Soil Composition and Soil Composition and Necessary AmendmentsNecessary AmendmentsSoil Composition and Soil Composition and

Necessary AmendmentsNecessary Amendments

David Wm. ReedDavid Wm. ReedDepartment of Horticultural SciencesDepartment of Horticultural Sciences

Texas A&M UniversityTexas A&M University

Physical Structure of Soil and Growing MediaPhysical Structure of Soil and Growing Media 11

Dynamic Nature of Soil and Growing MediaDynamic Nature of Soil and Growing Media 11

Mineral Particles of SoilMineral Particles of Soil

Mineral Mineral ParticleParticle

SizeSize CharacteristicsCharacteristics

SandSand 0.05 to 2 mm0.05 to 2 mm> aeration & drainage> aeration & drainage

< water holding capacity< water holding capacity

< nutrient holding capacity< nutrient holding capacity

SiltSilt 0.002 to 0.05 mm0.002 to 0.05 mm intermediateintermediate

ClayClay

<0.002 mm<0.002 mm< aeration & drainage< aeration & drainage

> water holding capacity> water holding capacity

> nutrient holding capacity> nutrient holding capacity

22

Soil Texture TriangleSoil Texture Triangle 22

Organic AmendmentsOrganic Amendments 33

C:N and Composting of AmendmentsC:N and Composting of Amendments 33

C:NC:N = the ratio of carbon to nitrogen in = the ratio of carbon to nitrogen in organic amendments organic amendments

Low C:NLow C:N – releases N upon decomposition – releases N upon decompositionHigh C:NHigh C:N – depletes N upon decomposition – depletes N upon decomposition

Must compost most organic amendments, otherwise:Must compost most organic amendments, otherwise:1)1) if high C:N, depletes Nif high C:N, depletes N2)2) if low C:N, may cause ammonia/ammonium burnif low C:N, may cause ammonia/ammonium burn3)3) if low C:N, may cause damage due to heat buildupif low C:N, may cause damage due to heat buildup

C:N of AmendmentsC:N of Amendments 44Low C:NLow C:N

(release N upon decomposition)(release N upon decomposition)

ManureManure 10:110:1

Alfalfa hayAlfalfa hay 13:113:1

Vegetable scrapsVegetable scraps 15:115:1

Coffee groundsCoffee grounds 20:120:1

Grass clippingsGrass clippings 20:120:1

High C:NHigh C:N(deplete N upon decomposition)(deplete N upon decomposition)

Autumn leavesAutumn leaves 60:160:1

StrawStraw 70:170:1

BarkBark 100:1100:1

PaperPaper 200:1200:1

Sawdust and wood chipsSawdust and wood chips 400:1400:1

Newspaper and cardboardNewspaper and cardboard 500:1500:1

Inorganic AmendmentsInorganic Amendments 44

Recipes for Making Growing MediumRecipes for Making Growing Medium

U.C. MixesU.C. MixesMixtures of Mixtures of

peat and sandpeat and sand

Peat-lite MixesPeat-lite MixesMixtures of Mixtures of

peat, bark, perlite and vermiculite,peat, bark, perlite and vermiculite,plus fertilizers & limeplus fertilizers & lime

7-97-9

Reed’s Recipe for Making Growing MediaReed’s Recipe for Making Growing Media

50-75%50-75%sphagnum peat or composted barksphagnum peat or composted bark

25-50%25-50%perlite, vermiculite or styrofoamperlite, vermiculite or styrofoam

25% maximum25% maximumany of the other amendmentsany of the other amendments

AdditivesAdditiveslime (5 lb/cu yd)lime (5 lb/cu yd)

granular fertilizer (1-2 lb/cu yd)granular fertilizer (1-2 lb/cu yd)

77

Shrinkage and Total Porosity ChangesShrinkage and Total Porosity ChangesUpon Mixing Different Soils & Growing MediaUpon Mixing Different Soils & Growing Media

1010

_______ ml_______ mlfine amendmentfine amendment

_______ ml_______ mlcoarse amendmentcoarse amendment

_______ ml_______ mlmixturemixture

_______ ml_______ mlmissing volumemissing volume

_______ %_______ %shrinkageshrinkage

Where did the missing volume go?Where did the missing volume go?How will this effect aeration and drainage?How will this effect aeration and drainage?Will sand increase drainage of bark or peat? Will sand increase drainage of bark or peat? Will sand increase drainage of soil, and if so how muchWill sand increase drainage of soil, and if so how much must be added? (hint look at soil texture triangle)must be added? (hint look at soil texture triangle)

Soil Texture TriangleSoil Texture Triangle 22

Water Holding Capacity and AerationWater Holding Capacity and Aerationof Soil and Growing Mediaof Soil and Growing Media

1111

> water holding capacity> water holding capacity< aeration porosity< aeration porosity

< water holding capacity< water holding capacity> aeration porosity> aeration porosity

intermediateintermediate