RLO 5 Lesson: Overview and importance of soil fertility

1. RLO 5 Lesson: Overview and importance of soil fertility After completing this lesson, you will be able to: Understand the meaning, concepts and components of soil fertility. Know the characteristics of a fertile and productive soil .

2. The overall ability of a soil to support vigorous crop growth by ensuring adequate plant nutrients and suitable conditions for water uptake, and by providing favourable conditions for root growth and development.ORA fertile soil is one that contains an adequate supply of all the nutrients required for the successful production of plant life Soil Fertility

3. Soil Fertility • A fertile soil is essential for optimum productivity, profitability and, yes, even protection of ground water quality and soil from erosion . • Soil fertility is divided into 3 groups, i.e. Physical, Chemical and Biological Soil Fertility, which are inter-related with each other (see next slide). • Better management of physical and chemical soil fertility improves soil biological fertility, which in turn can be further enhanced by good agronomic/ culttural practices. Hence, soil fertility is a key to sustainable agriculture (see next slide)

4. Sustainable agriculture Improved soil fertility and productivity Chemical Agronomic practices Soil Fertility (Living) plant roots Rhizosphere Physical Biological Bacteria Fungi,actinomycetes other organisms

5. Biological soil fertility: The capacity of organisms living in soil to contribute to the nutritional requirements of plants and foraging animals for productivity, reproduction and quality while maintaining biological processes that contribute positively to the physical and chemical state of the soil. • Chemical soil fertility: The capacity of soil to provide a suitable chemical and nutritional environment for the plants and foraging animals for productivity, reproduction and quality in a way that supports beneficial soil physical and biological processes, including those involved in nutrient cycling. • Physical soil fertility: The capacity of soil to provide physical conditions that support plant productivity, reproduction and quality without leading to loss of soil structure or erosion and supporting soil biological and chemical processes.

6. Components of soil fertility • Soil depth (determining the volume of soil accessible to the root system). Most arable crops prefer about one metre without any obstructing layer. • Soil structure (based on size distribution and aggregation of particles). This determines the distribution of pore sizes which is decisive for the supply of air and water to the roots. Contd…..

7. Components of soil fertility • Soil texture • It designates the proportion of different particle size fractions in the soil. • Of special importance to soil fertility is the percentage of soil particles of less than 2 mm in diameter, which constitute the fine soil. • Fine soil is composed of particles in three size groups: sand, silt and clay. • International size units used to classify soil particles in terms of their mean diameter are: • gravel (> 2.0 mm); • coarse sand (2.0–0.2 mm); • fine sand (0.2–0.02 mm); • silt (0.02–0.002 mm); • clay (< 0.002 mm).Contd…..

8. Soil texture influences to a large extent several components of soil fertility such as the amount of nutrient reserves and their proportion to the available nutrient fraction. It also influences several properties such as aeration, pore space distribution, WHC and drainage characteristics. Contd… Components of soil fertility

9. Components of soil fertility • Content of nutrients with different degrees of availability. • Storage capacity for soluble nutrients from the soil and fertilizers. • Soil pH/ reaction (an indicator and regulator of chemical processes and equilibria). Contd….. Picture in right side shows the availability of nutrients at varying soil pH

10. Components of soil fertility • Content of detrimental or toxic substances, either naturally occurring (e.g. salts in saline soils, aluminium in extremely acid soils) or man-made (e.g. from pollution). • Quantity and activity of soil organisms as agents of transformation processes. Contd….

11. Components of soil fertility • Soil Organic Matter (SOM) • It promotes soil structure improvement by plant residues and humic substances leading to higher WHC, better soil aeration and protection of soil against erosion. • Helps in keeping the nutrients in available forms and protecting them against losses. • Nutrient mobilization from decomposed organic nutrient sources and mineral reserves: N, P, S, Zn, etc. • nutrient gain as a result of N fixation from the air. It influences promotion or retardation of growth through growth hormones.

12. It is important to note: • Soil productivity is the crop yielding ability of a soil from a unit area. • Soil fertility is vital to a productive soil but, a fertile soil is not always a productive one. Poor drainage, weeds, insects, disease, drought and other factors can limit productivity even when fertility is adequate • Fertile soils are not always highly productive, but the productive soils are always fertile. • Very fertile and productive soils are rarely found in nature

13. A highly productive soil with high fertility: • mobilizessoil nutrients from the reserves; • transforms fertilizer nutrients into easily available forms; • stores water-soluble nutrients in easily available forms, thus preventing leaching; • offers the plants a balanced nutrient supply, due to its self-regulating system; • stores and supplies sufficient water; Contd….

14. A highly productive soil with high fertility: • maintains good soil aeration for the oxygen requirements of roots; • does not 'fix' nutrients, i.e. convert them into unavailable form; • Improves crop use efficiency of nutrients and resources such as water and light; and • Provides nutrients throughout the growing season and especially during critical peak periods of plant development