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Soil is a bioorganic - mineral complex of the loose surface layer of the earth’s crust. Soil microbiology is the science that deals with the millions of microscopic forms of life found in the soil. It is stated that one hectare - foot (one hectare to a depth of 30cm) contains 2 to 10 metric tons of living microorganisms. Soil microorganisms are in a constant struggle for existence and are believed to be in a state of dynamic equilibrium. Without microorganisms, the soil would be an inactive geological mass incapable of supporting plant life and without plant life, animal life would not be possible. This soil population consists mainly of bacteria, fungi, actinobacteria, algae, and protozoa. The soil ecosystem includes these microbial groups as well as the inorganic and organic constituents of a given site. The collections of cells represented in the community are considered as distinct populations. All the inhabitants of the particular locality make up the community.

Types of Microorganisms in Soil

Living organisms both plants and animals, constitute an important component of soil. The pioneering investigations of several early microbiologists showed for the first time that the soil was not an inert static material but a medium pulsating with life. The soil is now believed to be a dynamic or rather a living system, containing a dynamic population of organisms/microorganisms. Cultivated soil has relatively more population of microorganisms than the fallow land, and the soils rich in organic matter contain much more population than sandy and eroded soils. Microbes in the soil are important to us in maintaining soil fertility and productivity, cycling of nutrient elements in the biosphere, and sources of industrial products such as enzymes, antibiotics, vitamins, hormones, organic acids, etc. At the same time certain soil microbes are the causal agents of human and plant diseases.

History of Soil Microbiology

There is enough evidence in the literature to believe that microorganisms were the earliest of the living things that existed on this planet. Man depends on crop plants for his existence and crop plants in turn depend on soil and soil microorganisms for their nutrition. Scientists from the beginning studied the microorganisms from water, air, soil, etc. and recognized the role of microorganisms in natural processes and realized the importance of soil microorganisms in the growth and development of plants.Thus, microorganisms have been playing a significant role long before they were discovered by man. Today, the soil is considered to be the main source of scavenging the organic wastes through microbial action and is also a rich storehouse for industrial microflora of great economic importance.

Unlike soil science whose origin can be traced back to Roman and Aryan times, soil microbiology emerges as a distinct branch of soil science during the first half of the 19^th century. Some of the notable contributions made by several scientists in the field of soil microbiology are highlighted in the following paragraphs.

Anton Von Leeuwenhoek (1673) discovered and described microorganisms through his own made first simple microscope with a magnification of 200 to 300 times. He observed minute, moving objects which he called “animalcules” (small animals) which are now known as protozoa, fungi, and bacteria. He for the first time made the authentic drawings of microorganisms (protozoa, bacteria, fungi).

Soil represents a medium or substrate in which numerous microorganisms live and bring about a great variety of processes that are responsible for the continuation of the cycle of life in nature. The numerous living forms which spend their life in the soil, ranging from submicroscopic forms to the lower animal forms. With the growing recognition of the numerous processes carried out by the microorganisms in the soil there gradually emerged a branch of microbiology, which came to known as soil microbiology. It is a branch of soil science concerned with soil-inhabiting microorganisms and their functions and activities.

Since soil microbiology concerns soil microorganisms and their processes it is closely associated with soil biochemistry. Medical bacteriologists are interested in the soil as a medium for the growth and survival of disease-producing organisms. Agricultural chemists are also interested in the soil processes that result from the activities of microorganisms. General bacteriologists, zoologists, botanists are interested in a certain special group of organisms found in the soil. Recently, soil microbiology has expanded to include the study of the role of soil microorganisms in genetic engineering, in the biological control of pests and diseases, the degradation of pollutants, production and destruction of radioactive gases and its transfer. Thus microbial participation in several important processes emphasizes that soil microbiology has become a global science.

Salt affected soils occupy 962.2 m ha globally which accounts for 33% of the arable land. In India 8.373 m ha is affected with salts. Of which 2.359 m ha are alkali soils, 3.829 m ha are saline soils and 2.185 m ha coastal saline soils. Reclamation of these soils provides additional area for food grains production and employment.

SOIL MANAGEMENT PRACTICES

Good soil management is the basic for deriving greater benefits from the fertilizers used in crop production. Some of the good soil management practices are

Good tilth is the first feature of good soil management. It means a suitable physical condition of the soil and implies in addition a satisfactory regulation of soil moisture and air.

