Ebooks

Preface This book has been written as a text book for the students to have full grasp of nature and causes of Land Degradation, methods of evaluation, characterization and control measures for maintaining its productivity. The vast area of land degradation has been covered in a simple and concise form. The book offers sufficient materials for the students to prepare entire course of Problem soils and their management based on ICAR Syllabus and also for the students of allied agriculture and environmental sciences. Although much of research papers on the subject have been published, teachers of the subject have been handicapped by lack of a suitable text book. The students also faced problems when they are asked to refer several books for this course since, none of the books so far published contain all the chapters as per ICAR syllabus. Having more than forty years of teaching experiences on different courses namely soil physics, soil erosion and conservation, problem soils and their management, soil, water and air pollution, acid soils, land degradation and restoration at under graduate, post graduate and Ph.D levels, I am fortunate to go through several text books, review papers and published articles in different bulletins. Practical experiences in various aspects of the subject and fed back from the students through assignments has resulted in preparation of a complete set of notes which has been used to build up a course on Problem soils and their management. The book comprises of fifteen chapters covering all aspects of physical, chemical and biological processes leading to land degradation under different agro–ecosystems. Physical land degradation leading to soil compression, compaction, soil crusting, slow and highly permeable soils were discussed thoroughly. Chemical land degradation leading to iron and aluminium toxicity, soil acidity, acid sulphate soils, soil salinity and alkalinity have discussed. Equal emphasis has also been given to assess and monitor the extent of land degradation and its impact on soil and water using modern technology–Remote Sensing, GIS and GPS. For management of wastelands, the concept of watershed management based on land capability classification, land irrigability classification and land suitability classification were discussed in detail. Due emphasis was given to maintain soil health and soil quality for sustainable crop production.

I. Definition of wasteland Wasteland include degraded forest, overgrazed pastures, drought- struck pastures, eroded valley, hill slopes, water logged marshy lands, barren lands etc. Different authors have defined wastelands as: Land which is lying unproductive or which is not being utilized to its potential. Land which is incapable of producing material or services of value (American Society of Soil science). Land which has been abandoned and for which there is no further use (Mine spoils). Land which produces less than 20% of economic potential. e) Land where no greenery can be sustained. Land which is neither under forest cover or agricultural cover or assigned for specific purposes such as National park or National hydro power projects. The Technical Task Group Report of the National Wasteland Board defines the wasteland due to different constraints.

Crusting soils What is soil crusting? Soil crusting refers to formation of a compact thin layer having high bulk density and high penetration resistance at the soil surface when dries after dispersion of fine particles and clogging of pores due to beating action of rain drop and slaking of irrigation water. In arid and semiarid regions, crust formation occurs due to the destruction of soil aggregates. Crust formation occurs in all types of soils except sand. It is characterized by high bulk density, low non capillary pores, low hydraulic conductivity and aeration and high penetration resistance.

Calcareous soils In arid regions, calcareous soils are developed from limestone or marl parent materials. The content of calcium and magnesium carbonate may be as high as 60 to 70 per cent of the total soil mass. In calcareous soil lime content may vary from a small amount in some places in the profile to appreciable amounts throughout the profile. Calcium carbonate coatings occur in sand, silt and clay size fractions of calcareous soils. In sub soil, large amounts of lime forms hardpan under high water tables. In general, pH of the soil increases to alkaline pH with increasing the proportion of water to soil ratio. This may happen in part from a reduction of CO2 pressure. The dilution of salts in soil solution also permits greater hydrolysis of calcium clay. The dilution of calcium carbonate with production of hydroxyl ions may lead to higher pH as:

Iron Toxic Soils Lowland rice is being cultivated on approximately 128 million hectares of either irrigated or rainfed land out of which 100 million hectares suffer due to nutrient deficiency or toxicities. Among the toxicities, iron toxicity is well recognized as a nutritional disorder in low land rice production. Iron toxicity is a syndrome of disorder associated with high concentration of Fe2+ in soil solution. A wide range of soil types show iron toxicity problem including acid sulphate soils, acid clay soils, peat soil and valley bottom soil. During monsoon rains in the wet season, soluble iron (Fe2+) migrate to the surface and its iron content increases to subtoxic or toxic levels. In rolling topography and with heavy monsoon downpour there is considerable lateral flow of iron containing water from the adjacent uplands to mid – and low lands. This increases the iron content to toxic levels. Poorly drained sandy soils in valleys receiving interflow water from adjacent uplands with laterite horizon (Plinthudults) showed iron toxicity in Srilanka and Kerala and Odisha in India. These soil groups come under the taxonomic orders Alfisols, Ultisols and Oxisols occurring in association with Entisols and Inceptisols. The iron concentration (Fe2+) in soil solution that affect low land rice yield ranges from 10 to > 2000 mg L-1 Iron toxicity induced yield reduction which is associated with poor nutrients . status (deficiency of P, K and Zn) and H2S toxicities.

