Soil Nutrient Depletion and Imbalances

 

Soil Nutrient Depletion and Imbalances

Soil nutrient depletion refers to the loss of essential nutrients from the soil, which can occur due to a variety of factors such as overuse of the land for farming, urbanization, and poor agricultural practices. Nutrient imbalances occur when the soil contains too much or too little of certain nutrients, which can negatively impact plant growth and crop yields. To address these issues, farmers can use soil tests to determine the nutrient levels in their land and apply fertilizers or other soil amendments as needed to restore balance. Additionally, crop rotation, cover cropping, and other sustainable farming practices can help to conserve and replenish soil nutrients over time.

Plants take up nutrients from the soil throughout the growing season but the pattern of nutrient uptake differs from that of dry matter production. Initial uptake of nutrients is more rapid than dry matter production but uptake of nutrients slows as the crop approaches maturity. By anthesis, most of the nutrients present in the crop at maturity have been taken up. The nutritional requirements of the developing grain are largely met by mobilisation from leaf and stem tissues and, to a lesser extent, by absorption of nutrients from the soil.

Soil texture, organic matter concentration and pH have important affects on the concentration of available soil nutrients. In most soils these properties change with depth and subsoils are generally much different to those of the topsoil. The organic matter concentration of subsoils is inherently low and consequently the total nutrient pool and the availability of nutrients from mineralisation are low There can be a steep decline in nutrient concentrations and availability down the soil profile, especially for less mobile nutrients such as phosphorus (P) and zinc (Zn).

Mobile nutrients such as nitrate (NO3 - ) can be leached into the subsoil, however it is still commonly observed that NO3 - concentrations are much lower in the subsoil than in the topsoil. Subsoils therefore have much lower concentrations of many nutrients than the surface layers. The concentration of some nutrients increases with depth. In alkaline soils, for example, the high pH in the subsoil is associated with high concentrations of boron (B) and in sodic soils, the sodium (Na+) concentration increases in the subsoil.

The total concentration of a nutrient is the amount of all forms of the nutrient in the soil, which includes the nutrients present in organic matter, that attached to clay particles, and minerals and the soil solution. Even in infertile soils, the total nutrient concentration can be high, but most of the nutrients are not immediately available to plants.

While the total nutrient concentration can provide an indication of gross soil fertility, it is usually a poor predictor of nutrient sufficiency for plants. Nutrients must be in a chemical form that allows them to enter the soil solution and to be absorbed by plant roots. This is the available nutrient pool. Nutrients in the total pool are made available to plants by the break down of organic matter and soil minerals and by chemical exchange between the soil minerals, organic matter and the soil solution.

Soil pH, the presence of chemical species such as calcium carbonate and iron oxides, the soil moisture content and the soil’s biological activity are important influences on the availability of nutrients and hence the nutrient status of the plant.

These soil properties affect a plant’s nutrient status by:

• influencing the inherent fertility of the soil, which determines the total amount of nutrients potentially available to plants

• determining the availability of these nutrients and their movement to the root surface

• influencing the ability of roots to explore the soil, to take up nutrients and to use nutrients efficiently