No one fertilizer fits all plants. You should to know the needs of your crops. Determine if you need organic or inorganic fertilizers or inorganic fertilizers. Stress usually determines this need. If your crops are suffering from an infestation that is killing the plant, fast acting inorganic fertilizers are needed. Slow organic fertilizers can be used as needed when plants are healthy and disease free.

Test Your Soil

Test your soil to determine its needs. Soil testing kits, which test for soil nutrients and pH, cost $20 to $25, as of November 2009; follow the directions included with the soil test kit. Vegetables tend to like a slightly acidic based soil. Testing for the three basic nutrients--nitrogen, phosphorus and potassium--will tell you what types of fertilizers to add.

Needs Of Vegetables

Vegetables need different nutrients at different times. Mixed fertilizers reflect the three basic nutrients they include: nitrogen (N), phosphorus (P), and potassium (K), called the NPK rating. If a vegetable is leafy, green and bears fruit, it will need lots of nitrogen. A root plant, such as potatoes and carrots, will need lots of phosphorus--which stimulates root growth--and potassium.

Organic Fertilizer

Gardeners today trend to use organic fertilizers, which are derived from natural--animal or vegetable--matter. Natural fertilizers include peat moss, manure, seaweed, sewage, and guano, which is bird or bat droppings. You can mix your own organic fertilizer to meet your own needs. If you need a fertilizer that is high in nitrogen, buy bat guano that as 13 percent nitrogen from a nursery. Plants use just the nitrogen it needs. Organic fertilizers are slow to release so are used when the plant needs them. They also have low nutrient grade levels so they will not burn the plant.

Inorganic Fertilizer

Plants cannot tell the difference between synthetic, inorganic fertilizers and organic fertilizers, but the soil can. Inorganic fertilizers are salts, so they tend to burn and increase the salinity of the soil over time. They have high nutrient levels that usually provide more than what is needed by the plant, leaving nutrients that are not used in the soil. The advantage of inorganic fertilizers is they are fast acting.

Source:

vegetable gardening in Mississippi

Sunset Western Garden Problem Solver,Kathleen N. Brenzel Editor, 1998, pg 38 Fertilizer usage

California Master Gardener Handbook, Dennis R. Pittenger, Editor, University of California, 2002 pg 55