Soil erosion refers to detachment and transport of soil and soil particles from one place to other by the action of water, wind or gravity. Soil erosion consists of (i) detachment of soil particles from surface (ii) their transport from one place to other and (iii) deposition in another place. Soil erosion are of two types: Natural erosion and accelerated erosion. The natural or geological erosion is steady, nondestructive and slow process of nature. On the contrary the accelerated erosion caused due to human activities like cutting of forest, intensive cropping, construction of roads and building is very rapid and destructive. Surface one inch of soil which is formed in thousand years can be lost within one year due to accelerated erosion. In India, out of total 175 million hectares of degraded land, soil erosion due to water and wind accounts for 150 million hectare. Soil erosion due to shifting cultivation, salinity, alkalinity, water logging and shifting of water courses account for 25 million hectare. Average soil loss from various land surfaces in India has been estimated to be 5334 million tonnes per year out of which 29 percent is permanently lost to sea, 10 percent is deposited in reservoirs and 61 percent is transported from one place to other. The plant nutrients lost through 5334 million tonnes of eroded soils was estimated to be 8.4 million tonnes which includes 2.5 million tonnes of N, 3.3 million tonnes of P and 2.6 million tonnes of K. Siltation of reservoirs through water erosion is a major concern in India. This accelerated silting has considerably reduced the estimated life span of major reservoirs. The rate of siltation depends on the catchment area, soil erodability, topography and rainfall pattern. Larger the catchment area, smaller is the siltation load in the reservoirs because, the coarse fraction of eroded particles may be settle down in the stream valley before the water enters into the reservoir.

Acid soils occupy about 30 percent of the land area of the world out of which 67% acid soils support forests and wood lands and 18 percent are covered by grassland vegetation. Only 4.2 per cent (179 million hectare) of the acid soils across the globe is used for arable crops. Soil acidity is a major constraint in crop production. The removal of basic cations especially Ca and Mg by leaching and their replacement by acidic cations, H, Al and Fe on exchange complex leads to soil acidity. Soil developed from granite parent material are more acidic than those developed from basalt, shale or lime stone. In acid soils, low pH leading to toxic concentration of H+, Al3+, Mn2+ influences nutrient availability, organic matter decomposition and microbial activity. Efficient soil amelioration and nutrient management practices are necessary for crops susceptible to soil acidity.

Saline and alkali soils occur commonly under arid climate due either to the presence of an excess of soluble sodium salts or to the predominance of sodium among the exchangeable bases. Saline and alkali soils have been classified as follows 1. Saline soils Saline soils were originally called “White alkali” soils. Russians term them as “Solonchak” soils. The soils are classified as saline if the electrical conductivity of saturated soil paste is more than 4 dS /m at 250C, exchangeable sodium is less than 15 percent and pH is less than 8.5. 2. Alkali soils The soils have been classified as alkali if the electrical conductivity of saturated soil paste is less than 4 dS/m, exchangeable sodium is more than 15 percent and pH is 8.5 to 10.0.

Water used for irrigation contain some salts, but quantities and kinds vary greatly depending on the source of water. Since sodic status of soils can be greatly influenced by salts in irrigation waters, successful irrigation practices require the evaluation system to judge irrigation water quality and methods employed. The actual damage done by salt to plants or soils depends on the concentration in soil solution rather than the quality of irrigation water applied. Thus, the use of some water source for irrigation might lead to severe salt problem in soils where drainage is restricted. Criteria for evaluation of irrigation water Various criteria considered in evaluating the quality of irrigation water are: 1. Salinity hazard The most satisfactory method for rating the salt content of irrigation water involves measuring electrical conductivity. Various conductivity limits have been proposed to indicate the degree of salinity problems that might be anticipated with use of irrigation water on crops. There are four classes of salinity hazard such as C1, C2, C3, and C4.

In India rice is cultivated under two land situations. In uplands, rice is grown under rainfed conditions and the yield is normally low. In medium or low land conditions rice is grown under wet condition where plenty of rain water or irrigation water is available. Here an intensive tillage is practiced in wet to create a soft puddle condition and then paddy is transplanted. Land submergence is thus an essential condition for successful rice cultivation. Rice soils are not necessarily soils with water at or near the surface. Many soils have a fairly deep water table, but their surface is kept under submergence maintaining depth of 3-5 cm water. This condition is maintained either by puddling when wet or by having a compacted layer in the sub surface. A rice soil is characterized by reducing conditions, when it is cropped with rice during wet season and oxidizing conditions during dry season, when the land remained fallow or planted with dry season crops if, irrigation water is available.

