Harvest Time

Low-tech but cheap and reliable

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By Dr. Sosimo Ma. Pablico

LOWLAND RICE FARMERS can now easily assess the soil nutrient that is deficient in their fields by using a kit invented by a former soil science professor at the University of the Philippines at Los BaƱos (UPLB), former scientist of the International Rice Research Institute (IRRI) and now a senior consultant of the Philippine Rice Research Institute (PhilRice).

Dr. Cezar P. Mamaril calls it the MOET (minus one element technique) kit. Farmers can easily use this cheap technology without much coaching and be assured of reliable results, as the procedure can easily be followed step by step.

The MOET is based on the principle that rice plants will show reactions to limiting nutrients. The common indicators are reduced plant height (stunting) and tiller count, delayed maturity, small panicles, and distinct discoloration such as yellowing.

With the MOET small farmers can now diagnose soil nutrient deficiencies right in their farms or in their own backyard to closely monitor the results. Thus, the MOET savess them from the trouble of drying the paddy soil and locating the nearest soils laboratory as well as from paying the high cost of laboratory analysis. On top of this, they get accurate results since the MOET was intended for the analysis of flooded or anaerobic soils.

Because of great differences in the chemical processes in flooded and upland soils, chemical analysis in soils laboratories either underestimate or overestimate the availability of soil nutrients, says Dr. Mamaril, who at age 75 still finds enough strength and time going around the countryside to brief farmers and extension workers on the use of his invention.

He points out that the soil analyzed in any soils laboratory is dry and, hence, in oxidized condition. There’s a change in the state of some nutrients like nitrogen when the soil is flooded and, hence, the nutrients analyzed in oxidized form in the laboratory may no longer exist under flooded condition. Thus, nutrient status under flooded condition could be very different from the results of laboratory analysis.

Deficiency of some nutrients may not be diagnosed by chemical analysis, especially phosphorus, zinc, and sulfur which are highly sensitive to flooding. It may appear in a laboratory analysis that a soil has sufficient amount of these elements, but these may be either deficient or excessive under flooded condition.

Soil experts now agree that the MOET is a reliable technique that determines nutrient deficiency in actual field conditions. Any observed deficiency symptom tells farmers to apply additional fertilizer.

Because the chemical processes in flooded soils greatly differ from those in aerobic or upland soils, one has to understand these processes to fully attain benefits from them.

Dr. Mamaril explains that flooded and upland soils vary in the relative proportion of their components. Ideally, upland soil has considerable volume of pore spaces occupied by air, while flooded soil practically has no air space because most of the pore spaces are occupied by water. The presence or absence of air (oxygen) in the pore spaces has important implications on the biochemical processes in the soil, such as in the decomposition of organic materials and their mineralization or absorption by plants.

Differences in the physical properties of upland and lowland soils also influence the consequences of inputs or fertilizers applied in the soil. Thus, the strategies and approaches in applying inputs like fertilizer differ.

In lowland soils where oxygen is almost zero, the nitrogen absorbed by the plants is in ammonium form. If upland or oxidized soil is flooded, the soil is gradually devoid of oxygen and, hence, the availability of oxygen in the soil is reduced. Applied nitrogen fertilizer in flooded soil reacts with the hydrogen ion in the water, forming the absorbable ammonium.

In dry upland soil, applied nitrogen fertilizer reacts with the oxygen ion and nitrogen is converted into nitrate, the form that is absorbed by upland crops. What is not absorbed by the plants is further oxidized into nitrite and finally into nitrogen gas, which escapes into the atmosphere.

Lowland soils are generally dark because of poor drainage, reduced condition, and very slow oxidation, according to Dr. Mamaril. Dark color indicates high amount of organic matter.

Lowland soils are also generally poorly drained, puddled, and have shallow water table. Those with a hardpan deeper than 25 centimeters (cm) are more fertile than those with less than 25 cm.

PhilRice soil experts say that the MOET in combination with the LCC [leaf color chart] would go a long way in the national effort of attaining rice self-sufficiency.

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