Fundamentals of Soil Science (1+1)

Introduction

• The problem soils are those which owing to land or soil characteristics can not be economically used for cultivation of crops. These soils require remedial measures and management practices for satisfactory crop production.

Types of problem soils:

• The problem soils have been classified in two main categories on the basis of nature of constraints.

1. Physical nature: a) Highly eroded soils, ravines and soils on sloping lands b) Soil physical constraints
2. Chemical nature: i) Saline soils ii) Saline alkali soils iii) Alkali soils and iv) Acid soil

Physical nature:

• Highly eroded soils, ravines and soils on sloping lands: The areas affected by this problem are Western Rajsthan, Saurashtra region of Gujrat, Maharastra, ravines along the Jamuna and Chambal rivers. Kotar lands in Gujarat, steep slopes of hilly areas. The erosion is mainly caused by wind, water and land slides.
• Wind erosion: It occurs in arid and semiarid areas devoid of vegetation due to high wind velocity. Soil particles are lifted and blown off and when the velocity of the dust bearing wind is retarded, coarser soil particles are deposited in the form of dunes and thus fertile lands are unfit for cultivation.
• Water erosion: Water removes a thin covering of soil from large area uniformly during every rain which produces runoff. Its existence can be detected by muddy colour of the runoff from the fields. This is called sheet erosion. Later on , the silt laden runoff forms a well defined but minute finger shaped grooves over the entire field. Such thin channeling is known as rill erosion. The tiny grooves develop in to wider and deeper channels which may assume a huge size is known as gully erosion.
• Land slides or slip erosion: The outward and downward movement of the slope forming material composed of natural rocks, soil etc. is known as land slides or slip erosion. The main cause of land slides are topography, geological structure, type of rocks and their physical characteristics.

Agronomic measures for soil and water conservation:

• Interception of rain drops reduces the splash effect. The overland runoff can be reduced through use of contour cultivation, mulches, dense growing crops, strip cropping and mixed cropping.
• A simple practice of farming across the slope, keeping the same level as for as possible is called contour farming. It reduces runoff, soil erosion and loss of plant nutrients and increases crop yields.
• Surface mulches are used to prevent soil from being blown and washed away to reduce evaporation, increase infiltration, check weeds, improved soil structure and eventually to increase crop yields.
• Grow the crop which can provide and reduce runoff and soil losses. Legume furnishes better cover and hence provides better protection to cultivated land against erosion than ordinary crops.
• Grow the crops in strips of suitable width across the slopes by alternating the strips of soil protecting and erosion resisting crops.

Soil physical constraints:
1. Permeable soils:
Highly permeable coarse textured soils:

• The high permeability of these soils are associated with their sand and loamy sand texture. The soils has low bulk density and high hydraulic conductivity and infiltration rate which results in to high permeability and low water retention capacity.
• The fertilizer and water use efficiency is very low and nutrient losses are very high. Soil compaction and clay mixing should be done to improve these type of soils.

Slowly permeable soils:

• The slowly permeable soils occur in Madhya Pradesh, Maharashtra, parts of Rajsthan, Uttar Pradesh, Bihar and Tamil Nadu.
• The infiltration rate and hydraulic conductivity is low which results in to slow permeability of the soil and possibility of submergence during rainy season.
• The preavailing anaerobic conditions cause the accumulation of carbon dioxide and other by products which restrict the plant growth.
• These soils are associated with black clay soils. The black soils are sticky when moist, therefore, could be cultivated only within limited soil moisture range.
• These type of soils can be reclaimed by growing crops on raised beds, broad beds with drainage furrow in between, deep tillage through ploughing and chiseling to break the hard pan in sub-soil.

Crusting soils:

• When the rain drop strikes the exposed dry soil surface, there is disintegration and dispersion of soil aggregates.
• The finer clay particles moves down along with infiltrating water and clog the soil pores. As the water evaporates and soil dries, a thin layer of hard crust of soil is formed. The crust present a serious barrier for seedling emergence.
• Crusting of alluvial soils is a serious problem all over the country especially in the states of Haryana, Punjab, Rajasthan, Bihar and West Bengal.
• Application of farm yard manure or green manuring will improve these type of soils.

Chalka soils:

• The red sandy loam soils “Chalka soils” which cover a large area in Andhra Pradesh become very hard on drying with the result that growth of the crops are adversely affected.
• Incorporation of slow decomposing crop residues and other materials such as powdered ground nut shell, paddy husk improves these type of soils.

Sandy Soils:

• Sandy soils are weakly developed because of slow chemical weathering in dry and hot climate.
• The coarse texture of sandy soils causes a low water holding capacity and high infiltration rate which represents the main production constraint.
• Nutrient content and nutrient retention are normally low, thus causing a low inherent fertility status of the soil.
• The poor soil structure makes the soil very susceptible to wind erosion. The agricultural potential of sandy soils depends on the availability of sufficient water for crop cultivation and the provision of nutrients.
• If appropriately managed sandy soils can be highly productive.