Pollution Pollution is an undesirable change in physical, chemical or biological characteristics of air, water or land caused by excessive accumulation of pollutants (substances causing pollution). Kind of pollution Pollution can be classified in many ways:

Soil health Soil health is defined as the continued capacity of soil to function as a vital living system, by recognizing that it contains biological elements that are keys to ecosystem function within land use-boundaries. These functions are able to sustain biological activity of soil, maintain the quality of air and water as well as promote plant, animal and human health. The characteristics of a healthy soil depends on the physical, chemical and biological properties of soils which directly or indirectly influence crop production. Soil quality and soil health are terms that are discussed in agricultural community. Both these terms encompass a complex, dynamic concept, different to define and hard to measure. The term soil quality and soil health are often used interchangeably in the scientific literature, with scientists in general preferring soil quality and producers preferring soil health. Soil health may be considered as the state of soil at a particular time equivalent to the dynamic properties in short term. In contrast, soil quality may be considered for a particular purpose over a longer time scale, equivalent to static soil quality. In a broader way soil quality may refer to both permanent and static soil properties. (Fig. 11.1). A static soil property relates to natural characteristic of soil (texture) which are derived from pedogenic processes. These properties cannot be easily amended. The dynamic properties are readily related to management practices. The dynamic component is of most important for the growers because it allows the soil to come to its full potential.

Sustainable management of soil resources is essential for food, nutritional and economic security of the country. The continued degradation of soil resources is considered an important factor in lowering the total and partial factor productivity of agriculture in the country. The process like soil erosion, nutrient loss, water logging, desertification, acidification, compaction, crusting, salinization and soil contamination affect food and environmental security in most parts of the country. The future agricultural growth at higher rate cannot be sustained with a deteriorating soil resource base. We need to monitor the quality of soil resources and devise appropriate management strategies for sustainable crop production without deteriorating the environment. In India, several agencies like National Commission on Agriculture (NCA), Ministry of Agriculture (Soil and Water conservation Division), Society for Promotion of Waste lands Development (SPWD), NBSS&LUP, Nagpur have been constantly inventorizing and characterizing soil resource for drawing up land use and development plans at National and State levels. However, there is a great variance in estimates due to differences in approaches and criteria for assessment. For an example,the total degraded land as estimated by NCA is 148.09 Mha as against, 175.0 Mha by Ministry of Agriculture (Soil and water conservation Division), 129.58 Mha by SPWD and 187.7 Mha by NBSS&LUP, Nagpur. In soil profile development, we focused on vertical variability in soils - the differences among soil horizons. In this chapter we focused on horizontal variability- how soils differ from place to place across the landscape. Spatial variations in soil properties occurs across distances having geographic meaning for land management-from a few meters to many kilometers. We need to monitor regularly the status of our soil resources employing modern technologies to refine our understanding about them and renew our commitment to their preservation. The applications of Remote Sensing (RS), Geographical Information Systems (GIS) and Global Positioning System (GPS) have greater opportunities to offer in this regard.

Sustainable management of soil and water resources is essential for food, nutritional and environmental security of the country. The total and partial factor productivity of agricultures in India declined over years because of continued degradation of natural resources. The process leading to land degradation are generally triggered by excessive use of land and water resources to meet the growing demand of population for food, fibre and fodder. Various anthropogenic activities leading to accelerated land degradation through salinization, flooding, water logging, erosion of water and nutrients, drought reduced agricultural productivity and nutritional security in the country. These problems can be overcome by optimum utilization of land adopting suitable management practices. For effective land management practices, the soils should be interpreted in forms of their land capability, suitability for irrigation and crop growth. This will not only help the farming community and extension specialists, but also to the administrators and policy makers for using soils for sustainable agricultural production.

Trees are an integral and indispensable constituents of our natural surroundings. The trees keep the environment clean, make the soil healthy and provide food, fibre and shelter to mankind and wild animals. Trees help in stabilizing the soil, a vital natural resource, prevention of soil and water erosion, control run off water in the catchment areas, acts as a shelter belt against wind erosion in arid zone, act as a wind breaker to protect the coastal region during storm and cyclone besides contributing substantially to economic development. The National Commission on Agriculture stress the need for afforestation of about 40 million ha of land presently lying barren because of salinity, sodicity, waterloggings, ravines, coastal sandy areas, stony and gravelly lands, high altitude and slopping lands. Several agencies in various parts of the country are engaged in afforestation of these degraded lands.

Soil conservation in hilly areas Soil erosion is a major problem on hills because of steep slopes. It has been estimated that about 6 million ha of land requires intensive conservation measures in Himalayan and sub-Himalayan regions of Uttar Pradesh, Uttarakhand, Punjab and Himachal Pradesh. Anthropogenic activities like shifting cultivation, deforestation, over grazing accelerate soil erosion in hilly ecosystem.