1. Soil Erosion Soil erosion is the movement of soil components from one place to another, usually from wind or water. Plant anchor the soil so that it is not washed away faster than it forms Farming, logging, construction, overgrazing, off road vehicles, burning of vegetation all increase soil erosion Losing topsoil makes soil less fertile and decreases its water holding capacity. The sediments also chokes lakes and streams

2. How serious is global erosion: Topsoil is eroding faster than it forms on about on third of the earths cropland Each year we must feed 90 million more people with 26 million tons less topsoil The cost of erosion is about $400 billion worldwide in direct damage to agricultural lands, waterways, infrastructure and human health In the U.S. soil is eroding 16 times faster than it can be replaced.

3. Desertification: process whereby the productive potential of arid or semi-arid land drops by 10% or more – Overgrazing, deforestation, surface mining, irrigation techniques that lead to increased erosion, salt buildup and water logging of soils, farming on land with unsuitable terrain or soil, soil compaction due to farm machinery and cattle hooves. – Every year an area the size of Kansas undergoes severe enough erosion to make farming not feasible in the area. – The only way to stop this is to reduce all the causes and to reforest land.

4. Irrigation – Most irrigation water has very dilute salts that build up over time in the soil, this is called salinization. – It takes thousands of years for precipitation to wash the salt out of the soil – Water logging occurs when too much water is applied to crops and this water sinks down into the groundwater causing the water table to rise and then salty water can envelope the roots of plants, killing them.

6. Soil Conservation 1. Soil conservation: reducing the soil erosion and preventing and restoring soil fertility Conventional tillage farming: the land is plowed and the soil is broken up and smoothed to make a planting surface

7. Conservation tillage: the idea is to disturb the soil as little as possible while planting crops. Special tillers break up and loosen only subsurface soil without overturning topsoil, previous crop residues, or any cover vegetation. This saves fuel, cuts costs, hold in more water, keeps soil from getting packed down and allows more of a crop growing season Terracing: reduces erosion on slopes by creating a series of broad level terraces. Contour farming: on gently sloping land, you plant rows across rather than down the sloped contour of the land.

8. Strip cropping: rows crops like corn are planted in strips with another crop like grasses or legumes that completely cover the soil Agroforestry: intercropping with trees Windbreaks and shelter breaks Land classification: classifying land that is not suited to agriculture PAM (polyacrylamide): Gel that hold soil together

9. Conserving soil fertility 1.organic fertilizers Animal manure: the best for crops but expensive to haul Green manure: plowing under green vegetables Compost Crop rotation 2. Inorganic fertilizers » Phosphorus, potassium and nitrogen » Easily transported, stored and applied, without them we would starve » Problems: wash into lakes and streams, they do not add humus to the soil, only supplies 2 or 3 out of some 20 needed materials

10. Fig. 10.14, p. 222 Nitrogen fixing by lightning Commercial inorganic fertilizer 10-6-4 N-P-K Organic fertilizers, Animal manure, Green manure, compost Crop plant Dead organic matter Application to land Nitrogen fixing by bacteria Nitrogen fixing Weathering of rock Nutrient removal with harvest Decomposition Supply of available plant nutrients in soil Nutrient loss by bacterial processes such as conversion of nitrates to nitrogen gas Nutrient loss from soil erosion Absorption of nutrients by roots