Understand Correctly to Manage Soil Moisture and Crop Nutrition

As precision agriculture continues to advance, understanding soil moisture and crop nutrition is no longer a matter of intuition or traditional experience. It has become a problem of data, technology, and biology that requires farmers to be at once engineers, plant physiologists, and environmental risk managers.

Soil moisture is not just water:

The concept of soil moisture is not as simple as “dry” or “wet.” Technically, it is defined by three key parameters:

• Field Capacity – the maximum amount of water the soil can retain after excess free water has drained.
• Wilting Point – the level of moisture at which plants can no longer extract water.
• Optimal Range – between 30–60% of field capacity, which is the threshold where plants absorb water most efficiently.

Maintaining soil within this optimal moisture range not only helps plants grow stronger but also maximizes nutrient uptake, since soil moisture directly influences ion transport and the chemical interactions between minerals.

Three Forms of Soil Nutrients:

For many years, farmers were taught that having more N-P-K in the soil meant better plant growth. In reality, the total amount does not tell the whole story. Soil nutrients exist in three main forms:

• Total nutrients: This includes all forms, from dissolved ions to precipitated salts or nutrients tightly bound to clay minerals—many of which are not accessible to plants.
• Available nutrients: The portion that plants can actually absorb through their roots, typically ions such as NO₃⁻, NH₄⁺, K⁺, and PO₄³⁻.
• Soluble fraction: A small part of the “available” nutrients that are fully dissolved in the soil solution—this is the real nutrient stream that flows directly into the plant.

Interestingly, even if you apply the correct amount of NPK, if the soil pH is unsuitable (too acidic or too alkaline), many minerals will precipitate and become “invisible” to plant roots. For example, overly acidic soil (pH < 5.5) locks phosphorus into insoluble forms such as AlPO₄ or FePO₄.

Models and Data:

The technical development team in the recent project has implemented a root simulation model that allows prediction of available nutrient levels based on pH, moisture, and electrochemical sensor data. Using five input indicators, the model can regress to determine the actual amount of available nutrients—this is the key to adjusting fertilizer application flexibly in real time.

The system is also integrated with temperature and humidity sensors, creating a three-dimensional monitoring platform covering soil – air – crops. Electrical conductivity (EC) measurements help estimate the mineral concentration in the soil, thereby assessing risks of nutrient surplus or soil salinization.

Fertilization strategy:

The biggest lesson from recent studies is that fertilization should not follow a fixed schedule or generic recommendations. In the early growth stage, plants need more nitrogen to develop foliage, but extending high nitrogen into the fruiting stage leads to excess nitrogen, lush leaves with few flowers or fruit, and higher disease susceptibility.

Conversely, in the late stage, plants need potassium and micronutrients to support fruit development. Continuing to apply nitrogen at this point causes physiological imbalance. Understanding the needs of each growth phase is the decisive factor in modern fertilization.

From sensors and models to action:

An often overlooked but crucial point is that soil is alive. Microorganisms, organic matter, and biochar all affect soil porosity, water-holding capacity, and ion exchange. Adding organic fertilizers or biochar is not just supplying more nutrients; it is rehabilitating the “soil ecosystem,” allowing roots to grow deeper and stronger and absorb more effectively.

Managing moisture and nutrition is no longer a matter of guesswork. It is a data-driven science combined with applied biology. From sensors to models to real actions in the field, each step helps growers understand the soil better, understand their crops better, and ultimately understand themselves better in the role of partners with nature.