The rain washes away... the fertilizer replenishes!

We consider a soil to be more fertile when it has nutrients in sufficient quantities and in mineral forms that can be assimilated by plants. When they grow, plants take the nutrients they need from the soil and therefore deplete it. Conversely, when plants die, they are decomposed and allow nutrients to return to the soil and become available again. It is, therefore, a cyclical process of recycling nutrients.

However, this cycle is open and a soil can gain or lose nutrients. For example, rainwater can infiltrate the soil and take certain nutrients with it to groundwater and waterways, this is called leaching or drainage. Some soils are more sensitive to this loss than others, as is the case with sandy soils.

For example, an agricultural area being explored by a corn plantation, during its growth the plant takes nutrients from the soil and uses them to build its various organs: grains, leaves, branches, roots. When corn grains are harvested, the nutrients accumulated there are exported, leaving the soil poorer in nutrients, which ends up gradually leading to nutrient depletion and agricultural activity becoming compromised. Therefore, it is very important to renew the fertility of cultivated soils, regardless of the agricultural system implemented.

Throughout history, various methods of renewing soil fertility have been used and many of them are slow and take long years to restore lost nutrients. However, the technique that has been most successful is the use of fertilizers. The use of the term fertilizer is used here for any external matter brought into the soil to provide nutrients to plants. This material can be organic fertilizers, which contain very variable proportions of nutrients, but are not in forms immediately available to plants.

Unlike organic fertilizers, we can count on the addition of nutrients that are already in mineral form, in this case we are talking about mineral fertilizers. These have the advantage of being more concentrated and assimilated directly by plants. Mineral fertilizers are often mixtures of the three most important nutrients (because they are most often limited in soils): nitrogen, phosphorus and potassium – the so-called “NPK” fertilizers.

Right now, you might be wondering why we don't just return the nutrients that were taken away by food production?

To better understand this issue, we need to understand that nutrients are not removed from the soil only through export caused by the harvest of agricultural products, but can be easily transported to rivers and lakes through runoff and leaching, that is, it is the loss of nutrients through drainage in the soil profile. Thus, the high incidence of heavy and large rainfall, as has been happening in recent months, can reduce the availability of some nutrients for plants, especially nitrogen.

One of the ways to reduce losses is to adapt the dose of nutrients and the timing of fertilizer supply to the plant's growth and absorption capacity. Well-calibrated fertilization will limit the risk of nutrient losses. This will make it possible to offer greater efficiency to the fertilization process, without the need to replace lost nutrients.

All agricultural activity depletes the soil, exporting nutrients in the form of food for human beings. Renewing soil fertility is therefore essential to ensure long-term food security. Today, our food system is characterized by linear nutrient management. Nutrients are brought to crops mainly in the form of mineral fertilizers, which are transferred to our bodies and subsequently excreted in the form of urine and feces. These excrements are treated as pollutants to be eliminated. In short, they do not return to replace the withdrawals that occurred in the fields. An obvious path to system resilience is, therefore, to try to cycle nutrients, as in most ecosystems. Our hope is that our waste becomes nutritional resources again.