Physical Constraints Of Soil Productivity For Competitive Exam

Physical Constraints The following are the physical constraints.

• Highly permeable soils

• Impermeable soils (slowly permeable)

• Crusted soils

• Subsoil hard pan

• Fluffy paddy soils

1. Highly permeable soils

The high permeability is associated with sand and loamy sand texture of soils. These oils occur in coastal areas, river delta and in the desert belts. These soils cover large areas in Rajasthan and Haryana. In Tamil Nadu, a total area of about 15 lakh ha were affected by excessively permeable soils.

Characteristics

• The structure of soil is loose to very weakly developed depending upon clay content.

• Since most sandy soils are devoid of any structural development, these suffer from intensive erosion.

• Lack of cohesion, adhesion and plasticity in soil.

• The nature of excessive permeability of the sandy soils results in very poor water retention capacity, very high hydraulic conductivity and infiltration rates. So whatever the nutrients and water added to these soils are not utilized by the crops and subjected to loss.

• Soils are lighter in colour.

• Very low in organic carbon, nitrogen and medium in P and K.

• Low nutrient diffusivity and buffering capacity.

Remedial measures – To correct the textural weakness of these sandy soils and to make them suitable for sound farming, various ameliorative measures have been devised.

• Introduction of artificial barriers in the subsoil zone using asphalt, bitumen and cement have been found to arrest the higher rate of nutrient and water losses in sandy soils. This technology is costly.

•Compaction technology – The soils should be ploughed uniformly. About 24 hours after a good rainfall (or) irrigation, the soil should be rolled 10 times with 400 kg stone roller of 1 m long (or) an empty tar drum filled with 400 kg sand. This practice increases the bulk density of 0-30 cm layer to optimum range (1.5-1.7 mg/m3). Then, shallow ploughing should be given and crops can be raised.

• By mixing of a fine textured soil having 50% clay would reduce the hydraulic conductivity and infiltration rate and also increases the N use efficiency.

• Application of mulches is an effective means to conserve soil water and moderate soil temperature.

• Form small plots and apply minimum and frequent irrigations.

• Adopt more number of splits of N and K fertilizers.

2. Slowly permeable soils

The slow permeable soil is mainly due to very high clay content and poor drainage conditions which results in poor aeration and water stagnation and ultimately leads to poor crop growth and in certain case leads to complete death of crops. The slow permeability of the soil is mainly associated with black clay soils. These soils cover an area of 49.8 m.ha in the Central India comprising Madhya Pradesh, Andhra Pradesh, Gujarat and in Tamil Nadu, about 14.32 lakh ha of land affected by these soils.

Characteristics

• Very high clay content and bulk density

• Poor drainage, hydraulic conductivity and infiltration rate due to higher proportion of pores

• Temporary water logging of the soil develops oxygen stress in root zone

• Development of salinity with poor drainage

• High soil pH and calcareousness may promote ammonia volatilization

• Soils are low in organic carbon N, P, Zn and Fe

Remedial measures

• Addition of organics namely FYM/composted coir pith/press mud/urban compost at 12.5 t/ha found to be optimum for the improvement of the physical properties. It facilitates water movement to the root zone.

• Formation of ridges and furrows: For rain fed crops, ridges are formed along the slopes for providing adequate aeration to the root zone. Interception of drainage channels of about 50 cm wide and 15 cm deep provides effective surface drainage.

• Raised and sunken beds formation in between adjacent raised beds: The bulk density was found to be reduced due to increase in non-capillary pores in upper 10 cm layer of raised bed besides increase in yield of crops by forming raised and sunken beds. The 6–12 m wide and 20 cm high raised beds alternating with 6 m wide sunken beds provides in situ drainage. The raised beds are constructed by removing the soil from the sunken beds.

• Formation of broad beds: To reduce the amount of water retained in black clay soils during first 8 days of rainfall, broad beds of 3–9 m wide should be formed either along the slope (or) across the slope with drainage furrows in between broad beds.

• The productivity of sodic clay soils can be increased to a significant extent through use of gypsum and agricultural grade iron pyrites.

• Long term application of organic manures along with chemical fertilizer under well aerated condition improves the available status of nutrients.

3. Subsoil hard pans

The reasons for the formation of subsurface hard pan in red soils is due to the illuviation of clay to the subsoil horizons coupled with cementing action of iron, aluminium an calcium carbonate. In Tamil Nadu, red soils occupy about 8 million hectares. The occurrence of hard pan at shallow depths is the major prevalent soil physical constraints in these soils.

Characteristics

• The subsoil hard pan is characterized by high bulk density (more than 1.8 Mg m-3), which in turn lowers infiltration, water holding capacity, available water and movement of air and nutrients with concomitant adverse effect on the yield of crops.

