SOIL 43 Unit I - Introduction to Soil Fertility 2024-2025 PDF

S O I L 4 3 U n i t I - I n t r o d u c t i o n t o S o i l F e r t i l i t y Prepared By: Chelly S. Alovera Junesa U. Cristobal Allan G. Octat UNIT I. SOIL FERTILITY MANAGEMENT 1. Introduction 1.1. Soil fertility definition 1.2. Historical backgroun...

S O I L 4 3 U n i t I - I n t r o d u c t i o n t o S o i l F e r t i l i t y Prepared By: Chelly S. Alovera Junesa U. Cristobal Allan G. Octat UNIT I. SOIL FERTILITY MANAGEMENT 1. Introduction 1.1. Soil fertility definition 1.2. Historical background of soil fertility 1.3. Cause of the decline in soil fertility 1.4. Importance of soil fertility  1.1 Definition of Terms: 1. Soil fertility – refers to the inherent capacity of the soil to supply nutrients to plants in adequate amount and suitable proportion. 2. Fertilizer – any organic or inorganic substance that supply essential elements needed by plants for their growth and development. 3. Productivity – refers to the capacity of the soil to produce crops under a specified system of management. It is expressed in terms of yield.  Definition of Terms: 4. Soil fertility management – practices that include the use of fertilizers, organic inputs, crop rotation with legumes, and the use of improved germplasm, combined with the knowledge of how to adapt these practices to local conditions. 5. Sustainable Agriculture – refers to the management system for renewable and non-renewable natural resources that provides food, income, and livelihood for the present and future generations and that maintains or improves the economic productivity and ecosystem services of these resources.  Soil Fertility vs Soil Productivity Soil fertility deals with the availability of the mineral nutrients in the soil that are required for the growth and development of crops to produce yield obtained under a specific system of management of soil, water, lime, and nutrients as well as control of biotic factors (pests, diseases, and weeds). Soil productivity is affected by other factors of crop growth such as climatic, biotic, and the edaphic factors which include the nutrient-supplying capacity of the soil.  Soil Fertility vs Soil Productivity Scopes of Soil Fertility a. Soil nutrients and their availability b. Soil acidity c. Management of soil acidity and soil fertility  Concepts of Availability Availability is a term which described in a general way the relative ease in which a nutrient is supplied by the soil. Availability of nutrients in the soil depends on the following: a. Intensity factors b. Capacity factors  Intensity factor  This is essentially the concentration of nutrients in the soil solution.  These nutrients may be derived from the following: a. weathering of primary mineral b. decomposition of organic matter c. Deposition from the atmosphere d. Application of fertilizer materials  Once introduced, the nutrients vary considerably in their subsequent reaction.  Intensity factor Are very soluble and generally do not form insoluble compounds with any soil constituents/other nutrients. As a result, any NO3- & Cl- nitrate or chloride added to the soil generally remain in the soil solution until absorbed by plants, leached, denitrified or lost thru drainage water. SO4= Tends to be sorbed in strongly acidic soils high in Fe+++ and Al+++ Cu++, Zn++ Form complexes with organic matter Al+++ Form complexes with organic matter Fe+++ & Al+++ Form insoluble hydroxides and hydrous oxides Reacts with Al and Fe in acidic soils and reacts P with C a in alkaline soils/recently limed soils  Factors affecting the concentration of nutrients in the soil solution: a. Soil pH  Hydroxides of Fe and Al are insoluble at high pH, soluble at low pH  Carbonates are insoluble at high pH, soluble at low pH  Sulfate behave in a similar manner in neutral or alkaline soils but tend to be sorbed in acid soils  Cations such as copper (Cu++) and (Zn++) having Lewis acid properties (electron pair acceptors) form complexes with organic matter  Factors affecting the concentration of nutrients in the soil solution: a. Soil pH  Ferric ion and aluminum form insoluble hydroxides and hydrous oxides  Phosphate ions, H2PO4- and HPO 4=, form insoluble Fe, Al and Ca-phosphates Soil pH also affects many oxidatiom-reduction reactions, activities of microorganisms and determines the chemical forms of phosphates in soil solution. Phosphates: Fe(OH)2H2PO4 - soluble at high pH Al(OH)2H2PO4 - soluble at high pH Ca10(PO4)6(OH)2 – soluble at low pH  Factors affecting the concentration of nutrients in the soil solution: b. Redox potential Is the state of aeration of the soil. The principal reduction reactions occurring in paddy soils are as follow: Stage Eh, mv Reaction 0 800 O2 + 4H+ + 4e- 2H2O 1 430 2NO - + 12H+ + 10e- N + 6H O 3 2 2 2 410 MnO2 + 4H+ + 2e- Mn++ + 2H2O 3 130 Fe(OH)2 + e- Fe(OH)2 + OH- 4 -180 Organic acids (lactic,pyruvic) + 2H+ + e- Alcohols 5 -200 SO = + H O + 2e- SO = + 2OH- 4 2 3 6 -490 SO = + 3H O + 6e- S= + 6OH- 3 2  Capacity factor  The ability of the soil to replenish the amount of nutrients in the soil solution which are absorbed by plants from the solid phase. Categories of capacity factor: a. Those forms which are in rapid equilibrium with the soil solution (example: exchangeable cations) b. Those forms which are in moderate to slow equilibrium with the soil solution (example: fixed K, adsorbed P) c. Those forms which are not in equilibrium with the soil solution because of the absence of a reverse reaction (nutrients are released but not re- adsorbed) (example: release of N,P,S,Ca,Mg by organic matter decomposition)  Essential Elements Essential elements are elements required by plants for their life processes. Criteria for essentiality: 1) its necessity for the plant to complete its life cycle, 2) its direct involvement in the nutrition of the plant apart from possible effects in correcting some unfavorable conditions in the soil or culture medium, and 3) the element must be completely irreplaceable by another element,  Nutrient Supply and Availability If a soil is to produce crops successfully, it must have among other things, an adequate supply of all the necessary nutrients that plants take from the soil. Not only that must nutrient elements be present in the forms that plants can use, but there should be a balance between and among them in accordance with the amount needed by plants. If any of these elements is lacking or if not present in proper proportion, plants will not grow normally. 