Fred Magdoff Soil the unappreciated natural resource Many a hillside do the torrents furrow deeply, and down to the dark sea they rush headlong from the mountains, with a mighty roar, and the tilled fields of men are wasted. The Iliad You ask me to plow the ground. Shall I take a knife and tear my mothers breast? Native American Chief ... for soil thou art and unto soil shalt thou return. Book of Genesis Then God Yahweh formed man out of the soil of the earth Book of Genesis Adam from Hebrew word for soil Eve from the word for life Soil + Life Are you really made out of soil? Where did the following come from: calcium in your bones phosphorus in bones and fats and nucleic acids nitrogen in proteins iron, potassium, magnesium, etc. Are you really made out of soil? And where did the carbon come from? From plants growing on and in soils and that fixed atmospheric CO 2. What do plants need? Light Warmth Carbon dioxide (CO 2 ) Oxygen (O 2 ) Water Nutrients Anchorage What do plants need? Nutrients C, H, O, N, P, K, Mg, Ca, S, Fe, Cu, Co, Ni, Mn, Mo, B, Zn, Cl What do soils provide to plants? Oxygen (O 2 ) to roots Help roots get rid of CO 2 Water Most nutrients Anchorage What else do SOILS provide? Partitioning rainfall (runoff vs. infiltration) What else do SOILS provide? Partitioning rainfall (runoff vs. infiltration) Storage for Carbon carbon dioxide (CO 2 ) (0.04% in the atmosphere) root respiration and soil organic matter decomposition crop and animal residues photosynthesis respiration in stems and leaves crop harvest The role of soil organic matter in the carbon cycle. carbon in soil organic matter erosion What else do SOILS provide? Partitioning rainfall (runoff vs. infiltration) Storehouse for Carbon Cleansing pollutants (septic seepage fields, manures, sludges) Soils are a living filter As water percolates through a soil pathogens may be deactivated Phosphorus is removed Nitrogen is removed Carbon is removed Many harmful chemicals removed What else do SOILS provide? Partitioning rainfall (runoff vs. infiltration) Storehouse for Carbon Cleansing pollutants (seepage fields, manures, sludges) Building material What else do SOILS provide? Partitioning rainfall (runoff vs. infiltration) Storehouse for Carbon Cleansing pollutants (seepage fields, manures, sludges) Building material Something to build on (buildings, roads) What are soils made of? Minerals Organic matter Pores (water & air) What are soils made of? Minerals Organic matter Pores (water & air) What are soils made of? Minerals Organic matter Pores (water & air) Organic Matter Living Dead Very Dead Plants have evolved in a dynamic relationship with other organisms Living Beneficial and harmful Above and in the soil Living nematodes fungi bacteria mites earthworms springtails moles plant roots Soil organisms and their roles in decomposing residues. spore Dead Fresh residues in early stages of decomposition Food supply for the vast number of organisms that live in the soil VERY Dead Well decomposed material, humus Humus Well decomposed, colloidal Has many negative sites (can hold onto cations such as Ca ++, Mg ++, K + ) Add organic matter Increased biological activity (& diversity) Decomposition Nutrients released Aggregation increased Pore structure improved Humus and other growth promoting substances Reduced soil-borne diseases, parasitic nematodes Improved tilth and water storage HEALTHY PLANTS Harmful substances detoxified Figure 4.5 Corn grown in nutrient solution with (right) and without (left) humic acids. Photo by R. Bartlett. In this experiment by R. Bartlett and Yong Lee, adding humic acids to a nutrient solution increased the growth of both tomatoes and corn and increased the amount and branching of roots. What are soils made of? Minerals Organic matter Pores (water & air) air water minerals organic matter solidspores Soil wets-up during rain air water minerals organic matter solidspores Soil dries down