The maintenance of soil organic matter which encourages granulation is an important consideration of good tilth.

Tillage operations and timings should be adjusted as to cause the minimum destruction of soil aggregates. Good tilth minimizes erosion hazards.

The choice and sequence of adaptable crops or crop rotation are other very important considerations. These are related to climate, particularly rainfall and its pattern of distribution and the characteristics of the soil profile, including drainage and extent and duration of available soil moisture. A proper sequence of crop varieties greatly influences soil conditions. It is more realistic to evolve cropping patterns and land management practices according to land capability. Cropping patterns chosen and management practices adopted should aim at soil and moisture conservation for efficient nutrient and moisture utilization.

Integrated plant nutrition system conceptualized by food and agriculture organization is the maintenance or adjustment of soil fertility and of plant nutrient supply to an optimum level for sustaining the desired productivity through optimization of benefits from all possible sources of plant nutrients viz. organic manures, fertilizers, crop residues, compost or nitrogen fixing crops etc. in an integrated manner.

Biofertilizers act as complementary and supplementary sources of plant nutrients. Biofertilizers help in increasing the biologically fixed atmospheric nitrogen and enhancing phosphorus availability to the crops. Among the biofertilizers for increasing nitrogen supply, nitrogen fixing bacteria (Rhizobium, Azotobacter and Azospirillum), blue green algae (BGA) and Azolla are important. The availability of phosphorus is improved by phosphorus solublizing microorganisms (PSM) and mycorrhizae (VAM).

Rhizobium is of vital importance to various pulses and some of the oilseeds and fodder legumes as 80–90 per cent of their nitrogen requirement is met through biological nitrogen fixation (BNF). Rhizobium fixes atmospheric nitrogen ranging from 50–60 kg per ha in groundnut, 100–300 kg per ha in alfalfa. In pulses it is estimated at 50–110 kg/per ha. Field studies indicated a yield increase of 14–53 per cent due to Rhizobium inoculation. Nitrogen left over the demand of legumes in combination with the nitrogen present in roots of the legumes will enhance the soil fertility. Consequently the nutrient needs of the subsequent crop from applications will be reduced.

Green manure is defined as fresh organic matter/undecomposed plant material/ real organic matter, natural plant food added to the soil for the purpose of supplying plant nutrients.

CLASSIFICATION OF GREEN MANURES

Nonlegumes: Rape seed, buck wheat, niger, rye, oats and maize

Legumes:

Grain legumes: cowpea, mungbean, pigeon pea, soybean, khesari (Lathyrus sativus)

Dual purpose legumes: cluster bean (Cyamopsis tetragonoloba). pillipesara, Sesbania speciosa.

Non grain legumes: sunnhemp, dhaincha, pillipesera (Phaseolus trilobus), stylosanthes and desmodium.

Farmyard Manure is the manure prepared by using the mixture of dung and urine soaked litter by microorganisms.

Good farmyard manure is one

ZINC (Zn)

Chandler et al., (1932) deduced the requirement of zinc by plants while working solution for little leaf or “rosette” on peach. Zinc plays significant role in assimilation of NO₃ and for synthesis of tryptophan. Involved in biosynthesis of indole acetic acid which is responsible for f lowering and fruiting, it is an activator of several enzymes (triphosphate dehydrogenase and tryptophan synthetase), involved in photosynthesis and nitrogen metabolism.

Deficiency results in poor growth of the terminal bud. Decrease in stem length resulting in resetting and whorling of leaves. Zinc deficiency disorder in rice is called khaira. Common when zinc availability is < 0.7 ppm. White bud in maize and malformation of fruits, reduction in water uptake. Interveinal chlorosis often with necrosis and pigmentation and reduced leaf size in broad leaved crops known as little leaf and malformation of leaves.

The crops which are known to respond for zinc application are maize, rice, soyabean, castor, onion, barley, wheat, potato, sorghum and cotton

CALCIUM

Calcium is important in imparting structure and permeability to cell membrane. Deficiency produces general breakdown of membrane structure. Calcium enhances the uptake of NO₃ ^– N and interrelated with NO₃ ^– metabolism. It regulates cation uptake, required for cell elongation and cell division. Deficiency causes failure of terminal buds and apical tips of roots to develop. Blossom end rot of tomato, bitter pit of apples are due to calcium deficiency. Calcium is beneficial in imparting good soil structure.

