the biotic factors that affect productivity

• Plants decrease productivity through competition for nutrients, light or water, they increase productivity through pest control. 
• Insects decrease productivity through consumption and disease spread. They increase productivity through pollination and predation 
• Fungi reduce productivity through disease and increase productivity through mycorrhizal associations. 
• Bacteria reduce productivity through disease and increase it through bacterial associations. 
• Farmers need to reduce pest biotic factors that decrease productivity and increase beneficial factors that increase productivity. 
• Pesticides are toxic, there are hundreds of varieties for different pests. They are effective but have a low specificity. Some pesticides persist for a long time and can bioaccumulate or biomagnify. 
• Pesticides can be sprayed onto the soil or onto crops to kill pests that land or effect the leaves. 
• Seeds can be coated in fungicides to prevent disease. 
• Roundup is made of glyphosate is linked to cancer. 
• Systemic pesticides are applied to the soil and is taken up by plant roots and transported via the xylem, it makes the whole plant toxic. 
• Contact pesticides are sprayed onto the plant or the insect. The insect absorbs the chemical through their feet or eating the leaf. Contact pesticides have more potential to leach into environment. 
• The LD50 test is the lethal dose for 50% of a test animal population. 
• A chemical with a small LD50 is very highly toxic. 
• Acute toxicity = immediate severe effects 
• Chronic = long term gradual impacts. 
• Persistence is a measure of the length of time a chemical stays active in the environment. 
• Biodegradation = breakdown by bacteria 
• Photodegradation = breakdown by light  
• Adsorption is when pesticides can be attracted to soil particles depending on ionic charges, this makes them persistent in soils. Clay soils and DOM adsorb more pesticides.