Nutrient Flows and Cycling

A nutrient cycle (or ecological recycling) is the movement and exchange of inorganic and organic matter back into the production of matter.

While the transfer of minerals and nutrients is cyclical, the flow of energy is unidirectional and noncyclic. The Carbon, Sulphur, Nitrogen, Water, Phosphorus, and Oxygen cycles are only a few of the mineral cycles that are constantly recycled with other mineral components into beneficial ecological nutrition.

• Not all crop nutrients in the soil are available to plants. Even if an element such as potassium is part of the structure of a grain of sand, it is not available for the plant to use.

• Following death and decomposition, nutrients ingested by plants and animals are returned to the environment, continuing the cycle.

• In the recycling of nutrients, soil bacteria are crucial. They release nutrients by breaking down organic materials. They are crucial for capturing and transforming nutrients so that plant roots may absorb them from the soil.

Nutrients are taken up by plants from the soil solution, usually in the form of simple ions such as nitrate (NO3.), phosphate, potassium (K+), magnesium (Mg+2), and so on.

• Plants can access nutrients through solubilizing or desorbing them from minerals, as well as from the cation exchange capacity of clays and thoroughly decomposed organic waste. Additionally, several elements are converted by soil organisms from organic to inorganic compounds.

• The elements undergo this mineralization process and are transformed into forms that plants can utilize. Thus, soil organic matter is essential for nutrient cycling because it provides cation exchange capacity and stores nutrients that will eventually be progressively transformed into usable forms by biological activity. The majority of soil organisms take part in the breakdown process, which promotes nutrient recycling.

One of the problems of conventional agricultural production is the pollution of ground and surface waters with nutrients.

• Furthermore, the relatively high availability of nutrients in conventional agricultural production may lead to a reduction in the nutritional content of the food produced as well as a greater sensitivity to insect infestation.

• Leaching and/or runoff in sizeable volumes can happen when annual rainfall (plus irrigation) exceeds evapotranspiration. Groundwater is seriously contaminated at these periods if there are high nitrate concentrations. High levels of soil nitrate can develop when substantial amounts of manures or commercial fertilizers are employed, especially if such nutrients are easily available.

An ideal nutrient cycle would have these important characteristics:

• The presence of nutrients would be in forms that are readily available in amounts and proportions that are synchronized with the demands of the developing crop.

• Nutrient availability would be as minimal as feasible during the seasons of the year when leaching or runoff are anticipated.

• Another objective would be to reduce nutrient inputs from outside the farm and use nutrients from biological nitrogen fixation and internal cycling as much as feasible.

• There would be negligible losses of nutrients from the farm in this "tight" nutrient cycle unless crops and animals were sold.

• Leaching, volatilization, and runoff losses would be at an absolute minimum.

• Nutrients are also cycling on the farm from soil to plant to animal to manure and back to the soil.

When the difference between nutrient inputs and the nutrients in the agricultural products shipped off the farm is large, there is a large pool of excess nutrients that may cause environmental problems.

It's noteworthy to note that a sizable amount of the N, P, and K are being brought to the farm in the form of bought feed. Only around one-third of the N, P, and K that enter the dairy farm are thought to be released as milk, meat, and crops. This indicates that, at least temporarily, around two-thirds are still present. The risk of contaminating surface or groundwater increases considerably as soil nutrient levels rise.

Nutrient Flows and Cycling.

By K H AKHIL SRINIVAS.

(KHAS).