1.2 History of the development of concepts of soil fertility  The theories about plant nutrition and soil fertility varied widely from antiquity to the middle of the nineteenth century. The importance assigned to humus concerning soil fertility over the past two centuries was known as the humic period. The humic period may be conveniently divided into two distinct phases: the pre-nineteenth century debate and Thaer’s humus theory. The pre-nineteenth century debate In ancient Greece and Rome, soil fertility referred to soil physical properties rather than chemical properties. In the seventeenth century, Van Helmont, espoused Palissy’s ideas about the role of soil as a simple source of water and mineral nutrients for the plant (Boulaine 1989). During the eighteenth century, ‘humus’ was often understood to be soil, and many theories about plant nutrition were based on the belief that plants relied directly on humus for their carbon supply. The pre-nineteenth century debate Tull (1733) proposed a ‘new agriculture’ and fertilization practices based on soil tillage carried out as frequently as possible. This was based on the belief that since soil particles were a source of food for the plant, the soil structure had to be very finely divided to enhance uptake by roots. On the other hand, by the end of the eighteenth century, several authors like Priestley (1777), Fabbroni (1780), Ingen-Housz (1779), Senebier (1782), and de Saussure (1804), rejected these theories and experimentally demonstrated the gaseous origin of carbon during photosynthesis and the role of light. The pre-nineteenth century debate Contradictory debates arose on the subject, without referring to experimental facts, Hassenfratz (1972) asserted that a fraction of humus in the form of soluble carbon is directly assimilated by plants (carbon heterotrophy). Thaer’s humus theory Thaer’s ‘Principles of Rational Agriculture’ (1809) integrated analysis of fertility management and the perception of sustainability. His treatise contains some unverified theoretical developments on plant nutrition that served as a basis for the first rational and systemic approach to fertilization within the context of sustainable cropping practices (de Wit 1974; Feller et al. 2003). Thaer’s humus theory Thaer’s main contributions were the precision of his definitions and the use of both bibliographic and experimental sources in his effort to quantify certain principles of rational agriculture by creating an analytical tool based on an index of innate soil fertility (‘natural fecundity’) Thaer’s analyses also included an economic appraisal of existing farming systems using the same range of cropping patterns. This analysis included all costs (labor, space, care of animals, etc.) of organic maintenance of fertility based on fallowing and manuring. Thaer’s humus theory Conceptually, Thaer’s approach to fertility encompassed the plant-soil system as well as cropping patterns and rotations. He tackled modern agricultural issues such as the identification of soil quality indicators, systemic analysis, and the agroeconomic sustainability of farming systems. His work seriously influenced the thinking of his peers during the first half of the nineteenth century. Sprengel – Liebig’s mineral nutrition theory Liebig’s work in 1840 is often considered as the first demonstration, based on scientific experiments, of the origin of plant dry matter from mineral compounds. Such ground-breaking work led to the conclusion that carbon comes from carbon dioxide, hydrogen from water, and other nutrients from solubilized salts in soil and water. However, it was evident that Liebig, who had a gift for synthesis, took much of his ideas from the work of Sprengel (1838, in van der Ploeg et al. 1999) and others. Sprengel – Liebig’s mineral nutrition theory Since Liebig’s findings accounted rather satisfactorily for the fertilizing effect of mineral inputs, it provided the basis of modern agricultural science. Liebig promoted the use of fertilizers to compensate for soil mineral depletion, and his work, together with that of Lawesand Gilbert at Rothamsted (e.g., see Dyke 1993), paved the way for recommendations for the widespread use of chemical fertilization in cropping systems. SOM: the ecological period (1940–2000) Societal criticisms concerning the sustainability of intensive farming arose as early as the 1930s. Concerns about the impacts of high-input agriculture from the formal scientific sector came from the development of ‘alternative’ farming practices under the rubric of ‘organic agriculture.’  Concerns about the connection between loss of biological function and decrease in the fertility of heavily cropped soils managed without organic practices date back to ancient times. SOM: the ecological period (1940–2000) The term sustainable development came to global attention with the publication of the report of the World Commission on Environment and Development (WCED 1987), where it was defined as ‘development that meets the needs of present generations without compromising the ability of future generations to meet their own needs.’ This obvious congruence with the environmental concerns about the impact of intensive high-input agriculture, coupled with the failure to achieve persistent and consistent results in many parts of the world, notably Africa, stimulated substantial efforts to find sustainable means of agricultural production (Conway and Barbier 1990). SOM: the ecological period (1940–2000) The term sustainable development came to global attention with the publication of the report of the World Commission on Environment and Development (WCED 1987), where it was defined as ‘development that meets the needs of present generations without compromising the ability of future generations to meet their own needs.’ This obvious congruence with the environmental concerns about the impact of intensive high-input agriculture, coupled with the failure to achieve persistent and consistent results in many parts of the world, notably Africa, stimulated substantial efforts to find sustainable means of agricultural production (Conway and Barbier 1990). This focus naturally centered on the use of renewable natural resources. SOM: the ecological period (1940–2000) One of the key features of sustainable soil practice is the return to managing soil fertility through the combination of OM (crop residues, compost, or manure) and mineral nutrient inputs (Pieri 1992). This rediscovery of the benefits of the ancient concept of integrated nutrient management has become the mainstay of soil fertility management at the turn of the twentieth century (Mokwunye and Hammond 1992; Palm et al. 1997), and maintenance and/or improvement of the SOM status is central to its philosophy. SOM: the ecological period (1940–2000) The modern concept of SOM within science-based sustainable agriculture as a dynamic, biologically regulated pool of energy, carbon, and nutrients converges with the concept of fertility defined for organic agriculture by Balfour as ‘the capacity of soil to receive, store and transmit energy’ (Balfour 1976, in Merrill 1983). This had the effect of enhancing the status of SOM management as a component of the design of new cropping schemes.  Soil Fertility Management 1.3 Factors affecting the decline in soil fertility: 1. Crop removal of nutrients Different plants would remove different amounts of nutrients or bases. If these bases are continually removed from the soil, then the soil would become acidic. 2. Gaseous losses Loss of nutrients in the form of gases would also result to decline in soil fertility.  Soil Fertility Management 3. Leaching of nutrients The bases which have been replaced from the exchange sites of soils are removed in the drainage water.  This process removes the metallic cations that might compete with hydrogen and aluminum on the exchange complex. 2. Soil erosion losses Soil erosion is the wearing away of the land surface by running water, wind, ice, or other geological agents which would result to decline in soil fertility.  The following are the primary causes of loss of soil fertility: 1. the use of fertilizers without regard for field conditions 2. unsuitable cropping system; 3. continuous cultivation of crops; 4. intensive tillage; 5. monoculture cultivation; 6. complete clearing of crop residues; 7. soil erosion and land degradation; 8. unfavorable climate and extreme weather conditions.  1.4 Importance of Soil Fertility Types of Soil Fertility 1.Inherent or Natural Fertility:  The soil that naturally contains some nutrients and is considered fertile is known as inherent fertility. Some of the nutrients like nitrogen, phosphorus and potassium are considered essential for the normal growth and yield of the crop. These are naturally present in naturally fertile soil. The inherent fertility has a limiting factor from which fertility is not decreased. 2.Acquired Fertility: When the fertility of the soil is developed through external agents like manures and fertilizers, tillage, irrigation etc., it is known as acquired fertility. It has been found that the yield does not increase after a point by the application of an additional quantity of fertilizers. Thus, this becomes the limiting factor of acquired fertility.  1.4 Importance of Soil Fertility  Soil starts the chain of the food cycle wherein it feeds the plant which ultimately feeds us.  They are the primary organisms of the food chain.  With the improvement of soil, there will be a gradual increase in the quality of plant and crop production as well.  Some of the essential aspects of soil fertility are described below: 1) Soil provides direct nutrition and a foundation for plants. It is considered the most important factor in determining plant growth. 2) Soil is a result of the accumulation of decomposing plant and animal matter with the aging parent material. As this soil breaks down, these elements are released in the form of nutrients that are directly available to the growing plant.  How to Increase Soil Fertility?  There are a few ways in which one can increase soil fertility or replenish the nutrients removed from the soil. Some of these are discussed below: 1.Recycling Nutrients: This can be done by the use of plant and animal waste. 2.Use of fertilizers. 3.Through Microbial Action: This includes the use of nitrogen fixation which can be achieved through the use of grain legumes that initiates biological nitrogen fixation. This can also be done by other methods like fertilisers, green manures, etc. 4.Incorporating Cover Crops: Using cover crops can add organic matter to the soil improving soil fertility and making it healthy for plant production. Thank you for listening...