Organic and inorganic fertilizers work well

By Sosimo Ma. Pablico

Organic fertilizers are not enough to provide the nutrients needed by the rice plant.  Inorganic or chemical fertilizers must be added for higher yield.

PhilRice [Philippine Rice Research Institute] researchers led by Evelyn F. Javier made this observation in a study conducted in six consecutive seasons or three years. 

Earlier in a three-year study [1999 to 2001], Javier and Dr. Rodante Tabien found that nitrogen from organic fertilizer was good only before the maximum tillering stage.  This dictates a need to apply inorganic nitrogen fertilizer to produce a decent yield.

Javier and Tabien also observed that yield and tiller production decreased with the continuous application of organic fertilizer only.  Likewise, except potassium, the amount of all other nutrients in the soil, especially zinc, diminished over the three-year period. The amount of potassium increased, however.

In the second study, Javier and her co-workers combined organic materials [rice straw, chicken manure, wild sunflower] with inorganic fertilizer and effective microorganism inoculants.

They incorporated in the soil 10 tons of rice straw per hectare four weeks before planting.  In another treatment, they treated the same amount of rice straw per hectare with effective microorganism inoculants and incorporated it two weeks before transplanting.  In a third treatment, they applied 10 bags of commercial organic fertilizer seven days before transplanting.   The commercial organic fertilizer contained one percent each of nitrogen, phosphorus and potassium.

In a fourth treatment, 3 tons of dry chicken manure was incorporated in the soil seven days before transplanting.  Still in another treatment, 4 tons of wild sunflower was incorporated two days before transplanting.

The organic materials were applied either singly or in combination with two rates of inorganic fertilizers and micronutrient fertilizer.  One-third of the inorganic nitrogen fertilizer and all the inorganic phosphorus and potassium fertilizers were applied one day before transplanting or during the final harrowing.  The remaining inorganic nitrogen fertilizer was applied at panicle initiation [41 days after transplanting].

Results showed that with or without organic fertilizer, application of inorganic fertilizer and micronutrients still produced better growth and grain yield than organic fertilizer alone.  However, plots applied with organic fertilizer + inorganic fertilizer and micronutrient produced more panicles.

Amazingly, the yield of plots applied with chicken manure was comparative with those applied with inorganic fertilizer. 

Results also showed that application of the recommended inorganic fertilizer rate is enough to produce high yield during the wet season because plants applied with organic fertilizer, whether applied singly or combined with inorganic fertilizer, tend to lodge during heavy rains, resulting in low yield. 

Organic fertilizers also did not significantly increase organic matter in the soil after six rice crops.  With or without inorganic fertilizer, however, chicken manure application resulted in higher phosphorus content of the soil.  Without inorganic fertilizer, rice straw treated with effective microbial inoculants increased the potassium content of the soil and slightly decreased its bulk density.

Chicken manure, carbonized rice hull and commercial organic fertilizer increased the microbial biomass in the soil two weeks after application.  On the other hand, rice straw increased the soil microbial biomass only at 35 days after incorporation in the soil.

The findings show, however, that with the presence of the rice plants, the microbial biomass in the soil decreased, indicating a close competition between the plants and soil microorganisms for the available nutrients.

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