MANILA, Philippines - In the old days, American Indians found that if they dig into the poor soil and throw in a fish, it will rot and make their corn fields fertile. Up to modern times, farmers and gardeners knew that when they incorporate nitrogenous materials into the soil, it will make the soil more productive. Fertilizers became a necessary tool to improve farm fields and gardens.
A good thing used in excess is bad. This applies to fertilizers. Over-zealous gardeners tend to give a little more than what is necessary for the plants to be healthy.
Fertilizer alone is responsible for the demise or sickness of a big percentage of garden plants! This is usually the first tuition fee a collector-gardener pays in pursuit of gardening and results in loss of revenue for farmers.
Most plants have evolved through millions of years to grow in an environment where nutrients are given by nature slowly in low dosages. Dumping fertilizers around the root system results in plasmolysis (salting out effect) of the feeder roots. Damaged roots result in decreased water procurement activity of the plant. To maintain moisture balance within, the plant needs to shed the lower leaves as a consequence. This results in very unattractive leggy plants.
Plasmolyzed tissues are loaded with nutrients that they will serve as good meal for pathogens and saprophytes causing infection that kills the plants from inside.
The fertilizer damage is characterized by leaf margin and leaf tip burns of the younger set of leaves. Milder damage is manifested by marginal chlorosis or yellowing of the leaf edges. The soluble components of fertilizers are transported into the leaves and excreted through the hydatodes at the margin and tip of the leaves. This results in plasmolysis and damage in the said area.
What to do when over-fertilization is detected
In the event that the over-fertilization is detected early, the gardener should immediately flush the media with water. After most of the fertilizers are washed off the media, systemic fungicide like benomyl or carbendazim should be applied to discourage opportunistic microorganisms from infecting the damaged root system.
Organic Fertilizers
Organic fertilizers are good source of nutrients. The nutrients are released to the plants in small amounts slowly. They are relatively safe in small amounts and if the organic fertilizers are properly composted. Placing organic materials in soil will start up re-fermentation processes. While the soil is fermenting, the plants planted in it will become part of the compost.
Slow Release Fertilizers
Plastic-coated slow-release fertilizers may cause damage to plants also. The plastic prills holding the fertilizers start to absorb water and releases a high dose locally. The “nitrogen loading” may cause root burns also. 30 minutes to 1 hour after application or wetting of the slow-release prills, the plants need to be watered heavily to prevent flagging of leaves. Slow-release fertilizer-damaged plants normally recover without help. Ureaform and Magamp type slow release do not give this type of problem.
High Nitrogen Fertilizers
High nitrogen fertilizers give the biggest boost in growth. It is easy to double the rate of growth of plants fast using urea or in combination with other nitrogen sources. The plant tissues grow very fast and thick but the plant structure will be weak and the plant may fall sick or get damaged easily.
When high amounts of nitrogen are applied, other nutrients should follow suit otherwise deficiencies in secondary and trace elements will occur. This is the common mistake of commercial growers resulting in devastating damages.