Mobility And Critical Limits Of Nutrients In

The Soils

Mobility of nutrients in the soils:

• Mobility of nutrients in the soil has considerable influence on availability of nutrients to plants and method of fertilizer application.

• Based on the mobility in the soil, the nutrient ions can be grouped as mobile, less mobile and immobile.

1.Mobile: They are highly soluble and are not absorbed on clay complex.

E.g., NO3, SO4, BO3,Cl, Mn.

2. Less mobile: They are also soluble, but they are adsorbed on clay complex and so their mobility is reduced.

e.g., NH4, K, Ca, Mg and Cu.

3. Immobile: They are highly reactive and get fixed in the soil.

e.g., H2PO4, HPO4, Zn.

Mobility of Nutrients In Plants:

Mobility of nutrients in the plants helps in finding what nutrient is deficient. A mobile nutrient in the plant moves to the growing points in case of deficiency.

Deficiency symptoms, therefore, appear on the lower leaves.

1. N, P, K are highly mobile.2. Zn is moderately mobile.3. S, Fe, Mn, Cu, Mo and Cl are less

mobile.4. Ca and B are immobile.

The nutrients can also be classified into metals and non-metals as well as cations and anions based on their chemical nature:

Metals: K, Ca, Mg, Fe, Mn, Zn, Cu.

Non-Metals: N, P, S, B, Mo, Cl.

Cations: K, Ca, Mg, Fe, Mn, Zn, Cu.

Anions: NO3, H2PO4, SO4.

Critical Limits Of Nutrients:

Critical level is defined as a range of concentration at which growth of plants is restricted in comparison with that of plants at a higher nutrient level.

Plants with nutrient concentration below critical level will respond to applied fertilizers.

The critical level concentration can be expressed in soil as well as in plants.

The critical limit of nutrients in plants and soil studies have indicated following critical limits of nutrients:

MAJOR NUTRIENTS:

Contd….

Nutrients Plants Soil Limit

N 1.5% Below 250kg/ha Low

250-500kg/ha Medium

Above 500kg/ha High

P Below 0.2% Below 10kg/ha Low

10-20kg/ha Medium

Above 20kg/ha High

K 14% Below 100kg/ha Low

100-250kg/ha Medium

Above 250kg/ha High

Secondary and Micro Nutrients:

NUTRIENT PLANTS SOIL LIMITS

S Below 0.15-0.2% Below 10ppm

Ca Below 0.2% Below 50% of CEC

Mg 0.1-0.2% Below 4% of CEC

Zn Below 20ppm Below 0.6ppm

Fe Below 50ppm 2.5-4.5ppm

Mn Below 20ppm Below 2ppm

Cu Below 4ppm Below 0.2ppm

B Below 1ppm Below 0.5ppm

Mo Below 0.1ppm Below 0.2ppm