Soil Composition and Necessary Amendments David Wm. Reed Department of Horticultural Sciences Texas A&M University

Physical Structure of Soil and Growing Media 1

Dynamic Nature of Soil and Growing Media 1

Mineral Particles of Soil Mineral Particle SizeCharacteristics Sand 0.05 to 2 mm > aeration & drainage < water holding capacity < nutrient holding capacity Silt to 0.05 mm intermediate intermediate Clay <0.002 mm < aeration & drainage > water holding capacity > nutrient holding capacity 2

Soil Texture Triangle 2

Organic Amendments 3

C:N and Composting of Amendments 3 C:N = the ratio of carbon to nitrogen in organic amendments Low C:N – releases N upon decomposition High C:N – depletes N upon decomposition Must compost most organic amendments, otherwise: 1) if high C:N, depletes N 2) if low C:N, may cause ammonia/ammonium burn 3) if low C:N, may cause damage due to heat buildup

C:N of Amendments 4 Low C:N (release N upon decomposition) Manure10:1 Alfalfa hay 13:1 Vegetable scraps 15:1 Coffee grounds 20:1 Grass clippings 20:1 High C:N (deplete N upon decomposition) Autumn leaves 60:1 Straw70:1 Bark100:1 Paper200:1 Sawdust and wood chips 400:1 Newspaper and cardboard 500:1

Inorganic Amendments 4

Recipes for Making Growing Medium U.C. Mixes Mixtures of peat and sand Peat-lite Mixes Mixtures of peat, bark, perlite and vermiculite, plus fertilizers & lime 7-9

Reed’s Recipe for Making Growing Media 50-75% sphagnum peat or composted bark 25-50% perlite, vermiculite or styrofoam 25% maximum any of the other amendments Additives lime (5 lb/cu yd) granular fertilizer (1-2 lb/cu yd) 7

Shrinkage and Total Porosity Changes Upon Mixing Different Soils & Growing Media 10 _______ ml fine amendment _______ ml coarse amendment _______ ml mixture _______ ml missing volume _______ % shrinkage Where did the missing volume go? How will this effect aeration and drainage? Will sand increase drainage of bark or peat? Will 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 Triangle 2

Water Holding Capacity and Aeration of Soil and Growing Media 11 > water holding capacity water holding capacity < aeration porosity aeration porosity aeration porosity intermediate