Soil and Plant Nutrition

1. Soil and Plant Nutrition “The Nation that Destroys Its Soil Destroys Itself” - President Franklin D. Roosevelt Krystal, Caroline, Crystal

2. Abstract It is important to know how to conserve soil in order to sustain agriculture. Soil texture and composition play an important role in determining which soil conditions optimize plant growth. Soil particles come in many different forms: sand, silt, clay, etc. and result from the weathering of rocks. The type of soil helps determine the fertility of soil; the most fertile being loam which has pores that are half air, and half water allowing for good aeration, drainage, and water storage. Inorganic components involve positively and negatively charged mineral ions that form a soil solution through cation exchange which can be absorbed by roots. In cation exchange, cation minerals attached to soil particles are displaced by H+ so that the minerals are available for soil solution while the H+ binds to the soil. Cation nutrients are better retained in soil than anion nutrients because soil particles are usually negatively charged. Organic components are mainly found within humus, composed of decomposing organisms. The humus provides crumbly soil with pores that can retain water and aerate soil while increasing cation exchange and act as a mineral reserve. In order to sustain agriculture, farmers use irrigation to provide ample water, fertilization to prevent nutrient depletion, pH adjustment to maximize growth conditions, erosion control to prevent nutrient runoff, avoiding soil compaction to ensure pores are not reduced, and phytoremediation to detoxicate contaminated soils. In conclusion, since soil contains all the nutrients necessary for plant growth, it is crucial to know various methods to prevent soil degradation.

3. Soil: a living finite resource Plants absorb nearly all water/minerals from upper layers of soil, therefore it is important to know how to preserve these layers. 

4. SoilTexture • Texture depends on particle size (sand, slit, clay etc.) • Particles come from the weathering of rock • Soil horizons: soil layers (top soil most important contains most nutrients/minerals) • Water retained by attraction between negatively charged soil particles and water molecules • Bigger soil particles = more surface area for water retention • Loams: most fertile topsoil (pores:half air/half water)

6. Topsoil Composition • Inorganic components (minerals): • Binding ability (mineral to soil) depends on mineral charge (+/-) • Soil usually (-) therefore bind better with (+) minerals = less leaching • Roots absorb minerals as “soil solution” made by cation exchange • Cation Exchange: process to make soil solution by displacing minerals attached to soil with H+ • Cation exchange potential depends on adhesion sites and pH levels

9. Topsoil Composition • Organic components: • Includes organisms found in topsoil  affect physical/ chemical soil properties • Eg. Worms transport particles and help aerate soil • Humus is a major organic part of topsoil • Creates crumbly soil with pores that can retain water and aerate soil • Increases cation exchange capacity • Acts as mineral reserve

10. Soil Conservation and Sustainable Agriculture • If soil is fertilized, crops become renewable resource • HISTORY LESSON: Soil management helped establish first modern societies • Sustainable agriculture: includes different farming methods that are conservation minded, environmentally safe and profitable!

11. Soil Conservation and Sustainable Agriculture: Irrigation • Water is factor in plant growth  bring water from other resources to replenish soil • Limitation: • can destroy freshwater resources, • 75% earth’s water resources used for agriculture • Can lead to salinization (salt pile up when water evaporates) • Drip irrigation: requires less water, reduces saline

13. Soil Conservation and Sustainable Agriculture: Fertilization • Nutrient depletion is major cause of soil degradation • Add fertilizer (minerals) to replenish soil • Organic fertilizers: contain decomposing organic material (manure, fishmeal, compost, etc.) • Must be decomposed into inorganic nutrients that roots can absorb • Gradual release of minerals, retained for longer • Inorganic fertilizers: chemical compounds • Immediate release of minerals, easily lost by leaching • Runoff can lead to algal populations = oxygen depletion

15. Soil Conservation and Sustainable Agriculture: Adjusting pH • Affects cation exchange and chemical form of minerals (minerals tightly bound to soil; minerals in unabsorbable form) • Plants prefer slightly acidic soil (more H+ for cation exchange) • Difficult to adjust ( one absorption, while  another) • pH < 5, plant absorbs Al3+ stops root growth, stop Ca uptake • some plants secrete organic anions to bind to Al3+(make it harmless)

16. Soil Conservation and Sustainable Agriculture: Controlling Erosion • Major cause of soil depletion (nutrients carried away by wind/water) • Prevention: • rows of trees (windbreaker), terracing hillside crops, cultivating in contour pattern • Other crops = good ground cover to protect soil • No-till agriculture: creating furrows to minimize soil disturbance(soil not turned fertilizers still underground)

18. Soil Conservation and Sustainable Agriculture: Soil Compaction • Soil Compaction:squished soil that reduces pores = less water, absorption, drainage, gas exchange • Reduces root growth (hard to penetrate soil) • Avoid Soil Compaction: • Don’t farm wet soil, • Use lighter equipment

19. Soil Conservation and Sustainable Agriculture: Phytoremediation • In industrial areas, toxic substances contaminate soil/water • Soil remediation: detox of contaminated soils (REHAB) • Usually use nonbiological technologies (remove/store toxic soil in landfills)  costly and disrupt landscape • Phytoremediation: non-destructive biotechnology • Use other plants that have high affinity for toxic substances to harness those substances within the plant; thus toxic chemicals removed by removing plant

21. In Conclusion… • Soil properties (ability to retain water and minerals) determine the success of plant growth • Thus it is important to know various methods to conserve soil (especially topsoil) which contains the nutrients necessary for growth

22. Bibliography "3. Soil Analysis | My Science Box." Welcome to My Science Box! | My Science Box. N.p., n.d. Web. 9 June 2010. <http://www.mysciencebox.org/soilanalysis>. Cain, Michael L., Neil A. Campbell, Jane B. Reece, Lisa A. Urry, and Steven A. Wasserman. BIOLOGY: A P* Edition. 8 Har/Cdr ed. Columbus: Pearson, 2007. Print. "New York State Test Prep Social Studies 5 (Grade 3) People and their Physical Environments." studyzone.org. N.p., n.d. Web. 9 June 2010. <http://www.studyzone.org/testprep/ss5/b/comusanyl.cfm>.