It is immobile in plant. Very little translocation of calcium in the phloem is observed. Hence there is poor supply of calcium to fruits and storage organs. Downward translocation of calcium is also limited. Hence roots fail to enter the low calcium soils.

Glauber J. R. (1604–1670) in Netherlands first proposed that the salt peter (KNO₃) was the principle of vegetation. He obtained large increases in crop yield by addition of salt peter.

Mineral soils contain 0.04–3.0% K. Total potassium content of soils range from 3000 to 100000 kg per ha in the upper 0.2 m of soil profile. Of this total potassium approximately 98 percent is bound in mineral form whereas 2% in soil solution and exchangeable phases.

ROLE OF POTASSIUM

It is Involved in activating the enzymes (as many as 80) responsible for carbon dioxide reduction and required for synthesis of adenosine triphosphate. Hence deficiency of potassium reduces crop growth and yields.

Liebig (1840) on the basis of soil and plant analysis deduced the phosphorus requirement of plants. J.B. Lawes conducted series of field experiments to improve the fertilizer value of common sources of phosphorus such as bone meal, apatite, rock phosphate. Lawes (1843) produced super phosphate by treating apatite mineral containing phosphorus with sulphuric acid. He also stated that the phosphorus present in bones of higher animals can be made available by treating with sulphuric acid.

Phosphorus is the second most deficient nutrient in the world. Annual application of phosphorus fertilizers to crops is 36 million tons of which

1.32 m tones are consumed in India. Most of the arable soils in tropical and subtropical regions are deficient in phoshphorus, but the response of crops to phosphorus is uncertain. Phosphorus concentration in plants ranges from 0.1 to 0.4 per cent.

Greek scientist Theophrastus (300 BC) advocated legume rotation. As early as 1750 AD it was known that plants require Nitre. Louis Pasteure in 1860 AD stated the possibility of atmospheric nitrogen fixation by microorganisms. Hellriegel and Willfarth (1886) strengthened the views of Louis Pasteure by his observations on the irratic behaviour of legumes to nitrate nutrition. Beizerink (1890) isolated the organism involved in nitrogen fixation. The systematic field experiments conducted at Rothemstead experimental station showed that the plants respond to inorganic nitrogen.

ROLES OF NITROGEN IN CROPS

Plants contain 1-5 per cent nitrogen by weight. It is a structural component of chlorophyll, aminoacids and proteins. Plant proteins contain 16 per cent nitrogen (6.25 × %N = protein). Plants are dependent on protein for their propagation. Cereals possess a threshold protein level below which grain will not form.

Plants are the generators or the primary source of organic matter while animals are the transformers- secondary source of organic matter. In agriculture, plants add 10–30 percent of organic matter through their roots stubbles and leaf fall and exudations. The excreta of livestock, the organic wastes of urban and rural residential areas include the garbage and sewage and sludge. The by products of agro based industries viz. bagasse, vinasse, pressmud from sugar industries, the coir dust from the coir industries, dust of cotton from ginning industries, the fruit and food processing industries wastes.

Concept of nutrient availability: The ions in the soil solution are available to plant provided they can reach an active root or it can reach them. The concentration of ions in the soil solution at any given moment is however; usually low, except immediately after the application of water soluble fertilizers.

Most of the nutrients are taken up by the plant in the form of cations which are positively charged. Available cations either in the soil solution or held against leaching by negatively charged clay or humus particles are easily taken up by the plants. Other plant nutrients notably phosphorus, boron and molybdenum are taken up by the plant as anions which are negatively charged. The concentration of anions in the soil solution is usually low because they become converted to new less soluble forms e.g., soluble phosphate ions forms less soluble iron or aluminium phosphates. Minerals upon weathering and organic matter upon mineralization release nutrient ions.

Physical factors

However, much readily available nutrients a soil may contain various physical features of the soil make it impossible for the plant roots to absorb it. It then becomes positionally unavailable. These features include hard pans, undesirable soil structures, presence of hard clods, dry soil horizons and water logged situation.

Low soil cation exchange capacity leads to less retention of calcium, magnesium, potassium, copper and zinc.

ESSENTIAL ELEMENTS FOR PLANT GROWTH

Arnon (1954) set three criteria to state an element is essential to plants. They are:

1. The plant must be unable to grow normally or complete its life cycle in the absence of the element,
2. The element is specific and cannot be replaced by another and,
3. The element plays a direct role in metabolism.

