Soils for Serious Gardeners

Transcription

1 Soils for Serious Gardeners Patricia Steinhilber, Ph.D. Ag Nutrient Management Program University of Maryland College Park

2 What is Soil? the living skin of the Earth (Ian Pepper, soil microbiologist) crucible of terrestrial life (Daniel Hillel, soil physicist) the pedosphere the interface between the lithosphere, hydrosphere and atmosphere (ecologists) a medium for plant growth phenomena of nature (natural bodies) mysciencebox.org

3 Agenda soil composition hydrologic cycle and soil water importance of soil testing fertilizers soil acidity and liming soil as biochemical reactors

4 What are Soils? reactive, dynamic, three-phase ecosystems composed of solids, liquids and gases topsoil several days after rainfall or irrigation 25% 48% 25% 2% Minerals Air Water Organic Matter

5 First Things First: Soil Solids mineral or inorganic solids often classified based on particle size organic solids a.k.a. organic matter

6 Mineral Class Major Mineral Classes in a Soil Size of Mineral Particles sands millimeters (mm) gritty Feel of Particles silts millimeters (mm) smooth (like cornstarch or talcum powder) clays less than millimeters (mm) sticky when wet

7

8 60% silt 20% clay 20% sand

9

10 Soil Property Textural Groups coarse-textured medium-textured fine-textured drainage rapid slow to moderate very slow water- and nutrientholding capacity susceptibility to erosion leaching potential Effect of Soil Texture on Soil Properties low moderate high low high moderate high moderate low aeration good moderate poor

11 The Other Soil Solid Material: Organic Matter Humus 75% 10% 15% Biomass Residues & By-Products

12 Biomass: What It Is the living component of the soil consists of a range of creatures as small as microscopic viruses & bacteria as large as roots, worms and other creatures that are visible to the unaided eye and everything between

13 Microorganisms, Mesoorganisms and Macroorganisms nematode CAD of Ag springtail (detritivore) centipede (carnivore)

14 Source: USDA

15 Life in the Soil, Nardi, 2007

16 Biomass: What It Does participates in nutrient cycling comminute (shred or fragment) plant and animal residues, using what they can utilize and leaving behind what they cannot mineralization conversion of organic form of an element to an inorganic form amino acid to ammonium

17 Biomass: What It Does (cont.) creation of biopores larger organisms move through soil creating channels or pores channels promote water infiltration and create a healthy balance between large and medium pores disseminate spores and microbes

18 Resources about Soil Organisms TED Talk How Bacteria Communicate bassler_on_how_bacteria_commu nicate.html Soil Biology Primer /soil_biology/biology.html

19 Residues and By-products: What They Are dead stuff crop residues, dead roots and bodies of soil creatures by-products materials that plant roots and soil creatures release or exude into the soil

20 Amazing By-product! Streptomycin bacterial exudate soil organism, Streptomyces Dr. Selman Waksman soil microbiologist at Rutgers University recognized the antibacterial function and isolated the compound Nobel Prize in Medicine in 1952

21 Residues and By-products: What They Do fuel and nutrients for soil organisms energy and nutrient source for most of the soil creatures formation and maintenance of soil aggregates (structure or architecture) sticky and gummy by-products of residue decomposition hold soil particles together in clumps or aggregates

22 Last But Certainly Not Least: Humus relatively stable end product of residue decomposition composes the majority of organic matter resists further decomposition (1% per year) it is not a good nutrient or energy source for soil creatures

23 Humus: What It Does very small in particle size & high surface area charged sites at many locations on the surface effective at holding water and nutrients

24 The Other Half of Soil: Soil Pores (Void Space) soil water adequate (but not too much) quantity adequate supply of nutrients minimize runoff and leaching soil air source of oxygen for roots and most soil organisms constantly enriched with carbon dioxide from roots and soil organisms

25 The Interplay of Air and Water: Soil Aeration the exchange of O 2 and CO 2 between the soil pores and the ambient atmosphere Hillel

26 Comparison of Gasses in the Atmosphere and in Soil Air of Well-Structured Topsoil (several days after rainfall) Gas In the Atmosphere In Soil Air nitrogen 79% 79% oxygen 20.9% 20.6% carbon dioxide 0.035% 0.300%

27 Balance Between Water and Air macropores (large pores) drain quickly after rain or irrigation allow rapid infiltration of rainfall and replenishment of oxygen in the root zone mesopores (medium-sized pores) storage pores hold water in a form most plants can use micropores (very small pores) water is held too tightly to be use to most plants

28 Now, a Video Interlude - Dr. Ian Pepper, soil microbiologist, Arizona State University

29 Let s talk about the hydrologic cycle and soil water

30 Biological Classification of Soil Water excess or gravitational water water that drains from soil 1-3 days after a rainfall or irrigation (in macropores) available water that is in a form crop plants can use (in mespores) unavailable water that is held to tightly by the soil to be usable by most crop plants (in micropores)

31 Water and Textural Groups (% water) coarse- textured mediumtextured finetextured total excess available * 20 unavailable

32 Department of of Environmental Science and and Technology

33

34 Soil Solution keep well supplied with nutrients minimize adverse conditions for plant growth acidity salinity

35 Soil tests can help identify limiting nutrient factors. Fertilizers can enrich the soil solution when soil tests indicate an insufficiency.

