Synthetic Fertilizer Vs. Organic Fertilizer: Which Is Better For My Lawn?

Fertilizing presents two problems: Where to get the fertilizer and how much to apply. The first thing that you need to do is to fertilize when the lawn plant is growing and needs it. A strong dose of nitrogen at the end of the season could expose tender new growth to damaging weather conditions.

Should you use organic or synthetic fertilizers? Manures and other organic fertilizers have been used for thousands of years and are still valuable for enriching soil. Organic gardening advocates are very vocal in rejecting most if not all synthetics. Both forms of plant food should be regarded as serving a useful function, however, which sensible gardeners should use to best advantage.

First lets take a look at organic fertilizers. Natural organic nitrogen is locked up in compounds that micro-organisms must break down for roots to absorb. The organic camp argues pretty persuasively that having enough organic matter and fertilizer in the garden also makes the kind of soil a good garden needs. You can't fault that argument. The micro-organisms that do the yeoman work of soil building and nutrient extraction are inactive, however, when soil temperatures fall below 55 to 60 degrees. This limits their use as cool weather fertilizers. Also, because each organic mix is different you have to know the product for best results.

Despite any shortcomings the advantages of organic nitrogen are that (1) it releases nitrogen more slowly and stimulates plant growth over a longer period and (2) large doses of it won't injure plants. It costs more than chemical fertilizer, however, and is usually low in other plant nutrients.

What about synthetic fertilizers? Chemical fertilizers (synthetics) release more nitrogen faster and are cheaper, but they can "burn" the plant and often leach out of the soil quickly.

There are two main groups of water-soluble synthetics: The ammonia-based group - including ammonium sulfate, urea, and the ammonium phosphates - gradually acidify soils. They attach to the soil and do not leach out readily. They need nitrates, so will not work in cold soils. The nitrates - ammonium nitrate, caldum nitrate, and potassium nitrate - act fast and don't need to be nitrified, but they leach right out of the soil. When dissolved these fertilizers release negative nitrate ions that the plants can take up immediately. They wash out without adding to harm the soil and they work in cold or sterile soils. On the other hand, 30 to 40 percent may wash out without any benefit to the plants.

There are water-insoluble synthetic organic fertilizers that are slow-release. They offer the convenience of a single, long-term application with little chance of burning the plant. Some contain around 40 percent nitrogen, and are identified as Water Insoluble Nitrogen (W.I.N.) on package labels. Look for a fertilizer with a W.I.N. index of at least 50 percent by weight for a good slow-release fertilizer.

Fertilizers with less than 50 percent natural organics or so-called synthetic organics should be considered quick fixes with short term effects. They cause rapid leaf growth, which spurs thatch build-up in lawns, and require repeated applications. The synthetic organics include organic urea, caldum cyanamid, and urea-formaldehyde, and. The action of microbes in soil releases the nitrogen in slow-release synthetics. Other slow release synthetics are coated with waxes, acrylic resins or sulfur.

Can fertilizers “burn” the lawn grass? Fertilizers contain salts just like ordinary table salt. When they dissolve in water they increase the water's osmotic pressure. Osmotic pressure is the force that causes a liquid to diffuse by osmosis through a semi-permeable membrane. Normally, high osmotic pressure in the plant causes water from the soil, with a lower osmotic pressure, to enter the roots through its cell membranes. Water always crosses the membrane from low to high pressure; it's as if the compounds or salts suck up water. If fertilizer salts raise the osmotic pressure in the soil water above that in the plant, the plant loses water. Plant damage from this loss of water is called fertilizer burn.

Different fertilizers have different salt indexes. Table salt has an index of 114. Ammonium nitrate has one of 105. The synthetic organics have indexes of around 10, and the natural organics are around 5. If a soil test indicates a high salt level in the soil, use a fertilizer with a low salt index.

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