soil microbiology promotes better nutrient absorption, strengthens plant health and contributes to soil fertility. Balanced nutrition is therefore essential to optimize these processes.
Conversely, excess of certain minerals in the soil can be harmful to the proper development of some microorganisms. The best-known cases are:
- Excess phosphorus available in soils causes decline of mycorrhizae populations.
- Excess copper decreases microbial fauna diversity.
- Excess inorganic nitrogen causes a decline in bacteria free-living nitrogen-fixing populations.
Cation balance on the CEC (Cation Exchange Capacity) influences biological activity. A balanced soil in calcium, magnesium, potassium and sodium will be conducive to good biological activity as it needs water and air to develop. Too much magnesium will make the soil hydromorphic and compact, while excess calcium will make it dry and too aerated. The ideal balance for an Albrecht-type analysis is 68% calcium and 12% magnesium for an average agricultural soil. For sandy soils, a ratio of 60% calcium and 20% magnesium is preferred, and 80%/10% for calcareous soils.
Effectiveness of Plant Protection Products
The effectiveness of plant protection products is often closely linked to crop nutrition. Very often, the health problems encountered by plants are actually underlying nutritional imbalances. The use of plant protection products, whether authorized in organic farming or conventional agriculture, without taking into account the nutritional status of the crop, often does not solve the problem at its source. In fact, it can even worsen the situation by causing blockages in the assimilation of essential minerals by plants, because these products generally cause some stress to the crops.
To understand this in detail, it is essential to note that properly nourished plants are more resistant to pest and disease attacks. When a plant receives the nutrients it needs in a balanced way, it can strengthen its natural defense mechanisms. Conversely, a plant that is deficient or nutritionally unbalanced is more vulnerable.
Plant protection products generally aim to combat pests or pathogens directly. However, their intensive use can disrupt the biological balance of the soil and the plant itself. For example, excessive use of certain pesticides can kill not only the targeted pests but also beneficial soil organisms.
To effectively solve crop health problems, it is therefore important to adopt a holistic approach that integrates both plant nutrition and crop protection if needed. This involves carefully monitoring nutrient levels in the soil and plants, correcting nutritional deficiencies if necessary, and applying protection products in a reasoned manner.
Conversion from Conventional Agriculture to Agroecological Agriculture
A transition to agroecological agriculture requires a carefully thought-out nutritional approach to avoid the unfortunately too frequent failures. It allows solving health problems, restoring soil health, and ensuring more stable yields. This approach is the cornerstone for achieving higher fertility levels and more sustainable agriculture by securing yields.
For example, in no-till systems, yield losses can be significant because crops benefit much less from the mineralization of organic matter, hence the importance of reviewing the nutrition program with this type of practice.
Seed Quality
Mineral deficiencies in a crop inevitably reflect in the fruits or seeds. Crops that have benefited from rebalancing inputs are richer in minerals than untreated plants.
It is very likely that success is not guaranteed from the outset if the seeds have the same deficiencies as the soil on which they were produced. To anticipate this problem, an analysis of the seeds combined with a precision nutrient coating seems to be the best approach. Moreover, localized fertilization has proven effective and is also an option to consider.
This article was written thanks to the kind contribution of Benjamin Pierru from Symbiotik Agroécologie.
- ↑ James Moran, Casey McGrath. Comparison of methods for mapping rhizosphere processes in the context of their surrounding root and soil environments. 23 November 2021. https://doi.org/10.2144/btn-2021-0021