• The high bulk density in sub surface soil results in water stagnation on the soil surface after heavy rainfall (or) irrigation and the crops turn yellow due to oxygen stress.

• In high rainfall areas, sub surface layers at shallow depth reduce water storage capacity of the soil and run off starts even after a short shower, which cause floods in low-lying areas.

Remedial measures

To eradicate the problem of subsoil impervious layer, chisel plough is recommended. Chisel plough is a heavy iron plough which goes up to 45 cm depth, thereby shatters the hard pan in the subsoil.

• The field is to be ploughed with chisel plough at 50 cm interval in both the directions

• Chiseling helps to break the hard pan in the subsoil

• Farm yard manure (or) press mud (or) coir pith at 12.5 t/ha is to be spread uniformly on the surface

• The field should be ploughed with country plough twice for incorporating the added manures

• The broken hard pan and incorporation of manures make the soil to conserve more moisture

4. Soil surface crusting

Surface crusting is due to the presence of colloidal oxides of iron and aluminium in Alfisols, which binds the soil particles under wet regimes. On drying it forms a hard mass on the surface. The alluvial sandy loam soils in Haryana, Punjab, Rajasthan, Uttar Pradesh, Bihar and West Bengal form a crust on the soil surface, which interferes with germination and growth of crops. The red sandy loam soils ‘Chalkas’ which cover a large area of Andhra Pradesh become very hard on drying with the result that the crop growth is adversely affected.

In Tamil Nadu, this problem is prevalent mostly in red soil areas (Alfisols) and is of greater magnitude in districts like Trichy, Pudukottai, Ramnad and Tirunelveli. The crusting of soils is directly related with aggregate stability, rainfall characteristics and its chemical composition. The poorly aggregated soil particles in alluvial, red and lateritic soils disintegrate easily under the impact of rain drops. The quantity of dispersed soil increases with the increase in drop size, drop velocity and rainfall intensity. The hydration of aggregates causes a disruption through the process of swelling and explosion of entrapped air. The fine fractions go into the suspension, which may either enters into the soil and clog the macropores or resettles on the surface to form a crust.

(a) Impact on soil properties

• Prevents germination of seeds

• Retards/inhibits roots growth

• Results in poor infiltration

• Acceleration of surface run off

• Creates poor aeration in the rhizosphere

• Affects nodule formation in leguminous crops. Soil crusting generally found in laterite group of soils, which have high amounts of soluble iron and alumina.

(b) Remedial measures

• when the soil is at optimum moisture regime ploughing is to be given.

• lime at 2 t ha-1 may be uniformly spread and another ploughing given for blending of the amendment with the surface soil.

• FYM at 10 to ha-1 (or) composted coir pith at 12.5 t ha-1 (or) other organics may be applied to improve the physical properties of the soils after preparation of land to optimum tilth.

• combined application of lime and FYM enhanced the yield of crops besides improving the physical properties of the soil.

• scarping surface soil by tooth harrow will be useful.

• bold grained seeds may be suited for sowing on the crusted soils

• more number of seeds/hill may be adopted for small seeded crops.

• sprinkling water at periodical intervals may be done wherever possible. • resistant crops like cowpea can be grown.

• most of the red and laterite soils are poor in organic matter and therefore deficient in nitrogen. Organic manures and use of biofertilizers holds promise.

• these soils having high activity of Fe and Al in soil solution fix a good amount of soluble P. Application of rock phosphate will increase the available P and crop yield.

5. Fluffy paddy soils

The traditional method of preparing the soil for transplanting rice consists of puddling. This results in substantial break down of soil aggregates into a structure less mass. The solid and liquid phases of the soil are thus changed. Under continuous flooding and submergence in rice-rice-rice sequence, the soil particles are always in a stage of flux and the mechanical strength is lost leading to the fluffiness of the soils. This is further aggravated by in situ incorporation of rice stubbles and weeds during pudding. In Tamil Nadu fluffy rice soils are prevalent in Cauvery deltaic zone and in many parts of the state due to the continuous rice-rice cropping sequence.

Impact

• Sinking of draught animals and labourers is one of the problems during puddling in rice fields.

• Fluffiness of the soil led to very low bulk density and thereby leading to very rapid hydraulic conductivity and in turn the soil does not provide a good anchorage to the roots and the yield of crops is adversely affected.

Remedial measures

• The irrigation should be stopped 10 days before the harvest of rice crop.

• After the harvest of rice, when the soil is under semi-dry condition (proctor moisture level), compact the field by passing 400 kg stone roller or on empty drum filled with 400 kg of sand 8 times.

• Then the usual preparatory cultivation is carried out after compaction.