36 Value of Soil Tests best pre-plant indicator we have of potential nutritional products mine them for information! excellent investment

37 Soil Tests best if maintained in the high end of the optimum range or the low end of the excessive range low medium optimum excessive

38 Soil Test Value and Response to Nutrients Soil Test Category Fertility Index value (FIV) Likelihood of Response very low and low 0-25 almost always medium sometimes optimum not often excessive >100 almost never

39 What is a fertilizer? a compound that contains at least 1 plant nutrient ammonium nitrate (NH 4 NO 3 ) potassium nitrate (KNO 3 ) muriate of potash (KCl)

40 Where do N, P and K in fertilizers originate? N originates from the atmosphere natural gas is an energy source and a hydrogen source P originates from rock phosphates K originates K-bearing minerals, usually chlorides or sulfates

41 How do we describe the nutrient content of fertilizers? Ag-Gro-Pro lbs. This bag contains: 5% nitrogen--10% phosphate--15% potash or 2.5 lbs. nitrogen (N) 5 lbs. phosphate (P 2 O 5 ) 7.5 lbs. potash (K 2 O)

42 The fertilizer guarantee % nitrogen (total) % phosphate, P 2 O 5 (citrate-soluble) % potash, K 2 0 (soluble) P 2 O 5 x 0.44 = P P x 2.27 = P 2 O 5 K 2 0 x 0.83 = K K x 1.20 = K 2 0

43 Common Commercial N Fertilizers Material ammonia Analysis ammonium nitrate urea ammonium sulfate UAN (urea+ammonium nitrate) to

44 Less Common Commercial N Fertilizers sulfur-coated urea (SCU) ureaform methylene urea isobutylidene diurea (IBDU)

45 Common Commercial P Fertilizers Material Analysis superphosphate triple superphosphate monoammonium phosphate (MAP) diammonium phosphate (DAP)

46 Common Commercial K Fertilizers Material Analysis muriate of potash sulfate of potash potassium-magnesium sulfate potassium nitrate S-11Mg

47 Common Organic Fertilizers animal manures composts by-products of animal and crop harvesting fish meal, bone meal, blood meal corn gluten, soybean meal

48 soil acidity: the adverse condition on humid regions

49 Adverse Conditions Due to Soil Acidity (Low ph) Adverse Condition inadequate supply of some nutrients excessive or toxic supply of some nutrients or non-essential elements some nutrients bound in unavailable forms Soil Component Affected calcium and magnesium may be present in inadequate amounts in acidic soils aluminum, iron, zinc, manganese and copper can be present in excessive and even toxic amounts in acidic soils phosphorus and molybdenum are so tightly bound to soil clays that they are not available to plants in acidic soils inhospitable environment bacteria, such as those needed for nitrogen fixation, can not thrive in acidic soils

50

51 Soils are Biochemical Reactors the various components (soil air, soil water, minerals and organic matter) interact a wide array of chemical and biochemical processes occur

52 Clays and Humus center of chemical reactivity in soil engine driving chemical transformations in soil geoscienceworld.org fullwiki.org

53 Soil Model micro meso macro biomass soil solution sand organic solids residues & by-products soil air silt inorganic solids humus Pore space clay layer minerals clay oxides

54 SSSAJ v. 75 SSSAJ v. 75

55 Solid-Liquid Interface adsorption of water and nutrients occurs at surfaces small particles have more surface area than the same weight of large particles surfaces are often charged; most charge is negative negatively charged surfaces attract positively charged ions (cations)

56 Cation exchange is a big deal! cation exchange capacity (CEC) a soil s ability to hold cations on charged surfaces a measure of the negative charge on the particles correlated to clay and humus content of soils exchange phase those cations held on surfaces of charged particles

57 Importance of CEC nutrient cations exist on exchange phase are protected from leaching can replenish the soil solution when plant uptake or leaching removes nutrients the storehouse of cationic nutrients

58 Relationship of Textural Class Textural Group sand and loamy sands Range of Clay Content (%) Cation Exchange Capacity (CEC)* sandy loams loams and silt loams clay loams, sandy clay loams, silty clay loams clays, sandy clays, silty clays to Clay Content and CEC >49 >30 *cmol/kg or centimoles per kilogram, or an older mode of expression, milliequivalent per 100 grams.

59 Soil: The Most Complex Biomaterial on Earth Questions or comments?