Accordingly there are 16 elements essential for plant growth. They are carbon, hydrogen and oxygen called primary nutrients, calcium, magnesium and sulphur called secondary nutrients; iron, zinc, manganese, copper, boron, chlorine and molybdenum are known as micronutrients.

Our production systems are at a pivotal stage in terms of meeting consumer demand for affordable food while improving sustainability. Current intensive crop production practices designed to maximize yield have created an unstable, fragile, and non-sustainable production system. Such systems are prone to reduced soil quality, frequent insect and disease resurgence, emergence of resistant weed species, reduced food quality, and detrimental effects on the health and well-being of our communities. With increasing awareness among consumers of produce quality, nutritional value, methods of crop production and effects of production techniques on the environment, there has been a strong move to improve the quality of our production systems. Grower response to this change has been supportive. Growers have shown interest in developing resilient and stable production systems through the adoption of production practices that enhance soil health, crop productivity, and improve long-term farm sustainability and profitability. Such practices emphasize the use of natural processes within farming systems, often called ‘ecologically sound’ practices which build resilience through synergies and complementarities within the field, the farm, and across our landscape and communities.

Sustainable horticulture is nothing but a contemporary approach to horticulture that emphasizes organic/natural approaches and allows an integrated meshing of ideas with synthesized chemicals used sparingly or relegated to the “last resort.” High Tech & Low Tech are encouraged to create a long-term viable result. Short-Term techniques that impact the environment negatively and thwart the biodynamic continuum are rejected.

Introduction

With India’s population to catapult to a gigantic figure of 1.63 billion by 2050, it rests upon the shoulders of the country’s dwindling land resources to cater to the food demand to the surging human race with an eco-friendly manner. This requires a mammoth effort from the food producing machinery of the country-an effort which has to be inclusive of the technological innovation and extension in this field and to the fullest possible extent. Coping with the short-run challenges to food security posed by food price volatility is indeed a daunting task. But the serious concern is the long-term challenges of avoiding a perpetual food crisis under conditions of global warming. The decline of contributions of Indian Agriculture to the National GDP and an apparent stagnation of the growth rate in agriculture, non remunerative agricultural system, ever increasing population pressure, shrinking land resources, global warming and climate change, indiscriminate use of agricultural inputs, over exploitation of natural resource base and environmental quality have made the situation more vulnerable towards food security. In this backdrop, agricultural knowledge and technology accumulation, transfer, application, and diffusion are key to sustainable development and food security in an eco-friendly manner. The knowledge and technology revolution is critically different from the past industrial revolution in that it is based upon a shift of wealth creating assets from physical things to intangible resources based on knowledge and technologies. Thus, effective management and transfer of knowledge and technologies are believed to be the most critical capability of individuals, organizations, and nations in the globalized 21st knowledge society. Extension could play a pivotal role in fostering sustainability through its educational programs but there has been a growing realization that traditional extension models have not been sufficiently effective in promoting socialization of sustainable agricultural practices. Since sustainable agriculture is a knowledge-intensive system, it requires a new kind of knowledge, which differs from other forms on the basis of conventional agricultural practices. In fact, conventional extension system cannot accomplish sustainability in agriculture; because today’s agricultural extension must consider environmental implications, social issues, and overall economic growth within the agriculture sector. In such a situation, the present conceptual discussion shall be envisaging the dictum and destiny of evolving extension approaches by cherishing a clear focus on extension management perspectives towards sustainable development and environment protection and management so as to the well established extension approaches can be restructured and applied in the niche of extension management towards sustainability.

Introduction to sustainable livestock

Sustainable development has been defined by FAO as “the management and conservation of the natural resource base, and the orientation of technological and institutional change in such a manner as to ensure the attainment and continued satisfaction of human needs for present and future generations. In other words, the development that meets up the needs of the present without compromising the ability of future generations to meet their own needs. Such sustainable development (in the agriculture, forestry and fisheries sectors) conserves land, water, plant and animal genetic resources, is environmentally non-degrading, technically appropriate, economically viable and socially acceptable”. (FAO Council, 1989). Hence, sustainable livestock farming is “the efficient production of safe, high quality products, in a way that protects and improves the natural environment, the social and economic conditions of farmers, their employees and local communities, and safeguards the health and welfare of all farmed species”.